Hydrothermal Synthesis of CoSb₂O₄: In Situ Powder X-ray Diffraction, Crystal Structure, and Electrochemical Properties

MSb2O4 constitutes a relatively unexplored class of multinary oxides that is traditionally synthesized by high-temperature solid-state methods. Here, we report a facile synthesis of CoSb2O4 under hydrothermal conditions (T = 135–300 °C, 256 bar). Using in situ synchrotron powder X-ray diffraction (PXRD), the formation and growth of CoSb2O4 nanoparticles are followed in real time using different precursor stoichiometries. Phase-pure CoSb2O4 can be formed at 135 °C, although the formation mechanism changes with precursor stoichiometry. The crystallite size can be fine-tuned between 14 and 17.5 nm under nonstoichiometric conditions, but crystallites twice as large are found in the stoichiometric case. An activation energy of 65(12) kJ/mol is obtained for the crystallization from a nonstoichiometric precursor. Modeling of atomic displacement parameters obtained from Rietveld refinement of multi-temperature high-resolution synchrotron PXRD data gives a Debye temperature of 331(11) K. The thermal expansion coefficients for the material was found to be αa = 6.2(1) × 10–6 K–1 and αc = 3.1(4) × 10–6 K–1. Electrochemical measurement shows that CoSb2O4 displays a large irreversible capacity (1131 mAh/g) on the first cycle in Li-ion half-cells and that the capacity decreases significantly in the following cycles.