INTERMEDIATE PHASES OF THE ALPHA-SIGMA PHASE-TRANSITION IN THE FE-CR SYSTEM

(Fe100-xCrx)100-ySny alloys with 42.0 less-than-or-equal-to x less-than-or-equal-to 44.7 and 0 less-than-or-equal-to y less-than-or-equal-to 5.6 were annealed at 700-degrees-C for a period of up to 1000 h in order to cause a transformation of the alpha phase into the sigma phase. Room temperature Fe-57 Mossbauer spectra registered on the samples consist of a magnetic subspectrum, related to the alpha phase, and a nonmagnetic subspectrum, related to the sigma phase. Evidence is found that the isomer shift of the nonmagnetic subspectrum changes continuously with the amount of its relative contribution in the spectrum and it reaches the value characteristic of a pure sigma phase only when its contribution in the two-phase sample is larger than about 30%.