Abstrakt

Band structure,metallization and superconducting transition of CsBr under high pressure

T.ThusnavisVini, C.Nirmala Louis, A.Amalraj

The results of a full potential linear muffin-tin orbital (FP-LMTO) study on the electronic properties of ionic insulator cesiumbromide (CsBr) under pressure is presented. The equilibrium lattice constant, bulk modulus, pressure derivative of bulk modulus and the phase transition pressure at which the compounds undergo structural phase transition from CsCl to HCP structure is predicted from the total energy calculations. The ground state properties and band gap values are compared with the experimental results.At normal pressure CsBr is a direct bandgap semiconductor. When the pressure is increased there is enhanced overlapping between the wave functions of the neighbouring atoms.As a result thewidths of the valence and empty conduction bands increase. These changes lead to the narrow-ining and direct closing of band gap in CsBr (metallization). On further increase of pressure, CsBr becomes superconductor, and this material comes under the class of electron-phonon-mediated high pressure superconductor.The superconducting transition temperatures (Tc) of CsBr is obtained as a function of pressure for HCP structure. It is also confirmed that themetallization, structural phase transition and onset of superconductivity do not occur simultaneously in ionic compounds. Subject classification : 71, 71.15Fv , 61.50.Ks, 64.70.Kb, 74.62.Fj;