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MgO is a crystalline solid with significant practical and theoretical value in many fields. Brillouin scattering has long been regarded as a reliable method for accurately measuring the elasticity and photoelasticity of crystals; however, its practical application in photoelasticity has been stagnant. In this paper, three independent photoelastic constants of MgO have been measured for the first time by polarized Brillouin scattering spectroscopy and we have defined a scattering factor containing three photoelastic constants to connect with the Brillouin peak intensity. Accordingly, the ratios of ‖p11/p44‖ = 2.87 (1), ‖p12/p44‖ = 0.53 (2), and ‖p12/p11‖ = 0.18 (1) were accurately determined by comparing the intensities of transverse and longitudinal acoustic modes within the same spectrum. Then, a standard sample of CaF2 crystals was adopted to calculate the corresponding peak intensity of MgO to achieve the absolute values (‖p44‖ = 0.085 (1), ‖p11‖ = 0.244 (4) and ‖p12‖ = 0.045 (3)). Finally, all three constants were confirmed to be negative. These first-hand Brillouin scattering results can eliminate the long-standing discrepancies of the photoelastic constants of MgO. A standard process for the simultaneous measurement of elasticity and photoelasticity through Brillouin scattering was also constructed. [ABSTRACT FROM AUTHOR]

The local structure around germanium is a fundamental issue in material science and geochemistry. In the prevailing viewpoint, germanium in GeO2 melt is coordinated by at least four oxygen atoms. However, the viewpoint has been debated for decades due to several unexplained bands present in the GeO2 melt Raman spectra. Using in situ Raman spectroscopy and density functional theory (DFT) computation, we have found a [GeOØ2]n (Ø = bridging oxygen) chain structure in a GeO2 melt. In this structure, the germanium atom is coordinated by three oxygen atoms and interacts weakly with two neighbouring non-bridging oxygen atoms. The bonding nature of the chain has been analyzed on the basis of the computational electronic structure. The results may settle down the longstanding debate on the GeO2 melt structure and modify our view on germanate chemistry. The structure of GeO2 melt has been debated for decades due to several unexplained bands present in the GeO2 melt Raman spectra. Here authors present a promising way to analyse melt structures from Raman spectra and they demonstrate threefold coordinated germanium is formed in the GeO2 melt. [ABSTRACT FROM AUTHOR]

The effect of MgO on the microstructures and macroscopic properties of SiO2‐poor/rich MgO‐CaO‐SiO2 melts was investigated by in situ high temperature time‐gated Raman spectroscopy coupled with aerodynamic levitation heating of molten samples. Results of density functional theory calculations of Mg2SiO4, γ‐Ca2SiO4, and MgCaSiO4 crystals and quantum chemistry ab initio simulations of Q0 species (Q0 refers to tetrahedral Si‐O units without bridging oxygen) of SiO2‐poor series MgO‐CaO‐SiO2 molten samples certified that with the substitution of CaO by MgO, the variation of Raman intensity at 900–1100 cm−1 of xMgO‐(2‐x)CaO‐SiO2 melts was caused by the antisymmetric stretching vibration modes of distorted silicon‐oxygen tetrahedra. The experimental result of SiO2‐rich series of MgO‐CaO‐SiO2 molten samples could identify various Qi species quantitatively and demonstrated that with the substitution of CaO by MgO, the abundance of Q3 species dramatically decreased, but Q4 species increased slightly, whereas Q1 and Q2 species maintain insignificant change. A positive correlation between viscosity and the abundance ratio of Q3 to Q4 was assumed and illustrated. [ABSTRACT FROM AUTHOR]