Department of Physical Chemistry, University of Science and Technology Beijing, Beijing 100083, China.
Inorg Chem. 2011 Mar 21;50(6):2685-90. doi: 10.1021/ic200003n. Epub 2011 Feb 21.
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.
在研究的温度范围内，通过 DSC 和/或膨胀计测量观察到 TaVO(5)的两相同构转变。X 射线衍射和中子粉末衍射结构精修表明，在该温度以上，从空间群为 P2(1)/c 的单斜对称转变为空间群为 Pnma 的正交对称，在-14°C 时发生相转变。正交相中的刚性 TaO(6)八面体在-14°C 时变得不规则，导致从 Pnma 转变为 P2(1)/c。TaVO(5)在室温以上表现出负热膨胀特性。计算得到的体积热膨胀系数（TEC）在 20-600°C 范围内为-8.92×10(-6)°C(-1)，在 600°C 以上分别为-2.19×10(-5)°C(-1)。负热膨胀行为归因于 TaO(6)和 VO(4)多面体的倾斜，其中 VO(4)四面体的收缩导致 Ta-O-V 角在加热时增加，而 Ta-O1-Ta 角在框架中保持在 180°。
