Effect of polarizable lone pair cations on the second-harmonic generation (SHG) properties of noncentrosymmetric (NCS) Bi2−xYxTeO5 (x = 0–0.2)

Abstract

Y³⁺-doped noncentrosymmetric (NCS) bismuth tellurite materials, Bi_2−xY_xTeO₅ (x = 0, 0.1, and 0.2), have been synthesized through standard solid-state reactions and structurally characterized by powder neutron diffraction. The reported NCS materials crystallize in the orthorhombic space group Abm2 (no. 39), and exhibit pseudo-three-dimensional frameworks that are composed of BiO₃, BiO₅, and TeO₃ polyhedra. Detailed diffraction studies show that the cell volume of Bi_2−xY_xTeO₅ decreases with an increasing amount of Y³⁺on the Bi³⁺ sites. However, no ordering between Bi³⁺ and Y³⁺ was observed in the Bi_2−xY_xTeO₅. Powder second-harmonic generation (SHG) measurements, using 1064 nm radiation, reveal that Bi₂TeO₅, Bi_1.9Y_0.1TeO₅, and Bi_1.8Y_0.2TeO₅ exhibit SHG efficiencies of approximately 300, 200, and 60 times that of α-SiO₂, respectively. The reduction in SHG for Y³⁺-doped materials is consistent with the lack of net moment originating from polyhedra with a polarizable Bi³⁺ cation.