Solid State Ionics, Vol.72, 289-292, 1994
Fast Na+ Ionic-Conductivity in Glass and Crystalline Solids of Na2Moo4-Uo2So4 System
Ac electrical conductivity, DSC calorimetry and density measurements have been done on glass and crystalline phases for different compositions of the binary Na2MoO4-UO2SO4 system. The conductivity data show a positive dependence on Na2MoO4 reaching a maximum at ca. 3:2 mole ratio Na2MoO4:UO2SO4. In contrast with the Na2SO4:UO2SO4 binary system where sigma(glass) >> sigma(crystal) for the 2:1 mole ratio, the Na2MoO4-UO2SO4 composition exhibits a higher sigma for the crystalline phase. The higher sigma(crystal) versus sigma(glass) correlates with the increase in "free volume" for the crystal. The sigma-T behavior for the glass of composition 0.63Na(2)MoO(4):0.37UO(2)SO(4) shows three distinct conductivity regimes or discontinuities prior to complete devitrification. The onset temperatures of these regimes correlate with the observed DSC thermal effects. These regimes and thermal effects prior to complete devitrification suggest the existence of stable higher energy intermediate, mixed crystal-glass, structural states in the glass phase. These results are discussed relative to results of parallel studies on Na4UO2(SO4)(3), Na2O.2CaO.3SiO(2), LiTi2(PO4)(3) and Li2O.BaO.Nb2O5 systems already reported in the literature.