Effect of polarizable lone pair cations on the second-harmonic generation (SHG) properties of noncentrosymmetric (NCS) Bi_(2?x)Y_xTeO_5 (x = 0–0.2)?

摘要

Y~(3+)-doped noncentrosymmetric (NCS) bismuth tellurite materials, Bi_(2?x)Y_xTeO_5 (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 BiO_3, BiO_5, and TeO_3 polyhedra. Detailed diffraction studies show that the cell volume of Bi_(2?x)Y_xTeO_5 decreases with an increasing amount of Y_(3+)on the Bi~(3+) sites. However, no ordering between Bi~(3+) and Y~(3+) was observed in the Bi_(2?x)Y_xTeO_5. Powder second-harmonic generation (SHG) measurements, using 1064 nm radiation, reveal that Bi_2TeO_5, Bi_(1.9)Y_(0.1)TeO_5, and Bi_(1.8)Y_(0.2)TeO_5 exhibit SHG efficiencies of approximately 300, 200, and 60 times that of α-SiO_2, respectively. The reduction in SHG for Y~(3+)-doped materials is consistent with the lack of net moment originating from polyhedra with a polarizable Bi~(3+) cation.