Glass transition kinetics and radial distribution function to investigate the role of Cr 2O 3 on the structure of Li 2O–Al 2O 3–SiO 2 photonic glass

Abstract

Thermal kinetic parameters of Cr 2O 3 doped lithium-aluminum-silicate (LAS) photonic glass are calculated using differential thermal analysis (DTA). The dependence of kinetic parameters together with the glass forming ability of the investigated glass on the Cr 2O 3 doping level showed an anomalous behavior around 0.4 g. Correlation between the obtained thermal properties and the materials electronegativity and band gap is given. An energy band diagram is proposed explaining the density of energy states of Cr 3+ and its transformation to Cr 6+. The non-bridging oxygen bonds generated by Cr 2O 3 produce a deep donor level responsible for the red shift of the absorption edge. The local order structure is studied for the LAS glass network using the radial distribution function of XRD. The atomic pairs of Si–O, Li–O and Si–Si are clearly revealed in both short range (SRO) and medium range (MRO) orders, respectively. The addition of Cr 2O 3 into the glass network has changed appreciably both the atomic pair distances and the coordination numbers in the MRO due to the multivalent nature of Cr ions. The observed decrease in the fourth shell coordination number, N 4, reflects the atomic size decrease in the given glass network which means an increase in glass compactness.