n-type thermoelectric material Mg₂Sn₀.₇₅Ge₀.₂₅ for high power generation

• Published in: Proceedings of the National Academy of Sciences - PNAS 2015-03, Vol.112 (11), p.3269-3274
• Main Authors: Liu, Weishu, Kim, Hee Seok, Chen, Shuo, Jie, Qing, Lv, Bing, Yao, Mengliang, Ren, Zhensong, Opeil, Cyril P, Wilson, Stephen, Chu, Ching-Wu, Ren, Zhifeng
• Format: Article
• Language: English
• Subjects: Physical Sciences
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1424388112

Thermoelectric power generation is one of the most promising techniques to use the huge amount of waste heat and solar energy. Traditionally, high thermoelectric figure-of-merit, ZT , has been the only parameter pursued for high conversion efficiency. Here, we emphasize that a high power factor ( PF ) is equivalently important for high power generation, in addition to high efficiency. A new n-type Mg ₂Sn-based material, Mg ₂Sn ₀.₇₅Ge ₀.₂₅, is a good example to meet the dual requirements in efficiency and output power. It was found that Mg ₂Sn ₀.₇₅Ge ₀.₂₅ has an average ZT of 0.9 and PF of 52 μW⋅cm ⁻¹⋅K ⁻² over the temperature range of 25–450 °C, a peak ZT of 1.4 at 450 °C, and peak PF of 55 μW⋅cm ⁻¹⋅K ⁻² at 350 °C. By using the energy balance of one-dimensional heat flow equation, leg efficiency and output power were calculated with T ₕ = 400 °C and T c = 50 °C to be of 10.5% and 6.6 W⋅cm ⁻² under a temperature gradient of 150 °C⋅mm ⁻¹, respectively. Significance Thermoelectric materials have been extensively studied for applications in conversion of waste heat into electricity. The efficiency is related to the figure-of-merit, ZT = ( S ²σ / κ ) T , where S , σ , and κ are the Seebeck coefficient, electrical conductivity, and thermal conductivity, respectively. Pursuing higher ZT for higher efficiency has been the focus by mainly reducing the thermal conductivity. In this paper, we point out, for a given ZT , higher power factor ( S ²σ ) should be pursued for achieving more power because power is determined by ( T ₕ − T c) ²( S ²σ )/ L , where T ₕ, T c, and L are the hot and cold side temperatures, and leg length, respectively. We found a new material, Mg ₂Sn ₀.₇₅Ge ₀.₂₅, having both high ZT and high power factor.