Disorder-induced symmetry lowering in Ba(Y1/2Nb1/2)O3 ceramics probed by Raman spectroscopy.

This work investigates the evolution of the crystal structure of microwave-hydrothermal synthesized Ba(Y1/2Nb1/2)O3 powders as a function of firing temperature by Raman spectroscopy. The samples were produced at 200 ?C and fired at temperatures ranging from 600 to 1600 ?C. Raman spectra were obtained at room temperature for all samples and the results showed that materials fired at 1600 ?C exhibited tetragonal (I4/m or C5 4h) structure, whereas those fired at lower temperatures exhibited the triclinic (P1 or C1 i ) structure. The results were compared with those observed for ceramics obtained by conventional solid-state methods. It is believed that the lowering of the symmetry verified in materials fired below 1600 ?C is a consequence of the local disorder of Y+3 and Nb+5 ions in octahedral sites