Results are presented for lattice-parameter and magnetic-susceptibility measurements on a series of solid solutions of SmSe with SmAs. The lattice parameter shows a continuous transition (collapse in excess of Vegard's law) with increasing SmAs concentration similar to the valence transition in SmSe under increasing pressure. The estimated average Sm valence increases from divalent to trivalent as the SmAs concentration increases from 0 to 70%. This behavior is compared with the previously observed first-order valence transition in the solid solutions of SmS with SmAs at 5 to 10 at.% SmAs. The magnetic susceptibilities of the $\mathrm{Sm}{\mathrm{Se}}_{1-x}{\mathrm{As}}_x$ alloys with $x<\mathrm{}0.1\mathrm{}$ show a temperature dependence characteristic of a mixture of divalent and trivalent Sm ions. At higher concentrations of As the behavior is characteristic of Sm ions with intermediate valence.

• Received 9 June 1980

DOI:https://doi.org/10.1103/PhysRevB.23.3620