Crystal chemistry of the noncentrosymmetric eulytites: A(3)Bi(XO(4))(3) (X = V, A = Pb; X = P, A = Ca, Cd, Sr, Pb).

Eulytite compounds, A(3)Bi(XO(4))(3) (X = P, A = Ca, Cd, Sr, Pb), belong to the noncentrosymmetric space group I4̅3d (No. 220) as determined by single-crystal X-ray diffraction studies. The crystals were grown from the melt-cool technique with considerable difficulty as the compounds melt incongruently at their melting temperature, except for the compound Pb(3)Bi(PO(4))(3). The unit cell parameter a is 9.984(5), 9.8611(3), 10.2035(3), and 10.3722(2) Å for Ca(3)Bi(PO(4))(3), Cd(3)Bi(PO(4))(3), Sr(3)Bi(PO(4))(3), and Pb(3)Bi(PO(4))(3) respectively, and there are four formula units in the unit cell. The structure of Pb(3)Bi(VO(4))(3), a unique eulytite with vanadium substitution, is compared with all these phosphorus substituted eulytites. The A(2+) and Bi(3+) cations occupy the special position (16c) while the O anions occupy the general Wyckoff position (48e) in the crystal structure. Only one O position has been identified for Pb(3)Bi(PO(4))(3) and Pb(3)Bi(VO(4))(3), whereas two O atom sites were identified for Ca(3)Bi(PO(4))(3), Cd(3)Bi(PO(4))(3), and Sr(3)Bi(PO(4))(3). The UV-vis diffuse reflectance spectra indicate large band gaps for all the phosphate eulytites while a lower band gap is observed for the vanadate eulytite. The feasibility of the use of these compounds in optoelectronic devices has been tested by measuring the second-harmonic generation (SHG) values which have been found to be of a magnitude equivalent to the commercially used KDP (KH(2)PO(4)).