INTERMEDIATE VALENCE IN ALLOYS OF SMS WITH SMP

Results are presented for the lattice parameter and magnetic susceptibility as a function of temperature for a series of solid solutions of SmS with SmP. At room temperature the SmS1-xPx alloys with x>~0.06 exhibit a metallic appearance and a much smaller lattice constant and magnetic susceptibility as compared with SmS. For x>~0.15 the susceptibilities do not show a Curie-law divergence or magnetic ordering. These properties are consistent with the Sm ions being in a homogeneous intermediate-valence state similar to that of SmS under pressure. The intermediate valence estimated from the lattice parameter is 2.8 at x=0.06 and increases toward the pure trivalent value with increasing phosphorous concentration. Also, the color of the alloys changes from gold to red to silver grey. The alloys with 0.03<x<0.06 exhibit a varying mixture of two distinct phases, the gold intermediate-valence phase and the black phase characteristic of the x<0.03 alloys. The properties of the black phase are consistent with a mixture of Sm2+ and Sm3+ ions where Sm ions with one or more P ions as nearest neighbors are trivalent. The 0.04<~x<~0.08 alloys exhibit a transition from the gold phase to the black phase with decreasing temperature. This transition which is continuous at higher concentrations changes to a discontinuous one near x=0.06 as seen in the temperature variation of the lattice parameter. © 1979 The American Physical Society.