NEUTRON-DIFFRACTION STUDY OF FELDSPAR GLASSES - MIXED-ALKALI EFFECT

Radial distribution function analysis was made using neutron diffracti on on several glasses along the NaAlSi(3)O8-KAlSi3O8 (albite-orthoclas e) join as well as on a natural obsidian sample. Comparison of the int erference functions in reciprocal space shows a non-linear increase of the width of the first sharp diffraction peak which indicates a decre ase of the medium-range order (MRO) with increasing K2O content. The o bserved changes in the MRO were correlated with the non-linear variati on of the bulk transition temperature, T-g, and might reflect a strong temperature dependence of the corresponding liquid structures.