Synthesis, structure, and solid-state electrochemical properties of Cr3BO6: a new chromium(III) borate with the norbergite structure

A new compound in the Cr-B-O system with the (M3BO6)-B-III norbergite structure has been synthesized by a solid state reaction. Rietveld refinement of the powder X-ray diffraction pattern in the space group Pnma yielded unit cell parameters of a=9.8552(2), b=8.4007(2), c=4.4138(1) Angstrom. The compound is formed in highest purity using a hydrated chromium( III) sulfate precursor, which has the highest decomposition temperature of the reagents used in this synthesis. A reaction scheme is proposed to explain this observation. The electrochemical properties of this material as a negative electrode for lithium-ion batteries were investigated and found to be similar to those for the previously studied Fe3BO6, although the average Li-uptake potential was lowered to 1.0 V.