On the kinetic fragility of alumina containing metaphosphate glasses from viscosity-temperature curves analysis

• Viscosity-temperature curves of alumino-metaphosphate glasses have been determined. • Glass transition behaves linearly while fragility is non-linear with alumina content. • The melt structure drives the mechanism of viscous flow in the undercooled liquid. • Small ring structures change viscous flow mechanism leading to higher fragility. The glass transition and the dependence of the kinetic fragility of glasses on their structure remains to be an important topic of debate. Recent findings have allowed to establish correlations between the medium range order structure and the deviation from Arrhenius of the viscosity-temperature curves; however, the origin of how the glass structure is originated upon cooling of a melt remains to be elucidated. This work shows a study of the viscosity of metaphosphate glasses for increasing alumina contents and addresses how their structure can have an influence on the non-linear behaviour of the kinetic fragility found at T g as a function of the alumina content. The results have been further confirmed by the change of the ratio between the intensities of the Raman modes involving non-bridging and bridging oxygens as well as by the devitrification behaviour at the highest alumina composition.