KLnTiO4 (Ln=La, Nd, Sm, Eu, Gd, Dy): A New Series of Ruddlesden–Popper Phases Synthesized by Ion-Exchange of HLnTiO4

KLnTiO4 (Ln=La, Nd, Sm, Eu, Gd, Dy), a new series of n=1 Ruddlesden–Popper phases, was synthesized by a two-step ionexchange reaction. HLnTiO4 was first prepared by traditional acid exchange of NaLnTiO4, and the KLnTiO4 series was subsequently formed from the reaction of HLnTiO4 with hot aqueous KOH. The ion exchange is stoichiometric, and the KLnTiO4 phases are thermally stable to at least 700°C. All the KLnTiO4 phases are orthorhombic and crystallize in space group Pbcm. The structures of KSmTiO4, KEuTiO4, KGdTiO4, and KDyTiO4 were refined by the Rietveld method and found to be isostructural with their NaLnTiO4 precursors. All the KLnTiO4 phases form stable hydrates when exposed to a humidified atomosphere.