Origin of Projected Excellent Thermoelectric Transport Properties in d0-Electron AMN2 (A = Sr or Ba; M = Ti, Zr, Hf) Layered Complex Metal Nitrides

Layered materials have several properties that make them suitable as high-performance thermoelectric materials. In this study, we elucidated the potential of d(0)-electron layered complex metal nitrides, AMN(2) (A = Sr or Ba; M = Ti, Zr, Hf), with KCoO2-type and -NaFeO2-type crystal structures. The detailed electronic structures and electronic transport coefficients for AMN(2) compounds were calculated by using density-functional theory and Boltzmann theory, respectively. The KCoO2-type AMN(2) compounds show highly anisotropic thermoelectric properties. The effective masses at the lowest conduction bands in both KCoO2-type and -NaFeO2-type AMN(2) compounds were significantly smaller than that in three-dimensional perovskite SrTiO3, a well-known compound with good thermoelectric properties. The results suggest that the excellent thermoelectric transport properties arise from appropriate electronic structures and small effective masses in AMN(2) layered complex metal nitrides.