title: Phase transformation and negative thermal expansion in TaVO5.
abstract: Two phase transformations of TaVO(5) were observed by DSC and/or dilatometry measurements in the studied temperature range. X-ray diffraction and neutron powder diffraction structure refinements indicated a phase transformation at -14 °C from a monoclinic symmetry with space group P2(1)/c to an orthorhombic symmetry with space group Pnma above this temperature. The rigid TaO(6) octahedron in orthorhombic phase becomes nonregular at -14 °C, which results in the transition from Pnma to P2(1)/c. TaVO(5) was found to be a negative thermal expansion material above room temperature. The calculated volumetric thermal expansion coefficients (TECs) are -8.92 × 10(-6) °C(-1) in the range of 20-600 °C, and -2.19 × 10(-5) °C(-1) above 600 °C, respectively. The negative thermal expansion behavior is accounted for by the tilt of the TaO(6) and VO(4) polyhedra, where the shrinkage of the VO(4) tetrahedra result in the increase of Ta-O-V angles on heating, while the angle of Ta-O1-Ta maintains at 180° in the framework.
authors.affiliation: Department of Physical Chemistry, University of Science and Technology Beijing, Beijing 100083, China.
authors.forename: Xiaowei
authors.initials: X
authors.lastname: Wang
authors.forename: Qingzhen
authors.initials: Q
authors.lastname: Huang
authors.forename: Jinxia
authors.initials: J
authors.lastname: Deng
authors.forename: Ranbo
authors.initials: R
authors.lastname: Yu
authors.forename: Jun
authors.initials: J
authors.lastname: Chen
authors.forename: Xianran
authors.initials: X
authors.lastname: Xing