In order to assist in predicting the properties of molten cryolite-alumina electrolytes widely used in the Hall–Héroult process, the micro-structure of the molten binary system was investigated by in situ high temperature Raman spectroscopy from room temperature to 1273 K under an argon atmosphere. The symmetric stretching vibrational wavenumbers of possible clusters in the molten system were further calculated through quantum chemistry ab initio simulations and compared with the experimental Raman spectra of the molten system. The molten K₃AlF₆–Al₂O₃ system was found to consist of [AlF₅]²⁻, [AlF₆]³⁻, [Al₂OF₆]²⁻ and [Al₂O₂F₄]²⁻ clusters. With the increasing addition of Al₂O₃ to molten K₃AlF₆, the structure of six-coordinated Al atoms connected by terminal fluorine is partly believed to evolve into a structure of two four-coordinated Al atoms connected by single-bridging oxygen. The mole percentage of the species in the melt was also calculated from the experimental Raman spectra. As the Al₂O₃ content increased from 0 to 8.0 wt%, the content of [Al₂OF₆]²⁻ in the melt was found to increase swiftly from 0 to 33.0 mol%, while the [Al₂O₂F₄]²⁻ content decreased after reaching a maximum of 1.5 mol%.

Raman spectroscopy can be used to record the characteristic spectra of carbonaceous materials. The D and G bands are the most popular and most important spectral characteristics when discussing carbonaceous materials. In this paper, a Raman spectroscopic study of different coals was first carried out using a 355 nm wavelength laser beam as an excitation source. The spectral parameters of the resultant spectra were evaluated and analyzed. Raman spectral characteristics of different kinds of coals were explored. The high temperature-dependent Raman spectra of the coals were further collected in a temperature range from 298 to 1473 K in order to investigate the transformations of the internal structure of the coals during the pyrolysis process. An abnormal blue shift of the G band occurred at moderate temperature (600–900 K), and the intensity of the G band became weaker at high temperatures, indicating pyrolysis and graphitization of the sample at moderate and high temperature, respectively.