Pressure dependence of metallization and superconducting transition in AgCl and AgBr

The electronic band structure, metallization, structural phase transition and superconducting transition of silver chloride (AgCl) and silver bromide (AgBr) under pressure are studied using the TB-LMTO method. The ground state properties and bandgap values are compared with the experimental and previous theoretical results. These silver halides become metals and superconductors under high pressure, but before this they undergo structural phase transition from NaCl phase to CsCl phase. It is found that the charge transfers between Ag 5s, 4d and X n p, n d (X = Cl, Br; n = 3, 4) states cause metallization. It is found that the metallization pressure increases with decrease of lattice constant. The density of states at the Fermi level ( N ( E F )) is enhanced as the pressure is further increased, which leads to the superconductivity in AgCl and AgBr. Like CsI, AgCl and AgBr come under the class of pressure induced superconductors. The pressure effects on λ (electron–phonon mass enhancement factor) and μ * (electron–electron interaction parameter) clearly suggest that AgCl and AgBr are electron–phonon mediated superconductors. The non-occurrence of metallization, phase transition and onset of superconductivity simultaneously in ionic solids is also confirmed.