Non-Arrhenius Ionic Conductivities in Glasses due to a Distribution of Activation Energies

Abstract

Previously observed non-Arrhenius behavior in fast ion conducting glasses [Phys. Rev. Lett. 76, 70 (1996)] occurs at temperatures near the glass transition temperature, Tg, and is attributed to changes in the ion mobility due to ion trapping mechanisms that diminish the conductivity and result in a decreasing conductivity with increasing temperature. It is intuitive that disorder in glass will also result in a distribution of the activation energies (DAE) for ion conduction, which should increase the conductivity with increasing temperature, yet this has not been identified in the literature. In this paper, a series of high precision ionic conductivity measurements are reported for 0.5Na2S + 0.5] glasses with compositions ranging from 0 ≤ x ≤ 1. The impact of the cation site disorder on the activation energy is identified and explained using a DAE model. The absence of the non-Arrhenius behavior in other glasses is explained and it is predicted which glasses are expected to accentuate the DAE effect on the ionic conductivity.

NMR and conductivity studies of the mixed glass former effect in lithium borophosphate glasses

“…For all of the samples, σ dc was found to follow an Arrhenius temperature dependence, see however Ref. 47. The corresponding activation energies are summarized in Sec.…”

“…In view of the considerable uncertainty in determining the detailed shape of these DAE, however, we refrain from discussing any possible x-dependence of their widths, σ E , beyond stating that the x = 0 glass exhibits the narrowest distribution. Based upon recent studies 47 it might be expected that a 20% width of the average results in significant deviations from Arrhenius behavior in various Li + transport coefficients. However, such deviations become noticeable in an Arrhenius plot only at relatively low temperatures.…”

“…47 Samples were measured within the frequency range 10 −2 -10 6 Hz, between 200 and 550 K at an applied voltage of 20 mV on polished samples of 1 to 2 mm thickness and ∼20 mm diameter. To improve the contact to the electrodes, the sample surfaces were covered with a layer of gold by radio-frequency sputtering using an Anatech Hummer V sputtering device inside the glove box.…”

“…However, such deviations become noticeable in an Arrhenius plot only at relatively low temperatures. 47 We are in the process of measuring the Li + ion conductivity of these glasses to lower temperatures to examine their DAE in detail.…”

Short Range Structural Models of the Glass Transition Temperatures and Densities of 0.5Na2S + 0.5[xGeS2 + (1 – x)PS5/2] Mixed Glass Former Glasses

“…11, 13−21 In our studies of the Na + ion conductivities of the glasses in the 0.5Na 2 S + 0.5[xGeS 2 + (1 − x)PS 5/2 ] system, we have observed for the first time that they exhibit a negative MGFE and, furthermore, they are also found to exhibit a nonArrhenius temperature dependence in the Na + ion conductivity which we have attributed to the presence of the disordered structure of these glasses giving rise to a distribution of activation energies, DAE, for ionic conduction. 22 Since these MGF glasses are found to exhibit the first ever reported negative MGFE in the ionic conductivity, it is of great interest to determine whether this negative MGFE is present in other physical properties. To this end, in this study we report the composition dependence of the glass transition temperature, T g , and the density, ρ, of these 0.5Na 2 S + 0.5[xGeS 2 + (1 − x)PS 5/2 ] MGF glasses and a detailed atomic level model that is not only able to fully interpret the composition dependence of the T g and density, but in doing so we are able to refine our previously published model 23 of the composition dependence of the various short-range order (SRO) thiophosphate and thiogermanate structures present in these glasses.…”