Browsing by Author "Anthoniappen, J."

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Enhanced photovoltaic effects in A-site samarium doped BiFeO 3 ceramics: The roles of domain structure and electronic state
(2015) Tu, Chi-Shun; Chen, Cheng-Sao; Chen, Pin-Yi; Wei, H.-H.; Schmidt, V. Hugo; Lin, C.-Y.; Anthoniappen, J.; Lee, J.-M.
This work reports enhanced photovoltaic (PV) responses of (Bi1 − xSmx)FeO3 (x = 0.0, 0.05, 0.10) ceramics (BFO100xSm) with ITO film under near-ultraviolet irradiation (λ = 405 nm). The ceramics were characterized by micro-Raman scattering, high-resolution transmission electron microscopy, and synchrotron X-ray absorption spectroscopy (XAS). A rhombohedral R3c symmetry with tilted FeO6 octahedra has been confirmed. The Fe K-edge absorption spectra reveal a slight shift toward higher energy as A-site Sm3+ substitution increases. The oxygen K-edge XAS reveals an enhancement of hybridization between the O 2p and unoccupied Fe 3d states due to Sm doping. The optical band gaps are in the range of 2.15–2.24 eV. The maximal PV power-conversion and external quantum efficiencies respectively reach 0.37% and 4.1% in the ITO/BFO5Sm/Au heterostructure. The PV responses can be described quantitatively by a p-n-junction-like model. The domain structures and hybridization between the O 2p and Fe 3d states play important roles for the PV responses.
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.
Raman spectra and structural stability in B-site manganese doped (Bi0.5Na0.5)0.925Ba0.075TiO3 relaxor ferroelectric ceramics
(2015-11) Anthoniappen, J.; Tu, Chi-Shun; Chen, Pin-Yi; Chen, Cheng-Sao; Idzerda, Yves U.; Chiu, S.-J.
Soft X-ray absorption (XAS), transmission electron spectroscopy (TEM), Raman spectroscopy, and synchrotron XRD have been studied in B-site 0–2 mol% manganese (Mn) doped (Bi0.5Na0.5)0.925Ba0.075TiO3 (BN7.5BT) relaxor ferroelectric ceramics. High-resolution synchrotron XRD and TEM reveal two phase coexistence of rhombohedral R3c and tetragonal P4bm structures in 0 and 0.2%, and an orthorhombic structure in 1 and 2% Mn-doped BN7.5BT at room temperature. Raman spectra of 0% Mn reveal structural transition from two phase coexistence to tetragonal phase near 190 °C with a softening anomaly, while 0.2–2% Mn-doped BN7.5BT show softening behavior near 290 °C upon heating. Raman spectra and synchrotron XRD indicate that Mn doping can enhance structural thermal stability in BN7.5BT ceramics.
Structural stability and depolarization of manganese-doped (Bi 0.5 Na 0.5 ) 1-x Ba x TiO 3 relaxor ferroelectrics
(2014-10) Wang, S.-F.; Tu, Chi-Shun; Chang, T.-L.; Chen, Pin-Yi; Chen, Cheng-Sao; Schmidt, V. Hugo; Anthoniappen, J.
This work reveals that 0.5 mol. % manganese (Mn) doping in (Bi0.5Na0.5)1−xBaxTiO3 (x = 0 and 0.075) solid solutions can increase structural thermal stability, depolarization temperature (Td), piezoelectric coefficient (d33), and electromechanical coupling factor (kt). High-resolution X-ray diffraction and transmission electron microscopy reveal coexistence of rhombohedral (R) R3c and tetragonal (T) P4bm phases in (Bi0.5Na0.5)0.925Ba0.075TiO3 (BN7.5BT) and 0.5 mol. % Mn-doped BN7.5BT (BN7.5BT-0.5Mn). (Bi0.5Na0.5)TiO3 (BNT) and BN7.5BT show an R − R + T phase transition, which does not occur in 0.5 mol. % Mn-doped BNT (BNT-0.5Mn) and BN7.5BT-0.5Mn. Dielectric permittivity (ε′) follows the Curie-Weiss equation, ε′ = C/(T − To), above the Burns temperature (TB), below which polar nanoregions begin to develop. The direct piezoelectric coefficient (d33) and electromechanical coupling factor (kt) of BN7.5BT-0.5Mn reach 190 pC/N and 47%.