Variations of chemical bonds in silver halides under high pressures

Rocksalt structured AgI (rs-AgI), which appears under pressures between 0.4 and 11.3 GPa, shows high ionic conductivity as high as that in alpha-AgI, especially at high temperatures. Microscopic origins of ion conduction mechanisms have not been clarified until now and are therefore investigated using the discrete variational X alpha (DV-X alpha) cluster method. Comparable studies for AgCl and AgBr, which are known as high ionic conductors just below melting temperatures and form the rocksalt structure, are also done. Ionic interactions between a mobile Ag ion and remaining ions are almost the same between those under different pressures, while covalent interactions between the mobile Ag ion and the remaining Ag ions change drastically when the mobile Ag ion is migrating. Similar results are also obtained for AgCl and AgBr. The covalent interactions between the mobile Ag ion and the remaining Ag ions, which should affect the Ag ion migration, play important roles in not only rs-AgI but AgBr and AgCl.