Vibrational spectroscopic study of mimetite–pyromorphite solid solutions

A number of compounds of the mimetite Pb5(AsO4)3Cl–pyromorphite Pb5(PO4)3Cl solid solution series were synthesized at room temperature and analyzed with Raman and infrared spectroscopy. The fundamental antisymmetric stretching (ν3) and bending (ν4) vibrations of the mimetite–pyromorphite solid solutions occur in the regions 720–1040 cm−1 and 400–580 cm−1. The band originating from the ν3 and ν4 modes shifts to higher wavenumbers between mimetite and pyromorphite because the atomic mass of As is higher than P and As–O bonds are longer than P–O bonds. The position, shape and relative intensity of the bands vary primarily as a function of As/(As + P) in the analyzed solid. The strong correlations between the positions of the vibrational modes and the As/(As + P) ratio can be used to determine the composition of the investigated natural and synthetic samples of the minerals from the mimetite–pyromorphite series.

Graphical abstractThe fundamental antisymmetric stretching (ν3) and bending (ν4) vibrations of mimetite–pyromorphite solid solutions occur in the regions 720–1040 cm−1 and 400–580 cm−1. The observed correlation between the band positions and the extent of the anionic substitutions among the series can be used to estimate the As and P content in mimetite–pyromorphite solid solutions.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Mimetite–pyromorphite solid solution series were synthesized at room temperature. ► The solids were characterized by Raman and infrared spectroscopies. ► The position of the selected bands vary primarily as a function of the As/(As + P) ratio. ► The observed bands are shifted to higher wavenumbers with increasing bond strength.