Large crystals of the NaBa2Nb5O15-type with K substitututions for Na have been grown in unseeded molten solutions fluxed with excess alkali carbonates. Curie temperatures and phase match temperatures of these crystals are decreased by the substitution of K for Na. Crystal compositions lie in the ternary NaNbO31bKNbO31bBaNb2O6 system and are proportionately BaNb2O6-rich as is the case for crystals pulled from nominally stoichiometric melts. The crystals exhibit 50 to 100 μ regions which are optically uniform. © 1969.