Discovery of a Compound near Mg₃Sb₂ in the Mg-Sb-Ni System: The Crystal Structure, Stability, and Thermoelectric...

Thermoelectric conversion technology has tremendous potential for applications in energy and environmental fields. However, conventional thermoelectric materials suffer from drawbacks of toxic constituents and prohibitive costs. Consequently, the development of novel thermoelectric candidate materials has become increasingly important. In this study, we explored the Mg-Sb-Ni system and discovered a new thermoelectric compound, Mg₆Ni_0.9Sb_2.1, with composition close to Mg₃Sb₂. Differential scanning calorimetry measurements confirm the thermal stability of this compound below 883 K. The crystal structure was determined to be hexagonal (space group P6̅2m, no. 189) with Ni and Sb occupying mixed lattice sites, as revealed by Rietveld refinement analysis of synchrotron X-ray diffraction data. X-ray photoelectron spectroscopy analysis suggests a charge transfer from Mg to Sb, while density functional theory calculations predict metallic properties with lone pair electrons uniformly distributed around Sb atoms. Seebeck coefficient measurements identify Mg₆Ni_0.9Sb_2.1 as an n-type thermoelectric material. Comprehensive electrical property characterization reveals metallic behavior with an exceptionally high electrical conductivity of 1.572 × 10⁵ S/m at 298 K. Although Mg₆Ni_0.9Sb_2.1 exhibits limited thermoelectric performance, its metallic nature and compositional proximity to Mg₃Sb₂ make it useful as a second phase for enhancing Mg₃Sb₂'s thermoelectric performance by altering phase boundaries. This discovery validates the strategy of exploring ternary Mg-Sb-based systems for novel thermoelectric material development.