ON THE CRYSTAL-CHEMISTRY OF TELLURATES CO NTAINING MN2-STRUCTURE - (MN2,4CU0,6)TEO6, BA2MNTEO6 AND PB(MN0,5TE0,5)O-3( IN THE CATIONIC AND ANIONIC PART OF THE CRYSTAL)

Single crystals of (Mn2.4Cu0.6)TeO6 (I), Ba2MnTeO6 (II) and Pb(Mn0.5Te 0.5)O-3 (III) have been prepared by crystallization from fluxes. X-ray investigations led to rhombohedric symmetry (I): R (3) over tilde, (I I): R (3) over tilde m with the trigonal lattice constants (I): a = 8. 826(1), c = 10.687(2) Angstrom, Z = 2. (II): a = 5.817(8), c = 14.244( 3) Angstrom, Z = 3. Compound (III) crystallizes with cubic symmetry P4 (3) over bar m, a = 4.045(3) Angstrom, Z = 1. (I) is the first exampl e of a manganese(II) tellurate and belongs to the structure type of A( 3)XO(6) compounds like (Mn2In)SbO6, Mn3WO6 and Ca3UO6. (II) exemplifie s an ordered and (III) a disordered variation of the perovskites.