Thermal-Driven Fluorite–Pyrochlore–Fluorite Phase Transitions of Gd₂Zr₂O₇ Ceramics Probed in Large Range of Sintering Temperature

Abstract

Fluorite (F)–pyrochlore (P)–fluorite (F) phase transitions of Gd₂Zr₂O₇ were investigated from 573 K to 1873 K (300 °C to 1600 °C), by means of X-ray diffraction, infrared spectra (IR), and Raman spectra. The low-temperature F phase can stably exist below 1523 K (1250 °C) and the F–P transition occurs at 1523 K to 1573 K (1250 °C to 1300 °C). The ordering process of P phase forms at 1573 K to 1773 K (1300 °C to 1500 °C) and the ordering degree increases with increasing sintering temperature and heat preservation period. High-temperature phase transition from P to F occurs between 1773 K and 1823 K (1300 °C and 1550 °C). IR spectra of samples with different ordering degrees show an interesting shift at 510 cm⁻¹. Raman spectra show that only the A_1g mode displays a significant change between F and P phases. This ordering degree and phase transition temperature studies would allow a more targeted experimental optimization of Gd₂Zr₂O₇ to use in nuclear waste host, thermal barrier coatings, and solid oxide fuel cells.