TERNARY GERMANIDES LNAGGE (LN=Y,SM,GD-LU) WITH ORDERED FE2P-TYPE STRUCTURE

The title compounds were prepared from the elements by arc-melting and subsequent annealing at 970 K. They crystallize with the hexagonal Zr NiAl-type structure, a ternary ordered variant of the well known Fe2P type. The structures of GdAgGe, DyAgGe and ErAgGe (all space group P ( 6) over bar 2m) have been refined from single-crystal X-ray diffractom eter data: a = 715.4(2) pm, c = 423.7(1) pm, wR2 = 0.0467, 249 F-2 val ues and 14 variables for GdAgGe; a = 710.67(7) pm, c = 419.73(5) pm, w R2 = 0.0463, 245 F-2 values and 14 variables for DyAgGe; a = 706.34(3) pm, c = 416.87(2) pm, wR2 = 0.0514, 279 F-2 values and 14 variables f or ErAgGe respectively. The structures contain two crystallographicall y different germanium positions. Both of them are located in tricapped trigonal prisms: [Ge1Ln(6)Ag(3)] and [Ge(2)Ag(6)Ln(3)]. Magnetic susc eptibility measurements show antiferromagnetic ordering at Neel temper atures of 13.0(2) and 3.3(1) K for GdAgGe and ErAgGe respectively. DyA gCe shows ferromagnetic ordering at T-c = 14.0(2) K. The experimentall y determined magnetic moments at high temperature compare well with th ose expected for the free Ln(3+) ions. The latter three germanides are metallic conductors.