ICT2014 Abstracts

Layered compounds tend to have superior thermoelectric transport properties such as complex cobalt oxides, complex metal chalcogenides, and misfit layered compounds etc.[1] There are many complex metal nitrides with layered crystal structures, and they exhibit diverse properties.[2] In this study, we propose two-dimensional layered complex nitrides, SrTiN₂ with a KCoO₂ crystal structure as a new class of thermoelectric materials, using electronic structure and transport calculations based on density functional theory (DFT) and Boltzmann theory. We compare the chemical and crystal structure and the thermoelectric properties of the nitrides with those of the three-dimensional perovskite oxide, SrTiO₃, for which the electronic band structure and good thermoelectric properties have been well characterized. The electronic band structures and electronic transport properties of SrTiN₂ 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 k_z-direction perpendicular to the layer was found, indicating a two-dimensional electronic structure. Larger thermopower in SrTiN₂ was obtained than that in SrTiO₃. The results suggest that excellent thermoelectric properties arise from the two-dimensional electronic structures in SrTiN₂ layered complex metal nitrides.[3]

Reference

[1] K. Koumoto, T. Mori, Thermoelectric Nanomaterials, Springer, Heidelberg, Germany, 2013.

[2] R. Niewa, F. J. DiSalvo, Chem. Mater. 10, 2733 (1998).

[3] Isao Ohkubo and Takao Mori, Chem. Mater. in press.