Study on Thermoelectricc Properties of Mg2(Sn,Si,Ge) for power generation applications
The environmental impact caused by burning fossil fuel is increasing at an alarming rate. During the production of electricity most of the energy is lost as heat. Thermoelectric devices can convert heat into electrical energy and vice versa. In the past decade there has been extensive research work to improve the efficiency of thermoelectric materials. Thermoelectric devices are vastly used in deep space satellites for power generation due to its reliability in long term operation. Recently, n-type Mg2Sn0.75Ge0.25 has been reported as a promising thermoelectric material system in the temperature range from 300 K to 723 K. By ball milling and hot pressing, the pure phase of Mg2Sn0.75Ge0.25 can be obtained. In this study, we reported that the right choice of carrier and doping site is crucial to obtain better thermoelectric performance. Bi-doping to the Sn-site showed a peak power factor (PF) ~54 µW cm-1 K-2 at 577 K and a peak figure of merit (ZT) ~1.4 at 673 K which corresponds to a conversion efficiency of 12%. Significantly improved peak power factor led to higher power output which is beneficial for device application. For applications, thermoelectric generators should consist of both n- and p-type legs with equal performance. Motivated by the promising thermoelectric performance of the n-type Mg2Sn0.75Ge0.25, we explored the thermoelectric performance of the p-type by doping Li, Na, and Ga. Li-doping showed a better peak power factor (PF) ~18 μW cm-1 K-2 and a peak figure of merit (ZT) ~0.5 at 723 K compared to Na- and Ga-doping.Relatively high carrier concentrations have been achieved for Li-doped compounds. We have further analyzed the thermoelectric performance of Mg2Sn0.6Si0.4 and Mg2Sn0.6Ge0.4 upon Li-doping. Mg2Sn0.6Ge0.4 showed a higher peak power factor compared to Mg2Sn0.6Si0.4, due to the higher mobility. For both systems optimum carrier concentration has been achieved and Li-doping successfully improved the peak figure of merit (ZT) to ~0.5 at 700 K. This work highlights preferable dopants and doping sites to obtain better thermoelectric performance of n-type and p-type Mg2(Sn,Si,Ge). This detailed study also explores the possibility of using these material systems for practical applications.
Thermoelectric generators (TEG), Power factor, Efficiency
Networked Digital Library of Theses and Dissertations