High-pressure structural and elastic properties of Tl2O3.

The structural properties of Thallium (III) oxide (Tl₂O₃) have been studied both experimentally and theoretically under compression at room temperature. X-ray powder diffraction measurements up to 37.7GPa have been complemented with ab initio total-energy calculations. The equation of state of Tl₂O₃ has been determined and compared to related compounds. It has been found experimentally that Tl₂O₃ remains in its initial cubic bixbyite-type structure up to 22.0GPa. At this pressure, the onset of amorphization is observed, being the sample fully amorphous at 25.2GPa. The sample retains the amorphous state after pressure release. To understand the pressure-induced amorphization process, we have studied theoretically the possible high-pressure phases of Tl₂O₃. Although a phase transition is theoretically predicted at 5.8GPa to the orthorhombic Rh₂O₃-II-type structure and at 24.2GPa to the orthorhombic α-Gd₂S₃-type structure, neither of these phases were observed experimentally, probably due to the hindrance of the pressure-driven phase transitions at room temperature. The theoretical study of the elastic behavior of the cubic bixbyite-type structure at high-pressure shows that amorphization above 22GPa at room temperature might be caused by the mechanical instability of the cubic bixbyite-type structure which is theoretically predicted above 23.5GPa. [ABSTRACT FROM AUTHOR]