SMALL-ANGLE NEUTRON-SCATTERING OF THE SYSTEM FE80-XNIXB12SI8 IN THE AMORPHOUS STATE WITH 0-LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-80- COMPARISON WITH THE EVOLUTION OF CRYSTALLIZATION STUDIED BY THE CONTROLLED JOULE EFFECT ANALYSIS

The evolution of crystallization of amorphous ribbons has previously b een studied by the controlled Joule effect analysis (CJEA) in the syst em Fe80-xNixB12Si8. The sign and magnitude of resistivity changes due to the relaxation depend strongly on the Ni/Fe ratio. The anomalous be havior observed during crystallization was explained by large fluctuat ions of local environments of Ni and Fe atoms which have a high mobili ty in these glasses. Depending on x, small amorphous local units with different atomic compositions would be present in the glassy matrix. T o confirm these results, the small-angle neutron scattering (SANS) of these amorphous alloys has been measured at room temperature. A signif icant contribution to the SANS intensity is observed for all the alloy s. The radii of gyration of the scattering particles depend on x and v ary between 230 and 309 Angstrom. Except for 50 < x < 65, an interfere nce peak present in the intensity curves confirms the presence of nume rous other aggregates for which the radii of gyration are distributed between 65 and 90 Angstrom and their mean distances between 300 and 40 0 Angstrom. Sizes and distances have been determined with an accuracy equal to +/- 10% using more than one approximation method. Their rough volume has been evaluated from the normalized intensities assuming sp herical form and particular compositions defined from the X-ray patter ns. The presence of aggregates in the glasses partially explains the a nomalous behavior of resistivity but it is not possible to confirm the real composition of these aggregates for all x-values. (C) 1997 Elsev ier Science S.A.