1999 年 41 巻 2 号 p. 136-140
We review preparations and crystal structures of various kinds of new niobium oxides. Ilmenite-type ANbO3 (A=Li, Na), which were prepared by low temperature hydrothermal reaction and ion-exchange reaction, are the first examples of ilmenite-type niobium oxides. These niobium oxides are metastable phases and transform into the stable phases at elavated temperatures. A new reduced niobium oxide, Rb1.51Nb10O17 has a Nb6O12 cluster characteristic of strongly reduced niobium oxides. Weakly reduced niobium oxides, K2YNb5O15-δ and K6Nb10.9O30 have NaNb6O15F-type and tetragonal tungsten bronze type strcutures, respective-ly. In the A2O-MO- Nb2O5 (A=K, Rb, Cs; M=Mg, Fe) system, two types of compounds K2M2Nb4O13 and A (M, Nb) 2O5, which are isostructural with K2Ti6O13 and KTiNbO5 respectively, were obtained.