Transition from ionic to metallic glasses by rapid quenching of Bi-BiCl3 and Bi-BiCl3-KCl melts

Melts of Bi-BiCl3-KCl and Bi-BiCl3 mixtures have been rapidly quenched into the glassy state at cooling rates of similar to 10(6) K/s. In this way gla sses with electronic properties intermediate between the ionic and metallic state have been obtained for the first time. At low Bi-additions the optic al characteristics of these glasses are very similar to those of the corres ponding melts. Measurements of the electronic conductivity of Bi-BiCl3 glas ses indicate that the transition from nonmetallic to metallic. behavior occ urs at high Bi-doping of x(Bi) > 0.6 whereby the concentration dependence o f the conductivity in the glassy and liquid state within experimental error s is the same. Changes of the microscopic structure of these glasses have b een determined by small-angle X-ray scattering (SAXS) and by extended X-ray absorption fine structure (EXAFS) experiments. In the nonmetallic salt-ric h glasses the SAXS-results exhibit Guinier-type scattering behavior consist ent with Bi-clusters of spherical radii between 10 and 13 Angstrom. In the nonmetal-metal transition region the SAXS data follow a power law behavior indicating a coagulation of Bi-clusters and a percolative structure. From t he EXAFS results an intra-cluster Bi-Bi distance of 3.11 +/- 0.02 Angstrom is derived which remains constant for the Bi-x (BiCl3)(1-x) glasses studied (0.2 less than or equal to x less than or equal to 0.8).