Switching effect in transverse thermopower in single-crystal Bi microwires

Abstract

At room temperature we have investigated the transverse thermopower in thin single-crystal bismuth microwires for the purpose of using a microwire of bismuth to design an anisotropic thermoelectric generator. The single-crystal nanowire samples in the diameter range 2 - 15 μm were prepared by the high frequency liquid phase casting in a glass capillary using an improved Ulitovsky technique; they were cylindrical single-crystals with (1011) orientation along the wire axis. Bismuth microwire was placed between two polished aluminum plates, which were at different temperatures. At relative displacement of the plates the microwire was rotated around its axis. Transverse thermoelectric power varied by rotating microwires. The maximum thermoelectric power (Smax ∼ 200 – 600 μV/K at the length of the plates L = 4.5 cm) occurred at the direction of the transverse temperature gradient along the C3 axis. For the first time significant difference was found in the values of the thermoelectric power after turning micrwires at 180 degrees (i.e. when the direction of the temperature gradient is reversed). The value of this switching effect, defined by us as (‖Smax|−|Smin‖)/(|Smax|+|Smin|), depends on the diameter d microwire and varies from 0.4 (for microwires with d = 14 μm) to 0.75 for microwires with d = 5 μm. Different assumptions about the nature of the observed effect will be discussed.