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 results of modeling the properties of the semiconductor solid solution Lu1-xScxNiSb, x=0–0.10, which is a promising thermometric material for the manufacture of sensitive elements of thermocouples, are presented. Modeling of the electronic structure of Lu1-xScxNiSb was performed by the Korringa-Kohn-Rostoker (KKR) method in the approximation of coherent potential and local density and by the full-potential method of linearized plane waves (FLAPW). KKR simulations were performed using the AkaiKKR software package in the local density approximation for the exchange-correlation potential with parameterization Moruzzi, Janak, Williams. The Elk software package was used in the FLAPW calculations. To check the limits of the existence of the thermometric material Lu1-xScxNiSb by the KKR method, the change of the values of the period of the unit cell a(x) in the range x=0–0.10 was calculated. It is established that the substitution of Lu atoms in the crystallographic position 4a by Sc atoms is accompanied by a decrease in the values of the unit cell period a(x) Lu1-xScxNiSb. This behavior of a(x) Lu1-xScxNiSb is since the atomic radius Sc (rSc=0.164 nm) is smaller than that of Lu (rLu=0.173 nm). In this case, structural defects of neutral nature are generated in Lu1-xScxNiSb, because the atoms Lu (5d 1 6s 2 ) and Sc (3d 1 4s 2 ) are located in the same group of the Periodic Table of the Elements and contain the same number of d-electrons. To study the conditions for obtaining thermometric material Lu1-xScxNiSb, x=0–0.10, and to establish the energy feasibility of its formation in the form of a continuous solid solution, modeling of thermodynamic characteristics in the approximation of harmonic oscillations of atoms within the DFT density functional theory. The low values of the enthalpy of mixing ΔHmix(x) and the nature of the dependence behavior indicate the energy expediency of substitution in the crystallographic position 4a of Lu atoms for Sc atoms and the existence of a solid substitution solution for the studied samples Lu1-xScxNiSb, x=0–0.10. To understand the mechanisms of electrical conductivity of the thermometric material Lu1-xScxNiSb, x=0–0.10, various models of crystal and electronic structures of the basic semiconductor LuNiSb are considered. Assuming that the crystal structure of Lu1-xScxNiSb is ordered (crystallographic positions are occupied by atoms according to the MgAgAs structural type), the Elk software package was used to model the DOS electronic state density distribution for LuNiSb and Lu0.875Sc0.125NiSb. It is shown that in the LuNiSb compound the Fermi level lies in the middle of the band gap , and the bandwidth is =190.5 meV. DOS simulations for the ordered variant of the Lu0.875Sc0.125NiSb crystal structure show a redistribution of the density of DOS electronic states and an increase in the band gap . In this case, the Fermi level , as in the case of LuNiSb, lies in the middle of the band gap , and the generated structural defects are neutral. The DOS calculation for the disordered variant of the crystal structure of the LuNiSb compound was performed using a model that can be described by the formula Lu1+yNi1-2ySb. In this model, the Lu atoms partially move to the 4c position of the Ni atoms, and in this position, a vacancy (y) occurs simultaneously. Moreover, as many Lu atoms additionally move to the 4c position of Ni atoms, so many vacancies arise in this position. In this model of the crystal structure of the LuNiSb compound and the absence of vacancies (y=0), the calculation of the DOS electronic state density distribution indicates the presence of the band gap εg , and the Fermi level εF lies near the valence band εV. In the model of the structure of the LuNiSb compound at vacancy concentrations y=0.01, the DOS calculation also shows the presence of the band gap εg , and the Fermi level εF still lies near the valence band εV. Since Ni atoms make the greatest contribution to the formation of the conduction band εC, even at a concentration of y=0.02, the DOS calculation shows that the Fermi level εF now lies near the conduction band εC. This means that the main carriers of the electric current of the LuNiSb compound at y=0.02 are electrons, which does not correspond to the results of experimental studies. Based on the above model of the disordered crystal structure of the LuNiSb compound, the density distribution of DOS electronic states was calculated for the disordered variant of the crystal structure of the thermometric material Lu1-xScxNiSb, which is described by the formula Lu1-x+yScxNi1-2ySb. In this model of the Lu1-xScxNiSb crystal structure, the calculation of the DOS electronic state density distribution shows the presence of a band gap εg , in which small energy levels ("tail tails") are formed, which overlap with the zones of continuous energies. In this case, the Fermi level εF is localized at low energy levels, which makes it impossible to accurately determine the depth from the Fermi level εF. The proposed model is correct only for a small number of impurity Sc atoms since the partial occupation of the 4c position of Ni atoms by Lu atoms significantly deforms the structure with its subsequent decay. The results of experimental studies of the kinetic, energy, and magnetic properties of the thermometric material Lu1-xScxNiSb will show the degree of adequacy of the proposed model.

The results of a complex study of the semiconductor thermometric material TiСo1-xMnxSb, х=0.01–0.10, for the producing of sensitive elements of thermoelectric and electro resistive sensors are presented. Microprobe analysis of the concentration of atoms on the surface of TiСo1-xMnxSb samples established their correspondence to the initial compositions of the charge, and X-ray phase analysis showed the absence of traces of extraneous phases on their diffractograms. The produced structural studies of the thermometric material TiСo1-xMnxSb allow to speak about the ordering of its crystal structure, and the substitution of Co atoms on Mn at the 4c position generate structural defects of acceptor nature. The obtained results testify to the homogeneity of the samples and their suitability for the study of electrokinetic performances and the manufacture of sensitive elements of thermocouples. Modeling of structural, electrokinetic and energetic performances of TiСo1-xMnxSb, х=0.01–0.10, for different variants of spatial arrangement of atoms is performed. To model energetic and kinetic performances, particularly the behavior of the Fermi level, the band gap, the density of states (DOS) distribution was calculated for an ordered variant of the structure in which Co atoms at position 4c are replaced by Mn atoms. Substitution of Co atoms (3d74s2) by Mn (3d54s2) generates structural defects of acceptor nature in the TiСo1-xMnxSb semiconductor (the Mn atom contains fewer 3d- electrons than Co). This, at the lowest concentrations of impurity atoms Mn, leads to the movement of the Fermi level from the conduction band to the depth of the band gap. In a semiconductor with the composition TiCo0.99Mn0.01Sb, the Fermi level is located in the middle of the band gap, indicating its maximum compensation when the concentrations of ionized acceptors and donors are close. At higher concentrations of impurity Mn atoms, the number of generated acceptors will exceed the concentration of donors, and the concentration of free holes will exceed the concentration of electrons. Under these conditions, the Fermi level approach, and then the level of the valence band TiСo1-xMnxSb cross: the dielectric-metal conductivity transition take place. The presence of a high-temperature activation region on the temperature dependence of the resistivity ln(ρ(1/T)) TiСo1‑xMnxSb at the lowest concentration of impurity atoms Mn, х=001, indicates the location of the Fermi level in the band gap of the semiconductor thermopower coefficient α(Т,х) at these temperatures specify its position - at a distance of ~ 6 meV from the level of the conduction band . In this case, electrons are the main carriers of current. The absence of a low-temperature activation region on this dependence indicates the absence of the jumping mechanism conductivity. Negative values of the thermopower coefficient α(Т,х) TiСo0,99Mn0,01Sb at all temperatures, when according to DOS calculations the concentrations of acceptors and donors are close, and the semiconductor is maximally compensated, can be explained by the higher concentration of uncontrolled donors. However, even at higher concentrations of impurity Mn atoms in TiСo0,98Mn0,02Sb, the sign of the thermopower coefficient α(Т,х) remains negative, but the value of resistivity ρ(х,Т) increases rapidly, and the Fermi level deepens into the forbidden zone at a distance of ~ 30 meV. The rapid increase in the values of the resistivity ρ(х,Т) in the region of concentrations х=0.01–0.02 shows that acceptors are generated in the TiСo1-xMnxSb semiconductor when Co atoms are replaced by Mn, which capture free electrons, reducing their concentration. However, negative values of the thermopower coefficient α(Т,х) are evidence that either the semiconductor has a significant concentration of donors, which is greater than the number of introduced acceptors (х=0.02), or the crystal simultaneously generates defects of acceptor and donor nature. The obtained result does not agree with the calculations of the electronic structure of the TiСo1-xMnxSb semiconductor. It is concluded that more complex structural changes occur in the semiconductor than the linear substitution of Co atoms by Mn, which simultaneously generate structural defects of acceptor and donor nature by different mechanisms, but the concentration of donors exceeds the concentration of generated acceptors. Based on a comprehensive study of the electronic structure, kinetic and energetic performances of the thermosensitive material TiСo1-xMnxSb, it is shown that the introduction of impurity Mn atoms into TiCoSb can simultaneously generate in the semiconductor an acceptor zone (substitution of Co atoms for Mn) and donor zones and of different nature. The ratio of the concentrations of ionized acceptors and donors generated in TiСo1-xMnxSb will determine the position of the Fermi level and the mechanisms of electrical conductivity. However, this issue requires additional research, in particular structural and modeling of the electronic structure of a semiconductor solid solution under different conditions of entry into the structure of impurity Mn atoms. The investigated solid solution TiСo1-xMnxSb is a promising thermometric material.

A comprehensive study of the crystal and electronic structures, thermodynamic, electrokinetic, energy, and magnetic properties of the semiconductive solid solution Lu1-xScxNiSb, x = 0 – 0.10, revealed the possibility of doping Sc atoms of different crystallographic sites depending on their concentration. This leads to the generation of structural defects of donor and/or acceptor nature and the appearance of the corresponding energy levels (bands) in the band gap єg. The ratio of ionized donors and acceptors (degree of compensation) determines the position of the Fermi level єF in Lu1-xScxNiSb. The dependence of the rate of generation of energy levels and the position of the Fermi level єF on the impurity concentration Sc, which determines the mechanism of electrical conductivity of Lu1-xScxNiSb, is established. The investigated Lu1-xScxNiSb solid solution is a promising thermoelectric material.

Peculiarities of the structural, electrokinetic, energetic, and magnetic characteristics of Er1-xZrxNiSb semiconductive solid solution, х=0–0.10, were studied. It was suggested that when Zr (4d25s2) atoms were introduced into the structure of the ErNiSb half-Heusler phase by substitution of Er (5d06s2) atoms in 4a position, Zr atoms can also simultaneously occupy the 4c position of Ni (3d84s2) atoms. As a result, in Er1-xZrxNiSb semiconductor, the structural defects of donor nature in position 4a and ones of acceptor nature in position 4c were generated simultaneously. In this case, in the band gap of Er1-xZrxNiSb, the energy states of impurity donor  and acceptor  bands (donor-acceptor pairs) appear and determine the electrical conductivity mechanism of the semiconductor.