VALENCE CHANGE OF EUROPIUM ATOMS DUE TO COLD-WORKING OF MgEu ALLOYS

An investigation has been made of alloys of 50 to 6 300 ppm Eu in Mg. Data obtained by the use of the Mossbauer spectroscopy of IslEu, magnetic susceptibility and scanning electron microscopy show that solid solutions do not form in this system, but that the Eu precipitates into two eutectic intermetallics. While the Eu ions are in a divalent state at all temperatures for strain-free samples, introduction of cold-work causes a large fraction of the ions to convert to the trivalent state. Isochronal annealing measurements show that the divalent state is recovered at annealing temperatures above 450 C. Those results are discussed in terms of the formation and trapping of line defects and their subsequent annealing.