Wide-range tunable bandgap in Bi1-xCaxFe1-yTiyO3-δnanoparticles via oxygen vacancy induced structural modulations at room temperature

Title
Wide-range tunable bandgap in Bi1-xCaxFe1-yTiyO3-δnanoparticles via oxygen vacancy induced structural modulations at room temperature
Authors
Pavana SVMocherlaSanjeev Gautam채근화M. S. Ramachandra RaoC.Sudakar
Keywords
bandgap engineering; oxygen vacancies; Fe d-d transitions; XANES; HRTEM
Issue Date
2015-10
Publisher
Materials Research Express
Citation
VOL 2, 095012-095012
Abstract
Wedemonstrate that oxygen vacancies (VO) produced by aliovalent (Ca2+) doping in BiFeO3 (BCFO) and associated structural changes due toVO ordering result in systematic alteration of the bandgap (Eg) over a wide range from 1.5 eV to 2.3 eV. By contrast, the change in the bandgap of aCa2+ and Ti4+ co-doped BiFeO3 (BCFTO) system, wherein theVO formation is suppressed, is negligible. These contrastive results strongly confirm the role of oxygen vacancies in altering the bandgap of BCFO. Irrespective of doping, microstrain, which is found to be large (0.3 to 1.2%) below a critical size (dc∼&#61600;60 nm) also produces a small, yet linear change in the bandgap (Eg from 2.0 to 2.3 eV). The cubic phase stabilizes gradually in BCFO for x&#61600;>&#61600;0.1 through an orthorhombic phase (for 0.05&#61600;<&#61600;x&#61600;<&#61600;0.1), whereas it directly transforms for x&#61600;>&#61600;0.1 in BCFTO. This change in BCFO at 300 Ksuggests a highpressure- like (or high-temperature-like) effect of the oxygen vacancies and dopants on the structure. Systematic variations in the relative intensities and peak positions of Fe d&#8211;d transitions in BCFO reveal the local changes in Fe&#8211;O&#8211;Fe coordination. These results along with XANES andHRTEMstudies substantiate the observed structural changes.
URI
http://pubs.kist.re.kr/handle/201004/50891
ISSN
20531591
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KIST Publication > Article
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