Formation of transparent glass-ceramics including thermodynamically metastable cubic phase in Na₂Mn_0.5Fe_0.5SiO₄ glass

Optically transparent and electrically conductive glass-ceramics have been successfully prepared from 1Na2O–0.5MnO–0.5FeO–1SiO2 (Na2Mn0.5Fe0.5SiO4) glass by heat-treatment. Crystallization tendency was sensitive to the valence state of transition metal oxide. The as-quenched glass melted at 1400°C for 15 min, exhibited two exothermic peaks in the differential thermal analysis. Optically transparent glass-ceramics obtained at 493°C for 3 h showed simple X-ray diffraction pattern, which could be assigned to a cubic phase with a lattice constant of 0.74511 nm. A monoclinic Na2MSiO4 (M = Mn, Fe) phase appeared with the heat treatment above 610°C, suggesting that the crystal phase precipitated in the low temperature region was thermodynamically metastable. The transparent glass-ceramics showed an order of magnitude higher electrical conductivity than that of glass and the monoclinic phase.