engleski

How to improve the ionic conductivity in sodium phosphate glasses?

Nowadays, sodium phosphate glasses are widely investigated as a cheap and easily accessible material for application in electrochemical devices. However, these glasses usually suffer from low electrical conductivity and a significant research effort has been undertaken to improve this property. In this study we show that the increase in sodium mobility can be achieved in a simple manner, by the addition of WO3 and MoO3 which depolymerize condense phosphate glass network and hence facilitate transport of Na+ ions thus improving overall electrical conductivity. The research was conducted on two glass series, 40Na2O–xMoO3–(60-x)P2O5 and 40Na2O–xWO3–(60- x)P2O5 ; x=0-50 mol% prepared by melt-quenching. The electrical properties were studied by impedance spectroscopy in a wide frequency (0.01 Hz – 1 MHz) and temperature (-90 °C – 250 °C) range. The results showed a significant increase in electrical conductivity with the addition of transition metal ions, being four orders of magnitude in the case of WO3 and three in the case of MoO3. However, the trend in conductivity was not linear, yet exhibited the maximal value at 30 mol% of MoO3 and 40 mol% of WO3 (Figure 1). In order to follow structural evolution, 31P MAS-NMR spectroscopy was used where the compositional dependence of P-O-Mo/W linkages exhibited a similar trend as the electrical conductivity. This led us to conclude that the maximally interconnected phosphate and molybdenum/tungsten units form a favourable environment for fast sodium ion transport in contrast to the predominantly phosphate or molybdenu/tungsten glass network. Furthermore, tungsten oxide was found to be more interconnected with the various P2O5 units inducing therefore a higher electrical conductivity of the Na2O–WO3–P2O5 glasses.

Phosphate glasses ; Electrical properties ; 31P MAS NMR ; Mixed glass former effect

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