NdPtSb

NdPtSb, hP6 andLiGaGe, hP6, structures (AlB2-derivative types) Both structures are hexagonal, space group P63me, N. 186. with the following atomic positions ... 

The NdPtSb and LiGaGe structures have similar atomic positions but in NdPtSb the layers are slightly puckered whereas in LiGaGe we have strong distortions resulting in a 3D framework of Ga and Ge. Each Ga is surrounded by a Ge4 tetrahedron and each Ge by a Ga4 tetrahedron. 

GdCuSn crystallizes in the hexagonal NdPtSb-type structure (Pacheco et al. 1998), which is an ordered form of the Caln2 type, which had been reported as the structure of GdCuSn before (Komarovskaja et al. 1983). The correct structure of GdCuSn is described within the space group P6 mc with Gd on the 2a-sites (point symmetry 3m), Cu on the 2b-sites (also point symmetry 3m) with zcu 0.81 and Sn also on the 2b-sites with zsn w 0.23. The hexagonal unit cell of the structure is shown in fig. 12. 

Fig. 12. NdPtSb-lype hexagonal crystal structure of GdCuSn.

Nd-Pt-Sb. NdPtSb crystallizes with the Caln2 type structure, a = 0.4544, c = 0.7878 (Rossi et al., 1981 powder X-ray diffraction data). For the experimental details, see the LaPtSb. At variance with these data, Wenski and Mewis (1986a) reported the LiGaGe type structure for the NdPtSb compound, a = 0.4535, c = 0.7866 from X-ray single crystal investigation. For the sample preparation, see PrPtSb. 

Fig. 35. Projection of the NdPtSb (or LiGaGe) unit cell and coordination polyhedra of atoms.

The structure types Caln2, ZrBeSi, NdPtSb, LiGaGe, CaLiSn,... 

For the RAgPb series it is interesting to note that the plumbides with the early rare earth metals adopt the NdPtSb type structure up to Dy as rare earth metal. This change in structure type is driven by the size of the rare earth elements. A comparison with the series RCuPb and RAuPb is given by Marazza et al. (1988). 

A phonon contribution with an additional cubic term can be used to analyze the resistivity behavior of the metallic bismuthides YbAgBi and YbAuBi (Merlo et al. 1995). An anomaly occurs in the temperature dependence of the resistivity of YbCuBi at about 375 K, most likely resulting from a structural phase transition from the high-temperature ZrBeSi to the low-temperature NdPtSb modification. The anomaly in the resistivity is paralleled by a drop of the da ratio of the lattice parameters in the same temperature range. 

---