Study on Coordination of Aluminum Ions in Germanate, Borate and Phosphate Glasses on the Basis of AlK_{α1, 2} X-ray Fluorescence Spectra

Abstract

The chemical shifts of AlK_{α1, 2} X-ray fluorescence lines of germanate, borate and phosphate glasses have been determined in order to investigate the coordination number of Al³⁺ ions in glasses.
In Na₂O-Al₂O₃-GeO₂ glasses with 60 and 70mol% GeO₂ and the Al₂O₃/Na₂O ratios ranging from 0.5 to 1.5, the chemical shifts were nearly equal with each other and with that for orthoclase crystal, indicating that the Al³⁺ ions are fourfold-coordinated in the glasses.
The chemical shifts for CaO-Al₂O₃-B₂O₃ glasses largely depended on the B₂O₃ content of glass and not on the Al₂O₃/CaO ratio. The chemical shift increased from the value nearly equaling that for the orthoclase towards that for α-Al₂O₃ as the B₂O₃ content increased, indicating that the average coordination number of the Al³⁺ ions increases with increasing B₂O₃ content.
A wide variety of phosphate glasses with varying P/O ratio were melted from the batches containing various constituents besides Al₂O₃ and P₂O₅, and subjected to measurement of the AlK_{α1, 2} spectra, assuming that the P/O ratio of 0.333 would correspond to the metaphosphate and the ratio of 0.25 to the orthophosphate. It was found from the chemical shifts that glasses with the ratio near 0.333 contain a considerable fraction of six-coordinated Al³⁺ ions, while those with the ratio near or below 0.25 contain almost all Al³⁺ ions in four-coordination.