Rational Synthesis of Lead-Free Epitaxial BiFe0.5Cr0.5O3 Perovskite Thin Film: A Structure-Property Relationship Study for Emerging Optoelectronic Application

dc.contributor.advisor Wang, Danyang
dc.contributor.advisor Li, Sean Seyfouri, Moein 2022-02-16T01:21:42Z 2022-02-16T01:21:42Z 2021
dc.description.abstract Multiferroic BiFe0.5Cr0.5O3 (BFCO) in which ferroelectric and magnetic orders coexist has gained research interest owing to its potential applications, e.g., spintronic and resistive random-access memory. Moreover, multiferroics possess a narrower bandgap compared to typical ferroelectrics, extending their application to photovoltaic devices. In contrast to the conventional semiconductors, the polarization-induced electric field facilitates the photoexcited charge separation, leading to an above-bandgap photovoltage in ferroelectrics. Nevertheless, a long-standing issue is the relatively low absorption of visible light. Thus, it is essential but challenging to tune their bandgap without compromising ferroelectricity. This thesis explores structural phase transition in the epitaxial BFCO films grown on SrRuO3 buffered (001) SrTiO3 substrate via Laser Molecular Beam Epitaxy (LMBE). Reciprocal space mapping result shows strain relaxation mechanism is not solely by the formation of misfit dislocation but also by changing the crystal symmetry, transitioning from tetragonal-like to a monoclinically distorted phase as the thickness increases. The crystallographic evolution is also coupled with bandgap modulation, confirming that BFCO structure and its physical properties are strongly intertwined. Using spectroscopic ellipsometry, the slight redshift of the bandgap distinguishes the absorption process of the T-like BFCO layer from that of monoclinically distorted structure, further confirmed by spectral photocurrent measurement via conductive-atomic force microscopy. The preparation of pure phase BFCO film with a robust polarization is of paramount importance for practical application. Yet, similar to the parental bismuth ferrite, BFCO suffers from poor electrical leakage performance. We report a three-order of magnitude suppression in the leakage current for the BFCO film through judicious adjustment of the growth rate. Scanning probe microscopy (PFM, AFM and c-AFM) results reveal that both microstructure and ferroelectric properties can be tuned by lowering the growth rate, ensuing realization of the room-temperature ferroelectric polarization comparable to the ab-initio predicted value. This thesis provides a facile strategy to tailor the structure-property of epitaxial BFCO film and its functional response for emerging optoelectronic devices.
dc.language English
dc.language.iso en
dc.publisher UNSW, Sydney
dc.rights CC BY 4.0
dc.subject.other Multiferroic
dc.subject.other Epitaxy
dc.subject.other Thin Film
dc.subject.other Bandgap tuning
dc.subject.other photoferroelectric
dc.subject.other Bismuth Ferrite
dc.title Rational Synthesis of Lead-Free Epitaxial BiFe0.5Cr0.5O3 Perovskite Thin Film: A Structure-Property Relationship Study for Emerging Optoelectronic Application
dc.type Thesis
dcterms.accessRights embargoed access
dcterms.rightsHolder Seyfouri, Moein
dspace.entity.type Publication
unsw.accessRights.uri 2024-02-16
unsw.description.embargoNote Embargoed until 2024-02-16
unsw.relation.faculty Science
unsw.relation.faculty Engineering
unsw.relation.faculty UNSW Canberra School of Materials Science & Engineering School of Computer Science and Engineering School of Humanities and Social Sciences
unsw.subject.fieldofresearchcode 401605 Functional materials
unsw.thesis.degreetype PhD Doctorate
Resource type