Syntheses, structures, and second-harmonic generating properties in new quaternary tellurites: A2TeW3O12 (A=K, Rb, or Cs)

The syntheses, structures, and characterization of a new family of quaternary alkali tungsten tellurites, A2TeW3O12 (A=K, Rb, or Cs), are reported. Crystals of the materials were synthesized by supercritical hydrothermal methods using 1 M AOH (A=K, Rb, or Cs), TeO2, and WO3 as reagents. Bulk, polycrystalline phases were synthesized by standard solid-state methods combining stoichiometric amounts of A2CO3, TeO2, and WO3. Although the three materials are not iso-structural, each exhibits a hexagonal tungsten oxide layer comprised of corner-sharing W6+O6 octahedra. Te4+O3 groups connect the WO6 layers in K2TeW3O12, whereas the same groups cap the WO6 layers in Rb2TeW3O12 and Cs2TeW3O12. This capping results in non-centrosymmetric structures for Rb2TeW3O12 and Cs2TeW3O12. Powder second-harmonic generation measurements on Rb2TeW3O12 and Cs2TeW3O12 revealed strong SHG efficiencies of 200 and 400×SiO2, respectively. These values indicate an average non-linear optical susceptibility, 〈deff〉exp of 16 and 23 pm/V for Rb2TeW3O12 and Cs2TeW3O12, respectively. Crystallographic information: K2TeW3O12, monoclinic, space group P21/n (No. 14), a=7.3224(13) Å, b=11.669(2) Å, c=12.708(2) Å, β=90.421(3)°, Z=4; Rb2TeW3O12, trigonal, space group P31c (No. 159), a=b=7.2980(2) Å, c=12.0640(2) Å, Z=2.