Résumé
Gallium phases with electropositive elements are at interface between semiconductors and metals, the Ga-richest are characterised by macroanionic tridimensional frameworks built with clusters. The originality of these phases is due to the presence of locally delocalised electrons at clusters. Nevertheless these clusters display well defined electron numbers in adequacy with their geometries. This work reports the new phase diagrams of binary systems of gallium and alkali metals.Crystal structures of new gallium ternary compounds with alkali metals are described, they are non stoichiometric and contain condensed polyhedra.Ternary phases including a group 11 or 12 element (Cu, Zn, Cd, Ag and Au) are stoichiometric but some sites are filled complementarily by gallium and the second electronegative element.Some of the structures given in this work display an extended icosahedral symmetry, they are typical examples of approximant phases of quasicrystals.The alkali metals play a determining role in the formation of these phases, their electronic contribution role is necessary to stabilise the anionic network. The hypothesis of an electron transfer from the alkali metal to the anionic network has been confirmed with NMR experiments.Theoretical calculations (extended Hückel) have been very efficient to increase the comprehension of atomic bonding in these systems