DENSITY AND SURFACE-TENSION PROPERTIES OF MOLTEN POTASSIUM NIOBATE SYSTEM

The density and surface tension of the K2O-Nb2O5 molten system between 50 and 56 mol% K2O melts were measured from 1080 to 1180 degrees C. Excess K2O in the melt can reduce both density and surface tension, and there is a minimum both in the composition dependence and in the temperature dependence of the density within this composition range. It was found that the temperature coefficient of surface tension -d tau/dT was the smallest around the 52 mol% K2O region. The surface tension was observed to increase with soak time, but the temperature coefficient -d tau/dT decreased by the soak process. These properties and variations may explain why a KNbO3 crystal should be grown from the melt with a composition of 52 to 54 mol% K2O at a soak temperature above 1150 degrees C after several days.