Abstract
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.
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