Browsing by Author "Chan, Ting-Shan"

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A-site strontium doping effects on structure, magnetic, and photovoltaic properties of (Bi1−xSrx)FeO3−δ multiferroic ceramics
(2015-03) Tu, Chi-Shun; Xu, Zhe-Rui; Schmidt, V. Hugo; Chan, Ting-Shan; Chien, R.R.; Son, Hyungbin
Raman spectroscopy, X-ray diffraction (XRD), magnetization hysteresis loop, synchrotron X-ray absorption spectroscopy, and photovoltaic effects have been measured in (Bi1−xSrx)FeO3−δ (BFO100xSr) ceramics for x=0.0, 0.05, 0.10, and 0.15. Raman spectra and XRD reveal a rhombohedral R3c structure in all compounds. A-site Sr2+ doping increases fluctuations in cation-site occupancy and causes broadening in Raman modes. BFO15Sr exhibits a strong ferromagnetic feature due to reduction of Fesingle bondOsingle bondFe bond angle evidenced by the extended synchrotron X-ray absorption fine structure. The heterostructure of indium tin oxide (ITO) film/(Bi1−xSrx)FeO3−δ ceramic/Au film exhibit clear photovoltaic (PV) responses under blue illumination of λ=405 nm. The maximal power-conversion efficiency and external quantum efficiency in ITO/BFO5Sr/Au are about 0.004% and 0.2%, respectively. A model based on optically excited charges in the depletion region between ITO and (Bi1−xSrx)FeO3−δ can well describe open-circuit voltage and short-circuit current as a function of illumination intensity.
Magnetic and phonon transitions in B-site Co doped BiFeO3 ceramics
(2016-05) Chiang, Yueh-Sheng; Tu, Chi-Shun; Chen, Pin-Yi; Chen, Cheng-Sao; Anthoniappen, J.; Ting, Yi; Chan, Ting-Shan; Schmidt, V. Hugo
Magnetic susceptibility and phonons have been characterized in multiferroic Bi(Fe1−xCox)O3−δ ceramics for x=0.0, 0.05, and 0.10 (BFO100xCo) as functions of temperature. A preferred (100) crystallographic orientation and increasing average oxygen vacancies were observed in BFO5Co and BFO10Co. The Fe and Co K-edge synchrotron X-ray absorptions revealed mixed valences of Fe3+, Fe4+, Co2+, and Co3+ ions in BFO5Co and BFO10Co, which exhibit a ferromagnetic (or ferrimagnetic) phase below room temperature due to appearance of ferromagnetic B–O–B (B=Fe and Co) superexchange interactions. Field–cooled (FC) and zero–field–cooled (ZFC) magnetic susceptibilities exhibit a significant spin-glass splitting below room temperature in BFO5Co and BFO10Co. Two Raman-active phonon anomalies at ~170 K (or 200 K) and ~260 K were attributed to the Fe3+–O–Co3+ and Co3+–O–Co3+ magnetic orderings, respectively. This work suggests that the low-spin Co2+–O–Co2+, Fe3+–O–Fe3+ (or Fe4+), and high-spin Co2+–O–Co2+ superexchange interactions are responsible for phonon anomalies at ~290 (or ~300 K), ~400, and ~470 K (or ~520 K) in BFO5Co and BFO10Co.
Magnetization, phonon, and X-ray edge absorption in barium doped BiFeO3 ceramics
(2017-01) Ting, Yi; Tu, Chi-Shun; Chen, Pin-Yi; Chen, Cheng-Sao; Anthoniappen, J.; Schmidt, V. Hugo; Lee, Jenn-Min; Chan, Ting-Shan; Chen, Wei-Yu; Song, Rui-Wen
Magnetization hysteresis loops, dc and ac magnetic susceptibilities, and Raman vibrations have been characterized in (Bi1âˆ’xBax)FeO3âˆ’Î´ ceramics for x = 0.0, 0.05, 0.10, and 0.15 as functions of temperature. Ferromagnetic hysteresis loops were observed in Ba-doped compounds with increasing magnetization as Ba substitution increases. High-resolution synchrotron Fe K- and L2,3-edge X-ray absorptions reveal an Fe3+ valence and a modification of the Feâ€“Oâ€“Fe bond structure by the A-site Ba substitution. The oxygen K-edge X-ray absorption suggests that the hybridization of the O 2p and Fe 3d orbitals was reduced by the Ba2+ substitution. Field-cooled and zero-field-cooled magnetic susceptibilities reveal a spin-glass behavior, which was enhanced with increasing Ba substitution. Raman vibrations of the Bi- and Fe-sensitive E(2) and A1(1) modes reveal frequency softening and step-like anomalies in full-width-at-half-maximum in the vicinity of ~150â€“250 K, which were attributed to spinâ€“phonon interaction while magnetic ordering transitions take place.