Abstract
EXAFS measurements above the K-edge of Ga, As and the LIII-edge of Sb in GaAsySby are performed. The analysis of data above the Ga K-edge, on both sides of the miscibility gap (0 ⩽ y ⩽ .11, .9 ⩽ y ⩽ 1), leads to nearest-neighbor (NN) distances around Ga atom. The distribution of cation-anion distances is bimodal (d(Ga-As) = 2.46 ± 02 Å, d (Ga-Sb) = 2.63 ± .01 Å) and very close to the PAULING-HUGGINS limit. This great relaxation of the zinc-blende structure is explained by using a Valence-Force-Field model (Keating) and searching for the configuration at which the elastic forces acting upon every atom vanish : both sublattices are distorded and multimodal second-neighbor distribution of distance is predicted, in agreement with the broadening of the corresponding peak of the radial distribution (NNN distances).