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.

• Received 30 November 2009

DOI:https://doi.org/10.1103/PhysRevB.80.212102