Intermetallic compounds RE10RuAl3 (RE = Gd, Tb, Dy, Ho, Er, Tm): Synthesis, crystal structure and thermal properties

In the RE-Ru-Al systems, in the region with high content of rare earth elements a number of isostructural compounds RE10RuAl3 (RE = Gd, Tb, Dy, Ho, Er, Tm) were identified. The structures of the obtained compounds belong to ordered variant of anti-Co2Al5-type with a hexagonal cell, space group P63/mmc (No. 194), Pearson symbol hP28, Z = 2, the cell parameters a = 9.5901(19) Å, c = 9.6504(17) Å (Gd); a = 9.5029(17) Å, c = 9.5746(20) Å (Tb); a = 9.4761(17) Å, c = 9.5544(13) Å (Dy); a = 9.4235(9) Å, c = 9.5132(7) Å (Ho); a = 9.3967(6) Å, c = 9.4761(5) Å (Er); a = 9.3589(12) Å, c = 9.4277(10) Å (Tm). All compounds were synthesized by arc-melting the stoichiometric quantities of elementary components. The structures were determined by X-ray diffraction analysis of a single crystal and refined by the Rietveld method from powder X-ray diffraction patterns. In the structure of the compound Ho10RuAl3 one of the three holmium sites - Ho3 - was mixed with Al, which is reflected in the composition of the intermetallide: compound with Ho shows a small deviation from composition RE10RuAl3 and an adequate formula of the compound is Ho10‒xRuAl3+x (x = 0.07). The crystal structure of the compounds can be represented as rows of trigonal prisms with rare earth atoms at the vertices, centered by ruthenium atoms, alternating with a pair of empty octahedra of rare earth atoms along the direction c of the unit cell. Rows of prisms and octahedrons separate distorted icosahedrons RE[Al6RE6] with a rare earth atom in the center, connected by common triangular faces. All obtained compounds have a congruent melting pattern.