LaPtSi-type

Figure 6 A single LaPtSi-type net from the crystal structure of 6. Five more nets interpenetrate to fillthe void space created in a single net.

So far only two ternary compounds have been observed in the Ce-Pt-Si system. According to X-ray powder data by Klepp and Parthe (1982) the compound CePtSi crystallizes congruently from the melt and with the LaPtSi-type of structure [14] md, a = 4.1982(7), c = 14.488(3)]. For sample preparation, see LaPtSi. 

LalrSi was also described as a derivative structure of the SrSij-type, and comparison was made to the closely related tetragonal LaPtSi-type samples were arc melted under argon (La,lr 99.9% and Si 99.999%). 

For a correct setting of the bet-unit cell, a = 7.842 (a = o/V )-( ) ThSi2-type of structure (14,/amd) was claimed by Mayer and Felner (1973) from a refinement of X-ray powder data. The reUabihty value /t — 0.29 was in favor of an ordered Ni/Si distribution however, agreement was rather poor, thus the actual structure type might be better represented by the LaPtSi-type (ThSi2-derivative structure, 14, md see LaPtSi). 

According to X-ray powder diffraction analysis reported by Hovestreydt et al. (1982) the compound LaIrGe adopted the LaPtSi-type structure, a = 0.43166, c= 1.4430. The alloy was arc melted under argon and annealed at 1270 K for 1-2 weeks. Starting materials were La (3N), Ir (4N) and Ge (5N). 

The structure of YNiSn has been determined by using a single-crystal X-ray method (Fran9ois et al. 1985). This structure can also be described as an AIB2 type derivative and it may be compared with the LaPtSi-type structure, which is a derivative of the ThSi2 type (FrauQois et al. 1985). 

Fig. 24. Upper part The AIB and ThSi structure types, found with Ce(Ni, Si)j compounds, interpreted as structure block shifted variants (Parthe, 1967). The Ce(NijSi 5)2 compound probably has an ordered arrangement of Ni and Si atoms and thus crystallizes in the 6750 LaPtSi-type with space group 14,md. Lower part Arrangement of the atoms in the (1130) plane for the AlBj-type and two deformation variants, the CeCdj- or Cdij-type and the Cainj-type.

Figure 7.42. Characteristic sections of the tI12-a ThSi2 type structure and of its ordered derivative LaPtSi.

Figure 7.43. Unit cells of til 2-ThSi2 type, of its substitution derivative LaPtSi and of its defect-derivative tI8-NbAs types.

Mutual rotation of plane segments by 90" in the AIB2 structure leads to the formation of a-XhSi2, a-GdSi2, LaPtSi and CeGeo.66Sio.92 types. 

The LaPtSi structure is an ordered ternary derivative of the ThSi2 structure type. The geometrical relationship of the Th(iSi P+ -type to the Ali)B P+ -type is discussed with the 67(75) iCefNijsSi 75)2 compound. A drawing of the LaPtSi structure and of the LaIrSi structure, a Sr (i Si + -type derivative, is shown in fig. 22. 

Fig. 22. The LaPtSi and LalrSi structure types with their three-connected and three-dimensional Pt (or Ir)-Si framework.

A ternary derivative of the ThSi2-type with the same unit cell is discussed with 6750 LaPtSi. Here the symmetry is lowered from I4i/amd to I4,md. ... 

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