Crystal Structure of the Compound Sc1.33Pd3Al8 with Layers of R Atoms and Al3 Triangles
The crystal structure of the new ternary aluminide Sc1.33Pd3Al8was refined by the Rietveld method from X-ray powder diffraction data. It crystallizes with a Gd1.33Pt3Al8-type structure:hR51-14.00,R-3m,a= 4.29142(4),c= 38.1638(4) Å,RB= 0.0344. The main feature of the structure is the statistical distribution of Sc atoms and Al3triangles within atomic layers of composition Sc2Al3(Sc0.67Al within the translation unit here), which is likely to correspond to stacking disorder of ordered layers. During the final cycles of the refinement, the occupancies of the corresponding sites were fixed at occ. = 2/3 for Sc in Wyckoff position 6cand occ. = 1/3 for Al in 18h. The unit cell of Sc1.33Pd3Al8contains six Sc0.67Al layers, nine Pd and eighteen Al atom layers along the crystallographic direction [001]. Together with the structure types Tb0.67PdAl3, Y2Co3Ga9, Sc0.67Fe2Si5, Er4Pt9Al24, Yb0.67Ni2Al6, and ErNi3Al9, the structure type Gd1.33Pt3Al8forms a family of intergrowth structures built up of three kinds of similar monoatomic layer.