Anisotropic thermoelectric devices based on single-crystal BI microwires and films

Abstract

Here, we present a demonstration of an unconventional thermoelectric energy conversion that is based on a single element made of an anisotropic material. In such materials, a heat flow generates a transverse thermoelectric electric field lying across the heat flow. A feature of anisotropic

thermoelectrics is that the thermoelectric voltage is proportional to the element length and inversely proportional to the effective thickness. We have prepared an experimental sample consisting of a 10-m-long glass-insulated single-crystal tin-doped bismuth microwire (D=20 μm, d=4 μm) [1,2].

Crucial for this experiment is the ability to grow the microwire as a single- crystal using a technique of recrystallization with laser heating and under a strong electric field. The sample was wound as a

spiral, bonded to a copper disk, and used in various experiments. The sensitivity of the sample to heat flow is as high as 10-2 V/W with a time constant s of about 0.5 s. Polycrystalline Bi films with a thickness of 2-5 μm were deposited on the mica support by the vacuum thermal evaporation

method. Experimental samples of heat flux sensors were made on the basis of recrystallized Bi films under laser heating and in a strong electric field. The dynamics of voltage changes at the output of the developed heat flux sensors during the registration of modulated heat fluxes can be explained in the limit of the theory of an anisotropic thermoelement.