Increased stability of nanocrystals of Gd_2(Ti_(0.65)Zr_(0.35))_2O_7 pyrochlore at high pressure

摘要

Pyrochlore powders Gd_2(Ti_(0.65)Zr_(0.35))_2O_7, were synthesized by mechanical milling of constituent oxides, and their grain-sizes (from <20 nm to mu m-sized) were controlled by subsequent thermal treatments (800-1500 °C). Using in situ X-ray diffraction (XRD) measurements at pressures up to more than 40 GPa, the bulk moduli were determined to be greater (>10%) than the values of the end-member compositions: Gd_2Ti_2O_7 and Gd_2Zr_2O_7. The higher values are attributed to the mixed occupancy of cations at the A-and B-sites. There was also a significant increase in the stability of Gd_2(Ti_(0.65)Zr_(0.35))_2O_7 as the grain-size decreased below a critical value. The nanocrystalline sample, <20 nm, had a transition to the high-pressure phase that was approx 10 GPa higher than that for the same composition but with grain-size larger than 100 nm.