JP2006036578A - Method of manufacturing piezoelectric material and piezoelectric material using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric material adaptable to a piezoelectric product such as a laminated piezoelectric actuator or a laminated piezoelectric transformer and having a composition in the vicinity of a morphotropic phase boundary between a tetragonal phase and a rhombohedral phase of a lead titanate zirconate-based piezoelectric material and a method of manufacturing the same. <P>SOLUTION: In the method of manufacturing the piezoelectric material having the composition in the vicinity of the morphotropic phase boundary, the piezoelectric material having excellent piezoelectric characteristics is obtained by analyzing a piezoelectric material using an X-ray diffraction-Rietveld analysis to identify a ceramic crystal phase after sintering as a mixed crystal of the tetragonal phase with the rhombohedral phase. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a piezoelectric material having a composition close to the morphotropic phase boundary (MPB) of a lead zirconate titanate (PZT) piezoelectric material that can be applied to piezoelectric products such as piezoelectric actuators and piezoelectric transformers, and a method for manufacturing the same.

  With the recent demand for miniaturization, thinning, and high performance, development of piezoelectric devices such as piezoelectric actuators and piezoelectric transformers has become active, and development of piezoelectric materials having compositions near the MPB phase boundary has been actively conducted. With respect to a PZT piezoelectric ceramic composition having a composition near the MPB phase boundary, a piezoelectric ceramic composition has been disclosed in order to provide a highly durable piezoelectric body with little displacement characteristics in repeated driving.

As prior art document information related to the invention of this application, for example, Patent Document 1 is known.
JP-A-9-71463

  In order to obtain high piezoelectric characteristics in lead zirconate titanate-based piezoelectric materials, the composition near MPB is often used, but the reason why the piezoelectric characteristics are good in the composition near the MPB phase boundary has not been elucidated. It had the problem of being difficult.

  The present invention relates to a method for producing a lead zirconate titanate piezoelectric material having a composition near the morphotropic phase boundary, by performing analysis using an X-ray diffraction-Riet belt analysis method, thereby producing tetragonal crystals and rhombohedral crystals ( The present invention provides a piezoelectric material having excellent piezoelectric characteristics by identifying a mixed crystal with Rhombohedral) and controlling the phase ratio.

  To achieve the above object, the present invention includes a first step of weighing and blending raw materials in a piezoelectric material using a composition near the morphotropic phase boundary of a lead zirconate titanate piezoelectric material. A second step of mixing the raw materials, a third step of calcining the mixed raw materials, a fourth step of crushing the calcined powder, and forming the pulverized powder into a desired shape A fifth step of performing, a sixth step of degreasing the molded body at a temperature that does not sinter the molded body, a seventh step of firing the degreased molded body, and identification of the sintered ceramic crystal phase From the eighth step, the ninth step of processing the fired sintered body, the tenth step of forming electrodes for input / output, and the eleventh step of performing polarization that gives piezoelectric properties to the piezoelectric ceramic In the eighth step, the X-ray diffraction-Riet belt analysis method is used. The crystalline phase by performing analysis Te is the manufacturing method of the piezoelectric material to identify the mixed crystal of tetragonal (Tetragonal) phase and rhombohedral (rhombohedral) phase.

  Thereby, since a mixed crystal of a tetragonal phase and a rhombohedral phase can be accurately identified, a piezoelectric material having excellent piezoelectric characteristics can be provided.

  As described above, the present invention provides a piezoelectric material having excellent piezoelectric characteristics by making the ceramic crystal phase after sintering a mixed crystal of a tetragonal phase and a rhombohedral phase. Therefore, by controlling the crystal phase ratio, it is possible to select a piezoelectric material having the desired characteristics. In addition, PZT-based compositions with excessive addition of lead exhibit its effects, and can achieve both low-temperature firing and excellent piezoelectric properties, and can achieve both energy saving and low melting point with low-melting internal electrode material. Adaptation to is possible.

(Embodiment 1)
The invention described in claims 1 to 11 of the present invention will be described using the embodiments of the present invention with reference to the drawings.

  FIG. 1 is a flowchart of a manufacturing process of a PZT piezoelectric material in the present embodiment.

First, using a powder of lead oxide (PbO), titanium oxide (TiO ₂ ), zirconium oxide (ZrO ₂ ), zinc oxide (ZnO), niobium oxide (Nb ₂ O ₅ ) as a starting material, moles of metal elements Each raw material is weighed and blended so that the ratio becomes the following composition (FIG. 1 (a)).

Pb _1.02 (Zn _1/3 Nb _2/3 ) _0.10 Zr _x Ti _0.90-x O ₃
The specific blending amounts are shown in Table 1.

  These blended raw materials are put into a pot mill together with partially stabilized zirconia balls as water and media, and the pot mill is rotated for 20 hours to perform wet mixing. At this time, the weight ratio of the raw material to water is set to 1: 1, and the diameter of the media zirconia ball is 5 mm or less (FIG. 1B).

  Next, the wet-mixed slurry was transferred to a stainless steel vat or the like and dried overnight in a dryer at 200 ° C. The dried powder is coarsely pulverized in a mortar or the like and then transferred to an alumina crucible and subjected to heat treatment at a maximum temperature of 850 ° C. for 2 hours (temperature raising / lowering rate is 200 ° C./hour) to obtain calcined powder (FIG. )).

  Thereafter, the obtained calcined powder was coarsely pulverized using a crusher such as a rotor mill or a disk mill, and then this coarsely pulverized powder was wet pulverized for 10 hours using a pot mill in the same manner as in the above mixing. Thereafter, the pulverized slurry is transferred to a stainless bat or the like and dried in a drier at 200 ° C. for a whole day and night to obtain a pulverized powder of piezoelectric material (FIG. 1 (d)).

  Here, a predetermined amount of the obtained piezoelectric material powder is blended together with an organic binder, a plasticizer, and an organic solvent, and then slurry mixing is performed to produce a sheet forming slurry, and then sheet forming is performed by a doctor blade method, A green sheet of a piezoelectric material having a predetermined thickness to be a piezoelectric layer is obtained (FIG. 1 (e)).

  Next, as shown in FIG. 2, the internal electrode patterns 2a and 2b are printed on the green sheet 1 of the piezoelectric material with an Ag internal electrode paste so that the thickness after drying becomes about 10 μm. A green sheet 1 of piezoelectric material on which no electrode paste is printed is laminated on top, pre-pressurized, and printed again. Lamination, temporary pressurization, and printing are repeated, and only the final green sheet 1 of piezoelectric material is laminated and prepressurized without printing the internal electrode paste, and finally a pressure of 18 MPa is applied as the main pressurization. Is cut out to a predetermined size to obtain a substantially flat laminate (FIG. 1 (f)).

  Thereafter, the organic component is removed by degreasing the laminated body at 500 ° C. (FIG. 1G).

Here, the steps of FIGS. 1E, 1F, and 1G show the case of forming a laminated piezoelectric material, and FIG. 1 shows the case of forming a single-layer block-shaped piezoelectric material. After the polyvinyl alcohol binder is added to and mixed with the pulverized powder obtained in the step (d), it is formed by press molding at a pressure of about 1000 kg / cm ² . The obtained molded body is placed on an alumina material sheath and degreased by heating at 500 ° C. for 2 hours in an electric furnace.

  After the degreasing step, the degreased piezoelectric body is put into an electric furnace and held at a firing temperature of 950 ° C. or lower for 2 hours, and a laminated piezoelectric sintered body is obtained after the main firing (FIG. 1 (h)).

  Next, the obtained piezoelectric sintered body was finely pulverized with an alumina mortar and pestle without applying extra force, and after performing powder X-ray diffraction measurement, the result was subjected to Rietveld analysis to obtain an X-ray profile. The phase ratio between the tetragonal phase and the rhombohedral phase in the ceramic crystal phase is evaluated with high accuracy (FIG. 1 (i)). Thereby, since the phase ratio can be evaluated with high accuracy, a piezoelectric material having excellent piezoelectric characteristics can be obtained with low error and high accuracy.

  Thereafter, a silver paste containing glass frit is printed at a position of a predetermined external electrode and dried. Thereafter, the external electrode is baked on the piezoelectric sintered body at about 700 ° C. for 10 minutes, and the external electrodes 3a and 3b are formed on the piezoelectric sintered body using silver (Ag) as the internal electrode as shown in FIG. It forms (FIG.1 (j)).

  Next, an electric field of 3 kV / mm is applied for 30 minutes between the internal electrodes 2a and 2b in 100 ° C. silicone oil, and polarization treatment is performed, so that a laminated piezoelectric body having Ag as an internal electrode as shown in FIG. Get 4. The laminated piezoelectric body 4 after the polarization treatment is left at room temperature for 24 hours or longer (FIG. 1 (k)).

  Subsequently, with respect to the laminated piezoelectric body 4 obtained as described above, a coupling coefficient k31 which is a piezoelectric characteristic is measured using an impedance analyzer or the like (FIG. 1 (l)).

  Here, the characteristic evaluation result of the coupling coefficient k31 of the laminated piezoelectric material measured in FIG. 1 (l) and the tetragonal (Tetragonal) phase and rhomboid in the crystal phase of the piezoelectric sintered body evaluated in FIG. 1 (i). FIG. 4 shows the relationship with the phase ratio with the rhombohedral phase.

  From the result of FIG. 4, when the phase ratio of the rhombohedral phase is in the range of 0.5 to 25% of the entire crystal phase, the coupling coefficient k31, which is a piezoelectric property, satisfies the target value of 0.30 or more. As a result, it was found that the laminated piezoelectric material had excellent piezoelectric characteristics in this range. Similarly, in the case of a single-layer block-shaped piezoelectric body, the result that the piezoelectric characteristics were excellent in the range of 0.5 to 25% was obtained.

  In the present embodiment, the calcined powder obtained after the step of FIG. 1C is analyzed using an X-ray diffraction-Riet belt analysis method, and a tetragonal (Tetragonal) phase and rhombohedral ( By identifying the mixed crystal with the Rhombohedral phase, the phase ratio of the tetragonal crystal and rhombohedral crystal in the ceramic crystal phase can be controlled with high accuracy, and a piezoelectric material with higher characteristics can be obtained. .

In the present embodiment, as an example of the piezoelectric material,
Pb _1.02 (Zn _1/3 Nb _2/3 ) _0.10 Zr _x Ti _0.90-x O ₃
However, the same effect can be obtained by changing the blending amount of Pb (Zn _1/3 Nb _2/3 ) O ₃ , and Pb (Mg The same effect can be obtained by using _1/3 Nb _2/3 ) O ₃ , Pb (Ni _1/3 Nb _2/3 ) O ₃ , Pb (Sn _1/3 Nb _2/3 ) O ₃ .

In addition, when the composition of the piezoelectric material is expressed by Pb _A X _B O ₃ , A / B> 1.00, that is, if the composition is excessively added with lead, low temperature firing at 950 ° C. or less is possible, The effect is that heat energy consumption during firing can be suppressed, and that it can be applied to a laminated part with a low melting point and an inexpensive internal electrode material.

In Pb _A X _B O ₃ , the effect of this embodiment can be obtained in any case as long as X is a PZT system containing Ti and Zr.

  In the present invention, the laminated piezoelectric material having Ag as an internal electrode has been described as an example. However, the same effect can be obtained when not only Ag but also another metal material is used as the internal electrode and fired at a low temperature. In addition, the same effect can be obtained when used as a single-layer block-shaped piezoelectric ceramic sintered body.

  A method for manufacturing piezoelectric materials with a composition near MPB of tetragonal and rhombohedral phases of lead zirconate titanate-based piezoelectric materials applicable to piezoelectric products such as multilayer piezoelectric actuators and multilayer piezoelectric transformers Useful for.

Manufacturing flow chart of laminated piezoelectric material according to an embodiment of the present invention FIG. 1 is an internal structural diagram of a laminated piezoelectric material according to an embodiment of the present invention. The perspective view of the laminated piezoelectric material in the embodiment of the present invention Correlation diagram between phase ratio of rhombohedral phase and coupling coefficient k31 in the embodiment of the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Green sheet of piezoelectric material 2a 1st internal electrode layer 2b 2nd internal electrode layer 3a 1st external electrode 3b 2nd external electrode 4 Laminated piezoelectric material

Claims (11)

In a piezoelectric material using a morphotropic phase boundary vicinity composition of a lead zirconate titanate piezoelectric material, a first step of weighing and blending raw materials and a second step of mixing the blended raw materials are mixed A third step of calcining the raw material, a fourth step of crushing the calcined powder, a fifth step of molding the pulverized powder into a desired shape, and sintering the compact A sixth step of degreasing at a temperature that does not, a seventh step of firing the degreased compact, an eighth step of identifying the ceramic crystal phase after sintering, and the fired sintered body A ninth step of forming an input / output electrode, and an eleventh step of performing polarization that gives piezoelectric characteristics to the piezoelectric ceramic. In the eighth step, X-ray diffraction is performed. -By performing analysis using Rietveld analysis method, Method of manufacturing a piezoelectric material to identify the mixed crystal of tetragonal (Tetragonal) phase and rhombohedral (rhombohedral) phase. The piezoelectric according to claim 1, wherein the rhombohedral phase ratio of the sintered ceramic crystal phase identified by the X-ray diffraction-Riet belt analysis method in the eighth step is 0.5% to 25.0%. Material manufacturing method. By analyzing the crystal phase of the calcined powder obtained in the third step using an X-ray diffraction-Riet belt analysis method, a mixed crystal of a tetragonal phase and a rhombohedral phase is obtained. The method for producing a piezoelectric material according to claim 1, wherein: The composition of lead titanate zirconate piezoelectric material, Pb _A X _B when O ₃ and represents, manufacturing method of a piezoelectric material according to claim 1, formed so as to satisfy the mixing ratio A / B> 1.00 . In a piezoelectric material using a morphotropic phase boundary vicinity composition of a lead zirconate titanate piezoelectric material, a first step of weighing and blending raw materials and a second step of mixing the blended raw materials are mixed A third step of calcining the raw material, a fourth step of crushing the calcined powder, a fifth step of forming a ceramic green sheet from the pulverized powder, the ceramic green sheet and the interior A sixth step of forming a laminate using the electrode paste, a seventh step of degreasing the laminate at a temperature that does not sinter, an eighth step of firing the degreased laminate, The ninth step of identifying the ceramic crystal phase after the sintering, the tenth step of processing the sintered body, and the eleventh step of forming the input / output electrodes. In the process, X-ray diffraction-Rietveld By performing analysis using the precipitation method of the piezoelectric material in which the crystalline phase to identify mixed crystal of tetragonal (Tetragonal) phase and rhombohedral (rhombohedral) phase. The piezoelectric material according to claim 5, wherein a rhombohedral phase ratio of the sintered ceramic crystal phase identified by X-ray diffraction-Riet belt analysis in the ninth step is 0.5% to 25.0%. Manufacturing method. By analyzing the crystal phase of the calcined powder obtained in the third step using an X-ray diffraction-Riet belt analysis method, a mixed crystal of a tetragonal phase and a rhombohedral phase is obtained. The method for producing a piezoelectric material according to claim 5, wherein: The composition of lead titanate zirconate piezoelectric material, Pb _A X _B when O ₃ and represents, manufacturing method of a piezoelectric material according to claim 5 formed so as to satisfy the mixing ratio A / B> 1.00 . When the composition of the lead zirconate titanate piezoelectric material using the composition near the morphotropic phase boundary is expressed as Pb _A X _B O ₃ , the composition ratio is A / B> 1.00, and after sintering A piezoelectric material in which the ceramic crystal phase is a mixed crystal of a tetragonal phase and a rhombohedral phase. The piezoelectric material according to claim 9, wherein the rhombohedral phase ratio in the ceramic mixed crystal after sintering is 0.5% to 25.0%. The piezoelectric material according to claim 9, wherein the mixed powder is calcined, and the crystal phase of the calcined mixed powder is a mixed crystal of a tetragonal phase and a rhombohedral phase. .

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