Syntheses and Characterization of AM2V2O11 (A = Ba, Sr, Pb; M = Nb, Ta) Vanadates with Centrosymmetric and Noncentrosymmetric Structures.

Five isomorphous AM2V2O11 vanadates of niobium and tantalum, namely, BaNb2V2O11, BaTa2V2O11, SrNb2V2O11, SrTa2V2O11, and PbTa2V2O11, were prepared by solid-state reactions and structurally characterized by single-crystal and powder X-ray diffraction techniques. Barium and strontium compounds, respectively, have centrosymmetric and noncentrosymmetric types of layered structure, wherein [M2V2O11]2- anionic layers are interleaved with A2+ cations. Both types of layered structure are found for lead compound. The strontium and lead compounds are type I phase-matching materials with second-harmonic-generating efficiencies of 33-50% of LiNbO3, and their dielectric properties were evaluated. A three-dimensional structural variant was also identified for strontium compounds, which crystallize in noncentrosymmetric orthorhombic space group C2221.