X-ray absorption study of the potassium coordination environment in glasses from the NaAlSi3O8-KAlSi3O8 binary

Potassium K-EXAFS and XANES measurements were made using synchrotron radiation on selected glasses along the NaAlSi3O8-KAlSi3O8 (albite-orthoclase) binary to characterize the local structural environment of potassium: Comparison of XANES spectra indicates that the potassium environment in the glasses is more similar to that in crystalline KAlSi2O6 (leucite) than in crystalline KAlSi3O8 (orthoclase) or KNa3Al4Si4O16 (nepheline). Consequently, the potassium environment in these aluminosilicate glasses were modelled in the analysis of the EXAFS spectra using empirical phase and amplitude parameters for potassium in leucite. The derived K-O bond lengths and coordination numbers exhibit maxima near the composition albite50-orthoclase50. A model, based on previous theoretical and experimental investigations of crystalline and amorphous aluminosilicates and the mixed-alkali effect, is suggested to explain these variations in the local coordination environment of potassium across the binary alkali feldspar glass join.