Doped TiO2-Ge nanocomposites for thermoelectric applications

Hackendorn, Robert
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University of Delaware
Titanium dioxide has shown promise as the basis for a thermoelectric material as it is an excellent thermal insulator and is able to be alloyed, in this case with germanium, to enhance electrical properties. In general, this thermoelectric material will produce an electrical potential when there exists a temperature gradient across the material. As such, it is important for the material to have a high electrical conductivity and a low thermal conductivity, creating a conflict since these properties naturally increase or decrease simultaneously. RF sputtering has shown to be an efficient way of synthesizing TiO2-Ge thin films in such a way that the electrical properties are enhanced while minimally altering the thermal properties as compared to bulk TiO2. Films were deposited onto quartz substrates for two hours and heated to 600oC with RF power of 200W sent through the magnetron sputtering gun. Films at three different pressures, 5mtorr, 10mtorr, and 15mtorr were deposited with target TiO2:Ge:Sb compositions of 55:45:0, 30:70:0 and 54:45:1. The final composition introduced antimony as a dopant to enhance the electrical conductivity. Significant increases in the electrical conductivity was seen in the films as compared to bulk TiO2, and a slight increase was seen between the undoped to doped samples. The Seebeck measurements for each sample offered a positive trend in measurements up to 200oC, which is promising for higher temperature applications. Lastly, the amorphization of TiO2 can be seen while maintaining Ge crystallinity, which is promising for obtaining low thermal conductivity.