TiNiSi structure type

Pr-Rh-Sb. Malik and Adroja (1991b) established a KHg2 type with a = 0.4596, b = 0.7391, c = 0.7848 for the PrRhSb compound by using X-ray powder diffraction of an arc melted alloy. The purities of the metals were better than 99.99%. Adroja et al. (1999) observed the TiNiSi structure type for the PrRhSbo.976 compound from metallographic analyses and powder diffraction. 

Fig. 97. Connection of fragments (indicated by solid lines) of a-Fe, AlBj, Mo2NiB2 and TiNiSi structure types in the structure of ScjNijGeg. Unit cells are indicated by dashed lines. The structures are presented in the...

The TiNiSi structure type is a superstructure of the PbCU type. The Ti and Ni atoms form columns of trigonal prisms inside of which there are Si atoms. The columns are linked by the Ti-Ti edges in infinite crimped slabs, placed perpendicular to the Z axis. The structure can be presented as a totality of the nets (two per unit cell) which are parallel to XY plane. In the RMSn compounds the R, Ni and Sn atoms occupy the position of Ti, Ni, Si atoms, respectively. 

According to MaF, 73a, the NdFeSi compound crystallizes in the TiNiSi structure type, but it should be noted that the cell parameters indicated in that paper are incompatible with this type of structure. 

Co2Si (PbCl2), oP12, and TiNiSi, oP12, structural types. Orthorhombic, space group Puma, N. 62. 

GdIrSi is isotypic with the structure type of TiNiSi, Pnma, a = 6.913(6), b = 4.235(4), c = 7.434(7) (Hovestreydt et al., 1982 X-ray powder diffraction). For sample preparation, see YPdSi atom parameters as derived for ScPtSi. 

Thus, the comparison of the R-Ni-Ge systems, carried out above, shows a similarity in the interaction of rare-earth metals with nickel and germanium wifii the exception of europium, which forms a considerably smaller number of compounds. This is consistent with europium s divalent character, and its similar behavior observed in the other Eu-3d element-Ge systems. At the same time, the type of interaction and the crystal structures of compoimds formed are different for the elements of the light and heavy lanthanides. The only two ternary germanides of scandium, which are isotypic with lanthanide-containing compounds, are ScNiGe (structure type TiNiSi) and Sc3NinGe4 (structure type Sc3NinGe4). 

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