Towards modeling gadolinium–lead–borate glasses

Abstract

Infrared spectra of gadolinium–lead–borate glasses of the xGd 2O 3·(100 − x)[3B 2O 3·PbO] system, where x = 0, 5, 10, 15, 25, 35 and 50 mol.%, have been recorded to explore the role of content of gadolinium ions behaving as glass modifier. The FTIR spectroscopy data for the xGd 2O 3·(1 − x)[3B 2O 3·PbO] glasses show the structural role of lead ions as a network-formers and of the gadolinium ions network modifiers. Adding of the rare earth ion up to 35 mol.% into the glass matrix, the IR bands characteristic to the studied glasses become sharper and more pronounced. Structural changes, as recognized by analyzing band shapes of IR spectra, revealed that Gd 2O 3 causes a change from the continuous borate network to the continuous lead–borate network interconnected through Pb–O–B and B–O–B bridges and the transformation of some tetrahedral [BO 4] units into trigonal [BO 3] units. Then, gadolinium ions have affinity towards [BO 3] structural units which contain non-bridging oxygens necessary for the charge compensation because the more electronegative [BO 3] structural units were implied in the formation of B–O–Gd bonds and the transformation of glass network into a glass ceramic. We propose a possible structural model of building blocks for the formation of continuous random 3B 2O 3·PbO network glass used by density functional theory (DFT) calculations. DFT calculations show that lead atoms occupy three different sites in the proposed model. The first is coordinated with six oxygen atoms forming distorted octahedral geometries. The second lead atom has an octahedral oxygen environment and the five longer Pb–O bonds are considered as participating in the metal coordination scheme. The third lead atom has ionic character. In agreement with the results offered by the experimental FTIR data, the theoretical IR data confirm that our proposed structure is highly possible.