Electrodiffusion of alkali ions in alkali niobophosphate glasses and glass‐forming melts

Abstract

Electrical conductivity of Li(Na,K)2O‐Nb2O5‐P2O5 glasses and glass‐forming melts has been measured in a wide temperature range (298‐1173 K). Logarithm of the preexponential factor and activation energy of migration have been determined. Mixed alkali effect has been observed in niobophosphate glass‐forming melts. Diffusion coefficients for Li+, Na+, and K+ ions have been calculated. The influence of the type of alkali ion and Nb2O5 content on the diffusion coefficients has been determined.

Thermodiffusion of alkali ions in alkali niobophosphate glasses

“…As can be seen from Table 4, the Soret coefficients are in a weak dependence on temperature, in contrast to the self‐diffusion coefficients, which has been shown earlier 41 . The dependence of S T on the Nb 2 O 5 content is more significant than on temperature.…”

“…As shown earlier in the present paper, Soret coefficient characterizes the ratio of the coefficient of thermal diffusion ( D T ) and the coefficient of self‐diffusion ( D ) () 29 . In our case, the self‐diffusion coefficient was used, which was previously determined through electrical conductivity, 41 that is, D σ .…”

“…The results of the experiments on thermo EMF ions are shown in Table 1. It has been shown experimentally that, when the mobility of the alkali ions increases (from K to Li), 41 the thermo EMF increases accordingly. It is worth noting that in mixed alkali glasses this effect is less pronounced than in monoalkali glasses.…”

Nanoscale composition fluctuations and crystallization process: Case study in Li2O–SiO2‐based glasses

“…As reported by Sun, 38 single‐bond strengths of R 2 O are 150 kJ/mol for Li 2 O, 83.7 kJ/mol for Na 2 O, and 54.4 kJ/mol for K 2 O. It is well known that alkali metal R + ions can move easily in glasses and SCLs and their diffusion coefficients are related to the size of R + ions, that is, smaller ionic radius, larger diffusion coefficient, Li + >Na + >K + 70–72 . The values of optical basicity also indicate that the chemical bond strength of Li + –O bonds is high compared with Na + /K + –O bonds 66–68 .…”

“…The network-forming cations of Si 4+ have a high field strength of F(SiO 2 ) = 1.54 Å −2 , indicating a more covalency in Si-O bonds. On the other hand, R 2 O modifiers have low field strengths of F(Li 2 O) = .27, F(Na 2 O) = .18 Å −2 , and F(K Li + >Na + >K + [70][71][72]. The values of optical basicity also indicate that the chemical bond strength of Li + -O bonds is high compared with Na + /K + -O bonds [66][67][68].…”