PHASE DIAGRAM OF PROTON-CONDUCTING Ba(Zr_(0.8-x)Ce_xY_(0.2))O_(2.9) CERAMICS BY IN SITU MICRO-RAMAN SCATTERING AND X-RAY DIFFRACTION

摘要

In situ X-ray diffraction (XRD) and micro-Raman scattering have been used to study structures, lattice parameters, Raman vibrations, and phase transitions of Ba(Zr_(0.8-x)Ce_xY_(0.2))O_(2.9) (BZCY) ceramics (x = 0.0-0.8) as a function of temperature (20-900 ℃). The glycine-nitrate (G/N) combustion process was used to synthesize nano-sized proton-conducting BZCY ceramic powders as a function of cerium-to-zirconium ratio. The glycine-to-nitrate molar ratio used to fabricate BZCYs is G/N = 1/2. Second phase was not observed on BZCY ceramics after calcining at 1400 ℃ for 5 hours. A first-order structure transition from rhombohedral (R) to cubic (C) takes place upon heating for x = 0.5-0.8, in which transition temperature shifts toward higher temperature as cerium content increases, except for BCY82 (x = 0.8) which has a more complex transition sequence. The R-C phase transition was not observed for lower-cerium BZCYs (x = 0.0-0.4) in the region of 20-900 ℃, indicating a cubic phase at and above room temperature.