Concentration and temperature dependences of infrared reflectivity spectra in glass ionic conductor AgI– and Ag2X–AgPO3 systems (X = S, Se, Te)

Infrared reflectivity spectra of glass ionic conductors (AgI)y–(AgPO3)1−y and (Ag2X)y–(AgPO3)1−y (X = S, Se and Te) have been measured at several concentrations and temperatures. Of observed six intense bands, high or low frequency band results from PO4 or Ag-PO4 chain, and takes the shape similar to the reststrahlen band in crystal. Low frequency bands exhibit rapid frequency shifts at the structure transition temperatures of crystal Ag2X (X = Se and Te). From these results, we suggest crystal like arrangements of the frame chain and doped element in addition to the intermediate range ordering, and estimate strengthened binding of PO4 units and weakened inter-chain bindings. By proposing an empirical relationship between the ratio of short-range (fS) to long-range (fL) forces, fS / fL, and ionic activation energy, we clarify the importance of the combination of strengthened fS and weakened fL values for high ionic conduction and also for the expansion of inter-chain distance.