Thermal Stabilities, Physical and Optical Properties of K2O-Na2O-Nb2O5-TeO2 Glasses

The thermal stabilities, physical and optical properties of xK2O-(14-x)Na2O-14Nb2O5-72TeO2 (x = 0 ∼12 mol%) glasses have been studied. The glasses consisting of ca. 10 mol% K2O show high thermal stabilities with values of △T = Tx - Tg = ca. 105 o C against crystallization, where Tg and Tx are the glass transition and crystallization onset temperatures, respectively. The activation energy of grain growth of a cubic crystalline phase in the 10K2O-4Na2O-14Nb2O5-72TeO2 glass was 7.92 kJ/mol. The energy required for the phase transformation from the 10K2O-4Na2O-14Nb2O5-72TeO2 glass to the cubic crystalline phase was 190.74 kJ/mol. The optical and physical properties of the K2O-Na2O-Nb2O5-TeO2 glasses were obtained: refractive index, n = 1.88-1.97; ρ= 4.22-4.64 g/cm 3 ; optical energy band of the transmission cut-off wavelength, Eg (eV) = 3.17-3.14; relative permittivity, e r, = 28-29. The values of RM and α m for K2O-Na2O-Nb2O5-TeO2 glasses were much larger than those of Na2O-Nb2O5-TeO2 glasses.