Showing papers by "Claes-Göran Granqvist published in 1978"

Conductivity of inhomogeneous materials: Effective-medium theory with dipole-dipole interaction

Abstract: We extend the old effective-medium theory, originally due to Bruggeman, by incorporating dipole-dipole interactions to account for local-field effects. The interactions are represented approximately by use of effective depolarization factors. For close-packed clusters of conducting regions, a description which is appropriate at the percolation threshold, we predict an onset of percolation processes when 15.6 vol% is conducting. This is in very good agreement with numerical simulations as well as with experimental data for the metal-insulator transitions in metal-ammonia solutions and in alkali-tungsten bronzes.

Selective absorption of solar energy by ultrafine metal particles

Abstract: We prepared individually isolated chromium particles by gas evaporation onto KBr substrates in a reduced atmosphere of argon + air. Particle diameters were typically 5 to 13 nm. Optical transmittance at normal incidence was recorded in the wavelength interval 0.3<λ<25 μm by double beam spectrophotometry. Excellent spectral selectivity was found with high absorptance at λ < 2 μm and high transmittance further out in the infrared. The optical data were compared with calculations based on the Maxwell Garnett theory, which was generalized so as to encompass dipole-dipole interaction among aggregated spheres. Agreement between theory and experiments was achieved by considering particles forming linear chains.