Monoclinic–triclinic phase transition induced by pressure in fergusonite-type YbNbO₄

Abstract

We have carried out a high-pressure study on fergusonite-type YbNbO4. Synchrotron powder x-ray diffraction experiments and density-functional theory simulations have been performed. We found a gradual increase of symmetry under compression, with calculations predicting a second-order monoclinic-tetragonal transition at 15 GPa. However, experiments provided evidence of a transition at 11.6 GPa to a triclinic structure, described by space group P1-. The appearance of the triclinic phase seems to be related to the presence of non-hydrostatic stresses. The triclinic high-pressure phase remains stable up to 31.9 GPa and the phase transition is not reversible. We have determined the pressure dependence of unit-cell parameters of both phases and calculated their room-temperature equation of state. For the fergusonite-phase we have also obtained the isothermal compressibility tensor. In addition to the high-pressure studies, we report ambient-pressure Raman and infrared spectroscopy measurements which have been compared with density-functional theory calculations.

Exploring the crystal structure and properties of ytterbium orthoantimonate under high pressure

“…The high-pressure (HP) behaviour of MTO 4 bimetal oxides has been the focus of research interest during the last two decades. 1,2 The main objects of study have been phosphates, 3,4 vanadates, 5,6 tungstates, 7,8 molybdates, 9,10 chromates, 11,12 niobates, 13,14 and tantalates. 15,16 On the other hand, a group of compounds that have been barely studied under HP are orthoantimonates, among which only BiSbO 4 has been studied.…”