Yu. V. Stadnyk

Features of a priori heavy doping of the n-TiNiSn intermetallic semiconductor

The crystal structure, the distribution of electron density, and the energy, kinetic, and magnetic properties of the n-TiNiSn intermetallic semiconductor are investigated. It is shown that a priori doping of n-TiNiSn with donors originates from partial, up to 0.5 at %, redistribution of Ti and Ni atoms in crystallographic sites of Ti atoms. The correlation is established between the donor concentration, amplitude of modulation of the continuous energy bands, and degree of filling of low-scale fluctuation potential wells with charge carriers. The results obtained are discussed within the Shklovskii-Efros model of a heavily doped and compensated semiconductor.

Features of conductivity of the intermetallic semiconductor n-ZrNiSn heavily doped with a Bi donor impurity

The crystal structure, distribution of the electron density of states, and the energy, kinetic, and magnetic properties of the intermetallic semiconductor n-ZrNiSn heavily doped with a Bi donor impurity have been investigated in the ranges T = 80−400 K, NDBi ≈ 9.5 × 1019cm−3 (x = 0.005)−1.9 × 1021 cm−3 (x = 0.10), and H ≤ 0.5 T. It has been established that such doping generates two types of donor-like structural defects in the crystal, which manifest themselves in both the dependence of the variation in the unit cell parameter a(x) and temperature dependence of resistivity lnρ(1/T) of ZrNiSn1 − xBix (x = 0.005). It is shown that ZrNiSn1 − xBix is a new promising thermoelectric material, which converts thermal energy to electric energy much more effectively as compared to n-ZrNiSn. The results obtained are discussed within the Shklovskii-Efros model of a heavily doped and strongly compensated semiconductor.

Features of the band structure and conduction mechanisms in the n-HfNiSn semiconductor heavily doped with Ru

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.

Effect of the accumulation of excess Ni atoms in the crystal structure of the intermetallic semiconductor n-ZrNiSn

The crystal structure, electron density distribution, and energy, kinetic, and magnetic properties of the n-ZrNiSn intermetallic semiconductor heavily doped with a Ni impurity are investigated. The effect of the accumulation of an excess number of Ni1 + x atoms in tetrahedral interstices of the crystal structure of the semiconductor is found and the donor nature of such structural defects that change the properties of the semiconductor is established. The results obtained are discussed within the Shklovskii-Efros model of a heavily doped and strongly compensated semiconductor.

The mechanism of generation of the donor- and acceptor-type defects in the n-TiNiSn semiconductor heavily doped with Co impurity

Temperature dependences of resistivity, thermoelectric coefficient, and structural characteristics of the n-TiNiSn intermetallic semiconductor heavily doped with Co impurity (the Co concentration NCo ≈ 9.5 × 1019−1.9 × 1021 cm−3) have been studied in the temperature range 80–380 K; the distribution of the electron density of states is also calculated. It is shown that, in TiNi1 − xCoxSn with x < 0.03, the impurity atoms occupy crystallographic sites of atoms Ti and Ni simultaneously and in various proportions and generate the donor and acceptor defects, respectively. It is established that there is a relation between the impurity concentration, the amplitude of a large-scale fluctuation, and also the degree of filling of the potential well of a small-scale fluctuation (fine structure). The results are discussed in the context of the Shklovskiĭ-Éfros model of a heavily doped and compensated semiconductor.

Features of conductivity mechanisms in heavily doped compensated V1–xTixFeSb Semiconductor

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.

Structural defect generation and band-structure features in the HfNi1 − xCoxSn semiconductor

The crystal and electronic structure and magnetic, energy, and kinetic properties of the n-HfNiSn semiconductor heavily doped with the Co acceptor impurity (HfNi1 − xCoxSn) are investigated in the temperature and Co concentration ranges T = 80–400 K and NACo ≈ 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 − xCoxSn 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.

Energy conversion by thermoelectric properties of alloys

The solid solutions based on alloys are synthesized by arc-melting or HF induction furnace and the corresponding crystal structures are established by using the X-ray diffraction and the Rietveld refinement method. The resistivity and the thermoelectric Seebeck coefficient referred to the pure copper is measured in the temperature range 80-380 K. Static magnetic susceptibility is also measured at room temperature. Based on first-principles spin-density functional calculations and using mainly the Korringa-Kohn-Rostoker method (KKR) combined with the Coherent Potential Approximation (CPA), both electronic and magnetic structures of these alloys are investigated. Thermoelectric Seebeck coefficient calculations are performed and comparisons are made between experiments and simulated results. Energy conversion performance in terms of the efficiency and figure of merit will be discussed and comparisons with other thermoelectric materials will be presented.