| Abstract Scope |
Phase relations of the Nb2O5-CaO-MgO ternary system in equilibrium at 1523 K in air have been investigated by the high-temperature equilibration/quenching method. The compositions of equilibrium phase were determined by Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM-EDS) and X-ray diffraction (XRD). Seven sub-equilibrium regions in the Nb2O5-CaO-MgO system were measured at 1523 K in air, including Ca3MgNb2O9-MgO-CaO region, Ca3MgNb2O9-Ca2Nb2O7-Mg4Nb2O9 region, CaNb2O6-Mg5Nb4O15-MgNb2O6 region, CaNb2O6-Nb2O5-MgNb2O6 region, Ca2Nb2O7-CaNb2O6-Mg4Nb2O9 region, CaNb2O6-Mg5Nb4O15-Mg4Nb2O9 region, and Ca3MgNb2O9-Mg4Nb2O9-MgO region. Within the experimentally investigated composition range, a ternary compound, Ca3MgNb2O9, is present in the system. The solid solubility of MgO is 6.36 mol%, 6.12 mol%, and 4.21 mol%. The MgO phase, the MgNb2O6 phase, the Mg4Nb2O9, and the Mg5Nb4O15 phases can dissolve CaO. The solid solubility of CaO is 2.72 mol%, 3.70 mol%, 1.28 mol%, and 0.60 mol%. The determination of the Nb2O5-CaO-MgO ternary system further enriches the thermodynamic databases of silicates and niobates. |