Determining off-stoichiometry within calcium lanthanum sulfide ceramics using Raman spectroscopy

Advanced ceramics require well defined stoichiometries to exhibit their optimal electronic and optical behaviors. The CaS-La2S3 solid solution exhibits promising optical and thermoelectric properties but is also venerable to sulfur loss during processing. The characterization of this sulfur loss is difficult using traditional methods due to sample preparation, long acquisition times, and error bars which limit the usefulness of the measurement. In this paper, we show that our material system undergoes sulfur loss during processing and that this sulfur loss goes on to impact material physical properties. We access sulfur loss through the use of Raman spectroscopy and the evaluation of the full width at half maximum (FWHM) of the A1 peak of the system. We then correlate this Raman analysis and XRD to trends in the material properties as a function of sulfur loss.