Structure solution and refinement of stacking-faulted NiCl(OH)

Two samples of pure NiCl(OH) were produced by hydrothermal synthesis and characterized by chemical analysis, IR spectroscopy, high-resolution laboratory X-ray powder diffraction and scanning electron microscopy. Layers composed of edge-sharing distorted NiCl6x(OH)(6-6x) octahedra were identified as the main building blocks of the crystal structure. NiCl(OH) is isostructural to CoOOH and crystallizes in space group R (3) over barm [a = 3.2606 (1), c = 17.0062 (9) angstrom]. Each sample exhibits faults in the stacking pattern of the layers. Crystal intergrowth of (A gamma B)(B alpha C)(C beta A) and (A gamma B)(A gamma B) [C6 like, beta-Ni(OH)(2) related] stacked layers was identified as the main feature of the microstructure of NiCl(OH) by DIFFaX simulations. A recursion routine for creating distinct stacking patterns of rigid-body-like layers in real space with distinct faults (global optimization) and a Rietveld-compatible approach (local optimization) was realized and implemented in a macro for the program TOPAS for the first time. This routine enables a recursive creation of supercells containing (A gamma B)(B alpha C)(C beta A), (A gamma B)(A gamma B) and (C beta A)(B alpha C)(A gamma B) stacking patterns, according to user-defined transition probabilities. Hence it is an enhancement of the few previously published Rietveld-compatible approaches. This routine was applied successfully to create and adapt a detailed microstructure model to the measured data of two stacking-faulted NiCl(OH) samples. The obtained microstructure models were supported by high-resolution scanning electron microscopy images.