Temperature-dependent structures of proton-conducting Ba(Zr0.8-xCexY0.2)O2.9 ceramics by Raman scattering and x-ray diffraction

Abstract

In situ temperature-dependent micro-Raman scattering and x-ray diffraction have been performed to study atomic vibration, lattice parameter and structural transition of proton-conducting Ba(Zr0.8−xCexY 0.2)O2.9 (BZCY) ceramics (x = 0.0–0.8) synthesized by the glycine–nitrate combustion process. The Raman vibrations have been identified and their frequencies increase with decreasing x as the heavier Ce4+ ions are replaced by Zr4+ ions. The main Raman vibrations of Ba(Ce0.8Y 0.2)O2.9 appear near 305, 332, 352, 440 and 635 cm−1. The X–O ( X=Ce, Zr, Y) stretching modes are sensitive to the variation of Ce/Zr ratio. A rhombohedral–cubic structural transition was observed for x = 0.5–0.8, in which the transition shifts toward higher temperature as cerium increases, except for Ba(Ce0.8Y 0.2)O2.9. A minor monoclinic phase possibly coexists in the rhombohedral matrix for x = 0.5–0.8. The lower-cerium BZCYs (x = 0.0–0.4) ceramics do not exhibit any transition in the region of 20–900 °C, indicating a cubic phase at and above room temperature.