[Mg.sub.5.23][Sm.sub.0.77][Sb.sub.4]: An ordered superstructure derived from the [Mg.sub.3][Sb.sub.2] structure type

The production of the ternary polar intermetallic phase [Mg.sub.5.231(8)][Sm.sub.0.231(8)][Sb.sub.4] from solid state reactions at 700-850 degrees Celsius in sealed Ta or Nb containers when the synthetic conditions took into account its characteristic incongruent melting point is reported. The results present the first example of a superstructure of a[Mg.sub.3][Sb.sub.2]-like structure with a doubled c axis induced by ordering a mixture of the larger divalent Sm and Mg ions separately within alternate layers of octahedral sites.