Effect of synthesis route on the microstructure of SiO2 doped bismuth titanate ceramics

Synthesis and characterization of SiO 2 doped bismuth titanate ceramics were investigated. Four investigated compositions belonging to the system Bi 2 O 3 -TiO 2 -SiO 2 are located in the section Bi 4 Ti 3 O 12 -SiO 2 , near by it and in the binary Bi 2 O 3 -TiO 2 system. Melt quenching was applied for synthesis of SiO 2 doped bismuth titanate ceramics and for the sample 40Bi 2 O 3 ·60TiO 2 . The binary sample 70Bi 2 O 3 ·30TiO 2 is prepared by gradient heating of bulk materials near the liquidus temperature (modified solid state reaction). The influence of the thermal treatment on the phase formation and microstructure was evaluated using XRD, EDS and SEM. The binary samples prepared by solid state reaction at low temperature (1000°C) possess poly-phased dense microstructure, while secondary crystallization combined with porosity formation is typical for the sample obtained at high temperature (1150°C). The ternary Bi 2 O 3 -TiO 2 -SiO 2 samples, obtained by supercooling of the melts down to room temperature, are thermally treated at 700, 800°C. They consist of elongated crystals in amorphous matrix. The crystals have lower Bi 2 O 3 -content and higher TiO 2 -content than the nominal batch composition. The XRD data show that the main crystalline phases in the ceramics produced by melt quenching method and solid state reaction are β-Bi 2 O 3 , Bi 4 Ti 3 O 12 and one unknown new phase. It is proved that the applied methods of synthesis are suitable for generation of different microstructures in the bulk SiO 2 doped bismuth titanate ceramics, which is promising basis for modification of their electrical properties.