Intermediate valence in alloys of SmS with SmP

Abstract

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 SmS~"P"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 Sm + and Sm + 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.

Rare-earth pnictides and chalcogenides from first-principles

“…II III meV (erroneously specified as −5.6 eV in [5]) seems to point to a divalent semiconductor, susceptible of undergoing a localization-delocalization transition under pressure [55], as observed experimentally [102]. For SmO, the calculated positive energy difference,…”

“…It emerges that our understanding of the underlying physics of valence transitions in the rare earth chalcogenides under pressure remains incomplete. This is particularly obvious for SmS where the experimentally observed [102,104,178,179] semiconductor ('black phase') to metal ('golden phase') transition, at a relatively modest pressure of 0.65 GPa, has been extensively studied by means of such methods as LDA [154,180], LDA + SIC [55,181], LDA + U [182,183], and LDA + DMFT [184], with interpretations ranging from f-electron delocalization and f − d promotion to topological phase transition.…”

Rare earth monopnictides and monochalcogenides from first principles: towards an electronic phase diagram of strongly correlated materials

“…For SmS we find ∆E II−III = -5.6 eV, indicating a divalent semiconductor, but given the small energy difference, susceptible to undergo a localization-delocalization transition under pressure, 50 as has been observed experimentally. 51 In summary, this effective one-electron SIC-LSD methodology accurately predicts the phase transitions associated with the f -electron localization/delocalization. However, we should note here that because of the many-body effects, beyond those included in the SIC exchange-correlation energy functional, the representation of the calculated densities of states in terms of the described above phase diagram is most likely not the full picture of the underlying electronic structure.…”

Valence fluctuation phenomena

“…Finally we note that the low-temperature critical point probably exists for other solutes than Y and Gd, e.g. it can be deduced from the susceptibility and thermal expansion data for SmS1-,P, (Henry et al 1979). For this system there is a first-order B-tM transition at 300 IC near x= O.05; for x=0.06 there is a first-order low-temperature M + B transition near 130 K, and for x=0.08 the low-temperature transition is continuous.…”