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The influence of mechanical activation on the structure and properties of strontium titanate ceramics

dc.contributor.advisorJanaćković, Đorđe
dc.contributor.otherPavlović, Vera
dc.contributor.otherPetrović, Rada
dc.contributor.otherPavlović, Vladimir
dc.contributor.otherKosanović, Darko A.
dc.creatorŽivojinović, Jelena A.
dc.date.accessioned2020-08-06T10:54:01Z
dc.date.available2020-08-06T10:54:01Z
dc.date.issued2020-06-04
dc.identifier.urihttp://eteze.bg.ac.rs/application/showtheses?thesesId=7481
dc.identifier.urihttps://fedorabg.bg.ac.rs/fedora/get/o:22343/bdef:Content/download
dc.identifier.urihttp://vbs.rs/scripts/cobiss?command=DISPLAY&base=70036&RID=17167369
dc.identifier.urihttp://nardus.mpn.gov.rs/handle/123456789/17287
dc.description.abstractCilj ove doktorske disertacije je bio da se analizira i sagleda uticaj mehaničke aktivacije na strukturu i svojstva nedopiranog i dopiranog SrTiO3 praha, kao i uticaj na strukturu i svojstva keramike dobijene sinterovanjem ispresaka pomenutih prahova. U slučaju sinterovanih nedopiranih SrTiO3 uzoraka dodatno su razmatrane promene u brzini densifikacije i kinetici sinterovanja. Uticaj mehaničke aktivacije i dopanta na električna svojstva stroncijum-titanatne keramike je analiziran merenjem frekventne zavisnosti relativne dielektrične permitivnosti i tangensa ugla dielektričnih gubitaka na sobnoj temperaturi. Magnetnim merenjima, kod dopiranih SrTiO3 uzoraka dobijenih dodavanjem mangan(IV)-oksida, praćen je uticaj mehaničke aktivacije, koncentracije dopanta i jačine magnetnog polja na vrednost specifične magnetizacije. Mehanička aktivacija SrTiO3 praha je vršena u visoko-energetskom planetarnom mlinu sa kuglama, pri čemu je vreme aktivacije nedopiranog praha iznosilo: 5, 10, 30, 60, 90 i 120 minuta, dok je efekat dopiranja razmatran za aktivaciju od 10, 30 i 120 minuta. U cilju dobijanja SrTiO3:Mn sistema, tipa Sr1-xMnxTiO3 (SMnT) ili SrTi1-xMnxO3 (STMn), u polazni SrTiO3 prah je dodat mangan(IV)-oksid (MnO2), pri čemu su izabrane vrednosti za x bile: 0,03, 0,06 i 0,12. Raspodela veličina čestica je ukazala da je mehanička aktivacija dovela do usitnjavanja čestica polaznog praha, uz istovremenu pojavu šire raspodele veličina čestica pri dužim vremenima aktivacije. Skenirajućom i transmisionom elektronskom mikroskopijom (SEM i TEM) analizirana je mikrostruktura i morfologija polaznog i mehanički aktiviranih prahova. BET metodom je utvrđeno da se najviša vrednost specifične površine kod nedopiranih prahova postiže pri aktivaciji u trajanju od 60 minuta, dok pri daljoj aktivaciji specifična površina ostaje približno konstantne vrednosti, usled povećane sekundarne aglomerizacije. Pokazano je da je gustina ispreska kod praha aktiviranog tokom 10-30 minuta najveća. Zapaženo je sniženje intenziteta XRD pikova sa porastom vremena aktivacije, kao i širenje difrakcionih linija, usled smanjenja veličine kristalita i porasta mikronaprezanja. Primenjena mehanička aktivacija je omogućila formiranje kubnog nanokristalnog SrTiO3 praha, pri čemu veličina kristalita opada i do ~20 nm sa uvećanjem vremena aktivacije. Uočena promena u vrednosti parametra kristalne rešetke a je posredno ukazala i na moguće promene u koncentraciji kiseonikovih vakancija. Analizom Ramanovih spektara je praćen uticaj mehaničke aktivacije na promene u fononskom spektru prahova, sa posebnim akcentom na polarne TO mode, čiji oblik i intenzitet bitno zavise od defekata kao što su kiseonikove vakancije. Analiza optičkih svojstava kristalnih materijala pomoću UV-Vis spektroskopije je ukazala na sniženje energije zabranjene zone sa uvećanjem vremena aktivacije. Primenom dilatometrije je ispitivan uticaj mehaničke aktivacije na početni stadijum sinterovanja dvostrano presovanih SrTiO3 prahova. Uočeno je značajno smanjenje temperature početka skupljanja ispreska, kao i uticaj na brzinu skupljanja i na konačne gustine sinterovanih uzoraka. Primena Dornove metode je ukazala na značajno smanjenje efektivne energije aktivacije transporta mase u početnom stadijumu sinterovanja, sa porastom vremena mehaničke aktivacije polaznog praha. Za uzorke dobijene sinterovanjem do 1300 oC, uz izotermsko zadržavanje na maksimalnoj temperaturi u trajanju od 2h, je izvršena korelacija između zapaženih strukturnih promena i promena u dielektričnim svojstvima, nastalim usled mehaničke aktivacije. Posebna pažnja je posvećena uticaju promena: gustine, poroznosti, veličine zrna i kristalita, kao i uticaju promena parametra kristalne rešetke, na dielektrična svojstva. Promene vrednosti relativne dielektrične permitivnosti su razmatrane i sa stanovišta promena u oblasti granice zrna, posebno imajući u vidu rezultate koji su ukazali na promenu koncentracije kiseonikovih vakancija...sr
dc.description.abstractThe aim of this doctoral dissertation is to analyze and evaluate the effect of mechanical activation on the structure and properties of undoped and doped SrTiO3 powders, as well as the effect on the structure and properties of the ceramics obtained by sintering these powders. For the sintered undoped SrTiO3 samples, changes in the densification rate were also analyzed. The effect of mechanical activation and dopant on the electrical properties of strontium titanate ceramics was analyzed by measuring the frequency-dependent relative dielectric permittivity and the loss tangent at room temperature. Magnetic measurements performed on the doped SrTiO3 samples obtained by the addition of manganese(IV) oxide were used to monitor the influence of mechanical activation, dopant concentration and magnetic field strength on magnetization. The mechanical activation of the SrTiO3 powder was performed in a high-energy planetary ball mill; the activation times of the undoped powder were: 5, 10, 30, 60, 90, and 120 minutes, while the doping effect was analyzed for the activation periods of 10, 30, and 120 minutes. In order to obtain SrTiO3:Mn systems belonging to Sr1-xMnxTiO3 (SMnT) or SrTi1-xMnxO3 (STMn) compound types, manganese(IV) oxide (MnO2) was added to the starting SrTiO3 powder, where the values selected for x were: 0.03, 0.06 and 0.12. The particle size distribution indicated that mechanical activation resulted in the comminution of the starting powder particles, accompanied with a wider particle size distribution at longer activation times. The microstructural and morphological analysis of the starting and mechanically activated powders was performed using scanning and transmission electron microscopy (SEM and TEM). The BET method revealed that 60-minute activation resulted in the highest specific surface area in undoped powders, while further activation led to a relatively constant specific surface due to increased secondary agglomeration. The density of the powder activated for 10-30 minutes was the highest. The intensity of XRD peaks decreased with longer activation times and diffraction lines broadened due to decreased crystallite sizes and increased microstrain. Mechanical activation led to the formation of cubic nanocrystalline SrTiO3 powder, with the minimum crystallite size of 20 nm. The observed change in the value of the crystal lattice parameter indirectly indicated possible changes in the concentration of oxygen vacancies. The analysis of Raman spectra revealed the effect of mechanical activation on the phonon spectrum of powders, with particular emphasis on polar TO modes which shape and intensity generally depend on defects such as oxygen vacancies. The analysis of the optical properties of crystalline materials by UV-Vis spectroscopy indicated a correlation between decreased band gap energy and increased activation times. The effect of mechanical activation on the initial stage of sintering of bilaterally pressed SrTiO3 powders was investigated by dilatometry. A significant decrease in the temperature of the onset of densification was observed, as well as the effect of mechanical activation on the densification rate and on the final density of the sintered samples. The application of the Dorn method indicated a significant decrease in the effective activation energy of mass transport in the initial sintering stage, with a longer time of the mechanical activation of the starting powder. For the samples obtained by sintering up to 1300 °C, with isothermal retention at the maximum temperature for 2 h, a correlation between the structural changes and the changes in dielectric properties resulting from mechanical activation was observed. Particular attention was paid to the effect of changes: density, porosity, grain and crystallite size, as well as the effect of crystal lattice parameter changes on the dielectric properties. The changed values of the relative dielectric permittivity were analyzed in the context of the changes in the grainboundary region, with special respect to the results indicating changes in the oxygen vacancy concentration.en
dc.formatapplication/pdf
dc.languagesr
dc.publisherУниверзитет у Београду, Технолошко-металуршки факултетsr
dc.relationinfo:eu-repo/grantAgreement/MESTD/Basic Research (BR or ON)/172057/RS//
dc.rightsopenAccessen
dc.sourceУниверзитет у Београдуsr
dc.subjectstroncijum-titanatsr
dc.subjectstrontium titanateen
dc.subjectmechanical activationen
dc.subjectsinteringen
dc.subjectdopingen
dc.subjectelectrical propertiesen
dc.subjectmagnetic propertiesen
dc.subjectmehanička aktivacijasr
dc.subjectsinterovanjesr
dc.subjectdopiranjesr
dc.subjectelektrična svojstvasr
dc.subjectmagnetna svojstvasr
dc.titleUticaj mehaničke aktivacije na strukturu i svojstva stroncijum-titanatne keramikesr
dc.title.alternativeThe influence of mechanical activation on the structure and properties of strontium titanate ceramicsen
dc.typedoctoralThesisen
dc.rights.licenseBY-NC-ND
dc.identifier.fulltexthttp://nardus.mpn.gov.rs/bitstream/id/64357/Disertacija.pdf
dc.identifier.fulltexthttp://nardus.mpn.gov.rs/bitstream/id/64358/IzvestajKomisije22893.pdf


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