Solid progress in research on the thermal motor of the beryllium copper mine

[ Instrument Network Instrument Development ] Recently, Qin Xiaoying, a researcher at the Institute of Solid State Physics, Hefei Institute of Material Science, Chinese Academy of Sciences, studied the thermoelectric properties of Cu12Sb4S13 in beryllium copper. When the S-site Se substitution and the Cu-site Zn substitution, the Cu3SbS4 impurity phase content was found. Significant changes occur, causing a change in the stoichiometry of the main phase, resulting in changes in S vacancies and hole concentrations. Finally, due to the optimization of carrier concentration, interface potential energy-dependent carrier scattering, the power factor is greatly improved, and the impurity and interface phonon scattering reduce the thermal conductivity, which improves the thermoelectric figure of Cu12Sb4S13. Related research results were published in Applied Physics Letters.

Figure (a) Cu12Sb4S13-xSex sample resistivity as a function of temperature; (b) electron concentration change due to S vacancies in Cu12Sb4S13-xSex sample; (c) Seebeck coefficient of Cu12Sb4S13-xSex sample as a function of temperature; (d) Relationship between power factor of Cu12Sb4S13-xSex sample with temperature

With the advancement of society, energy and environmental issues have become the most serious challenges facing humanity in the new century. Thermoelectric materials can be directly converted between thermal energy and electrical energy, and have the characteristics of small volume, high reliability, no emission of pollutants, wide temperature range, and environmental friendliness. In recent years, the beryllium copper ore Cu12Sb4S13 has attracted great attention due to its inexpensive constituent elements, low intrinsic lattice thermal conductivity and excellent electrical transport properties. Although Cu12Sb4S13 has an ultra-low lattice thermal conductivity, its thermoelectric performance is still low due to its high carrier concentration and low thermoelectric potential. At present, most of the research uses high-valent element Cu doping to reduce the optimized carrier concentration, increase the thermoelectric potential, and then improve the thermoelectric performance. However, few people have studied and paid attention to the substitution of elements in the formation of heterogeneous phase in the beryllium copper sample and its main phase. The effect of the stoichiometric ratio of Cu12Sb4S13 causes a change in thermoelectric properties.

Based on this, the research team prepared a series of Cu12Sb4S13 samples with different contents of Se and Zn in the S and Cu positions by melting and vacuum hot pressing. Studies have shown that in the same-price substitution (Se instead of S), the impurity phase Cu3SbS4 content changes significantly, which causes the change of the stoichiometric ratio of Cu12Sb4S13, which leads to the change of S vacancy d, the electron concentration caused by the change of S vacancy The change (Fig. 1(b)) optimizes the carrier concentration.

In order to further optimize and improve the thermoelectric performance of Cu12Sb4S13-xSex, the researchers selected the best performance samples (Cu12Sb4S12.8Se0.2) and replaced Cu1+ with Zn2+ to further optimize the carrier concentration and enhance the phonon impurities. Scattering; at the same time, the interface between the heterophase and the main phase caused by double substitution enhances phonon scattering and reduces thermal conductivity. In addition, the energy filtering effect caused by the interface potential causes an increase in the thermoelectric potential. The final double-substitute sample Cu12-yZnySb4S12.8Se0.2, (y=0.025 and 0.05) has a thermoelectric figure of 0.9 (723K), and the ZT value of the undoped sample (0.64) has increased by 41% (Fig. 2(c)). It indicates that the double substitution of elements can effectively regulate and improve the thermoelectric properties of beryllium copper.

This work is supported by the National Natural Science Foundation.

Fig. (a) The relationship between the total thermal conductivity of Cu12-yZnySb4S12.8Se0.2 sample and temperature; (b) The relationship between the thermal conductivity of Cu12-yZnySb4S12.8Se0.2 sample with temperature; (c) Cu12- yZnySb4S12.8Se0.2 sample thermoelectric figure of merit as a function of temperature; (d) the maximum ZT value we obtained and the maximum ZT value of the reported high performance Cu12Sb4S13 material