Research of thermometric material Er1-xscxNiSb. I. Modelling of performances
Date
2021-02-23
Journal Title
Journal ISSN
Volume Title
Publisher
Видавництво Львівської політехніки
Lviv Politechnic Publishing House
Lviv Politechnic Publishing House
Abstract
Automated The results of modeling performances of the semiconductor solid solution Er1–xScxNiSb are
presented, which can be a promising thermometric material for the manufacture of sensitive elements of thermoelectric and
electroresistive thermocouples. Fullprof Suite software was used to model the crystallographic characteristics of the Er1-xScxNiSb
thermometric material. Modeling of the electronic structure of Er1–xScxNiSb was performed by Coring-Kon-Rostocker methods in
the approximation of coherent potential and local density using the exchange-correlation potential Moruzzi-Janak-Williams and
Linear Muffin-Tin Orbital in the framework of DFT density functional theory. The Brillouin zone was divided into 1000 k-points,
which were used to model energetic performances by calculating DOS. The width of the energy window was 22 eV and was
chosen to capture all semi-core states of p-elements. Full potential (FP) was used in the representation of the linear MT orbital in
the representation of plane waves. The accuracy of calculating the position of the Fermi level was εF ± 6 meV.
To verify the existence of a continuous solid solution, Er1–xScxNiSb substitution, the change in the values of the period of
the unit cell a (x) was calculated within the framework of the DFT density functional theory in the range x = 0–1.0. It is presented
that the calculated and experimentally obtained dependences of the period of the unit cell a(x) Er1–xScxNiSb are almost parallel,
which confirms the correctness of the used tools and the obtained modeling results.
To research the possibility of obtaining thermometric material Er1–xScxNiSb in the form of a continuous solid solution was
performed modeling of thermodynamic calculations in the approximation of harmonic oscillations of atoms in the theory of DFT
density functional for a hypothetical solid solution Er1–xScxNiSb, x = 0–1.0. It is shown that the change in the values of free energy
ΔG(x) (Helmholtz potential) passes through the minimum at the concentration x≈0.1 for all temperatures of possible homogenizing
annealing of the samples, indicating the solubility limit of Sc atoms in the structure of the ErNiSb compound. The presence of this
minimum indicates that the substitution of Er atoms for Sc atoms in the ErNiSb compound is energetically advantageous only up
to the concentration of impurity atoms Sc, x ≈ 0.1. At higher concentrations of Sc atoms, x > 0.10, stratification occurs (spinoidal
phase decay). It is shown that modeling of the mixing entropy behavior S even at a hypothetical temperature T = 4000 K shows the
absence of complete solubility of Sc atoms in Er1–xScxNiSb.
To model the energetic and kinetic performances of the semiconductor thermometric material Er1–xScxNiSb, particularly the
behavior of the Fermi level e F , bandgap width e g the distribution of the density of electronic states (DOS) and the behavior of
its electrical resistance ρ(x, T) is calculated for an ordered variant of the structure in which the Er atoms in position 4a are replaced
by Sc atoms. It is shown that the ErNiSb compound is a semiconductor of the electronic conductivity type, in which the Fermi
level is located near the level of the conduction band e C . The modeling showed that at higher concentrations of Sc atoms, the
number of generated acceptors exceeds the concentration of uncontrolled donors, and the concentration of free holes exceeds the
concentration of electrons. Under these conditions, the Fermi level e F approaches, and then the level of the valence band
Er1–xScxNiSb crosses: the dielectric-metal conductivity transition occurs. The experiment should change the sign of the thermo-
EMF coefficient α(x, T) Er1–xScxNiSb from negative to positive, and the intersection of the Fermi level e F and the valence band
changes the conductivity from activating to metallic: on the dependences ln(ρ(1/T)) the activation sites disappear, and the
values of resistivity ρ increase with temperature.
Description
Keywords
Electric conductivity, Thermopower coefficient, Fermi level
Citation
Research of thermometric material Er1-xscxNiSb. I. Modelling of performances / Volodymyr Krayovskyy, Volodymyr Pashkevych, Andriy Horpenuk, Volodymyr Romaka, Yuriy Stadnyk, Lyubov Romaka, Andriy Horyn, Vitaliy Romaka // Measuring equipment and metrology. — Lviv : Lviv Politechnic Publishing House, 2021. — Vol 82. — No 2. — P. 16–21.