Superconductivity of metal deficient silicon clathrate compounds, Ba8-xSi46 (0< x < or = 1.4).
Single crystals of the Ba-containing silicon clathrate superconductor Ba(7.76)Si(46) were prepared using a high-pressure and high-temperature condition (3 GPa, 1300 degrees C). It crystallized in the cubic space group Pm-3n with a = 10.3141(7) A and Z = 1. There are two crystallographically different types of Ba sites, at the centers of Si dodecahederal (Ba@Si(20)) and Si tetrakaidecahedral (Ba@Si(24)) cages. On evacuation at 527 degrees C, a part of Ba atoms were removed from the Ba@Si(20) sites. The superconducting transition temperature (T(c)) decreased from 9.0 to 6.0 K with the decrease of the Ba content from 7.76 to 6.63 Ba/Si(46). The Ba deficient sites and the deficiency were determined by the structural refinement in the single-crystal X-ray analyses.
Fukuoka
Hiroshi
H
Department of Applied Chemistry, Graduate School of Engineering, Hiroshima University, Higashi-Hiroshima 739-8527, Japan. hfukuoka@hiroshima-u.ac.jp
Kiyoto
Junichi
J
Yamanaka
Shoji
S