Preparation And Characterization Of Powders And Thin Film Of PMN-PT Relaxor Ferroelectric Composition Derived From A Sol-Gel Method Using Inorganic Salts As Metal Sources

Perovskite type lead magnesium niobate (PMN) is a relaxor ferroelectric. PMN-based ceramics, with very high dielectric constant, large electrostrictrive strain and a tunable effective piezoelectric effect, have been wildly and will be used in the manufacture of capacitors, MLCCs, actuators and micro-electro-optic mechanics etc. With the increasing demand for electronic equipment of reduced size and higher integrated density, electronic circuit miniaturization has been continuously made. And circuit devices and components are required to have a compact design, high performance, and high reliability and be cost-effective. This trend leads to the R&D on the preparation and the applications of PMN-based ferroelectric thin films.Sol-Gel technique was used to prepare materials with high purity, compositional stoichiometry and homogeneity in composition and microstructure. The low sintering temperature of the Sol-Gel derived films make it possible to compact with integrated circuits. Sol-Gel method is especially suitable to be used in preparing thin films by spin coating. The processing of the thin film by sol-gel method is rather simple in a low price, without the need to use very expensive and complicated equipment and machine. It has been widely employed in the preparation of ferroelectric thin films with simple composition. Furthermore, thin films could be prepared in a large scale using the Sol-Gel method.The sol-gel method could be classified into three kinds of ruts: colloidal sol-gel route, inorganic polymeric gel route, and organic polymeric gel route. The basic inorganic polymeric gel route is based upon the hydrolysis of metal alkoxides, which has been successfully developed and used. But, metal alkoxides, especially niobate alkoxides, are expensive and sensitive to moisture in air. The great difference of the hydrolysis rate between metal alkoxides leads to the difficulty in controlling the processing technology for the preparation of inorganic materials with multi-component. Therefore Sol-Gel method using metal-alkoxides as precursors is not a good method for the preparation of oxides with multi-component, e.g., PMN and PMN-PT-like relaxor type ferroelectrics.In this work, a new organic polymeric gel method, soluble inorganic salt-chelate-gel method was studied and developed. In the studies, inorganic compounds: PbO, MgO, Nb₂O₅, TiCl₄ were used as starting chemicals, citric acid and EDTA are used as a complex chelate agent, and ethylene glycol as solvent.