Crystal chemistry, optical spectroscopy and crystal field calculations of Co3TeO6 and solid solutions Co3 xZnxTeO6

Abstract

Solid solutions Co3-xZnxTeO6 (x = 0-3) were prepared both in polycrystalline and single‐crystalline form using solid state reactions and chemical vapour transport reactions, respectively. Miscibility between the isotypic end members was established over the complete range (C2/c, Z = 12, a ≈ 14.85, b ≈ 8.83, c ≈ 10.34 Å, β ≈ 93°). Crystal structure determinations, performed on basis of single crystal laboratory X‐ray (at 295 K) and synchrotron (at 10 and 100 K) data of Co3TeO6 and selected solid solutions, revealed no structural phase transition and allowed a detailed insight into the Co → Zn substitution mechanism. The coordination polyhedra of the five crystallographically independent M2+ cations are distorted octahedra (for three cations), one distorted tetrahedron and one distorted square pyramid. With increasing Zn content the polyhedral distortions increase, and the preference of the Zn2+ cation for the tetrahedral coordination becomes distinctive. Optical absorption and diffuse reflectance spectroscopy reveal extraordinary strong crystal field absorption effects, over wide x ranges predominantly governed by Co2+ in the single tetrahedral and one strongly acentric distorted octahedral site. Superposition Model crystal field calculations yield intrinsic and power‐law exponent parameters in general agreement with previous data for Co2+. The five cation sites show comparatively high crystal field strengths at generally very low interelectronic repulsion parameters, indicating prominent covalent contribution to Co-O bonding in Co3-xZnxTeO6 solid solutions.