Incommensurate composite modulated Nb2Zrx-2O2x+1

Abstract

The compound Nb2Zrx-2O2x+1 has been studied by X-ray powder diffraction and transmission electron microscopy. It was previously thought to be an homologous series MnO2n+2 (n ≡ 2x, M = metal) but is more correctly described as a Type II, or composite, modulated structure. Reciprocal space is dominated by a conspicuous set of strong matrix reflections G corresponding to the metrically orthorhombic, average metal subcell (A--a, aM {reversed tilde equals} 5.1, bM {reversed tilde equals} 4.9, cM {reversed tilde equals} 5.2 Å). A rather weaker set of incommensurate satellite reflections occur at G ± mq, m being an integer and q {reversed tilde equals} 1 xa*M + b*M. Electron diffraction data, however, show rows of satellite reflections to be slightly canted away from a*M, implying that q has a very small incommensurate component in both the b*M, and c*M, directions of reciprocal space, i.e., the oxygen subcell is triclinic, and only pseudoorthorhombic. Show more