Strong Second Harmonic Generation (SHG) Originating from Combined Second-Order Jahn–Teller (SOJT) Distortive Cations in a New Noncentrosymmetric Tellurite, InNb(TeO₄)₂

Pure polycrystalline bulk samples and single crystals of a novel polar noncentrosymmetric (NCS) indium niobium tellurium oxide, InNb(TeO4)2, have been synthesized through solid-state reactions with In2O3, Nb2O5, and TeO2. InNb(TeO4)2 exhibits a three-dimensional structural backbone consisting of layers of corner-shared InO6 octahedra, layers of corner-shared NbO6 octahedra, and chains of corner-shared TeO4 polyhedra. The infrared spectrum shows In-O, Nb-O, and Te-O vibrations, and the UV-vis diffuse reflectance spectrum shows a band gap of 3.5 eV for the reported material. Thermal analysis indicates that InNb(TeO4)2 is thermally stable to 740 °C. Powder second-order nonlinear optical (NLO) measurements reveal that InNb(TeO4)2 has a strong second harmonic generation (SHG) efficiency, 100 times that of α-SiO2. A detailed structural examination indicates that the strong SHG is due to the combined net polarization originating from the distorted environment of second-order Jahn-Teller (SOJT) cations such as Nb(5+) and Te(4+). Elemental analysis, the magnitude of distortion, and calculations of dipole moments for InNb(TeO4)2 are also presented.