  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
NaSn$_2$As$_2$, 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 NaSn$_2$As$_2$. Given that our sample preparation procedure is
readily scalable, the present work shows the possibility for preparing
transverse thermoelectric devices using polycrystalline NaSn$_2$As$_2$ with a
preferred orientation.
