Predicting transition pressures for obtaining nanoporous semiconductor polymorphs: oxides and chalcogenides of Zn, Cd and Mg.

The energy versus volume equations of state are calculated for seven known and hypothetical polymorphic forms of ZnX, CdX, and MgX (where X = O, S, Se, Te). From these data the phases of lowest enthalpy are extracted with respect to decreasing pressure starting at the ground state for all compositions. Following these paths of minimum enthalpy, with respect to the polymorphs considered, we predict the transition pressures required to convert the ground-state phase into the novel, as yet hypothetical, nanoporous SOD phase (an analogue of the silicate zeolite sodalite). Our results suggest that the SOD phase would be thermodynamically stable for all compositions considered under suitable negative pressures. Of all the compositions considered CdX and MgX with relatively large anions (i.e. Se and Te) are specifically predicted to be the most amenable materials for the experimental preparation of the SOD phase.