Crystal Growth of Two New Niobates, La2KNbO6 and Nd2KNbO6: Structural, Dielectric, Photophysical, and Photocatalytic Properties

Single crystals of La 2 KNbO 6 and Nd 2 KNbO 6, space group C 2/ m, a = 12.746(2) Å, b = 5.7906(1) Å, c = 8.8719(2) Å, β = 105.965(1)° and a = 12.545(3) Å, b = 5.6985(1) Å, c = 8.7196(2) Å, β = 105.803(1)°, respectively, were grown out of a reactive hydroxide melt. The two niobates crystallize in a new structure type in which niobium is located in a rare 5-coordinate, square pyramidal coordination environment. La 2 KNbO 6 exhibits room-temperature photoluminescence with bright blue emission upon excitation at 260 nm. Semiempirical PM6 calculations were performed to better understand the origin of the photoluminescence. The dielectric properties of La 2 KNbO 6 were measured from −150 to 200 °C at four different frequencies. Finally, to assess the photocatalytic properties of La 2 KNbO 6, the photocatalytic degradation of methylene blue by La 2 KNbO 6 was determined.