Phase Equilibria in the System CuO-NiO-P4O10 and Synthesis, Crystal Structure, and Characterization of the New Copper Nickel Oxide Phosphate Cu3NiO(PO4)2
文摘
The system CuO-NiO-P4O10 was investigated using a solid state reaction between CuO, NiO, and (NH4)2HPO4 in quartz crucibles at 900 °C. The powder samples were characterized by X-ray diffraction, TG/DTA, electrochemical measurements, IR, and UV/Vis spectroscopy. Single crystals of a new quaternary phase Cu3NiO(PO4)2 were achieved by cooling the melted compound in a sealed, evacuated quartz ampoule. Cu3NiO(PO4)2 crystallizes in the monoclinic space group P21/n (no 14) with a = 8.2288(2) Å, b = 9.8773(2) Å, c = 8.2777(3) Å, β = 107.82(2)°, Z = 4. The three-dimensional framework consists of distorted tetragonal pyramides [Cu1O5], distorted planar squares [Cu2O4], octahedra [Cu3O6], and [NiO6] and [PO4] tetrahedra. The TG-DTA of the new phase showed an incongruent melting at 1055 °C. The open circuit voltage of this material was measured to determine the electrochemical properties. The measurement revealed an initial capacity of 236 Ah·g–1 and a voltage plateau at 2.05 V. Furthermore, it was possible to identify the phase equilibria and to obtain the phase diagram at 900 °C.