Order-disorder (OD) polytypism of K₃FeTe₂O₈(OH)₂(H₂O)₁₊ₓ

Abstract

K₃FeTe₂O₈(OH)₂(H₂O)₂ was synthesized under hydrothermal conditions from Te(OH)₆, FeSO₄·7H₂O and 85 wt% KOH in a 1:2:6 molar ratio. The crystal structure is built of a triperiodic network. One disordered water molecule per formula unit is located in a channel and can be partially removed by heating. Systematic one-dimensional diffuse scattering indicates a polytypic character, which is best described by application of the order-disorder theory. The major polytype is monoclinic with pseudo-orthorhombic metrics. It is interrupted by fragments of an orthorhombic polytype. The diffraction intensities are analyzed using structure factor calculations.