Zn₁₃Sb₁₀: A Structural and Landau Theoretical Analysis of Its Phase Transitions

Composition, crystal structures, polymorphic transformations, and stability of the thermoelectric material known in the literature as “Zn 4 Sb 3 ” have been studied on a polycrystalline sample and Bi-flux-grown single crystals using X-ray diffraction techniques, resistance, and Seebeck coefficient measurements at various temperatures ranging from 4 to 773 K. Microprobe analysis yields the composition of the flux-grown crystals to be close to Zn 13 Sb 10, with minor Bi doping. High-temperature X-ray and Seebeck coefficient studies show that the phase is unstable at high temperatures in a vacuum because of Zn losses. Both X-ray diffraction and resistivity measurements indicate the presence of two consecutive symmetry-breaking transitions below room temperature, in agreement with our previous results on polycrystalline samples. Application of Landau theory suggests that the first R 3̄ c → C 2/ c symmetry breaking may be second-order in nature. The second, low-temperature symmetry breaking may proceed along two routes. One of these pathways, a first-order C 2/ c → C 1 symmetry reduction, may lead to an incommensurate structure and is consistent with our experimental observations.