Phase Equilibria in the KNbO 3 ‐SrNb 2 O 6 and KNbO 3 ‐BaNb 2 O 6 Systems

Phase equilibrium studies of the KnbO 2 ‐SrNb 2 O 6 system revealed that tetragonal tungsten bronze‐type solid solutions extend from 59 to 87 mol% SrNb 2 O 6 . The solid solution field has a relatively flat liquidus peaking at 1486°C and 78 mol% SrNb 2 O 6 . In contrast, solid solutions are limited to 67 to 75 mol% BaNb 2 O 6 in the KnbO 3 ‐BaNb 2 O 6 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.