Gadolinium-environment in borate–tellurate glass ceramics studied by FTIR and EPR spectroscopy

Abstract

Modifications of the gadolinium-environment in borate–tellurate glass ceramics system, where 0 ⩽ x ⩽ 30 mol%, under heat treatment have been investigated by FTIR and Electron Paramagnetic Resonance (EPR) spectroscopy. Glass ceramics with a molar composition of xGd 2O 3·(100 − x)[6TeO 2·4B 2O 3] where 0 ⩽ x ⩽ 30 mol%, was prepared by one-step crystallization heat treatment of the parent glass at temperatures of 400 and 475 °C, respectively. After the heat treatment applied at 400 °C, some structural changes were observed and the B 2O 3 crystalline phase appeared in the structure of the samples. The crystallization of the B 2O 3 crystalline phase increases with increasing of the gadolinium concentration because the excess of the oxygen yields the formation of free BO 3 - 3 orthoborate units capable for charge compensation of the gadolinium ions. By increasing of the treatment temperature up to 475 °C, the increase of the capacity of migration inside the glass ceramics network yields the apparition of B 2O 3 and TeO 2 crystalline phases. When a higher Gd 2O 3 content is introduced, more [BO 3] structural units are coupled with gadolinium ions, the Te–O–Te linkages are deformed showing that the Gd 2O 3 behaves as a glass-former by means of the intercalation of [GdO 4] entities in the [TeO 4] chain network. The changes produced by devitrification suggest the competition between cations of tellurium and boron with non-bridging oxygens to compensate the positive charge of the gadolinium ions. Thus, gadolinium ions play a dual role of network former (475 °C) and network modifier (400 °C) in the studied samples