Simple oxides, structural and electronic phase transitions

Simple oxides, structural and electronic phase transitions 

The simple oxides regarded as possible lower mantle components have proved amenable to a number of approaches involving quantum-mechanical calculations. For both MgO and CaO, the bonding, equations of state, and relative stabilities of the NaCl-type (51) and the CsCl-type (52) structures have been calculated using both modified electron-gas studies 

When the simple oxide involves a transition metal, other transformations than structure changes are possible at high pressures, in particular, changes in spin state. As early as 1960, Fyfe suggested that a pressure-induced high-spin- low-spin transition in Fe might have important consequences for the interior of the Earth, and this theme was later devel- 

The order of the predominantly Fe hd (crystal-field-type) orbitals in 

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