Rentgenska praškovna analiza keramike iz binarnega sistema La2O3-Ta2O5

Kóša, Filip (author), Golobič, Amalija (mentor)

V literaturi sem našel več nekoliko različnih variant faznega diagrama binarnega sistema La2O3 – Ta2O5. S pomočjo zbirk podatkov ICSD, PDF-2 in PDF-4+ sem zbral podatke o dimenzijah osnovne celice, o prostorski skupini, o tipu vzorca in difraktograma lantan tantalovih oksidov v njih. Namen dela je bil ugotoviti, katere od teh spojin obstajajo v tem sistemu pri 1350 °C. Rentgenske praškovne difraktograme vzorcev oksidov, ki so jih sintetizirali na Inštitutu Jožef Stefan z žganjem zmesi La2O3 in Ta2O5 pri 1350 °C, sem analiziral z računalniškimi programi. Za kvalitativno analizo sem uporabil program Crystallographica Search-Match (CSM). S programom ICSD-Desktop sem za identificirane faze poiskal pripadajoče strukturne modele, s pomočjo katerih sem izvedel kvantitativno analizo vzorcev s programom TopasR2-1, pri tem sem z Rietveldovim prilagajanjem prilagajal napako ničle ter skalni faktor, parametre osnovne celice, velikost kristalitov in napetost v kristalih za vsako v vzorcu prisotno kristalno fazo. Ker strukturnega modela za spojino LaTa5O14 ni v nobeni zbirki, sem za kvantitativno analizo uporabil model izostrukturne spojine LaNb5O14, pri čemer pa sem niobijev atom zamenjal s tantalovim ter v tem primeru prilagajal tudi koordinate atomov. Strukture trdnin, ki so bile prisotne v vzorcih, sem tudi prikazal s programom ATOMS V6.4. V binarnem sistemu La2O3 – Ta2O5 so pri 1350 °C prisotni ortorombski La3TaO7, ortorombski LaTaO4, tetragonalni LaTa3O9, heksagonalni LaTa7O19, ortorombski LaTa5O14, opazili pa smo tudi ortorombski La4,67Ta22O62. V do sedaj objavljenih faznih diagramih binarnega sistema La2O3 – Ta2O5 ta snov ni bila navedena, je pa opisana v obliki monokristala pri 1685 °C. V naših vzorcih se ne pojavi vedno, ko bi jo glede na sestavo vzorca pričakovali, česar zaenkrat še nismo uspeli pojasniti.

• Language: Slovenian
• Keywords: binarni sistem La2O3 – Ta2O5, rentgenska praškovna difrakcija, Rietveldovo prilagajanje
• Work type: Bachelor thesis/paper
• Typology: 2.11 - Undergraduate Thesis
• Organization: FKKT - Faculty of Chemistry and Chemical Technology
• Year: 2022
• PID: 20.500.12556/RUL-139063
• COBISS.SI-ID: 121699587
• Publication date in RUL: 29.08.2022

Secondary language

• Language: English
• Title: X-ray powder analysis of ceramics from the La2O3-Ta2O5 binary system

Abstract

In the literature I found several different variants of the phase diagram of the binary system La2O3 – Ta2O5. With the help of the ICSD, PDF-2 and PDF-4+ databases, I collected data on the unit cell dimensions, space group, sample type and diffractograms of the lanthanum tantalum oxides in them. The purpose of the work was to determine which of these compounds exists in this system at 1350 °C. I analyzed X-ray powder diffraction patterns of oxide samples using computer programs. The samples were synthesized at the Jožef Stefan Institute by sintering a mixture of La2O3 and Ta2O5 at 1350 °C. I used the Crystallographica Search-Match (CSM) program for qualitative analysis. With the ICSD-Desktop program, I searched for the corresponding structural models for the identified phases, with the help of which I performed a quantitative analysis of the samples with the TopasR2-1 program, while using Rietveld refinement to refine the zero error, the scale factor, the cell parameters, the size of the crystallites and the crystal strain for each crystalline phase present in the sample. Since there is no structural model for the compound LaTa5O14 in any database, I used the model of the isostructural compound LaNb5O14 for the quantitative analysis, replacing the niobium atom with tantalum atom and in this case also adjusting the coordinates of the atoms. I also displayed the crystal structures that were present in the samples using the ATOMS V6.4 program. In the binary system La2O3 – Ta2O5, orthorhombic La3TaO7, orthorhombic LaTaO4, tetragonal LaTa3O9, hexagonal LaTa7O19, orthorhombic LaTa5O14 are present at 1350 °C. We also observed orthorhombic La4,67Ta22O62. In the phase diagrams of the binary system La2O3 – Ta2O5 published so far, this substance was not mentioned, but it is described in the form of a single crystal at 1685 °C. It does not always appear in our samples when we would expect it based on the composition of the sample. So far, we have not been able to explain this unrepeatability.

• Keywords: binary system La2O3 – Ta2O5, X-ray powder diffraction, Rietveld refinement