Novel ternary alkaline-earth and rare-earth metal antimonides from gallium or indium flux. Synthesis, structural characterization and 121Sb and 151Eu Mossbauer spectroscopy of the series A7Ga8Sb8 (A = Sr, Ba, Eu) and Ba7In8Sb8

Reported are the synthesis and the structural characterization of the new ternary antimonides Eu7Ga8Sb8, Sr7Ga8Sb8, Ba7Ga8Sb8, and Ba7In8Sb8. They have been synthesized from reactions of the corresponding elements, using gallium or indium as metal fluxes. The four compounds are isostructural and crystallize with the space group P6(3)/mmc (no. 194) with lattice parameters as follows: a = 4.4942(8), c = 17.274(6) angstrom for Eu7Ga8Sb8; a = 4.5409(8), c = 17.486(4) angstrom for Sr7Ga8Sb8; a = 4.7045(12), c = 18.123(9) angstrom for Ba7Ga8Sb8; and a = 4.8274(3), c = 18.421(2) angstrom for Ba7In8Sb8. The temperature dependence of the magnetic susceptibility of Eu7Ga8Sb8 confirms that the Eu ions are in the typical divalent state (Eu2+) with a room temperature effective magnetic moment mu(eff) = 8.02 mu(B). A phase transition from a paramagnetic to an antiferromagnetically ordered structure occurs in this material below 6 K. These results are corroborated by Eu-151 Mossbauer spectroscopy at 4.2 and 78 K, respectively. Eu7Ga8Sb8, Ba7In8Sb8 and the previously reported Sr7Ga2Sb6 derivative of the cubic Th3P4 type, were also investigated by Sb-121 Mossbauer spectroscopy.