Syntheses, Crystal Structure, and Second Harmonic Generation Response of Noncentrosymmetric Layered Selenites and Tellurites of Antimony(V), ASb<inf>3</inf>X<inf>2</inf>O<inf>12</inf>(A = K, Rb, Cs, Tl; X = Se, Te)

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) A and c = 11.8978(4)-12.0478(3) A. 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.