Microstructure and piezoelectricity of Bi3TiNbO9 ceramics from mechanochemically activated precursors

Bi3TiNbO9 is one of the Aurivilius-type structure compounds, of general for mula [Bi2O2][A(n-1)B(n)O(3n+1)], made from pseudoperovskite (with n=2) laye rs alternating with Bi2O2 layers. It belongs to an ensemble of high transit ion temperature ferroelectrics that attracts nowadays a great deal of inter est as piezoelectric materials for high temperature use (p.e. in non-destru ctive testing of materials by ultrasounds for siderurgy, nuclear plants or petrochemical industry). When prepared as thin films, they have interest as non-volatile computer memories (FERAM), due to their reduced fatigue, larg e polarization retention and low leakage currents. In solid state reaction and sintering, the lamellae-like growing habit, tha t resembles the layered crystalline structure, gives place to porous cerami cs. Previous works used hot uniaxial pressing in order to obtain dense cera mics at low temperatures, avoiding changes in stoichiometry and exagerated grain growth. But, such ceramics have anisotropic properties. In order to o vercome these problems, Bi3TiNbO9 ceramics were obtained by cold-pressing o f amorphous powder and sintering. The amorphous precursor was obtained by m echanochemical activation of a stoichiometric oxides mixture. The quantitat ive microstructural, ferro and piezoelectric characterization of the cerami cs reveals that these ceramics have lower porosity, higher hardness, are be tter polarizable and show higher piezoelectric response that those prepared from solid state reaction powder.