Change in local order of TM80-xRExMe20 amorphous alloys: a structural model

The local order in TM80-xRExMe20 (TM = transition metal, RE = rare earth, M e = metalloid) amorphous alloys is investigated by considering two limit ca ses: either (TM80-xMe20)REx, where the alloy would be a dilute solution of RE atoms in a (TM100-yMey) distorted prismatic network, or (TM80-xREx)Me-20 , where the alloy would be a dilute solution of RE atoms in a polytetrahedr al compact network of TM atoms containing interstitial Me atoms. The compar ison of the calculated atomic pairs with the experimental results provides evidence for a critical RE concentration range close to 8-9 at.%. This is i n agreement with a previous Mossbauer study of Fe80-xRExB20 amorphous alloy s, which pointed out a structural modification of the iron environments in this rare earth concentration range.