JP4900008B2 - Method of manufacturing a piezoelectric ceramic - Google Patents

Description

  The present invention relates to a method for manufacturing a piezoelectric ceramic.

  Conventionally, piezoelectric elements have been used in various applications such as sounding bodies, sensors, and actuators. As a piezoelectric element, a single plate piezoelectric element or a multilayer piezoelectric element is known. A single plate piezoelectric element has a structure including a piezoelectric layer made of a piezoelectric ceramic between a pair of electrode layers. The multilayer piezoelectric element has an element body having a structure in which piezoelectric layers and internal electrodes are alternately stacked. In this multilayer piezoelectric element, the element body is generally covered with a protective layer composed of a plurality of piezoelectric layers at both end surfaces in the stacking direction.

A piezoelectric ceramic material used for such a piezoelectric element is disclosed in, for example, Patent Document 1 below.
JP-A-5-24917

  In the piezoelectric layer of the piezoelectric ceramic as described above, it has been desired to relax strain generated during firing and to stabilize crystal grain growth. The inventors have found that strain relaxation and stabilization of crystal grain growth can be realized by using a piezoelectric material containing phosphorus. However, since phosphorus in the piezoelectric material has an adverse effect on the piezoelectric strain characteristics, the inventors have conducted research on the piezoelectric strain characteristics and finally found a technique for suppressing the deterioration of the piezoelectric strain characteristics.

  That is, an object of the present invention is to provide a method of manufacturing a piezoelectric ceramic that can suppress deterioration of piezoelectric strain characteristics while reducing strain during firing and stabilizing crystal grain growth.

The inventors include P in the piezoelectric material used in the piezoelectric ceramic, and P is mixed as P ₂ O ₅ in a predetermined range from the TiO ₂ raw material and the ZrO ₂ raw material in the piezoelectric material, and When the P ₂ O ₅ added to the piezoelectric material as a sub-component is less than a predetermined ratio, the strain during firing and the stabilization of the crystal grain growth can be realized, and the deterioration of the piezoelectric strain characteristics can be suppressed. As a result, the present invention has been completed.

That is, the manufacturing method of the piezoelectric ceramic according to the present invention comprises a TiO ₂ material and ZrO ₂ raw material and Pb O raw material as a main component, and, P ₂ O ₅ is fired piezoelectric material that is added as an auxiliary component A piezoelectric ceramic manufacturing method for producing a piezoelectric ceramic, wherein the piezoelectric material contains P ₂ O ₅ contained in the TiO ₂ raw material and the ZrO ₂ raw material in a range of 40 ppm to 350 ppm, and is contained in the piezoelectric material. of _P 2 _{O 5} which is characterized in that the ratio of _P 2 _{O 5} is added as a sub-component is less than 30% greater than 0%.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the piezoelectric ceramic which can suppress deterioration of a piezoelectric distortion characteristic, aiming at the relaxation of the distortion at the time of baking, and stabilization of a crystal grain growth is provided.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, embodiments that are considered to be the best in carrying out the invention will be described in detail with reference to the accompanying drawings. In addition, the same code | symbol is attached | subjected about the same or equivalent element, and the description is abbreviate | omitted when description overlaps.

  First, a piezoelectric element manufactured by a manufacturing method according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a perspective view showing a piezoelectric element according to an embodiment of the present invention. A piezoelectric element 1 shown in FIG. 1 is a single plate piezoelectric element, and includes a piezoelectric layer 2 of a piezoelectric ceramic and a pair of electrode layers 3A and 3B arranged so as to sandwich the piezoelectric layer 2 therebetween. In the piezoelectric element 1, when a voltage is applied between the electrodes 3A and 3B, an electric field is generated in the piezoelectric layer 2 sandwiched between them, and the piezoelectric layer 2 is displaced (expanded / contracted).

  The piezoelectric layer 2 is a layer mainly composed of a piezoelectric material of PZT-based piezoelectric ceramic. The piezoelectric material of the piezoelectric layer 2 contains phosphorus element. In the piezoelectric material, the phosphorus element is included in the form of a compound with an atom, an oxide, or another metal included in the piezoelectric layer 2. The phosphorus element is preferably uniformly dispersed in the piezoelectric layer 2.

  The electrode layers 3A and 3B are conductive layers mainly composed of metal. Examples of the metal contained in the electrode layers 3A and 3B include Ag, Au, Cu, Ni, Pd, and alloys thereof (for example, Ag—Pd alloy).

  Next, a procedure for manufacturing the piezoelectric element will be described with reference to FIG. FIG. 2 is a flowchart showing a method for manufacturing a piezoelectric element according to an embodiment of the present invention.

When manufacturing the piezoelectric element 1, first, a starting material is prepared (step 11). This starting material is a PZT-based piezoelectric material, which includes a powder material such as PbO, TiO ₂ , ZrO ₂ , ZnO, Nb ₂ O ₅ as a main component, and a P ₂ O ₅ reagent (or P ₄ as an accessory component). O ₁₀ reagent, H ₃ PO ₄ reagent). And each raw material is weighed so that these raw materials may become a predetermined composition ratio. At this time, the amount of the P ₂ O ₅ reagent is adjusted so as to be 30% or less of the P ₂ O ₅ contained in the piezoelectric material.

  Next, the above starting materials are wet mixed for about 24 hours by a ball mill using stabilized zirconia balls as media (step S12). Subsequently, the mixed raw materials are dried (step S13). And the temporary baking which performs the heat processing for about 2 hours at the temperature of about 850 degreeC, for example with respect to the mixed raw material is performed (step S14). Thereby, a raw material composition of a composite oxide piezoelectric material having a perovskite structure mainly containing Pb, Zr, and Ti elements is obtained.

  After this raw material composition is wet pulverized by a ball mill (step S15), it is dried (step S16) to obtain a raw material composition powder (piezoelectric ceramic powder). Subsequently, granulation is performed by adding a binder such as polyvinyl alcohol to the piezoelectric ceramic powder (step S17), and this is formed into a square plate shape by press molding or the like (step S18). Thereby, the piezoelectric molded product used as a piezoelectric ceramic is obtained.

  After the obtained piezoelectric molded product is placed on a stabilized zirconia setter or the like, it is heated in an air atmosphere to perform a degreasing process to remove the binder or the like contained in the piezoelectric molded product (step S19; Debinding). And the baking processing (main baking) which heats for about 2 hours, for example to 1050-1200 degreeC is performed with respect to a piezoelectric molded object in the sealed container (step S20).

  Finally, a silver paste is baked on both sides of the obtained fired body to form electrode layers 3A and 3B (step S21). As a result, the piezoelectric element 1 shown in FIG. 1 including the piezoelectric layer 2 which is a fired piezoelectric ceramic and the electrode layers 3A and 3B baked on both surfaces thereof is obtained.

As described above, the inventors include P in the piezoelectric material used in the piezoelectric ceramic, and the P is P ₂ O ₅ , and is within a predetermined range from the TiO ₂ raw material and the ZrO ₂ raw material in the piezoelectric material. When the amount of P ₂ O ₅ added as a subsidiary component to the piezoelectric material is equal to or less than a predetermined ratio, strain relaxation during firing and stabilization of crystal grain growth are realized, and piezoelectric It has been found that the deterioration of the distortion characteristic (d31) can be suppressed.

Specifically, the phosphorus element content of the TiO ₂ powder raw material and the ZrO ₂ powder raw material in the piezoelectric material is adjusted to a range of 40 ppm or more and 350 ppm or less on a molar basis in terms of P ₂ O ₅ . That is, this amount of phosphorus element is mixed in the piezoelectric material. If the phosphorus element content is less than 40 ppm, the piezoelectric material may not be sufficiently sintered by firing, and the density of the piezoelectric layer 2 may be reduced, making it difficult to obtain sufficient displacement. On the other hand, when the phosphorus element content exceeds 350 ppm, the value of the piezoelectric strain constant (d31) falls below a practical level.

Then, P is mixed as P ₂ O ₅ from the TiO ₂ raw material and the ZrO ₂ raw material in the piezoelectric material, and the addition ratio of the P ₂ O ₅ reagent added to the piezoelectric material as a subcomponent is reduced to 30% or less. In the following examples, it was confirmed that the deterioration of the piezoelectric strain characteristics was effectively suppressed. Thereby, as compared with the case of increasing the content _of P ₂ O ₅ in the piezoelectric material by adding P ₂ O ₅ reagent, while maintaining the piezoelectric strain constant to or greater than a predetermined reference value, the more P ₂ O _{Since 5} can be contained in the piezoelectric material, further strain relaxation and stability of crystal grain growth can be achieved.

  Instead of the method described above, an electrode paste (for example, a paste containing an Ag—Pd alloy) to be the electrode layers 3A and 3B is applied to the piezoelectric body, and then the binder removal process (step S19) and the main firing (step) By performing S20), an element similar to the piezoelectric element 1 of FIG. 1 can be obtained. In this case, the metal contained in the electrode paste layer easily diffuses into the piezoelectric molded product during the main firing, but phosphorus elements that easily react with the metal are dispersed in the piezoelectric molded product. The metal diffusion occurs uniformly in the piezoelectric molded product. As a result, the piezoelectric molded product (piezoelectric layer 2) contracts more uniformly by sintering than when the piezoelectric molded product does not contain a phosphorus element. As a result, the piezoelectric layer 2 has a shape with less distortion, and the entire piezoelectric element 1 also has less distortion.

Hereinafter, the present invention will be described in more detail with reference to examples.
(First embodiment)

First, Steps S11 to S16 shown in FIG. 2 were performed to obtain a piezoelectric material raw material composition powder (starting raw material). This starting material contains TiO ₂ and ZrO ₂ containing P ₂ O ₅ and PbO, ZnO, and Nb ₂ O ₅ . Then, after firing these starting materials, a piezoelectric ceramic having a composition of Pb _0.99 [(Zn _1/3 Nb _2/3 ) _0.1 Ti _0.44 Zr _0.46 ] O ₃ is obtained. Weighed and blended.

  Next, as shown in step S17, after adding a polyvinyl alcohol binder to the powder of the raw material composition of the piezoelectric material and granulating, press molding shown in step S18 is performed at about 196 MPa, and one side is about 196 MPa. A square plate-like piezoelectric molded product having a size of 20 mm and a thickness of 1.5 mm was obtained.

  Thereafter, as shown in step S19, the binder is removed from the piezoelectric body, and as shown in step S20, the piezoelectric body is placed in a magnesia (MgO) sealed container and heated at 1150 ° C. for 2 hours. Went. Thereby, a square plate-shaped piezoelectric ceramic was obtained.

  Finally, the obtained piezoelectric ceramic is processed to a height of 1.0 mm, and further, a silver-baked electrode is formed on both sides thereof, and a single plate piezoelectric element (12 mm × 3 mm) similar to the piezoelectric element shown in FIG. Produced. Furthermore, this single plate piezoelectric element was subjected to polarization treatment (treatment conditions: 3 kV / mm, 15 minutes) in 120 ° C. silicone oil.

The piezoelectric strain constant (d31) of the single-plate piezoelectric element obtained as described above was measured. As a measurement method, a piezoelectric strain constant was calculated from the capacitance, resonance frequency, and antiresonance frequency of the element measured using an impedance analyzer. In addition, the cross section of the piezoelectric ceramic was observed with a scanning electron microscope, and the average particle diameter of the piezoelectric particles was set to the equivalent circle diameter and measured using image processing software (Mac View).
(Comparative example)

Similarly to the above-described example, steps S11 to S16 shown in FIG. 2 were performed to obtain a powder of the raw material composition of the piezoelectric material. This starting material contains TiO ₂ , ZrO ₂ , PbO, ZnO, Nb ₂ O ₅ , and a P ₂ O ₅ reagent is added thereto. Then, a piezoelectric material having a composition of Pb _0.99 [(Zn _1/3 Nb _2/3 ) _0.1 Ti _0.44 Zr _0.46 ] O ₃ after firing is added to the starting material to which P ₂ O ₅ is added. The porcelain was weighed and blended to obtain a porcelain.

  Next, as shown in step S17, after adding a polyvinyl alcohol binder to the powder of the raw material composition of the piezoelectric material and granulating, press molding shown in step S18 is performed at about 196 MPa, and one side is about 196 MPa. A square plate-like piezoelectric molded product having a size of 20 mm and a thickness of 1.5 mm was obtained.

  Thereafter, as shown in step S19, the binder is removed from the piezoelectric body, and as shown in step S20, the piezoelectric body is placed in a magnesia (MgO) sealed container and heated at 1150 ° C. for 2 hours. Went. Thereby, a square plate-shaped piezoelectric ceramic was obtained.

  Finally, the obtained piezoelectric ceramic is processed to a height of 1.0 mm, and further, a silver-baked electrode is formed on both sides thereof, and a single plate piezoelectric element (12 mm × 3 mm) similar to the piezoelectric element shown in FIG. Produced. Furthermore, this single plate piezoelectric element was subjected to polarization treatment (treatment conditions: 3 kV / mm, 15 minutes) in 120 ° C. silicone oil.

  The piezoelectric strain constant of the single-plate piezoelectric element obtained as described above was measured in the same manner as in the example. In addition, the cross section of the piezoelectric ceramic was observed with a scanning electron microscope, and the average particle diameter of the piezoelectric particles was set to the equivalent circle diameter and measured using image processing software (Mac View).

The piezoelectric strain constants measured by the above examples and comparative examples were as shown in the following Table 1 and the graph of FIG. Here, the horizontal axis of the graph of FIG. 3 indicates the P ₂ O ₅ content (ppm) in the piezoelectric material, and the vertical axis indicates the piezoelectric strain constant (pC / N).

From these measurement results (Table 1 and the graph of FIG. 3), compared to the comparative example in which P ₂ O ₅ was directly added to the piezoelectric material, the piezoelectric material was transformed into P ₂ O ₅ from the TiO ₂ powder raw material and the ZrO ₂ powder raw material. It was found that the piezoelectric strain constant value was higher in the example in which was mixed. Furthermore, when the content of the phosphorus element in the TiO ₂ powder raw material and the ZrO ₂ powder raw material in the piezoelectric material is 350 ppm or less on a molar basis in terms of P ₂ O ₅ , the piezoelectric strain constant is practically sufficient. It became a value (200 pC / N or more). On the other hand, when P ₂ O ₅ exceeded 350 ppm, the piezoelectric strain constant was below 200 pC / N. Therefore, it is preferable _P 2 _{O 5} to be mixed from the TiO ₂ material and ZrO ₂ raw material in the piezoelectric material is less than 350 ppm.

Moreover, the micrographs in Examples and Comparative Examples were as shown in FIG. From this photograph, as a result of measuring the average particle diameter of the piezoelectric particles, the graph shown in FIG. 5 was obtained. Here, the horizontal axis of the graph of FIG. 5 indicates the P ₂ O ₅ content (ppm) of the piezoelectric material, and the vertical axis indicates the average particle diameter (μm) of the piezoelectric particles.

From these measurement results (photograph of FIG. 4 and graph of FIG. 5), when P ₂ O ₅ having the same concentration is contained in the piezoelectric material, P ₂ O ₅ is directly added to the piezoelectric material (comparative example). In comparison with the piezoelectric material, when the P ₂ O ₅ is mixed from the TiO ₂ powder raw material and the ZrO ₂ powder raw material into the piezoelectric material (Example), the piezoelectric ceramic is composed of piezoelectric particles having a large average particle diameter. Recognize. That is, in the predetermined P ₂ O ₅ content range (40 ppm or more and 350 ppm or less), when compared at an arbitrary content, the average particle size according to the example is larger than the average particle size according to the comparative example. Thus, since an average particle diameter becomes large compared with a comparative example in an Example, the piezoelectric ceramic which concerns on an Example can implement | achieve higher sinterability.
(Second embodiment)

First, Steps S11 to S16 shown in FIG. 2 were performed to obtain a piezoelectric material raw material composition powder (starting raw material). This starting material contains TiO ₂ and ZrO ₂ containing P ₂ O ₅ and PbO, ZnO, and Nb ₂ O ₅ . A predetermined amount of P ₂ O ₅ reagent is added to this starting material. And these starting materials are Pb _0.94 Sr _0.05 [(Zn _1/3 Nb _2/3 ) _0.1 (Mg _1/3 Nb _2/3 ) _0.2 Ti _0.38 Zr after firing. _0.32 ] It was weighed and blended to obtain a piezoelectric ceramic having a composition containing 0.4 wt% of NiO in O ₃ .

  Next, as shown in step S17, after adding a polyvinyl alcohol binder to the powder of the raw material composition of the piezoelectric material and granulating, press molding shown in step S18 is performed at about 196 MPa, and one side is about 196 MPa. A square plate-like piezoelectric molded product having a size of 20 mm and a thickness of 1.5 mm was obtained.

  After that, as shown in step S19, the binder is removed from the piezoelectric body, and as shown in step S20, the piezoelectric body is put in a magnesia (MgO) sealed container and heated at 1100 ° C. for 2 hours. Went. Thereby, a square plate-shaped piezoelectric ceramic was obtained.

  Finally, the obtained piezoelectric ceramic is processed to a height of 1.0 mm, and further, a silver-baked electrode is formed on both sides thereof, and a single plate piezoelectric element (12 mm × 3 mm) similar to the piezoelectric element shown in FIG. Produced. Furthermore, this single plate piezoelectric element was subjected to polarization treatment (treatment conditions: 3 kV / mm, 15 minutes) in 120 ° C. silicone oil.

  The piezoelectric strain constant (d31) of the single-plate piezoelectric element obtained as described above was measured. As a measurement method, a piezoelectric strain constant was calculated from the capacitance, resonance frequency, and antiresonance frequency of the element measured using an impedance analyzer.

In this example, samples in which the total amount of P ₂ O ₅ contained in the piezoelectric material (P ₂ O ₅ total amount) was 35 ppm, 150 ppm, 250 ppm, 350 ppm, and 400 ppm were prepared, respectively, and the TiO ₂ raw material in the piezoelectric material was prepared. and the amount of _P 2 _{O 5} which is mixed from ZrO ₂ raw material _(P 2 _{O 5} mixed amount) 250 ppm, 150 ppm, as 35 ppm, an amount of a reagent of _P 2 _{O 5} the shortfall _(P 2 _{O 5} amount) I make up for it.

The piezoelectric strain constants measured by the above examples were as shown in Tables 2 to 4 below. _{Incidentally,} P 2 _{O 5} added amount (ppm) is a value relative to the piezoelectric ceramic 1 mole of converted from the starting compound.

The graph showing the measurement result, in FIG. 6 a graph showing the relationship between the P ₂ O ₅ amount and d31 characteristic in Examples 1-3 above, the relationship between the mixing ratio and d31 characteristic in Examples 1-3 above Is shown in FIG. Here, the horizontal axis of the graph of FIG. 6 indicates the total amount (ppm) of P ₂ O ₅ of the piezoelectric material, and the vertical axis indicates the d31 characteristic (pC / N). In addition, the horizontal axis of the graph of FIG. 7 indicates the addition ratio (%) of the added amount of P ₂ O ₅ , and the vertical axis indicates the d31 characteristic (pC / N).

Similarly to Examples 1 to 3 described above, Steps S11 to S16 shown in FIG. 2 were performed to obtain a powder of the raw material composition of the piezoelectric material. This starting material contains TiO ₂ and ZrO ₂ containing P ₂ O ₅ and PbO, ZnO, and Nb ₂ O ₅ , but unlike the above Examples 1 to 3, P ₂ O ₅ No reagent is added. Then, the starting material to which P ₂ O ₅ was added was calcined with Pb _0.94 Sr _0.05 [(Zn _1/3 Nb _2/3 ) _0.1 (Mg _1/3 Nb _2/3 ) _{0. 2} Ti _0.38 Zr _0.32 ] O ₃ was weighed and blended to obtain a piezoelectric ceramic having a composition containing 0.4 wt% of NiO.

  Next, as shown in step S17, after adding a polyvinyl alcohol binder to the powder of the raw material composition of the piezoelectric material and granulating, press molding shown in step S18 is performed at about 196 MPa, and one side is about 196 MPa. A square plate-like piezoelectric molded product having a size of 20 mm and a thickness of 1.5 mm was obtained.

  Thereafter, as shown in step S19, the binder is removed from the piezoelectric body, and as shown in step S20, the piezoelectric body is placed in a magnesia (MgO) sealed container and heated at 1150 ° C. for 2 hours. Went. Thereby, a square plate-shaped piezoelectric ceramic was obtained.

  Finally, the obtained piezoelectric ceramic is processed to a height of 1.0 mm, and further, a silver-baked electrode is formed on both sides thereof, and a single plate piezoelectric element (12 mm × 3 mm) similar to the piezoelectric element shown in FIG. Produced. Furthermore, this single plate piezoelectric element was subjected to polarization treatment (treatment conditions: 3 kV / mm, 15 minutes) in 120 ° C. silicone oil.

The piezoelectric strain constant of the single-plate piezoelectric element obtained as described above was measured in the same manner as in Examples 1 to 3. The measured piezoelectric strain constants were as shown in Table 5 below and FIG.

That is, when P ₂ O ₅ having the same concentration is contained in the piezoelectric material, P ₂ O ₅ is mixed in the piezoelectric material from a TiO ₂ powder raw material and a ZrO ₂ powder raw material in a predetermined content range (40 ppm to 350 ppm). Thus, the average particle size is increased, the sinterability of the piezoelectric ceramic is improved, and as can be seen from the measurement results (Tables 2 to 5 and the graph of FIG. 7), P ₂ added to the piezoelectric material as a subcomponent. By reducing the addition ratio of the O ₅ reagent to 30% or less, the piezoelectric strain constant became a practically sufficient value (200 pC / N or more).

Thereby, as compared with the case of increasing the content _of P ₂ O ₅ in the piezoelectric material by adding P ₂ O ₅ reagent, while maintaining the piezoelectric strain constant to or greater than a predetermined reference value, the more P ₂ O _{Since 5} can be contained in the piezoelectric material, further strain relaxation and stability of crystal grain growth can be achieved.

  The present invention is not limited to the above embodiment, and various modifications are possible. For example, a single plate piezoelectric element has been described as an example of a piezoelectric element, but the present invention can also be applied to a multilayer piezoelectric element as appropriate.

It is a perspective view which shows the piezoelectric element which concerns on the Example of this invention. It is a flowchart which shows the manufacturing method of the piezoelectric element shown in FIG. It is the graph which showed the measurement result which concerns on the Example of this invention. It is the microscope picture which showed the measurement result which concerns on the Example of this invention. It is the graph which showed the measurement result which concerns on the Example of this invention. It is the graph which showed the measurement result which concerns on the Example of this invention. It is the graph which showed the measurement result which concerns on the Example of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Piezoelectric element, 2 ... Piezoelectric layer, 3A, 3B ... Electrode layer.

Claims (2)

And a TiO ₂ material and ZrO ₂ raw material and Pb O raw material as a main component, and, by firing a piezoelectric material P ₂ O ₅ as a sub-component has been added, in the manufacturing method of the piezoelectric ceramic to produce a piezoelectric ceramic There,
In the piezoelectric material, P ₂ O ₅ contained in the TiO ₂ raw material and the ZrO ₂ raw material is mixed in a range of 40 ppm to 350 ppm,
A method for manufacturing a piezoelectric ceramic, wherein the proportion of P ₂ O ₅ added as the sub-component in the P ₂ O ₅ contained in the piezoelectric material is greater than 0% and 30% or less. Firing of the piezoelectric material includes main firing and pre-baking performed at a lower temperature than the main firing before the main firing, and P ₂ O ₅ added as the subcomponent is pre-baked. The method for manufacturing a piezoelectric ceramic according to claim 1, wherein the piezoelectric ceramic is added before.