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Title: Investigation of boro-germanate and germanium disulfide glasses : relation between structure and properties
Author: Buscemi, Michela
ISNI:       0000 0004 7967 8139
Awarding Body: University of Bath
Current Institution: University of Bath
Date of Award: 2019
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The method of neutron diffraction with isotopic substitution was used to investigate the structure of GeS2 glasses and the full set of partial structure factors was measured. Results confirm that the structure of GeS2 is formed of edge- and corner-sharing GeS4/2 tetrahedra with a Ge-S bond distance of 2.21(2) °A. The fraction of Ge atoms in edgesharing configuration is 46(5) %. The first sharp diffraction peak is mainly due to GeGe correlations. No Ge-Ge or S-S homopolar bonds are observed. The data were compared with simulations, showing some discrepancies, particularly in the GeGe partial pair distribution functions. A comparison of the structures of GeO2, GeS2 and GeSe2 has shown that the rearrangement of their tetrahedral units differ in both the intermediate and extended range order. The composition dependent structural and material properties of boro-germanate glasses was studied by combining boron nuclear magnetic resonance, Raman spectroscopy, xray diffraction, differential scanning calorimetry, viscosity and density measurements. The results show that the local coordination environment of both boron and germanium remains constant at ¯n O B = 3.0(1) and ¯n O Ge = 3.9(1), respectively for all the compositions. However, the addition of GeO2 destroys the boroxol rings. It was found that the structure of the mixed materials cannot be predicted by a weighted mean of the pure oxides. A structural model which predicts the nearest neighbour O-O and B-B coordination numbers was developed. The pressure induced change to the structure of (11B2O3)0.303(GeO2)0.697 was investigated by neutron diffraction, upon compression of the material up to 8.2(5) GPa. At ambient conditions, the glass network is constructed from corner-linked triangular BO3/2 and tetrahedral GeO4/2 motifs. At higher pressures, the BO3/2 units transform to four-fold coordinated boron. This takes place at the same pressure as measured for pure B2O3, however the presence of GeO2 increases the fraction of units converted. No significant transformations of GeO4/2 units occur in the pressure range investigated. On decompression, the BO3/2 units are almost entirely reformed, but the intermediate range order is altered to give a 20 % increase in glass density and the fraction of boron in boroxol rings is diminished from 24(5) % to 21(5) %.
Supervisor: Zeidler, Anita ; Salmon, Philip Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available