Abstract
Ab initio total energy calculations have been performed to study the phase stability of Gd2Ti2O7
and Gd2Zr2O7 pyrochlores over the pressure range from 0 to 60 GPa. Both compounds are
unstable under pressure, and phase transformations to the defect-cotunnite structure are
predicted. The phase transformation pressure of 43.6 GPa for Gd2Ti2O7 is considerably larger
than the value of 13 GPa for Gd2Zr2O7, in good agreement with experiments. The decreased
structural stability of Gd2Zr2O7 under pressure, relative to Gd2Ti2O7, is a consequence of the
lower compressibility of the Zr–O bond and the higher compressibility of the Gd–O bond.
In addition, the Gd 4f electrons are found to have only a small effect in determining the pressure
induced phase transformation.