(NIXMG1-X)10GE3O16 - A NEW PHASE WITH STRUCTURE RELATED TO OLIVINE AND SPINEL

A new compound, (Ni//xMg//1// minus //x)//1//0Ge//3O//1//6(x approximately equals 0. 4-0. 5), has been identified at atmospheric pressure in the NiO-MgO-GeO system. Its unit cell is rhombohedral with the (hexagonal) parameters alpha equals 5. 887(1) A, c equals 26. 603(4) A, and Z equals 3 for a phase with the Ni//4Mg//6Ge//3O//1//6 composition. A structural model has been derived from powder X-ray diffraction data: the M//1//0Ge//3OD 1//6(M equals Ni plus Mg) structure results from a regular intergrowth of left brace 111 right brace layers of the spinel and rock-salt structures. It can also be described as an intergrowth of (001) olivine layers (Pnma setting) with left brace 111 right brace layers of a cation-deficient rock-salt structure.