Raman scattering, IR reflectance and modulated-DSC measurements were

performed on specifically prepared dry (AgI)x(AgPO3)1−x glasses over a wide range

of compositions 0%<x<60%. A reversibility window was observed in the

9.5%<x<37.8% range, which fixes the elastically rigid but unstressed regime also

known as the intermediate phase. Glass compositions at x<9.5% were stressedrigid,

while those at x>37.8% were elastically flexible. Raman optical elasticity

power laws, trends in the nature of the glass transition endotherms, corroborate the

three elastic phase assignments. Ionic conductivities revealed a step-like increase

when glasses become stress-free at x>xc(1) = 9.5% and a logarithmic increase in

conductivity (σ~(x−xc(2))μ) once they become flexible at x>xc(2) = 37.8% with a

power law μ = 1.78. The power law was consistent with percolation of 3D

filamentary conduction pathways. Traces of water doping lower Tg and narrow the

reversibility window, and can also completely collapse it. Ideas on network

flexibility promoting ion conduction were in harmony with the unified approach of

Ingram et al (2008), who emphasized the similarity of process compliance or

elasticity relating to ion transport and structural relaxation in decoupled systems.

Boson mode frequency and scattering strength displayed thresholds that coincide

with the two elastic phase boundaries. In particular, the scattering strength of the

boson mode increases almost linearly with glass composition x, with a slope that

tracks the floppy mode fraction as a function of mean coordination number r

predicted by mean-field rigidity theory. These data suggested that the excess low

frequency vibrations contributing to the boson mode in flexible glasses come

largely from floppy modes.

Elastic Flexibility, Fast-Ion Conduction, Boson and Floppy Modes in AgPO3–AgI

Glasses. D.I.Novita, P.Boolchand, M.Malki, M.Micoulaut. Journal of Physics -

Condensed Matter, 2009, 21[20], 205106