New RE ₁₁ Co ₄ In ₉ ( RE = Pr, Nd, Sm, Tm, Lu) Nd ₁₁ Pd ₄ In ₉ -type compounds. Electronic structure of Pr ₁₁ Co ₄ In ₉

Novel phases RE 11 Co 4 In 9 ( RE = Pr, Nd, Sm, Tm, Lu) were obtained by arc-melting of the elements in an argon atmosphere followed by annealing at T = 870 K for 1,500 h in evacuated and sealed silica ampoules. All samples were characterized through their powder X-ray diffraction patterns and metallographic and quantitative phase analyses. The structure of the Pr 11 Co 4 In 9 compound was refined from powder X-ray diffraction patterns using the FullProf program package. The compound crystallizes in Nd 11 Pd 4 In 9 type structure (orthorhombic space group Cmmm , Z = 2; a = 14.801(10); b = 22.119(14); c = 3.746(2) Å) and belongs to a large family of two-layer structures (with layers perpendicular to the short unit cell axis) based on the intergrowth of AlB 2 - and CsCl-type related slabs. Pr 11 Co 4 In 9 - together with the Mo 2 FeB 2 , Mn 2 AlB 2 , o-La 2 Ni 2 In, Lu 5 Ni 2 In 4 types structure, in which the ternary indides crystallize – forms a homologous series RE m+n T 2n X m , where m is the number of REX (CsCl type) slabs and n the number of RET 2 (AlB 2 type) slabs ( T = Co, X = In). For Pr 11 Co 4 In 9 the values are m = 18, n = 4. The isostructural compounds were obtained with Nd, Sm, Tm, Lu and complete the series of RE 11 Co 4 In 9 ( RE = Sc, Y, Gd, Tb, Dy, Ho, Er) compounds. The electronic structure calculations were performed by means of the TB-LMTO-ASA program indicating a covalent interaction between In1–In1 atoms and metallic bonding between other In, Pr and Co atoms.