Electronic and Thermoelectric Properties of Layered Oxychalcogenides (BiO)Cu Ch ( Ch = S, Se, Te).

We study the new details of electronic and thermoelectric properties of polycrystalline layered oxychalcogenide systems of (BiO)Cu Ch ( Ch = Se, Te) prepared by using a solid-state reaction. The systems were characterized by using photoemission (PE) spectroscopy and four-probe temperature-dependent electrical resistivity ρ( T). PE spectra are explained by calculating the electronic properties using the generalized-gradient approximation method. PE spectra and ρ( T) show that (BiO)CuSe system is a semiconductor, while (BiO)CuTe system exhibits the metallic behavior that induces the high thermoelectric performance. The calculation of electronic properties of (BiO)Cu Ch ( Ch = S, Se, Te) confirms that the metallic behavior of (BiO)CuTe system is mainly induced by Te 5p states at Fermi energy level, while the indirect bandgaps of 0.68 and 0.40 eV are obtained for (BiO)CuS and (BiO)CuSe systems, respectively. It is also shown that the local symmetry distortion at Cu site strongly stimulates Cu 3d-t2g to be partially hybridized with Ch p orbitals. This study presents the essential properties of the inorganic systems for novel functional device applications.