Zirconate pyrochlores under high pressure

Abstract

Ab initio total-energy calculations and X-ray diffraction measurements have been combined to study the phase stability of zirconate pyrochlores (A₂Zr₂O_7; A = La, Nd and Sm) under pressures up to 50 GPa. Phase transformations to the defect-cotunnite structure are theoretically predicted at pressures of 22, 20 and 18 GPa, in excellent agreement with the experimentally determined values of 21, 22 and 18 GPa for La₂Zr₂O₇, Nd₂Zr₂O₇ and Sm₂Zr₂O₇, respectively. Analysis of the elastic properties indicates that elastic anisotropy may be one of the driving forces for the pressure-induced cubic-to-noncubic phase transformation.