CA4.3(2)W10O30 - A TETRAGONAL TUNGSTEN BRONZE WITH A HIGH-CALCIUM CONTENT

Violet crystals of Ca-4.3(2)W10O30 were obtained by a slow oxidation r eaction of mixtures of Ca3N2, Ca and W at 850 degrees C with flowing A r, resp. N-2 diluted by oxygen. The compound is a bronze and it crysta llizes tetragonal in the space group P4/mbm and Z = 1 with the unit ce ll parameters a = 12.280(4) Angstrom and c = 3.8265(9) Angstrom. The c rystal structure contains corner sharing (WO6) octahedra. They are arr anged in such a way that trigonal prismatic, tetragonal prismatic and pentagonal prismatic interstices occur. Calcium occupies the pentagona l prismatic sites almost completely and the tetragonal sites statistic ally to approximately one fourth.