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

In the present work, three different solid solutions whose end-members are the orthorhombic sulfates celestite (SrSO4), barytes (BaSO4) and anglesite (PbSO4) are studied using FT-Raman spectroscopy. Sulfate anion symmetric in ternal modes have been examined in detail by means of band-shape analysis a nd component fitting procedures. The symmetric stretching mode v(1)(A(1)) c hanges its wavenumber position linearly with the cationic composition of th e samples which further confirms 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 un derstood as an effect of the positional disorder induced by random cationic substitution. Similar results are observed in the symmetric bending mode, v(2)(E). The study of the low frequency spectral region permits one to diff erentiate translational modes of the sulfate anion, which changes its waven umber position when the alkali-earth metal ion changes from rotational mode s. This permits the tentative band assignment of the anglesite rotational R aman bands at 134 and 152 cm(-1), which were previously not assigned.