PREPARATION AND CRYSTAL-STRUCTURE OF K6NB10.9O30

Single crystals of a reduced potassium niobium oxide, K6Nb10.9O30 were prepared in a H-2 atmosphere at 1200 degrees C. The reduced potassium niobium oxide crystallized in the tetragonal space group P4/mbm with a=12.582(1), c=3.992(3)Angstrom and Z=1, and the final R-factors were R=0.047 and Rw=0.055 for 1570 unique reflections. This reduced potassi um niobium oxide is isostructural with K5.75Nb10.85O30, K6Ta10.8O30 an d K5.3Mo9.2Nb0.8O30. Their crystal structures have the three dimension al framework similar to that of the tetragonal tungsten bronze-type st ructure and additional M atoms (M=Nb,Ta) are Statistically distributed in the tricapped trigonal prism cavity in the framework. The potassiu m atoms are located in both the perovskite-like cuboctahedral cavity a nd pentagonal tunnel.