Phase equilibria and magnetic studies in the ternary system U-Au-Sn

The phase equilibria in the ternary system U-Au-Sn have been established in the isothermal section at 750 degrees C. The existence and magnetic properties of the previously reported ternary compounds have been confirmed: UAuSn (hexagonal CaIn2 structure type, a = 4.729(1) Angstrom, c = 7.219(3) Angstrom, antiferromagnet T-N = 35 K), U3Au3Sn4 (cubic Y3Au3Sb4 structure type, a = 9.819(1) Angstrom, paramagnet), and UAu2Sn which exhibits a polymorphic transition from a high temperature cubic MnCu2Al structure type, a = 6.983(2) Angstrom, paramagnet) to a low temperature (<820 degrees C) hexagonal ZrPt2Al structure type (a = 4.719(2) c = 9.202(2) Angstrom, antiferromagnet, T-N = 13 K). This high temperature form is stabilised in the gold-rich part of the homogeneity region UAu2+xSn1-x so that it is also observable at 750 degrees C between the compositions 0.1 < x < 0.33. The binary compounds of the systems U-Au and U-Sn admit significant solubility of Sn and Au, respectively. For UAu2, this solubility extends up to a composition UAu1.55Sn0.45, and superstructure reflections appear for higher Au substitutions, up to the limiting formula corresponding to the ternary composition U3Au4Sn2 which is considered as being a new phase in this system. (C) 2000 Elsevier Science S.A. All rights reserved.