In-Situ Studies of Structure Transformation and Al Coordination of KAl(MoO₄)₂ during Heating by High Temperature Raman and 27Al NMR Spectroscopies

Temperature-Dependent Raman Spectroscopic Study of the Double Molybdate KBi(MoO4)2

In situ high-temperature Raman spectra of polycrystalline KBi(MoO₄)₂ were recorded from room temperature to 1073 K. Thermal stability of the monoclinic KBi(MoO₄)₂ was examined by temperature-dependent XRD. The monoclinic phase transformed into the scheelite tetragonal structure at 833 K, and then to the monoclinic phase at 773 K. Quantum chemistry ab initio calculation was performed to simulate the Raman spectra of the structure of KBi(MoO₄)₂ high-temperature melt. The experimental Raman band at 1023 K was deconvoluted into seven Gaussian peaks, and the calculated results were in good agreement with the experimental data. Therefore, the vibrational modes of Raman peaks of molten KBi(MoO₄)₂ were assigned. It was confirmed that the isolated structure of [Bi(MoO₄)₂]^- monomer, consisting of Mo⁶⁺ centers and Bi³⁺ sub-centers connected by edge-sharing, mainly exists in the melt of KBi(MoO₄)₂.

Raman Spectroscopic Study of Coal Samples during Heating

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.

Quantitative Studies on the Structure of Molten Binary Potassium Molybdates by in Situ Raman Spectroscopy and Quantum Chemistry ab Initio Calculations

The quantitative distribution of different species ( Q _i^jklm and H _i^jklmno) in binary potassium molybdate melts has been investigated by in situ high temperature Raman spectroscopy in conjunction with quantum chemistry (QC) ab initio calculations. The symmetric stretching vibrational wavenumbers of molybdenum nonbridging oxygen bonds in high wavenumber range and their respectively corresponding Raman scattering cross sections were determined and analyzed. Deconvolution of the stretching bands of molybdenum nonbridging oxygen bonds of molten Raman spectra by using the Voigt function was carried out. The six-coordinated molybdenum oxygen octahedra [MoO₆]^6- have been proposed to be present in molten molybdates, apart from the well-known existence of the four-coordinated [MoO₄]^2- tetrahedra. The quantitative analysis of different species in the molten K₂MoO₄-MoO₃ system and their dependence on the content of MoO₃, as well as the relationship with the viscosities of the melts, were also discussed. The quantitative results have been integrated with published data on physical and chemical properties of the melts.