First-principles calculation of the phonon spectrum ofMgAl2O4spinel

Abstract

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Si-Disordering in MgAl2O4-Spinel under High P-T Conditions, with Implications for Si-Mg Disorder in Mg2SiO4-Ringwoodite

“…The weak peak at ~715 cm −1 evidently emerged or intensified at high T, and persisted to ambient T after cooling, so that it could be confidently attributed to the high-T structural disorder process. Theoretical investigations have confirmed this attribution [81,83]. In comparison, an even weaker Raman peak at ~222 cm −1 was detected at high T by Slotznick & Shim [57] only, and was similarly attributed to the high-T structural disorder process.…”

“…Five Raman-active fundamental vibrations, A 1g + E g + 3T 2g , are predicted [78]. Theoretical calculations yield the A 1g at~762 cm −1 , E g at~408 cm −1 , and T 2g at~667 cm −1 (T 2g (2) ),~557 cm −1 (T 2g(3) ) and~317 cm −1 (T 2g (1) ; [79][80][81][82][83][84][85]). The intensity of these Raman modes decreases in the order of E g > T 2g(2) > A 1g > T 2g (1) > T 2g (3) [83].…”

Dynamical stability of the α and θ phases of alumina

“…18 In that sense, we may relate two Raman modes of A g symmetry at 20.758 and 23.465 THz, which are AlO 4 -tetrahedron breathing and stretching of the Al T -O bond, respectively, to the same modes in the spinel structure. The close agreement between these frequencies, and their common origin from the tetrahedrally coordinated Al, point to the high stability of such coordination, despite the very different chemical environment.…”

Optical and Physical Properties of Cobalt Oxide Films Electrogenerated in Bicarbonate Aqueous Media

“…78 For this structure, the A 1g , E g , and three T 2g modes are Raman active. [79][80][81][82] Concerning the CoO oxide, it is well known that, at room temperature, its crystal structure is of face-centered cubic (fcc) type, in which Co 2+ ions are octahedrally coordinated to six O 2-ions. 5,[83][84][85] Then, theoretically, the O h symmetry of CoO should lead to the observation of at least three Raman active modes (A 1g , E g , and T 2g ).…”