Publication Date:
2016-01-08
Description:
Mott proposed that impurity bands in corundum-symmetry Ti 2 O 3 at high temperatures caused a collapse in the bandgap. However, the origin of the impurity bands has not yet been clarified. We examine the local structural properties of metal-to-insulator-transition Ti 2 O 3 using in-situ x-ray absorption fine structure (XAFS) measurements at the Ti K edge in the temperature range from 288 to 739 K. The Ti 2 O 3 powder is synthesized by using a chemical reaction method. X-ray diffraction (XRD) measurements from Ti 2 O 3 with a Rietveld refinement demonstrate a single-phased R-3c symmetry without additional distortion. Extended-XAFS combined with XRD reveals a zigzag patterned Ti position and an anomalous structural disorder in Ti-Ti pairs, accompanied by a bond length expansion of the Ti-Ti pairs along the c -axis for T 〉 450 K. The local structural distortion and disorder of the Ti atoms would induce impurity levels in the band gap between the Ti 3 d a 1g and e g π bands, resulting in a collapse of the band gap for T 〉 450 K.
Print ISSN:
0021-8979
Electronic ISSN:
1089-7550
Topics:
Physics
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