Investigation of phosphate glasses with the general formula A_xB_yP₃O₁₂ where A = Li, Na or K and B = Fe, Ga, Ti, Ge, V or Nb

Abstract

Physical and thermal properties, crystallization behaviour and dc conductivity of glasses with the general formula A_xB_yP₃O₁₂ where A is an alkali ion and B = Fe, Ga, Ti, Ge, V or Nb have been investigated. Glasses of compositions A₃B₂P₃O₁₂, A₅BP₃O₁₂ and A₄BP₃O₁₂ have been prepared by quenching the melts. Molar volumes of these glasses change considerably on inter alkali substitution (by 30-40% on going from Li to K). The glass transition temperatures are within the small range of 30 K for the Li, Na and K members, except in the vanadium containing glasses. The glasses with B = Fe, Ti or Ge are found to crystallize immediately above the glass transition temperature. Iso-compositional crystallization was observed in Na₃Fe₂P₃O₁₂. The DSC crystallization exotherms are often not simple, indicating stages of crystallization. Crystallization kinetics of the Na₃Fe₂P₃O₁₂ glass reveal a lower activation energy for isothermal crystallization than for the non-isothermal crystallization. The dc conductivities estimated from impedance plots are in the range of 10^-9 Ω^-1 cm^-1 to 10^-7 Ω^-1 cm^-1 at 298 K and the conductivity activation energies are in the range 0.5-0.8 eV, with no variation between Li⁺ and K⁺ containing glasses, greater than errors of measurement.