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Updated: Jun 10, 2026
Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses
Published on: June 7, 2018
High-pressure Raman spectroscopy of the new Mg(Cr,Al)2O4 and Mg2(Al,Cr)2O5 post-spinel phases
A V Iskrina1, A V Spivak1, A V Bobrov2
1D.S. Korzhinskii Institute of Experimental Mineralogy of Russian Academy of Sciences, Chernogolovka 142432, Russia.
Abstract:
Phase relationships in the MgO-Al2O3-Cr2O3 system have been studied experimentally at pressures of 12, 14, 18 and 22 GPa and a temperature 1600 °C. The first set of experimental runs returned several phases with varying proportions of MgAl2O4 and MgCr2O4 end-members. In the second series, two phases with stoichiometrical formulae MgCr1.43Al0.57O4 and Mg1.93Al1.22Cr0.79O5 calculated, simplified as Mg(Cr,Al)2O4 and Mg2(Al,Cr)2O5, respectively, were obtained. The first phase has a calcium titanate-type structure, orthorhombic unit cell (a = 2.8328 (Litasov et al., 2004 (4)) Å, b = 9.3956 (Bindi et al., 2014 (15)) Å, c = 9.5898 (Bindi et al., 2014 (15)) Å, V = 255.2407 (Akaogi, 2007 (5)) Å3, Z = 4) and the space group Cmcm. The second phase is orthorhombic as well, has a modified ludwigite-type structure with unit cell parameters a = 12.3490 (Sirotkina et al., 2018 (18)) Å, b = 9.4937 (Wang et al., 2002 (13)) Å, c = 2.8299(4) Å, V = 331,77 (Ricolleau et al., 2010 (7)) Å3, Z = 4 and a space group Pbam. Pressure-induced changes of the new post-spinel phases Mg(Cr,Al)2O4 and Mg2(Al,Cr)2O5 have been examined by in situ Raman spectroscopy at pressures up to 30 GPa. At 12-16 GPa the crystal color changes from green to red, which persists with further pressure increase. The studied phases are stable at lower mantle conditions, can be considered as post-spinel phases and may accommodate crustal elements in the deep interiors of the Earth.
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