Local Structure of Thermally Stable Super Ionic Conducting AgI Confined in Mesopores

AgI confined in mesopores of Al2O3 exhibits high ionic conductivity for a very wide temperature range. The mechanism of this attractive feature was revealed by detailed investigation of local structure using 109Ag nuclear magnetic resonance (NMR) spectroscopy and X-ray absorption spectroscopy (XAS). All data of NMR and XAS data as well as X-ray diffraction, differential scanning calorimetry, transmission electron microscopy, and a.c. impedance spectroscopy were carefully analyzed to reach the most plausible model. It was revealed that the local structure of the super ionic conducting phase of AgI in mesopores is amorphous, which is similar to α-AgI structure, and was stabilized for a very wide temperature range from 30 K to melting point around 850 K.