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Публікація Percolation effects and self-organization processes in cold-pressed Bi2(Te1−xSex)3 solid solutions(Elsevier Ltd, 2021) Rogacheva, E. I.; Martynova, E. V.; Shelest, T. N.; Doroshenko, A. N.; Nashchekina, O. N.It was established that the dependences of thermoelectric and mechanical properties of cold-pressed Bi2(Te1−xSex)3 alloys on composition (x = 0–0.07) exhibit a non-monotonic behavior in certain concentration ranges: an anomalous decrease in the Seebeck coefficient, thermoelectric power factor, and microhardness, and increase in electrical conductivity with increasing x. We observed similar anomalies earlier for cast Bi2(Te1−xSex)3 alloys and explained them by percolation and self-organization phenomena. Thus, the existence of the anomalies does not depend on the method of sample preparation. However, in pressed samples as compared to cast ones conductivity type changes from p to n and thermoelectric power factor increases.Публікація Percolation effects and self-organization processes in Bi₂(Te₁₋ₓSeₓ)₃ solid solutions(Easy Conferences Ltd, 2019) Rogacheva, E. I.; Shelest, T. N.; Martynova, E. V.; Doroshenko, A. N.; Nashchekina, O. N.Документ Thermal conductivity of PbSe1-xTex (x = 0 – 0.04) solid solutions(Institute of Thermoelectricity National Academy of Sciences of Ukraine, 2020) Nikolaenko, G. O.; Vodoriz, O. S.; Rogacheva, E. I.; Tavrina, T. V.; Lisachuk, G. V.The dependence of lattice thermal conductivity λL of pressed samples of PbSe1-xTex solid solutions on the composition (x = 0 – 0.04) at a temperature of 325 K is obtained. The λL(х) curve shows a maximum near х = 0.0075. Measurement of the temperature dependence of λL in the range of 150-600 K showed that a concentration anomaly in the same range of compositions is also observed on the composition dependence of power factor β in the temperature dependence of λL . The non-monotonic character of the λL(х) and β(х) dependences is associated with critical phenomena accompanying the transition of the percolation type from dilute to concentrated solid solutions. In the study and practical application of PbSe1-xTex solid solutions, it is necessary to take into account the non monotonic nature of the change in thermal conductivity with composition. Bibl. 15, Fig. 3.Документ Thermoelectric and mechanical properties of (Bi₁₋ₓSbₓ )₂Te₃(x = 0÷0.07) semiconductor solid solutions(National Academy of Sciences of Ukraine, 2016) Rogacheva, E. I.; Martynova, K. V.; Bondarenko, A. S.The dependences of thermoelectric properties and microhardness on the composition of polycrystalline (Bi₁₋ₓSbₓ )₂Te₃ solid solutions in the concentration range x = 0÷0.07 at room temperature were investigated. A drastic growth of microhardness was discovered with a simultaneous reduction of the Hall coefficient, the Seebeck coefficient and electric conductivity with increase in antimony content x = 0.005 – 0.01, following which with further increase in x to x = 0.01 – 0.015, the type of the dependences was reversed. The observed effect is attributable to a high degree of crystal lattice disorder with the introduction of the first portions of impurity and to subsequent relaxation processes with formation of percolation channels in crystal impurity subsystem. With further increase in x, the Hall coefficient and the Seebeck coefficient practically do not change with composition, and the observed more complicated dependence of microhardness and electric conductivity on x is interpreted as a manifestation of short-range processes in a solid solution.Документ Concentration anomaly of heat capacity in PbTe based solid solutions(2002) Rogacheva, E. I.; Sinelnik, N. A.; Krivulkin, I. M.The temperature dependences of the heat capacity in the Pb₁₋ₓMnₓTe and Pb₁₋ₓGeₓTe (x = 0-0.04) solid solutions based on PbTe were obtained in the temperature range of 100-670 K. Pronounced peaks were observed in the isotherms of the heat capacity in the vicinity of x ~ 0.01-0.015. The presence of the peaks is explained on the basis of the idea about the existence of concentration phase transitions of percolation type, which take place in any solid solution and are related to transformation of impurity discontinuum into impurity continuum.Публікація Peculiarities of concentration dependences of thermal conductivity in (PbTe)₁₋ₓ (Bi₂Te₃)ₓ semiconductor solid solutions(Інститут термоелектрики НАН України, 2014) Rogacheva, E. I.; Vodorez, O. S.; Nashchekina, O. N.; Dresselhaus, M. S.For the semiconductor (PbTe)₁₋ₓ (Bi₂Te₃)ₓ solid solutions, the temperature (T = 250 – 670 K) and concentration (x = 0 – 0.07) dependences of the total λ and lattice λp thermal conductivities were obtained. It was established that the dependences λ(x), λp(x) and β(x) (where β is the exponent in the λp ~ T⁻ᵝ dependence) have a non-monotonic dependence on x in this range of x. While showing a general tendency to decrease with increasing x, the three variables λ, λp, and β exhibit maxima at x = 0.005, 0.015 and x = 0.03. The oscillatory character of these dependences is attributable to the changes in thermal transfer processes and the mechanisms of phonon scattering under transitions from the dilute to the concentrated and associated solid solutions, with the transitions due to spatial ordering processes. The effective cross-section σs for phonon scattering by impurity atoms was estimated on the basis of the experimental data and theoretical calculations in accordance with the Klemens theory. The mean σs value in the homogeneity region of PbTe (x = 0 – 0.05) found experimentally coincides with the theoretically calculated σs value. However, in the region of the dilute solid solutions (x < 0.005), the σs value considerably exceeds the mean σs value. Also long-term aging reduces λ by ~ 15%.Публікація Galvanomagnetic properties of polycrystalline Bi₁₋ₓSbₓ solid solutions in the concentration range x = 0-0.25(Науково-технологічний комплекс "Інститут монокристалів", 2020) Rogacheva, E. I.; Doroshenko, A. N.; Drozdova, A. A.; Nashchekina, O. N.; Men'shov, Yu. V.The dependences of the Hall coefficient, electrical conductivity, magnetoresistance, electron and hole concentration and mobility on the Bi₁₋ₓSbₓ solid solution composition in the concentration range x = 0-0.25 at 77 and 300 K in magnetic fields 1 T and 0.05 T were obtained. It was shown that all the dependences exhibit a distinct nonmonotonic oscillating behavior at both temperatures and in both magnetic fields. The presence of concentration-dependent anomalies of galvanomagnetic properties is attributed to critical phenomena accompanying the percolation-type transition from dilute to concentrated solid solutions and electronic phase transitions: a transition to a gapless state, the semimetal – semiconductor transition, and indirect – direct band gap semiconductor transition.Публікація Percolation effects and self-organization processes in Bi₂(Te₁₋ₓSeₓ)₃ solid solutions(Науково-технологічний комплекс "Інститут монокристалів", 2019) Rogacheva, E. I.; Shelest, T. N.; Martynova, E. V.; Doroshenko, A. N.; Nashchekina, O. N.; Men'shov, Yu. V.The room-temperature dependences of microhardness H, electrical conductivity σ, the Seebeck coefficient S, and thermoelectric power factor P on composition of Bi₂(Te₁₋ₓSeₓ)₃ solid solutions were measured in the concentration range x = 0 - 0.07. In the intervals x = 0.0075 - 0.0175 and x = 0.025 - 0.035, an anomalous decrease in H and S and increase in σ with increasing x were observed. The first concentration-dependent anomaly was attributed to critical phenomena, accompanying a percolation-type phase transition. The percolation threshold xc and the radius of deformation spheres R₀ around Se impurity atoms were estimated. The second anomaly is assumed to be connected with a short-range ordering in the solid solution. The non-monotonic character of the dependences of H on the load on an indenter, whose behavior depended on the impurity concentration, was attributed to the interaction of the deformation fields created by dislocations and impurity atoms.