title: Crystal structure and superconductivity of BaIr₂Ge₇ and Ba₃Ir₄Ge₁₆ with two-dimensional Ba-Ge networks.
abstract: The Ba-Ir-Ge ternary compounds BaIr2Ge7 and Ba3Ir4Ge16 exhibit superconductivity (SC) at 2.5 and 5.2 K, respectively. Detailed single-crystal structural analysis revealed that these compounds share unique quasi-two-dimensional networks composed of crown-shaped Ge rings that accommodate Ba atoms at the center, referred to as "edge-shared crown-shaped BaGe16 polyhedra". The layered Ba-Ge network yielded a modest anisotropy of 1.3-1.4 in the upper critical field, which is in good agreement with the band structure calculations. The Ba-Ge structural unit is similar to cage structures seen in various clathrates in which the anharmonic vibration of the central atoms, the so-called "rattling" behavior, brings about strong-coupling SC. However, each Ba-Ge unit is relatively small compared to these materials, which likely excludes the possibility of unconventional SC.
authors.affiliation: National Institute of Advanced Industrial Science and Technology (AIST) , Tsukuba 305-8568, Japan.
authors.forename: Shigeyuki
authors.initials: S
authors.lastname: Ishida
authors.forename: Yousuke
authors.initials: Y
authors.lastname: Yanagi
authors.forename: Kunihiko
authors.initials: K
authors.lastname: Oka
authors.forename: Kunimitsu
authors.initials: K
authors.lastname: Kataoka
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Fujihisa
authors.forename: Hijiri
authors.initials: H
authors.lastname: Kito
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Yoshida
authors.forename: Akira
authors.initials: A
authors.lastname: Iyo
authors.forename: Izumi
authors.initials: I
authors.lastname: Hase
authors.forename: Yoshito
authors.initials: Y
authors.lastname: Gotoh
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Eisaki