FTIR spectroscopic and DFT theoretical study on structure of europium-phosphate-tellurate glasses and glass ceramics

Glasses and glass ceramics in the ternary xEu(2)O(3)center dot(100 - x)[7TeO(2)center dot 3P(2)O(5)] systems with 0 <= x <= 60 mol% have been prepared from melt quenching method. Influence of europium ions on structural behavior in phosphate-tellurate glasses has been investigated using infrared spectroscopy. The addition of high Eu2O3 content resulted in gradual depolymerization of the phosphate chains and formation of the EuPO4 crystalline phase. Presence of the multiple cations of europium and tellurium in the glasses to attract the [PO4] structural units for compensation of charge yield a competition between these cations. This preference is decided by the potential of ionization of the cations. The changes of the IR spectral features produced by devitrification suggest that this competition explains the drastic reduction of the characteristic features corresponding to the [PO4] structural units in bandwidth, position and intensity. After the heat treatment applied at 500 degrees C for 24 h two crystalline phases appear, namely the Te4P2O13 and EuPO4. The Te4P2O13 crystalline phase is characteristic of the host glass ceramic. The strong affinity of the Eu+3 ions towards the phosphorus groups containing non-bridging oxygen is responsible for the disappearance of Te4P2O13 crystalline phase. We propose a possible structural model of building blocks for the formation of continuous random 7TeO(2)center dot 3P(2)O(5) glass network used by density functional theory (DFT) calculations. Comparing the theoretical and experimental IR spectral characteristic features, we conclude that the performance of the method/basis sets used on the prediction of the structural data and vibrational modes is good. (c) 2009 Elsevier B.V. All rights reserved.