New discoveries in the ternary transition metal pnictide class of Zintl phases

Abstract

The crystal structures of the new intermetallic compounds Eu2ZnPn2 (Pn = Sb, Bi) and Sr2ZnPn2 (Pn = Sb, Bi) are reported. They have been synthesized from their corresponding elements through high-temperature reactions using the flux-growth method. The structures for Eu2ZnPn2 (Pn = Sb, Bi) and Sr2ZnPn2 (Pn = Sb, Bi) have been established by single-crystal X-ray diffraction. In those cases, the X-ray patterns can be successfully indexed based on a hexagonal cell with unit cell parameters in the range a=4.6-4.7 Å and c=8.2-8.5 Å. Structure solutions in the space group P63/mmc suggest the defect ZrBeSi type (Pearson's symbol hP6; 3 unique positions) as the likely model; however, subsequent refinements indicate nearly 50% occupancy on the Zn site. Based off the evidence that I will present in the following paper, I believe it is plausible that the crystal structures of the reported compounds have a long-range order of zinc-vacancies. These systematic vacancies further suggest the compounds may have thermoelectric properties. Evidence for such was sought using powder X-ray diffraction, single crystal X-ray diffraction, electron diffraction, X-ray dispersive spectroscopy, and magnetic susceptibility measurements.