Crystal growth and cation order of Ni3−xCoxB2O6 oxyborates

Abstract

A series of single crystals of Ni_3−xCo_xB₂O₆ compounds with the kotoite structure and with different concentrations of transition metal ions (x = 0; 0.19; 0.6; 0.93 and 2) were obtained. The lattice parameters and atomic coordinates were determined using X-ray diffraction. The theoretical calculations using the WIEN2k package predict that nickel ions tend to occupy the 4f crystallographic position, while cobalt ions tend to occupy the 2a crystallographic position. The study of the diffuse scattering spectra and comparison of the Racah parameters for the compounds Ni₃B₂O₆ and Co₂NiB₂O₆ provides experimental evidence that nickel ions occupy crystallographic position 4f.