Micro‐Raman scattering in Nb₂O₅–TiO₂ ceramics

Abstract

Single-phase (Nb 2 O 5 ) 1−x (TiO 2 ) x ceramics were prepared for x = 0.00, 0.05, 0.08 and 0.11 compositions using a solid-state reaction technique. The effect of TiO 2 substitution on the vibrational and phase transition behavior of Nb 2 O 5 was studied using the micro-Raman scattering technique and compared with similar results on Ta 2 O 5 . The external modes resulting from interaction among various polyhedra were observed and vibrational changes were studied in the temperature range −200 to 1100 • C. An increase in structural disorder was reflected in the Raman spectra with increasing TiO 2 content in both Nb 2 O 5 and Ta 2 O 5 . Ta 2 O 5 shows a phase transition at about 300 • C . However, a low-temperature phase transition was observed about 50 • C from (Nb 2 O 5 ) 1−x (TiO 2 ) x compositions.

Raman and IR studies of BaBi2Ta2O9 prepared by a sol–gel process

“…The Raman spectrum of the sample annealed at 800 • C shows strong bands at 841, 592, 224 and 160 cm −1 and weak bands at 790, 501, 447 and 302 cm −1 . This spectrum is very similar to the spectrum of Bi-layered BBT reported by Dobal and Katiyar [8] but we could not observe the modes located below 80 cm −1 owing to the experimental limit of the FT-Raman instrument. This result indicates that a nearly pure phase of BBT was obtained at this temperature.…”

“…[8,25] The previous studies of BBT microcrystalline powders showed, however, that fewer bands than expected were observed due to overlapping of the weaker bands by the stronger ones. [2,8,9] Room temperature Raman and IR spectra of the synthesized samples are presented in Figs 2 and 3, respectively. Raman spectrum of the sample annealed at 600 • C consists of broad bands at 770, 550, 480, 270, 220 and 142 cm −1 .…”

“…[5] The room temperature structure of BBT is pseudotetragonal (I4/mmm) and consists of microdomains with orthorhombic distortion, which causes the relaxor-type ferroelectric transition around 60 • C. [6,7] BBT microcrystalline powders were the subject of a few Raman and infrared (IR) studies. [2,8,9] Raman studies showed that the lowest wavenumber mode of CaBi 2 Ta 2 O 9 and SrBi 2 Ta 2 O 9 (SBT) exhibited partial softening and a marked increase in damping on heating when the phase transition temperature from the orthorhombic to tetragonal phase was approached from below. [8,9] This behavior was attributed to displacive character of the phase transition.…”

“…[2,8,9] Raman studies showed that the lowest wavenumber mode of CaBi 2 Ta 2 O 9 and SrBi 2 Ta 2 O 9 (SBT) exhibited partial softening and a marked increase in damping on heating when the phase transition temperature from the orthorhombic to tetragonal phase was approached from below. [8,9] This behavior was attributed to displacive character of the phase transition. In contrast to observation of the underdamped soft mode in CaBi 2 Ta 2 O 9 and SBT, Raman studies of BBT suggested that the soft mode in this material is strongly overdamped.…”

“…[10] Some Raman and IR data for BBT have been published previously. [2,8,9] However, they were obtained only at room temperature and for microcrystalline samples. Furthermore, there are no reports on the temperature dependence of the Raman and IR spectra of BBT.…”