Electronic structure ofCsBi4Te6: A high-performance thermoelectric at low temperatures

Abstract

proved figure of merit for the former may be of electronic origin. In this paper we discuss the results of ab initio electronic structure calculations in this rather complex material: We find a large anisotropy in the carrier effective masses, which can explain the large value of ZT seen in the hole doped systems. Our electronic structure calculations suggest that the holes near the top of the valence band ~responsible for thermoelectric properties of p-doped samples! move in quasi-two-dimensional layers which are separated by poorly conducting regions of about 13 A width. Surprisingly, the layers in which the charges are confined to move are almost perpendicular to the crystallographic layers formed by Bi-Te slabs separated by layers of Cs ions. This, as we will show, is due to the presence of Bi-Bi bonds which is unique for systems consisting of Bi/Te networks. Indeed, the novel quantum architecture of CsBi4Te6 provides the possibility of using a bulk material for fabrication while the reduced dimensionality of the charge transport enhances the thermoelectric properties.