Mikrostrukturna svojstva cinkovog oksida istraživana difrakcijom rendgenskog zračenja pri visokom tlaku

master's thesis

• Title (english): Microstructural properties of zinc oxide investigated by high-pressure X-ray diffraction
• Author: Petra Gazdek
• Mentor: Martina Vrankić (mentor)
• Mentor: Željko Skoko (komentor)
• Committee member: Željko Skoko (predsjednik povjerenstva)
• Committee member: Martina Vrankić (član povjerenstva)
• Committee member: Maja Planinić (član povjerenstva)
• Committee member: Mario Novak (član povjerenstva)
• Committee member: Ivica Smolić (član povjerenstva)
• Granter: University of Zagreb; Faculty of Science; (Department of Physics); Zagreb
• Defense date and country: 2022-04-04, Croatia
• Scientific / art field, discipline and subdiscipline: NATURAL SCIENCES; Physics

Abstract

Metodom rendgenske difrakcije u polikristalu istraživan je utjecaj visokog tlaka (~0–20 GPa) na strukturne i mikrostrukturne parametre cinkovog oksida, ZnO. Podaci o točnim parametrima jedinične ćelije, veličini kristalita i deformacijama kristalne rešetke dobiveni su korištenjem Rietveldove metode utočnjavanja difrakcijske slike. Opaženo je da povećanjem tlaka dolazi do pomicanja difrakcijskih maksimuma prema većem Braggovom kutu što ukazuje na smanjenje bridova kristalne rešetke, kao i do faznog prijelaza iz heksagonske kristalne strukture u kubnu. Postupak utočnjavanja heksagonske i kubne strukture ZnO pokazao je da je heksagonska struktura kompresibilnija u smjeru c, te da dolazi do linearnog smanjenja omjera c/a. Prijelaz iz heksagonske u kubnu strukturu praćen je naglim smanjenjem volumena jedinične ćelije ZnO za ~20%. Pri tome su omjeri d(100)/d(002) za heksagonsku fazu i d(020)/d(220) za kubnu fazu u velikoj korelaciji s promjenama tlaka - omjer d(100)/d(002) raste linearno s tlakom prije faznog prijelaza i odstupa od linearnog odnosa u prijelaznoj zoni, dok omjer d(020)/d(220) lagano opada s tlakom nakon faznog prijelaza. Nakon smanjenja tlaka sa 17,92 GPa na 0 GPa ne dolazi do reverzibilnog povrata kubne strukture ZnO u isključivo heksagonsko uređenje – relativni težinski udio kubne faze pri 0 GPa iznosi ~52%, dok na heksagonsku fazu otpada ~48%. Primjena tlaka uzrokovala je proširenje difrakcijskih maksimuma i smanjenje veličine kristalita s ~35 nm pri atmosferskim uvjetima na 18 nm pri 17,92 GPa. S druge strane, deformacije kristalne rešetke su pod utjecajem mehaničkog tlaka porasle sa 0,35% na 0,68%. Smanjenje tlaka s 17,92 GPa na 0 GPa pokazalo je djelomično reverzibilan učinak na mikrostrukturne parametre – veličina kristalita je porasla s ~18 nm na ~30 nm, dok su se deformacije kristalne rešetke smanjile s 0,68% na 0,39%. Dobiveni rezultati u skladu su s istraživanjima objavljenim u literaturi.

Abstract (english)

The influence of high pressure (~0–20 GPa) on the structural and microstructural parameters of zinc oxide, ZnO, was investigated using the X-ray powder diffraction. The information on unit cell parameters, crystallite size, and microstrainsunder both, compression and decompression was obtained using the Rietveld refinement. It was observed that the increase in pressure shifts the diffraction maxima towards higher Bragg angles, and induces a phase transition from hexagonal to cubic structure. The structure refinement revealed that the hexagonal structure of ZnO is more compressible in the c-direction, and that there is a linear decrease in the c/a ratio. The transition from hexagonal to cubic arrangement was accompanied by a sharp decrease in the volume of the ZnO unit cell by ~20%. It appears that the ratios d(100)/d(002) for the hexagonal and d(020)/d(220) for the cubic phase are highly correlated with the pressure changes - the ratio d(100)/d(002) increases linearly with the pressure before phase transition and deviates from the linear relationship in the transition zone, while the ratio d(020)/d(220) decreases slightly with the pressure after the phase transition. After the pressure drops from 17.92 GPa to 0 GPa, no reversible return of the cubic ZnO structure to the exclusively hexagonal arrangement was observed - the relative weight percentage of the cubic phase at 0 GPa is ~52%, while the hexagonal phase accounts for ~48%. The line profile analysis by Rietveld refinement showed the broadening of the diffraction maximaleading to the reduction of the crystallite size from 35 nm at atmosphere conditions to 18 nm at 17.92 GPa. On the other hand, the microstrains increased from 0.35% to 0.68% under the influence of mechanical pressure. Decompression from 17.92 GPa to 0 GPa showed a partially reversible effect on microstructural parameters - crystallite size increased from ~18 nm to ~30 nm, while microstrains decreased from 0.68% to 0.39%.These results are in accordance with the research published in the literature.

• Keywords: visoki tlak; rendgenska difrakcija u polikristalu; sinkrotron; Rietveldovo utočnjavanje; veličina kristalita; deformacije kristalne rešetke; cinkov oksid
• Keywords (english): high-pressureX-ray diffraction; synchrotron; Rietveld refinement; cyrstallite size; lattice strain; zinc oxide
• Language: croatian
• URN:NBN: urn:nbn:hr:217:067048
• Study programme: Title: Physics; specializations in: Education; Course: Education; Study programme type: university; Study level: integrated undergraduate and graduate; Academic / professional title: magistar/magistra edukacije fizike (magistar/magistra edukacije fizike)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Open access; Embargo expiration date: 2024-04-04
• Created on: 2022-07-01 08:06:45