CHARACTERIZATION OF INTERMEDIATE-RANGE ORDER IN SUPERIONIC AGPO3-AGI, AGPO3-AGBR, AGPO3-AGCL GLASSES BY NEUTRON-DIFFRACTION

AgPO3-AgX glasses present a prepeak in the 0.5-0.9 angstrom-1 Q-range. Using isotopic substitution in 0.75 AgPO3-0.25 AgCl(Cl-35, Cl-37, natural Cl and Cl-35-Cl-37) provokes a dramatic variation in the prepeak intensity, which is strong with Cl-37 and disappears for Cl-35. The intensity of the prepeak is well correlated to the contrast term (rho-AgPO3-rho-AgX)2 corresponding to the square of the relative neutron scattering length densities. As in colloidal systems, this peak can be associated with an intermediate structure of particles lying inside a continuous host. The interparticle distance (comprised between 8 and 10 angstrom) may be analysed in two models (i) "AgX" microdomains repeated in AgPO3 matrix or (ii) "(PO3) infinity" chain microdomains repeating inside a connective tissue made essentially of disordered AgI. The latter model could be more appropriate to describe other physical properties such as ionic conductivity.