The gallium intermetallics REPdGa3 (RE = La, Ce, Pr, Nd, Sm, Eu) with SrPdGa3-type structure
Résumé
The gallium-rich intermetallic phases REPdGa3 (RE = La, Ce, Pr, Nd, Sm, Eu) were obtained by arc-melting of the elements and subsequent annealing for crystal growth. The samples were studied by X-ray diffraction on powders and single crystals. The structures of three crystals were refined from X-ray diffractometer data: SrPdGa3 type, Cmcm, a = 634.3(1), b = 1027.2(1), c = 593.5(1) pm, wR = 0.0621, 380 F2 values, 20 variables for CePd0.80(4)Ga3.20(4), a = 635.9(1), b = 1027.5(1), c = 592.0(1) pm, wR = 0.1035, 457 F2 values, 19 variables for CePdGa3, and a = 640.7(1), b = 1038.2(1), c = 593.7(1) pm, wR = 0.0854, 489 F2 values, 19 variables for EuPdGa3. The REPdGa3 gallides are orthorhombic superstructure variants of the aristotype ThCr2Si2. The palladium and gallium atoms build up polyanionic [PdGa3]δ− networks with Pd–Ga and Ga–Ga distances of 248–254 and 266–297pm, respectively, in EuPdGa3. The rare earth atoms fill cavities within the polyanionic networks. They are coordinated by five palladium and twelve gallium atoms. Taking CePdGa3 as an illustrative representative, the band structure calculations show largely dispersive itinerant s, p bands and little dispersive d (Pd) and f (Ce) bands, the latter crossing the Fermi level at large magnitude leading to magnetic instability in a spin-degenerate state and a subsequent antiferromagnetic ground state with a small moment of ±0.36 μB on Ce. The bonding characteristics indicate a prevailing Ce–Ga bonding versus Pd–Ga and Ce–Pd. Temperature-dependent magnetic susceptibility and 151Eu Mössbauer spectroscopic measurements point to stable trivalent lanthanum, cerium, praseodymium, and neodymium, but divalent europium. SmPdGa3 shows intermediate valence. Antiferromagnetic ordering occurs at TN = 5.1(5), 7.0(5), 6.3(5), 11.9(5), and 23.0(5) for RE = Ce, Pr, Nd, Sm, and Eu, respectively.
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