Ca6.5Pb1.5ZnBi(VO4)(7), a novel whitlockite-type vanadate: crystal structure refinement and properties characterization

摘要

Novel compounds Ca8-xPbxZnBi(VO4)(7) (0 <= x <= 1.5) solid solution with the whitlockite-type structure were synthesized by a standard solid-state method. The unit-cell parameters were determined by X-ray powder diffraction and using Le Bail decomposition. The crystal structural of Ca6.5Pb1.5ZnBi(VO4)(7) was refined by Rietveld method. It is found that Pb2+ cations occupy a half of the M3 site, whereas the M1 and M2 sites are predominantly occupied by calcium with admixture of Bi3+ cations. The M5 site is fully occupied by Zn2+ cations. The M4 site in the structure of studied sample remains vacant and does not participate in the cations arrangement. Optical second harmonic generation demonstrates high non-linear optical activity. Dielectric investigations confirm polar space group R3c. Changes in the non-linear optical and ferroelectric parameters are matched with lead and zinc cation distribution over the sites of the whitlockite-type structure. (C) 2017 International Centre for Diffraction Data.