Ternary aluminides R0.67Ni2Al6 (R=Sc, Y, Gd–Lu) with partly disordered structures

Ten rare-earth nickel aluminides R0.67Ni2Al6 (R=Sc, Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) were synthesized by arc melting and their crystal structures studied by X-ray powder diffraction. They crystallize in the hexagonal structure type Yb0.67Ni2Al6: Pearson symbol hP11-2.33, space group P-6m2, a=4.18904(2), c=9.09816(6) Å, which can be decomposed into three kinds of layer. The sequence of layers along [001] is Yb0.67Al–NiAl2–Al–NiAl2, but stacking faults appear due to relative shifts of consecutive Yb0.67Al layers containing two rare-earth metal atoms for one Al-atom triangle. An ordered superstructure is the type ErNi3Al9 (Pearson symbol hR78, space group R32, a  =3a0, c=3c0), refined on single crystals.The physical properties of the R0.67Ni2Al6 (R=Tb, Er, Tm, Yb, and Lu) compounds were determined by means of magnetic and electrical transport measurements. All these materials but Lu0.67Ni2Al6 exhibit Curie–Weiss paramagnetic behavior due to the trivalent R ions, and order magnetically at low temperatures. They show good metallic conductivity. The Yb-containing compound is a dense Kondo system with distinct features in the paramagnetic state of the interplay between Kondo and crystalline electric field interactions.

Stacking of layers along [001] in the Yb0.67Ni2Al6-type structure. Figure optionsDownload as PowerPoint slideHighlights
► The aluminides R0.67Ni2Al6 (R=Sc, Y, Gd–Lu) adopt a partly disordered structure.
► The structure is characterized by R2Al3 layers with two R atoms for one Al3 triangle.
► The compounds with R=Tb, Er, Tm are paramagnets at rt and order magnetically at lt.
► The Yb-compound exhibits a magnetically ordered Kondo lattice with strong CEF effect.