Identifying the Point Defects in Single-Crystalline Mg₃Sb₂

Point defects play a critical role in the transport properties of Mg 3 Sb 2 -based thermoelectric materials. However, the determination of point defects is rather challenging. Herein, Mg 3 Sb 2 single crystals were prepared by the self-flux method with the Sb flux (p-type sample) and Mg flux (n-type sample). The crystal structure as well as the atomic occupancy parameters of these samples were determined by single-crystal and synchrotron powder X-ray diffractions. Comparison between the experimental and calculated Fourier electron density maps generated by single-crystal data indicates the existence of Mg interstitials [1/3, 2/3, 0.38(3)] and vacancies at the Mg2 sites [2/3, 1/3, 0.8653(3)] in the n-type sample and Mg vacancies at both the Mg1 and Mg2 sites in the p-type sample. In addition, differences in the peak positions and intensities of the two types of Mg–Sb vibration modes in Raman spectra were observed between different Mg 3 Sb 2 crystals, which suggests that point defects can impact the vibration modes.