JPH02271955A - Synthesizing method for piezoelectric and dielectric ceramics powder - Google Patents

Abstract

PURPOSE:To easily select and utilize arbitrary A site element and B site element by mixing three substances consisting of individually prepared hydroxides of group Va elements, oxalates of A and B site elements and thereafter roasting this mixture in the synthesis of composite perovskite which has an ABO3 type structure and incorporates group Va elements. CONSTITUTION:The four stages described hereunder are utilized: (1) An oxalic acid aq. soln. of group Va elements being B site element is mixed with alcohol. pH is regulated to >=3 and ppt. of hydroxide of group Va elements is produced. This ppt. is filtered, washed and dried. (2) Oxalic acid is added to alcohol and thereafter this mixed soln. is mixed with a soln. contg. one kind of the ions of Ca, Sr, Ba and rare earth elements (A site element). The ppt. of oxalate is produced and thereafter filtered, washed and dried. (3) Oxalic acid is added to alcohol and thereafter this mixed soln. is mixed with a soln. contg. one kind of the ions of Mg, Cr, Mn and Zr (B site element). Hereinafter the same stage as (2) is performed. (4) Three kinds of dried powder obtained by 1-3 stages are mixed in accordance with the aimed composition and this mixed power is roasted.

Description

Detailed Description of the Invention: Industrial Field of Application This invention relates to easily sinterable piezoelectric and dielectric powders containing elements of Group Va of the periodic table (hereinafter referred to as Group Va elements) in the crystal structure or added as an auxiliary agent. Concerning a method of synthesizing.

Perovskite oxides containing Va group elements such as Nb and Ta, or solid solutions of two or more of these compounds, are widely used in electronic components as dielectric materials and piezoelectric/electrostrictive materials.

Conventional technology The method for synthesizing composite perovskite piezoelectric and dielectric ceramic powders containing Group Va elements is as follows (1).
, There was a method like (2).

(1) A method of synthesis by mixing and calcining compounds containing the constituent elements of perovskite, such as oxides and carbonates.

As an example of this, in the case of Pb(MgL/3Nb2/3)03, which is well known as a ferroelectric material, PbO, Mg
If O, Nb, and 05 are simply mixed and calcined, in addition to the desired perovskite phase, a pyrochlore phase that significantly impairs the material properties will be generated.
5 was mixed and calcined to synthesize a compound called MgNb2O6, to which pbo was added and calcined again to form Pb (MgL/3N
b2/3)03 perovskite phase has been obtained (S.

L, 5vartz et al, Mat, Res
, Bull, 17 (1982).

+245), but because the calcination temperature had to be high, it was difficult to synthesize a powder with a submicron average particle size and a sharp particle size distribution, and the sinterability was poor.

(2) A method of synthesizing perovskite by forming a precipitate from a solution containing ions of its constituent elements, and drying and calcining the precipitate.

In this case, the following methods were used to generate the precipitate.

(2-A) Alkoxide method in which alkoxides of constituent element ions are hydrolyzed and coprecipitated; (2-8) Method in which p)l of an aqueous solution is increased to a certain value or more to cause coprecipitation as hydroxide; (2 -C:) A method of adding an alcoholic solution of oxalic acid to an aqueous solution and co-precipitating it as oxalate.

The features of these methods are briefly listed below.

The alkoxide method (2-A) yields highly pure and highly homogeneous products, but the manufacturing method is complicated because each component ion must be synthesized once as an alkoxide, and it is economical because expensive alkoxides are used. It is also disadvantageous.

In the hydroxide coprecipitation method (2-8), there are elements that do not precipitate completely even at very high pH, including alkaline earth metals such as Mg, Sr, and Ba. It is difficult to coprecipitate more than one type of element.

The oxalic acid alcohol method (2-C) takes advantage of the fact that metal oxalate salts are almost insoluble in alcohol, so it is relatively easy to make a precipitate with the desired composition ratio, and the solvent Since this is alcohol, particle aggregation is prevented and particles with good dispersibility can be obtained (Japanese Patent Publication No. 82-8
However, a major drawback of 4) is that the important Va group salts in piezoelectric and dielectric materials are soluble in alcohol and cannot be applied to substances containing Va groups.

The precipitation method allows the synthesis of the desired compound at a relatively low calcination temperature, and can synthesize a powder with a uniform composition, submicron average particle size, and sharp particle size distribution, but it is impossible to synthesize each of them. Va
It has been difficult to synthesize piezoelectric, electrostrictive, and dielectric ceramics containing group elements, such as perovskite-type oxides with high practical utility, such as Pb(MgL/3Nb2/3)03.

Therefore, the present inventors developed a piezoelectric material containing Va group elements.

Invented a method for synthesizing electrostrictive dielectric ceramics by combining the oxalic acid ethanol method with hydroxide coprecipitation and filed an application (Japanese Patent Application Laid-Open No. 155348/1982).
.

For example, in the case of PMN, this method involves mixing alcohol with an oxalic acid solution of Nb, which is a member of the Va group, and then adding Pb, Hg
Aqueous solutions of nitrates are mixed and precipitated as oxalate. Thereafter, by adjusting the pH of the 5 solution to 3 or more, P is precipitated as a hydroxide, stirred and mixed in the solution, and filtered, washed, dried and calcined the precipitate.
This is a method for creating b(Mg, 3Nb2/3)03.

Compared to the conventional oxide mixing method, this method requires only one calcination instead of the 2 calcinations in the oxide mixing method, and the calcination temperature can be lowered by about 200°C, resulting in uniform and fine particles. On the one hand, it has the advantage of being able to obtain a fine powder, but whenever the composition of the ceramic to be synthesized changes, it is necessary to determine the optimum pH during synthesis so that almost no ions of the constituent elements of the perovskite remain in the filtrate after precipitation. there were.

Problems to be Solved by the Invention The present invention relates to a method for producing perovskite, which is suitable as a piezoelectric and dielectric material, and solves the problem that there are elements that do not precipitate even at high pH in the hydroxide coprecipitation method, which was a problem with the conventional precipitation method. Restrictions on the elements that can be applied to the precipitation method arise, and restrictions on the elements that can be applied to the precipitation method arise from the fact that Va group oxalates are partially soluble in alcohol in the oxalic acid alcohol method. Solve the problem and make any A
The present invention provides a manufacturing method that allows site elements and B-site elements to be easily obtained as constituent elements.

Means for Solving the Problems The present invention provides C which is an A-site element of a composite perovskite.
a, Sr, Ba, Bi, Pb or rare earth elements, Va group elements which are B site elements, and Ng, Cr
, Kn, Fe, Co, Nt, Cu, Zn,
Each component such as Ti, Zr, He, etc. is synthesized singly as a hydroxide containing one type of Va group element or an oxalate containing one type of A-site and B-site element, and the desired one of these is synthesized. The method is characterized in that powders of a predetermined hydroxide and an acid salt containing the elements necessary for perovskite synthesis are mixed and then calcined to form a perovskite-type composite oxide. The present invention will be explained in detail below.

An oxalic acid solution containing one type of Va group element (solution I) and A
Site elements Ga, Sr, Ha, Bi, P
b or rare earth element, B site element Mg, C
r, Mn, Fe, Co, Ni, Cu, Zn,
A solution containing one type of Ti, Zr, Hfc7) ions (
Prepare solution ■) and alcohol. As solution II,
For example, aqueous solutions of nitrates, oxynitrates, chlorides, etc. are used.

The hydroxide of a group Va element is prepared by adding a solution dropwise while stirring the alcohol, and then adding a solution of aqueous ammonia and ethanol dropwise at the same speed, so that p)I is 3 or more and 12 or less, preferably 5. Above 9 or less, it is precipitated as a hydroxide.

For oxalate containing one type of other element, after adding oxalic acid to alcohol, add solution (■) dropwise while stirring, then drop a solution of aqueous ammonia and ethanol at the same rate to adjust the pH. 3 or more and 12 or less, preferably 5 or more and 9
As shown below, the rate of one drop to precipitate oxalate is preferably 1 to 100 liters per minute.

Each precipitate obtained in the above manner was filtered, washed with ethanol three times, and finally filtered again.
After drying at 20° C. for 12 hours, a white powder of each single salt is obtained.

After mixing these powders in a predetermined ratio, the mixture is heated to 700-800°C.
The mixture is calcined for 10 minutes to 48 hours to obtain the desired perovskite fine powder.

Function The method of this invention combines the oxalic acid ethanol method with the hydroxide coprecipitation method (Japanese Patent Application No. 82-155).
It is possible to more easily synthesize piezoelectric and dielectric ceramic powders having the same properties as the powder synthesized using the method (No. 348). Namely.

It has the following effects.

(1) Method applying the oxalic acid ethanol method (patent application 1988)
No. 2-155348), hydroxides of Va group elements and oxalates of other elements are precipitated simultaneously, and 11!
It was necessary to optimize the synthesis conditions such that almost no perovskite constituent element ions remain in the solution, for example, the conditions such as p)1 of the solution.1 However, since the present invention is a method of mixing single elements, the objective The composition is easy to realize.

(2) Ammonia added to the floss reacts with excess oxalic acid and forms acicular ammonium oxalate between grains, which improves filtration during washing.
In addition, the grains are prevented from clumping together and abnormally growing during heat treatment, and as a result, a fine powder with a small particle size and uniform size can be obtained.

(3) If a large amount of each individual salt is synthesized in advance, the process of synthesizing piezoelectric and dielectric ceramics is very simple, as it only requires mixing and calcination using the usual method.

Example 1 Lead-based composite perovskite Pb(Mgl, 3Nb2
/3) 03-PbTi03 (hereinafter referred to as PMN-FT,
) will be described. Here, the amount of PbTiO3 added is mo1%, which is 1 to 50% of the total. The synthesis of oxalates of Pb, Mg, and Ti, which are constituent elements of perovskite, and hydroxide of Wb will be described below.

For Nb, which is a member of the Va group, niobium hydroxide is synthesized by adding aqueous ammonia to niobium pentachloride, which is filtered and washed, and then dissolved in hot oxalic acid to create a niobium oxalic acid aqueous solution (solution X). Aqueous ammonia is added to titanium tetrachloride to synthesize titanium hydroxide, which is filtered and washed, then dissolved in nitric acid to create a titanyl nitrate solution. Pb and Mg are prepared as an aqueous solution of nitrate and salt, and each of these is 1 solution
00-, and call it solution Y.

To prepare a single salt of Nb, add 100 mm of solution X dropwise to 800 mm of ethanol while stirring vigorously. The dropping rate at this time was 20+ai/win in both cases.Next, a solution of aqueous ammonia and ethanol mixed in a ratio of 1=4 was dropped at the same rate, and the pH was adjusted to 8 to form a hydroxide precipitate. .

Individual salts of Pb, Mg, and Ti were prepared using ethanol 800-
After adding sulfur and stirring, solution Y was added dropwise at the same speed as above, and then aqueous ammonia and ethanol were mixed at 1:4.
was added dropwise at the same rate to bring the pH to 8 and form an oxalate precipitate.

Each precipitate obtained in the above manner was filtered, washed with ethanol three times, and finally filtered again.
The mixture was dried at 20° C. for 12 hours to obtain a white powder of each single salt.

The composition of the obtained powders was analyzed and each powder was quantified.

After mixing this powder in a predetermined ratio, it was heat-treated at 800°C for 2 hours to form Pb(MgL/3Nb2/3)03-, Pb
It was made into fine powder of TiO3.

On the other hand, apart from this, there is a method previously applied (Japanese Patent Application No. 155-1982)
PMN-FT was synthesized using the following method (No. 348). and,
The pyrochlore phase ratios of these two types of calcined powders were compared.

The results are shown in Table 1. Here, the amount of pyrochlore is calculated from the main peak value of X-ray diffraction by the ratio of pyrochlore phase to perovskite phase, 1pyro/(1pero+1
pyro) However, i pero: intensity of the main peak of the perovskite phase 1
pyro: Expressed as the intensity of the main peak of the pyrochlore phase.

(Leaving space below) Table 1 Comparison of the method of the present invention and the method of the prior application From this 1. The present invention uses a simple process of mixing individual salts of Pb, Mg, and Ti oxalates and Nb hydroxide. It can be seen that a powder containing less pyrochlore phase was obtained.

Example 2 Ba(ZnヮJb2i)03 is known as a material exhibiting an electrostrictive effect, and is also used as an additive to improve the properties of the above-mentioned PMN-FT system.

The synthesis method is the same as in Example 1, and Ba and Zn are synthesized as precipitates of oxalates, and Nb is synthesized as precipitates of hydroxide, and then dried to obtain raw material powders. After mixing these, they were calcined at 800° C. for 2 hours, resulting in a single phase of perovskite.

Example 3 Ba (B'
A compound represented by the formula 1/3B"2/3)Oa is used. Here, Bo is Zn or Mg, and B" is Nb.
Or Ta. Here, Ba (ZnL/3↑a
2/3)03, Ba(MgL/3Ta2/3)O:i
+7) Synthesis was carried out in the same manner as in Example 1.

For example, in the case of Ha(ZnL/3Ta2/3)03,
Ba and Zn are each synthesized as a precipitate of oxalate, and Ta is synthesized as a precipitate of hydroxide, and then dried to obtain each raw material powder. After mixing these, they were calcined at 800° C. for 2 hours, resulting in a single phase of perovskite.

Similar results were obtained for Ba(Mg, 3Ta2/3)03.

Example 4 Pb(Fel/3Nb2/3)03, Pb(Niv3N
b2/3)03 is a material that is being researched for use in capacitors because it exhibits a high dielectric constant. These syntheses were performed in the same manner as in Example 1.

For example, in the case of Pb(Fe1,3 Nb2/3)03,
Pb and Fe are each synthesized as an oxalate precipitate, and Nb is synthesized as a hydroxide precipitate, and then dried to obtain each raw material powder. After mixing these, they were calcined at 800° C. for 2 hours, resulting in a single phase of perovskite.

Similar results were obtained for Pb(Niv3Nb2/3)03.

Effects of the Invention In the synthesis of composite perovskites containing group Va elements, the conventional precipitation method produces precipitation of hydroxides of group Va elements and oxalates of other elements at the same time, resulting in a method in which almost no perovskite constituent elements remain in the filtrate. Although it was necessary to optimize the synthesis conditions, such as the pH of the solution, the desired composition could be achieved by the method of preparing a precipitate of the perovskite constituent elements of the present invention alone, drying it, then mixing and calcining it. has become easier than conventional precipitation methods.

Claims (1)

[Claims] Generally, in the synthesis of a composite perovskite containing a group Va having the structure ABO_3, (1) an aqueous solution of oxalic acid of a group Va element of the periodic table, which is a B-site element, is mixed with alcohol, and the pH is adjusted to is 3 or more,
(2) After adding oxalic acid to alcohol, Ca, Sr,
A step of mixing with a solution containing one type of ion of Ba, Bi, Pb or a rare earth element (hereinafter referred to as A site element) to form a precipitate of oxalate, and filtering, washing and drying the precipitate; (3) ) After adding oxalic acid to alcohol, Mg, Cr,
Mixing with a solution containing one type of ion of Mn, Fe, Co, Ni, Cu, Zn, Ti, Zr or Hf (hereinafter referred to as B site element) to generate a precipitate of oxalate, filtering the precipitate, (4) the Va group hydroxide dry powder from the step (1) above;
Va group A method for synthesizing piezoelectric and dielectric ceramic powder, characterized by synthesizing a perovskite-type composite oxide containing elements.