Relationship between the local electronic and local crystal structures of intermediate-valence Sm1−x Y x S

Abstract

Samarium sulfide (SmS) belongs to the class of compounds with homogeneous intermediate valence, which is observed in a metal phase at a pressure of տ 0.6 GPa above the point of the dielectric-metal phase transition because of a partial delocalization of the 4 f 6 electron [1]. Upon the transition, the crystal lattice decreased significantly in volume with the retention of the NaCl symmetry. An intermediate-valence state can also be achieved by replacing a portion of samarium ions by other smaller radius rare earth or transition metal ions (Y 3+ , Yb 3+ , Gd 3+ , etc.). It is believed that the resulting chemical contraction serves as an equivalent of external pressure. However, attempts to initiate the dielectric-metal phase transition using chemical contraction upon the insertion of bivalent ions, such as Ca 2+ , were unsuccessful, although x-ray absorption spectroscopic data indicated the appearance of an intermediate-valence state [2]. This suggests that doping and the resulting chemical contraction inevitably affect the electronic and crystal structures at a local level and thereby change the properties of the intermediatevalence state and the macroscopic properties of the compound.The recently growing interest in compounds based on samarium sulfide is considerably related to a number of anomalies observed in these compounds, such as a negative coefficient of thermal expansion in the metallic phase of SmS Thus, in order to reveal the nature of the intermediate-valence state, determine the role of doping, and explain the macroscopic properties of Sm 1 -x Y x S, a study of the local electronic and crystal structure peculiarities is brought to the forefront. For this purpose, in this work, we used a combination of x-ray absorption near-edge structure (XANES) and extended x-ray absorption fine structure (EXAFS) techniques, which allowed us to simultaneously study the valence states and local environment parameters of the test ions.The samples with the yttrium contents x = 0.17 and 0.33 were prepared at the Ioffe Physicotechnical Institute, Russian Academy of Sciences (St. Petersburg, Russia), and the samples with x = 0.25 and 0.45 were prepared at Tohoku University (Sendai, Japan).The x-ray absorption spectra of Sm 1 -x Y x S ( x = 0.17, 0.25, 0.33, and 0.45) were measured over the temperature range 20-300 K above the Sm L III and Y K edges at the beamlines E 4 and A 1 of the HASYLAB synchrotron center (DESY, Germany). The use of a Si (111

Kondo-Induced Giant Isotropic Negative Thermal Expansion

“…Alternatively, the first-order transition can be smeared out macroscopically due to local disorder, which is neglected in the Kondo lattice model. Results from previous experimental studies converge towards the latter scenario [13,14,41,42]. Macroscopic susceptibility and dilatometry data, for instance, reveal an appreciable hysteresis in the temperature dependence of Sm 1−x Y x S with x close to 0.17, suggesting an xT -phase diagram in which the transition remains locally first order up to 0.27 < x c < 0.45 [14,42].…”

Nanotubes from the Misfit Layered Compound (SmS)1.19TaS2: Atomic Structure, Charge Transfer, and Electrical Properties

“…The shape of the Sm L 3 XANES spectrum (Figure a) and the position of the “white line” maxima at 6722 eV (edge position 6719.5 eV, corresponding to 2 p to 5 d transition) is characteristic of the Sm 3+ state . No signature of the Sm 2+ “white line” in the range 6711–6713 eV was found, indicating that there is no mixed/intermediate valence state of Sm, which in turn signifies a strong charge transfer. − This observation is in-line with the XPS and also with the literature reports. , …”

Regulation of magnetoresistance in SmxMn1-xS by weak external pressure

“…In the absence of a magnetic order, the rearrangement of the electronic structure can be caused by orbital magnetic moments [6]. In manganese chalcogenides substituted with rare-earth elements of variable valence, due to the electron-lattice interaction, it is possible to change transport characteristics [7][8][9]. The magnetic structure in semiconductors also depends on the spin-phonon interaction, and at certain interaction parameters a gap appears in the spectrum of spin excitations, the type of magnetic ordering changes.…”