FT-Raman study of three syntetic solid solutions formed by orthorhombic sulfates: Celestite-barytes, barytes-anglesite and celestite-anglesite

Abstract

In, the present work, three different solid solutions whose end-members are the orthorhombic sulfates celestite (SrS04), barytes (BaS04) and anglesite (PbS04) are studied using FT-Raman spectroscopy. Sulfate anion symmetric internal modes have been examined in detail by means of band-shape analysis and component fitting procedures. The symmetric stretching mode v,(A,)changes its wavenumber position lillearly with the cationic composition of the samples which further confirrns the ideal character of the solid solutions studied. The corresponding full-width at half-height is strongly increased in the central components of the different solid solutions which can be understood as an effect of the positional disorder induced by random cationic substitution. Similar results are observed in the syrnmetric bending mode, ~(E). The study of the low frequency spectral region permits one to differentiate traslational modes of the sulfate anion, which changes its wavenumberposition when the alkali-earth metal ion changes from rotational modes. This permits the tentative band assignement of the anglesite rotational Raman bands at 134 and 152 cm-1, which were previously not assigned.