Three-dimensionality of electronic structures and thermoelectric transport in SrZrN₂ and SrHfN₂ layered complex metal nitrides.

Abstract

Layered materials have several properties that make them suitable as high-performance thermoelectric materials. In this study, we focus on the complex metal nitrides SrZrN2 and SrHfN2, which have an α-NaFeO2 layered crystal structure. To determine their electronic band structure features and potential thermoelectric transport properties, we calculated the electronic band structures and electronic transport coefficients for SrZrN2 and SrHfN2 using density-functional theory and Boltzmann transport theory, respectively. Despite the layered crystal structure, SrZrN2 and SrHfN2 both had three-dimensional electronic structures and isotropic electronic transport because of the contribution of the Sr 4d(x(2)-y(2)) + 4d(xy) orbitals to the bottom of the conduction bands in addition to that of the Zr 4d(z)(2) (Hf 5d(z)(2)) orbital. The three-dimensional electronic structures predict the appearance of large Seebeck coefficients (-145 μV K(-1) at 300 K, -370 μV K(-1) at 1200 K) and large electronic thermoelectric figures of merit.