Pressure-induced structural transitions in Tb-pyrochlore oxides

The structure of Tb 2 Ti 2 O 7 , Tb 2 Sn 2 O 7 , and Tb 2 TiSnO 7 were studied at high pressures ( P < 1 Mbar ) using synchrotron radiation and angular dispersive x-ray diffraction. The cubic lattice was shown to distort into a monoclinic phase before exhibiting total structural disorder (amorphization) in all three samples. Our experiments demonstrate that partial replacement of Sn with Ti significantly enhances the bulk modulus and increases the structural stability (crystalline state) to much higher pressures. Furthermore, pressure induces anion before cation disorder during the order-disorder transition. These results are compared to radiation damage studies that show order-disorder transitions.