Two New Non-centrosymmetric n = 3 Layered Dion–Jacobson Perovskites: Polar RbBi2Ti2NbO10 and Nonpolar CsBi2Ti2TaO10

Two new non-centrosymmetric (NCS) n = 3 layered perovskites, RbBi2Ti2NbO10 and CsBi2Ti2TaO10, have been synthesized through high temperature solid state reactions. X-ray diffraction analyses suggest that RbBi2Ti2NbO10 crystallizes in the orthorhombic polar space group, Ima2 (No. 46), whereas CsBi2Ti2TaO10 crystallizes in the tetragonal nonpolar space group, P4̅ (No. 81). Interestingly, CsBi2Ti2TaO10 is the first Dion–Jacobson (DJ)-type layered perovskite with a NCS nonpolar space group. Powder second-harmonic generation (SHG) measurements with 1064 nm radiation reveal that both of the reported materials have SHG efficiencies of approximately 100 times that of α-SiO2 and are phase-matchable (type I). Piezoelectricity measurements suggest that the estimated d 33 values for polar RbBi2Ti2NbO10 and nonpolar CsBi2Ti2TaO10 are 170 and 67 pm V–1, respectively. The net polarization direction arising from the constituent distorted polyhedra and the key component causing microscopic deformations in NCS structure are introduced. Polarization measurements are also presented along with other characterizations such as the UV–vis diffuse reflectance, and infrared spectra, elemental analyses, and electronic structure calculations for the reported materials.