Summary:

This project focuses on the implementation of transverse thermoelectric effects on single-crystal semimetal microwires for localized electric energy generation and heat flux sensing. We intend to develop anisotropic thermoelectric generators (ATG) which will use human heat for generating voltages suitable for power supply of devices with low current consumption (for example, hearing aid). It can be used also in many other heat harvesting applications.

Theoretically, in thermoelectric crystals that are anisotropic, the electric potential is perpendicular to the thermal flow and proportional to the temperature difference between the isothermal faces, the thermopower anisotropy, and the length of the crystal and inversely proportional to the height of the crystal. An anisotropic thermoelement can be made from a single specimen of suitable dimensions without any thermoelectric junctions.

The practical utilization of this effect is new. In our preliminary work we developed a method to produce long, single crystalline, microwires of Bi and its alloys in glass coating using high frequency liquid phase casting in a glass capillary. The microwires were cylindrical single-crystals with trigonal axis C3 inclined to the wire axis at an angle of ~70o. The core diameters of the microwires can be in the range between 50 microns and 50 nanometers.

We have manufactured an experimental sample of ATG by winding the microwire into a flat spiral, in which the direction of heat flow was perpendicular to the plane of the spiral. During manufacture of the flat spiral the direction of the C3 axis was not controlled so when we tested the sample (we put the ATG in contact with a surface at 38 C (the temperature of the human hand) the output was only 3 mV (but theoretically, with the right crystalline orientation, the output should be ~1 V).

According to our investigation, the single-crystal Bi microwires transverse thermoelectric power is a maximum when the temperature gradient is towards the C3 axis. We have addressed this by improving our zone-melting recrystallization methods and constructed a new installation in which a molten zone scanned across the thin microwire being in a strong electric field up to 6*103 V/cm. As a result, after passing through this zone the main crystallographic axis C3 of the microwire change its direction according to the direction of the electric field. We will use this installation when we will make the ATG module.

The project involves collaborations in Moldova and international notably with T.E. Huber of HowardUniversity in the US; also involves development of technology for the production of long semimetal wires with thin glass cover and having special orientation of C3 axis relative to wires axis.

Our proposed project will have a significant effect on the development of infrastructure of science and engineering of Moldova. The proposed project aims to develop human resources and involves a number of undergraduates from the Moldova Technical University. Moldova has companies working with microwires (such as MicroFIR Technologies), and this project meets their activities.