JP2006032468A - Method of manufacturing oxide piezoelectric material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing an oxide piezoelectric material composed of a tungsten bronze structure of a low sintering temperature and no characteristic dispersion by a simple process. <P>SOLUTION: To a solution in which alkoxide of niobium and the nitrate of the other components are dissolved, amino acid of a mol number which is 1.5 to 3 times of the total mol number of the alkoxide and nitric acid is added. Atomization is performed while forming the complex of metal ions and the amino acid in the solution, a solvent is removed, the amino acid complex is made to burn itself, and the powder of the tungsten bronze structure compound containing niobium is obtained. Since the grain diameter of the powder is extremely fine and composition is uniform, low temperature sintering is possible and a sintered compact expresses excellent piezoelectric characteristics with less dispersion. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing a tungsten bronze type oxide piezoelectric material used in piezoelectric ceramic products.

Conventionally, as a piezoelectric ceramic material, lead zirconate titanate-based (PbTiO ₃ —PbZrO ₃ , hereinafter referred to as PZT) ceramics can be used in various applications such as sensors, actuators, filters, etc. because large piezoelectricity is obtained. Has been used.

  However, the PZT material is mainly composed of lead, which has a very large burden on the environment, and it accounts for 60% by weight or more in the whole. Lead oxide is reduced relatively easily to produce lead. Lead is highly volatile even at low temperatures, and it is inevitable that it will leak into the atmosphere during pre-baking and sintering during manufacturing. It was necessary to take measures to prevent diffusion to the surrounding area.

  In addition, if PZT is discarded without taking any countermeasures, lead will be eluted. Therefore, a huge amount of capital investment is required for measures to prevent environmental pollution, that is, waste disposal. There is a need for materials that exhibit properties.

For this reason, many lead-free piezoelectric materials have been searched. As one of them, a tungsten bronze structure compound has been studied for practical use. Tungsten bronze structure, the general formula is represented by A _x B _y O _z. Here, A is an alkali element or alkaline earth element, and B is a trivalent to pentavalent element typified by Mo, Nb, Ti or the like.

As an example of such a material, in Patent Document 1, the general formula is represented by (A1) ₂ (A2) B ₅ O ₁₅ , A1 is at least one selected from Sr, Ba, and Ca, A2 is Na, Tungsten in which at least one of Bi _1/3 , B is at least one selected from Nb, Ta, and V, and a part of B is substituted with an element selected from Mn, Cr, Fe, Co, Ti, and Zr Bronze structural compounds are disclosed.

  On the other hand, the demand for high performance, miniaturization, and cost reduction of electronic parts themselves is increasing day by day. Looking at the raw materials, the conventional manufacturing methods can no longer meet the above requirements. It is reaching the limit. For example, in the manufacturing process of a piezoelectric actuator, in order to realize downsizing, there is a method of laminating green sheets obtained by forming a paste film in which raw material powder is dispersed in a solution composed of a binder and a solvent. Has been done.

  In the case of such a multilayer piezoelectric actuator, the internal electrode is formed on the green sheet surface by printing using a paste in which conductive powder is dispersed, and then laminated and sintered. It is necessary to select one having a melting point higher than the setting temperature. In the case where the piezoelectric material and the electrode are simultaneously sintered, Ag—Pd is generally used as the electrode.

  Although Pd has a high melting point of 1552 ° C., it is expensive. Therefore, it is advantageous in terms of cost to use a conductor having a high Ag ratio. However, since the melting point of Ag is 961 ° C., there is a limit to increasing the Ag ratio. Therefore, if the sintering temperature of the piezoelectric material can be lowered, an inexpensive conductor having a large Ag ratio can be used as the electrode.

  As is well known, in sintering metals and ceramics, the sintering temperature can be lowered by reducing the particle size of the raw material powder. In the case of a compound having a tungsten bronze structure, the general production method is the same as that of known ceramics.

  In other words, a so-called hot forging method, in which a powder of a tungsten bronze structure compound obtained by mixing a constituent element oxide powder or carbonate powder with a ball mill or the like and then pre-baking and pulverizing processes is heated and heated. Thus, the sintered body of the target tungsten bronze structure compound is obtained by making a green compact by pressing and preparing a green compact and sintering it. The sintering temperature in this case is usually 1300-1400 ° C.

  In the conventional manufacturing method, in order to lower the sintering temperature, it is necessary to obtain a fine powder by the above-mentioned pulverization step. However, since the particle size of the pre-baked powder obtained by this method is as large as several μm, it is necessary to prepare a fine powder by taking a long time for pulverization. Such a conventional method requires a long period of pulverization, resulting in an increase in cost, and further has a disadvantage that the mixing of foreign substances derived from the pulverization medium increases and the composition ratio is shifted.

Further, regarding the piezoelectric characteristics and the crystal grain size of the sintered body, the dielectric constant εr and the piezoelectric constants d ₃₃ and K _{33 at} room temperature are almost constant regardless of the crystal grain size. It is known that the quality factor Qm tends to increase. Piezoelectric materials are polarized during the manufacturing process, but the larger the crystal grain size, the greater the stress generated by the movement of the particles. The internal stress is greatly related to the mechanical quality factor. In the piezoelectric body after polarization, the smaller the crystal grain size, the smaller the internal stress, and thus a higher Qm value can be obtained.

  The crystal grain size of the sintered body is related to the grain size of the raw material powder. To refine the crystal, it is considered necessary to perform low-temperature sintering using a raw material powder with a small grain size. However, as described above, in the conventional method, there is a limit to the refinement of the raw material powder.

  Further, in the conventional manufacturing method, since the tungsten bronze structure is formed by a solid phase reaction, mixing of raw materials and pre-baking are indispensable steps. That is, a compound having a uniform tungsten bronze structure cannot be obtained unless the raw materials are sufficiently mixed and prefired.

  Therefore, the raw material is first mixed for a long time, pre-fired at a temperature of around 1050 to 1150 ° C., and the oxide is completely made into a tungsten bronze structure compound and then sintered, and then a two-step high temperature treatment process There was a drawback of having to go through. Moreover, it is impossible to manufacture a material having a completely uniform composition even through such a manufacturing process, and since it always includes a composition variation, it causes a variation in characteristics.

JP 2004-75448 A

  Accordingly, an object of the present invention is to provide a method for producing an oxide piezoelectric material comprising a tungsten bronze structure compound having a low sintering temperature and no characteristic variation in a simple process.

  As a result of various studies to solve the above-mentioned problems, the present inventor found niobium alkoxide and other elements constituting the tungsten bronze structure compound in the process of producing the powder of the tungsten bronze structure compound containing niobium. It has been found that by using a powder obtained by heating a solution containing a nitrate and an amino acid as a raw material, it can be sintered at a temperature much lower than that of the conventional production method, and the present invention has been made.

  That is, the present invention relates to a method for producing an oxide piezoelectric material having a tungsten bronze structure compound containing niobium, in which a niobium alkoxide, nitrates of other elements constituting the tungsten bronze structure compound, and amino acids are dissolved in a solvent. A step of heating the solution to remove the solvent and producing a tungsten bronze structure compound powder, a step of subjecting the powder to particle orientation, and a step of molding and pressing the powder subjected to the grain orientation. A method for producing an oxide piezoelectric material comprising a step of producing a powder and a step of sintering the green compact.

  In addition, the present invention provides the method for producing the oxide piezoelectric material, wherein a ratio of the number of moles of the amino acid to the number of moles of the nitrate is 1.5 or more and 3 or less.

  Further, the present invention provides the method for producing the oxide piezoelectric material, wherein the step of producing the powder includes a step of spraying and heating the solution.

  It is known that fine metal oxide particles can be obtained by hydrolysis of metal alkoxides. On the other hand, if the solvent is removed by heating the metal amino acid complex solution, the residue self-combusts. It is known. In addition, since this combustion is completed in a very short time, very fine oxide particles are generated.

  That is, when a mixed solution of niobium alkoxide and an amino acid complex of an element constituting the tungsten bronze structure compound is heated and the solvent is removed, an extremely fine tungsten bronze compound powder can be obtained. When the tungsten bronze structure compound powder produced by such a method is used, sintering at a low temperature is possible, so that the crystal grain size of the sintered body is reduced and high Qm can be achieved.

  Furthermore, as an extremely excellent feature resulting from such a production method, since powder production starts from a solution state, not only the mixing of each component is easy, but also a homogeneous reaction, For example, it is difficult to obtain a uniform compound powder with a very small compositional deviation, which is difficult with a conventional production method using a solid phase reaction.

  In the present invention, in order to obtain an amino acid complex, nitrates of elements constituting the tungsten bronze structure compound and amino acids are mixed in a solution. The ratio of the number of moles of amino acids to the number of moles of nitrates is as follows. The reason why it is 5 or more and 3 or less is that a fine and uniform tungsten bronze structure compound powder can be obtained only in this range.

  That is, when this ratio is 1.5 or less, self-combustion does not occur even when the solvent of the solution is removed, and when the reaction is performed in a range where this ratio exceeds 3, the obtained tungsten bronze structure This is because the particle size of the compound powder becomes large.

In order to further improve the characteristics of the tungsten bronze structure compound, Y ₂ O ₃ , La ₂ O ₃ , Dy ₂ O ₃ , Nd ₂ O ₃ , Yb ₂ O ₃ , Sm ₂ O ₃ , Er ₂ O _{3 are used.} , Gd ₂ O ₃ , CaO and the like are known to be useful. Even in the case of using these, when preparing a solution of the complex of the main component element and the amino acid, the nitrate of each additive element is mixed and dissolved in the above solution, so that the distribution of the main component element and the additional element is increased. Uniform tungsten bronze structure compound powder can be obtained, and characteristics can be improved more effectively.

  Further, according to the present invention, when self-combustion is caused, the temperature should be raised to a temperature at which the solvent can be removed. Therefore, even in a furnace set at a relatively low temperature, a solution containing an amino acid complex If fine droplets are formed by spraying, it is possible to quickly evaporate the solvent and obtain a tungsten bronze structure compound powder.

  The present invention is characterized in that an amino acid complex of a constituent element is used to form a tungsten bronze structure, and that a temperature rise is necessary when spraying a solution containing the amino acid complex, and a known production apparatus Can be used.

  Examples of amino acids that can be used in the present invention include glycine, alanine, proline, arginine, threonine, and the like, but any amino acid that forms a complex with a metal ion contained in nitrates is not limited thereto. .

  In the present invention, there are various types of solvents for dissolving nitrates and amino acid complexes, including organic solvents, but water is preferable in consideration of cost and ease of handling in drying by spraying.

Next, the present invention will be described with specific examples. High-purity Sr (NO ₃ ) ₂ , NaNO ₃ , Nb (OC ₂ H ₅ ) ₅ are weighed so as to be Sr ₂ NaNb ₅ O ₁₅ in an oxide equivalent composition and the total amount is 100 g. Dissolved in and mixed well. Further, twice the number of moles of glycine relative to the total number of moles of the alkoxide and nitrate was weighed and added to this solution, and sufficiently stirred and mixed to dissolve.

This solution was then sprayed into a furnace maintained at 400 ° C. The water content of the sprayed droplets instantly evaporated in the furnace, and at the same time, the residue self-combusted and a powdery product was obtained. When this powder was evaluated by X-ray diffraction, it was confirmed that the powder had the same structure as the Sr ₂ NaNb ₅ O ₁₅ powder produced by the conventional production method.

Further, when the particle size of the powder was measured by a laser diffraction type particle size distribution measuring device, the D ₅₀ value was 0.10 μm, and the particle size distribution was very sharp compared to the case of the conventional production method. The obtained powder was shaped after the particles were oriented by a hot forging method. Subsequently, the compact was sintered at 1000 ° C., 1100 ° C., 1200 ° C., 1300 ° C., and 1400 ° C. for 4 hours, respectively, to obtain an oxide piezoelectric material composed of the tungsten bronze structure compound of Example 1.

High-purity Ba (NO ₃ ) ₂ , NaNO ₃ , Nb (OC ₂ H ₅ ) ₅ was weighed so that it would be Ba ₂ NaNb ₅ O _{15 in} terms of oxide composition and the total amount would be 100 g. And mixed well. In addition, 2.5 times the number of moles of alanine was weighed out relative to the total number of moles of the alkoxide and nitrate, and added to this solution. Using this solution, a raw material powder was obtained in the same manner as in Example 1.

When this powder was evaluated by X-ray diffraction, it was confirmed that the powder had the same structure as the Ba ₂ NaNb ₅ O ₁₅ powder produced by the conventional production method. Further, when the particle size of the powder was measured with a laser diffraction particle size distribution measuring device, the D ₅₀ value was 0.12 μm, and as in Example 1, the particle size distribution was much sharper than in the case of the conventional production method. there were. This powder was sintered in the same manner as in Example 1 to obtain an oxide piezoelectric material composed of the tungsten bronze structure compound of Example 2.

Comparative example

Next, for comparison, an oxide piezoelectric material made of a tungsten bronze structure compound was prepared by a known manufacturing method. Here, high-purity Sr (CO ₃ ) ₂ , Na ₂ CO ₃ , and Nb ₂ O ₅ are used as raw materials, and each component is weighed so as to have the same composition as that of Example 1, and is ball-milled for 45 hours. After mixing, pre-baking was performed at 1100 ° C.

  Subsequently, the pre-fired powder was pulverized with a ball mill for 20 hours and 100 hours, and the particle size of the powder was measured to be 1.0 μm and 0.5 μm, respectively. Using these two raw material powders, oxide piezoelectric materials comprising the tungsten bronze structure compounds of Comparative Examples 1 and 2 were obtained in the same manner as in Example 1. Here, a powder having a powder particle diameter of 0.5 μm is referred to as Comparative Example 1, and a powder having a powder particle diameter of 1.0 μm is referred to as Comparative Example 2.

Next, with respect to Example 1, Example 2, Comparative Example 1, and Comparative Example 2, the sintered body density, the crystal grain size of the sintered body, the relative dielectric constant εr, the piezoelectric constants d ₃₃ and K ₃₃ , and the Curie temperature Tc are set. It was measured. FIG. 1 is a diagram collectively showing the relationship between the sintering temperature and the sintered body density in Example 1, Comparative Example 1, and Comparative Example 2. Table 1 also shows the crystal grain size and piezoelectricity of the sintered bodies with the sintering temperature of 1100 ° C. in Examples 1 and 2 and the sintered bodies with the sintering temperature of 1400 ° C. in Comparative Examples 1 and 2. The characteristics are summarized.

  As is apparent from FIG. 1, in Example 1, the sintered body density has almost reached the saturation state even at the sintering temperature of 1100 ° C., and the effect of refining the raw material powder is remarkable. On the other hand, in Comparative Example 1 and Comparative Example 2, it can be seen that a high temperature of 1400 ° C. is required to reach the sintered body density at 1100 ° C. of Example 1.

Further, according to Table 1, although the grain size and Tc is not seen a marked difference between the Examples and Comparative Examples, the d ₃₃ and K _33, apparent difference is observed, the raw material powder fine As a result, the crystal grain size of the sintered body is reduced, compositional deviation in the sintered body is eliminated to a considerable degree, and it can be estimated that this contributes to improvement of the piezoelectric characteristics.

The figure which showed collectively the relationship between sintering temperature and a sintered compact density.

Claims (3)

  In the method for producing an oxide piezoelectric material having a tungsten bronze structure compound containing niobium, a step of preparing a solution by dissolving niobium alkoxide, nitrates and amino acids of other elements constituting the tungsten bronze structure compound in a solvent; A step of heating the solution to remove the solvent and producing a tungsten bronze structure compound powder, a step of subjecting the powder to particle orientation, and a step of molding the powder subjected to the grain orientation to produce a green compact And a method for producing the oxide piezoelectric material, comprising the step of sintering the green compact.   2. The method of manufacturing an oxide piezoelectric material according to claim 1, wherein the ratio of the number of moles of the amino acid to the number of moles of the nitrate is 1.5 or more and 3 or less.   The method for producing an oxide piezoelectric material according to claim 1 or 2, wherein the step of producing the powder includes a step of spraying and heating the solution.

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