ABSTRACT
Eight quaternary selenites and tellurites of antimony(V), ASb3X2O12 (A = K, Rb, Cs, Tl; X = Se, Te), have been synthesized by solid state reactions and structurally characterized by single crystal X-ray diffraction. They are isostructural compounds, which crystallize in the polar noncentrosymmetric P63mc space group with hexagonal unit cell parameter values in the ranges of a = 7.1538(1)-7.2429(1) Å and c = 11.8978(4)-12.0478(3) Å. Their noncentrosymmetric layered structure consists of hexagonal-tungsten-oxide-related (Sb3X2O12)- layers interleaved with A+ ions. They have optical band gap values of 2.90-4.46 eV and showed powder second harmonic generation response equivalent to 1.0-37.2 × KDP.
ABSTRACT
The quaternary A 2W3SeO12 (A = NH4, Cs, Rb, K or Tl) selenites have been prepared in the form of single crystals by hydro-thermal and novel solid-state reactions. They were characterized by X-ray diffraction, thermal and spectroscopic studies. All of them have a hexa-gonal tungsten oxide (HTO) related [W3SeO12]2- anionic framework with pyramidally coordinated Se4+ ions. The known A 2W3SeO12 (A = NH4, Cs or Rb) compounds are isostructural with the Cs2W3TeO12 compound and have a non-centrosymmetric layered structure containing intra-layer Se-O bonds. The new compound K2W3SeO12(α) is isostructural with the K2W3TeO12 compound and has a centrosymmetric three-dimensional structure containing inter-layer Se-O bonds. It is inferred that the new Tl2W3SeO12 compound has the same three-dimensional structure as K2W3SeO12(α).
