Kvantově-mechanická analýza vlastností fází TiSe a TiSe2

Bc. Valentína Berecová

Bachelor's thesis

Quantum-mechanical analysis of properties of TiSe and TiSe2 phases

Abstract:

This bachelor thesis is focused on quantum-mechanical modelling of properties of Ti in hexagonal close-packed structure, phases TiSe, TiSe2 and TiSe supercells, which contain vacancies in sublattice 2a or admixtures of titanium in sublattice 2c. Equilibrium lattice parameters of titanium with hexagonal close-packed structure are a = b = 2.923 Å and c = 4.626 Å. Equilibrium lattice parameters for phase TiSe are a = b = 3.416 Å, c = 6.808 Å and for phase TiSe2 are a = b = 3.527 Å, c = 6.656 Å. Heats of formation of phases TiSe and TiSe2 are 105.00 kJ/mol at and -106.26 kJ/mol at. Average heats of formation of one vacancy in TiSe supercells are positive quantities ranging from 0.7198 eV/Va for phase TiSeVa_13 to 1.2103 eV/Va for phase TiSeVa_25. It was further found that ripping out a pair of titanium atoms is less energetically demanding than ripping out two independent titanium atoms. That means vacancies might tend to arise two at once. The presence of vacancies in TiSe structure results in larger magnetic moments on Ti atoms (maximum value 0.716 μB/at). Average heats of exchange of Se in sublattice 2c in TiSe structure for standard Ti are: 4.3668 eV/exchange for phase TiSemix_93, 3.7021 eV/exchange for phase TiSemix_87 and 3.2277 eV/exchange for phase TiSemix_81.

Abstract:

Táto práca je zameraná na kvantovo-mechanické modelovanie vlastností Ti v najtesnejšom hexagonálnom usporiadaní, fáz TiSe, TiSe2 a superbuniek TiSe obsahujúcich vakancie v podmriežke 2a alebo prímesi titánu v podmriežke 2c. Rovnovážne mriežkové parametre titánu v najtesnejšom hexagonálnom usporiadaní sú a = b = 2,923 Å a c = 4,626 Å. Fáza TiSe má rovnovážne parametre a = b = 3,416 Å, c = 6,808 Å a fáza TiSe2 a = b = 3,527 Å, c = 6,656 Å. Tvorné teplo fáze TiSe má hodnotu 105,00 kJ/mol at a pre fázu TiSe2 bola stanovená hodnota -106,26 kJ/mol at. Priemerné tvorné teplá jednej vakancie v superbunkách TiSe nadobúdajú kladných hodnôt od 0,7198 eV/Va pre fázu TiSeVa_13 po 1,2103 eV/Va pre fázu TiSeVa_25. Ďalej bolo zistené, že odtrhnutie dvojice atómov Ti je menej energeticky náročné ako odtrhnutie dvoch nezávislých atómov titánu. Z toho vyplýva, že vakancie môžu mať tendenciu vznikať dve naraz. Pri zavedení vakancií do štruktúry TiSe sa u atómov Ti prejavuje výraznejší magnetický moment (s maximálnou hodnotou 0,716 μB/at). Priemerné teplá výmeny Se v podmriežke 2c u štruktúr TiSemix za štandardný Ti majú hodnoty: 4,3668 eV/výmena pre fázu TiSemix_93, 3,7021 eV/výmena pre fázu TiSemix_87 a 3,2277 eV/výmena pre fázu TiSemix_81.

Keywords

ab initio výpočty, DFT, titán, TiSe, TiSe2, program VASP, tvorné teplo, vakancie, prímesi titánu, titanium, ab initio calculations, VASP code, heat of formation, vacancies, admixtures of titanium

Language used: Slovak

Date on which the thesis was submitted / produced: 1. 6. 2022

Thesis defence

• Date of defence: 27. 6. 2022
• Supervisor: doc. Mgr. Jana Pavlů, Ph.D.
• Reader: prof. RNDr. Mojmír Šob, DrSc.

Masaryk University

Faculty of Science

Bachelor programme / field:
Chemistry / Chemistry