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 C. The existence and magnetic properties of the previously reported ternary compounds have been confirmed: UAuSn (hexagonal CaIn2 structure type, a=4.729(1) A, c=7.219(3) A, antiferromagnet TN=35 K), U3Au3Sn4 (cubic Y3Au3Sb4 structure type, a=9.819(1) A, paramagnet), and UAu2Sn which exhibits a polymorphic transition from a high temperature cubic MnCu2Al structure type (a=6.983(2) A, paramagnet) to a low temperature (<820 C) hexagonal ZrPt2Al structure type (a=4.719(2) c=9.202(2) A, antiferromagnet, TN=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 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. (orig.)