title: Experimental and theoretical investigations on the structure-properties interrelationship of the gadolinium-vanadate-germanate glasses.
abstract: Glasses in the system xGd₂O₃·(100-x)[GeO₂·V₂O₅] with 0 ≤ x ≤ 20 mol% have been prepared from the melt quenching method. In this paper, we investigated changes in germanium coordination number in gadolinium-vanadate-germanate glasses through molar volume analysis, measurements of densities, investigations of FTIR and UV-VIS spectroscopy, calculations of density functional theory (DFT). Analyzing the structural changes resulted from the IR spectra we found that the gadolinium ions have a pronounced affinity toward [VO₄] structural units which contain non-bridging oxygens necessary for the charge compensation. The introduction of the excess of oxygen yields the formation of [VO₅] structural units. This attains maximum value at 5 mol% Gd₂O₃, in agreement with the density measurements. Further, the addition of the surplus of oxygen implies the transformation of [VO₅] to [VO₄] structural units and the formation of VO₄⁻³ orthovanadate structural units. The UV-VIS spectra show a broad UV absorption band located in the 300-500 nm region. These bands are assumed to originate from the combination of vanadium ions possibly present in the three states of valence. The presence of Ge-Ge wrong bonds attains its maximum values in the samples with x = 5 and 15 mol% Gd₂O₃ (bands centered in the 250-300 nm range). DFT calculations show the massive vibrations of the [VO(n)] structural units coupled with each other via [GeO₆] and [GeO₄] structural units. This leads to the splitting of the bridge modes and a multiplication of the number of these bands.
authors.affiliation: Department of Physics, Technical University of Cluj-Napoca, 400020 Cluj-Napoca, Romania. Simona.Rada@phys.utcluj.ro
authors.forename: Simona
authors.initials: S
authors.lastname: Rada
authors.forename: Ramona
authors.initials: R
authors.lastname: Chelcea
authors.forename: Eugen
authors.initials: E
authors.lastname: Culea
mesh_terms: D005682:Gadolinium / Q000737:chemistry*; D005898:Glass / Q000737:chemistry*; D008956:Models, Chemical; D017550:Spectroscopy, Fourier Transform Infrared; D014638:Vanadates / Q000737:chemistry*
chemical_list: D014638:Vanadates; D005682:Gadolinium
references.citation: J Phys Chem A. 2008 Nov 6;112(44):11251-5
references.pmid: 18847248