X‐ray Diffraction and Physical Properties of Potassium Borate Glasses*

Data are presented from X‐ray studies and from measurements of the physical properties of potassium borate glasses in the composition range from 0 to 40% by weight of KzO. Calculations based on the X‐ray diffraction patterns show a change from three‐ to fourfold coordination with an increase to 22% in K 2 O content. The potassium ions form single‐bonded oxygens and thus produce a weakening of the structures with a K 2 O content greater than 22%. With 20 to 25% of K 2 O, the coefficient of thermal expansion is a minimum, which shows that the majority of the boron atoms are in four‐fold coordination. The curves of the composition versus the trans formation point, softening point, density, refractive index, and viscosity for 200° to 400°C. also show a change of slope in the composition range of 20 to 30% of K 2 O. The random structure picture as well as the tendency of boron atoms to assume tetrahedral coordination in alkaline borate glasses serve to explain satisfactorily the X‐ray diffraction curves and the otherwise anomalous physical behavior of the potassium borate glasses.