NEW M(2+)M(4+)NB(2)O(8) PHASES

Samples of composition MO-MO(2)-Nb2O5 (M(2+)=Be, Mg, Ca, Mn, Co, Ni, Z n, Cd; M(4+)=Ti, Zr, Ge, Sn) have been prepared by annealing pressed p owders at temperatures between 1073 and 1673 K and were investigated b y the X-ray method. In most cases solid solutions are formed, except i n the systems with GeO2 and BeO and in the combinations MnO(CuO)SnO2. Three structure types, i.e. rutile, wolframite and ixiolite, were obse rved. The lattice parameters and homogeneity ranges are given. A corre lation between ionic size and structure type was established.