Identification, structural characterization and transformations of the high-temperature Zn9−δSb7 phase in the Zn–Sb system

Abstract

The Zn_9−δSb₇ phase has been identified via high-temperature powder diffraction studies. Zn_9−δSb₇ adopts two modifications: an α form stable between 514 °C and 539 °C and a Zn-poorer β form stable from 539 °C till its melting temperature of 581 °C. The Zn_9−δSb₇ structure was solved from the powder data using the simulated annealing approach. Both modifications adopt the same hexagonal structure (P6/mmm) but with slightly different lattice parameters. The α-to-β transformation is abrupt and first-order in nature. The Zn atoms occupy the tetrahedral holes created by Sb atoms. The ideal Zn₉Sb₇ composition can be explained by its tendency to adopt a charge balance configuration. Out of 7 Sb atoms, 3 Sb atoms form dimers (Sb²⁻ ions) and 4 Sb atoms are isolated (Sb³⁻ ions), which require 9 Zn²⁺ cations for charge neutrality.