n-and p-Type behaviour of the gold-substituted type-I clathrate,B a8 Au_xSi_(46_x) (x=5.4 and 5.9)

摘要

Two samples of the gold-substituted silicon clathrate,Ba8AuxSi_(46-x),have been synthesized from the elements at high temperature,one without subsequent treatment (so-called AG for as-grown) and the other after annealing in a silica tube (so-called A for annealed).A structure analysis on single crystal of both samples shows that the x Au content for the AG and A sample is 5.4 and 5.9,respectively.Both samples have been characterized by Seebeck coefficient and electrical conductivity measurements,as well as by ~(29)Si MAS NMR spectroscopy.The AG sample is an n-type semi conductor close to a metal,whereas the A one exhibits a p-type metallic behaviour.The NMR spectra are consistent with a high contribution to the conductivity of the Si(3s) orbitals at the Fermi level.