Phase Equilibria in the KNbO3-SrNb2O6 and KNbO3-BaNb2O6 Systems

Phase equilibrium studies of the KnbO₂-SrNb₂O₆ system revealed that tetragonal tungsten bronze-type solid solutions extend from 59 to 87 mol% SrNb₂O₆. The solid solution field has a relatively flat liquidus peaking at 1486°C and 78 mol% SrNb₂O₆. In contrast, solid solutions are limited to 67 to 75 mol% BaNb₂O₆ in the KnbO₃-BaNb₂O₆ system, with peritectic decomposition occurring at the 75 mol% solid-solution limit. The diagrams establish conditions for perfecting the growth and stoichiometry of potassium-strontium and potassium-barium niobate electrooptic crystals. Dielectric and crystallographic properties of crystals grown in these systems are presented, and the phase relations are compared to previous work in the sodium-barium niobate system.