Solution calorimetric investigation of AgCl-AgI ionic conductor compositesat 298 K: observation of metastable AgI modifications

The enthalpies of solution of pure silver halides AgCl and AgI and a compos ite material with molar composition 0.5 AgCl-0.5 AgI were measured at 298 K in a mixture of Na2S2O3 (1 M) and NH4OH (1 M). X-ray diffraction patterns showed that the composite material contained the metastable gamma -AgI phas e; different mechanisms for its stabilization were discussed. The phase tra nsition enthalpies of AgI modifications and the enthalpy of formation of th e composite material were deduced from the measurements. The latter could b e related to a change of interfacial enthalpies. (C) 2001 Elsevier Science Ltd. All rights reserved.