Two-Dimensional Layered Complex Nitrides as a New Class of Thermoelectric Materials

Two-dimensional layered materials are promising candidates for high-performance thermoelectric materials. We focus on AMN2 layered complex metal nitrides as a new class of two-dimensional materials. Density-functional theory and Boltzmann transport theory calculations of the electronic band structures and electronic transport coefficients for AMN2 (A = Sr, Ba; M = Ti, Zr, Hf) with a KCoO2 crystal structure showed that the electronic band structures and electronic transport properties were highly anisotropic. Large in-plane electronic transport and small electronic transport perpendicular to the layers along the c-axis arose from reduced electronic dispersion along the c-axis compared with other in-plane directions. A cylindrical constant-energy surface with an axis in the kz-direction perpendicular to the layer was found, indicating a two-dimensional electronic structure. The results suggest that excellent thermoelectric properties arise from the two-dimensional electronic structures in AMN2 layered complex metal nitrides.