RARE EARTH OXIDES PYROCHLORE COMPOUNDS BY SOFT CHEMISTRY

摘要

Rare-earth zirconates (Re_2Zr_2O_7, Re= rare element) have attracted particular interest in thermal barrier coating (TBC) applications due to suitable thermal properties such as low conductivity and efficient phase stability at elevated temperatures. Among them, lanthanum zirconate (La_2Zr_2O_7 - LZ) with a pyrochlore structure has been proposed as potential candidate. Recently, rare-earth cerates, especially lanthanum cerate (La_2Ce_2O_(7-δ) - LC) has been also developed and considered as new TBC ceramic material. This study is interested in synthesizing these compounds by soft chemistry processes: alkoxide and citrate synthesis route. X-ray diffraction (XRD) was used to analyze the powder after calcinations under air. Pyrochlore and fluorite structures were identified at relatively low temperature (1000℃) for LZ and LC respectively. Chemical reactivity tests under reducing atmosphere were performed at 1400℃ and investigated by XRD analysis. The lanthanum zirconate is the most stable and interesting material under Ar_((g))/2%H2_((g)) atmosphere.