Browsing by Author "Rokomanyuk, Mariya"

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Experimental Study of the Y-Cu-Ge System at 870 K
(Видавництво Львівської політехніки, 2020-01-24) Konyk, Mariya; Romaka, Lyubov; Demchenko, Pavlo; Romaka, Vitaliy; Krayovskyy, Volodymyr; Rokomanyuk, Mariya; Ivan Franko Lviv National University; Lviv Polytechnic National University; Institute for Solid State Research, IFW-Dresden
Діаграма фазових рівноваг потрійної системи Y-Cu-Ge побудована за 870 К методами рентгенівської дифракції, металографічного аналізу і енергодисперсійної рентгенівської спектроскопії в повному концентраційному інтервалі. Встановлено утворення шести тернарних сполук YCuGe (структурний тип LiGaGe), YCu2Ge2 (структурний тип CeAl2Ga2), Y3Cu4Ge4 (структурний тип Gd3Cu4Ge4), Y2CuGe6 (структурний тип Ce2CuGe6) YCu0.67Ge1.33 (структурний тип AlB2) і YCu0.3Ge2 (структурний тип CeNiSi2).
Investigation of thermometric material Ti1-xScxCoSb modeling of characteristics
(Видавництво Львівської політехніки, 2020-02-24) Krayovskyy, Volodymyr; Rokomanyuk, Mariya; Romaka, Volodymyr; Horpenyuk, Andriy; Stadnyk, Yuriy; Romaka, Lyubov; Horyn, Andriy; Lviv Polytechnic National University; Ivan Franko National University of Lviv
The second part of the complex research of Ti1-xScxCoSb thermometric material for the sensitive elements of thermoelectric and electro resistant thermal converters is presented. Simulation of thermodynamic, electrotechnical, energetic and structural characteristics of Ti1-xScxCoSb semiconductor thermometric material for various options of atoms placement is performed. It is determined that under the orderly variant of the crystal structure Ti1-xScxCoSb the characteristic simulation results do not correspond to the experimental research results of temperature and concentration dependences of the resistivity, thermoEMF coefficient of the Fermi εF level behavior character, etc. Thus, for the ordered structure of Ti1-xScxCoSb, the simulation showed that the substitution in the crystallographic position 4a of the TiCoSb compound of atoms Ti (3d24s2) at Sc (3d14s2) generates structural defects of the acceptor nature since the Sc atom has fewer 3 d-electrons. Adding to the TiCoSb the smallest in the experiment concentration of Sc atoms by replacing the Ti atoms radically changes the behavior of the resistivity ρ and the coefficient of thermo-EMF α Ti0.995Sc0.005CoSb. In the 80–350 K temperature range, the resistivity value ρ increases with temperature increasing, and the conductivity of Ti0.995Sc0.005CoSb is metallic. It means that the addition of the smallest in the experiment concentration of atoms Sc (x=0.005) which should generate acceptors changed the position of the Fermi level εF in a way that could only cause the appearance of donors in the semiconductor. Thus, if in TiCoSb the Fermi level εF laid in the restricted area, then the metallization of the conductivity Ti0.995Sc0.005CoSb indicates that it not only approached the conduction zone but also crossed its leakage level, and electrons remain the main carriers of electricity. This is indicated by the negative values of the thermo-EMF coefficient α Ti0.995Sc0.005CoSb, which is only possible if donors of unknown nature are generated. The metallization of the conductivity Ti0.995Sc0.005CoSb also does not match the results of the electronic structure simulation for the ordered structure variant. After all, the simulation demonstrates that at the smallest concentration of the Sc acceptor impurity, the Fermi level εF drifts from the conduction zone εC to the middle of the restricted zone εg. Therefore, in the high-temperature area of dependence ln(ρ(1/T)), there must be an activation area associated with the thermal emission of electrons from the Fermi level εF into the conduction zone εC, and the value of the electron activation energy ε1ρ should be greater than in the case of TiCoSb. To clarify the crystalline and electronic structure of the TiCoSb compound, electronic state density distribution (DOS) simulations were performed for various options of occupying crystallographic positions by atoms, as well as occupying by atoms of tetrahedral voids of structure that make up ~24 % of the unit cell volume. It is shown that structural defects of the donor and acceptor nature are present in the TiCoSb base compound as a result of the location in the tetrahedral voids of the structure of additional Co * atoms and the presence of vacancies in the crystallographic position of 4a of the Ti atoms. Introduction to TiCoSb compound of impurity Sc atoms by substitution at position 4a of Ti atoms generates structural defects of acceptor nature, and the ratio of Ti1-xScxCoSb in the concentrations of available defects of donor and acceptor nature determines the location of the Fermi level εF and mechanisms of conductivity. The obtained results allow us to predictably simulate and obtain thermometric materials Ti1- xScxCoSb for the sensitive elements of thermotransducers.
Sensitive elements of temperature converters based on HfNi1-xCuxSn thermometrical material
(Видавництво Львівської політехніки, 2023-02-28) Krayovskyy, Volodymyr; Rokomanyuk, Mariya; Luzhetska, Nataliya; Pashkevych, Volodymyr; Romaka, Volodymyr; Stadnyk, Yuriy; Romaka, Lyubov; Horyn, Andriy; Lviv Polytechnic National University; Ivan Franko National University of Lviv
The results of experimental studies of sensitive elements of temperature transducers based on semiconductor thermometric material HfNi1-xCuxSn are presented. Thermometric materials HfNi1-xCuxSn, x=0.01–0.10, were produced by fusing a charge of components in an electric arc furnace with a tungsten electrode (cathode) in an atmosphere of purified argon under a pressure of 0.1 kPa on a copper water-cooled base (anode). Heat treatment of the alloys consisted of homogenizing annealing at a temperature of 1073 K. The samples were annealed for 720 hours. in quartz glass ampoules vacuumed to 1.0 Pa in muffle electric furnaces with temperature control with an accuracy of ±10 K. Diffraction data arrays were obtained on a STOE STADI-P powder diffractometer (Cu Kα1 radiation), and the structural characteristics of HfNi1-xCuxSn were calculated using the Fullprof program. The chemical and phase compositions of the samples were monitored using metallographic analysis (scanning electron microscope Tescan Vega 3 LMU). The thermoelectric pair platinum-thermometric material Pt-HfNi0.99Cu0.01Sn was the basis of the thermoelectric converter. Modeling of thermometric characteristics of sensitive elements of thermotransducers in the temperature range of 4.2– 1000 K was carried out by the full potential linearized plane wave method (Full Potential Linearized Augmented Plane Waves, Elk software package). The results of experimental measurements served as reference currents for modeling characteristics. X-ray phase analysis showed the absence of traces of extraneous phases in the diffractograms of the studied samples of HfNi1-xCuxSn thermometric materials, and the microprobe analysis of the concentration of atoms on their surface established the correspondence to the original composition of the charge. Refinement of the crystal structure of HfNi1-xCuxSn showed that the introduction of Cu atoms orders the structure, which makes it stable, and the kinetic characteristics are reproducible during thermocycling at temperatures T=4.2–1000 K. Ordering the structure of the thermometric material HfNi1-xCuxSn leads to changes in the electronic structure. At the same time, the number of donors decreases – Ni leaves the Hf position, and the substitution of Ni atoms for Cu leads to the generation of structural defects of the donor nature (Cu atoms contain more 3d-electrons), and another donor band εD Cu will appear in the band gap εg. For the sensitive elements of thermoconverters at Cu impurity concentrations x=0.005 and x=0.01, the temperature dependences of the specific electrical resistance ln(ρ(1/T)) contain activation areas, which is consistent with the results of electronic structure modeling. This indicates the location of the Fermi level εF in the band gap εg, and the negative value of the thermopower coefficient α(T) at these temperatures specifies its position – near the conduction band εC. The value of the activation energy from the Fermi level εF to the bottom of the conduction band εC was calculated. For the base semiconductor n-HfNiSn, the Fermi level εF lies at a distance of εF=81 meV from the co εC conduction band εC, and in the sensitive elements of thermoconverters with concentrations of HfNi0.995Cu0.005Sn and HfNi0.99Cu0.01Sn – at distances of εF=1 meV and εF=0.3 meV respectively. Therefore, an increase in the concentration of the Cu donor impurity leads to a rapid movement of the Fermi level εF to the bottom of the conduction band at a rate of ΔεF/Δx≈81 meV/%Cu. The impurity concentration x=0.01 is sufficient for the metallization of the conductivity of sensitive elements of HfNi1-xCuxSn converters at low temperatures. This is possible if the Fermi energy εF is close to the conduction band εC (εF=0.3 meV), which simplifies the thermal ionization of donors and the appearance of a significant number of free electrons. However, this impurity donor zone still does not intersect with the bottom of the conduction band εC. At concentrations of the Cu donor impurity in HfNi1-xCuxSn, x=0.2–0.07, the high-temperature activation regions disappear on the temperature dependences of the resistivity ln(ρ(1/T, x)), which indicates the movement of the Fermi level εF from the band gap εg to the conductivity εC. At the same time, the values of specific electrical resistance ρ(T, x) increase monotonically with increasing temperature), and the scattering of electrons by phonons determines the conductivity of sensitive elements of thermotransducers based on the thermometric material HfNi1-xCuxSn. The metallization of the electrical conductivity of the thermometric material HfNi1-xCuxSn at concentrations x>0.01 is accompanied by a rapid decrease in the values of the thermopower coefficient α(x, T). Thus, if in n-HfNiSn at a temperature of T=80 K, the value of the thermal erst coefficient was αx=0=–178 μV/K, then in the HfNi0.93Cu0.07Sn material αx=0.07=–24 μV/K. The results of the kinetic properties of HfNi1-xCuxSn are consistent with the conclusions of structural and energetic studies. The simulation of the conversion functions of the sensitive elements of the resistance thermometer and the thermoelectric converter in the temperature range of 4.2–1000 K was carried out. As an example, the conversion functions of the thermoelectric pair Pt-HfNi0.99Cu0.01Sn are given. The ratio of change of thermo-EMF values to the range of temperature measurements in thermocouples is greater than all known industrial thermocouples. However, due to the metallization of the conductivity of the thermometric material HfNi1-xCuxSn, x>0.01, the temperature coefficient of resistance (TCR) of the obtained resistance thermometers is greater than the TCR of metals, but is inferior to the value of TCR of sensitive elements made of semiconductor materials.
Дослідження кінетичних характеристик чутливих елементів термоперетворювачів на основі Ti1-xMoxCoSb
(Видавництво Львівської політехніки, 2019-02-28) Крайовський, В. Я.; Рокоманюк, М. В.; Ромака, В. А.; Ромака, Л. П.; Стадник, Ю. В.; Горинь, А. М.; Krayovskyy, Volodymyr; Rokomanyuk, Mariya; Romaka, Volodymyr; Romaka, Lyubov; Stadnyk, Yuriy; Horyn, Andriy; Національний університет “Львівська політехніка”; Львівський національний університет ім. І. Франка; Lviv Polytechnic National University; Ivan Franko National University of Lviv
Виконано математичне моделювання та експериментальні вимірювання кінетичних та енергетичних характеристик чутливих елементів термоперетворювачів на основі термометричного матеріалу Ti1-xMoxCoSb у діапазоні температур 80–400 К. Попередні дослідження електрофізичних, енергетичних та структурних властивостей термометричних матеріалів, отриманих легуванням напівгейслерової фази TiCoSb атомами Ni та V, відповідно, показали, що вони володіють стабільними та відтворюваними характеристиками у температурному діапазоні 4,2–1000 К. Встановлено, що результати моделювання термометричних характеристик чутливих елементів на основі TiCo1-xNixSb та Ti1-xVxCoSb не узгоджувалися з результатами експериментальних вимірювань, що унеможливило їхнє використання для виготовлення чутливих елементів термометрів опору та термоелектричних перетворювачів. Моделювання електронної структури термометричних матеріалів Ti1-xMoxCoSb методом функцій Гріна (метод Корінги–Кона–Ростокера (KKR)) у наближенні когерентного потенціалу (Coherent Potential Approximation) та локальної густини (Local Density Approximation) з використанням ліцензованого програмного забезпечення AkaiKKR та SPR-KKR для обмінно- кореляційного потенціалу з параметризацією Moruzzi-Janak-Williams показало, що заміщення атомів Ti на Mo генерує у кристалі структурні дефекти донорної природи (у Mo більше 3d-електронів, ніж у Ti), а в забороненій зоні поблизу зони провідності εС утворюється домішковий донорний рівень (зона) 2D e. Експериментальні вимірювання електрокінетичних характеристик термометричних матеріалів Ti1-xMoxCoSb встановили наявність високотемпературних активаційних ділянок на залежностях питомого опору ln(ρ(1/T)), що вказує на розташування рівня Фермі εF у забороненій зоні напівпровідника, а це можливо за умови генерування акцепторів, які захоплюють вільні електрони, зменшуючи їхню концентрацію, та гальмують рух рівня Фермі εF до рівня протікання зони провідності εС. Отже, легування сполуки TiCoSb домішкою Mo призводить до генерування у кристалі структурних дефектів акцепторної та донорної природи. Встановлено механізми електропровідності чутливих елементів термоперетворювачів.