Piezoelectric actuator, liquid ejection head and recording device

Abstract

Disclosed is a piezoelectric actuator which comprises a piezoelectric element that is deformed by the application of a voltage. The piezoelectric element comprises a piezoelectric ceramic body and an electrode that applies a voltage to the piezoelectric ceramic body. The electrode comprises metal oxides and a base material that contains a noble metal, and the metal oxides are scattered inside the base material.

Description

Piezoelectric actuator, liquid ejection head and recording apparatus

[0001] The disclosed embodiments relate to a piezoelectric actuator, a liquid ejection head, and a recording apparatus.

[0002] 2. Description of the Related Art Known printing devices include inkjet printers and inkjet plotters that use an inkjet recording method. Such inkjet printing devices are equipped with a liquid ejection head for ejecting liquid.

[0003] The liquid ejection head ejects the liquid in the pressure chamber from the nozzle by driving a piezoelectric element located above the pressure chamber to change the pressure in the pressure chamber. The piezoelectric element has a piezoelectric ceramic body and electrodes that apply a voltage to the piezoelectric ceramic body.

[0004] When a voltage is applied to the piezoelectric ceramic body, the domains move within the piezoelectric ceramic body so that the c-axis faces the electric field direction, displacing the piezoelectric ceramic body and generating a driving force.

[0005] Japanese Patent Application Laid-Open No. 2000-094681

[0006] A piezoelectric actuator according to the present disclosure includes a piezoelectric element that deforms when a voltage is applied. The piezoelectric element includes a piezoelectric ceramic body and an electrode that applies a voltage to the piezoelectric ceramic body. The electrode includes a matrix containing a noble metal and a metal oxide, and the metal oxide is dispersed within the matrix.

[0007] FIG. 1 is a schematic side view of a printer according to an embodiment. FIG. 2 is a schematic plan view of a printer according to an embodiment. FIG. 3 is a schematic exploded perspective view of a liquid ejection head according to an embodiment. FIG. 4 is an enlarged plan view of a head main body according to an embodiment. FIG. 5 is an enlarged view of the area surrounded by the dashed line in FIG. 4. FIG. 6 is a cross-sectional view taken along the line VI-VI in FIG. 4. FIG. 7 is a SEM image of the cross-section of a surface electrode of Example 1. FIG. 8 is a SEM image of the cross-section of a surface electrode of Example 3. FIG. 9 is a SEM image of the cross-section of a surface electrode of Example 5. FIG. 10 is a SEM image of the cross-section of a surface electrode of Reference Example 2. FIG. 11 is a graph showing the relationship between the baking temperature of a surface electrode and the area ratio of metal oxide within the surface electrode and at the interface of the surface electrode. FIG. 12 is a graph showing the relationship between the baking temperature of a surface electrode and the area ratio of metal oxide within the electrode relative to the metal oxide at the interface of the surface electrode. FIG. 13 is a SEM image of the surface state of a surface electrode of Example 1. FIG. 14 is a SEM image of the surface state of a surface electrode of Example 3. Fig. 15 is a diagram showing an SEM image of the surface state of the front electrode of Example 5. Fig. 16 is a diagram showing an SEM image of the surface state of the front electrode of Reference Example 2. Fig. 17 is a diagram showing the relationship between the baking temperature of the front electrode and the area ratio of metal oxide on the surface of the front electrode. Fig. 18 is a diagram showing the relationship between the baking temperature of the front electrode and the coercive electric field of the piezoelectric element. Fig. 19 is a diagram showing the progression of drive deterioration of the piezoelectric element of Example 3 and the piezoelectric element of Reference Example 1.

[0008] Hereinafter, embodiments of the piezoelectric actuator, the liquid ejection head, and the recording apparatus disclosed in the present application will be described, but the present disclosure is not limited to the embodiments described below.

[0009] 2. Description of the Related Art Known printing devices include inkjet printers and inkjet plotters that use an inkjet recording method. Such inkjet printing devices are equipped with a liquid ejection head for ejecting liquid.

[0010] The liquid ejection head ejects the liquid in the pressure chamber from the nozzle by driving a piezoelectric element located above the pressure chamber to change the pressure in the pressure chamber. The piezoelectric element has a piezoelectric ceramic body and electrodes that apply a voltage to the piezoelectric ceramic body.

[0011] When a voltage is applied to the piezoelectric ceramic body, the domains move within the piezoelectric ceramic body so that the c-axis faces the electric field direction, displacing the piezoelectric ceramic body and generating a driving force.

[0012] However, in the above-mentioned conventional technology, when the piezoelectric element is continuously driven, a phenomenon may occur in which the domains inside the piezoelectric ceramic body gradually become fixed, which gradually reduces the displacement of the piezoelectric element, and there is a risk that the desired driving amount of the piezoelectric element cannot be obtained.

[0013] Therefore, there is a need for a technology that can solve the above problems and reduce the driving deterioration of piezoelectric elements.

[0014] <Printer Configuration> First, an overview of a printer 1, which is an example of a recording apparatus according to an embodiment, will be described with reference to Figures 1 and 2. Figure 1 is a schematic side view of the printer 1 according to an embodiment. Figure 2 is a schematic plan view of the printer 1 according to an embodiment. The printer 1 according to an embodiment is, for example, a color inkjet printer.

[0015] As shown in FIG. 1, the printer 1 has a paper feed roller 2, a guide roller 3, an applicator 4, a head case 5, a plurality of conveying rollers 6, a plurality of frames 7, a plurality of liquid ejection heads 8, a conveying roller 9, a dryer 10, a conveying roller 11, a sensor unit 12, and a recovery roller 13.

[0016] Furthermore, the printer 1 has a control unit 14 that controls each part of the printer 1. The control unit 14 controls the operations of the paper feed roller 2, the guide roller 3, the coater 4, the head case 5, the plurality of transport rollers 6, the plurality of frames 7, the plurality of liquid ejection heads 8, the transport roller 9, the dryer 10, the transport roller 11, the sensor unit 12, and the recovery roller 13.

[0017] The printer 1 records images and characters on the recording medium P by causing droplets to land on the recording medium P. The recording medium P is, for example, paper. However, the recording medium P is not limited to this, and may be cloth or the like. Before use, the recording medium P is wound around a paper feed roller 2. The printer 1 transports the recording medium P wound around the paper feed roller 2 into the interior of a head case 5 via a guide roller 3 and a coater 4.

[0018] The coater 4 applies the coating agent uniformly to the recording medium P. This allows the surface of the recording medium P to be treated, thereby improving the printing quality of the printer 1.

[0019] The head case 5 houses a plurality of transport rollers 6, a plurality of frames 7, and a plurality of liquid ejection heads 8. Inside the head case 5, a space is formed that is isolated from the outside except for a portion that is connected to the outside, such as a portion where the recording medium P enters and leaves.

[0020] At least one of the control factors such as temperature, humidity, and air pressure of the internal space of the head case 5 is controlled by the control unit 14 as necessary. The transport roller 6 transports the recording medium P inside the head case 5 to the vicinity of the liquid ejection head 8.

[0021] The frame 7 is a rectangular flat plate, and is positioned above and in close proximity to the recording medium P being transported by the transport rollers 6. As shown in Fig. 2, the frame 7 is positioned so that its longitudinal direction is perpendicular to the transport direction of the recording medium P. Inside the head case 5, a plurality of (for example, four) frames 7 are positioned at predetermined intervals along the transport direction of the recording medium P.

[0022] In the following description, the transport direction of the recording medium P may be referred to as the "sub-scanning direction," and the direction perpendicular to the sub-scanning direction and parallel to the recording medium P may be referred to as the "main scanning direction."

[0023] A liquid, such as ink, is supplied from a liquid tank (not shown) to the liquid ejection head 8. The liquid ejection head 8 ejects the liquid supplied from the liquid tank.

[0024] The control unit 14 controls the liquid ejection head 8 based on data such as images and characters, and ejects liquid toward the recording medium P. The distance between the liquid ejection head 8 and the recording medium P is, for example, about 0.5 to 20 mm.

[0025] The liquid ejection head 8 is fixed to the frame 7. The liquid ejection head 8 is positioned so that its longitudinal direction is perpendicular to the direction in which the recording medium P is transported.

[0026] That is, the printer 1 according to the embodiment is a so-called line printer in which the liquid ejection head 8 is fixed inside the printer 1. Note that the printer 1 according to the embodiment is not limited to a line printer, and may also be a so-called serial printer.

[0027] A serial printer is a printer that alternates between recording by moving the liquid ejection head 8 back and forth in a direction that intersects the transport direction of the recording medium P, for example, in a direction that is approximately perpendicular to the direction of transport, and transporting the recording medium P.

[0028] As shown in Fig. 2, a plurality of (for example, five) liquid ejection heads 8 are fixed to one frame 7. Fig. 2 shows an example in which three liquid ejection heads 8 are positioned in front and two in the rear in the transport direction of the recording medium P, and the liquid ejection heads 8 are positioned so that the centers of the respective liquid ejection heads 8 do not overlap in the transport direction of the recording medium P.

[0029] A head group 8A is made up of multiple liquid ejection heads 8 positioned on one frame 7. The four head groups 8A are positioned along the transport direction of the recording medium P. The same color ink is supplied to the liquid ejection heads 8 belonging to the same head group 8A. This allows the printer 1 to print with four colors of ink using the four head groups 8A.

[0030] The colors of ink ejected from each head group 8A are, for example, magenta (M), yellow (Y), cyan (C), and black (K). The control unit 14 controls each head group 8A to eject ink of multiple colors onto the recording medium P, thereby printing a color image on the recording medium P.

[0031] In order to perform surface treatment on the recording medium P, a coating agent may be ejected onto the recording medium P from the liquid ejection head 8 .

[0032] Furthermore, the number of liquid ejection heads 8 included in one head group 8A and the number of head groups 8A mounted on the printer 1 can be changed as appropriate depending on the object to be printed and the printing conditions. For example, if a single color is printed on the recording medium P and the printing range is to be printed with one liquid ejection head 8, the number of liquid ejection heads 8 mounted on the printer 1 may be one.

[0033] The recording medium P that has been printed inside the head case 5 is transported to the outside of the head case 5 by transport rollers 9 and passes through the inside of a dryer 10. The dryer 10 dries the recording medium P that has been printed. The recording medium P that has been dried in the dryer 10 is transported by transport rollers 11 and collected by a collection roller 13.

[0034] In the printer 1, by drying the recording medium P in the dryer 10, it is possible to reduce adhesion between the recording media P that are wound up in a pile on the recovery roller 13 and rubbing of undried liquid.

[0035] The sensor unit 12 is composed of a position sensor, a speed sensor, a temperature sensor, etc. The control unit 14 can determine the state of each part of the printer 1 based on information from the sensor unit 12 and control each part of the printer 1.

[0036] The printer 1 described so far has been shown to use a recording medium P as the printing object (i.e., the recording medium), but the printing object in the printer 1 is not limited to the recording medium P, and the printing object may also be a roll of cloth or the like.

[0037] Furthermore, the printer 1 may transport the recording medium P on a transport belt instead of directly transporting the recording medium P. By using a transport belt, the printer 1 can print on sheets of paper, cut pieces of cloth, wood, tiles, and the like.

[0038] The printer 1 may also print wiring patterns for electronic devices by ejecting a liquid containing conductive particles from the liquid ejection head 8. The printer 1 may also produce chemicals by ejecting a predetermined amount of liquid chemicals or liquid containing chemicals from the liquid ejection head 8 toward a reaction vessel or the like.

[0039] <Configuration of Liquid Ejection Head> Next, the configuration of the liquid ejection head 8 according to the embodiment will be described with reference to Fig. 3. Fig. 3 is a schematic exploded perspective view of the liquid ejection head 8 according to the embodiment.

[0040] The liquid ejection head 8 has a head main body 20, a wiring section 30, a housing 40, and a pair of heat sinks 45. The head main body 20 has a flow path member 21, a piezoelectric actuator substrate 22 (see FIG. 4), and a reservoir 23.

[0041] In the following description, for convenience, the direction in which the head body 20 is provided in the liquid ejection head 8 may be referred to as "downward," and the direction in which the housing 40 is provided relative to the head body 20 may be referred to as "upward."

[0042] The flow path member 21 of the head main body 20 has a generally flat plate shape and has a first surface 21a (see FIG. 6) which is one main surface, and a second surface 21b (see FIG. 6) located on the opposite side of the first surface 21a. The first surface 21a has an opening (not shown), and liquid is supplied into the flow path member 21 from a reservoir 23 (described later) through this opening.

[0043] A plurality of ejection holes 63 (see FIG. 6) that eject liquid onto the recording medium P are located on the second surface 21b. In other words, the second surface 21b is the nozzle surface of the head main body 20. The flow path member 21 has a flow path therein that allows liquid to flow from the first surface 21a to the second surface 21b. The ejection holes 63 are an example of a nozzle.

[0044] The piezoelectric actuator substrate 22 is located on the first surface 21a of the flow path member 21. The piezoelectric actuator substrate 22 has a plurality of piezoelectric elements 70 (see FIG. 6). The flexible substrate 31 of the wiring section 30 is electrically connected to the piezoelectric actuator substrate 22. The configuration of the piezoelectric actuator substrate 22 will be described later with reference to FIGS. 4 to 6.

[0045] A reservoir 23 is located on the piezoelectric actuator substrate 22. Specifically, the reservoir 23 is located on the first surface 21a of the flow path member 21 so as to cover the piezoelectric actuator substrate 22.

[0046] The reservoir 23 supplies liquid to a pressurizing chamber 62 (described later) of the flow path member 21. Specifically, the reservoir 23 has openings 23a at both ends in the longitudinal direction. The reservoir 23 has a flow path therein, and liquid is supplied from the outside through the openings 23a. The reservoir 23 has the function of supplying liquid to the pressurizing chamber 62 of the flow path member 21 and the function of storing the supplied liquid.

[0047] The wiring section 30 has a flexible substrate 31, a head substrate 32, a driver IC 33, a pressing member 34, and an elastic member 35. The flexible substrate 31 has a function of transmitting a predetermined signal sent from the outside to the head main body 20. As shown in Figure 3, the liquid ejection head 8 according to the embodiment has two flexible substrates 31.

[0048] One end of the flexible substrate 31 is electrically connected to the piezoelectric actuator substrate 22 of the head body 20. The other end of the flexible substrate 31 is pulled upward so as to pass through the opening 23b of the reservoir 23, and is electrically connected to the head substrate 32.

[0049] This allows electrical connection between the piezoelectric actuator substrate 22 of the head body 20 and the outside. The flexible substrate 31 is, for example, a film-like substrate (COF) made of polyimide, and a driver IC 33 and the like are mounted on the substrate.

[0050] The head substrate 32 is located above the head main body 20. The head substrate 32 has the function of distributing signals to the driver IC 33. The driver IC 33 is provided on one main surface of the flexible substrate 31. The driver IC 33 drives the piezoelectric actuator substrate 22 of the head main body 20 based on signals sent from the control unit 14 (see FIG. 1). In this way, the driver IC 33 drives the liquid ejection head 8.

[0051] The pressing member 34 has a substantially U-shape in cross section, and presses the driver IC 33 on the flexible substrate 31 from the inside toward the heat sink 45. As a result, in this embodiment, heat generated when the driver IC 33 is driven can be efficiently dissipated to the heat sink 45 on the outside.

[0052] The elastic member 35 is positioned so as to contact the outer wall of the pressing portion (not shown) of the pressing member 34. By providing such an elastic member 35, it is possible to reduce the possibility that the pressing member 34 will damage the flexible substrate 31 when the pressing member 34 presses the driver IC 33.

[0053] The elastic member 35 is made of, for example, double-sided foam tape. Furthermore, by using, for example, a non-silicon heat conductive sheet as the elastic member 35, it is possible to improve the heat dissipation of the driver IC 33. However, the elastic member 35 is not necessarily required.

[0054] The housing 40 is positioned on the head main body 20 so as to cover the wiring portion 30. This allows the housing 40 to seal the wiring portion 30. The housing 40 is made of, for example, resin or metal.

[0055] The housing 40 has a box shape that extends long in the main scanning direction, and has a first opening 40a and a second opening 40b on a pair of side surfaces that face each other in the main scanning direction. The housing 40 also has a third opening 40c on its bottom surface and a fourth opening 40d on its top surface.

[0056] One side of the heat sink 45 is positioned in the first opening 40a so as to close the first opening 40a, and the other side of the heat sink 45 is positioned in the second opening 40b so as to close the second opening 40b.

[0057] The heat sink 45 is provided so as to extend in the main scanning direction and is made of a highly heat-dissipating metal, alloy, etc. The heat sink 45 is provided so as to be in contact with the driver IC 33, and dissipates heat generated by the driver IC 33.

[0058] The pair of heat sinks 45 are each fixed to the housing 40 by screws (not shown). Therefore, the housing 40 to which the heat sinks 45 are fixed has a box shape in which the first opening 40a and the second opening 40b are closed and the third opening 40c and the fourth opening 40d are open.

[0059] The third opening 40c is positioned so as to face the reservoir 23. The flexible substrate 31 and the pressing member 34 are inserted through the third opening 40c.

[0060] The fourth opening 40d is provided for inserting a connector (not shown) provided on the head substrate 32. If the space between the connector and the fourth opening 40d is sealed with resin or the like, it becomes difficult for liquid, dust, and the like to enter the inside of the housing 40.

[0061] The housing 40 also has a heat insulating portion 40e. The heat insulating portion 40e is located adjacent to the first opening 40a and the second opening 40b, and is provided so as to protrude outward from a side surface of the housing 40 along the main scanning direction.

[0062] The heat insulating portion 40e is formed to extend in the main scanning direction. That is, the heat insulating portion 40e is located between the heat sink 45 and the head main body 20. By providing the heat insulating portion 40e in the housing 40 in this way, heat generated by the driver IC 33 is less likely to be transmitted to the head main body 20 via the heat sink 45.

[0063] It should be noted that the configuration of the liquid ejection head 8 shown in FIG. 3 is merely an example, and the configuration of the liquid ejection head 8 is not limited to the configuration shown in FIG.

[0064] <Configuration of Head Main Body> Next, the configuration of the head main body 20 according to this embodiment will be described with reference to Figs. 4 to 6. Fig. 4 is an enlarged plan view of the head main body 20 according to this embodiment. Fig. 5 is an enlarged view of an area V surrounded by a dashed line shown in Fig. 4. Fig. 6 is a cross-sectional view taken along the line VI-VI shown in Fig. 4.

[0065] 4, the head main body 20 has a flow path member 21 and a piezoelectric actuator substrate 22. The flow path member 21 has a supply manifold 61, a plurality of pressure chambers 62, and a plurality of ejection holes 63.

[0066] The plurality of pressurizing chambers 62 are connected to the supply manifold 61. The plurality of discharge holes 63 are connected to the plurality of pressurizing chambers 62, respectively.

[0067] The pressurizing chamber 62 is open to the first surface 21a (see FIG. 6) of the flow path member 21. The first surface 21a of the flow path member 21 has an opening 61a that is connected to the supply manifold 61. Liquid is supplied from the reservoir 23 (see FIG. 2) to the inside of the flow path member 21 through the opening 61a.

[0068] 4, the head main body 20 has four supply manifolds 61 inside the flow path member 21. The supply manifolds 61 have an elongated shape extending along the longitudinal direction of the flow path member 21 (i.e., the main scanning direction), and openings 61a of the supply manifolds 61 are formed on the first surface 21a of the flow path member 21 at both ends thereof.

[0069] A plurality of pressure chambers 62 are formed in the flow path member 21, spreading out two-dimensionally. As shown in Fig. 5, the pressure chambers 62 are hollow regions having, for example, a generally diamond-shaped planar shape with rounded corners. The shape of the pressure chambers 62 is not limited to the example shown in the figure. The pressure chambers 62 are open to the first surface 21a of the flow path member 21, and are closed by bonding the piezoelectric actuator substrate 22 to the first surface 21a.

[0070] The pressure chambers 62 form pressure chamber rows arranged in the longitudinal direction. The pressure chambers 62 in a pressure chamber row are positioned in a staggered pattern between two adjacent pressure chamber rows. Four pressure chamber rows connected to one supply manifold 61 form one pressure chamber group. In the example of FIG. 4 , the flow path member 21 has four such pressure chamber groups.

[0071] The relative arrangement of the pressure chambers 62 within each pressure chamber group is the same, and the pressure chamber groups are positioned slightly offset from each other in the longitudinal direction.

[0072] The discharge holes 63 are located at positions that avoid the area of ​​the flow path member 21 that faces the supply manifold 61. In other words, when the flow path member 21 is seen through from the first surface 21 a side, the discharge holes 63 do not overlap with the supply manifold 61.

[0073] Furthermore, in plan view, the discharge holes 63 are positioned so as to fit within the mounting area of ​​the piezoelectric actuator substrate 22. Such discharge holes 63 as a group occupy an area of ​​approximately the same size and shape as the piezoelectric actuator substrate 22.

[0074] In the liquid ejection head 8, the driver IC 33 displaces the piezoelectric elements 70 (see FIG. 6) of the piezoelectric actuator substrate 22 based on a signal sent from the control unit 14 (see FIG. 1). This causes the pressure chambers 62 to be pressurized, causing the liquid in the pressure chambers 62 to be ejected from the ejection holes 63.

[0075] 6, the flow path member 21 has a laminated structure in which a plurality of plates are stacked. For example, the flow path member 21 has, in order from the top surface of the flow path member 21, a cavity plate 21A, a base plate 21B, an aperture plate 21C, a supply plate 21D, manifold plates 21E, 21F, and 21G, a cover plate 21H, and a nozzle plate 21I.

[0076] A large number of holes are formed in the plate. The thickness of the plate is approximately 10 μm to 300 μm. This allows for high accuracy in forming the holes. The plates are aligned and stacked so that the holes communicate with each other to form predetermined flow paths.

[0077] In the flow path member 21, the supply manifold 61 and the discharge holes 63 are connected by individual flow paths 64. The supply manifold 61 is located on the second surface 21b side inside the flow path member 21, and the discharge holes 63 are located on the second surface 21b of the flow path member 21.

[0078] The individual flow path 64 has a pressurizing chamber 62 and an individual supply flow path 65. The pressurizing chamber 62 is located on the first surface 21a of the flow path member 21, and the individual supply flow path 65 is a flow path that connects the supply manifold 61 and the pressurizing chamber 62.

[0079] Furthermore, the individual supply flow path 65 includes a restriction 66 that is narrower than the other portions. The restriction 66 has a high flow path resistance because it is narrower than the other portions of the individual supply flow path 65. When the flow path resistance of the restriction 66 is high in this way, the pressure generated in the pressurizing chamber 62 is less likely to escape to the supply manifold 61.

[0080] The piezoelectric actuator substrate 22 has piezoelectric ceramic layers 22A and 22B, an internal electrode 71, a surface electrode 72, a connection electrode 73, a dummy connection electrode 74, and a surface electrode 75 (see FIG. 4). The piezoelectric ceramic layer 22A is an example of a piezoelectric ceramic body, and the surface electrode 72 is an example of an electrode.

[0081] The piezoelectric ceramic layer 22B, the internal electrode 71, the piezoelectric ceramic layer 22A, and the surface electrode 72 are stacked in this order from the bottom, that is, from the flow path member 21 side.

[0082] The piezoelectric ceramic layers 22A and 22B each extend on the first surface 21a of the flow path member 21 so as to straddle the multiple pressure chambers 62. The piezoelectric ceramic layers 22A and 22B each have a thickness of approximately 20 μm. The piezoelectric ceramic layers 22A and 22B are made of, for example, a ferroelectric ceramic material such as lead zirconate titanate (PZT).

[0083] The internal electrode 71 is formed over substantially the entire surface in the region between the piezoelectric ceramic layer 22A and the piezoelectric ceramic layer 22B. In other words, the internal electrode 71 overlaps with all of the pressure chambers 62 in the region facing the piezoelectric actuator substrate 22.

[0084] The thickness of the internal electrode 71 is about 2 μm and is made of a metal material such as an Ag—Pd system.

[0085] The surface electrode 72 includes a main electrode 72a and an extraction electrode 72b. The main electrode 72a is located on the piezoelectric ceramic layer 22A in an area facing the pressure chamber 62. The main electrode 72a is slightly smaller than the pressure chamber 62 and has a shape that is approximately similar to the pressure chamber 62.

[0086] The extraction electrode 72b is extracted from the main electrode 72a to the outside of the region facing the pressure chamber 62. The surface electrode 72 is made of a base material such as a noble metal material such as Au or Ag. Details of the surface electrode 72 will be described later.

[0087] The connection electrode 73 is located on the extraction electrode 72b and is formed in a convex shape with a thickness of about 15 μm. The connection electrode 73 is electrically connected to an electrode provided on the flexible substrate 31 (see FIG. 3). The connection electrode 73 is made of, for example, silver-palladium containing glass frit.

[0088] The dummy connection electrodes 74 are located on the piezoelectric ceramic layer 22B so as not to overlap with various electrodes such as the surface electrodes 72. The dummy connection electrodes 74 connect the piezoelectric actuator substrate 22 and the flexible substrate 31, increasing the connection strength.

[0089] The dummy connection electrodes 74 also stabilize the electrical connection by uniformly distributing the contact positions between the piezoelectric actuator substrates 22. The dummy connection electrodes 74 are preferably made of the same material as the connection electrodes 73, and are preferably formed in the same process as the connection electrodes 73.

[0090] 4 is formed on the piezoelectric ceramic layer 22B at a position that avoids the surface electrode 72. The surface electrode 75 is connected to the internal electrode 71 through a via hole formed in the piezoelectric ceramic layer 22A.

[0091] As a result, the surface electrode 75 is grounded and maintained at the ground potential. The surface electrode 75 is preferably made of the same material as the surface electrode 72 and is preferably formed in the same process as the surface electrode 72.

[0092] In order to individually control the potential of the surface electrodes 72, each is electrically connected to the control unit 14 (see FIG. 1) via the flexible substrate 31 and wiring. When the surface electrodes 72 and the internal electrodes 71 are set to different potentials and an electric field is applied in the polarization direction of the piezoelectric ceramic layer 22A, the portion of the piezoelectric ceramic layer 22A to which the electric field is applied operates as an active portion that is distorted by the piezoelectric effect.

[0093] That is, in the piezoelectric actuator substrate 22 , the surface electrode 72 , the piezoelectric ceramic layer 22 A, and the portion of the internal electrode 71 that faces the pressure chamber 62 function as the piezoelectric element 70 .

[0094] When the piezoelectric element 70 undergoes unimorph deformation, the pressure chamber 62 is pressed, and droplets are ejected from the ejection holes 63 .

[0095] Here, the driving procedure of the liquid ejection head 8 according to this embodiment will be described. The surface electrode 72 is set in advance to a higher potential (hereinafter referred to as "high potential") than the internal electrode 71. Then, each time an ejection request is made, the surface electrode 72 is temporarily set to the same potential as the internal electrode 71 (hereinafter referred to as "low potential"), and then is set to the high potential again at a predetermined timing.

[0096] As a result, when the surface electrode 72 becomes low potential, the piezoelectric ceramic layers 22A, 22B return to their original shapes, and the volume of the pressure chamber 62 increases from the initial state, i.e., the state of high potential. At this time, a negative pressure is applied within the pressure chamber 62, so that the liquid within the supply manifold 61 is sucked into the pressure chamber 62.

[0097] Thereafter, when the surface electrode 72 is again set to a high potential, the piezoelectric ceramic layers 22A and 22B deform so as to become convex toward the pressure chamber 62. In other words, the volume of the pressure chamber 62 decreases, and the pressure inside the pressure chamber 62 becomes positive. As a result, the pressure of the liquid inside the pressure chamber 62 increases, and droplets are ejected from the ejection holes 63.

[0098] That is, the control unit 14 supplies a drive signal including a pulse based on a high potential to the surface electrode 72 using the driver IC 33 in order to eject droplets from the ejection hole 63. The pulse width may be set to AL (Acoustic Length), which is the length of time it takes for a pressure wave to propagate from the restriction 66 to the ejection hole 63.

[0099] As a result, when the pressure inside the pressure chamber 62 changes from a negative pressure state to a positive pressure state, the two pressures are combined, and droplets can be ejected with a stronger pressure.

[0100] In gradation printing, gradation is expressed by the number of droplets continuously ejected from the ejection holes 63, i.e., the amount (volume) of droplets is adjusted by the number of liquid ejections. Therefore, liquid is ejected continuously from the ejection holes 63 corresponding to the specified gradation expression a number of times.

[0101] In the embodiment, the surface electrode 72 of the piezoelectric element 70 may have a base material BM (see FIG. 7) containing a noble metal and a metal oxide MO (see FIG. 7). In the embodiment, the metal oxide MO may be scattered inside the base material BM.

[0102] This increases the hardness of the surface electrode 72, so that when the piezoelectric element 70 is driven, excessive strain is less likely to occur in the inactive portion adjacent to the active portion of the piezoelectric ceramic layer 22A.

[0103] Therefore, the fixation of domains caused by excessive strain is reduced in the inactive portion adjacent to the active portion of the piezoelectric ceramic layer 22 A. Therefore, according to the embodiment, the coercive electric field of the piezoelectric element 70 is increased, and thus the driving deterioration of the piezoelectric element 70 is reduced.

[0104] In the embodiment, the area ratio of the metal oxide MO scattered inside the base material BM may be 15% to 30%, and preferably 20% to 30%. In other words, in the SEM cross-sectional photograph of the surface electrode 72, the area ratio of the metal oxide MO not in contact with the interface IF to the base material BM is 15% to 30%, more preferably 20% to 30%.

[0105] By setting the area ratio of the metal oxide MO within the above range, fixation of domains caused by excessive strain is further reduced in the inactive portion adjacent to the active portion of the piezoelectric ceramic layer 22 A. Therefore, according to the embodiment, the coercive electric field of the piezoelectric element 70 is further increased, and thus the driving deterioration of the piezoelectric element 70 is further reduced.

[0106] In the embodiment, a metal oxide MO may be located at the interface IF (see FIG. 7) between the base material BM and the piezoelectric ceramic layer 22A, thereby improving the adhesion between the surface electrode 72 and the piezoelectric ceramic layer 22A, thereby improving the reliability of the liquid ejection head 8.

[0107] In the embodiment, the area ratio of the metal oxide MO scattered inside the base material BM to the metal oxide MO located at the interface IF between the base material BM and the piezoelectric ceramic layer 22A may be 20% to 60%, and is preferably 40% to 60%. In other words, in the SEM cross-sectional photograph of the surface electrode 72, the area ratio of the metal oxide MO in contact with the interface IF to the base material BM is 20% to 60%, and more preferably 40% to 60%.

[0108] By setting the area ratio of the metal oxide MO within the above range, fixation of domains caused by excessive strain is further reduced in the inactive portion adjacent to the active portion of the piezoelectric ceramic layer 22 A. Therefore, according to the embodiment, the coercive electric field of the piezoelectric element 70 is further increased, and thus the driving deterioration of the piezoelectric element 70 is further reduced.

[0109] In the embodiment, the metal oxide MO may be exposed on the surface of the base material BM in the surface electrode 72 of the piezoelectric element 70 .

[0110] This increases the hardness of the surface electrode 72, so that when the piezoelectric element 70 is driven, excessive strain is less likely to occur in the inactive portion adjacent to the active portion of the piezoelectric ceramic layer 22A.

[0111] Therefore, the fixation of domains caused by excessive strain is reduced in the inactive portion adjacent to the active portion of the piezoelectric ceramic layer 22 A. Therefore, according to the embodiment, the coercive electric field of the piezoelectric element 70 is increased, and thus the driving deterioration of the piezoelectric element 70 is reduced.

[0112] In the embodiment, the area ratio of the metal oxide MO exposed on the surface of the base material BM may be 0.5% to 6%, and preferably 2% to 6%. In other words, in the SEM surface photograph of the surface electrode 72, the area ratio of the metal oxide MO exposed on the base material BM to the base material BM is 0.5% to 6%, and more preferably 2% to 6%.

[0113] By setting the area ratio of the metal oxide MO within the above range, fixation of domains caused by excessive strain is further reduced in the inactive portion adjacent to the active portion of the piezoelectric ceramic layer 22 A. Therefore, according to the embodiment, the coercive electric field of the piezoelectric element 70 is further increased, and thus the driving deterioration of the piezoelectric element 70 is further reduced.

[0114] In addition, in the embodiment, the metal oxide MO may include an oxide of a metal contained in the piezoelectric ceramic layer 22 A. For example, when the piezoelectric ceramic layer 22 A is made of PZT, the metal oxide MO may include at least one of oxides of lead (Pb), zirconium (Zr), and titanium (Ti) contained in PZT.

[0115] This improves the adhesion between the surface electrode 72 and the piezoelectric ceramic layer 22A, thereby improving the reliability of the liquid ejection head 8.

[0116] In the embodiment, the metal oxide MO may contain Pb oxide. This can prevent the surface electrode 72, which is made of a precious metal base material BM, from being excessively hardened by the addition of the metal oxide MO. Therefore, according to the embodiment, it is possible to prevent the unimorph deformation of the piezoelectric element 70 from being hindered by excessive hardening of the surface electrode 72.

[0117] Furthermore, in this embodiment, since the metal oxide MO contains Pb oxide, the adhesion between the surface electrode 72 and the piezoelectric ceramic layer 22A is improved, and therefore the reliability of the liquid ejection head 8 is improved.

[0118] In addition, in the embodiment, the base material BM may be mainly composed of a noble metal, such as Au or Ag, which can prevent the surface electrode 72 from becoming excessively hard, thereby reducing the interference with the unimorph deformation of the piezoelectric element 70 caused by the surface electrode 72.

[0119] In the embodiment, the piezoelectric element 70 may have a base material BM containing a precious metal and a metal oxide MO, with the metal oxide MO scattered inside the base material BM, as the surface electrode 72. This increases the coercive electric field of the piezoelectric element 70, thereby reducing drive deterioration of the piezoelectric element 70.

[0120] In the piezoelectric element 70, the electrode having the base material BM containing a precious metal and the metal oxide MO, with the metal oxide MO scattered inside the base material BM, is not limited to the surface electrode 72, but may be the internal electrode 71. This also increases the coercive electric field of the piezoelectric element 70, thereby reducing driving deterioration of the piezoelectric element 70.

[0121] Examples of the present disclosure will be described below in detail. Note that in the examples described below, PZT is used as the piezoelectric ceramic layer 22A, Au is used as the base material BM of the surface electrode 72, and Pb oxide is used as the metal oxide MO, but the present disclosure is not limited to the following examples.

[0122] Example 1 First, a laminate was prepared by laminating a flow path member 21 (see FIG. 6) and a piezoelectric actuator substrate 22 (see FIG. 6). Next, a paste containing Au and Pb oxide was applied by screen printing to the surface of the piezoelectric ceramic layer 22A of the piezoelectric actuator substrate 22. Note that this paste was applied in a position and shape corresponding to the surface electrode 72 (see FIG. 6).

[0123] Next, the laminate coated with the paste containing Au and Pb oxides was subjected to a baking process. This baking process was performed in the atmosphere at a maximum temperature (hereinafter also referred to as the baking temperature) of 660°C. As a result, the paste containing Au and Pb oxides was baked, and surface electrodes 72 were formed on the surfaces of the piezoelectric ceramic layers 22A.

[0124] Next, a head main body 20 (see Figure 6) was formed by providing a connection electrode 73 (see Figure 6) on the surface electrode 72, and the components shown in Figure 3 were attached to the formed head main body 20 to obtain the liquid ejection head 8 (see Figure 3) of Example 1.

[0125] Examples 2 to 5 Liquid ejection heads 8 of Examples 2 to 5 were obtained using a method similar to that of Example 1. In Examples 2 to 5, the baking process of the paste containing Au and Pb oxides was performed in the atmosphere at baking temperatures of 675°C, 690°C, 705°C, and 720°C, respectively.

[0126] <Reference Examples 1 and 2> Liquid ejection heads 8 of Reference Examples 1 and 2 were obtained using a method similar to that of Example 1. In Reference Examples 1 and 2, the baking process of the paste containing Au and Pb oxides was performed in the atmosphere at baking temperatures of 750°C and 780°C, respectively.

[0127] <Various Evaluations> Next, various evaluations were performed on the liquid ejection heads 8 of Examples 1 to 5 and Reference Examples 1 and 2 obtained above. First, the cross-sectional state of the surface electrode 72 in Examples 1 to 5 and Reference Examples 1 and 2 was observed using a SEM (Scanning Electron Microscope). The observation results are shown in FIGS. 7 to 10.

[0128] 7 to 10 are SEM images of the cross-sectional state of the surface electrode 72 in Examples 1, 3, 5 and Reference Example 2. FIG.

[0129] 7 to 9, metal oxides MO composed of Pb oxides were scattered within the base material BM composed of Au in the surface electrodes 72 of Examples 1, 3, and 5. Although not shown, metal oxides MO composed of Pb oxides were also scattered within the base material BM composed of Au in the surface electrodes 72 of Examples 2 and 4.

[0130] 10, in the surface electrode 72 of Reference Example 2, the metal oxide MO made of Pb oxide was not scattered but was located locally inside the base material BM made of Au. Although not shown, in the surface electrode 72 of Reference Example 1, the metal oxide MO made of Pb oxide was also not scattered but was located locally inside the base material BM made of Au.

[0131] 7 to 10, metal oxide MO was also located at the interface IF between the base material BM and the piezoelectric ceramic layer 22A in the surface electrodes 72 of Examples 1 to 5 and Reference Examples 1 and 2. Note that the black dots in Figures 7 to 10 are not metal oxide MO but voids.

[0132] Next, from SEM images of the cross-sectional state of the surface electrode 72 of each of the examples and reference examples described so far, the area ratio of the metal oxide MO in the electrode per unit area and the area ratio of the metal oxide MO at the interface IF per unit area were calculated.

[0133] 11 is a diagram showing the relationship between the baking temperature of the surface electrode 72 and the area ratio of the metal oxide MO within the electrode and at the interface IF of the surface electrode 72. In each example (baking temperature 720°C or lower), the metal oxide MO was scattered within the base material BM, and therefore, as shown in FIG. 11, the area ratio of the metal oxide MO within the electrode was higher than in each reference example (baking temperature 750°C or higher).

[0134] In each example, the area ratio of the metal oxide MO in the electrode was within the range of 15% to 30%. In Examples 1 to 4 (baking temperatures of 660°C to 705°C), the area ratio of the metal oxide MO in the electrode was within the range of 20% to 30%.

[0135] As shown in FIG. 11, in Examples 1 to 5 and Reference Examples 1 and 2, the area ratio of the metal oxide MO at the interface IF did not change so much.

[0136] 12 is a diagram showing the relationship between the baking temperature of the surface electrode 72 and the area ratio of the metal oxide MO inside the electrode to the metal oxide MO at the interface IF of the surface electrode 72. In each example (baking temperature 720°C or less), the metal oxide MO was scattered inside the base material BM, and as shown in FIG. 12, the ratio of the metal oxide MO inside the electrode to the interface IF was higher than in Reference Examples 1 and 2 (baking temperature 750°C or more).

[0137] In each example, the area ratio of the metal oxide MO in the electrode to the interface IF was within the range of 20% to 60%. In addition, in examples 1 to 4 (baking temperatures of 660°C to 705°C), the area ratio of the metal oxide MO in the electrode to the interface IF was within the range of 40% to 60%.

[0138] Next, the surface states of the surface electrodes 72 in Examples 1 to 5 and Reference Examples 1 and 2 were observed by SEM. The observation results are shown in Figures 13 to 16. Figures 13 to 16 are diagrams showing SEM images of the surface states of the surface electrodes 72 in Examples 1, 3, 5, and Reference Example 2.

[0139] 13 to 15, granular metal oxide MO composed of Pb oxide was exposed on the surface of the base material BM composed of Au in the surface electrodes 72 of Examples 1, 3, and 5. Although not shown, granular metal oxide MO composed of Pb oxide was also exposed on the surface of the base material BM composed of Au in the surface electrodes 72 of Examples 2 and 4.

[0140] 16, the metal oxide MO made of Pb oxide was not exposed on the surface of the base material BM made of Au in the surface electrode 72 of Reference Example 2. Although not shown, the metal oxide MO made of Pb oxide was also not exposed on the surface of the base material BM made of Au in the surface electrode 72 of Reference Example 1.

[0141] Next, the area ratio of the metal oxide MO on the electrode surface per unit area was determined from SEM images of the surface state of the surface electrode 72 of each of the examples and reference examples described above. Fig. 17 is a graph showing the relationship between the baking temperature of the surface electrode 72 and the area ratio of the metal oxide MO on the surface of the surface electrode 72.

[0142] 17, in each example, the area ratio of the metal oxide MO on the surface was within the range of 0.5% to 6%. In addition, in examples 2 to 4 (baking temperatures of 675°C to 705°C), the area ratio of the metal oxide MO on the surface was within the range of 2% to 6%. On the other hand, in reference examples 1 and 2 (baking temperatures of 750°C or higher), the metal oxide MO was not exposed on the surface of the base material BM, and therefore the area ratio of the metal oxide MO on the surface was zero.

[0143] Next, the coercive electric field of the piezoelectric element 70 of each example and each reference example was evaluated. Specifically, a flying probe device was used to apply a voltage in the range of -100 V to 100 V to measure the hysteresis curve of the piezoelectric element 70. The coercive electric field of the piezoelectric element 70 was then calculated from the value of the point where the measured hysteresis curve intersects with the x-axis (i.e., y = 0).

[0144] Fig. 18 is a diagram showing the relationship between the baking temperature of the surface electrode 72 and the coercive electric field of the piezoelectric element 70. As shown in Fig. 18, the values ​​of the coercive electric field in the piezoelectric element 70 were higher in each example (baking temperature 720°C or less) than in each reference example (baking temperature 750°C or more).

[0145] Furthermore, from the observation results of the cross-sectional SEM images (see Figures 7 to 10) and the results of Figure 18, it can be seen that in the embodiment, the value of the coercive electric field in the piezoelectric element 70 is increased due to the presence of metal oxide MO scattered inside the base material BM.

[0146] This is presumably because the hardness of the surface electrode 72 is increased by the presence of metal oxide MO scattered inside the base material BM, and when the piezoelectric element 70 is driven, excessive distortion is less likely to occur in the inactive portions adjacent to the active portions of the piezoelectric ceramic layer 22A, thereby reducing domain fixation in such inactive portions.

[0147] Furthermore, from the results of Figures 11 and 18, it can be seen that in the embodiment, the value of the coercive electric field in the piezoelectric element 70 is increased by setting the area ratio of the metal oxide MO in the electrode to a range of 15% to 30%.

[0148] Furthermore, from the results of Figures 11 and 18, it can be seen that in the embodiment, the value of the coercive electric field in the piezoelectric element 70 is further increased by setting the area ratio of the metal oxide MO in the electrode to the range of 20% to 30%.

[0149] Furthermore, from the results of Figures 12 and 18, it can be seen that in the embodiment, the value of the coercive electric field in the piezoelectric element 70 is increased by setting the area ratio of the metal oxide MO in the electrode to the metal oxide MO at the interface IF in the range of 20% to 60%.

[0150] Furthermore, from the results of Figures 12 and 18, it can be seen that in the embodiment, the value of the coercive electric field in the piezoelectric element 70 is further increased by setting the area ratio of the metal oxide MO in the electrode to the metal oxide MO at the interface IF in the range of 40% to 60%.

[0151] Furthermore, from the results of Figures 17 and 18, it can be seen that in the embodiment, the value of the coercive electric field in the piezoelectric element 70 is increased by setting the area ratio of the metal oxide MO on the surface in the range of 0.5% to 6%.

[0152] Furthermore, from the results of Figures 17 and 18, it can be seen that in the embodiment, the value of the coercive electric field in the piezoelectric element 70 is further increased by setting the area ratio of the metal oxide MO on the surface in the range of 2% to 6%.

[0153] Next, the progress of drive deterioration was evaluated for the piezoelectric elements 70 of Example 3 and Reference Example 1. Specifically, for the liquid ejection heads 8 of Example 3 and Reference Example 1, the initial ejection amount was measured, and then a pulse waveform of a predetermined frequency was applied to the piezoelectric element 70 to cause drive deterioration, and the ejection amount was measured again after a predetermined number of cycles of driving.

[0154] 19 is a diagram showing the progress of drive deterioration of the piezoelectric element 70 of Example 3 and the piezoelectric element 70 of Reference Example 1. A comparison between the piezoelectric element 70 of Example 3 and the piezoelectric element 70 of Reference Example 1 reveals that the drive deterioration of the piezoelectric element 70 is reduced as the value of the coercive electric field in the piezoelectric element 70 increases.

[0155] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present disclosure.

[0156] Further advantages and other aspects may readily occur to those skilled in the art. Therefore, the disclosure in its broader aspects is not limited to the specific details and representative embodiments shown and described above. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

[0157] The present technology can also be configured as follows. (1) A piezoelectric actuator including a piezoelectric element that deforms when a voltage is applied, the piezoelectric element including: a piezoelectric ceramic body; and an electrode that applies a voltage to the piezoelectric ceramic body, the electrode including a base material containing a precious metal and a metal oxide, the metal oxide being scattered within the base material. (2) The piezoelectric actuator according to (1), wherein an area ratio of the metal oxide scattered within the base material is 15% to 30%. (3) The piezoelectric actuator according to (1), wherein an area ratio of the metal oxide scattered within the base material is 20% to 30%. (4) The piezoelectric actuator according to any one of (1) to (3), wherein the metal oxide is located at the interface between the base material and the piezoelectric ceramic body. (5) The piezoelectric actuator according to (4), wherein an area ratio of the metal oxide scattered within the base material to the metal oxide located at the interface between the base material and the piezoelectric ceramic body is 20% to 60%. (6) The piezoelectric actuator according to (4), wherein the area ratio of the metal oxide scattered inside the base material to the metal oxide located at the interface between the base material and the piezoelectric ceramic body is 40% to 60%. (7) A piezoelectric actuator comprising a piezoelectric element that deforms when a voltage is applied, the piezoelectric element comprising: a piezoelectric ceramic body; and an electrode that applies a voltage to the piezoelectric ceramic body, the electrode comprising a base material containing a noble metal and a metal oxide, the metal oxide being exposed on the surface of the base material. (8) The piezoelectric actuator according to (7), wherein the area ratio of the metal oxide exposed on the surface of the base material is 0.5% to 6%. (9) The piezoelectric actuator according to (7), wherein the area ratio of the metal oxide exposed on the surface of the base material is 2% to 6%. (10) The piezoelectric actuator according to any one of (1) to (9), wherein the metal oxide includes an oxide of a metal contained in the piezoelectric ceramic body. (11) The piezoelectric actuator according to any one of (1) to (9), wherein the metal oxide includes Pb oxide.(12) The piezoelectric actuator according to any one of (1) to (11), wherein the electrode is a surface electrode located on the surface of the piezoelectric ceramic body. (13) A liquid ejection head comprising: a nozzle for ejecting droplets; a pressure chamber connected to the nozzle; and a piezoelectric element that deforms upon application of a voltage to deform the pressure chamber, wherein the piezoelectric element comprises a piezoelectric ceramic body and an electrode that applies a voltage to the piezoelectric ceramic body, and the electrode has a base material containing a noble metal and a metal oxide, the metal oxide being scattered within the base material. (14) A recording device having the liquid ejection head according to (13).

[0158] REFERENCE SIGNS LIST 1 Printer (an example of a recording device) 8 Liquid ejection head 22A Piezoelectric ceramic layer (an example of a piezoelectric ceramic body) 62 Pressure chamber 63 Ejection hole (an example of a nozzle) 70 Piezoelectric element 72 Surface electrode (an example of an electrode) BM Base material MO Metal oxide IF Interface

Claims

1. It has a piezoelectric element that deforms when a voltage is applied, The piezoelectric element is a piezoelectric ceramic body; an electrode for applying a voltage to the piezoelectric ceramic body; and The electrode has a base material containing a noble metal and a metal oxide, and the metal oxide is scattered inside the base material. Piezoelectric actuator.

2. The area ratio of the metal oxides scattered inside the base material is 15% to 30%. The piezoelectric actuator according to claim 1 .

3. The area ratio of the metal oxides scattered inside the base material is 20% to 30%. The piezoelectric actuator according to claim 1 .

4. The metal oxide is located at the interface between the base material and the piezoelectric ceramic body. The piezoelectric actuator according to claim 1 .

5. The area ratio of the metal oxides scattered inside the base material to the metal oxides located at the interface between the base material and the piezoelectric ceramic body is 20% to 60%.

5. The piezoelectric actuator according to claim 4.

6. The area ratio of the metal oxides scattered inside the base material to the metal oxides located at the interface between the base material and the piezoelectric ceramic body is 40% to 60%.

5. The piezoelectric actuator according to claim 4.

7. It has a piezoelectric element that deforms when a voltage is applied, The piezoelectric element is a piezoelectric ceramic body; an electrode for applying a voltage to the piezoelectric ceramic body; and The electrode has a base material containing a noble metal and a metal oxide, and the metal oxide is exposed on the surface of the base material. Piezoelectric actuator.

8. The area ratio of the metal oxide exposed on the surface of the base material is 0.5% to 6%.

8. The piezoelectric actuator according to claim 7.

9. The area ratio of the metal oxide exposed on the surface of the base material is 2% to 6%.

8. The piezoelectric actuator according to claim 7.

10. The metal oxide includes an oxide of the metal contained in the piezoelectric ceramic body. The piezoelectric actuator according to any one of claims 1 to 9.

11. The metal oxide includes Pb oxide. The piezoelectric actuator according to any one of claims 1 to 9.

12. The electrode is a surface electrode located on the surface of the piezoelectric ceramic body. The piezoelectric actuator according to any one of claims 1 to 9.

13. a nozzle for ejecting droplets; a pressurizing chamber connected to the nozzle; a piezoelectric element that deforms when a voltage is applied to the piezoelectric element, thereby deforming the pressure chamber; and The piezoelectric element is a piezoelectric ceramic body; an electrode for applying a voltage to the piezoelectric ceramic body; and The electrode has a base material containing a noble metal and a metal oxide, and the metal oxide is scattered inside the base material. Liquid ejection head.

14. A recording apparatus comprising the liquid ejection head according to claim 13.