Gas sensor element and gas sensor

Abstract

A gas sensor element (10, 10a, 10b) with: a solid electrolyte element (11) extending in an axial direction and containing ZrO2 with oxygen ion conductivity; an external electrode (100) which is provided on one of the surfaces of the element made of solid electrolyte (11) and comes into contact with a gas to be measured; and an internal electrode (200) which is provided on an opposite surface of the solid electrolyte element (11) and comes into contact with a reference gas, wherein the inner electrode (200) has an inner sensing electrode region (220, 220a, 220b) arranged on a front end face in the axial direction and sensing a specific gas contained in the gas to be measured, and an inner connection region (210) arranged behind the inner sensing electrode region (220, 220a, 220b), connected to the inner sensing electrode region (220, 220a, 220b), and in contact with a connection port (70) for external output, wherein the inner electrode (200) has an electrically conductive oxide layer (OCL1, OCL1b, OCL2, OCL2b) the main component of which is a perovskite phase composed according to a composition formula with La a M b Ni c O x is represented (where M is an element in the form of Co and / or Fe, a + b + c = 1, 1.25 ≤ x ≤ 1.75), has a perovskite-like crystal structure; the coefficients a, b and c satisfy 0.459 ≤ a ≤ 0.535, 0.200 ≤ b ≤ 0.475 and 0.025 ≤ c ≤ 0.350; the internal connection area (210) has a lanthanum zirconate layer (LZL) between the electrically conductive oxide layer (OCL1, OCL1b, OCL2, OCL2b) and the solid electrolyte element (11); and the internal detection electrode region (220, 220a, 220b) is designed such that (i) no lanthanum zirconate layer (LZL) is formed between the electrically conductive oxide layer (OCL1, OCL1b, OCL2, OCL2b) and the solid electrolyte element (11), or (ii) a lanthanum zirconate layer (ZLZ) formed between the electrically conductive oxide layer (OCL1, OCL1b, OCL2, OCL2b) and the solid electrolyte element (11) is thinner than the lanthanum zirconate layer (LZL) of the internal connection region (210).

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention

[0001] The present invention relates to a gas sensor element using electrodes made of an electrically conductive oxide and a gas sensor including the gas sensor element. 2. Description of the state of the art

[0002] Until now, a gas sensor has been known that includes a gas sensing element whose electrical characteristics change according to the concentration of a specific gas component contained in a gas to be measured. For example, Patent Document 1 discloses a gas sensing element including a solid electrolyte element in the shape of a downwardly tapered tube closed at its front end; an internal electrode (a reference electrode) formed on the inner surface of the solid electrolyte element; and an external electrode (a detection electrode) formed on a front end portion of the outer surface of the solid electrolyte element. Such a gas sensor is suitably used for detecting the concentration of a specific gas contained in exhaust gas discharged from, for example, a combustion unit or an internal combustion engine.Patent Documents 2 and 3 also disclose various types of electrically conductive oxides. These electrically conductive oxides can be used as an electrode material for a gas sensor element.

[0003] With the tightening of emission control standards in recent years, the requirements for gas sensors are becoming increasingly stringent year by year. These requirements include (i) higher gas detection accuracy, (ii) excellent heat resistance, and (iii) low cost. When the electrically conductive oxides disclosed in Patent Documents 2 and 3 are used as an electrode material for a gas sensor element, electrodes with sufficiently low electrical resistance are obtained. Therefore, it becomes possible to obtain a gas sensor element that has improved gas detection accuracy, is cost-effective compared to the case where only a noble metal is used as an electrode material, and has excellent heat resistance.

[0004] Further relevant prior art is disclosed in the following document: DE 102 61 299 B4. [Patent document 1] JP 2009 - 63 330 A [Patent Document 2] JP 3417090 B2 [Patent Document 3] WO 2013 / 150 779 A1 3. Problems to be solved by the invention

[0005] For the electrodes of a gas sensor element, not only low electrical resistance and heat resistance are required, but also resistance to mechanical influences (impact resistance). Each electrode of a gas sensor element has a sensing electrode region used for gas sensing and a terminal region for outputting an output signal from the sensing electrode region to an external circuit. In some cases, the terminal region is in contact with a connection terminal for electrically connecting to the external circuit. In such a case, the terminal region must have sufficiently high impact resistance. Electrically conductive oxide is brittle and has low impact resistance compared to noble metal materials. Therefore, if only an electrically conductive oxide is used as an electrode material for a gas sensor element, sufficiently high impact resistance cannot be achieved.Therefore, a problem arises that such a gas sensor element and a gas sensor containing the element cannot provide the required behavior. OVERVIEW OF THE INVENTION

[0006] The present invention was conceived to solve the problems described above. Furthermore, an object of the present invention is to provide a gas sensor element and a gas sensor with sufficient impact resistance even when an electrically conductive oxide is used as an electrode or an electrode terminal.

[0007] To solve the above-described problem, a gas sensor element having the features of claim 1 is provided. Furthermore, a gas sensor element having the features of claim 6 is provided. Further advantageous embodiments are defined in the dependent claims.

[0008] The above object is achieved by providing (1) a gas sensor element comprising: a solid electrolyte element extending in an axial direction and containing ZrO2 having oxygen ion conductivity; an outer electrode provided on one of surfaces of the solid electrolyte element and contacting a gas to be measured; and an inner electrode provided on an opposite surface of the solid electrolyte element and contacting a reference gas. The inner electrode includes an inner detection electrode portion disposed on a front end side in the axial direction and detecting a specific gas contained in the gas to be measured, and an inner terminal portion disposed rearward of the inner detection electrode portion, connected to the inner detection electrode portion, and contacting a connection terminal for outputting to the outside.The inner electrode has an electrically conductive oxide layer, the main component of which is a perovskite phase characterized by a composition according to the formula La. a M b Ni c O x(where M is the element Co and / or Fe, a + b + c = 1, 1.25 ≤ x ≤ 1.75) and has a perovskite-type crystal structure, and the coefficients a, b and c satisfy the condition 0.459 ≤ a ≤ 0.535, 0.200 ≤ b ≤ 0.475 and 0.025 ≤ c ≤ 0.350. The inner terminal region includes a lanthanum zirconate layer between the electrically conductive oxide layer and the solid electrolyte member, and the inner detection electrode region is formed such that (i) no lanthanum zirconate layer is formed between the electrically conductive oxide layer and the solid electrolyte member, or (ii) a lanthanum zirconate layer formed between the electrically conductive oxide layer and the solid electrolyte member is thinner than the lanthanum zirconate layer of the inner terminal region.

[0009] Since the gas sensor element (1) has a lanthanum zirconate layer between the electrically conductive oxide layer of the internal lead portion and the solid electrolyte element, the adhesion between the electrically conductive oxide layer and the solid electrolyte element, which sandwich the lanthanum zirconate layer from both sides, is increased, thereby improving the impact resistance of the internal lead portion. Meanwhile, in the internal detection electrode portion, no lanthanum zirconate layer is formed between the electrically conductive oxide layer and the solid electrolyte element, or a lanthanum zirconate layer thinner than the lanthanum zirconate layer of the internal lead portion is formed between the electrically conductive oxide layer and the solid electrolyte element.This structure, in which the lanthanum zirconate layer is a high-resistivity layer, can prevent the interface resistance between the internal detection electrode region and the solid electrolyte element from increasing excessively.

[0010] In a preferred embodiment (2) of the gas sensor element (1) of the above, a reaction prevention layer containing rare earth element-added cerium oxide as a main component is provided between the internal detection electrode portion and the solid electrolyte member.

[0011] According to the above structure (2), the reaction prevention layer delays the occurrence of a reaction between La in the electrically conductive oxide layer and ZrO2 in the solid electrolyte element. Therefore, even in the case of a gas sensor element in which a lanthanum zirconate layer is formed in the absence of the reaction prevention layer, the formation of the lanthanum zirconate layer can be avoided or the thickness of the lanthanum zirconate layer can be reduced by providing the reaction prevention layer. Note that the term "containing rare earth element-added ceria as a main component" means that, among the components, rare earth element-added ceria is contained in the reaction prevention layer in the largest proportion.

[0012] In another preferred embodiment (3) of the foregoing gas sensor element (2), the reaction prevention layer is provided only on the front end side of the gas sensor element with respect to a holding member that holds the gas sensor element when the gas sensor element is included in a gas sensor.

[0013] When the gas sensor element is mounted in a gas sensor, the gas sensor element may be inserted into a housing, such as a metallic shell, and held by a holding member, such as talc, interposed between the housing and the gas sensor element. In such a case, in the gas sensor element, the holding member exerts a very large compressive force on the outer surface of a portion of the solid electrolyte element where the holding member is disposed. However, due to the influence of this compressive force, a tensile force acts on the inner surface of the portion of the solid electrolyte element where the holding member is disposed. As a result, the reaction prevention layer may be cracked. Therefore, the reaction prevention layer is provided only in a region on the front end side of the gas sensor element with respect to the holding member.In this case, the tensile force does not affect the reaction prevention layer, and crack formation in the reaction prevention layer can be restricted.

[0014] In still another preferred embodiment (4), the gas sensor element according to any one of the preceding aspects (1) to (3) is configured such that the internal detection electrode region has an electrically conductive intermediate layer formed between the reaction prevention layer and the electrically conductive oxide layer, wherein the electrically conductive oxide layer does not contain rare earth element enriched cerium oxide and has a perovskite phase represented by the composition formula La a M b Ni c O x and the electrically conductive intermediate layer has a perovskite phase represented by the composition formula La a M b Ni c O xrepresented, and cerium oxide mixed with a rare earth element.

[0015] According to the above structure (4), the electrically conductive oxide layer does not contain rare earth element-added ceria. Therefore, the electronic conductivity of the electrically conductive oxide layer is increased at room temperature, which can reduce the electrical resistance. Meanwhile, since the electrically conductive oxide layer does not contain rare earth element-added ceria, the adhesion between the electrically conductive oxide layer and the reaction-preventing layer can be reduced. However, since the electrically conductive intermediate layer containing the perovskite phase and rare earth element-added ceria is formed between the reaction-preventing layer and the electrically conductive oxide layer, the adhesion between the reaction-preventing layer and the electrically conductive oxide layer can be enhanced.Furthermore, since the electrically conductive intermediate layer of the internal detection electrode region contains the perovskite phase and a cerium oxide added with a rare earth element, it is possible to dampen an excessive increase in the interface resistance between the internal detection electrode region and the solid electrolyte element during the measurement of a gas concentration.

[0016] In still another preferred embodiment (5), the gas sensor element according to any one of the preceding aspects (1) to (3) is formed such that the electrically conductive oxide layer comprises a first electrically conductive oxide layer forming the internal terminal region and a second electrically conductive oxide layer forming the internal detection electrode region, wherein the electrically conductive oxide layer and the second electrically conductive oxide layer each contain the perovskite phase and a rare earth element-added cerium oxide, and wherein the proportion of the rare earth element-added cerium oxide in the second electrically conductive oxide layer is equal to or greater than the proportion of the rare earth element-added cerium oxide in the first electrically conductive oxide layer.

[0017] According to the above configuration (5), the proportion of cerium oxide added with a rare earth element is increased in the electrically conductive oxide layer constituting the internal sensing electrode region. Therefore, the internal sensing electrode region has a porous structure, thereby increasing the area of ​​the tri-phase interface, and thus the interface resistance can be reduced. Furthermore, since the proportion of cerium oxide added with a rare earth element is reduced in the internal terminal region, the internal terminal region has a dense structure. Consequently, the electronic conductivity is improved and the strength of the internal terminal region is increased, thereby further increasing the impact resistance of the internal terminal region.

[0018] The present invention can be implemented in various ways. For example, the present invention can be implemented as a gas sensor element, a gas sensor including the gas sensor element, a gas sensor including the gas sensor element and a holding member for holding the gas sensor element, and a method for manufacturing the gas sensor element, or a method for manufacturing the gas sensor. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a sectional view showing the structure of a gas sensor. Fig. 2A to 2D are explanatory views showing the structure of a gas sensor element according to an embodiment. Fig. 3A to 3D are explanatory views showing the structure of a gas sensor element according to another embodiment. Fig. 4A to 4D are explanatory views showing the structure of a gas sensor element according to still another embodiment. Fig. 5 is a flow chart showing a method for producing the Fig. 2 shows the gas sensor element. Fig. 6 is a flow chart showing a method for producing the Fig. 3 shows the gas sensor element. Fig. 7 is a flow chart showing a method for producing the Fig. 4 shows the gas sensor element. Fig. Figures 8A to 8D are cross-sectional SEM images of samples tested in the mechanical impact test. Fig. Figure 9 is a graph showing the results of electrode interface resistance measurement. Description of reference signs and symbols

[0019] Reference numerals used to identify various features in the drawings include the following. 10, 10a, 10b Gas sensor element 11 Element with solid electrolyte 12 Flange area 13 bottom end area 18 Basic area 20 metallic sleeves 20a curved area 20b Step area 20c flange area 20d male screw area 29 Seal 31 powder-enriched area (holding element) 32 Insulation element 33 metal ring 34 Separator 35 through hole 36 cable entry 37 filters 38 protective outer tube 39 second inlet hole 40 outer tube 41 first inlet hole 60 connecting cable 62 protective element 70 connection port 100 outer electrode 110 External connection area 114 longitudinal connection area 115 Ring connection area 120 external detection electrode area 200 internal electrode 210 Internal connection area 220, 220a, 220b internal detection electrode area 300 gas sensor BL reaction prevention layer ICL electrically conductive intermediate layer LZL lanthanum zirconate layer (reaction layer) OCL1, OCL1b, OCL2, OCL2b electrically conductive oxide layer DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] The invention will now be described in more detail with reference to the drawings. However, the present invention should not be construed as being limited thereto. A. Structure of the gas sensor

[0021] Fig. Fig. 1 is a sectional view showing the structure of a gas sensor 300 according to a first mode of the present invention. The gas sensor 300 has an elongated shape extending along an axial line O. In the following description, the lower side of the Fig.1 is referred to as a front end side, and the upper side thereof is referred to as a rear end side. Further, a direction perpendicular to the axial line O and directed outward from the axial line O is referred to as the "radial direction." The gas sensor 300 is an oxygen concentration sensor and can be used, for example, to detect the concentration of oxygen contained in exhaust gas discharged from a vehicle. The gas sensor 300 includes a gas sensor element 10, a metallic shell 20, a protective member 62, an outer tube 40, a protective outer tube 38, and an electrode wiring structure (electrodes and a lead wire), which are described below.

[0022] The gas sensor element 10 is an oxygen sensor element having a pair of electrodes provided on opposite surfaces of a solid electrolyte element 11 having ionic conductivity (oxygen ion conductivity). The gas sensor element 10 serves as an oxygen concentration cell and outputs a detection value corresponding to the partial pressure of oxygen. The gas sensor element 10 includes the solid electrolyte element 11 in the shape of a downwardly opening tube that tapers so that its outer diameter decreases toward the front end; an outer electrode 100 formed on an outer surface of a front end portion of the solid electrolyte element 11; and an inner electrode 200 (reference electrode) formed on the inner surface of the solid electrolyte element 11.When the gas sensor element 10 is used, a reference gas atmosphere is created in the interior of the gas sensor element 10, and a gas to be detected is brought into contact with the outer surface of the gas sensor element 10. In this state, gas detection is performed. A lead wire 60 for leading the detection signal from the inner electrode 200 extends outward from the rear end of the gas sensor 300. A flange portion 12 protruding in the radial direction is formed at an approximately central portion of the gas sensor element 10 in the axial direction such that the flange portion 12 extends over the entire circumference of the gas sensor element 10.

[0023] The metallic sleeve 20 is a member made of metal (e.g., stainless steel) that surrounds the gas sensor element 10, and a front end portion of the gas sensor element 10 protrudes from a front end portion of the metallic sleeve 20. The metallic sleeve 20 has a stepped portion 20b provided on its inner surface such that the inner diameter decreases toward the front end. The metallic sleeve 20 has a polygon-shaped flange portion 20c provided at a position near the center of the metallic sleeve 20 and projecting radially outward. A fastening tool, such as a hexagon wrench, is engaged with the polygon-shaped flange portion 20c. Further, a male screw portion 20d is formed on the outer surface located on the front end side of the flange portion 20c.The male screw portion 20d of the metallic sleeve 20 is attached to a screw hole of an exhaust pipe of, for example, an internal combustion engine, thereby positioning the front end of the gas sensor element 10 in the exhaust pipe. This makes it possible to detect the concentration of oxygen contained in the gas to be detected (exhaust gas). Furthermore, a gasket 29 is fitted into a recess between a surface on the front end side of the flange portion 20c and the rear end of the male screw portion 20d. The gasket 29 prevents gas leakage when the gas sensor 300 is attached to the exhaust pipe.

[0024] The protective member 62 is a tubular member made of metal (e.g., stainless steel) and covers the front end portion of the gas sensor element 10, which protrudes from the front end portion of the metallic shell 20. A rear end portion of the protective member 62 is bent outward in the radial direction. This rear end portion is held between the surface of the front end side of the flange portion 12 of the gas sensor element 10 and the step portion 20b of the metallic shell 20, thereby fixing the protective member 62. When the metallic shell 20 and the gas sensor element 10 are assembled, the protective member 62 is inserted into the metallic shell 20 from the rear end side of the metallic shell 20, and the rear end portion of the protective member 62 is brought into contact with the step portion 20b of the metallic shell 20.Subsequently, the gas sensor element 10 is inserted into the metallic shell 20 from its rear end side, and the surface on the front end side of the flange portion 12 is brought into contact with the rear end portion of the protective member 62. As described below, a ring terminal portion 115 of the outer electrode 110 is provided on the surface on the front end side of the flange portion 12 of the gas sensor element 10, and the outer electrode 110 is electrically connected to the metallic shell 20 via the ring terminal portion 115 and the protective member 62. Note that the protective member 62 has a plurality of holes for introducing exhaust gas into the interior of the protective member 62. The exhaust gas that has flowed through the interior of the protective member 62 through the plurality of holes is supplied to the outer electrode 100 as a gas to be detected.

[0025] A powder-filled region 31 (corresponding to the retaining element in the claims) is arranged in a gap between the metallic shell 20 and the rear end of the flange portion 12 of the gas sensor element 10. The powder-filled region 31 is formed by filling a powder material containing talc powder and compressing the filled powder material. The powder-filled region 31 seals the gap between the gas sensor element 10 and the metallic shell 20. A tubular insulating member (ceramic sheath) 32 is arranged on the rear end side of the powder-filled region 31.

[0026] The outer tube 40 is a member made of a metallic material such as stainless steel and connected to the rear end portion of the metallic sleeve 20 such that the outer tube 40 covers a rear end portion of the gas sensor element 10. A metallic ring 33 made of a metallic material such as stainless steel is interposed between the inner surface of a rear end portion of the metallic sleeve 20 and the outer surface of a front end portion of the outer tube 40. The front end portion of the outer tube 40 is caulked by the rear end portion of the metallic sleeve 20, thereby securing the metallic sleeve 20 and the outer tube 40 to each other. As a result of the caulking, a bent portion 20a is formed on the rear end side of the flange portion 20c.As a result of forming the bent portion 20a at the rear end portion of the metallic shell 20, the insulating member 32 is pressed toward the front end side. Consequently, the powder-filled portion 31 is compressed, whereby the insulating member 32 and the powder-filled portion 31 are fixed by caulking, and the gap between the gas sensor element 10 and the metallic shell 20 is sealed.

[0027] An insulating separator 34 with an approximately cylindrical shape is arranged inside the outer tube 40. The separator 34 has a through-hole 35 extending through the separator 34 in the direction of the axial line O and through which the lead wire 60 passes. The lead wire 60 is electrically connected to a connection terminal 70. The connection terminal 70 is a member for leading the sensor output signal to the outside and is arranged to contact the inner electrode 200. A cable grommet 36 with an approximately round columnar shape is arranged in the outer tube 40 such that the cable grommet 36 is in contact with the rear end of the separator 34. The cable grommet 36 has a through-hole extending along the axial line O and through which the lead wire 60 passes.The cable bushing 36 can be made of rubber material, such as silicone rubber or fluoro rubber.

[0028] The outer tube 40 has a plurality of first inlet holes 41 formed on its side wall at a position on the front end side of the position of the cable grommet 36 such that the first inlet holes 41 are arranged at predetermined intervals in the circumferential direction. A tubular gas-permeable filter 37 is fitted into the radially outer side of a rear end portion of the outer tube 40 so as to cover the first inlet holes 41. Further, the tubular protective outer tube 38 formed of metal encloses the filter 37 from the radially outer side. The protective outer tube 38 may be made of, for example, stainless steel. The protective outer tube 38 has a plurality of second inlet holes 39 formed on its side wall such that the second inlet holes 39 are arranged at predetermined intervals in the circumferential direction.Thus, an external gas can be introduced into the interior of the outer tube 40 through the second inlet holes 39 of the protective outer tube 38, the filter 37, and the first inlet holes 41 of the outer tube 40, and then to the inner electrode 200 of the gas sensor element 10. Note that the filter 37 is held between the outer tube 40 and the protective outer tube 38 by caulking the outer tube 40 and the protective outer tube 38 on the front and rear ends of the second inlet holes 39. The filter 37 can be made of a porous structure of a water-repellent resin, such as fluorocarbon resin. Because the filter 37 is water-repellent, the filter 37 allows a reference gas (the atmosphere) to be introduced into the space inside the gas sensor element 10 while preventing the passage of external water.

[0029] Fig.Fig. 2A shows the exterior of a gas sensor element 10 according to an embodiment. The solid electrolyte element 11 of the gas sensor element 10 has the aforementioned flange portion 12, a downwardly tapered portion or downwardly open portion 13 formed on the front end side (in Fig. 2A, the left side) of the flange portion 12, and a base portion 18 provided on the rear end side of the flange portion 12. The bottom-tapered portion 13 is tapered so that its diameter gradually decreases toward the front end side and has a closed front end. The base portion 18 is a portion generally shaped like a hollow cylinder and has an opening at its rear end. The outer electrode 100 is formed on the outer surface of the solid electrolyte element 11.

[0030] The outer electrode 100 has an outer terminal portion 110 and an outer detection electrode portion 120. The outer detection electrode portion 120 is formed to cover the outer surface of a front-end portion of the bottom-end portion 13 of the solid electrolyte element 11. The outer detection electrode portion 120 is provided at a position where it comes into contact with a gas to be measured. The outer detection electrode portion 120 forms an oxygen concentration cell in conjunction with an inner electrode detection portion (described below) of the inner electrode 200 and the solid electrolyte element 11, and generates an electromotive force (voltage) corresponding to the gas concentration of the gas to be measured.

[0031] The external terminal portion 110 is connected to the rear end of the external detection electrode portion 120. The external terminal portion 110 has a longitudinal terminal portion 114 and a ring terminal portion 115. The ring terminal portion 115 is formed on the surface on the front end side of the flange portion 12 (a step portion between the flange portion 12 and the bottom-terminating portion 13) such that the ring terminal portion 115 extends over the entire circumference of the gas sensor element 10 and forms an annular shape. The ring terminal portion 115 is in electrical contact with the protective element 62 ( Fig.1). The longitudinal terminal portion 114 is formed to extend linearly along the direction of the axial line O and connects the rear end of the external detection electrode portion 120 and the ring terminal portion 115. Note that an electrode protection layer (not shown) for protecting the external detection electrode portion 120 may be formed on the surface of the external detection electrode portion 120. Note that the shape and configuration of the external electrode 100 are merely examples, and various other shapes and configurations may be used.

[0032] The solid electrolyte element 11 is made of a solid electrolyte comprising ZrO2, which has oxygen ion conductivity. Generally, stabilized zirconia containing an added stabilizer is used as the solid electrolyte. An oxide selected from yttrium oxide (Y2O3), calcium oxide (CaO), magnesium oxide (MgO), cerium oxide (CeO2), ytterbium oxide (Yb2O3), scandium oxide (Sc2O3), and the like can be used as a stabilizer.

[0033] Fig. 2B is a longitudinal sectional view of the gas sensor element 10. As described above, the internal electrode 200 (reference electrode) is provided on the inner surface of the solid electrolyte element 11. The internal electrode 200 includes an internal terminal portion 210 and an internal detection electrode portion 220.

[0034] The internal detection electrode portion 220 is formed to cover the inner surface of a portion on the front end side of the solid electrolyte element 11. The internal terminal portion 210 is connected to the rear end of the internal detection electrode portion 220 and is connected to the connection terminal 70 ( Fig. 1) in contact to establish an electrical connection therewith. The internal detection electrode region 220 and the internal terminal region 210 as a whole cover substantially the entire inner surface of the solid electrolyte element 11. As described below, the internal terminal region 210 has a higher impact resistance than the internal detection electrode region 220. In the example of Fig. 2B, the boundary between the internal detection electrode portion 220 and the internal terminal portion 210 is located at a position corresponding to the flange portion 12 of the solid electrolyte element 11. As described with reference to Fig.1, the holding member (the powder-filled region 31) is arranged on the rear end side of the flange portion 12. Preferably, not the internal detection electrode portion 220 but the internal terminal portion 210 is formed in a region of the inner surface located on the rear end side of the flange portion 12 where the powder-filled region 31 is located. The reason for this is as follows. As a result of caulking, a considerably high compressive force acts on the outer surface of a portion on the rear end side of the flange portion 12 where the powder-filled region 31 is located. Therefore, a tensile force acts on the inner surface of the portion on the rear end side of the flange portion 12. As a result, as described below, a reaction prevention layer BL provided on the internal detection electrode portion 220 may be cracked.In contrast, when the inner terminal portion 210 is provided on the inner surface of the portion on the rear end side of the flange portion 12, the reaction prevention layer BL is not subjected to such a tensile force, and cracking in the reaction prevention layer BL can be prevented.

[0035] The inner sensing electrode region 220 and the inner terminal region 210 are preferably formed from an electrically conductive oxide layer. Meanwhile, the outer sensing electrode region 120 and the outer terminal region 110 are made of a noble metal, such as platinum (Pt), or a noble metal alloy, such as a platinum alloy.

[0036] Fig.2C is an explanatory view showing, on a larger scale, the sectional structure of the internal detection electrode region 220. The internal detection electrode region 220 is constituted by an electrically conductive oxide layer OCL2 formed on the inner surface of the solid electrolyte element 11 and has a single-layer structure. The electrically conductive oxide layer OCL2 preferably contains, as a main component, a crystalline phase (perovskite phase) having a perovskite-like oxide crystal structure described by the following composition formula. La a M b Ni c O x (1)

[0037] In the composition formula, element M represents elements of Co and / or Fe, where a + b + c = 1 and 1.25 ≤ x ≤ 1.75. The coefficients a, b, and c preferably satisfy the following relationships. 0.459≤a≤0.535 0.200≤b≤0.475 0.025≤c≤0.350

[0038] A perovskite-type electrically conductive oxide having a composition represented by the above-described composition formula has an electrical conductivity of 250 S / cm or greater at room temperature (25 °C) and a B constant of 600 K or less. Therefore, such a perovskite-type electrically conductive oxide possesses good properties; that is, it has a higher electrical conductivity and a smaller B constant compared to the case where the above-described relationships are not satisfied. Furthermore, since the perovskite-type electrically conductive oxide has a lower activation energy of the interfacial resistance compared to a noble metal electrode, the interfacial resistance can be sufficiently reduced even at low temperatures.It should be noted that when a Pt electrode is exposed to an air atmosphere at a temperature of approximately 600 °C, the Pt electrode oxidizes and the interfacial resistance increases. In contrast, the electrically conductive perovskite-type oxide has the advantage of having a low probability of change over time.

[0039] The coefficients b and c preferably satisfy the following relations (3b) and (3c) instead of the previously described relations (2b) and (2c). 0.200≤b≤0.375 0.125≤c≤0.300

[0040] In this case, the electrically conductive perovskite-type oxide can have a higher electrical conductivity and a smaller B constant.

[0041] The coefficient x of O (oxygen) in the above-described formula (1) is theoretically 1.5 in the case where the entire electrically conductive oxide with the above-described composition is formed with the perovskite phase. However, since the oxygen content may deviate from the stoichiometric composition, the range of x is defined as 1.25 ≤ x ≤ 1.75 as a typical example.

[0042] Note that the electrically conductive oxide layer OCL2 may further contain an oxide in addition to the perovskite phase having the above-described composition. For example, the electrically conductive oxide layer OCL2 may contain the perovskite phase and cerium oxide to which a rare earth element oxide other than cerium oxide is added (hereinafter, this will be referred to as "rare earth element-added cerium oxide"). Note that in the following description, the rare earth element-added cerium oxide is also referred to as a "Co material." For example, La2O3, Gd2O3, Sm2O3, and / or Y2O; may be used as a rare earth element oxide other than cerium oxide. The proportion of the rare earth element RE in the cerium oxide mixed with a rare earth element can be determined in such a way that the molar proportion of the rare earth element RE; ie, the value of {RE / (Ce+RE)}, is in a range of, for example, 10 mol% to 50 mol%. The volume ratio of the rare earth element-added cerium oxide in the electrically conductive oxide layer OCL2 can also be set to be in the range of, for example, 10 vol% to 40 vol%. Although such rare earth element-added cerium oxide is an insulator at low temperatures (room temperature), it serves as a solid electrolyte with oxygen ion conductivity at high temperatures (temperatures at which the gas sensor 300 is used). Therefore, when the electrically conductive oxide layer OCL2 contains the rare earth element-added cerium oxide, it is possible to reduce the interfacial resistance of the electrically conductive oxide layer OCL2 when the gas sensor 300 is in use.However, in order to reduce the electrical resistance at room temperature, the electrically conductive oxide layer OCL2 preferably does not contain cerium oxide mixed with a rare earth element.

[0043] The electrically conductive oxide layer OCL2 may contain an alkaline earth metal element in a very small amount, as long as the alkaline earth metal element does not affect the electrical conductivity of the electrically conductive oxide layer OCL2. However, preferably, the electrically conductive oxide layer OCL2 is substantially free of alkaline earth metal elements. In such a case, the occurrence of a change in the weight of the electrically conductive oxide layer OCL2, that is, absorption or release of oxygen, becomes less likely even when the electrically conductive oxide layer OCL2 is exposed to a wide temperature range from room temperature to a temperature of approximately 900°C when the gas sensor 300 is in use. Consequently, the electrically conductive oxide layer OCL2 suitable for use in a high-temperature environment is obtained.It should be noted that in this description, “essentially free of alkaline earth metal elements” means that no alkaline earth metal element can be detected or identified by X-ray fluorescence (XRF).

[0044] Fig.2D is an explanatory view showing, on a larger scale, the sectional structure of the inner terminal region 210. The inner terminal region 210 has a multilayer structure including a lanthanum zirconate layer LZL formed on the inner surface of the solid electrolyte element 11 and an electrically conductive oxide layer OCL1 formed on the inner surface side of the lanthanum zirconate layer LZL. The electrically conductive oxide layer OCL1 has a structure substantially similar to that of the electrically conductive oxide layer OCL2 of the previously described internal sensing electrode region 220. However, the proportion of the rare earth element-added cerium oxide in the electrically conductive oxide layer OCL2 constituting the internal sensing electrode region 220 is preferably equal to or greater than the proportion of the rare earth element-added cerium oxide in the electrically conductive oxide layer OCL1 constituting the internal terminal region 210.This is because when the proportion of cerium oxide added with a rare earth element is increased in the internal sensing electrode region 220, the internal sensing electrode region 220 has a porous structure, thereby increasing the area of ​​the triphase interface and reducing the interfacial resistance. Furthermore, when the proportion of cerium oxide added with a rare earth element is reduced in the internal terminal region 210, the internal terminal region 210 has a dense structure. This increases the electron conductivity and increases the strength of the internal terminal region 210, further improving its impact resistance.

[0045] The lanthanum zirconate layer LZL is formed during heating of the inner terminal region 210 as a result of a reaction between lanthanum (La) contained in the electrically conductive oxide layer OCL1 and ZrO2 contained in the solid electrolyte element 11. Such a lanthanum zirconate layer LZL is also referred to as a "reaction layer LZL." The formation of the lanthanum zirconate layer LZL strengthens the adhesion between the lanthanum zirconate layer LZL and the electrically conductive oxide layer OCL1 and also increases the adhesion between the lanthanum zirconate layer LZL and the solid electrolyte element 11, thereby improving impact resistance. Therefore, in a region where the inner terminal portion 210 is present, the lanthanum zirconate layer LZL is preferably formed between the electrically conductive oxide layer OCL1 and the solid electrolyte member 11 in order to improve the impact resistance.

[0046] It should be noted that since the lanthanum zirconate layer LZL has no oxygen ion conductivity, the lanthanum zirconate layer LZL is preferably not formed in the internal detection electrode region 220 ( Fig.2C). However, a thin lanthanum zirconate layer LZL may be formed in the internal sensing electrode region 220, provided the ensured oxygen ion conductivity is practically sufficient. In other words, the internal sensing electrode region 220 is preferably formed such that (i) the lanthanum zirconate layer LZL is not formed between the electrically conductive oxide layer OCL2 and the solid electrolyte element 11, or (ii) the lanthanum zirconate layer LZL formed between the electrically conductive oxide layer OCL2 and the solid electrolyte element 11 is thinner than the lanthanum zirconate layer LZL formed between the solid electrolyte element 11 and the electrically conductive oxide layer OCL1 of the internal terminal region 210.Since the lanthanum zirconate layer, which is a high-resistance layer, is formed in this case, the interface resistance between the electrically conductive oxide layer OCL2 and the solid electrolyte element 11 is prevented from increasing excessively.

[0047] Fig. 3A to 3D are explanatory views showing a gas sensor element 10a according to another embodiment. The gas sensor element 10a shown in Fig. 3A to 3D is different from that shown in Fig. 2A to 2D only in two points; ie, the sectional structure at the position of the internal detection electrode portion 220a ( Fig. 3C) and the position of the interface between the internal detection electrode region 220a and the internal terminal region 210 ( Fig. 3B). With regard to other structural characteristics, the gas sensor element 10a shown in Fig. 3A to 3D, is the same as the gas sensor element 10 shown in Fig.2A to 2D. As shown in Fig.As shown in FIG. 3C, the internal detection electrode region 220a has a multilayer structure including a reaction prevention layer BL formed on the inner surface of the solid electrolyte member 11 and the electrically conductive oxide layer OCL2. The reaction prevention layer BL is an oxide layer composed of the rare-earth element-added cerium oxide. As described above, the rare-earth element-added cerium oxide serves as a solid electrolyte having oxygen ion conductivity at high temperatures. Regarding the characteristics of the reaction prevention layer BL, the internal detection electrode region 220a can be considered to have a single-layer structure of the electrically conductive oxide layer OCL2, and the reaction prevention layer BL is formed between the internal detection electrode region 220a (=OCL2) and the solid electrolyte member 11.The function of the reaction prevention layer BL is to prevent the reaction between La in the electrically conductive oxide layer OCL2 and the ZrO2 in the solid electrolyte element 11. By providing the reaction prevention layer BL, the formation of the lanthanum zirconate layer LZL is advantageously prevented even when heating is carried out under conditions under which the lanthanum zirconate layer LZL (reaction layer) would be formed if the reaction prevention layer BL were not present.

[0048] Fig. 4A to 4D are explanatory views showing a gas sensor element 10b according to still another embodiment. Fig. The gas sensor element 10b shown in Figures 4A to 4D differs from that shown in Fig. 3A to 3D only in two points; ie, in the sectional structure at the position of the internal detection electrode portion 220b ( Fig.4C) and in the composition of the electrically conductive oxide layers OCL1b and OCL2b. Regarding other structural properties, the Fig. 4A to 4D is the same as the gas sensor element 10b shown in Fig. 3A to 3D shown gas sensor element 10a. As shown in Fig. 4C, the internal detection electrode region 220b has a multi-layer structure including a reaction prevention layer BL formed on the inner surface of the solid electrolyte member 11, an electrically conductive intermediate layer ICL formed on the inner surface of the reaction prevention layer BL, and the electrically conductive oxide layer OCL2b. Note that if the reaction prevention layer BL is considered to be different from the internal detection electrode region 220b formed in the embodiment of Fig.3A to 3D, the internal detection electrode region 220b has a double-layer structure composed of the electrically conductive intermediate layer ICL and the electrically conductive oxide layer OCL2b. This structure is obtained by adding the electrically conductive intermediate layer ICL to the structure shown in Fig. 3C. The electrically conductive intermediate layer ICL preferably contains the perovskite phase as a main component and contains the cerium oxide mixed with a rare earth element as a secondary component. Just like the electrically conductive oxide layers OCL1 and OCL2 shown in the Fig.2A to 2D and 3A to 3D, the electrically conductive interlayer ICL has both ionic conductivity and electronic conductivity at high temperatures (during use of the gas sensor 300). Therefore, the electrically conductive interlayer ICL exhibits a sufficiently low interfacial resistance. Furthermore, in this structure, the electrically conductive oxide layers OCL1b and OCL2b can be formed by the perovskite phase without adding the rare earth element-added cerium oxide. In such a case, since the electronic conductivities of the electrically conductive oxide layers OCL1b and OCL2b increase at room temperature, the electrical resistance can be reduced. B. Manufacturing process

[0049] Fig. 5 is a flow chart showing a method for producing the Fig.2A to 2D. In step T210, the material (e.g., powder of yttria-stabilized zirconia) of the solid electrolyte element 11 is compressed to obtain a compact element, which is then processed into a shape (tubular shape) as shown in Fig.2A, thereby obtaining a preliminary body (preliminary compact). In step T230, a solution of an electrically conductive oxide is prepared. In step T230, for example, powders of raw materials of the electrically conductive oxides are weighed and wet-mixed, and the resulting mixture is dried, thereby preparing a raw material powder mixture. For example, La(OH)3 or La2O3; and Co3O4, Fe2O3, and NiO can be used as the raw material powder of the perovskite phase. Likewise, CeO2 and La2O3, Gd2O3, Sm2O3, Y2O3, and the like can be used as the raw material powder of the rare earth element-added cerium oxide. The mixture of these raw material powders is pre-baked at 700 to 1200°C for 1 to 5 hours in the atmosphere, thereby preparing a pre-baked powder.This preheated powder is pulverized to a predetermined grain size using, for example, a wet ball mill and dissolved together with a binding material, such as ethyl cellulose, in a solvent, such as terpineol or butylcarbitol, to obtain a suspension.

[0050] In step T240, a suspension of a noble metal oxide, such as a Pt paste, is applied to an area in which the outer electrode 100 ( Fig. 2A) is to be produced, and the suspension of an electrically conductive oxide is applied to an area in which the internal connection region 210 ( Fig.2B). In order to prevent the suspension of electrically conductive oxide from being applied to a region in which the internal detection electrode region 220 is to be formed, a mask element is preferably applied to this region in advance. In step T250, after drying, the preliminary compact element is annealed at an annealing temperature of, for example, 1250 °C to 1450 °C (preferably 1350 ± 50 °C). In this case, as in Fig.2D, the lanthanum zirconate layer LZL is formed between the electrically conductive oxide layer OCL1 of the inner lead region 210 and the solid electrolyte member 11. As described above, the lanthanum zirconate layer LZL is a layer formed as a result of a reaction between lanthanum (La) contained in the electrically conductive oxide layer OCL1 and ZrO2 contained in the solid electrolyte member 11. Note that the higher the annealing temperature and the smaller the proportion of cerium oxide containing a rare earth element, the greater the thickness of the lanthanum zirconate layer LZL. Therefore, the thickness of the lanthanum zirconate layer LZL can be adjusted by adjusting these parameters.

[0051] In step T260, the suspension of electrically conductive oxide is applied to an area in which the internal detection electrode region 220 ( Fig.2B). In step T270, after drying, annealing is carried out at an annealing temperature of, for example, 800 °C to 1050 °C (preferably 1000 ± 50 °C). If the annealing temperature in step T260 is limited to 1050 °C or lower, the lanthanum zirconate layer LZL is not formed at all or is formed to have a thickness smaller than the thickness of the lanthanum zirconate layer formed in the inner terminal region 210. As a result, as shown in Fig. 2C, the lanthanum zirconate layer LZL is hardly interposed between the electrically conductive oxide layer OCL2 of the internal detection electrode region 220 and the solid electrolyte element 11.

[0052] Fig. 6 is a flow chart showing a method for producing the Fig. 3A to 3D. Step T310 is the same as step T210 of the Fig.5. In step T330, the suspension of electrically conductive oxide and the suspension for the reaction prevention layer BL ( Fig. 3C). The suspension of electrically conductive oxide is the same as that used in step T230 of Fig.5 is prepared. As previously described, a reaction prevention layer BL is formed from the rare earth element-added cerium oxide. Accordingly, the suspension for the reaction prevention layer BL is prepared by dissolving a commercially available rare earth element-added cerium oxide (La2O3, Gd2O3, Sm2O3, Y2O3, and the like) together with a binder material, such as ethyl cellulose, in a solvent, such as terpineol or butyl carbitol. The rare earth element-added cerium oxide is prepared by a solid phase method or a co-precipitation method. In step T340, the suspension of noble metal oxide, such as a Pt paste, is applied to a region in which the outer electrode 100 ( Fig.3A), and a suspension of the cerium oxide mixed with a rare earth element is applied to a region in which the reaction prevention layer BL is to be formed. Furthermore, the suspension of electrically conductive oxide is applied such that a region in which the internal connection region 210 ( Fig. 3B) is to be produced, and an area on the side of the inner surface of the reaction prevention layer BL is covered, in which the internal detection electrode region 220a ( Fig.3C). In this case, the internal sensing electrode region 220a and the internal terminal region 210 are formed from the same electrically conductive oxide. Note that if the composition of the electrically conductive oxide of the internal sensing electrode region 220a differs from the composition of the electrically conductive oxide of the internal terminal region 210, suspensions with different compositions are applied to the respective regions.

[0053] In step T350, after drying, the preliminary compact element is annealed at an annealing temperature of, for example, 1250°C to 1450°C (preferably 1350 ± 50°C). Since at this time the reaction prevention layer BL is present between the electrically conductive oxide layer OCL1 of the internal detection electrode region 220a and the solid electrolyte element 11, as shown in Fig.3C, the lanthanum zirconate layer LZL is not formed. Since the steps of Fig. 6 a small number of baking steps compared to the steps of Fig. 5, the manufacturing process described in Fig. 6, has the advantage that the overall production time is shorter.

[0054] Fig. 7 is a flow chart showing a method for producing the Fig. 4A to 4D. The gas sensor element 10b shown in Fig. The manufacturing process shown in Figure 7 is the same manufacturing process shown in Fig. 6, with the exception of two steps; ie, steps T330a and T340a. The step T330a of the Fig. 7 differs from step T330 of the Fig.6 in that in step T330a, two types of suspensions of electrically conductive oxides are prepared, ie, a suspension of an electrically conductive oxide containing a cerium oxide added with a rare earth element, and a suspension of an electrically conductive oxide not containing a cerium oxide added with a rare earth element. Step T340a of Fig. 7 differs from step T340 of the Fig. 6 in that in step T340a, after the application of the suspension for the reaction prevention layer BL, the suspension for the electrically conductive intermediate layer ICL ( Fig.4C), and then the suspension for the electrically conductive oxide layer OCL2b of the internal detection electrode region 220b is applied. As previously described, the electrically conductive intermediate layer ICL contains the perovskite phase and the rare earth element-added cerium oxide. Meanwhile, the electrically conductive oxide layer OCL2b does not contain the rare earth element-added cerium oxide and is formed only in the perovskite phase. Therefore, in step T340a, the two types of suspensions of electrically conductive oxides and the suspension for the reaction prevention layer BL prepared in step T330a are used to apply a suspension suitable for each region. Therefore, it is possible to apply the suspension described in Fig. 4A to 4D, the preliminary compact element is baked at a baking temperature of, for example, 1250 °C to 1450 °C (preferably 1350 ± 50 °C) in step T350.

[0055] It should be noted that the various manufacturing conditions used in the Fig. The manufacturing processes shown in Figures 5 to 7 are merely examples and can be freely modified according to the intended use of products and the like. C. Mechanical impact resistance test

[0056] Table 1 below shows the results of a mechanical impact strength (impact resistance) test of the inner lead portion 210. Samples S01 and S02 are examples, and samples S03 and S04, whose sample numbers are indicated by an asterisk, are comparative examples. Zirconia with yttrium oxide added (5YSZ) (yttrium oxide: 5 mol%) was used for the solid electrolyte element 11 of each sample. In preparing each sample, a suspension for the electrically conductive oxide film OCL1 was applied to a portion of the solid electrolyte element 11 corresponding to the inner lead portion 210, and this portion was dried.This suspension was prepared by mixing a powder of the electrically conductive perovskite-type oxide with a composition represented by the previously described formula (1), cerium oxide with gadolinium added (GDC) as a secondary component, a binder, and an organic solvent. As shown in Table 1, LaCo was obtained. 0.5 Ni 0.5 O3 (which is referred to as “LCN”) or LaFe 0.5 Ni 0.5O3 (referred to as "LFN") was used as an electrically conductive oxide powder. The gadolinium content of the gadolinium-added cerium oxide was 20 mol%. The content of gadolinium-added cerium oxide in the electrically conductive oxide layer OCL1 was set to 30 vol%. For the preparation of samples S01 and S02, the suspension was applied to the preliminary compact element of the solid electrolyte element 11 and dried, and the preliminary compact element was annealed at 1350 °C for 1 hour. Meanwhile, for the preparation of samples S03 and S04, the preliminary compact element of the solid electrolyte element 11 was annealed at 1350 °C for 1 hour, the suspension was applied and dried, and then heat treated at 1000 °C for 1 hour. Table 1 TEST OF MECHANICAL IMPACT RESISTANCE OF THE INTERNAL CONNECTION AREA Sample No. Composition and bakeout temperature of the internal connection area 210 Damage to the connection area Perovskite phase Co-Matrix Reaction layer LZL Bake-out temperature S01 LCN GDC (30 vol%) Planned 1350 °C Not observed S02 LFN GDC (30 vol%) Planned 1350 °C Not observed S03* LCN GDC (30 vol%) Not planned 1000 °C Observed S04* LFN GDC (30 vol%) Not planned 1000 °C Observed LCN = LaCo 0,,5 Ni0,5 O3 LFN = LaFe 0,5 Ni 0,5 O3 GDC = 20 mol% Gd-CeO2

[0057] Fig.Figures 8A to 8D show cross-sectional SEM images of the interface between the electrically conductive oxide layer OCL1 of the inner lead region 210 and the solid electrolyte element 11 for samples S01 to S04. The SEM images show that the reaction layer LZL is absent in samples S03 and S04 (comparative examples), whereas the reaction layer LZL (the lanthanum zirconate layer) is present in samples S01 and S02 (examples). This difference arises because the annealing temperature was set to 1350 °C for samples S01 and S02 and 1000 °C for samples S03 and S04. That is, by setting the annealing temperature to a temperature higher than 1000 °C, the reaction layer LZL (the lanthanum zirconate layer) can be formed between the electrically conductive oxide layer OCL1 and the solid electrolyte element 11.It should be noted that for the formation of the reaction layer LZL, the annealing temperature is preferably set to a temperature of 1250 °C to 1450 °C, and more preferably to 1350 ± 50 °C.

[0058] In the mechanical impact resistance test, the connection terminal 70, which is made of SUS ( Fig.1) was used, and the insertion and removal of the connection terminal 70 was repeated 30 times. After that, each sample was cut in half, and a portion of the inner terminal region 210 with which the connection terminal 70 came into contact was observed with a magnifying glass. In samples S01 and S02 (examples), damage to the inner terminal region 210 was not observed. In samples S03 and S04 (comparative examples), peeling of the inner terminal region 210 occurred (see the right side of Table 1). Presumably, the reason why damage to the inner terminal region 210 was not observed in samples S01 and S02 (examples) is that in samples S01 and S02, the reaction layer LZL serves as an adhesion layer between the electrically conductive oxide layer OCL1 and the solid electrolyte element 11, which, with reference to Fig.2D. Therefore, the interface is highly rigid. As can be seen from the test results, in order to improve the impact resistance of the internal electrode 200, the reaction layer LZL (the lanthanum zirconate layer) is preferably formed between the electrically conductive oxide layer OCL1 of the internal terminal region 210 and the solid electrolyte element 11. D. Measurement of electrode interface resistance

[0059] Table 2 below shows the results of a test in which the electrode interface resistance for gas sensor elements with the structure as described in Fig.2A to 2D and 3A to 3D. Samples S11 to S15 are examples, and sample S16, whose sample number is marked with an asterisk, is a comparative example. Table 2 shows the composition and annealing temperature of the internal sensing electrode region 220, the composition and annealing temperature of the internal terminal region 210, and the measured electrode interface resistance for each sample. In the composition columns, the compositions are shown in a simplified manner. For example, the composition of the internal sensing electrode region 220 (i.e., the electrically conductive oxide layer OCL2) of sample S11 is such that 30 vol% of GDC (gadolinium-added cerium oxide containing 20 mol% gadolinium), which is a secondary component, is added to LCN (LaCo 0,5 Ni 0,5 O3), which is a main component. It should be noted that in samples S14 and S15, the reaction prevention layer BL ( Fig.3(C)) is provided in the internal detection electrode region 220. However, in other samples S11 to S13 and S16, the reaction prevention layer BL is not provided. Yttria-stabilized zirconia (5YSZ) containing 5 mol% yttria was used for the solid electrolyte element 11 of each sample.

[0060] Samples S11 to S13 were prepared according to the procedure described in Fig. 5. In step T240 of the Fig. 5, a suspension prepared by mixing 30 vol% of yttria-stabilized zirconium oxide (5YSZ) in a platinum (Pt) powder was used as a suspension for the outer electrode 100. Furthermore, suspensions with the compositions Fig. 10 are optionally used as a suspension for the internal connection area 210. In step T250 of the Fig.5, the annealing was carried out at 1350 °C, and in step T270, the annealing was carried out at 1000 °C. As a result, the gas sensor elements of the samples S11 to S13 were each heated to the temperature Fig. The structure shown in Figures 2A to 2D is preserved.

[0061] Samples S14 and S15 were prepared according to the procedure described in Fig. 6. A suspension prepared by mixing 30 vol% of yttria-stabilized zirconia (5YSZ) into a platinum (Pt) powder was used as a suspension for the outer electrode 100. Suspensions with the compositions shown in Table 2 were also used as suspensions for other regions. In step T350 of the Fig. 6, the annealing was carried out at 1350 °C. As a result, the gas sensor elements of samples S14 and S15 were each heated to the temperature Fig. The structure shown in Figures 3A to 3D is preserved.

[0062] Sample S16 (comparative example) was tested according to the Fig. 6. A suspension prepared by mixing 30 vol% of yttria-stabilized zirconia (5YSZ) into a platinum (Pt) powder was used as a suspension for the outer electrode 100. Suspensions with the Fig. 10 were used as suspensions for other areas. However, in sample S16, the suspension for the reaction prevention layer BL was not applied. In step T350 of the Fig. 6, annealing was carried out at 1350 °C. As a result, an element in which the reaction layer LZL (the lanthanum zirconate layer) was formed neither in the internal detection electrode region 220 nor in the internal terminal region 210 was obtained as the gas sensor element of Sample S16.

[0063] Two samples were prepared for each of the previously described samples S11 to S16. The cross section of one of the two obtained samples was observed under an SEM (scanning electron microscope). Furthermore, the state of the reaction layer LZL between the internal detection electrode region 220 and the solid electrolyte element 11 and the state of the reaction layer LZL between the internal terminal region 210 and the solid electrolyte element 11 were examined. That is, the presence / absence of the reaction layer LZL and the thickness of the reaction layer LZL were examined by observing the backscattered electron SEM images and by applying EDS (energy dispersive X-ray spectrometry). As shown in Table 2, in samples S11 to S15, the reaction layer LZL was not formed in the internal detection electrode region 220, and in sample S16, the reaction layer LZL was formed in the internal detection electrode region 220.Furthermore, in all samples S11 to S16, the reaction layer LZL was formed in the inner connection region 210.

[0064] Using the other of the two specimens prepared for each sample S11 to S16, the electrode interfacial resistance was measured. That is, the specimen of each sample was placed in a furnace with the temperature set at 550 °C, and the electrode interfacial resistance was measured using an AC impedance method. The voltage amplitude for the measurement was set to 10 mV. Table 2 Measurement of electrode interface resistance Sample No. Composition and bakeout temperature for the internal detection electrode area 220 Composition and bakeout temperature for the internal connection area 210 Electrode interface resistance [Ω] composition Reaction prevention layer BL Reaction layer LZL Bake-out temperature composition Reaction layer LZL Bake-out temperature S11 LCN / GDC (30 vol%) Not provided ( Fig. 2C) Not planned 1000 °C LCN / GDC (30 vol%) Planned 1350 °C 55 S12 LCN / GDC (30 vol%) Not provided ( Fig. 2C) Not planned 1000 °C LCN / GDC (30 vol%) Planned 1350 °C 52 S13 LFN / GDC (30 vol%) Not provided ( Fig. 2C) Not planned 1000 °C LFN / GDC (30 vol%) Planned 1350 °C 172 135 S14 LCN / GDC (30 vol%) GDC ( Fig. 3C) Not planned 1350 °C LCN / GDC (30 vol%) Planned 1350 °C 135 S15 LFN / GDC (30 vol%) GDC ( Fig. 3C) Not planned 1350 °C LFN / GDC (30 vol%) Planned 1350 °C 420 1350 °C S16 LCN / GDC (30 vol%) Not planned Planned LCN / GDC (30 vol%) Planned 1350 °C 2505 LCN = LaCo 0,5 Ni 0,5 O3 LFN = LaFe 0,5 Ni 0,5 O3 GDC = 20 mol% Gd-CeO2 LDC = 40 mol% La-CeO2

[0065] Fig.Figure 9 is a graph showing the measurement results of the electrode interface resistances of samples S11 to S16. While the electrode interface resistances of samples S11 to S15 are 500 Ω or less and sufficiently small from a practical point of view, the electrode interface resistance of sample S16 (comparative example) is greater than 2000 Ω and is thus very high. As can be seen from these results, the electrode interface resistance can be sufficiently reduced and the internal resistance of the gas sensor element can be significantly reduced by using the structure of the Fig. 2A to 2D or Fig. 3A to 3D, in which the reaction layer LZL (the lanthanum zirconate layer) is not formed in the internal detection electrode region 220. • Modifications:

[0066] It should be noted that the present invention is not limited to the examples and embodiments described above and can be implemented in various ways without departing from the scope of the invention. • Modification 1:

[0067] In the above-described embodiments, an oxygen concentration sensor is described as an example of the gas sensor of the present invention. However, the present invention can be applied to an oxygen sensor including a plate-shaped gas sensor element and to a gas sensor for a gas other than oxygen.

[0068] The invention is described in detail with reference to the foregoing embodiments. However, the invention should not be construed as being limited thereto. It should also be apparent to those skilled in the art that various changes in form and detail may be made to the invention as shown and described above. Such changes are intended to be included within the spirit and scope of the appended claims.

Claims

[1] A gas sensor element (10, 10a, 10b) comprising: a solid electrolyte element (11) extending in an axial direction and containing ZrO2 with oxygen ion conductivity; an external electrode (100) provided on one of surfaces of the solid electrolyte element (11) and coming into contact with a gas to be measured; and an internal electrode (200) provided on an opposite surface of the solid electrolyte element (11) and coming into contact with a reference gas, wherein the internal electrode (200) has an internal detection electrode portion (220, 220a, 220b) arranged on a front end side in the axial direction and detecting a specific gas contained in the gas to be measured, and an internal terminal portion (210) arranged behind the internal detection electrode portion (220, 220a, 220b), connected to the internal detection electrode portion (220, 220a, 220b), and in contact (70) with a connection terminal for output to the outside, wherein the internal electrode (200) has an electrically conductive oxide layer (OCL1, OCL1b, OCL2, OCL2b) whose main component is a perovskite phase represented by a composition formula with La a M b Ni c O x (where M is an element in the form of Co and / or Fe, a + b + c = 1, 1.25 ≤ x ≤ 1.75), and has a perovskite-like crystal structure; the coefficients a, b and c satisfy 0.459 ≤ a ≤ 0.535, 0.200 ≤ b ≤ 0.475 and 0.025 ≤ c ≤ 0.350; the internal connection region (210) has a lanthanum zirconate layer (LZL) between the electrically conductive oxide layer (OCL1, OCL1b, OCL2, OCL2b) and the solid electrolyte element (11); and the internal detection electrode region (220, 220a, 220b) is formed such that (i) no lanthanum zirconate layer (LZL) is formed between the electrically conductive oxide layer (OCL1, OCL1b, OCL2, OCL2b) and the solid electrolyte element (11), or (ii) a lanthanum zirconate layer (ZLZ) formed between the electrically conductive oxide layer (OCL1, OCL1b, OCL2, OCL2b) and the solid electrolyte element (11) is thinner than the lanthanum zirconate layer (LZL) of the internal connection region (210). [2] The gas sensor element (10, 10a, 10b) according to claim 1, wherein a reaction prevention layer (BL) containing cerium oxide added with a rare earth element as a main component is provided between the internal detection electrode region (220, 220a, 220b) and the solid electrolyte member (11). [3] The gas sensor element (10, 10a, 10b) according to claim 2, wherein the reaction prevention layer (BL) is provided only on the front end side of the gas sensor element (10, 10a, 10b) with respect to a holding member that holds the gas sensor element (10, 10a, 10b) when the gas sensor element (10, 10a, 10b) is incorporated in a gas sensor (300). [4] The gas sensor element (10, 10a, 10b) according to any one of claims 1 to 3, wherein the internal detection electrode region (220, 220a, 220b) has an electrically conductive intermediate layer (ICL) formed between the reaction prevention layer (BL) and the electrically conductive oxide layer (OCL1, OCL1b, OCL2, OCL2b), the electrically conductive oxide layer (OCL1, OCL1b, OCL2, OCL2b) does not contain cerium oxide mixed with a rare earth element and comprises a perovskite phase characterized by the composition formula La a M b Ni c O x is represented, and the electrically conductive intermediate layer (ICL) is a perovskite phase characterized by the composition formula La a M b Ni c O x and has a cerium oxide mixed with a rare earth element. [5] The gas sensor element (10, 10a, 10b) according to any one of claims 1 to 3, wherein the electrically conductive oxide layer (OCL1, OCL1b, OCL2, OCL2b) comprises a first electrically conductive oxide layer forming the internal terminal region (210) and a second electrically conductive oxide layer forming the internal detection electrode region (220, 220a, 220b), the first electrically conductive oxide layer and the second electrically conductive oxide layer each comprise the perovskite phase and a cerium oxide mixed with a rare earth element, and the proportion of cerium oxide mixed with a rare earth element in the second electrically conductive oxide layer is equal to or greater than the proportion of cerium oxide mixed with a rare earth element in the first electrically conductive oxide layer. [6] A gas sensor (300) with: a gas sensor element (10, 10a, 10b) according to one of claims 1 to 5; and a holding element for holding the gas sensor element (10, 10a, 10b).

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