A new LiCoPO4 polymorph via low temperature synthesis

Non-olivine LiCoPO4 microcrystals have been synthesized at low temperatures by microwave-assisted hydrothermal synthesis. The resulting octahedra-like micrometer-sized crystals exhibit a Pn2(1)a symmetry and are isostructural to LiZnPO4. The orthorhombic lattice constants are a = 10.023(8) angstrom, b = 6.724(7) angstrom, and c = 4.963(4) angstrom. The microcrystals are metastable and transform to olivine LiCoPO4 upon heating above T approximate to 220 degrees C under an argon atmosphere. The magnetic properties confirm a phase pure material with a Co-valence of 2+, and imply long-range antiferromagnetic ordering below T-N = 11 K. Electrochemical analysis by means of cyclic voltammetry displays a reversible redox couple at around 5.1 V/4.8 V vs. Li/Li+.