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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 np, nd (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(EF)) 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.

Acid–base properties in 1 to 14 M H3PO4 solutions are characterized with a R0(H) acidity function and [Formula: see text], [Formula: see text], [Formula: see text] functions which respectively represent the H+ activity in these media and their ability to give [Formula: see text], [Formula: see text], [Formula: see text] species. The thermodynamic limits of potential and the nature of the ionization equilibrium are studied. H and R acidity levels in phosphoric media are compared to those of sulfuric, hydrochloric, and hydrofluoric acid media. The identity of their R0(H) acidity level for the same value of water activity is shown.

The electronic band structure, metallization, structural phase transition and superconductivity of cubic zinc blende-type GaP and GaN are investigated. The equilibrium lattice constant, bulk modulus and pressure at which the compounds undergo a structural phase transition from ZnS structure to NaCl structure are predicted from the total energy calculations. The density of states at the Fermi level (N(E F )) is enhanced after metallization, which leads to the superconductivity in GaP and GaN. The superconducting transition temperatures (T c ) of GaP and GaN are obtained as a function of pressure for both the ZnS and NaCl structures and GaP and GaN come under the category of pressure-induced superconductors. When pressure is increased T c increases in both the normal and high-pressure structures. The dependence of T c on the electron-phonon mass enhancement factor λ shows that GaP and GaN are electron-phononmediated superconductors. Also, it is found that GaP and GaN retained in their normal structure under high pressure give appreciably high T c .

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