Competition between Burgers mechanism and Bain deformation in alkaline-earth metals:: Host-guest structures of barium and strontium

The structural mechanisms underlying the high-pressure phase transitions in alkaline-earth metals are described and analyzed theoretically in the framework of an extension of the Landau approach to reconstructive phase transitions. All the high-pressure structures are interpreted as resulting from the full or partial realization of the Burgers and Bain deformation mechanisms. The host-guest structures found in strontium and barium are shown to reflect the competition between the two preceding mechanisms, which expresses at the structural level the competition occurring at the electronic level between the bonding changes induced on pressurization. Further experimental measurements and calculations are suggested for testing our theoretical analysis of the transition mechanisms.