A Composite Modulated Structure Versus Superstructure Approach to the Refinement of >Zr₁₀₈N₉₈F₁₃₈

Abstract

Zr₁₀₈N₉₈F₁₃₈ is an x = 2.185 member of a wide range non- stoichiometric solid solution Zr (N,O,F)x, 2.12 ≤ x ≤ 2.25, in the zirconium nitride oxide fluoride system. The structure is rerefined as a composite modulated structure composed of two mutually incommensurable Q and H substructures with overall superspace group symmetry Acmm (0,0,1.185..)0s0. The Q substructure has lattice parameters a = 5.186, b = 5.368 and c_Q = 5.374 Ǻ, and substructure superspace group symmetry Acmm (0,0,1.185..)0s0. The H substructure has lattice parameters a = 5.186, b_H = 1/2b = 2.684 and C_H = 4.534 Ǻ, and substructure superspace group symmetry Pmcm (0,±,0.844...)s00. While employing almost an order of magnitude fewer positional parameters than the previous study, refinement on 956 unique reflections converged to R = 0.057 instead of R = 0.113.