Preparation And Properties Of BiFeO₃-（Ba,Ca）TiO₃-based Piezoelectric Materials

With the development trend of miniaturization of electronic devices,functional materials with good ferroelectric properties and piezoelectric response have attracted much more attention.BiFeO3 has become a research highlight because of its rich physical properties,such as ferroelectricity with high Curie temperature,anti-ferromagnetism with high Neel temperature and high temperature piezoelectric properties.However,the synthesis conditions of BiFeO3 are strict.It is easy to generate defects such as impurities and oxygen vacancies resulting in poor insulation and is difficult to obtain good electrical properties because of the volatilization of Bi and the change of Fe ion valence.The construction of BiFeO3-based solid solution with other ABO3 perovskite ferroelectrics is an effective method to improve the ferroelectric and piezoelectric properties of BiFeO3.Therefore,we explored the preparation of BiFeO3-based solid-solution ceramics with the addition of sintering aids by the solid-state reaction and BiFeO3-based composite films by chemical solution deposition.The main contents of our work are as follows:1.0.74BiFeO3-0.26Ba0.85Ca0.15TiO3 solid solution ceramics with the different amount of sintering aids BaO-2B2O3 and B2O3 were prepared by traditional solid-state reaction method.The optimal component of different sintering aids for the film with good ferroelectric properties was determined.2.We prepared three kinds of BiFeO3-based solid-solution films,including BiFe0.93Mn0.07O3-BiFe0.975Ti0.025O3,BiFe0.93Mn0.07O3-Ba0.85Ca0.15TiO3 and BiFe0.93Mn0.07O3CaTiO3 by chemical solution deposition.Compared with the properties of single-phase BiFe0.93Mn0.07O3 film,the introduction of ABO3 ferroelectrics containing high valence ions such as Mn4+ and Ti4+ greatly reduced the leakage current of BiFeO3-based solid-solution films.At the same time,the remanent polarization of BiFe0.93Mn0.07O3-BiFe0.975Ti0.025O3 can reach 90.4μC/cm2 resulting from the decrease of oxygen vacancies.3.Based on the study of binary solid solution films,we prepared ternary BiFe0.93Mn0.07O30.82BiFe0.975Ti0.025O3-0.18CaTiO3 layered composite films on Pt/Si(100)substrates and investigated the microstructural,ferroelectric and piezoelectric properties of films under different annealing processes.The remanent polarization and the piezoelectric coefficient can reach as high as 112.6 μC/cm2 and 878.2 pm/V,respectively,when the annealing temperature is 500℃ and the annealing atmosphere is nitrogen.This result is attributed to the coexistence of rhombohedral and pseudo-cubic phases and the enhancement of films compactness.