Defect-induced valence instabilities in rare-earth semiconducting compounds

Abstract We investigate a possible mechanism for local valence instabilities in a NaCl-type rare earth compound (semiconducting SmS) containing p -substitutional anionic impurities ( A = O , Se , Te , P …) or sulphur vacancies ( A = υ ). Using group theory analysis we discuss the nature of the defect levels from considering the whole cluster Sm 6 A formed by a point defect A and the six neighbouring Sm atoms. Phase diagrams for valence transitions are obtained in terms of the defect potential matrix elements from the competition between the promotion energy of an f electron into the conduction bands and the available band structure energy. Especially, possible solutions are presented for A = O , Se , Te .