Cascade of phase transitions in Tm1−Sm S due to Tm and Sm valence changes

Brillouin scattering on intermediate valent Sm 1 − x Tm x S

“…C 12 gets negative for doping concentrations of 15% and 25% Tm, and thereby Poisson's ratio gets negative, too. This behaviour stands in good agreement with measurements of the lattice constants and its interpretation by Smirnov [7].…”

“…Already a small pressure is now enough to increase the probability of a 4f -electron to be in the 5d state and therefore to provoke an isotropic collapse of the crystal. The behaviour of the calculated elastic constants corresponds well with Smirnov's measurement of the lattice constants and his interpretation of the Sm 1−x Tm x S valence [7]. In the range up to 15% Tm both the Sm cation as well as the Tm cation are in the divalent state and no intermediate valence can be found.…”

“…Pure TmS is a metal and in this state the thulium is trivalent, whereas in only weakly doped SmS it is divalent. Following Smirnov et al [7] three different doping ranges can be distinguished. From 0% to 16% both cations are divalent.…”