- The formation of a new phase of composition Mg54Al28Ag18 was observed as a result of plasma immersion ion implantation of Ag into the compound Mg17Al12. The new structure was characterized using a micro-beam diffraction technique. It was found that the implantation-induced phase transition occurs when the retained dose of the implanted ions is within the range of about 1015–1016 ions/cm2. The implanted system has been studied theoretically by means of density-functional electronic structure calculations and a new ab initio approach has been developed to evaluate the specific concentrations of the implanted ions that might cause the phase transition effect in the implanted matrix. The theoretically estimated values of concentrations are in good agreement with experimental observations.