IONIC CHARACTER, PHASE TRANSITIONS, AND METALLIZATION IN ALKALINE-EARTH METAL OXIDES AND CHALCOGENIDES UNDER PRESSURE

The structural and thermodynamic properties of the alkaline-earth metal oxides and chalcogenides (AEMOCs) with the cubic structure (CaX , SrX , and BaX , where X =O, S, Se, and Te) and the parameters of the pressure-induced B1-B2 structural phase transitions in them have been calculated from the first principles. The crystalline and ionic radii in the AEMOCs are studied including the dependences of the ionic radii in the B1 and B2 structures on the pressure. The magnitudes of interband transitions and the band gaps in the examined compounds are calculated in the framework of the first-principles approach of the density functional theory and using the method of pseudopotential. The first-principles band calculations are carried out to determine the metallization pressures for the researched compounds.