Browsing by Author "Romaka, V.V."

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    The influence of heavy doping of TiCoSb intermetallic semiconductor with Cr atoms on structural, kinetic and energetic properties
    (Ivano-Frankivsʹk : Fizyko-chimičnyj instytut DVNZ, 2024) Stadnyk, Yu.; Romaka, L.; Romaka, V.A.; Horyn, A.; Romaka, V.V.; Lukovskyy, T.; Poplavskyi, O.
    The structural, electrokinetic, and energetic properties of the TiСо1-xCrxSb semiconductor obtained by doping TiCoSb with Cr atoms introduced into the structure by substituting Co atoms in the crystallographic position 4c were studied. It was shown that in TiСо1-xCrxSb the structural defects of donor and acceptor nature are generated simultaneously in different ratios depending on the impurity concentration. At concentrations of х ≥ 0.02, the conductivity of TiСо1-xCrxSb has a metallic character, and the contribution of current carrier scattering mechanisms to the value of electrical resistivity is of the same order as changes in the concentration of current carriers. It was established that at all temperatures in the range of concentrations x = 0–0.02, the rate of generation of donors exceeds the rate of generation of acceptors, and at concentrations x > 0.02, on the contrary, the rate of generation of acceptors is greater than that of donors. This is indicated by the positive values of thermopower coefficient α(х,Т) of TiСо1-xCrxSb for х > 0.03.
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    Interaction between the components in Tm-Cr-Ge system at 1070 K
    (Ivano-Frankivsʹk : Fizyko-chimičnyj instytut DVNZ "Prykarpatsʹkyj nacionalʹnyj universytet imeni Vasylja Stefanyka", 2022) Romaka, L.; Stadnyk, Y.; Romaka, V.V.; Konyk, M.
    The phase equilibrium diagram of the Tm-Cr-Ge ternary system was constructed at a temperature 1070 K based on the results of X-ray phase, microstructural analyzes and energy-dispersive X-ray spectroscopy in the whole concentration range. At the temperature of investigation, two new ternary compounds are realized in the system: TmCr6Ge6 (SmMn6Sn6 structure type, space group P6/mmm, a=0.51506(1), c=0.82645(2) nm) and Tm4Cr4Ge7 (Zr4Co4Ge7 structure type, space group I4/mmm, а=1.39005(9), с=0.54441(1) nm). Inclusion of Cr atoms in the structure of the binary germanide TmGe2 (structure type ZrSi2) up to 10 at. % Cr leads to the formation of a solid solution TmCrxGe2 (x = 0-0.33).
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    Modeling of the properties of the semiconductor solid solution Lu1-xVxNiSb in the presence of magnetic ordering; [Моделювання властивостей напівпровідникового твердого розчину Lu1-xVxNiSb за наявності магнітного упорядкування]
    (Ivano-Frankivsʹk : Fizyko-chimičnyj instytut DVNZ "Prykarpatsʹkyj nacionalʹnyj universytet imeni Vasylja Stefanyka", 2023) Romaka, V.V.; Romaka, V.A.; Stadnyk, Yu.; Romaka, L.; Horyn, A.; Pashkevych, V.; Haraniuk, P.
    Modeling of the thermodynamic, structural, energetic and magnetic properties of the semiconductor solid solution Lu1-xVxNiSb was carried out under the condition of the presence of a magnetic moment on the V atoms and the occurrence of spontaneous magnetization. It is shown that the change in the unit cell parameter a(x) and the mixing enthalpy ΔHmix(х) depends little on the presence or absence of spontaneous magnetization. Modeling of the distribution of the density of electronic states DOS in the presence of a magnetic moment on V atoms revealed the splitting of energy states with spins up and down while preserving the band gap εg of Lu1-xVxNiSb. The relationship between the concentration of magnetic V atoms in Lu1-xVxNiSb and the Curie temperature ТС, when spontaneous magnetization is destroyed and the substance becomes paramagnetic, is established. The solid solution semiconductor Lu1-xVxNiSb, provided spontaneous magnetization is present, can be considered as a promising magnetocaloric.
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    Phase equilibria in the Gd–Cr–Ge system at 1070 K
    (Ivano-Frankivsʹk : Fizyko-chimičnyj instytut DVNZ "Prykarpatsʹkyj nacionalʹnyj universytet imeni Vasylja Stefanyka", 2021) Konyk, M.; Romaka, L.; Stadnyk, Yu.; Romaka, V.V.; Pashkevych, V.
    The isothermal section of the phase diagram of the Gd–Cr–Ge ternary system was constructed at 1070 K over the whole concentration range using X-ray diffractometry, metallography and electron microprobe (EPM) analysis. Three ternary compounds are realized in the Gd–Cr–Ge system at the temperature of annealing: Gd117Cr52Ge112 (Tb117Fe52Ge112 structure type,  space group Fm-3m, Pearson symbol cF1124, a = 2.8971(6) nm), GdCr6Ge6 (SmMn6Sn6 structure type, space group P6/mmm, Pearson symbol hP16, a = 0.51797(2), c = 0.82901(4) nm) and GdCr1-хGe2 (CeNiSi2 structure type, space group Cmcm, Pearson symbol oS16, a = 0.41569(1)-0.41593(8), b = 1.60895(6)-1.60738(3), c = 0.40318(1)-0.40305(8) nm). For the GdCr1-xGe2 compound the homogeneity range was determined (x=0.73 – 0,69).
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    Phase equilibrium diagram of Y-Cu-Sb system at 870 K
    (Ivano-Frankivsʹk : Fizyko-chimičnyj instytut DVNZ "Prykarpatsʹkyj nacionalʹnyj universytet imeni Vasylja Stefanyka", 2023) Romaka, L.; Stadnyk, Yu.; Romaka, V.V.; Zelinskiy, A.; Klyzub, P.; Horyn, A.
    The interaction of the components in the Y-Cu-Sb ternary system was investigated using the methods of X-ray phase analysis, microstructure, and energy-dispersive X-ray spectroscopy in the whole concentration range at 870 K. At the temperature of investigation Y-Cu-Sb system is characterized by the formation of three ternary compounds: Y3Cu22Sb9 (Dy3Cu20+xSb11-x structure type, space group F-43m, a=1.6614(3) nm), Y3Cu3Sb4 (Y3Au3Sb4 structure type, space group I-43d, а = 0.95357(5) nm), YCuSb2 (HfCuSi2 structure type, space group P4/nmm, a = 0.42580(1), c = 0.98932(3) nm). The solubility of copper in the binary compound YSb (NaCl structure type) extends up to 8 at. %.