On the Crystal Structure, Metal Atom Site Preferences and Magnetic Properties of Nd(5-x)Er(x)Tt(4) (Tt = Si or Ge)

A crystallographic Study of the Nd/Er site preferences in the Nd(5-x)Er(x)Tt(4) (Ti = Si, Ge) series prepared by high-temperature methods is presented. For Nd5-xErxSi4, phases with x <= 1.0 adopt the tetragonal Zr5Si4-type structure. On the other hand, phases in the composition range of 2.0 <= x <= 5.0 exhibits the Gd5Si4-type Structure. For all silicides, all silicon atoms belong to Si-Si dimers. In the Nd5-xErxGe4 system, phases with x < 3.2 and x = 4.0 adopt the orthorhombic Sm5Ge4-type Structure. For the composition range of 3.2 <= x <= 4.0, a monoclinic U2Mo3Si4-type structure (space group P2(1)/c) Occurs as the majority phase. This monoclinic Structure, until recently, wits not reported for similar RE5T4 systems, and differs from the known monoclinic Gd5Si2Ge2-type (space group P2(1)/a) because till Ge center dot center dot center dot Ge contacts between slabs tire equivalent. The structural relationships between the Zr5Si4-type, Gd5Si4-type, Sm5Ge4-type, and U2Mo3Si4-type structures tire discussed. Single crystal refinements of the metal atom occupancies for the three different metal sites in the asymmetric unit of all structure types reveal a partially ordered nonstatistical arrangement of neodymium and erbium atoms. The magnetic properties of some Nd5-xErxGe4 phases are also reported. Nd4ErGe4 shows an anti-ferromagnetic-type transition similar to Gd5Ge4. As the erbium concentration increases (2 <= x <= 4), these phases exhibit, at least, ferromagnetic-type ordering.