Electrical and thermal transport properties of a polycrystalline carrier-doped wide-gap semiconductor LaCu1-δ S0.5Se0.5O (δ = 0.01), in which the CuCh (Ch = S, Se) layer works as conducting layer, were measured at temperatures 473~673 K. The presence of δ = 0.01 copper defects dramatically reduces the electrical resistivity (ρ) to approximately one part per million compared to that of δ = 0 at room temperature. The polycrystalline δ = 0.01 sample exhibited ρ of 1.3 × 10-3 Ωm, thermal conductivity of 6.0 Wm-1 K-1, and Seebeck coefficient (S) of 87 μVK-1 at 673 K. The maximum value of the dimensionless figure of merit (ZT) of the δ = 0.01 sample was calculated to be 6.4 × 10-4 at T = 673 K. The ZT value is far smaller than a ZT ~ 0.01 measured for a nominal LaCuSeO sample. The smaller ZT is mainly due to the small S measured for LaCu1-δS0.5Se0.5O (δ = 0.01). According to the Debye model, above 300 K phonon thermal conductivity in a pure lattice is inversely proportional to T, while thermal conductivity of the δ = 0.01 sample increases with increasing T.

Abstract
1. Introduction
2. Experimental Procedure
3. Results and Discussion
    3.1. Results
    3.2. Discussion
4. Conclusion
Acknowledgement
References
Author Information

• Nobuhiko Azuma(Department of Applied Physics and Physico-Informatics, Faculty of Science and Technology, Keio University, Yokohama 223-8552, Japan) Corresponding author
• Hiroki Sawada(Department of Applied Physics and Physico-Informatics, Faculty of Science and Technology, Keio University, Yokohama 223-8552, Japan)
• Hirotaka Ito(Department of Applied Physics and Physico-Informatics, Faculty of Science and Technology, Keio University, Yokohama 223-8552, Japan)
• Ryosuke Sakagami(Department of Applied Physics and Physico-Informatics, Faculty of Science and Technology, Keio University, Yokohama 223-8552, Japan)
• Yuya Tanaka(Department of Applied Physics and Physico-Informatics, Faculty of Science and Technology, Keio University, Yokohama 223-8552, Japan)
• Tatsuhide Fujioka(Department of Applied Physics and Physico-Informatics, Faculty of Science and Technology, Keio University, Yokohama 223-8552, Japan)
• Masanori Matoba(Department of Applied Physics and Physico-Informatics, Faculty of Science and Technology, Keio University, Yokohama 223-8552, Japan, Center for Spintronics Research Network (CSRN), Keio University, Yokohama 223-8552, Japan)
• Yoichi Kamihara(Department of Applied Physics and Physico-Informatics, Faculty of Science and Technology, Keio University, Yokohama 223-8552, Japan, Center for Spintronics Research Network (CSRN), Keio University, Yokohama 223-8552, Japan)