Pressure evolution of two polymorphs of Tb_2(MoO_4)_3

摘要

We have studied the high pressure behavior of the α and β'-phases of Tb_2(MoO_4)_3 using a combination of powder X-ray diffraction and ab initio calculations. The α-Tb_2(MoO_4)_3 phase did not undergo any structural phase transition in the pressure range from 0 up to the maximum experimental pressure of 21 GPa. We observed line broadening of the diffraction patterns at pressures above 7 GPa, which may be due to non-hydrostatic conditions. The complete amorphization of the sample was not reached in the pressure range studied, as expected from previous Raman studies. The behavior under pressure of the β'-Tb_2(MoO_4)_3 phase is similar to that of other rare-earths trimolybdates with the same structure at room temperature. A phase transition was observed at 2 GPa. The new phase, which can be identified as the δ-phase, has never been completely characterized by diffraction studies. A tentative indexation has been performed and good refined cell parameters were obtained. We detect indications of amorphization of the δ-Tb_2(MoO_4)_3 phase at 5 GPa.