SYNTHESIS AND STRUCTURE OF A COMPOSITELY MODULATED SOLID-SOLUTION IN THE ZIRCONIUM NITRIDE OXIDE FLUORIDE SYSTEM

The phase Zr(N,O,F), has been studied by X-ray powder diffraction and transmission electron microscopy. It had previously been described as an oxygen free nitride fluoride and the structure of one composition f rom the solid solution field solved as a so-called Vernier superstruct ure approximation. More correctly the phase should be described as an incommensurate, compositely modulated structure, with a continuously v ariable, composition-dependent, primary modulation wave-vector. The to tal anion to cation ratio can be uniquely determined from careful meas urement of diffraction patterns and is shown to be continuously variab le and to range between 2.12 and 2.25. The cell parameters of the comp onent substructures are determined and show a linear dependence upon t he anion to cation ratio. Apparent valence calculations are used to in vestigate anion ordering. (C) 1994 Academic Press, Inc.