Synergistic Influence of d0 (Nb5+) and d10 (Cd2+) Cations in Stabilizing Noncentrosymmetric Dion-Jacobson Layered Perovskites, A'Cd2Nb3O10 (A' = Rb, Cs).

New Dion-Jacobson (n = 3) layered perovskites, A'Cd2Nb3O10 (A' = Rb, Cs), have been synthesized by a solid-state method. Powder X-ray diffraction measurements confirm the noncentrosymmetric orthorhombic (space group Ima2) structures for both rubidium- and cesium-containing layered oxides. The distorted octahedral coordination of the d0 metal cations (Nb5+) coupled with the increased covalency in the lattice by the introduction of d10 metal cations (Cd2+) is responsible for the acentric structures. The resulting second-harmonic-generation (SHG) efficiencies of the polycrystalline samples (size 45-63 μm) using 1064 nm radiation reveal comparable values for CsCd2Nb3O10 and nearly 5 times higher output values for RbCd2Nb3O10 with respect to potassium dihydrogen phosphate. These structures were further confirmed from transmission electron microscopy and Raman spectroscopy measurements. The optical characteristics show interesting variations to the expected photocatalytic activities. Ion-exchange reactions result in the synthesis of proton- and lithium-containing oxides, which are otherwise inaccessible by direct solid-state reactions. The mobilities of the interlayer ions have also been confirmed by ionic conductivity measurements.