JP4552450B2 - Method for manufacturing piezoelectric stack - Google Patents

Description

  The present invention relates to a method for manufacturing a piezoelectric stack that can be used in a piezoelectric actuator used in an automobile fuel injection device or the like.

A piezoelectric actuator employing a piezoelectric stack may be used as a drive source of a fuel injection device for an internal combustion engine for a vehicle such as an automobile.
The piezoelectric stack in the piezoelectric actuator is hermetically sealed in a hermetic package to protect it from hot fuel and external moisture.

Japanese Patent Laid-Open No. 5-234807 JP 2001-181041 A

However, the piezoelectric layer of the piezoelectric stack is made of polycrystalline ceramic, and therefore there are a large number of grain boundaries inside. There are voids at the grain boundaries as shown in FIG.
When the piezoelectric stack is exposed to a high temperature and sealed environment, the moisture that was originally adsorbed, the decomposition products of the constituent resin materials, and various substances constituting the internal electrode layer and the piezoelectric layer may enter the crystal grain boundary. Yes, this phenomenon changes the physical properties such as the insulation resistance value of the piezoelectric layer.
This phenomenon causes deterioration in performance and reliability of the piezoelectric stack.
In particular, when the entering material is a conductive material, the insulation resistance value of the piezoelectric layer may be reduced.

  An object of the present invention is to provide a method for manufacturing a piezoelectric stack which is less likely to deteriorate in performance and has high reliability.

The first invention is to produce a piezoelectric stack formed by alternately laminating piezoelectric layers made of PZT (lead zirconate titanate) and internal electrode layers.
Laminating a green sheet for a piezoelectric layer printed with a conductive paste for an internal electrode layer to produce a green laminate,
The unfired laminate is fired so that Pb-based glass precipitates at the crystal grain boundaries inside the piezoelectric layer to obtain a fired stack,
After that, the Pb-based glass grain boundary filling factor at the crystal grain boundary (where the grain boundary filling factor is the grain boundary length of the region filled with the Pb-based glass in the crystal grain, that is, the interface of the crystal grains) (Where Jb is the length of the portion where the Pb-based glass adheres to J1 and J is the total grain boundary length in the crystal grains), the grain boundary filling factor is a value represented by J1 / J × 100). A method for manufacturing a piezoelectric stack (Claim 1) is characterized in that a grain boundary filling heat treatment is performed so as to be 95% or more.

Alternatively, when the second invention is to produce a piezoelectric stack formed by alternately laminating piezoelectric layers made of PZT and internal electrode layers,
An unfired laminate is obtained by laminating an unfired sheet for a piezoelectric layer containing Pb in excess of the stoichiometric ratio in PZT (lead zirconate titanate) and printed with a conductive paste for an internal electrode layer. Make and
In the green laminate, volatilization of excess Pb before and after firing is within 5% of Pb contained in excess of the stoichiometric ratio , and the Pb-based glass with respect to the crystal grain boundary inside the piezoelectric layer Grain boundary filling factor (however, the grain boundary filling factor is the grain boundary length of the region filled with Pb-based glass in the crystal grains, that is, the length of the portion where the Pb-based glass adheres to the interface of the crystal grains. And the total grain boundary length in the crystal grains is J, the grain boundary filling factor = a value represented by J1 / J × 100)). It is in the manufacturing method of a stack (claim 5).

In the manufacturing method according to the first invention, the unfired laminate is fired under conditions such that the Pb-based glass is precipitated at the grain boundaries to obtain a fired stack.
Then, by performing a grain boundary filling heat treatment on the fired stack, the Pb-based glass precipitated at the crystal grain boundaries is melted, and the crystal grain boundaries are filled with the Pb-based glass, so that there is almost no room for moisture or other substances to enter. be able to.

Moreover, in the manufacturing method concerning 2nd invention, it bakes so that it may remain in a crystal grain boundary, so that Pb-type glass can fill a crystal grain boundary by suppressing volatilization of Pb.
Thereby, the crystal grain boundary of the piezoelectric layer is filled with the Pb-based glass, and there is almost no room for moisture or other substances to enter.

  As described above, according to the first and second inventions, the physical properties such as the insulation resistance value of the piezoelectric layer are hardly changed, and it is possible to prevent the performance deterioration and the reliability deterioration of the piezoelectric stack.

The piezoelectric stack according to the first and second inventions is formed by alternately laminating piezoelectric layers and internal electrode layers. By energizing the internal electrode layers, a potential difference is applied to each piezoelectric layer, and the piezoelectric layers are It is intended to stretch. The internal electrode layer is energized by energizing a side electrode provided on the side surface of the piezoelectric stack.
In addition, the piezoelectric stack has an overall electrode configuration in which an internal electrode layer is formed on the entire surface of the piezoelectric layer, and a partial electrode configuration in which the internal electrode layer is partially provided on the piezoelectric layer (see FIGS. 1 and 2 described later). As is known, the first and second inventions can produce either piezoelectric stack.
In addition, another layer such as a dummy layer that does not expand by energization may be provided on the end face in the stacking direction of the piezoelectric stack.

In the piezoelectric stacks obtained in the first and second inventions, the piezoelectric layer is made of sintered PZT polycrystal, and there is a crystal grain boundary between crystal grains, and Pb in the crystal grain boundary The grain boundary filling factor of the system glass is 95% or more.
Here, the grain boundary filling rate is the grain boundary length of the entire crystal grain of interest, as shown in Example 4, which will be described later, and FIG. 5 and FIG. Divided value (%).
Here, the total grain boundary length is “filled grain boundary length (that is, the length of the portion where the Pb-based glass adheres to the interface of the crystal grains) + not filled in the crystal grain of interest. Grain boundary length ".
If the grain boundary filling factor is less than 95%, moisture and other substances may enter and the characteristics of the piezoelectric layer may change. The grain boundary filling factor is most preferably 100%.

The Pb-based glass is made of a material contained in the piezoelectric layer or the internal electrode layer, and is made of a glass material mainly containing, for example, Pb—WO ₃ or Pb—MoO ₃ . This glass material is substantially amorphous. It also contains substances other than Pb, W, and Mo.

In addition, a method for obtaining a fired stack by firing the unfired laminate so that Pb-based glass precipitates at the crystal grain boundaries inside the piezoelectric layer will be described.
Since the piezoelectric layer is made of PZT, it is necessary to use a compound containing Pb as a raw material for the piezoelectric layer. In this case, by using a raw material containing Pb slightly more than the stoichiometric ratio of PZT, a glass component in which Pb and other substances are combined can be precipitated at the crystal grain boundary.
In addition, Pb is included in the firing atmosphere when firing the unfired laminate to form a fired stack to prevent volatilization of Pb from the unfired laminate or actively forming a Pb-excess atmosphere. Thus, the glass component in which Pb and another substance are combined can enter the crystal grain boundary which is a gap, and can be precipitated at the crystal grain boundary due to a temperature decrease accompanying the end of firing.

The grain boundary filling heat treatment is preferably performed at a temperature of 600 to 900 ° C. (Claim 2).
Thereby, the Pb-based glass can sufficiently fill the crystal grain boundaries.
If it is less than 600 ° C., the melting of the Pb-based glass does not proceed, and it may be difficult to fill the crystal grain boundaries. If the temperature exceeds 800 ° C., the volatilization of Pb is promoted, so that Pb volatilizes from the crystal grain boundary, which may make filling difficult.

The grain boundary filling heat treatment is preferably performed for 5 to 300 minutes.
As a result, the Pb-based glass can sufficiently fill the crystal grain boundaries.
If it is less than 5 minutes, melting of the Pb-based glass does not proceed, and it may be difficult to fill the crystal grain boundaries. If it exceeds 300 minutes, the volatilization of Pb is promoted, and therefore Pb volatilizes from the crystal grain boundary, which may make filling difficult.

Moreover, it is preferable to perform the grain boundary filling heat treatment after grinding the fired stack to a desired shape.
Since grinding is generally performed while the firing stack is immersed in a grinding fluid or the like, the grinding fluid may permeate into the firing stack and moisture and other components may enter the crystal grain boundaries. Therefore, by performing the grain boundary filling heat treatment after grinding, moisture and other components remaining at the crystal grain boundaries can be volatilized and removed.
Further, when the fired stack is ground, residual strain or the like occurs, but the residual strain can be removed by heating the fired stack in the grain boundary filling heat treatment. Furthermore, the stress can be relaxed by heating, and the ground surface of the fired stack can be densified.

  In the second invention, the unfired laminate is fired so that the volatilization of excess Pb before and after firing is within 5%. This is because the weight of Pb before and after firing is the chemistry of M0, M1, and PZT. When the weight of Pb in the piezoelectric stack derived from the stoichiometric ratio is M, the value of (M0−M1) / (M0−M) is 5% or less (see Example 10). Note that the volatilization of Pb can be made zero.

Further, as a method for suppressing the volatilization of Pb within 5% before and after firing, there is a method in which an atmosphere conditioner capable of releasing Pb vapor is disposed in the firing atmosphere (see Example 2 described later). ).
In the second invention, a piezoelectric stack is produced using an unsintered sheet for a piezoelectric layer containing Pb in excess of the stoichiometric ratio in PZT. This piezoelectric stack is made of ABO3 type dielectric ceramics. In general, it is blended so as to have a molar ratio of A: B: O = 1: 1: 3, but the total of the components of the A site containing lead is 1.00 molar ratio or more when the B site is 1. Thus, an unsintered sheet with Pb excess can be produced by adding lead excessively to the A site.

Moreover, in 2nd invention, it is preferable to perform baking at the temperature of 950-1030 degreeC (Claim 6).
Thereby, the Pb-based glass can sufficiently fill the crystal grain boundaries.
When the temperature is lower than 950 ° C., the element is not sufficiently sintered and it may be difficult to satisfy the displacement performance as the actuator. If the temperature exceeds 1030 ° C., the volatilization of Pb is promoted, so that Pb volatilizes from the crystal grain boundary, which may make filling difficult.

Example 1
A method for manufacturing a piezoelectric stack according to the present invention will be described.
That is, the piezoelectric stack according to this example is formed by alternately stacking piezoelectric layers made of PZT (lead zirconate titanate) and internal electrode layers as shown in FIGS.
In order to manufacture this, an unfired laminate is produced by alternately laminating unfired sheets for piezoelectric layers and unfired sheets for internal electrode layers, and the unfired laminate is made of crystal grains inside the piezoelectric layer. A fired stack is obtained by firing so that Pb-based glass is deposited on the boundary, and then a grain boundary filling heat treatment is performed on the fired stack so that the grain boundary filling rate of the Pb-based glass at the crystal grain boundary is 95% or more. .

Details will be described below.
First, as shown in FIGS. 1 and 2, the piezoelectric stack of this example includes a piezoelectric layer 111 in which an internal electrode layer 121 is provided in a portion other than the electrode holding portion 110 and an internal electrode layer 122 in a portion other than the electrode holding portion 110. The piezoelectric layers 112 provided with are laminated alternately.
An end portion of the internal electrode layer 121 is exposed on the side surface 101, and an end portion of the internal electrode layer 122 is exposed on the side surface 102. The exposed ends can be conducted by side electrodes 15 and 16, respectively. The piezoelectric layers 111 and 112 are made of PZT, the internal electrode layers 121 and 122 are made of Ag—Pd, and the side electrodes are made of Ag. The piezoelectric layers 131 and 132 disposed on both end surfaces in the stacking direction are dummy layers that do not expand when energized.

A method for manufacturing the piezoelectric stack 1 will be described in detail.
First, preparation of a slurry for the piezoelectric layer will be described.
The raw material powder of the piezoelectric layer is weighed, and the raw material powder and the dispersing agent are mixed with a mixer, then dried, and crushed with a likai machine.

The pulverized raw material powder is calcined to form calcined powder, the dispersant is mixed with the calcined powder, wet pulverized, dried, and then pulverized again by a laika machine. Next, a dispersant, a solvent, a plasticizer, and a binder are added and mixed to form a slurry. This is defoamed, and the viscosity is adjusted and filtered through a filter to obtain a slurry for the piezoelectric layer.
Next, a paste for the internal electrode layer is prepared and obtained.

Next, a green sheet is produced from the slurry for the piezoelectric layer using a doctor blade method. The green sheet was cut to an appropriate size, dried, and punched out with a mold to obtain an unfired sheet for the piezoelectric layer.
A paste for the internal electrode layer was printed on the green sheet and dried, and then a predetermined number of sheets were pressed and laminated to obtain a green laminate.

The firing of the unfired laminate will be described.
The unfired laminated body is fired so that Pb-based glass is deposited at the crystal grain boundaries inside the piezoelectric layer, thereby obtaining a fired stack.
Specifically, the setter 22 in which the atmosphere adjusting agent 23 and the setter 21 in which the unfired laminate 20 are arranged are stacked and set in the firing furnace 2 as shown in FIG. As the atmosphere control agent 23, lead zirconate (PbZrO ₃ ) was used.
Thus, firing was performed at a temperature of 1045 ° C. for 2 hours to obtain a fired stack.

Next, the outer dimensions of the fired stack were inspected, and grinding was performed with a surface grinder so as to obtain a predetermined dimension.
After finishing the grinding, the external dimensions were measured again, and the fired stack that reached the predetermined value was washed and further dried.
Thereafter, a grain boundary filling heat treatment is performed so that the grain boundary filling rate of the Pb-based glass at the grain boundary becomes 95% or more. This grain boundary filling heat treatment was performed in an air atmosphere in a mesh belt furnace.
Finally, a side electrode printing paste is applied and baked to obtain the side electrode according to FIG. Finally, the piezoelectric stack 1 was obtained by washing and drying.

In the manufacturing method according to this example, the unfired laminate is fired under conditions such that the Pb-based glass precipitates at the crystal grain boundaries to obtain a fired stack.
Then, by performing a grain boundary filling heat treatment on the fired stack, the Pb-based glass precipitated at the crystal grain boundaries is melted, and the crystal grain boundaries are filled with the Pb-based glass, so that there is almost no room for moisture or other substances to enter. be able to.
Therefore, according to this example, it is possible to manufacture a piezoelectric stack in which the physical properties such as the insulation resistance value of the piezoelectric layer are hardly changed, and the performance and reliability are hardly deteriorated.

(Example 2)
In this example, a manufacturing method different from that in Example 1 will be described.
That is, Pb is contained in excess of the stoichiometric ratio in PZT (lead zirconate titanate), and an unfired laminate is formed by laminating unfired sheets for piezoelectric layers on which conductive paste for internal electrode layers is printed. The green laminate is fired so that the Pb volatilization before and after firing is within 5% and the grain boundary filling rate of the Pb-based glass with respect to the crystal grain boundaries inside the piezoelectric layer is 95% or more. To do.

Details will be described below.
A piezoelectric layer paste and an internal electrode layer paste are prepared in the same procedure as in Example 1.
At this time, the raw material powder for the piezoelectric layer is one containing Pb in excess of the stoichiometric ratio of PZT. In other words, this stack, which is an ABO3 type dielectric ceramic, is usually formulated so as to have a molar ratio of A: B: O = 1: 1: 3, but the total of the components of the A site containing lead is the B site. When it is set to 1, lead A is excessively contained at the A site so that the molar ratio is 1.00 or more.
Other details are the same as in Example 1, and an unfired laminate is produced.

The green laminate is fired so that the volatilization of Pb before and after firing is within 5%, and the Pb-based glass has a grain boundary filling ratio of 95% or more with respect to the crystal grain boundaries inside the piezoelectric layer.
Specifically, the setter 22 in which the atmosphere adjusting agent 23 and the setter 21 in which the unfired laminate 20 are arranged are stacked and set in the firing furnace 2 as shown in FIG. As the atmosphere control agent 23, lead zirconate (PbZrO ₃ ) was used.
Thus, the temperature was 990 ° C. for 2 hours.
After firing, as in Example 1, the side electrode printing paste is applied and baked to obtain the side electrode according to FIG. Finally, the piezoelectric stack 1 was obtained by washing and drying.

In the manufacturing method of this example, by suppressing the volatilization of Pb, firing is performed so that the Pb-based glass can fill the crystal grain boundary and remain in the crystal grain boundary. Thereby, the crystal grain boundary of the piezoelectric layer is filled with the Pb-based glass, and there is almost no room for moisture or other substances to enter.
Thus, according to the invention of this example, the physical properties such as the insulation resistance value of the piezoelectric layer are unlikely to change, and it is possible to prevent the piezoelectric stack from being deteriorated in performance and reliability.

(Example 3)
In this example, the crystal grain boundary filling rate of Pb-based glass and the performance of the piezoelectric stack are evaluated.
The piezoelectric stack is the one described in FIGS. 1 and 2, but the comparative sample C1 is manufactured by a conventional manufacturing method, and the grain boundary filling factor of the crystal grain boundary is about 10% to 15%.
Comparative sample C2 was produced by the production method according to Example 1, but the temperature of the grain boundary filling heat treatment was as low as 400 ° C., and the grain boundary filling ratio was around 50%.
Sample 1 was the manufacturing method according to Example 1, and the temperature of the grain boundary filling heat treatment was set to 850 ° C. Sample 2 was produced by the production method according to Example 2. Samples 1 and 2 each had a grain boundary filling rate exceeding 95%.
Two piezoelectric stacks for each sample and comparative sample were prepared and measured for each.

Each of these samples is sealed in an airtight package and allowed to stand at a temperature of 190 ° C. for 1000 hours. If the insulation resistance value before leaving is IR0 and the insulation resistance value after leaving is IR1, the value of IR1 / IR0 is the vertical axis. The horizontal axis is shown in the diagram of FIG. 4 as the grain boundary filling factor.
Here, the airtight package has a structure capable of shielding the piezoelectric stack from the atmosphere and inputting / outputting electric signals to / from the piezoelectric stack.
As shown in FIG. 4, it was found that the higher the grain boundary filling rate, the smaller the decrease in the insulation resistance value, and the higher the reliability of the piezoelectric stack.
The method for measuring the grain boundary filling rate was described in Example 4 described later, and the method for measuring the insulation resistance value was described in Example 5 described later.

Example 4
A method for measuring the microstructure of the piezoelectric layer and the grain boundary filling factor will be described.
As shown in FIG. 5, the microstructure of the piezoelectric layer in the piezoelectric stack includes a Pb-based glass 32 filled in a gap formed in a crystal grain boundary 310 between the amorphous crystal grains 31 and the crystal grains 31. Consists of.
Here, the grain boundary filling factor was measured from a reflected electron image (composition image) of the crystal grains 31 in the piezoelectric layer obtained from a reflected electron detector incorporated in a scanning electron microscope (SEM).
The conditions of the backscattered electron detector used in the measurement of Example 3 are described below.
Equipment used: Scanning electron microscope Manufacturer: Hitachi, Ltd. Model: S4300
Vapor deposition on sample (piezoelectric stack fracture surface): No vapor deposition Acceleration voltage: 5 kV
Observation magnification: several hundred times to 10,000 times WD (working distance): 15 mm
Backscattered electron detector: YAG Young scintillator type

Observation was carried out on the fracture surface of the piezoelectric stack in the region to which an electric field was applied, and the grain boundary filling rate was calculated for one crystal grain 31 of the piezoelectric layer as follows.
That is, as shown in FIG. 6, the grain boundary filling factor is a value (%) obtained by dividing the grain boundary length J1 of the region filled with the Pb-based glass by the total grain boundary length J.
Here, as shown in FIG. 6, the total grain boundary length J is defined as “filled grain boundary length J1 (that is, Pb-based glass adheres to the interface between crystal grains) in one crystal grain 31 of interest. The length of the portion that is filled) + the unfilled grain boundary length J0 ”.
In actual measurement, the fracture surface of the piezoelectric stack was observed at a magnification of 10,000 times, and two crystal particles were picked up and measured for each fracture surface, and this measurement was performed on three fracture surfaces.
Thus, the average value of the grain boundary filling factor obtained from a total of six crystal grains was used as the “grain boundary filling factor of the piezoelectric stack”.

(Example 5)
A method for measuring the insulation resistance value will be described.
As shown in FIG. 7, the piezoelectric stack 1 includes a circuit protection resistor 42, a 10 kΩ resistor 43, and a DC power supply 41 connected in series, and a measurement circuit comprising a digital multimeter 44 connected in parallel to the 10 kΩ resistor 43. 4 connected.
In this measurement circuit 4, a DC voltage of 150 V is applied from the side electrodes 15, 16 of the piezoelectric stack 1. Then, the value of the digital multimeter 44 is read after 2 minutes, and the circuit current value is obtained from this voltage, whereby the insulation resistance value of the piezoelectric stack 1 can be calculated from insulation resistance value = 150 / circuit current value.

(Example 6)
In this example, in the manufacturing method of Example 1, after the grinding stack was ground, the grain boundary filling rate was compared between Sample 3 subjected to the grain boundary filling heat treatment and Comparative Sample C3 not subjected to the grain boundary filling heat treatment. This is shown in the diagram.
Two piezoelectric stacks for each sample and comparative sample were prepared and measured for each.
As is clear from the figure, the grain boundary filling rate was close to 100% by performing the grain boundary filling heat treatment at 850 ° C. after grinding. In the state of being ground, the grain boundary filling rate was smaller than 20%.

(Example 7)
In this example, the grain boundary filling ratios of Samples 5 and 6 according to the manufacturing method of Example 2 and Sample 4 fired at 980 ° C. and Comparative Sample C4 fired at a high temperature of 1045 ° C. were compared. The other points of the manufacturing method of the comparative sample C4 were the same as in Example 2, and two piezoelectric stacks of each sample and comparative sample were prepared and measured. And it plotted in FIG. 9 which took the firing temperature on the horizontal axis and the grain boundary filling factor on the vertical axis.

From the same figure, it was found that Samples 5 and 6 have an excess Pb volatilization of 5% or less, so that a grain boundary filling factor of 95% or more can be obtained.
Sample 4 having a low firing temperature has a high grain boundary filling rate, but displacement performance may be slightly inferior due to insufficient sintering.
Further, the comparative sample C4 fired at a high temperature was likely to cause Pb volatilization because of the high firing temperature, and even if an atmosphere control agent was arranged, the excess Pb volatilization could not be suppressed to 5% or less. And the grain boundary filling factor was 20% or less.
The explanation of excess Pb is described in Example 10.

(Example 8)
In this example, the piezoelectric stack according to Samples 7 to 10 (the temperatures of the grain boundary filling heat treatment are different from each other) produced by the production method of Example 1 and the production method similar to Example 1 were used. The piezoelectric stack according to the comparative sample C5 that was not subjected to the above was enclosed in an airtight package similar to that in Example 3, and left in an environment at a temperature of 190 ° C.
Then, assuming that the leaving time is on the horizontal axis, the insulation resistance value before being left is IR0, and the insulation resistance value after being left is IR1, the value of IR1 / IR0 is plotted on the vertical axis and shown in the diagram of FIG.
Two piezoelectric stacks for each sample and comparative sample were prepared and measured for each.

As a result, it was found that the insulation resistance values of Samples 7 to 10 subjected to the grain boundary filling heat treatment did not decrease so much even after 1000 hours were sealed in an airtight package and left in an environment of 190 ° C.
On the other hand, it was found that the insulation resistance value of Comparative Sample C5 that did not perform the grain boundary filling heat treatment decreased rapidly after 400 hours.

Example 9
This example is a piezoelectric stack according to Samples 9 to 11 manufactured by the manufacturing method of Example 1 (the time taken for the grain boundary filling process is different, and the temperature of the grain boundary filling heat treatment is 850 ° C.). Two piezoelectric stacks were prepared for the comparative sample C6 that was manufactured by the same manufacturing method as in Example 1, but was not subjected to the grain boundary filling heat treatment, and sealed in an airtight package similar to that in Example 8. Left in the environment.
Then, assuming that the leaving time is on the horizontal axis, the insulation resistance value before being left is IR0, and the insulation resistance value after being left is IR1, the value of IR1 / IR0 is plotted on the vertical axis and shown in the diagram of FIG.
As a result, it was found that by increasing the duration of the grain boundary filling heat treatment, a piezoelectric stack in which the insulation resistance value is more difficult to decrease can be obtained.

(Example 10)
In this example, the piezoelectric stacks of Samples 12 and 13 produced by the production method of Example 2 (the firing temperatures are different from each other) and the production method similar to Example 2 were produced, but the firing temperature was high ( 1045 ° C.), two piezoelectric stacks were prepared for the comparative sample C7 that could not suppress the volatilization of lead.
Then, the volatilization rate and the grain boundary filling rate of Pb before and after firing were examined.
The volatilization rate of Pb is determined by measuring the Pb amount (M0) in the unfired laminate and the Pb amount (M1) in the fired piezoelectric stack using a fluorescent X-ray apparatus, and the stoichiometric ratio of PZT. From the Pb amount calculated from (M), (M0−M1) / (M0−M) was defined as the volatility.

  As a result, samples 12 and 13 have a small amount of lead volatilization, and the Pb-based glass grain boundary filling ratio exceeds 95%, but comparative sample C7 has most of the excess lead volatilized, and thus Pb-based glass particles. The field filling factor was significantly below 95%.

FIG. 3 is a cross-sectional explanatory view of the piezoelectric stack according to the first embodiment. 1 is a plan view of a piezoelectric layer and internal electrode layers according to Example 1. FIG. Explanatory drawing of baking of the unbaking laminated body concerning Example 1. FIG. The diagram which shows the relationship between the grain boundary filling rate by Pb type glass concerning Example 3, and the change of an insulation resistance value. FIG. 6 is an explanatory diagram illustrating crystal grains and crystal grain boundaries of a piezoelectric layer according to Example 4; Explanatory drawing concerning Example 4 which shows the grain boundary length J1 with which the crystal grain was filled, and the grain boundary length J0 with which it is not filled. Explanatory drawing of the measuring circuit concerning Example 5 which measures the insulation resistance value. The diagram which shows the relationship between the presence or absence of the grain boundary filling heat treatment and the Pb-based grain boundary filling factor according to Example 6. The diagram which shows the relationship between the calcination temperature concerning Example 7, and a Pb-type grain-boundary filling factor. The diagram which shows the relationship between the durable time concerning Example 8, and the change of an insulation resistance ground. The diagram which shows the relationship between the durable time concerning Example 9, and the change of an insulation resistance ground. The diagram which shows the relationship between the calcination temperature concerning Example 10, excess Pb volatilization rate, and a Pb-type glass grain-boundary filling factor.

Explanation of symbols

1 Piezoelectric stack 111, 112 Piezoelectric layer 121, 122 Internal electrode layer

Claims (6)

In producing a piezoelectric stack in which piezoelectric layers made of PZT (lead zirconate titanate) and internal electrode layers are alternately laminated,
Laminating a green sheet for a piezoelectric layer printed with a conductive paste for an internal electrode layer to produce a green laminate,
The unfired laminate is fired so that Pb-based glass precipitates at the crystal grain boundaries inside the piezoelectric layer to obtain a fired stack,
After that, the Pb-based glass grain boundary filling factor at the crystal grain boundary (where the grain boundary filling factor is the grain boundary length of the region filled with the Pb-based glass in the crystal grain, that is, the interface of the crystal grains) (Where Jb is the length of the portion where the Pb-based glass adheres to J1 and J is the total grain boundary length in the crystal grains), the grain boundary filling factor is a value represented by J1 / J × 100). A method for manufacturing a piezoelectric stack, comprising performing grain boundary filling heat treatment so as to be 95% or more.   2. The method of manufacturing a piezoelectric stack according to claim 1, wherein the grain boundary filling heat treatment is performed at a temperature of 600 to 900.degree.   3. The method of manufacturing a piezoelectric stack according to claim 1, wherein the grain boundary filling heat treatment is performed for 5 to 300 minutes.   4. The method of manufacturing a piezoelectric stack according to claim 1, wherein the grain boundary filling heat treatment is performed after the fired stack is ground into a desired shape. In producing a piezoelectric stack formed by alternately laminating piezoelectric layers made of PZT and internal electrode layers,
An unfired laminate is obtained by laminating an unfired sheet for a piezoelectric layer containing Pb in excess of the stoichiometric ratio in PZT (lead zirconate titanate) and printed with a conductive paste for an internal electrode layer. Make and
In the green laminate, volatilization of excess Pb before and after firing is within 5% of Pb contained in excess of the stoichiometric ratio , and the Pb-based glass with respect to the crystal grain boundary inside the piezoelectric layer Grain boundary filling factor (however, the grain boundary filling factor is the grain boundary length of the region filled with Pb-based glass in the crystal grains, that is, the length of the portion where the Pb-based glass adheres to the interface of the crystal grains. And the total grain boundary length in the crystal grains is J, the grain boundary filling factor = a value represented by J1 / J × 100)). Stack manufacturing method.   6. The method of manufacturing a piezoelectric stack according to claim 5, wherein the firing is performed at a temperature of 950 to 1030.degree.

Images