Structural, electrical, and thermoelectric properties of distorted 1T-Ta_1−xNb_xTe₂ single crystals

¹ Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences Hefei 230031, PRC
² High Magnetic Field Laboratory, Chinese Academy of Sciences - Hefei 230031, PRC
³ Collaborative Innovation Centre of Advanced Microstructures, Nanjing University - Nanjing 210093, PRC

^(a) wjlu@issp.ac.cn
^(b) ypsun@issp.ac.cn

Received: 20 October 2014
Accepted: 18 December 2014

Abstract

A series of isovalent Nb-substituted Ta_1−xNb_xTe₂ ($0 \leq x \leq 1$ ) single crystals, which crystallizes in a monoclinically distorted CdI₂-type structure with the $C2/m$ space group, were grown by the chemical-vapor-transport (CVT) method. For TaTe₂ ($x = 0$ ), a first-order transition at ${\sim}178\ \text{K}$ is observed by heat capacity $(C_{\text{p}})$ measurement, accompanying with an anomaly in electrical resistivity $(\rho)$ , Hall resistivity $(R_{\text{H}})$ , and especially, the sign change of thermoelectric power $(S)$ , implying the multi-band transport. This transition can be gradually suppressed by isovalent Nb substitution and disappears as $x \geq 0.2$ , and correspondingly, an enhancement of electronic density of states (DOS) near the Fermi level is obtained. In addition, the local Ta-Te/Ta-Ta bonding instability may play an important role for the structural phase transition of TaTe₂.