Axis-dependent carrier polarity in polycrystalline NaSn2As2

Abstract

Transverse thermoelectric devices consist of only one thermoelectric material, unlike conventional longitudinal thermoelectric devices that require two types of thermoelectric materials with p- and n-type polarities. However, scalable synthesis of materials that demonstrate axis-dependent carrier polarity, which is a prospective component to demonstrate the transverse thermoelectric device, is challenging. This paper reports that polycrystalline NaSn2As2, which was prepared by using uniaxial hot pressing, displayed axis-dependent carrier polarity. The preferred orientation of the sample was confirmed through x-ray diffraction measurements. Seebeck coefficient measurements indicate that carrier polarity depends on the measurement direction, which is consistent with recently reported results on single crystals of NaSn2As2. Given that our sample preparation procedure is readily scalable, the present work shows the possibility for preparing transverse thermoelectric devices using polycrystalline NaSn2As2 with a preferred orientation.