Monitoring sulfur loss in polycrystalline solid solutions of CaS-La₂S₃ by Raman spectroscopy and X-ray diffraction

Controlling stoichiometry in materials is a critical consideration in advanced applications. Non-stoichiometry due to sulfur excess or sulfur loss is observed in the CaS-La2S3 (CLS) solid solution, a promising optical and thermoelectric material. We show that Raman spectroscopy can be used to assess deviation from stoichiometry in polycrystalline CLS. Use of this technique shows an increase in the full width at half maximum (FWHM) of the A1 vibrational peak, associated with disorder on the sulfur sublattice. This method is validated using X-ray diffraction, where a decrease in the lattice parameter is observed on either side of the stoichiometric composition. This paper illustrates the usefulness of Raman spectroscopy as a complementary metrology technique to assess stoichiometry in sulfide-based polycrystalline ceramics.