Direct observation of a local impurity induced valence transition

The local environment of As in SmS1-xAsx has been determined by EXAFS. The collapse of the six Sm neighbors from divalent to trivalent is directly observed. At low concentrations, the valence transitions is localized around each As ion, the host remaining divalent. At higher concentrations all Sm undergoes a transition to higher valence. © 1985.