Micro-Raman scattering and x-ray diffraction studies of (Ta2O5)1-x(TiO2)x ceramics

High dielectric constant (Ta2O5)1−x(TiO2)x ceramics for x=0.00, 0.05, 0.08, and 0.11 were prepared and studied utilizing micro-Raman scattering and x-ray diffraction techniques. The modification in the lowest frequency phonon mode of pure Ta2O5 with increasing TiO2 content in these ceramics was assigned as Ta–Ti vibrations originating from the interaction between TiO6 octahedra and TaOn5-2n or Ta6O12+6 clusters. Raman spectra, in the range −200–900 °C, reveal a softening of this mode with increasing temperature followed by a structural transformation. A triclinic to monoclinic phase (Hmon′) transition was observed at about 300, 360, 450, and 540 °C for x=0.00, 0.05, 0.08, and 0.11, respectively. It was also found that reannealing at 1150 °C for 12 h transforms these ceramics from triclinic to a metastable monoclinic phase Hmon, which was found to be an irreversible process.