JPH07100624B2 - Method for manufacturing PMN-based ferroelectric - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a PMN-based ferroelectric material, and in particular, a low firing temperature and an inexpensive Ag—Pd alloy or an internal electrode material as an internal electrode material.
The present invention relates to a method of manufacturing a ferroelectric material that can be used as a laminated capacitor material that can use Ag or an actuator material that can adjust the optical path length and position on the order of submicrons.

(Background Art) Pb (Mg _1/3 Nb _2/3 ) O ₃ (hereinafter abbreviated as PMN) is a ferroelectric substance having a composite perovskite structure, which was first synthesized in 1950. However, since it has excellent dielectric and electrostrictive properties and can be synthesized at a low temperature, it has recently received attention as a material for a multilayer capacitor or an actuator.

Various methods have been conventionally proposed as a method for manufacturing the PMN sintered body, but in such a conventional manufacturing process, a lead-niobate-based pyrochlore phase (Pb ₂ Nb ₂ O ₇ , Pb ₃ Nb ₄ O ₁₃ , Pb ₃ Nb ₂ O ₈ ) coexisted, and it was difficult to obtain a single-phase PMN perovskite phase. Further, the dielectric constant of this pyrochlore phase is about 200, which is significantly smaller than 15000 to 20000 of PMN single crystal, which significantly reduces the dielectric properties and electrostriction effect, which is a practical obstacle. Therefore, it is desired to develop a method for producing a sintered body composed of a PMN single phase that does not contain such a pyrochlore phase.

By the way, the most inexpensive method of manufacturing PMN sintered bodies known in the past is the method of mixing the component oxides. However, in the manufacturing method using this oxide mixing method, the diffusion rate of MgO is slow. Therefore, the reaction of MgO is delayed as compared with the reaction of PbO and Nb ₂ O ₃ , and the dispersibility of MgO during mixing is poor.
The gO remains in the PMN grains and becomes isolated from the pyrochlore phase, and PbO volatilizes during the calcination and firing, deviating from the stoichiometric composition. It was almost impossible to synthesize the PMN of.

As a countermeasure, a method of adding excess PbO and MgO is considered. According to this method, Pb ₂ Nb ₂ O ₇ and Pb
_It forms unstable PbO-rich pyrochlore phase such as ₃ Nb ₂ O ₈ and prevents the stable Pb ₃ Nb ₄ O ₁₃ pyrochlore phase from remaining, thereby forming a liquid phase and low temperature sintering. Is possible, and volatilizes during calcination and firing.
PbO can be supplemented, and excess MgO has the effect of promoting grain growth and eliminating the pyrochlore phase from grain boundaries.
However, it is not only difficult to reproducibly control the excess amount of PbO and MgO, but the excess amount is detrimental to the mechanical properties and aging of the product.

In addition, the corumbite precursor method, which is one method for obtaining a PMN sintered body, is MgO and Nb ₂ O ₃ to MgNb ₂ O ₆ (corumbite).
PMN is produced in advance, and PMN is produced by the reaction of this with PbO. However, this method has the inherent problem that it requires two calcination steps and that MgO particles remain unavoidably. are doing.

Furthermore, according to the method known as the metal alkoxide method or the sol-gel method, it is possible to synthesize a fine powder with high homogeneity and high purity at a low temperature. Therefore, the diffusion rate and dispersibility of MgO and the volatilization of PbO are The problem of is solved, and it is possible to synthesize high-purity, high-homogeneous PMN powder at a low temperature of 775 ° C, but this method requires expensive raw materials, and it takes a long time to dry the gel.
There is an inherent problem that the firing temperature does not fall below 1200 ° C unless an excessive amount of PbO is added.

(Problem to be Solved) Here, the present invention has been made in view of such circumstances, and its object is to suppress the production of a bilochlor phase and control the dielectric characteristic and the electrostrictive characteristic. It is intended to provide a skillful manufacturing method of a PMN single-phase sintered body capable of producing the PMN single-phase sintered body, and also to advantageously manufacture such a PMN single-phase ferroelectric sintered body.

(Solution Means) In order to solve the above problems, the present invention provides Pb (Mg
_1/3 Nb _2/3 ) O ₃ : 40-80 mol%, BaTiO ₃ : 30 mol% or less, Pb
TiO _3: The raw material blend to give 20 to 50 mol% having a composition was prepared, the preparation of the PMN-based ferroelectric, characterized by firing the molded to the desired shape, which as its gist Is.

(Specific Configuration / Operation) By the way, the present invention is
And it was completed based on the knowledge obtained by it.

First, the present inventor conducted a detailed study on a system in which BaTiO ₃ (hereinafter abbreviated as BT) was solid-solved in PMN, and as a result, found that the solid solution had a large effect of suppressing the formation of the bilochlor phase, and also the Curie temperature It has been clarified that does not change in proportion to the solid solution amount of BT and has the minimum value as shown in FIG. In addition, for the system in which PbTiO ₃ (hereinafter, abbreviated as PT) is formed as a solid solution, the temperature characteristics of the dielectric constant and the electrostriction constant are extremely flat compared to PMN alone,
It also exhibits excellent electrostrictive characteristics such as extremely small electrostrictive hysteresis, and its Curie temperature changes linearly with the solid solution amount of PT, as shown in FIG. Become.

Therefore, the inventor of the present invention further relates to a system in which BT, which has a large effect of suppressing the pyrochlore structure with respect to PMN, and two types of ferroelectrics, PT, which can improve the dielectric and electrostrictive properties, are solid-solved. With regard to the crystal structure, the composition of PMN-based 40 mol% or more was studied in detail, and as a result, the relation between the crystal structure and the dielectric property of each composition as shown in FIG. 3 and the examples described later are shown. The relationship between the Curie temperature and the dielectric characteristics of the ferroelectric substance was obtained.

The present invention shows that PMN: 40 to 80 mol% and BT: 30
In the composition range of mol% or less, PT: 20 to 50 mol%, a PMN-based ferroelectric material is realized. Among them, PMN: 50 to 70 mol%, PT: 20 to 30 mol%, BT: 10 to 30 A composition of mol% is advantageously adopted, for example PMN: 60 mol%, PT: 20 mol%, BT: 20.
A PMN single-phase ferroelectric substance with a Curie temperature of about 30 ° C and a dielectric constant of about 7,000 (1 KHz) is obtained at a mol% composition, and at the time of its production, firing at a low temperature of about 1100 ° C Is possible.

When manufacturing a PMN-based ferroelectric according to the present invention, a raw material mixture is prepared in the same manner as in the conventional method so as to give the above composition. For example, such raw material blends are generally in the form of oxides, carbonates, etc., respectively, for the purposes of PbO source raw material, MgO source raw material, Nb ₂ O ₅ source raw material, TiO ₂ source raw material, and BaO source raw material. It can be prepared by mixing so as to achieve the above ratio, and methods such as directly mixing PMN, BT, and PT can also be appropriately adopted.

Further, the raw material mixture which gives the predetermined composition of PMN, BT, and PT thus obtained is molded into a desired shape according to the shape required for the target sintered body (PMN-based ferroelectric). After that, it will be fired in the same manner as in the past, but the firing can be performed at a low temperature, for example, by firing at a temperature of about 1100 ° C., the desired sintered body can be obtained. Of.

(Examples) Hereinafter, several examples of the present invention will be shown to clarify the present invention more specifically, but the present invention does not impose any restrictions due to the description of such examples. Needless to say, it is not something to receive.

In addition to the following embodiments, the present invention further includes various changes and modifications based on the knowledge of those skilled in the art, in addition to the above specific description, without departing from the spirit of the present invention. It should be understood that improvements and the like can be added.

First, dried raw materials: PbO, MgO, Nb ₂ O ₅ , TiO ₂ , and BaCO ₃ powders were weighed so as to have a stoichiometric composition shown in Table 1 below, and ball-milled in ethyl alcohol. It was done for 24 hours. Then, the obtained slurry was dried at a temperature of 100 ° C. for 24 hours and then pulverized to obtain various mixed powders (raw material mixture). Then, mix this powder with 30
After molding by uniaxial pressure of 0MPa, 900 ℃ in the air, 4
After calcination for a certain time, the calcinated body is crushed for about 30 minutes, 2% by weight aqueous solution of methylcellulose is added as a binder, uniaxial pressure molding is performed at 30 MPa, and further 200 MPa is applied by a cold isostatic press. Molding was performed under the pressure of 1 to obtain a predetermined molded body. Furthermore, this molded body is heated to 300 ° C / atmospheric pressure.
After raising the binder to 500 ° C at a heating rate of Hr and holding it for 1 hour to scatter the binder, raise the temperature to 1100 ° C at a heating rate of 300 ° C / Hr and hold at the same temperature for 2 hours. Was fired to obtain a desired sintered body.

Curie temperature (Tc), crystal structure, dielectric constant (ε) and dielectric loss (tan δ) of the thus obtained sintered bodies of various compositions were examined, and the results are also shown in Table 1 below. The symbols for crystal structure and dielectric properties in Table 1 have the following meanings.

Crystal structure c: cubic crystal, pc: pseudo-cubic crystal, t: tetragonal crystal Dielectric property P: paramagnetic material, F: ferromagnetic material As is clear from the results shown in Table 1, PMN according to the present invention.
By dissolving other compounds having a perovskite structure (PT, BT) in solid solution, the generation of pyrochlore phase is suppressed, and the dielectric and electrostrictive properties can be effectively controlled, and PMN
It is possible to advantageously obtain a system ferroelectric.

(Effects of the Invention) As is apparent from the above description, according to the present invention,
While it was difficult to obtain a PMN single-phase perovskite-phase ferroelectric sintered body, by dissolving BT having a perovskite structure in the PMN phase, the formation of the pyrochlore phase is suppressed, and at the same time PT It has become possible to manufacture PMN-based single-phase ferroelectrics by controlling the dielectric properties and electrostrictive properties by making solid solution, and there is a significant technical significance of the present invention there. is there.

[Brief description of drawings]

1 and 2 are graphs showing the Curie temperature of PMN-BT system and Curie temperature of PMN system-PT system, respectively, and FIG. 3 is the crystal structure of each composition of PMN, BT, and PT. It is a figure which shows a dielectric characteristic.

Claims (1)

[Claims] 1. Pb (Mg _1/3 Nb _2/3 ) O ₃ : 40-80 mol%, BaTiO 3
_{3. A} method for producing a PMN-based ferroelectric material, which comprises preparing a raw material mixture which gives a composition of 30 mol% or less and PbTiO ₃ : 20 to 50 mol%, molding the mixture into a desired shape and firing the mixture. .