Physical Properties of Cu_2-xTe: Charge Density Waves and Thermoelectric Potential

Ramesh Lalmani Yadav^1*, Yung-Kang Kuo¹, Chia-Nung Kuo², Chin-Shan Lue²

¹Physics, National Dong Hwa University, Hualien 97401, Taiwan
²Physics, National Cheng Kung University, Tainan 70101, Taiwan

* Presenter:Ramesh Lalmani Yadav, email:810814301@gms.ndhu.edu.tw

We conducted a comprehensive investigation of the Cu_2-xTe system with x ~ 0.11, uncovering its charge-density-wave (CDW) properties and thermoelectric potential over a temperature range from 10 K to 400 K. Our study unveiled distinct thermal hysteresis during heating and cooling cycles, likely due to a first-order transition. Upon heating, we observed commensurate CDW anomalies at transition temperatures T_CI (172 K) and T_CII (314 K), along with an incommensurate CDW transition at T^* (380 K), confirmed through temperature-dependent resistivity ρ(T), Seebeck coefficient S(T), thermal conductivity κ(T), and specific heat C_P(T) measurements. Below 35 K, the ρ(T) data exhibited a T² dependency, indicative of strong electron-electron correlations. Above 35 K, ρ(T) displayed a T^1.5 dependency, suggesting electron-phonon coupling. The S(T) data revealed diffusive behavior at lower temperatures and a change in sign at both T_CI and T_CII transitions, reflecting Fermi surface modifications. The κ(T) data indicated that heat conduction in the material was primarily due to phonons, with soft phonon modes dominating during the CDW transition. Furthermore, C_P(T) measurements confirmed a significant entropy change at T_CII compared to T_CI and T^* anomalies. Moreover, we observed a promising trend in the figure of merit, approaching 0.01 at 400 K due to the low κ(T) values, underscoring the material’s potential for thermoelectric applications. In summary, our study provides valuable insights into the temperature-dependent behavior of Cu_2-xTe, highlighting the impacts of strong correlations, superionic mobility, and electron-phonon interactions

Keywords: Charge-density-wave, Thermoelectric, Seebeck coefficient, Thermal conductivity, Specific heat