Ab initio investigation of phase stability of Y2Ti2O7 and Y2Zr2O7 under high pressure

The phase stabilities of Y2Ti2O7 and Y2Zr2O7 under high pressure were investigated by ab initio methods. Pyrochlore-structured Y2Ti2O7 and defect-fluorite Y2Zr2O7 exhibit different responses to high pressure. Both the defect-fluorite and defect-cotunnite structures are energetically more stable at high pressure in Y2Ti2O7, but comparison with experimental results suggest that only the transformation to the defect-fluorite structure is kinetically favored. For Y2Zr2O7, the defect-fluorite phase should undergo a structural transformation to the defect-cotunnite state under high pressure.