Crystal structure and phase transitions of Sr1±xBi2±yTa2O9 ceramics

Crystal structural parameters, such as space group, lattice parameters, apparent valences (AV), and site occupancies were analyzed in Sr1±xBi2±yTa2O9 ceramics with varying ceramic compositions and diffraction temperature. The crystal structure was refined by Rietveld method using neutron and X-ray powder diffraction data. The phase transition temperature Tc was measured on these ceramics. The spontaneous polarization Ps was calculated from the refined parameters. The measured Tc decreased with increasing Sr-content. The crystal structure of Sr1Bi2Ta2O9 changed from A21am at room temperature to B2cb at temperature above 400°C and to a higher symmetry one eventually. The cation place exchanges were observed between Sr2+ and Bi3+ and the calculated AVs were in accordance with the cation exchanges.