Fourier transform infrared spectroscopic study of hydroxylpyromorphite Pb10(PO4)6OH2-hydroxylmimetite Pb10(AsO4)6(OH)2 solid solution series

A total of seven compounds of the hydroxylmimetite Pb-10(AsO4)(6)(OH)(2)-hydroxylpyromorphite Pb-10(PO4)(6)(OH)(2) (HPY-HMI) solid solution series were synthesized at 80 degrees C from aqueous solutions and characterized using XRD, SEM-EDS and FTIR. The substitution effect of [PO4](3-) anions by [AsO4](3-) on systematic changes in lattice parameters and spectral properties has been explained based on correlation between chemical composition and the peak positions. The substitution results in systematic linear increase in unit cell parameters and unit cell volume. Isomorphic substitutions are apparent in IR as a change in the position and intensity of bands derived from phosphates, arsenates and hydroxyl ions. Main bands attributed to stretching and bending vibrations appear at 1109-948 cm(-1) and 577-511 cm(-1) for phosphates in HPY and bending vibrations at 853-747 cm(-1) for arsenates in HMI. The most sensitive for substitution are v(1)-PO4 and v(3)-PO4 bands which shift toward lower wavenumbers from 931 cm(-1) to 911 cm(-1) for v(1)-PO4 and from 1109 cm(-1) to 1086 cm(-1) for v(3)-PO4. Arsenate bands are less sensitive for substitution: v(3)-AsO4 shift from 853 cm(-1) to 831 cm(-1). The strong correlations between the positions of the vibrational modes and the As/As + P ratios can be used to determine the composition of the phases from the hydroxylmimetite-hydroxylpyromorphite series. (C) 2015 Elsevier Ltd. All rights reserved.