Barium-induced effects on structure and properties of β-Ca3(PO4)2-type Ca9Bi(VO4)7

Ca9-xBaxBi(VO4)(7) (0 <= x <= 1.5) solid solutions with the beta-Ca-3(PO4)(2)-type structure were prepared by a solid-state method. Powder X-ray diffraction study of 0 <= x <= 0.7 showed that Bi3+ and Ba2+ cations were completely incorporated into the beta-TCP-type host framework up to x = 0.7. Ca9-xBaxBi(VO4)(7) (x = 0.25, 0.5) structures were refined by the Rietveld method using powder synchrotron X-ray diffraction data. DSC, SHG and dielectric properties measurements of Ca9-x BaxBi(VO4) (x = 0, 0.25, 0.5) revealed two reversible first-order phase transitions (PT1 and PT2). Increase of Ba2+ content in Ca9-xBaxBi(VO4)(7) leads to lowering PT1 and PT2 phase transitions temperatures due to the increase of cell volume and the structure looseness. Nonlinear optical activity of Ca9-xBaxBi(VO4)(7) reaches its maximum response at x = 0.5. The amount of (M1-(M3)-M2) dipoles in Ca9-xBaxBi(VO4)(7) (0 < x <= 0.7) structures increases with increasing Ba2+ content from 0.25 to 0.5 and decreases with changing x from 0.5 to 0.7. (C) 2019 Elsevier B.V. All rights reserved.