Thermoelectric Properties of N-type Mg₃La_0.005Mn_xSbBi Materials Doped with La and Mn

Mg3Sb2-based n-type materials are consisted of earth-abundant elements and possess comparable thermoelectric properties with n-type Bi2Te3 at low temperatures, which make them promising candidates for cooling and power generation applications in terms of cost and performance. Substitution of Sb atom with chalcogen elements (Te, Se S) is a conventional method for n-type doping, but doping cations such as rare-earth elements and transition metals is also widely studied for its unique advantages. In this study, La and Mn were selected for co-doping of Mg3SbBi, and the thermoelectric performances of the doped materials were investigated. Mg3La0.005MnxSbBi (0 <= x <= 0.015) polycrystalline samples were made by sintering the fine powders of the mother alloy after arc melting, in which elemental Mn and LaSb compound were included for n-type dual doping. Considering the loss of Mg at elevated temperatures by vaporization, the molar ratio of Mg, Sb, and Bi in the mixture for arc melting was set to 4 : 1 : 1 with excess Mg. Analysis shows that all the samples are n-type, and the electrical conductivity of Mg3La0.005Mn0.015SbBi increased by 62% from the Mn-free Mg3La0.005SbBi at 298 K. In addition, the lattice thermal conductivity (kappa(lat)) decreased with increasing Mn content in the measured temperature range of 298-623 K. The minimum value of kappa(lat) was about 0.60 W m(-1)K(-1) in Mg3La0.005Mn0.015SbBi at 523 K, which is about 19% smaller than that of the Mn-free sample. As a result of these enhancements in thermoelectric performance, the maximum figure of merit (zT(max)) of 1.12 was obtained in Mg3La0.005Mn0.01SbBi and Mg3La0.005Mn0.015SbBi at 573 K, and the zT at 298 K increased by 73% to 0.35 in Mg3La0.005Mn0.015SbBi compared to Mn-free Mg3La0.005SbBi, which is beneficial to room-temperature applications.