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The energy expediency of the existence of Er1-xScxNiSb substitutional solid solution up to the concentration x≈0.10 was established by modeling the variation of free energy ΔG(x) values (Helmholtz potential). At higher Sc concentrations, x> 0.10, there is stratification (spinoidal decomposition of phase). It is shown that in the structure of p-ErNiSb semiconductor there are vacancies in positions 4a and 4c of Er and Ni atoms, respectively, generating structural defects of acceptor nature. The number of vacancies in position 4a is twice less than in position 4c. This ratio also remains for p-Er1-xScxNiSb. Doping of p-ErNiSb semiconductor by Sc atoms by substitution of Er atoms is also accompanied by the occupation of vacancies in position 4a. In this case, Ni atoms occupy vacancies in position 4c, which can be accompanied by the process of ordering the p-Er1-xScxNiSb structure. Occupation of vacancies by Sc and Ni atoms leads to an increase of the concentration of free electrons, an enlarge of the compensation degree of semiconductor, which changes the position of the Fermi level εF and the mechanisms of electrical conductivity.

Samples of Er1-xScxNiSb (x = 0–0.10) solid solution were synthesized by an arc-melting and the effect of doping by Sc atoms on the electrokinetic and energetic characteristics of the half-Heusler ErNiSb phase was investigated. It was established that at the studied concentrations the main carriers of electricity in the Er1-xScxNiSb semiconductor are holes. It was shown that doping of p-ErNiSb compound by Sc atoms introduced by substitution of Er atoms in 4a position is accompanied by the occupation of presented vacancies in position 4a, which leads to the reduction and elimination of structural defects of acceptor nature and corresponding acceptor band. The concentration ratio of ionized acceptors and donors generated in Er1-xScxNiSb determines the position of the Fermi level and the mechanisms of electrical conduction. The investigated solid solution Er1-xScxNiSb is a promising thermoelectric material.

The effect of doping of the TiCoSb compound (MgAgAs structure type) by Mo atoms on the features of the structural characteristics and behavior of the electrokinetic, energetic and magnetic properties of the Ti1-xMoxCoSb semiconducting solid solution (х = 0 - 0.06) in the temperature interval 80 - 400 K was studied. It was shown that including of Mo atoms (rМо= 0.140 nm) in the ToCoSb structure by substitution of Ti atoms (rТі= 0.146 нм) in 4a position is accompanied with non-monotonous variation of the lattice parameter values а(х), indicating unpredictable structural changes. Based on analysis of the variation of the electric resistivity values, thermopower coefficient, magnetic susceptibility and energetic characteristics, it was concluded that simultaneous generation in the crystal of the structural defects of the donor and acceptor nature (donor-acceptor pairs), which generate corresponding energy levels in the band gap of semiconductor and determine its electrical conductivity.

The isothermal section of the phase diagram of the Er–Cr–Ge ternary system was constructed at 1070 K over the whole concentration range using X-ray diffractometry, metallography and electron microprobe analysis (EPMA). At the temperature of investigation the interaction of components in the Er–Cr–Ge system is characterized by the formation of two ternary compounds: ErCr6Ge6 (MgFe6Ge6-type, space group P6/mmm, Pearson symbol hP13; a = 5.15149(3), c = 8.26250(7) Ǻ; RBragg = 0.0493, RF = 0.0574) and ErCr1-xGe2 (CeNiSi2-type, space group Cmcm, Pearson symbol oS16, a = 4.10271(5), b = 15.6652(1), c = 3.99017(4) Ǻ; RBragg = 0.0473, RF = 0.0433). For the ErCr1-xGe2 compound, the homogeneity region was determined (ErCr0.28-0.38Ge2, a = 4.10271 (5)-4.1418 (9), b = 15.6652 (1)-15.7581(4), c = 3.99017 (4)-3.9291(1) Ǻ).

The samples of ZrNi1-хVxSn solid solution (x = 0 – 0.10) based on the ZrNiSn half-Heusler phase (MgAgAs structure type) were synthesized by direct arc-melting with homogenous annealing at 1073 K. The electrokinetic and energy state characteristics of the ZrNi1-хVxSn semiconducting solid solution were investigated in the temperature range T = 80 - 400 K. An analysis of behavior of the electrokinetic and energetic characteristics, in particular, the motion rate of the Fermi level, ΔεF/Δx for ZrNi1-хVxSn, allows to assume about the simultaneous generation of the structural defects of donor and acceptor nature in the crystal. The additional researches are required to establish the mechanisms of donor generation.

The isothermal sections of the phase diagrams of the Lu–V–Ge and Lu-V-Sn ternary systems were constructed at 870 K over the whole concentration range using X-ray diffraction and EPM analyses. In the Lu-V-Ge system a formation of the substitutional solid solution Lu5Ge3-xVx based on the Lu5Ge3 binary compound (Mn5Si3 structure type) was found up to 6 at. % V. Insertion of the V atoms in the structure of the LuGe2 binary germanide (ZrSi2 structure type, up to 5 aт. % V) results in the formation of the LuV0,15Ge2 ternary phase (CeNiSi2 structure type, space group Cmcm, a=0.40210(4), b=1.5661(1), c=0.38876(3) nm), which corresponds to the limit composition of the interstitial solid solution LuVxGe2. The interaction between the elements in the Lu-V-Sn system results in the formation of one ternary compound LuV6Sn6 (SmMn6Sn6-type, space group P6/mmm, a=0.5503(2), c=0.9171(4) nm) at investigated temperature.

The features of electrokinetic, energy state and magnetic characteristics of ZrNi1-xRhxSn semiconductive solid solution were investigated in the ranges: T = 80-400 K, x = 0-0.10. It was shown that substitution of Ni atoms (3d84s2) by Rh atoms (4d85s1) in the structure of ZrNiSn compound generated the structural defects with acceptor nature, and holes became the main charge carriers in the ZrNi1-xRhxSn at low temperature. Based on analysis of the motion rate of the Fermi level ΔεF/Δх in ZrNi1-xRhxSn to the valence band and change of sign of thermopower coefficient from positive to negative it was suggested that the structural defects of acceptor and donor natures were generated simultaneously (donor-acceptor pairs), and deep donor band ɛD2 was formed.

The interaction of the components in the Gd-Mn-Sn ternary system was studied using the methods of X-ray and microstructure analyses, in the whole concentration range. The phase diagrams of the Gd-Mn-Sn system were constructed at 873 and 673 K. At both temperature of investigation the Gd-Mn-Sn system is characterized by existence of two ternary compounds: GdMn6Sn6 (MgFe6Ge6 structure type, space group P6/mmm) and Gd4Mn4Sn7 (Zr4Co4Ge7 structure type, space group I4/mmm). The formation of the interstitial solid solution GdMnхSn2 based on GdSn2 (ZrSi2-type) binary compound was found up to 10 at. % Mn at 873 K and 673 K. The existence of the substitutional solid solution based on GdMn2 (MgCu2-type) was observed up to 5 at.% Sn and 3 at. % Sn at 873 K and 673 K, respectively. Key words: intermetallics, ternary system, phase equilibria, crystal structure, solid solution.

The phase diagram of the V–Co–Sb ternary system was constructed at 870 K over the whole concentration range using X-ray powder diffraction and electron probe microanalysis. The formation of one ternary compound VCoSb with MgAgAs type structure (half-Heusler phase, space group F-43m, a = 0.57838(2) nm) was confirmed. The influence of V doping on electrical transport property behavior of the binary skutterudite CoSb3 (CoAs3-type, space group Im-3) was studied by measurements of electrical resistivity and Seebeck coefficient as well as ab initio DFT calculations.

The structure characteristics, temperature and concentration dependences of the electrical resistivity and the thermopower coefficient for the Vx+yCo1-ySb3 skutterudite were investigated in the ranges: T = 80 - 400 K, x = 0.02 - 0.20. It was shown that the introduction of V atoms into the structure of CoSb3 thermoelectric material was accompanied by an increase in the efficiency of conversion of thermal energy into electrical energy. It was established that the inversion in the sign of the thermopower coefficient for Vx+yCo1-ySb3 not observed for these concentrations of V impurity atoms. Based on the analysis of electrokinetic and energy state characteristics of Vx+yCo1-ySb3, it was assumed that the V (3d34s2)impurity atoms simultaneously replaced Co (3d74s2)atoms, generating structural defects of acceptor nature, and were located in the icosahedral voids of the crystal structure and generated donors. Keywords: crystal structure, electrical resistivity, thermopower coefficient.

The crystalline and electronic structures, energy, kinetic, and magnetic characteristics of n-HfNiSn semiconductor heavily doped with Y acceptor impurity are studied in the ranges: T = 80–400 K, N A Y ≈ 1.9 × 1020–5.7 × 1021 cm–3 (x = 0.01–0.30), and H ≤ 10 kG. The nature of the mechanism of structural defect generation is determined, which leads to a change in the band gap and the degree of semiconductor compensation, the essence of which is the simultaneous reduction and elimination of structural donor-type defects as a result of the displacement of ~1% of Ni atoms from the Hf (4a) site, and the generation of structural acceptor-type defects by substituting Hf atoms with Y atoms at the 4a site. The results of calculations of the electronic structure of Hf1–x Y x NiSn are in agreement with the experimental data. The discussion is performed within the Shklovskii–Efros model of a heavily doped and compensated semiconductor.

Crystal and electronic structure, transport and energy state characteristics of the Zr1−xVx NiSn (0.01 ≤ x ≤ 0.1) thermoelectric material are investigated in the 80–400 K temperature interval. A mechanism of simultaneous generation of structural defects of the acceptor and donor nature, which determines the electric conductivity of the material, is established. It is shown that energetically expedient is a simultaneous occupation of the 4c position of Ni (3d84s2) atoms by V (3d34s2) atoms, which generates structural defects of the acceptor nature and the impurity acceptor band Ꜫ1A, as well as the 4a position of Zr (4d25s2) atoms, generating structural defects of the donor nature and the impurity donor band Ꜫ2D., Дослiджено кристалiчну та електронну структуру, транспортнi та енергетичнi характеристики термоелектричного матерiалу Zr1−xVx NiSn (0,01 ≤ x ≤ 0,1) в iнтервалi температур 80–400 К. Встановлено механiзми генерування структурних дефектiв акцепторної та донорної природи, якi визначають електропровiднiсть матерiалу. Показано, що енергетично вигiдним є одночасне заповнення як кристалографiчної позицiї 4c атомiв Ni(3d84s2) атомами V (3d34s2), якi генерують структурнi дефекти акцепторної природи та створюють домiшкову акцепторну зону Ꜫ1A, так i позицiї 4a атомiв Zr (4d25s2), якi генерують структурнi дефекти донорної природи та створюють домiшкову донорну зону Ꜫ2D.

Interaction of Yttrium and Thulium with Nickel and Antimony was studied at 870 K in the whole concentration range based on XRD and EPM analyses. Four ternary compounds are realized in the Y–Ni–Sb system: Y5Ni2Sb (Mo5SiB2-type), Y5NixSb3-x (Yb5Sb3-type), YNiSb (MgAgAs-type), and Y3Ni6Sb5 (Y3Ni6Sb5-type). At 870 K the Tm–Ni–Sb system is characterized by the formation of two ternary antimonides: Tm5Ni2Sb (Mo5SiB2-type) and TmNiSb (MgAgAs-type). Temperature dependencies of the electrical resistivity and Seebeck coefficient of the YNiSb and TmNiSb half-Heusler compounds were measured in the temperature range 80–380 K. Both compounds behave as doped and compensated semiconductors. The DFT calculations were performed for the ordered and disordered models of YNiSb to explain the homogeneity region and transport properties.

The phase equilibria in the Gd–Ni–Sb and Lu-Ni-Sb ternary systems were studied at 873 K by X-ray and metallographic analyses in the whole concentration range. The interaction of the elements in the Gd–Ni–Sb system results the formation of five ternary compounds at investigated temperature: Gd5Ni2Sb (Mo5SiB2-type), Gd5NiSb2 (Yb5Sb3-type), GdNiSb (MgAgAs-type), Gd3Ni6Sb5 (Y3Ni6Sb5-type), and GdNi0.72Sb2 (HfCuSi2-type). At investigated temperature the Lu-Ni-Sb system is characterized by formation of the LuNiSb (MgAgAs-type), Lu5Ni2Sb (Mo5SiB2-type), and Lu5Ni0.56Sb2.44 (Yb5Sb3-type) compounds. The disordering in the crystal structure of half-Heusler GdNiSb and LuNiSb was revealed by EPMA and studied by means of Rietveld refinement and DFT modeling. The performed electronic structure calculations are in good agreement with electrical transport property studies.

The crystal and electronic structure and also the energy and kinetic properties of n-VFeSb semiconductor heavily doped with the Ti acceptor impurity are investigated in the temperature and Ti concentration ranges of T = 4.2–400 K and NATi ≈ 9.5 × 1019–3.6 × 1021 cm–3 (x = 0.005–0.20), respectively. The complex mechanism of the generation of acceptor and donor structural defects is established. It is demonstrated that the presence of vacancies at Sb atomic sites in n-VFeSb gives rise to donor structural defects (“a priori doping”). Substitution of the Ti dopant for V in VFeSb leads simultaneously to the generation of acceptortype structural defects, a decrease in the number of donor defects, and their removal in the concentration range of 0 ≤ x ≤ 0.03 via the occupation of vacancies by Sb atoms, and the generation of donor defects due to the occurrence of vacancies and an increase in their number. The result obtained underlies the technique for fabricating new n-VFeSb-based thermoelectric materials. The results are discussed in the context of the Shklovsky–Efros model for a heavily doped compensated semiconductor.

Electrical transport properties of the RCr 6 Ge 6 (R = Y, Gd, Tb, Dy, Lu) compounds with the MgFe 6 Ge 6 structure type (space group P 6/ mmm ) were studied. Polycrystalline samples were prepared by arc melting of the stoichiometric amounts of the constituent elements (nominal purities: Y, Gd, Tb, Dy, Lu − 99.9 wt. %, Cr − 99.99 wt. %, Ge − 99.999 wt. %) on a water-cooled copper hearth under a protective Ti-gettered argon atmosphere. Subsequently the buttons were annealed at 1070 K for 720 h in evacuated silica tubes, followed by quenching in cold water. Quality of the prepared samples was tested by X-ray powder diffraction (diffractometer DRON-2.0M, Fe K α -radiation) and Scanning Electron Microscopy (REMMA 102-02 electron microscope equipped with an energy-dispersive spectroscopy X-ray analyser). XRPD data were collected in the transmission mode on a STOE STADI P diffractometer, Cu K α 1 radiation. The crystal structure refinement of LuCr 6 Ge 6 was performed using X-ray powder diffraction method (structure type MgFe 6 Ge 6, space group P 6/ mmm , Pearson symbol hP 13, a = 5.1617(1), c = 8.2745(1) A). The atomic parameters are: Lu in (1 a ): 0 0 0, B iso = 0.6(0) (hereafter A 2 ); site occupations G = 0.64(4), Cr in (6 i ): 1/2 0 z , z = 0.2518(3); B iso = 0.6(0); Ge1 in (2 d ): 1/3 2/3 1/2, B iso = 0.6(0); Ge2 in (2 c ): 1/3 2/3 0; B iso = 0.6(0); Ge3 in (2 e ): 0 0 z; z = 0.3491(4); site occupations G = 0.86(1), R Bragg = 0.0660, R f = 0.0590. The temperature dependencies of electrical resistivity were measured in the temperature range 11−300 K employing two-probe method on millimeter-scale, well-shaped pieces cut by spark erosion from the polycrystalline samples using the helium cooler with closed cycle (Advanced Research systems, USA). Electrical resistivity measurements showed that the resistivity values of the all studied compounds increase with temperature indicating metallic type of conductivity. The slope change of the resistivity at low temperature part of r ( T ) dependencies for the GdCr 6 Ge 6 and TbCr 6 Ge 6 compounds is connected with their magnetic ordering. Change of the resistivity caused by magnetic ordering was not observed for the DyCr 6 Ge 6 compound in the studied temperature interval. In the paramagnetic region, the resistivity data of RCr 6 Ge 6 can be approximated by the Bloch–Gruneissen–Mott (BGM) formula and values of the Debye temperature Θ D were calculated. Keywords: intermetallics, electrical resistivity, X-ray diffraction, crystal structure.

The mechanism of simultaneous generation of donor-acceptor pairs in ZrNiSn1-xGax semiconductor solid solution is established. The modeled distribution of atoms in the crystal lattice of ZrNiSn1-xGax showed that the speed of movement of Fermi level εF, obtained from the band structure calculations is in agreement with experimental extracted from lnρ(1/T) dependencies. It is shown that with substitution of Sn (5s25p2) with Ga (4s24p1) atoms in 4b crystallographic site both acceptor and donor (vacancies in 4b site) defects are generated. Keywords: crystal and electronic structures, conductivity, thermopower coefficient., Встановлена природа механізму генерування донорно-акцепторних пар у напівпровідниковому твердому розчині ZrNiSn1-xGax. Показано, що при зайнятті атомом Ga (4s24p1) позиції 4b атомів Sn (5s25p2) одночасно генеруються як структурні дефекти акцепторної природи, так і донорної (донорно-акцепторні пари) у вигляді вакансій у позиції 4b. Знайдено таке просторове розташування атомів в елементарній комірці rNiSn1-xGax, коли швидкість руху рівня Фермі εF, отримана з розрахунків розподілу густини електронних станів DOS, співпадає з експериментально встановленою з температурних залежностей питомого електроопору lnρ(1/T). Ключові слова: кристалічна і електронна структури, електропровідність, коефіцієнт термо-ерс.

The crystal and electronic structure and magnetic, energy, and kinetic properties of the n-HfNiSn semiconductor heavily doped with the Co acceptor impurity (HfNi1 − x Co x Sn) are investigated in the temperature and Co concentration ranges T = 80–400 K and N Co ≈ 9.5 × 1019-5.7 × 1021 cm−3 (x = 0.005–0.30), respectively, and under magnetic field H ≤ 10 kOe. It is established that the degree of compensation of the semiconductor changes due to transformation of the crystal structure upon doping, which leads to the generation of acceptor and donor structural defects. The calculated electronic structure is consistent with the experiment; the HfNi1 − x Co x Sn semiconductor is shown to be a promising thermoelectric material. The results obtained are discussed within the Shklovsky-Efros model for a heavily doped and compensated semiconductor.

The crystal and electronic structure and energy and kinetic properties of the n-HfNiSn semiconductor heavily doped with a Ru acceptor impurity are investigated in the temperature and Ru concentration ranges T = 80–400 K and NARu ≈ 9.5 × 1019−5.7 × 1020 cm−3 (x = 0–0.03), respectively. The mechanism of structural-defect generation is established, which changes the band gap and degree of compensation of the semiconductor and consists in the simultaneous concentration reduction and elimination of donor structural defects by means of the displacement of ∼1% of Ni atoms from the Hf (4a) positions, the generation of acceptor structural defects upon the substitution of Ru atoms for Ni atoms in the 4c positions, and the generation of donor defects in the form of vacancies in the Sn (4b) positions. The calculated electronic structure of HfNi1 − xRuxSn is consistent with the experiment. The results obtained are discussed within the Shklovsky-Efros model for a heavily doped and compensated semiconductor.

The component interaction in the V–Cu–Sb ternary system was studied at 773 K by X-ray and EPM analyses in the whole concentration range. One new ternary compound V 2 Cu 3 Sb 4 was found. The structure of V 2 Cu 3 Sb 4 ( Z = 2, space group P 6 3 /mmc – hgdca , a = 0.852905(5), c = 0.529456(4) nm, R I = 0.0302) represents a new structure type of intermetallic compounds belonging to AlB 2 -family, and is derived from high-temperature modification of V 1.5 Sb phase (Ni 2 In-type). The magnetic and electrical property measurements showed that V 2 Cu 3 Sb 4 compound is a Pauli paramagnet and characterized by metallic behavior of conductivity. The band structure calculations of V 2 Cu 3 Sb 4 using the FP-LAPW method confirmed the metallic type of conductivity.

The phase equilibria in the Zr–Co–Sb ternary system were studied at 873 K by means of X-ray and metallographic analyses in the whole concentration range. The interaction between the elements results the formation of four ternary compounds at investigated temperature: ZrCoSb (MgAgAs-type), Zr6CoSb2 (K2UF6-type), Zr5CoSb3 (Hf5CuSn3-type) and Zr5Co0.5Sb2.5 (W5Si3-type). The limited composition Zr5CoSb3 of the solid solution based on the Zr5Sb3−4 binaries is considered as compound with Hf5CuSn3 structure type. The influence of the disordering and defects in the crystal structure of ZrCoSb on the physical properties was analyzed. The performed electronic structure calculations are in good agreement with electrical and magnetic studies.