JPH0517189B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for producing a sintered body of lead zirconate titanate (hereinafter referred to as "PZT") used as a piezoelectric material, pyroelectric material, etc. [Conventional technology] Conventionally, PZT sintered bodies have been manufactured using lead (Pb), zirconium (Zr), and titanium (Ti).
A dry method in which powders of each oxide are mixed in the required proportions, calcined, then crushed and shaped, and the shaped product is sintered at a temperature of approximately 1200℃ in air containing lead oxide (PbO) or oxygen. has been used. In this dry method, the raw material powder obtained by calcination has a low uniformity of composition and a large average particle size of several μm, resulting in poor sinterability. A high temperature of about 1200°C was required. Therefore, a method is desired in which the powder to be sintered is easily sinterable and a sintered body having a high sintered density can be obtained even when sintered at a low temperature. As such a method, a method is known in which calcined powder to be subjected to sintering is produced by a wet co-precipitation method. That is, in order to obtain a precipitate with a composition corresponding to the desired sintered body composition, an aqueous solution in which the required amount of compounds of each element of titanium, zirconium, and lead are dissolved is simultaneously mixed with a basic precipitate forming solution. This is a method in which precipitates of seed elements are simultaneously formed (co-precipitated), the resulting precipitate is calcined, and after molding, it is sintered. [Problem to be solved by the invention] However, since the precipitate forming ability of each element in one precipitate forming solution (for example, the solubility product of the precipitate of each element at a constant pH) is different, it is not always possible to Precipitated fine particles of the same composition are not always obtained, and when forming precipitates, they tend to aggregate to form secondary particles, resulting in improved sinterability, but this is still insufficient. . Furthermore, it is desirable to use titanium tetrachloride, which is inexpensive, as a raw material compound for titanium, but chlorine ions produced when titanium tetrachloride is dissolved react with lead to form a white precipitate, so it cannot be used at the same time as a lead compound. There was also the problem that it was not possible. An object of the present invention is a method that can produce a sintered body having a high sintered density even when sintered at a low temperature,
Another object of the present invention is to provide a method that can easily produce a sintered body having a desired composition. [Means for Solving the Problems] The present invention solves the problems of the method for manufacturing a sintered body using powder by the conventional coprecipitation method.
A precipitate containing the one or two elements selected from Pb, Zr, and Ti is generated from a solution containing a compound of one or two elements selected from Pb, Zr, and Ti, and then the precipitate obtained is In a dispersed state, from a solution containing a compound of the remaining two or one of the three elements, the two or one of the remaining two or one of the three elements is heated under ultrasonic waves.
Perform the operation to generate a precipitate containing the seed elements a necessary number of times to precipitate all the three types of elements, and then the obtained precipitate containing the three types of elements.
Calcinate at 550 to 750°C to obtain fine powder, and further sinter the fine powder at 900 to 1200°C to obtain a powder with a composition of Pb _x Zr _A Ti _1-A
The present invention provides a method for producing a PZT sintered body, which comprises obtaining a sintered body expressed by O ₃ (0.9≦x≦1.2, 0.1≦A≦0.98). In the production method of the present invention, when forming a precipitate, Pb, Zr
This is a method (hereinafter referred to as "multi-stage wet method") in which the three elements, Ti and Ti, are not precipitated (co-precipitated) at the same time, but are formed in two or more stages. Specifically, for example, one of these three elements may be precipitated in the first stage and the remaining two elements may be co-precipitated in the second stage, or vice versa. A method in which two types of elements are co-precipitated by eye, and the remaining one element is precipitated in the second stage. Precipitate formation is performed sequentially for each of the three types of elements, so the precipitate formation is performed in three stages. A further example is a method of forming a precipitate in four or more stages by dividing one element into a plurality of stages to form a precipitate. Usually, precipitation is formed in two or three stages. Another feature of the present invention is that all of these two or more steps of precipitation formation are carried out under ultrasonic waves. Examples of Pb, Zr and Ti compounds that can be used as raw materials in the production method of the present invention include:
Salts and hydroxides of organic or inorganic acids such as oxychlorides, carbonates, oxynitrates, sulfates, nitrates, acetates, formates, and oxalates of these elements;
Examples include, but are not limited to, chlorides and oxides. As a solvent for preparing a solution containing these compounds, water, alcohol, and a mixture thereof are usually used, but the solvent is not limited thereto. If it is not soluble in these solvents, it can be used by adding a mineral acid or the like to solubilize it. Since the present invention employs a multi-stage wet method, compounds that cannot be used in conventional coprecipitation methods due to poor compatibility can be used in combination.
For example, the aforementioned titanium tetrachloride can also be used if Ti and Pb are precipitated in separate steps. Formation of the precipitate is carried out by mixing a solution containing the raw material compound with an excess amount of the precipitate forming liquid. Examples of the precipitation forming liquid used include ammonia,
Examples include solutions of ammonium carbonate, alkali metal hydroxides, sodium carbonate, oxalic acid, ammonium oxalate, and organic reagents such as oxins and amines. You can choose from these. If the precipitate forming liquid used for precipitate formation in one step and the precipitate formation in the next step is the same, add the element to be precipitated in the next step directly to the solution containing the precipitate obtained in the precipitate formation in the previous step. What is necessary is to mix a solution containing the precipitate, and in this case, since an excessive amount of the precipitate-forming liquid has already been added, there is no need to add it again depending on the case. In addition, if the precipitate-forming liquid in the next step is different from the precipitate-forming liquid in the previous step, and it is desirable that the precipitate-forming liquid used in the previous step not exist in the next step, After the precipitate is formed, the precipitate is washed, and then the next step of precipitate formation may be carried out in a state where it is dispersed in a solvent or a solution containing the element to be precipitated in the next step. The precipitated particles thus obtained are fine particles with an average particle size on the order of several tens of angstroms, and the formation of secondary particles due to aggregation is extremely suppressed as a result of being formed in ultrasonic waves. The obtained precipitate is subjected to the next calcination after washing and drying, and it is preferable to use an alcohol such as ethanol for washing, so that agglomeration during drying and calcination can be further suppressed. Calcination of the obtained precipitate is carried out at 550-750°C, preferably 600-700°C in air or oxygen. The calcining time may be approximately 1 to 2 hours. This calcination yields the following fine powder consisting of a single phase of PZT, with an average particle size of less than 1 μm, and an average pore size of 300 Å or less. Temperature of calcination is 550℃
If it is less than 100%, PbTiO ₃ and PbZrO ₃ phases coexist, and a PZT single phase in which the specific reaction is completed does not occur. Also,
If the temperature exceeds 750°C, grain growth becomes significant and it is not possible to obtain a fine powder that is easily sinterable. Next, the fine powder obtained by calcination is crushed if necessary, then shaped and subjected to sintering. The sintering atmosphere is, for example, air, oxygen, or
Examples include an atmosphere containing PbO vapor, but preferably an atmosphere containing PbO, and the sintering temperature is 900°C.
~1200℃. If the sintering temperature is less than 900℃, a high-density sintered body with a relative density of 95% or more cannot be obtained.
If the temperature exceeds 1200°C, the evaporation of PbO becomes significant, causing changes in composition and abnormal grain growth, making it impossible to obtain a uniform high-density sintered body. The PZT sintered body thus obtained has a general formula: Pb _X Zr _A Ti _1-A O ₃ (0.9≦X≦1.2, 0.1≦
A≦0.98). If X is less than 0.9, a high-density sintered body cannot be obtained at 1000°C or less, while if X exceeds 1.2, a lead oxide phase will precipitate in the sintered body, making it difficult to achieve uniform sintering. Can't get the body. Also, A is less than 0.1 or
If it exceeds 0.98, it can no longer be called PZT. The manufacturing method of the present invention is advantageous in that a high-density sintered body can be obtained even at a temperature of 900 to 1000°C, which is 1000°C or lower. Furthermore, according to such low temperature sintering,
The evaporation of PbO during the sintering process is extremely low, making it easy to produce a sintered body with the desired composition, and eliminating the need to use a PbO-containing atmosphere, which makes loading the sample into the crucible in the furnace easier. becomes extremely simple. In addition, it is possible to obtain a uniform sintered body with small grain size and less likely to cause abnormal grain growth. especially,
When manufacturing laminated elements used in pyroelectric films, piezoelectric films, or piezoelectric actuators by screen printing, etc., abnormal grain growth is less likely to occur.
A film with uniform particle size can be produced, and the film is not easily deformed. In addition, when printing electrode paste on a pellet-like molded body or thick film molded body and sintering this (for example, for laminated elements), there are advantages such as being able to use Ag-based inexpensive electrode materials. Therefore, the PZT sintered body obtained by the production method of the present invention has extremely great industrial significance. Incidentally, the sintering time during the above sintering is preferably 2 to 100 hours, particularly 20 to 100 hours when sintering at 900 to 1000°C. [Operation] When ultrasonic waves are applied to the precipitate formation process, a vibration field and a cavitation phenomenon are generated in the liquid, and mechanical force is applied, making it possible to stir an extremely small area. For example, when a solution of a compound of an element to be precipitated is added dropwise to a precipitate-forming solution subjected to ultrasonic waves, the solution immediately reacts to form precipitate particles. It is considered that the agglomeration of the precipitated particles is suppressed to a minimum by the mechanical force of the continuously applied ultrasonic waves. In the precipitate formation process after the second stage, the fine particles dispersed by ultrasonic waves are used as cores to form precipitates on top of them and grains grow, or
It is presumed that extremely microscopic mixing of each element is possible because the particles are generated as new precipitated particles and mixed with the already dispersed fine particles. In this way, a precipitate is obtained in which the three types of elements are microscopically mixed as fine particles of several tens of angstroms in size, and as a result, they are easily converted into PZT particles in the next calcination step, and easily sintered in the submicron order. It is thought that a sinterable PZT fine powder is obtained, and therefore the sinterability at low temperatures is improved. [Example] Hereinafter, the present invention will be specifically explained with reference to Examples. Example: An aqueous solution of 2.535 g of zirconium oxynitrate and 1.922 g of titanium tetrachloride dissolved in 500 ml of water was added dropwise to 600 ml of 5N ammonia water in an ultrasonic bath while stirring to form a precipitate of hydroxides of zirconium and titanium. Ivy. 200 ml of an aqueous solution containing 6.983 g of lead nitrate was added dropwise to the solution in which the coprecipitate was dispersed in an ultrasonic bath to obtain a hydroxide precipitate of zirconium, titanium, and lead. After washing and drying the precipitate, the precipitate was calcined at 600℃ for 1 hour, and PbZr _0.52 Ti _0.48 O ₃ was determined by X-ray diffraction.
A raw material powder consisting of only a PZT single phase was obtained. The raw material powder was molded at 2t/ ^cm2 , and the molded product was molded under normal pressure in an oxygen atmosphere containing a saturated amount of PbO vapor.
Sintered at various temperatures within the range of 900-1200°C. The sintered density of the obtained sintered body was measured, and the relative density with respect to the theoretical density (~8 g/cm ³ ) was determined. Also,
The presence or absence of abnormal grain growth in the sintered body was investigated, and the average grain size was measured. These results are shown in Table 1. As is clear from Table 1, the theoretical density (8 g/
A PZT high-density sintered body with a relative density of 95% or more to cm ³ ) was obtained. In addition, there was no abnormal particle growth,
The average grain size at 900°C was as small as 3.0 μm, and a uniform, high-density sintered body was obtained. Comparative Example Raw material powder was obtained in the same manner as in the example except that the precipitate formation process was not carried out in ultrasonic waves, and sintered at various temperatures under the same conditions as in the example. The results shown in 2 were obtained. A high-density sintered body was obtained at a sintering temperature of 1000°C or higher, but no high-density sintered body was obtained at a sintering temperature of 900°C.

【table】

〔Effect of the invention〕

By using the production method of the present invention, it is possible to easily obtain a sintered body having the desired composition, and also to have a high sintered density even at a low sintering temperature of 900° C. or higher. Therefore, it is advantageous from the viewpoint of energy saving, and as a result of suppressing the evaporation of PbO during the sintering process, it is not necessary to use an atmosphere containing PbO vapor, and furthermore, a sintered body with a uniform small particle size can be obtained, so it is possible to stack Easy to print. Therefore, the sintered body is excellent as a piezoelectric material, a pyroelectric material, etc.

Claims (1)

[Claims] 1. A solution containing a compound of one or two elements selected from lead, zirconium, and titanium is subjected to ultrasonic waves to generate a precipitate containing the one or two elements, and then , in a state where the obtained precipitate is dispersed, from a solution containing a compound of the remaining two or one of the three elements, the two or one of the remaining two or one of the three elements is heated under ultrasonic waves.
Perform the operation to generate a precipitate containing the seed elements a necessary number of times to precipitate all the three types of elements, and then the obtained precipitate containing the three types of elements.
Calcinate at 550 to 750°C to obtain a fine powder, and further sinter the fine powder at 900 to 1200°C to obtain a powder with a composition of Pb _x Zr _A Ti _1-A
A method for producing a lead zirconate titanate sintered body, which comprises obtaining a sintered body represented by O ₃ (0.9≦x≦1.2, 0.1≦A≦0.98).