Metal oxide sintered body for thermistors, thermistor element, and method for manufacturing metal oxide sintered body for thermistors

Abstract

In a metal oxide sintered body for thermistors, a thermistor element, and a method for manufacturing a metal oxide sintered body for thermistors of the present invention, by having a protection layer other than an Y2O3 layer, a change in resistance value caused by reduction is minimized even at a high temperature and a change in resistance value occurring during formic acid reflow mounting is suppressed. A metal oxide sintered body 1 for thermistors according to the present invention has an (Ma, Y) oxide layer 3 formed on the surface of a complex oxide sintered body part 2 represented by a general formula: (1-z)(Ma1-yMby)(Cr1-xMnx)O3+zY2O3 (wherein Ma represents at least one trivalent metal element having an ion radius greater than that of Y, Mb represents at least one of Mg, Ca, Sr, and Ba, and 0.0≤x≤1.0, 0.0<y<0.5, and 0<z≤0.8 are satisfied).

Description

Metal oxide sintered body for thermistor, thermistor element, and method for producing metal oxide sintered body for thermistor

[0001] The present invention relates to a metal oxide sintered body for thermistors, used for temperature measurement in automobiles, etc., a thermistor element, and a method for producing a metal oxide sintered body for thermistors.

[0002] Thermistor temperature sensors are generally used as temperature sensors for measuring catalyst temperatures around automobile engines, exhaust system temperatures, etc. The thermistor elements used in these thermistor temperature sensors are used as temperature sensors for, for example, the above-mentioned automobile-related technologies, information devices, communication devices, medical devices, housing equipment, etc., and use elements made of a sintered oxide semiconductor with a large negative temperature coefficient.

[0003] Conventionally, thermistor elements made of various metal oxide sintered bodies have been used. A representative material is, for example, Y(Cr,Mn)O, as described in Patent Documents 1 and 2 and Non-Patent Document 1. ３ In recent years, thermistor elements capable of high-temperature measurement have been required to be mounted using formic acid reflow in addition to high-temperature measurements. However, the low-oxygen atmosphere during formic acid reflow reduces the thermistor element, resulting in unstable thermistor characteristics.

[0004] As a metal oxide sintered body that solves the above problem, Patent Document 3 discloses a metal oxide sintered body used for a thermistor, which has the general formula: (1-z)ABO ３ +zY ２ O ３ (However, ABO ３ is a perovskite oxide, and 0<z≦0.8) is a composite oxide sintered body having a layer thickness of 3 μm or more on the surface thereof. ２ O ３ The complex oxide sintered body portion has a layer formed thereon, and the layer is a layer of a compound represented by the general formula: (1-z)Y(Cr １－ｘ Mn ｘ ) O ３ +zY ２ O ３(where 0.0≦x≦1.0, 0<z≦0.8) is described. In this metal oxide sintered body for thermistors, oxygen is removed from the composite oxide sintered body by reduction, and a thick Y sintered body on the surface prevents this. ２ O ３ The layer suppresses the change in resistance value.

[0005] Patent No. 3362651 Patent No. 3776691 Patent No. 5402553

[0006] Kurano, "Development of a catalyst temperature sensor for NOx catalyst control," Denso Technical Review, Vol. 5, No. 2, 2000

[0007] As described above, the Y(Cr,Mn)O ３ In the case of perovskite oxides, the thermistor element is reduced in a low-oxygen atmosphere during high-temperature measurement or formic acid reflow, resulting in unstable thermistor characteristics. ２ O ３ The layer serves as a protective layer and is formed of a compound of the general formula: (1-z)Y(Cr １－ｘ Mn ｘ ) O ３ +zY ２ O ３ (where 0.0≦x≦1.0, 0<z≦0.8) prevents oxygen from being removed by reduction from the complex oxide sintered body part. However, there is also a demand for complex oxide sintered body parts and protective layers made of other materials that can achieve similar effects, and in particular, protective layers with high adhesion are required.

[0008] The present invention has been made in view of the above-mentioned problems, ２ O ３ The present invention aims to provide a metal oxide sintered body for thermistors, a thermistor element, and a method for manufacturing a metal oxide sintered body for thermistors, which have a small change in resistance due to reduction even at high temperatures due to a protective layer other than the layer, and which are highly reliable when mounted with formic acid reflow.

[0009] The present inventors have investigated the perovskite oxide (ABO ３ ) and conducted intensive research. ２ O ３ It has been found that a specific protective layer other than the above layer also suppresses the change in resistance value. Therefore, the present invention has been made based on the above findings, and the following configuration is adopted to solve the above problems.

[0010] That is, the metal oxide sintered body for thermistors according to the first invention is a metal oxide sintered body used for thermistors, and has the general formula: (1-z)(Ma １－ｙ Mb ｙ ) (Cr １－ｘ Mn ｘ ) O ３ +zY ２ O ３ (wherein Ma represents at least one trivalent metal element having an ionic radius larger than that of Y, and Mb represents at least one of Mg, Ca, Sr, and Ba; 0.0≦x≦1.0, 0.0<y<0.5, 0<z≦0.8), and a (Ma, Y) oxide layer is formed on the surface of the sintered complex oxide represented by the formula:

[0011] In this metal oxide sintered body for thermistors, the general formula: (1-z)(Ma １－ｙ Mb ｙ ) (Cr １－ｘ Mn ｘ ) O ３ +zY ２ O ３ (where Ma represents at least one trivalent metal element having a larger ionic radius than Y, and Mb represents at least one of Mg, Ca, Sr, and Ba; 0.0≦x≦1.0, 0.0<y<0.5, 0<z≦0.8) Since a (Ma, Y) oxide layer is formed on the surface of the complex oxide sintered body represented by the formula: 0.0≦x≦1.0, 0.0<y<0.5, 0<z≦0.8), the (Ma, Y) oxide layer on the surface acts as a protective layer to prevent oxygen from being removed from the complex oxide sintered body by reduction, thereby suppressing changes in resistance value. The (Ma, Y) oxide layer represents an oxide containing Ma and Y (yttrium).

[0012] The metal oxide sintered compact for thermistors according to the second invention is characterized in that, in the first invention, the (Ma, Y) oxide layer has a thickness of 3.8 μm or more. That is, in this metal oxide sintered compact for thermistors, since the thickness of the (Ma, Y) oxide layer is 3.8 μm or more, it is possible to suppress the rate of change in resistance value during formic acid reflow mounting to 0.85% or less.

[0013] A thermistor element according to a third invention is characterized by comprising a metal oxide sintered body for thermistors according to any one of the first and second inventions formed in a rectangular parallelepiped shape, and a pair of electrodes formed spaced apart from each other on the surface of the metal oxide sintered body for thermistors.

[0014] A fourth aspect of the present invention is a method for producing a metal oxide sintered body for thermistors according to any one of the first and second aspects of the present invention, which comprises mixing and firing raw material powders to produce a metal oxide sintered body for thermistors having the general formula: (1-z)(Ma １－ｙ Mb ｙ ) (Cr １－ｘ Mn ｘ ) O ３ +zY ２ O ３ (wherein Ma represents at least one trivalent metal element having an ionic radius larger than that of Y, and Mb represents at least one of Mg, Ca, Sr, and Ba; 0.0≦x≦1.0, 0.0<y<0.5, 0<z≦0.8), and in the firing step, the raw material powder is a mixture of a Ma compound, an Mb compound, a Cr compound, a Mn compound, and Y. ２ O ３ are mixed together, pulverized, and then molded to prepare a molded body, which is then fired in the air or in an atmosphere with an oxygen partial pressure of 20% or more, and cooled to room temperature after firing, to form a (Ma, Y) oxide layer on the surface of the complex oxide sintered body.

[0015] That is, in the method for producing a metal oxide sintered body for a thermistor, a raw material powder containing a Ma compound, an Mb compound, a Cr compound, an Mn compound, and a Y compound is used in the firing step. ２ O ３are mixed together, pulverized, and then molded to form a molded body. The molded body is then fired in the air or in an atmosphere with an oxygen partial pressure of 20% or more, and cooled to room temperature after firing. This forms a (Ma, Y) oxide layer on the surface of the complex oxide sintered body, making it possible to obtain a (Ma, Y) oxide layer with high adhesiveness.

[0016] A fifth aspect of the present invention relates to a method for producing a metal oxide sintered body for thermistors, which is similar to the fourth aspect of the present invention, but in the firing step, the firing is carried out in air or an oxygen atmosphere at a firing temperature of 1450°C or higher, for a firing time of 5 hours or longer, and for a cooling time to room temperature after firing of 6 hours or longer, thereby forming a (Ma, Y) oxide layer on the surface of the complex oxide sintered body. That is, in this method for producing a metal oxide sintered body for thermistors, the firing step is carried out in air or an oxygen atmosphere at a firing temperature of 1450°C or higher, for a firing time of 5 hours or longer, and for a cooling time to room temperature after firing of 6 hours or longer, thereby forming a (Ma, Y) oxide layer on the surface of the complex oxide sintered body, and therefore a (Ma, Y) oxide layer having a thickness of 3.8 μm or more can be precipitated on the surface of the complex oxide sintered body.

[0017] The present invention provides the following effects: That is, the metal oxide sintered body for thermistors and the method for producing the same according to the present invention are obtained by using a metal oxide sintered body for thermistors having a general formula: (1-z)(Ma １－ｙ Mb ｙ ) (Cr １－ｘ Mn ｘ ) O ３ +zY ２ O ３(where Ma represents at least one trivalent metal element having a larger ionic radius than Y, and Mb represents at least one of Mg, Ca, Sr, and Ba; 0.0≦x≦1.0, 0.0<y<0.5, 0<z≦0.8) Since a (Ma, Y) oxide layer is formed on the surface of the complex oxide sintered body represented by the formula (where Ma represents at least one trivalent metal element having a larger ionic radius than Y, and Mb represents at least one of Mg, Ca, Sr, and Ba, 0.0≦x≦1.0, 0.0<y<0.5, 0<z≦0.8), the (Ma, Y) oxide layer on the surface prevents oxygen from being removed from the complex oxide sintered body by reduction, thereby suppressing changes in resistance value and achieving good heat resistance and reduction resistance. Therefore, the thermistor element of the present invention can be mounted using formic acid reflow, exhibits little change over time at high temperatures, and provides sufficient measurement accuracy over a wide range from low to high temperatures, making it particularly suitable as a high-temperature measurement sensor for detecting catalyst temperatures and exhaust system temperatures around automobile engines.

[0018] 1 is a diagram schematically showing a cross section of a main part of a metal oxide sintered body for thermistors in one embodiment of a metal oxide sintered body for thermistors, a thermistor element, and a method for manufacturing a metal oxide sintered body for thermistors according to the present invention. FIG. 2 is a front view showing a thermistor element in the present embodiment. FIG. 3 is a diagram showing an example of distance measurement when the thickness definition of an oxide layer is used in the present embodiment. FIG. 4 is a graph showing the thickness of an oxide layer versus the oxide layer formation temperature in the present embodiment. FIG. 5 is an SEM image showing a cross section (a) of a metal oxide sintered body for thermistors produced at a firing temperature of 1450°C and a cross section (b) of a metal oxide sintered body for thermistors produced at a firing temperature of 1600°C in the present embodiment. FIG. 6 is a graph showing the change in resistance (ΔR) during formic acid reflow mounting versus the formation temperature (firing temperature) of the (Ma, Y) oxide layer in an example of a metal oxide sintered body for thermistors, a thermistor element, and a method for manufacturing a metal oxide sintered body for thermistors according to the present embodiment. FIG. 7 is a plan view (a) and a front view (b) showing another example of a thermistor element in the present embodiment. FIG. 8 is a plan view (a) and a front view (b) showing another example of a thermistor element in the present embodiment.

[0019] Hereinafter, an embodiment of a metal oxide sintered body for thermistors, a thermistor element, and a method for producing a metal oxide sintered body for thermistors according to the present invention will be described with reference to FIGS. 1 to 5. FIG.

[0020] The metal oxide sintered body 1 for thermistors of this embodiment is a metal oxide sintered body used for thermistors, and as shown in FIG. 1, １－ｙ Mb ｙ ) (Cr １－ｘ Mn ｘ ) O ３ +zY ２ O ３ (where Ma represents at least one trivalent metal element having a larger ionic radius than Y. Mb represents at least one of Mg, Ca, Sr, and Ba. 0.0≦x≦1.0, 0.0<y<0.5, 0<z≦0.8) A (Ma, Y) oxide layer 3 is formed on the surface of a complex oxide sintered body part 2 represented by the formula: 0.0≦x≦1.0, 0.0<y<0.5, 0<z≦0.8). The thickness of the (Ma, Y) oxide layer 3 is preferably 3.8 μm or more. Although there is no upper limit to the thickness of the (Ma, Y) oxide layer 3, if it is too thick, the characteristics will vary widely, so that the thickness is preferably about 20 μm or less. The (Ma, Y) oxide layer 3 may further contain Mb. １－ｙ Mb ｙ ) (Cr １－ｘ Mn ｘ ) O ３ In Fig. 1, the white circles represent (Ma, Y) oxide crystal grains A, and the black circles represent perovskite oxide crystal grains B.

[0021] 2, the thermistor element 5 of this embodiment has a metal oxide sintered compact for thermistors 1 formed in a rectangular parallelepiped shape, and a pair of electrodes 1a formed spaced apart from each other on the surface of the metal oxide sintered compact for thermistors 1. The electrodes 1a of this thermistor element 5 are a pair of end surface electrodes formed on both end surfaces of the metal oxide sintered compact for thermistors 1.

[0022] A method for producing this metal oxide sintered body for thermistors, and a method for producing and structure of a thermistor element and a thermistor temperature sensor using the same will be described below with reference to FIGS. 2 to 5. FIG.

[0023] The method for producing a metal oxide sintered body for a thermistor of this embodiment comprises mixing and firing raw material powders to form a sintered body of the general formula: (1-z)(Ma １－ｙMb ｙ ) (Cr １－ｘ Mn ｘ ) O ３ +zY ２ O ３ (wherein Ma represents at least one trivalent metal element having a larger ionic radius than Y, and Mb represents at least one of Mg, Ca, Sr, and Ba; 0.0≦x≦1.0, 0.0<y<0.5, 0<z≦0.8). In the firing step, raw material powders containing a Ma compound, an Mb compound, a Cr compound, an Mn compound, and Y are used. ２ O ３ These are mixed together, pulverized, and molded to form a molded body. The molded body is then fired in air or in an atmosphere with an oxygen partial pressure of 20% or more. After firing, the molded body is cooled to room temperature, forming a (Ma, Y) oxide layer on the surface of the complex oxide sintered body. An atmosphere with 100% oxygen may be used, but if the oxygen concentration is higher than that of air, an atmosphere with an oxygen partial pressure of 50% to 70% is preferred. In particular, in the firing step, firing is preferably performed in air or an oxygen atmosphere at a firing temperature of 1450°C or higher, for a firing time of 5 hours or more, and for a cooling time to room temperature after firing of 6 hours or more, thereby forming a (Ma, Y) oxide layer on the surface of the complex oxide sintered body. The upper limits of the firing temperature, firing time, and cooling time are approximately 1700°C, 20 hours, and 20 hours, respectively.

[0024] For example, when La is used as Ma and Ca is used as Mb, first, 0.5 (La ０．８ Ca ０．２ ) (Cr ０．４５ Mn ０．５５ ) O ３ +0.5Y ２ O ３ La(OH) ３ , CaCO ３ , Cr ２ O ３ , MnCO ３ , Y ２ O ３The powder is weighed and heated for 10 hours at a firing temperature of 1400° C. to prepare a perovskite oxide powder. The powder is coarsely crushed in a mortar, and then crushed for 1 hour using a ball mill or the like and dried.

[0025] Next, 5 wt% of PVA (polyvinyl alcohol, 10 wt% aqueous solution) was added and mixed, and the mixture was dried to obtain a mixed calcined powder. This dried mixture was uniaxially press-molded (1000 kg / cm) using a square mold with a cross section of 15 mm on each side. ２ Next, after the binder removal treatment, the mixture is fired in the atmosphere at a firing temperature of 1600°C or higher, for a firing time of 10 hours or more, and for a cooling time to room temperature after firing of 6 hours or more.

[0026] Next, the sintered wafer is polished to a thickness of 0.5 mm and cut at 0.5 mm intervals to produce strips with a square cross section of 0.5 mm on each side and a length of 15 mm. The strips are then sintered in air at a temperature of 1550°C or higher, for a period of 10 hours or longer, and cooled to room temperature for 6 hours or longer after sintering, to form a (La, Y) oxide layer 3 with a thickness of 5.8 μm on the surface of the strip. In this manner, the metal oxide sintered body 1 for thermistors of this embodiment is produced.

[0027] Furthermore, this 15 mm strip of metal oxide sintered body 1 for thermistors is cut out at 1 mm intervals, Pt paste is printed on both end surfaces, and heat treatment is performed at 1400° C. to produce a chip-type thermistor element 5 equipped with a pair of electrodes 1 a, as shown in Fig. 2. The corners of the chip-shaped thermistor element 5 may be rounded (R) by deburring or chamfering.

[0028] The thickness of the (Ma, Y) oxide layer 3 is measured using the following procedure. First, as shown in Figure 3, a cross section of the metal oxide sintered compact for thermistors is taken, and 50 positions are positioned in the planar direction at intervals of 2.5 μm, with the center of each position aligned with the center of a side. Next, at each positioned point, the distance from the outermost surface of the metal oxide sintered compact for thermistors to the internal thermistor particles (particles of perovskite-type oxide) is measured and averaged. The distance to the thermistor particles is measured using SEM-EDX, the wt% of each element is calculated, and the distance to the point (gray particle) where the ratio of Ma / (Ma + Mb + Cr + Mn + Y) is 35% or more is taken as the distance. Measurements are made along all four sides in the same manner, and the average value is calculated.

[0029] Next, as shown in Fig. 4, a value is calculated in the same manner for a metal oxide sintered body of the same composition that does not have the (Ma, Y) oxide layer 3 formed thereon, and the difference is defined as the thickness of the (Ma, Y) oxide layer 3. The thickness of the (Ma, Y) oxide layer 3 calculated in this manner is almost identical to the actual thickness when confirmed in an SEM image, as shown in Figs.

[0030] In this way, in the metal oxide sintered body 1 for thermistors of this embodiment, the general formula: (1-z)(Ma １－ｙ Mb ｙ ) (Cr １－ｘ Mn ｘ ) O ３ +zY ２ O ３ (where Ma represents at least one kind of trivalent metal element having an ionic radius larger than that of Y, and Mb represents at least one kind of Mg, Ca, Sr, and Ba; 0.0≦x≦1.0, 0.0<y<0.5, 0<z≦0.8) Since the (Ma, Y) oxide layer 3 is formed on the surface of the complex oxide sintered body part 2 represented by the formula: 0.0≦x≦1.0, 0.0<y<0.5, 0<z≦0.8), the (Ma, Y) oxide layer 3 on the surface acts as a protective layer to prevent oxygen from being removed from the complex oxide sintered body part 2 by reduction, and thus it is possible to suppress a change in resistance value.

[0031] In particular, by making the thickness of the (Ma, Y) oxide layer 3 3.8 μm or more, it is possible to suppress the rate of change in resistance value to 0.85% or less. The reason why the thickness of the (Ma, Y) oxide layer 3 is made 3.8 μm or more is that if the thickness is less than 3.8 μm, the suppressing effect of the (Ma, Y) oxide layer 3 is not fully exerted. Furthermore, the thickness of the (Ma, Y) oxide layer 3 is preferably made 10 μm or less. This is because the suppressing effect remains almost unchanged even if the thickness of the (Ma, Y) oxide layer 3 exceeds 10 μm, and this is to prevent the firing time from becoming longer than necessary, thereby preventing a decrease in production efficiency.

[0032] In the method for producing a metal oxide sintered body for a thermistor according to the present embodiment, a sintering step involves mixing a Ma compound, an Mb compound, a Cr compound, and a Mn compound as raw material powders, pulverizing the mixture, molding the mixture, and firing the molded body in air or an oxygen atmosphere. The resulting molded body is then cooled to room temperature after firing, forming a (Ma, Y) oxide layer on the surface of the complex oxide sintered body. This allows for the formation of a (Ma, Y) oxide layer with high adhesion. In particular, the sintering step involves firing in air at a temperature of 1450° C. or higher, a firing time of 5 hours or longer, and a cooling time to room temperature of 6 hours or longer to form a (Ma, Y) oxide layer on the surface of the complex oxide sintered body. This allows for the deposition of a (Ma, Y) oxide layer with a thickness of 3.8 μm or greater on the surface of the complex oxide sintered body.

[0033] Next, the metal oxide sintered body for thermistors, thermistor element, and method for manufacturing a metal oxide sintered body for thermistors according to the present invention will be specifically described with reference to FIG. 6, showing the results of evaluation of examples in which the metal oxide sintered body for thermistors was actually produced.

[0034] Example 1: A composite oxide sintered body was produced by the manufacturing method specifically described in the above embodiment, and the composite oxide sintered body part had a thickness of 0.5 (La ０．８ Ca ０．２ ) (Cr ０．４５ Mn ０．５５ ) O ３ +0.5Y ２ O ３The metal oxide sintered body for thermistors in which the (Ma, Y) oxide layer is changed to a (La, Y) oxide layer is designated as Example 1 of the present invention. ０．８ Ca ０．２ ) (Cr ０．４５ Mn ０．５５ ) O ３ +0.5Y ２ O ３ The raw material is mixed with Pr ２ (CO ３ ) ３ , CaCO ３ , Cr ２ O ３ , MnCO ３ Example 2 of the present invention was prepared in the same manner as in Example 1, except that the (Ma, Y) oxide layer was replaced with a (Pr, Y) oxide layer. Example 3: Raw materials having the same composition as in Example 1 were mixed, and a thermistor sheet was formed using the green sheet method so that the thickness after sintering would be 1 mm. Subsequently, Pt end electrodes were printed on the sheet, the sheet was cut at 0.5 mm intervals, and the sheet was fired at 1600°C for 10 hours. Example 3 of the present invention was prepared in the same manner as in Example 1, except that raw materials having the same composition as in Example 1 were mixed, and strips were formed using an extrusion method. The strips were then fired and diced to form chips. Subsequently, Pt end electrodes were printed on the cut end faces, and the electrodes were baked. Example 4 of the present invention was prepared in the same manner as in Example 1, except that the strips were fired at 1600°C for 10 hours.

[0035] Example 5: The composition ratio was 0.5 (Nd ０．８ Ca ０．２ ) (Cr ０．４５ Mn ０．５５ ) O ３ +0.5Y ２ O ３ The raw material was Nd ２ O ３ , CaCO ３ , Cr ２ O ３ , MnCO ３Example 5 of the present invention was prepared in the same manner as in Example 1, except that the (Ma,Y) oxide layer was replaced with a (Nd,Y) oxide layer. Example 6 of the present invention was prepared in the same manner as in Example 1, except that the heat treatment temperature of the strip in Example 1 was 1450°C and a 3.8 μm thick (Ma,Y) oxide layer of the (La,Y) oxide layer was formed on the surface. Example 7 of the present invention was prepared in the same manner as in Example 1, except that the raw materials having the same composition as in Example 1 were mixed and formed into a thermistor sheet by the green sheet method so that the thickness after sintering would be 0.2 mm. Thereafter, Pt end electrodes were printed, the sheet was cut at 1.5 mm intervals, and the sheet was sintered at 1600°C for 10 hours. Example 7 of the present invention was prepared in the same manner as in Example 1, except that the heat treatment step of the strip at 1550°C in Example 1 was omitted and a (Ma,Y) oxide layer of the (La,Y) oxide layer was not formed on the surface. Comparative Example 1 of the present invention was prepared in the same manner as in Example 1, except that the heat treatment step of the strip at 1550°C in Example 1 was omitted and a (Ma,Y) oxide layer of the (La,Y) oxide layer was not formed on the surface.

[0036] For these examples and comparative examples, the initial resistance value was measured at 25°C, and then the rate of change in resistance when formic acid reflow was performed at 300°C for 2 minutes using 5% formic acid was measured. The results are shown in Table 1 and Figure 6. As can be seen from these results, the resistance change was large at 2.62% in Comparative Example 1, which did not form a (Ma,Y) oxide layer, while the resistance change was small at 0.85% or less in each of the examples of the present invention, which formed a (Ma,Y) oxide layer. That is, each of the examples of the present invention was fabricated at a firing temperature of 1450°C or higher, a firing time of 5 hours or longer, and a cooling time of 6 hours or longer, and a (Ma,Y) oxide layer of 3.8 μm or more was deposited. In particular, in the examples fabricated at a firing temperature of 1550°C or higher, a (Ma,Y) oxide layer of 5.7 μm or more was deposited, and the rate of increase in resistance was significantly reduced to 0.22% or less compared to the comparative examples.

[0037]

[0038] The technical scope of the present invention is not limited to the above-described embodiments and examples, and various modifications can be made without departing from the spirit of the present invention.

[0039] For example, in the above embodiment, the pair of electrodes of the thermistor element is a pair of end surface electrodes formed on both end surfaces of the chip-shaped metal oxide sintered body for thermistors. However, as shown in Figures 7 and 8, the pair of electrodes of the thermistor element may be a pair of electrodes spaced apart from each other on a surface other than the end surfaces of the metal oxide sintered body for thermistors. That is, as shown in Figure 7, a thermistor element 5A may be formed in which a pair of electrodes 1a facing each other are formed on the upper and lower surfaces of a metal oxide sintered body for thermistors 1 formed in a plate or flake shape. Furthermore, as shown in Figure 8, a thermistor element 5B may be formed in which a pair of electrodes 1a spaced apart from each other are patterned on only one of the upper and lower surfaces of a metal oxide sintered body for thermistors 1 formed in a plate or flake shape. Note that this pair of electrodes 1a may be arranged facing each other and have a comb-shaped pattern in which comb portions are alternately arranged.

[0040] REFERENCE SIGNS LIST 1... Metal oxide sintered body for thermistor, 1a... Electrode, 2... Composite oxide sintered body part, 3... (Ma, Y) oxide layer, 5, 5A, 5B... Thermistor element

Claims

1. A metal oxide sintered body used in a thermistor, having the general formula: (1-z) (Ma １－ｙ Mb ｙ ) (Cr １－ｘ Mn ｘ ) O ３ +zY ２ O ３ (wherein Ma represents at least one trivalent metal element having an ionic radius larger than that of Y, and Mb represents at least one of Mg, Ca, Sr, and Ba; 0.0≦x≦1.0, 0.0<y<0.5, 0<z≦0.8), wherein a (Ma, Y) oxide layer is formed on the surface of a complex oxide sintered body part represented by the formula:

2. The metal oxide sintered body for thermistors according to claim 1, wherein the thickness of the (Ma, Y) oxide layer is 3.8 μm or more.

3. A thermistor element comprising the metal oxide sintered body for thermistors according to claim 1 formed in a rectangular parallelepiped shape, and a pair of electrodes formed spaced apart on the surface of the metal oxide sintered body for thermistors.

4. A method for producing a sintered metal oxide for thermistors according to claim 1, comprising mixing and firing raw material powders to produce a sintered metal oxide having the general formula: (1-z)(Ma １－ｙ Mb ｙ ) (Cr １－ｘ Mn ｘ ) O ３ +zY ２ O ３ (wherein Ma represents at least one trivalent metal element having an ionic radius larger than that of Y, and Mb represents at least one of Mg, Ca, Sr, and Ba; 0.0≦x≦1.0, 0.0<y<0.5, 0<z≦0.8), and in the firing step, the raw material powder is a mixture of a Ma compound, an Mb compound, a Cr compound, a Mn compound, and Y. ２ O ３ and Y are mixed together, pulverized, and then molded to prepare a molded body, which is then fired in the air or in an atmosphere with an oxygen partial pressure of 20% or more, and cooled to room temperature after firing, thereby forming a (Ma, Y) oxide layer on the surface of the complex oxide sintered body.

5. A method for producing a metal oxide sintered body for thermistors according to claim 4, characterized in that in the firing step, firing is carried out in air or in an atmosphere with an oxygen partial pressure of 20% or more at a firing temperature of 1450°C or more, for a firing time of 5 hours or more, and for cooling to room temperature after firing for 6 hours or more, thereby forming a (Ma, Y) oxide layer on the surface of the complex oxide sintered body.

Images