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

Abstract

Recent interest in optimizing composition and synthesis conditions of functional crystals, and the further exploration of new possible candidates for tunable solid-state lasers, has led to significant research on compounds in this family MIMIII(MVIO4)2 (MI = alkali metal, MIII = Al, In, Sc, Fe, Bi, lanthanide; MVI = Mo, W). The vibrational modes, structure transformation, and Al coordination of crystalline, glassy, and molten states of KAl(MoO4)2 have been investigated by in-situ high temperature Raman scattering and 27Al magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy, together with first principles density functional simulation of room temperature Raman spectrum. The results showed that, under the present fast quenching conditions, Al is present predominantly in [AlO6] octahedra in both KAl(MoO4)2 glass and melt, with the tetrahedrally coordinated Al being minor at approximately 2.7%. The effect of K+, from ordered arrangement in the crystal to random distribution in the melt, on the local chemical environment of Al, was also revealed. The distribution and quantitative analysis of different Al coordination subspecies are final discussed and found to be dependent on the thermal history of the glass samples.

Structural origin of thermally induced refractive index changes in Yb3+/Al3+/P5+/F−‐co‐doped silica glass

“…This result indicates that the glass became more disordered after fire polishing. The results are supported by the high‐temperature 27 Al NMR method; the Al is presented predominantly in Al Ⅴ and Al Ⅵ units in the melt or glasses quenched from the liquids 35‐38 . The subsequent annealing of the fire‐polished YbAPF0.85 glass led to the narrowing of the spectrum and a slight decrement in the Al Ⅴ units, as shown in Table 4.…”

“…The results are supported by the high-temperature 27 Al NMR method; the Al is presented predominantly in Al Ⅴ and Al Ⅵ units in the melt or glasses quenched from the liquids. [35][36][37][38] The subsequent annealing of the fire-polished YbAPF0.85 glass led to the narrowing of the spectrum and a slight decrement in the Al Ⅴ units, as shown in Table 4. Figure 5C shows the 31 P MAS NMR spectra of the investigated glasses.…”

In‐situ high‐temperature Raman spectroscopic studies of the vibrational characteristics and microstructure evolution of sodium tungstate dihydrate crystal during heating and melting

“…Luz‐Lima et al studied the low‐temperature cubic and high‐temperature orthorhombic phases of NWO (Na 2 WO 4 ) crystal and further performed mode assignment on the basis of the lattice dynamics calculations of Na 2 MoO 4 . Previous report on the theoretical calculation of Raman active vibrational modes of molybdate showed that the wavenumber simulated by density functional theory (DFT) is more satisfied with experiment than that by lattice dynamics calculations . The vibrational mode of these two phases is therefore revisited by DFT simulation based on NWO itself, and some minor modifications are hence made in this paper.…”

Raman Spectroscopic Study of Coal Samples during Heating

“…This cooling allowed for the cleaning of the silica glass prior to measurement. Figure 6, it is clear that the peak position of the D band related to the low molecular weight carbon organics, while the intensity of the D band changed negligibly with the increasing temperature [26,27]. This implies an increase in the graphitization degree along with the increase in temperature.…”