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

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Single crystals of La2KNbO6 and Nd2KNbO6, space group C2/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. La2KNbO6 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 La2KNbO6 were measured from −150 to 200 °C at four different frequencies. Finally, to assess the photocatalytic properties of La2KNbO6, the photocatalytic degradation of methylene blue by La2KNbO6 was determined.