Crystal Structure Refinement and Electronic Properties of Si(cI16)

Si(cI16) is prepared in polycrystalline form at 12(1.5) GPa at temperatures between 800(80) K and 1200(120) K. The crystal structure is refined by a full-profile method using x-ray powder diffraction data. Si(cI16) is diamagnetic (chi(0) = -5.6(1.8) X 10(-6) emu center dot mol(-1)) and shows a weakly temperature-dependent electrical resistivity [p(300 K) = 0.3 X 10(-3) Omega center dot m]. Computations of structural and electronic properties of Si(cI16) within the local density approximation evidence the metastable character of the allotrope with respect to diamond-type silicon. The calculations yield a Positional parameter which is in perfect agreement with the refined value. In agreement with the experimentally observed electrical conductivity properties, the computed density of states evidence that the Fermi level of Si(cI16) is located in a pseudo-gap.