title: Synthesis, crystal structure, and physical properties of the type-I clathrate Ba(8-δ)Ni(x)□(y)Si(46-x-y).
abstract: Type-I clathrate phase Ba(8)Ni(x)□(y)Si(46-x-y) (□ = vacancy) was obtained from the elements at 1000 °C with the homogeneity range 2.4 ≤ x ≤ 3.8 and 0 ≤ y ≤ 0.9. In addition, samples with low Ni content (x = 1.4 and 1.6; y = 0) and small Ba deficiency were prepared from the melt by steel-quenching. Compositions were established by microprobe analysis and crystal structure determination. Ba(8-δ)Ni(x)□(y)Si(46-x-y) crystallizes in the space group Pm ̅3n (No. 223) with lattice parameter ranging from a = 10.3088(1) Å for Ba(7.9(1))Ni(1.4(1))Si(44.6(1)) to a = 10.2896(1) Å for Ba(8.00(3))Ni(3.82(4))Si(41.33(6)). Single-crystal X-ray diffraction data together with microprobe analysis indicate an increasing number of framework vacancies toward compositions with higher Ni content. For all compositions investigated, Ni K-edge X-ray absorption spectroscopy measurements showed an electronic state close to that of elemental Ni. All samples exhibit metallic-like behavior with moderate thermopower and low thermal conductivity in the temperature range 300-773 K. Samples with compositions Ba(7.9(1))Ni(1.4(1))Si(44.6(1)) and Ba(7.9(1))Ni(1.6(1))Si(44.4(1)) are superconducting with T(c) values of 6.0 and 5.5 K, respectively.
authors.affiliation: Max-Planck-Institut für Chemische Physik fester Stoffe, Nöthnitzer Strasse 40, 01187 Dresden, Germany. aydemir@cpfs.mpg.de
authors.forename: U
authors.initials: U
authors.lastname: Aydemir
authors.forename: C
authors.initials: C
authors.lastname: Candolfi
authors.forename: A
authors.initials: A
authors.lastname: Ormeci
authors.forename: H
authors.initials: H
authors.lastname: Borrmann
authors.forename: U
authors.initials: U
authors.lastname: Burkhardt
authors.forename: Y
authors.initials: Y
authors.lastname: Oztan
authors.forename: N
authors.initials: N
authors.lastname: Oeschler
authors.forename: M
authors.initials: M
authors.lastname: Baitinger
authors.forename: F
authors.initials: F
authors.lastname: Steglich
authors.forename: Yu
authors.initials: Y
authors.lastname: Grin