DEVITRIFICATION AND METASTABILITY - REVISITING THE PHASE-DIAGRAM OF THE SYSTEM AGI-AG2MOO4

The phase diagram of the AgI(1-x)(Ag2MoO4)(x) system has been investig ated by differential scanning calorimetry (DSC) and X-ray powder diffr action (XRD). Besides an incongruent I:1 compound that was previously reported by our group, a metastable 2:1 crystalline phase is formed at similar to 110 degrees C over the whole composition range. The stabil ity of this phase is strongly temperature-controlled: at similar to 18 0 degrees C the crystal decomposes in the time scale of a DSC experime nt. For x<0.5 it gives beta-AgI and the 1:1 compound, whereas for x>0. 5 the 1:I and Ag2MoO4 are formed. The glass-forming region spans over the range 0.20<x<0.40. Annealing the samples with 0 less than or equal to x less than or equal to 0.33 near 70 degrees C causes all AgI in e xcess with respect to the 2:1 compound to crystallize as beta phase. ( C) 1998 Academic Press.