Structural chemistry and magnetic behaviour of the ternary silicides UCuxSi2-x (0.28 <= x <= 0.96)

The ternary silicides UCuxSi2-x with 0.28 less than or equal to x less than or equal to 0.96 have been prepared and investigated by X-ray powder diffr action, electron diffraction, electrical resistivity and magnetization meas urements. A structural change occurs with the sequence alpha-ThSi2 (tetrago nal)-->AlB2 (hexagonal)-->Ni2In (hexagonal) as x increases, respectively, f or x congruent to 0.5 and x>0.84. The existence of Ni2In-type, evidenced by transmission electron microscopy, is explained by a crystallographic order between copper and silicon atoms. This system exhibits an interesting magn etic phase diagram: (i) for x<0.50 the compounds show a spin-fluctuation be haviour; (ii) a ferromagnetic ordering appears for 0.50 less than or equal to x less than or equal to 0.80 where the Curie temperature goes through a maximum at 91(1) K for x=0.70; (iii) finally the richest compositions in co pper 0.93 less than or equal to x less than or equal to 0.96 order antiferr omagnetically with T-N around 43-40 K. (C) 1999 Elsevier Science S.A. All r ights reserved.