Ca25Co22O56(OH)28: A layered misfit compound

The high pressure synthesis, structure and magnetic properties of Ca25Co22O56(OH)28 are reported. The compound has a misfit structure, consisting of double, square calcium oxide hydroxide rock-salt-like layers between hexagonal CoO2 layers. The misfit compound crystallizes in the monoclinic space group C2/m, and can be characterized by the coexistence of two subsystems with common a = 4.893(5) Å, c = 8.825(9) Å and β = 95.745(8) parameters, and different b parameters: bRS = 4.894(5) Å, and bHEX = 2.809(3) Å, for the rock-salt and hexagonal type planes, respectively. The compound shows Curie–Weiss paramagnetism with an antiferromagnetic Weiss temperature of −43 K and a reduced Co moment. Substantial deviations from Curie–Weiss behavior are seen below 50 K with no indication of magnetic ordering. No superconductivity was observed down to a temperature of 2 K.