In situ high-pressure x-ray-diffraction study of TlReO₄ to 14.5 GPa: pressure-induced phase transformations and the equation of state

Abstract

In situ high-pressure x-ray-diffraction studies have been carried out on TlReO₄ up to 14.5 GPa at room temperature using a diamond-anvil cell. The x-ray data show that the orthorhombic D_2h¹⁶ TlReO₄ (I) transforms to another closely related orthorhombic phase, TlReO₄ (I') around 1.0 GPa, then to a wolframite-related monoclinic phase TlReO₄ (II) near 2.0 GPa, and finally to a BaWO₄ (II)-related monoclinic phase TlReO₄ (III) at about 10 GPa. The volume change at the first transition is negligible, and about 2% and 9%, respectively, at the two subsequent transitions. The results suggest a very minor change in structure at the first transition. The 2% ΔV at the second transition is consistent with the proposed structural arrangement from pseudoscheelite phase (I') to the wolframite phase (II). The large ΔV at the third transition is attributed to a change to a truly octahedral coordination for Re with respect to oxygens. All the three high-pressure phases of TlReO₄ are unquenchable and revert back to the low-pressure orthorhombic phase (I) on release of pressure. The results are in very good agreement with those obtained in a previous high-pressure Raman study up to 15 GPa. From pressure-volume data, we obtain a value of 26 GPa for the bulk modulus K₀ of phases (I) and (I'). The bulk moduli of phases (II) and (III) have been calculated as 45.6 and 47.6 GPa, respectively.