Pressure evolution of two polymorphs of Tb2(MoO4)3

We have studied the high pressure behavior of the alpha and beta'-phases of Tb (2)(MoO (4))(3) using a combination of powder X-ray diffraction and ab initio calculations. The alpha-Tb-2(MoO4)(3) phase did not undergo any structural phase transition in the pressure range from 0 up to the maximum experimental pressure of 21GPa. We observed line broadening of the diffraction patterns at pressures above 7GPa, 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 beta'-Tb-2(MoO4)(3) phase is similar to that of other rare-earths trimolybdates with the same structure at room temperature. A phase transition was observed at 2GPa. The new phase, which can be identified as the delta-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 delta-Tb-2(MoO4)(3) phase at 5GPa.