Karakterizacija izbrane keramike iz ternarnega sistema La2O3-Ta2O5-TiO2

Zakošek, Žan (author), Golobič, Amalija (mentor)

V diplomskem delu sem se odločil za sintezo in strukturno karakterizacijo keramike na osnovi trdnih raztopin na veznici LaTaTiO6-La4Ti9O24, ki je del ternarnega sistema La2O3-Ta2O5-TiO2. Vzorce sem pripravil z reakcijo v trdnem pri dveh različnih temperaturah (1350 in 1410 °C). Na podlagi izmerjenih rentgenskih praškovnih difraktogramov vzorcev sem z uporabo programa CSM določil njihovo kvalitativno fazno sestavo. Pri vseh je prevladujoča faza vzorca kazala zelo dobro ujemanje z difraktogramom monoklinske modifikacije spojine LaTaTiO6. Strukturni model monoklinske modifikacije spojine LaTaTiO6 sem uporabil za izvedbo metode Rietveldovega prilagajanja s programom Topas2.1. V strukturnem modelu sem spremenil zasedenosti atomskih mest, da je strukturna formula modela ustrezala zatehtanemu množinskemu razmerju kovinskih ionov. Od strukturnih parametrov sem prilagajal parametre osnovne celice, koordinate atomov in en parameter atomskega odmika v strukturi. Določil sem, kako se parametri osnovne celice spreminjajo s sestavo vzorca in temperaturo žganja. Pri obeh temperaturah velja, da z naraščanjem vrednosti x oziroma z naraščanjem deleža Ti4+ v sestavi trdne raztopine s formulo La1+3xTa1-xTi1+8xO6+18x, volumen osnovne celice kristalne strukture pada, kar je v skladu z manjšim ionskim radijem Ti4+ glede na Ta5+ in z manjšo zasedenostjo mest La3+ in O2-. Volumni osnovne celice trdnih raztopin z enako sestavo, ki so bili žgani pri različnih temperaturah pa se med seboj ne razlikujejo bistveno. Trdno topnost smo še opazili pri vzorcu z x=0,10, medtem ko smo pri vzorcih z x = 0,125 in 0,20 že opazili soobstoj faze, ki je izostrukturna z La4Ti9O24 in ki jo pričakujemo glede na predvideni fazni diagram v tem področju ternarnega sistema.

• Language: Slovenian
• Keywords: ternarni sistem La2O3-Ta2O5-TiO2, rentgenska praškovna difrakcija, Rietveldovo prilagajanje
• Work type: Bachelor thesis/paper
• Typology: 2.11 - Undergraduate Thesis
• Organization: FKKT - Faculty of Chemistry and Chemical Technology
• Year: 2021
• PID: 20.500.12556/RUL-129731
• COBISS.SI-ID: 79130371
• Publication date in RUL: 07.09.2021

Secondary language

• Language: English
• Title: Characterization of selected ceramics from ternary system La2O3-Ta2O5-TiO2

Abstract

In the thesis I have decided for the synthesis and structural characterization of the LaTaTiO6-La4Ti9O24 based solid solution, which is a part of investigation of the La2O3-Ta2O5-TiO2 ternary system. Samples were prepared by the conventional solid-state reaction technique at two different temperatures (1350 and 1410 °C). Qualitative phase analysis of samples was made using the CSM program based on their X-ray powder diffraction pattern. The main phase of the sample has shown very good match with the diffractogram of the monoclinic modification of the LaTaTiO6. Structural model of the monoclinic modification of the LaTaTiO6 was used for the Rietveld refinement using Topas2.1 program. In the structural model the occupancy of atoms sites were changed in a way that the formula of the model corresponded with weighted mole ratio of metal ions. Of the structural parameters, I refined the unit cell parameters, the coordinates of the atoms, and one atomic displacement parameter in the structure. Changing of unit cell parameters with sample composition and sintering temperature was determined. The volume of the unit cell of solid solutions La1+3xTa1-xTi1+8xO6+18x in both cases decreases with the increase of x, that is with the increase of Ti4+ content which is in accordance with the smaller ionic radius of Ti4+ with respect to Ta5+ and with a decreasing of occupancies of La3+ and O2-. Solid solubility was still observed in the sample with x = 0.10, while in the samples with x = 0.125 and 0.20 we already observed the coexistence of the phase, which is isostructural with La4Ti9O24 and which is expected according to the expected phase diagram in this region of the ternary system.

• Keywords: ternary system La2O3-Ta2O5-TiO2, X-ray powder diffraction, Rietveld refinement