Pressure-temperature phase diagram of Ti2O3 and physical properties in the golden Th2S3-type phase

In this paper, the pressure and temperature conditions of the synthesis of a recently discovered golden Th2S3-type phase of titanium sesquioxide (Ti2O3) are studied, along with its physical properties. In combined x-ray diffraction and Raman high-pressure studies at room-temperature we found signatures of an isostructural transition at pressures near similar to 8-10 GPa. This finding was addressed to the well-known isostructural semiconductor-semimetal transition that occurs at ambient pressure near 400-450 K. Above similar to 10 GPa the golden phase was synthesized under appropriate heating. Based on both in-situ high-pressure high-temperature (HP-HT) studies in diamond anvil cells and ex-situ studies on samples synthesized at HP-HT conditions in multianvil cells, we constructed a pressure-temperature phase diagram of Ti2O3 for the first time. The samples of the golden polymorph were examined by Raman, absorption, and reflectance spectroscopy as well as by measurements of electrical resistivity, Hall effect, thermoelectric power (Seebeck effect), and magnetoresistance. In addition, electronic band-structure calculations were performed. We established that at ambient conditions the golden polymorph of Ti2O3 behaves as a semiconductor with an energy gap of similar to 0.1-0.2 eV and determined its typical electronic band structure parameters.