Synthesis-Controlled Polymorphism, Magnetic and Electrochemical Properties of Li3Co2SbO6

<div>Li3Co2SbO6 is found to adopt two highly distinct structural forms: a hexagonal layered O3- LiCoO2 type phase with “honeycomb” 2:1 ordering of Co and Sb; and an orthorhombic superstructure of rock-salt type, isostructural with Li3Co2TaO6 but with the addition of significant Li/Co ordering. Pure samples of both phase scan be obtained by conventional solid-state synthesis from the same precursors, Li3SbO4 and CoO, by controlling particle size and reaction time. Both phases show relatively poor performance as lithium-ion battery cathode materials in their as-made states, but complex and interesting low-temperature magnetic properties. The honeycomb phase orders antiferromagnetically below TN = 14 K, but a positive Weiss constant θw = 18.1 K points to strong ferromagnetic interactions in the paramagnetic regime above TN; and isothermal magnetisation below TN shows evidence for a field-induced “spin-flop” transition at H ~ 0.7 T. The rock-salt type superstructure phase orders antiferromagnetically below TN = 112 K, then undergoes two more transitions at 80 K and 60, suggesting close competition between at least three ground states. Consistent with such competition, the Weiss constant θw = -181 K indicates some frustration, there is a strong field-cooled / zero field-cooled divergence below TN, and isothermal magnetisation shows it to be magnetically soft with low coercivity.<br></div>