Thermal Transport Properties of a Mixed Anion Layered Compound, Polycrystalline LaCu_1-δS_0.5Se_0.5O (δ = 0.01)

Electrical and thermal transport properties of a polycrystalline carrier-doped wide-gap semiconductor LaCu_1-δ S_0.5Se_0.5O (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 LaCu_1-δS_0.5Se_0.5O (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.