High-pressure behavior of structural, optical, and electronic transport properties of the golden Th2S3-type Ti2O3
Physical Review B
Recently, a golden colored, dense polymorph of titanium sesquioxide, Ti 2 O 3 with a Th 2 S 3 -type structure, has been synthesized at high-pressure high-temperature conditions. In this paper, we present results of investigations of structural, optical, and electronic transport properties of this unusual golden polymorph of Ti 2 O 3 under high pressure. Several experimental techniques were used, including x-ray diffraction studies using synchrotron radiation, Raman spectroscopy, electrical
... tivity, and thermoelectric power. The structural studies showed that the Th 2 S 3 -type lattice is conserved under pressure, while it is subjected to an isostructural phase transition with a ∼0.7% volume drop at 38.5 GPa. We speculated that this transition could be driven by the s → d electron transfer in the Ti atoms. For the Th 2 S 3 -type Ti 2 O 3 , we have established a bulk modulus value, B 0 = 258.3 GPa at B 0 = 4.1. A full profile analysis of the diffraction patterns allowed us to discover anomalies in the compression behavior of the Th 2 S 3 -type structure. The bond valence sums method suggested that at ambient conditions the Ti cations have predominantly Ti 3+ oxidation state, but applied pressure stimulates a partial charge disproportionation between the Ti1 and Ti2 sites achieving the maximal effect-reduction of the Ti1 cations to ∼Ti 2.5+ and oxidation of the Ti2 ones to ∼Ti 3.5+ near 14 GPa. Pressure evolution of Raman spectra across the above crossovers showed distinct changes corroborating the above findings. The high-pressure electronic transport studies confirmed that the Th 2 S 3 -type Ti 2 O 3 remains semiconducting up to 21 GPa at ambient and low temperatures down to 4.2 K. These studies found additional features, e.g., in the activation energy curve near 7 GPa, that is accompanied by inversion of the dominant conductivity type from electron to hole. The intriguing high-pressure behavior of Ti 2 O 3 with the Th 2 S 3 -type structure can contribute to better understanding of high-pressure properties of transition-metal sesquioxides.