Browsing by Author "Chen, Cheng-Sao"

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Bulk optical characterization of dissolved organic matter from semiarid wheat-based cropping systems
(2017-11) Romero, Carlos M.; Engel, Richard E.; D'Andrilli, Juliana; Chen, Cheng-Sao; Zabinski, Catherine A.; Miller, Perry R.; Wallander, R.
Dissolved organic matter (DOM) plays a critical role in the cycling of nutrients and long-term agricultural sustainability. The composition of DOM in soil is likely altered due to management, yet there is limited knowledge on the effect of long-term cropping on DOM chemical character. Here, we characterized water extractable DOM composition along a gradient of soil organic carbon (SOC) affected by differing cropping and tillage intensity in a semiarid climate of the northern Great Plains, USA. Soil samples (0–10, 10–20, 20–30 cm) were collected from conventional till-fallow winter wheat (Triticum aestivum L.; Ftill-W), no-till spring pea/oilseed-wheat (Pisum sativum L.; Pg/O-W), and no-till continuous wheat (W-W) fields, and analyzed using UV/Vis absorbance and excitation-emission matrix fluorescence spectroscopy. The concentration of DOM decreased with depth and was significantly greater (P < 0.05) under W-W or Pg/O-W than Ftill-W. The absorbance at 254 nm (Abs254), a proxy for DOM aromatic nature, indicated that aromaticity decreased with depth and lower biomass-C inputs (i.e. W-W ≥ Pg/O-W ≥ Ftill-W). Multidimensional parallel factor (PARAFAC) analysis revealed humic-like (C1, C2), monolignol-like (C3), and protein/tannin-like (C4) components with varying fluorescence intensities as a function of cropping system and soil depth. DOM humification, indicated by the humification index (HIX), increased significantly with depth (P < 0.05) and was higher for Ftill-W (2.95) than W-W (2.61) or Pg/O-W (2.28). Overall, DOM became depleted of plant-derived constituents and was enriched by more decomposed, condensed substances in Ftill-W, as compared to W-W or Pg/O-W soils. DOM composition is strongly affected by cropping intensity and such changes are important drivers controlling SOC accretion in arable soils.
Comparison of respiratory activity and culturability during monochloramine disinfection of binary population biofilms
(1994-05) Stewart, Philip S.; Griebe, Thomas; Srinivasan, Rohini; Chen, Cheng-Sao; Yu, Feipeng Philip; de Beer, Dirk; McFeters, Gordon A.
Biofilm bacteria challenged with monochloramine retained significant respiratory activity, even though they could not be cultured on agar plates. Microbial colony counts on agar media declined by approximately 99.9% after 1 h of disinfection, whereas the number of bacteria stained by a fluorescent redox dye experienced a 93% reduction. Integrated measures of biofilm respiratory activity, including net oxygen and glucose utilization rates, showed only a 10 to 15% reduction. In this biofilm system, measures of microbial respiratory activity and culturability yielded widely differing estimates of biocide efficacy.
Dielectric properties in lead-free piezoelectric (Bi0.5Na0.5)TiO3-BaTiO3 single crystals and ceramics
(2014) Chen, Cheng-Sao; Tu, Chi-Shun; Chen, Pin-Yi; Ting, Yi; Chiu, S.-J.; Hung, C.-M.; Lee, H.-Y.; Wang, S.-F.; Anthoninappen, J.; Schmidt, V. Hugo; Chien, R. R.
The 0.93(Bi0.5Na0.5)TiO3–0.07BaTiO3 (BNB7T) piezoelectric single crystals and ceramics have been grown respectively by using the self-flux and solid-state-reaction methods. The real (ε′) and imaginary (ε″) parts of the dielectric permittivity of BNB7T crystals and ceramics were investigated with and without an electric (E) poling as functions of temperature and frequency. The BNB7T crystal shows a stronger dielectric maximum at Tm~240 °C than the ceramic at Tm~300 °C. The dielectric permittivity of BNB7T ceramic shows an extra peak after poling at an electric field E=40 kV/cm in the region of 80–100 °C designated as the depolarization temperature (Td). A wide-range dielectric thermal hysteresis was observed in BNB7T crystal and ceramic, suggesting a first-order-like phase transition. The dielectric permittivity ε′ obeys the Curie–Weiss equation, ε′=C/(T−To), above 500 °C, which is considered as the Burns temperature (TB), below which polar nanoregions begin to develop and attenuate dielectric responses.
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.
Photovoltaic conversion and quantum efficiency in perovskite multiferroic ceramics
(2018-05) Tu, Chi-Shun; Chen, Pin-Yi; Chen, Cheng-Sao; Schmidt, V. Hugo; Chien, R. R.; Lin, Chun-Yen
Junction-driven photovoltaic effects in lead-free perovskite BiFeO3 multiferroic materials have demonstrated promising applications in energy harvesting and optical sensors. This study highlights remarkable photon-to-electron external quantum efficiency (EQE) of ∼9% and light-to-electric power-conversion efficiency (PCE) of ∼0.8% in the heterostructure consisting of A-site neodymium-doped BiFeO3 ceramic and indium-tin-oxide (ITO) thin film under irradiation of wavelength λ = 405 nm. A theoretical p-n-junction model based on the photo-generated carriers was employed to quantitatively describe open-circuit voltage (Voc) and short-circuit current density (Jsc) as functions of irradiation intensity, and to calculate junction widths and carrier densities. The direct band gap and the degree of local disorder (or defect state) were estimated using the photon-energy-dependent optical attenuation coefficient with the Tauc and Urbach relations.
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.
Raman vibrations and photovoltaic conversion in rare earth doped (Bi 0.93 RE 0.07 )FeO 3 (RE=Dy, Gd, Eu, Sm) ceramics
(2016-01) Chang, L.-Y.; Tu, Chi-Shun; Chen, Pin-Yi; Chen, Cheng-Sao; Schmidt, V. Hugo; Wei, H.-H.; Huang, D.-J.; Chan, T.-S.
High-resolution Raman spectra, X-ray diffraction, oxygen vacancies, synchrotron X-ray absorption spectroscopy, magnetization, optical band gap, and photovoltaic (PV) conversion have been studied in BiFeO3 (BFO) and (Bi0.93RE0.07)FeO3 (RE=Dy, Gd, Eu and Sm) multiferroic ceramics (7%Dy–BFO, 7%Gd–BFO, 7%Eu–BFO, and 7%Sm–BFO). 7%Dy–BFO exhibits a weak ferromagnetic behavior instead of the linear antiferromagnetic responses found in the other compounds. Optical transmissions reveal band gaps of 2.20–2.21 eV, which are slightly smaller than 2.24 eV in pure BFO. The current vs. voltage (I–V) characteristic curves of indium tin oxide (ITO)/(Bi0.93RE0.07)FeO3 ceramics/Au heterostructures suggest a p–n-junction-like behavior. The maximal PV power-conversion efficiencies under illumination of λ=405 nm in ITO/7%Dy–BFO/Au, ITO/7%Gd–BFO/Au, ITO/7%Eu–BFO/Au, and ITO/7%Sm–BFO/Au respectively reach 0.22%, 0.35%, 0.27%, and 0.24%, which are much larger than 0.017% in ITO/BFO/Au. The PV open-circuit voltage and short-circuit current can be reasonably described by a junction model as a function of illumination intensity.
Raman vibrations, domain structures, and photovoltaic effects in A-site La-modified BiFeO 3 multiferroic ceramics
(2015) Tu, Chi-Shun; Chen, Cheng-Sao; Chen, Pin-Yi; Xu, Zhe-Rui; Idzerda, Yves U.; Schmidt, V. Hugo; Lyu, M.-Q.; Chan, T.-S.; Liu, C.-Y.
Micro‐Raman spectroscopy, X‐ray diffraction, high‐resolution transmission electron microscopy (TEM), oxygen vacancies, synchrotron X‐ray absorption spectroscopy, magnetizations, optical band gaps, and photovoltaic (PV) effects have been studied in (Bi1−xLax)FeO3 (BFO100xL) ceramics for x = 0.0, 0.05, 0.10, and 0.15. XRD, Raman spectra, and TEM confirm a rhombohedral R3c symmetry with the tilted FeO6 oxygen octahedra in all compounds. The low‐frequency Raman vibrations become broader and shift toward higher frequency as La3+ increases. Fe K‐edge synchrotron X‐ray absorptions reveal that Fe3+ valence and Fe–O–Fe bond angle are not modified by the La3+ substitution. All compounds exhibit a linear antiferromagnetic feature. Optical transmission reveals band gaps in the range of 2.22–2.24 eV. The heterostructures of indium tin oxide (ITO) film/(Bi1−xLax)FeO3 ceramics/Au film show a p–n junction‐like I–V characteristic behavior. The maximal PV power conversion efficiency can reach 0.19% in ITO/BFO15L/Au under illumination of λ = 405 nm. A junction‐like theoretical model can reasonably describe open‐circuit voltage and short‐circuit current as a function of illumination intensity.
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%.
Tailoring microstructure and photovoltaic effect in multiferroic Nd-substituted BiFeO3 ceramics by processing atmosphere modification
(2018-11) Tu, Chi-Shun; Chen, Pin-Yi; Chen, Cheng-Sao; Lin, Chun-Yen; Schmidt, V. Hugo
This study highlights significant effects of processing atmosphere ratio (O2/N2) on microstructure, impurity phases, atomic hybridization, band gap, and photovoltaic properties in (Bi0.93Nd0.07)FeO3 (BFO7Nd) ceramics. A Rietveld-refinement analysis indicates increased oxygen and bismuth vacancies in the specimens processed in the O2-rich atmosphere (hereafter called O2-rich-atmosphere specimens). In the matrix containing mainly Fe3+ ions, Fe4+ cations were identified with O2 concentration decreasing in the atmosphere by Fe K/L-edges synchrotron X-ray absorption. Oxygen K-edge absorption reveals reduced hybridizations of the O 2p–Fe 3d and the O 2p–Bi 6sp orbitals in the O2-rich-atmosphere specimens. Photovoltaic effects in the ITO/BFO7Nd/Au heterostructures under near-ultraviolet irradiation (λ = 405 nm) exhibit strong dependences on O2/N2 ratio. A p-n-junction model was used to describe open-circuit voltage and short-circuit current density as functions of irradiation intensity. The calculated carrier densities (in BFO7Nd ceramics) and p-n-junction widths (in the dark) are ∼1023 m−3 and a few hundred nanometers, respectively.