Ionic transport in mixed sodium rubidium germanate glasses

Impedance spectroscopy and NMR studies of fast ion conducting chalcogenide glasses

“…The superimposed plots in The temperature independence of the loss peaks may contradict the idea of a distribution of activation energies which has been suggested to explain the conductivity dispersion [58][59][60][61][62][63][64][65][66][67][68][69][70][71][72], however, the possibility exists that the distribution of activation energies may be frequency and thermally activated with the same d.c. activation energy. Alternatively, the possibility that the conductivity dispersion may be due to a second mechanism that contributes to the total conductivity and has a constant slope on a log frequency plot and is temperature independent.…”

“…This phenomenon has been widely reported for most alkali glasses in a similar composition range [57][58][59][60][61][62][63][64][65][66][67][68][69][70][71][72]. Martin and Angell have explained this phenomenon by suggesting that the ac tivation energy is a function of the amount of overlap between the potential energy wells of cation sites [57,65,70].…”

“…Others, especially Martin and Ngai [61] have correlated B with a "primi tive" activation energy, Although this correlation does work well for many glasses, the correlation to fit p to a structurally recognizable variable, the alkali ion separation distance, is perhaps more significant. 1 1 1 1 1 1 r 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 I 1 1 1 1 1 1 1 1 1 1 Figure 5.24 shows that the P parameter for germanate glasses modified by rubidium is larger than that for sodium for the same ion-ion separation distance [66][67][68]. If a decrease in ion-ion interaction contributes to larger P then it must be the case that rubidium ion interacts less than the sodium ion.…”

“…Many researchers have reported for various glass systems the compositional contribu tions to the non-exponential conductivity relaxation [7,8,[57][58][59][60][61][62][63][64][65][66][67][68][69]. p values for all these glasses are far less than one and are weakly compositionally dependent.…”

“…Conductivity data have been modeled in the electrical modulus formalism with great suc cess for frequencies less than one decade above the average relaxation frequency [8,[57][58][59][60][61][62][63][64][65][66][67][68] and an example is shown in Figure ( [54,55] and others believe that for all glasses, the conductivity slope will increase from zero in Region 1 (cax « 1) to a final value of one in Region 2 (cox » 1) at lowest temperature and/or highest frequency. This suggests that the degree of non-exponential behavior P -> 1 increases with frequency while in the case of the KWW fits to the electrical modulus the degree of non-exponential behavior is constant.…”