Karakterizacija izbrane keramike iz ternarnega sistema La$_2$O$_3$-Ta$_2$O$_5$-TiO$_2$ z rentgensko praškovno difrakcijo

Ziherl, Nadja (avtor), Golobič, Amalija (mentor)

V okviru diplomskega dela sem s pomočjo rentgenske praškovne difrakcije opravila kvalitativno in kvantitativno fazno analizo več vzorcev keramik iz ternarnega sistema La$_2$O$_3$-Ta$_2$O$_5$-TiO$_2$, ki se nahajajo na veznici La$_{1/3}$TaO$_3$-LaTaTiO$_6$ s formulo La$_{(1+x)/3}$Ta$_{1-x}$Ti$_x$O$_3$ za x od 0 do 0,5. Za sintezo vzorcev je bila izvedena reakcija v trdnem s sledečim večkratnim mletjem, homogenizacijo in žganjem pri temperaturi 1350 °C. Izmerjene difraktograme sem najprej analizirala kvalitativno s pomočjo računalniškega programa Crystallographica Search Match (CSM). Faze, ki sem jih identificirala v vzorcih sta monoklinska in ortorombska polimorfna oblika spojine LaTaTiO$_6$ ter snov s podobnim difraktogramom, kot ga ima La$_{1/3}$TaO$_3$ (imenovana tudi LaTa$_3$O$_9$), ki ima defektno perovskitno strukturo. Ugotovila sem, da gre za trdne raztopine na osnovi La$_{1/3}$TaO$_3$. Strukturo slednje spojine sem uporabila za strukturni model trdne raztopine. Predpostavila sem, da se Ti$^{4+}$ in Ta$^{5+}$ v trdni raztopini naključno razporejata na isto kristalografsko mesto. Zasedenost slednjega sem opisala glede na sintezno razmerje, glede nanj sem povečala tudi zasedenost lege lantana. Z Rietveldovim prilagajanjem v programu Topas 2.1, sem tako strukturno okarakterizirala dve enofazni trdni raztopini sestave La$_{0,36}$Ta$_{0,92}$Ti$_{0,08}$O$_3$ in La$_{0,37}$Ta$_{0,89}$Ti$_{0,11}$O$_3$. Kristalne strukture, ki sem jih določila, sem opisala in narisala s pomočjo kristalografskega programa Mercury. Rietveldovo metodo sem uporabila tudi za kvantitativno analizo preostalih, večfaznih vzorcev. Določila sem območje trdne topnosti, ki se pojavi le na eni strani veznice, kjer se nahajajo trdnine s sestavo La$_{(1+x)/3}$Ta$_{1-x}$Ti$_x$O$_3$ za x od 0 do vključno 0,11. Ugotovila sem manjšanje volumna osnovne celice teh trdnin z naraščanjem vrednosti x, ki se pojavi zaradi manjšega ionskega radija Ti$^{4+}$, katerega prisotnost v spojini se v tej smeri veznice povečuje. Vzorci izhodiščne sestave 0,11 < x < 0,5 so bili po vzpostavitvi ravnotežja dvofazni, in sicer iz nasičene tetragonalne trdne raztopine (La$_{1/3}$TaO$_3$)ss in ortorombske spojine LaTaTiO$_6$. Z večanjem vrednosti x, se je zmanjševal masni delež prve in povečeval masni delež druge snovi. Vzorec izhodiščne sestave za x=0,5 je vseboval samo LaTaTiO$_6$, vendar presenetljivo v dveh kristalnih oblikah: ortorombski in monoklinski. Tudi po večkratnih žganjih, z vmesnim hlajenjem in mletjem, so analize pokazale, da pri temperaturi 1350 °C nismo uspeli pripraviti enofaznega vzorca spojine LaTaTiO$_6$ (x = 0,5) in tudi po šestem žganju je vzorec vseboval znatno količino obeh polimorfnih oblik.

• Jezik: Slovenski jezik
• Ključne besede: ternarni sistem La$_2$O$_3$-Ta$_2$O$_5$-TiO$_2$, rentgenska praškovna difrakcija, Rietveldovo prilagajanje
• Vrsta gradiva: Diplomsko delo/naloga
• Tipologija: 2.11 - Diplomsko delo
• Organizacija: FKKT - Fakulteta za kemijo in kemijsko tehnologijo
• Leto izida: 2025
• PID: 20.500.12556/RUL-171785
• COBISS.SI-ID: 252426755
• Datum objave v RUL: 02.09.2025

Sekundarni jezik

• Jezik: Angleški jezik
• Naslov: Characterization of selected ceramics from ternary system La$_2$O$_3$-Ta$_2$O$_5$-TiO$_2$ by X-ray powder diffraction

Izvleček

In my diploma thesis, I performed qualitative and quantitative phase analysis of several ceramic samples from the ternary system La$_2$O$_3$-Ta$_2$O$_5$-TiO$_2$, located on the tie line La$_{1/3}$TaO$_3$-LaTaTiO$_6$, with the general formula La$_{(1+x)/3}$Ta$_{1-x}$Ti$_x$O$_3$ for x ranging from 0 to 0,5; using X-ray powder diffraction. The samples were prepared using conventional solid-state reaction technique, involving repeated grinding, homogenization and air quenching at 1350 °C. The measured diffractograms were qualitatively analyzed using the Crystallographica Search Match (CSM) software. The phases identified in the samples were the monoclinic and orthorhombic polymorphs of LaTaTiO$_6$ and a phase with a diffractogram similar to La$_{1/3}$TaO$_3$ (also LaTa$_3$O$_9$), which has a defective perovskite structure. It was established that these correspond to solid solutions based on La$_{1/3}$TaO$_3$. The structure of this compound was employed as a structural model for the solid solution. It was assumed that Ti$^{4+}$ and Ta$^{5+}$ are randomly distributed over the same crystallographic site in the solid solution. The site occupancy was described according to the synthesis ratio, with a corresponding increase in lanthanum site occupancy. By applying Rietveld refinement in Topas 2.1, two single-phase solid solutions with compositions La$_{0,36}$Ta$_{0,92}$Ti$_{0,08}$O$_3$ and La$_{0,37}$Ta$_{0,89}$Ti$_{0,11}$O$_3$ were structurally characterized. The crystal structures determined were later described and drawn using the crystallographic program Mercury. Rietveld refinement was also used for the quantitative analysis of the remaining multiphase samples. The solubility range occured only on one side of the tie line, in compounds with x in the formula La$_{(1+x)/3}$Ta$_{1-x}$Ti$_x$O$_3$ from 0 up to 0,11. A decrease in unit cell volume with increasing x was observed, which is attributed to the smaller ionic radius of Ti$^{4+}$, whose presence in the compound increases in this direction along the tie line. Samples with the initial compositions 0,11 < x < 0,5 were biphasic at equilibrium, consisting of a saturated tetragonal solid solution (La$_{1/3}$TaO$_3$)ss and the orthorhombic compound LaTaTiO$_6$. With increasing x, the mass fraction of the former decreased, while that of the latter increased. The sample with the initial composition x=0,5 contained only one phase LaTaTiO$_6$, but surprisingly in two polymorphic forms: orthorhombic and monoclinic. Even after multiple calcinations with intermediate cooling and milling, the analyses showed that at 1350 °C it was not possible to obtain a single-phase LaTaTiO$_6$ (x=0,5) sample; even after the sixth calcination, the sample still contained significant amounts of both polymorphic forms.

• Ključne besede: ternary system La$_2$O$_3$-Ta$_2$O$_5$-TiO$_2$, X-ray powder diffraction, Rietveld refinement