title: New ordered phase in the quasi-binary UAl3-USi3 system.
abstract: The industrial importance of the U-Al-Si system stems from the fact that during processing the Al-based alloy (containing Si as impurity), used for the cladding of U (fuel in nuclear reactors), undergoes heat treatment which stimulates diffusion between the fuel and the cladding. One of the possible ways to represent the ternary U-Al-Si phase diagram is the construction of an UAl3-USi3 quasi-binary phase diagram. On the one hand, since the UAl3 and USi3 phases are isostructural, an isomorphous phase diagram is expected; on the other hand, some researchers observed a miscibility gap at lower temperatures. During our study of the UAl3-USi3 quasi-binary phase diagram, a new stable U(Alx,Si1 - x)3 phase was identified. The structure of this phase was determined, using a combination of electron crystallography and powder X-ray diffraction methods, as tetragonal [I4/mmm (No.139) space group], with lattice parameters a = b = 8.347 (1), c = 16.808 (96) Å. Its unit cell has 64 atoms and it can be described as an ordered variant of the U(Al,Si)3 solid solution. A Bärnighausen tree was constructed using the original U(Al,Si)3 structure as an aristotype.
authors.affiliation: Materials Department, Nuclear Research Center of Negev (NRCN), PO Box 9001, Beer-Sheva, Israel.
authors.forename: Gennady
authors.initials: G
authors.lastname: Rafailov
authors.affiliation: Materials Department, Nuclear Research Center of Negev (NRCN), PO Box 9001, Beer-Sheva, Israel.
authors.forename: Isaac
authors.initials: I
authors.lastname: Dahan
authors.affiliation: Department of Materials Engineering, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel.
authors.forename: Louisa
authors.initials: L
authors.lastname: Meshi
keywords: electron crystallography; ordering; powder X-ray diffraction; structure solution