Ab initioinvestigation of phase stability ofY2Ti2O7andY2Zr2O7under high pressure

Abstract

The phase stabilities of ${\text{Y}}_{2}{\text{Ti}}_{2}{\text{O}}_{7}$ and ${\text{Y}}_{2}{\text{Zr}}_{2}{\text{O}}_{7}$ under high pressure were investigated by ab initio methods. Pyrochlore-structured ${\text{Y}}_{2}{\text{Ti}}_{2}{\text{O}}_{7}$ and defect-fluorite ${\text{Y}}_{2}{\text{Zr}}_{2}{\text{O}}_{7}$ exhibit different responses to high pressure. Both the defect-fluorite and defect-cotunnite structures are energetically more stable at high pressure in ${\text{Y}}_{2}{\text{Ti}}_{2}{\text{O}}_{7}$, but comparison with experimental results suggest that only the transformation to the defect-fluorite structure is kinetically favored. For ${\text{Y}}_{2}{\text{Zr}}_{2}{\text{O}}_{7}$, the defect-fluorite phase should undergo a structural transformation to the defect-cotunnite state under high pressure.