Abstract
X-ray diffraction experiments are used to obtain short-range order information of gallium phosphate glasses of meta- and pyrophosphate compositions. Parameters of the first-neighbor peaks, such as coordination numbers and distances, are obtained. A strong decrease of the Ga-O coordination number from 6.05±0.2 to 4.64±0.2 upon Ga2O3 addition is found, which is accompanied by a shortening of the Ga-O distances. Only GaO6 octahedra exist at the metaphosphate composition. Close to the pyrophosphate composition, the majority of Ga atoms occupies already tetrahedral sites. The Ga-O coordination number behaves equivalent with the ratio MTO = n(OT)/n(Ga), thus, with the number n(OT) of terminal oxygen atoms (OT) in phosphorus-OT bonds which are available for the coordination of each Ga atom. Thus, P-OT-Ga bridges are formed for all OT atoms. The GaOn polyhedra neither share OT atoms nor form Ga-O-Ga bridges. With increasing fraction of GaO4 tetrahedra and decreasing lengths of the phosphate chains the network expands.
Original language | English |
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Pages (from-to) | 709-715 |
Number of pages | 7 |
Journal | Zeitschrift fur Naturforschung - Section A Journal of Physical Sciences |
Volume | 57 |
Issue number | 8 |
DOIs | |
State | Published - Aug 2002 |
Externally published | Yes |
Funding
Parameters of the P-O, Ga-O and O-O first-neighbor peaks of gallium phosphate glasses at meta-and pyrophosphate compositions are well determined using X-ray diffraction experiments of high resolving power. A strong decrease of Ga-O coordination numbers from 6.0 0.2 to 4.6 0.2 upon Ga2O3 additions is detected, which is accompanied by clear shortening of Ga-O separations. Only GaO6 octahedra exist at metaphosphate composition. Close to the pyrophosphate composition, already a majority of Ga atoms (75%) is found in tetrahedral sites. The Ga-O coordination number behaves equivalently with the ratio TO = (OT)/ (Ga), thus, with the number of terminal oxygen atoms (OT)in P-OT bonds which are available for coordination of each Ga atom. This relation leads to conlcude that P-OT-Ga bridges are formed for all OT atoms. The shorter the formed phosphate chains, the more the network expands. This strange behavior is due to the change from GaO6 octahedra to GaO4 tetrahedra as the bridging units. The GaO polyhedra neither share OT atoms nor form Ga-O-Ga bridges. Acknowledgements Financial support of Deutsche Forschungsgemein-schaft is gratefully acknowledged.
Keywords
- Phosphate Glasses
- Short-range Order
- X-ray Scattering