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Abstract:
We investigate the regions of thermodynamic stability of possible
modifications of the alkali oxides M2O as a function of pressure and
type of alkali metal (M=Li,Na,K,Rb,Cs). The results are in good
agreement with experiment at standard pressure, and we find that at
elevated pressures, all systems should exhibit a transition from the
experimentally observed modifications (CaF2- and CdCl2-type) to one or
more high-pressure modifications exhibiting structures belonging to the
extended cotunnite family, e.g., the high-pressure (hp)-BaF2-, the
PbCl2-, the gamma-US2-, or the Theta-Ni2Si-type. Metastable
modifications that would be stable at sufficiently large negative
pressures exhibit the CaCl2- or the CdCl2-structure type.
