High-pressure behavior of structural, optical, and electronic transport properties of the golden Th2S3-type Ti2O3

Article

关键词: HIGH-TEMPERATURE SYNTHESIS;    POST-PEROVSKITE PHASE;    X-RAY-DIFFRACTION;    CRYSTAL-STRUCTURE;    CHARGE-TRANSFER;    TRANSITION;    TRANSFORMATION;    STABILITY;    CONDUCTIVITY;    POLYMORPH;   

DOI  :  10.1103/PhysRevB.88.184106

来源: SCIE

【 摘 要 】

Recently, a golden colored, dense polymorph of titanium sesquioxide, Ti2O3 with a Th2S3-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 Ti2O3 under high pressure. Several experimental techniques were used, including x-ray diffraction studies using synchrotron radiation, Raman spectroscopy, electrical resistivity, and thermoelectric power. The structural studies showed that the Th2S3-type lattice is conserved under pressure, while it is subjected to an isostructural phase transition with a similar to 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 Th2S3-type Ti2O3, we have established a bulk modulus value, B-0 = 258.3 GPa at B-0(1) = 4.1. A full profile analysis of the diffraction patterns allowed us to discover anomalies in the compression behavior of the Th2S3-type structure. The bond valence sums method suggested that at ambient conditions the Ti cations have predominantly Ti3+ oxidation state, but applied pressure stimulates a partial charge disproportionation between the Ti-1 and Ti-2 sites achieving the maximal effect-reduction of the Ti-1 cations to similar to Ti2.5+ and oxidation of the Ti-2 ones to similar to Ti3.5+ 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 Th2S3-type Ti2O3 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 Ti2O3 with the Th2S3-type structure can contribute to better understanding of high-pressure properties of transition-metal sesquioxides.

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