A. V. Golubkov

Defect Samarium Ions and Electromotive-Force Generation in SmS

A model explaining electromotive-force generation in SmS under heating in the absence of external temperature gradients is considered. An analysis of data on the density of SmS single crystals with compositional deviations from stoichiometry in the homogeneity range suggests that excess samarium ions occupy vacancies on the sulfur sublattice. Possible concentrations of defect samarium ions are determined (up to 2.8×1021 cm−3). The temperature interval within which electromotive force appears in various SmS samples (440–640 K) and the critical conduction-electron concentrations at which the generation sets in [(6.0–8.5)×1019 cm−3] are calculated. An expression permitting estimation of the magnitude of the observed effect is proosed.

The structure of a metallic-phase film produced by mechanical polishing of polycrystalline SmS

X-ray diffraction is used to study the structure of a metallic-phase film that forms during controlled polishing of homogeneous polycrystalline semiconducting Sm1+xS samples. Structural changes that appear in the semiconducting phase under these conditions were studied. The x dependence of the thickness of the metallic layer forming on the sample surface is analyzed to explain the effect of excess samarium ions on the transformation parameters. The cause of the stabilization of the metallic modification of SmS after polishing is terminated is explained using estimates based on the measured sizes of coherent domains in samples of different compositions. The appearance and stabilization of the metallic phase are related to a decrease in and subsequent conservation of the coherent-domain size, respectively.

Thermovoltaic effect in samarium sulfide-based Sm1 − xEuxS heterostructures

The thermovoltaic effect in samarium sulfide-based Sm1 − xEuxS bulk heterostructures in the temperature interval 300–520 K is considered. It is shown that this effect is due to an artificially produced samarium ion concentration gradient, rather than to an external temperature gradient.

Efficiency of Transformation of Heat Energy into Electric Energy Due to the Thermovoltaic Effect

Direct measurements of the efficiency of the transformation of heat energy to electric energy on the basis of the thermovoltaic effect are carried out for the first time. Experiments are performed using samarium sulfide specimens. The values of efficiency vary from 7.5 to 28%.

Defect structure in SmS

The experimental dependence of the concentration of conduction electrons on the size of x-ray coherent scattering regions is obtained. The dependence is analyzed within the previously developed concentration model of the energy spectrum of samarium sulfide SmS. It is shown that the impurity donor levels in the SmS compound correspond to the samarium defect ions located at the boundaries of coherent scattering regions.

Features of the infrared reflection spectra of SmS semiconductor in the homogeneity range

Infrared reflection spectra in the range of 5200–380 cm−1 were measured for polycrystalline samarium monosulfide samples in the semiconductor phase with compositions Sm1 + xS lying within the homogeneity range (0 ≤ x ≤ 0.17) in the temperature range of 300–600 K. Five peaks with energies in the range of 1150–880 cm−1, whose positions depend weakly on the composition and temperature. It was shown that the reflection peaks are associated with 7F0–7F2 transitions of 4f electrons of Sm2+ ions.

Thermopower of a moderate heavy-fermion compound YbZnCu4

The thermopower coefficients S of samples of a moderate heavy-fermion compound YbZnCu4 and metallic LuZnCu4 are measured in the temperature range 5–300 K. Data on the temperature dependence of the thermopower coefficient S of YbZnCu4 suggest that this material is a heavy-fermion compound with a Kondo temperature of ∼50 K.

The efficiency of thermal energy conversion into electricity by means of the thermovoltaic effect

The efficiency of thermal energy conversion into electricity based on the thermovoltaic effect has been studied. Experiments were performed on samarium sulfide (SmS) samples containing a region doped with excess samarium up to Sm1.04S. The conversion efficiency increases with time from 17 to 36% due to a decrease in the amount of absorbed thermal energy at unchanged power of the generated electric energy.

Thermoelectric properties of TmTe under pressure up to 20 GPa

The effect of quasi-hydrostatic pressure up to 20 GPa on thermopower of single-crystal samples of thulium monotelluride and monosulfide was studied. The pressure dependences of the thermopower of thulium monotelluride were found to have features in pressure regions of 2 and 6 GPa, which can be associated with phase transitions to the cation mixed-valence state and tetragonal structure, respectively. The upper pressure boundary of stability of the thulium ion mixed-valence state in monotelluride was evaluated by comparing the pressure dependences of the thermopower of TmTe and TmS.

Thermovoltaic effect in samarium sulfide-based heterostructures

The thermovoltaic effect in samarium sulfide-based bulk heterostructures with compositions Sm1 − xEuxS and Sm1 − xGdxS is considered in the temperature interval 300–460 K. It is shown that this effect can be observed when an external temperature gradient is absent, i.e., when the sample temperatures near the contacts from which a generated voltage is tapped off are the same. The temperature is measured with thermocouples and also by a contactless method using a thermal imager.