Electrical conductivity and activation volume of the solid electrolyte phaseα-AgI and the high-pressure phase fcc AgI

The $\alpha$ phase of silver iodide which is stable between 147 and 555°C at normal pressure is a classical example of a solid electrolyte. In this investigation the temperature and pressure dependences of the electrical conductivity in $\alpha$-AgI have been studied for pressures up to 0.9 GPa. This phase is characterized by a large electrical conductivity, a low migration enthalpy of 0.098 eV, and a low activation volume of 0.8-0.9 ${\mathrm{cm}}^3$ ${\mathrm{mole}}^{-1\mathrm{}}$. For pressures between 0.4 and 10 GPa a rocksalt-structure phase fcc AgI is stable at room temperature. The temperature and pressure dependences of the electrical conductivity in this phase have been studied for pressures up to 1.0 GPa and for temperatures between room temperature and 330°C. The electrical conductivity resembles that in AgCl and AgBr, and it is indicated that Frenkel defects dominate also in fcc AgI. At high temperature and pressure, however, a gradual increase of the electrical conductivity takes place in fcc AgI, similar to the gradual transitions that have been reported for many materials with the fluorite structure. The electrical conductivity in this temperature and pressure range of fcc AgI is approximately 1 ${\mathrm{\Omega }}^{-1\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$, i.e., only slightly less than the electrical conductivity in the $\alpha$ phase.