Browsing by Author "Hsu, Ying-Ya"

Now showing 1 - 15 of 15

Characterization of magnetic properties of Sr2CuWO6 and Sr2CuMoO6
(2014-04-21)
Vasala, Sami
;
Saadaoui, Hassan
;
Morenzoni, Elvezio
;
Chmaissem, Omar
;
Chan, Ting-Shan
In this work we examine the low-temperature magnetic properties of the two double-perovskite compounds Sr2CuWO6 and Sr2CuMoO6 using magnetic susceptibility, muon spin rotation and relaxation, and neutron powder diffraction measurements. Additionally, the most relevant spin exchange interaction constants are derived from ab initio electronic structure calculations, aided by x-ray absorption spectroscopy. The compounds exhibit quasi-two-dimensional magnetic properties, with broad maxima at T-max = 83 and 95 K for Sr2CuWO6 and Sr2CuMoO6, respectively. However, three-dimensional long-range order takes place below T-N = 24(1) and 28(2) K for Sr2CuWO6 and Sr2CuMoO6, respectively. Our results show that the low-dimensional magnetic correlations are mainly due to the significant next-nearest-neighbor interactions in the ab plane of the double-perovskite structure, whereas three-dimensional long-range magnetic order is caused by weaker next-nearest-neighbor interactions along the c axis. Next-nearest-neighbor interactions are also slightly frustrated by weaker nearest-neighbor interactions within the ab plane. Based on these results we predict the low-temperature magnetic structure in these compounds to be type-II antiferromagnetic order of the double-perovskite lattice.
Characterization of magnetic properties of Sr2CuWO6 and Sr2CuMoO6
(2014-04-21)
Vasala, Sami
;
Saadaoui, Hassan
;
Morenzoni, Elvezio
;
Chmaissem, Omar
;
Chan, Ting-Shan
In this work we examine the low-temperature magnetic properties of the two double-perovskite compounds Sr2CuWO6 and Sr2CuMoO6 using magnetic susceptibility, muon spin rotation and relaxation, and neutron powder diffraction measurements. Additionally, the most relevant spin exchange interaction constants are derived from ab initio electronic structure calculations, aided by x-ray absorption spectroscopy. The compounds exhibit quasi-two-dimensional magnetic properties, with broad maxima at T-max = 83 and 95 K for Sr2CuWO6 and Sr2CuMoO6, respectively. However, three-dimensional long-range order takes place below T-N = 24(1) and 28(2) K for Sr2CuWO6 and Sr2CuMoO6, respectively. Our results show that the low-dimensional magnetic correlations are mainly due to the significant next-nearest-neighbor interactions in the ab plane of the double-perovskite structure, whereas three-dimensional long-range magnetic order is caused by weaker next-nearest-neighbor interactions along the c axis. Next-nearest-neighbor interactions are also slightly frustrated by weaker nearest-neighbor interactions within the ab plane. Based on these results we predict the low-temperature magnetic structure in these compounds to be type-II antiferromagnetic order of the double-perovskite lattice.
Chemical Capture of Phosphine by a Sol-Gel-Derived Cu/TiO(2) Adsorbent - Interaction Mechanisms
(2011-02-10)
Chang, Sue-Min
;
Hsu, Ying-Ya
;
Chan, Ting-Shan
;
環境工程研究所
;
Institute of Environmental Engineering
In this study, a novel sol gel-derived Cu/TiO(2) adsorbent has been demonstrated to exhibit exceptional capacities of 40,62, 49.52, and 108.48 mg PH(3)/g Cu/TiO(2) for the oxidative capture of phosphine (PH(3)) in N(2), air, and humidified air, respectively. We have proposed the oxidative mechanisms for PH(3) on the Cu/TiO(2) sample on the basis of elemental, chemical state, functional group, and microstructural analysis. Moreover, the influence of O(2) and water vapor on the capture capacity is discussed. The transformation of PH(3) followed the sequence of PH(2) -> H(2)P-OH -> HP(OH)(2) -> P(OH)(3) -> HO-P=O -> H(3)PO(4). At the same time, the CuO/Cu(OH)(2) moieties in the TiO(2) lattice were reduced to Cu(0). The H(2)P-OH and HO-P=O are the two stable intermediates, and they occupied the active species to inhibit further chemisorption. Direct oxidation of PH(3) or the intermediates with adsorbed O(2) was not efficient. However, the Cu/TiO(2) sample catalyzed their interactions via reduction and then oxidation of the Cu(2)+ ions. Water vapor acts as a cocatalyst to facilitate the oxidation of the intermediates. The end product, H(3)PO(4), migrated to bound the TiO(2) support and free the CuO/Cu(OH)(2) for the following catalytic processes. Although competitive adsorption of water molecules initially retarded the adsorption rate, the high extent of oxidation greatly promoted the capture capacity of the Cu/TiO(2) in humidified air.
Chemical Capture of Phosphine by a Sol-Gel-Derived Cu/TiO2 Adsorbent - Interaction Mechanisms
(2011-02-10)
Chang, Sue-Min
;
Hsu, Ying-Ya
;
Chan, Ting-Shan
;
環境工程研究所
;
Institute of Environmental Engineering
In this study, a novel sol gel-derived Cu/TiO2 adsorbent has been demonstrated to exhibit exceptional capacities of 40,62, 49.52, and 108.48 mg PH3/g Cu/TiO2 for the oxidative capture of phosphine (PH3) in N-2, air, and humidified air, respectively. We have proposed the oxidative mechanisms for PH3 on the Cu/TiO2 sample on the basis of elemental, chemical state, functional group, and microstructural analysis. Moreover, the influence of O-2 and water vapor on the capture capacity is discussed. The transformation of PH3 followed the sequence of PH2 -> H2P-OH -> HP(OH)(2) -> P(OH)(3) -> HO-P=O -> H3PO4. At the same time, the CuO/Cu(OH)(2) moieties in the TiO2 lattice were reduced to Cu-0. The H2P-OH and HO-P=O are the two stable intermediates, and they occupied the active species to inhibit further chemisorption. Direct oxidation of PH3 or the intermediates with adsorbed O-2 was not efficient. However, the Cu/TiO2 sample catalyzed their interactions via reduction and then oxidation of the Cu-2+ ions. Water vapor acts as a cocatalyst to facilitate the oxidation of the intermediates. The end product, H3PO4, migrated to bound the TiO2 support and free the CuO/Cu(OH)(2) for the following catalytic processes. Although competitive adsorption of water molecules initially retarded the adsorption rate, the high extent of oxidation greatly promoted the capture capacity of the Cu/TiO2 in humidified air.
Efficacies of dopants in thermoelectric BiOCuSe
(2016-07-01)
Chou, Ta-Lei
;
Tewari, Girish C.
;
Srivastava, Divya
;
Yamamoto, Atsushi
;
Chan, Ting-Shan
Moderately-doped BiOCuSe-based materials are actively investigated worldwide as new promising candidates for intermediate-temperature thermoelectric power generation. Here we explain for two differently doped BiOCuSe materials, i.e. Cu-deficient BiOCu1-xSe and Ca-for-Bi substituted (Bi1-yCay) OCuSe systems, the differences in their efficacies to enhance the thermoelectric performance of the pristine BiOCuSe material using theoretical calculations and x-ray absorption spectroscopy (XAS) at various edges. In the Cu-deficient system the doping dominantly induces an oxide layer-to-selenide layer charge transfer process. On the other hand, the Ca-for-Bi substitution not only gives lower electrical resistivity but also better thermal stability thanks to the increased ionic bonding character in the selenide block. Density of states nearby the Fermi level suggests that even though the Bi-Se distance is much longer than the Bi-O bond, its contribution cannot be ruled out. The Se-Bi-O chain contributes to the hole states at the VBM with the Cu 3d - Se 4p antibonding state. (C) 2016 Elsevier B.V. All rights reserved.
ENVR 32-Fabrication of novel Cu/TiO2-based imprinted polymers for detection of phosphine
(2009-08-16)
Chang, Sue-Min
;
Hsu, Ying-Ya
;
Yen, Shao-I
;
Li, Shou-Nan
;
環境工程研究所
EXAFS study of thermoelectric BiCuOSe: Effects of Cu vacancies
(2015-03-01)
Chou, Ta-Lei
;
Tewari, Girish C.
;
Chan, Ting-Shan
;
Hsu, Ying-Ya
;
Yamauchi, Hisao
Excellent thermoelectric performance has been reported for the ZrCuSiAs-type BiCuOSe derivatives; for these materials the transport properties can be effectively adjusted by chemical substitutions or by introducing Cu vacancies. In this work we compare stoichiometric BiCuSeO and its Cu-deficient derivative BiCu0.95SeO by utilizing temperature dependent extended X-ray absorption fine structure (EXAFS) measurements. Such a local probe evidences that Cu vacancies make the lattice more ductile and susceptible to temperature variation. (C) 2015 Elsevier Ltd. All rights reserved.
Heterojunction of Zinc Blende/Wurtzite in Zn1-xCdxS Solid Solution for Efficient Solar Hydrogen Generation: X-ray Absorption/Diffraction Approaches
(2015-10-14)
Hsu, Ying-Ya
;
Suen, Nian-Tzu
;
Chang, Chung-Chieh
;
Hung, Sung-Fu
;
Chen, Chi-Liang
In the past decade, inorganic semiconductors have been successfully demonstrated as light absorbers in efficient solar water splitting to generate chemical fuels. Pseudobinary semiconductors Zn1-xCdxS (0 <= x <= 1) have exhibited a superior photocatalytic reactivity of H-2 production from splitting of water by artificial solar irradiation without any metal catalysts. However, most studies had revealed that the extremely high efficiency with an optimal content of Zn1-xCdxS solid solution was determined as a result of elevating the conduction band minimum (CBM) and the width of bandgap. In addition to corresponding band structure and bandgap, the local crystal structure should be taken into account as well to determine its photocatalytic performance. Herein, we demonstrated the correlations between the photocatalytic activity and structural properties that were first studied through synchrotron X-ray diffraction and X-ray absorption spectroscopy. The crystal structure transformed from zinc blende to coexisted phases of major zinc blende and minor wurtzite phases at a critical point. The heterojunction formed by coexistence of zinc blende and wurtzite phases in the Zn1-xCdxS solid solution can significantly improve the separation and migration of photoinduced electron hole pairs. Besides, X-ray absorption spectra and UV-vis spectra revealed that the bandgap of the Zn0.45Cd0.55S sample extended into the region of visible light because of the incorporation of Cd element in the sample. These results provided a significant progress toward the realization of the photoelectrochemical mechanism in heterojunction between zinc blende and wurtzite phases, which can effectively separate the charge-carriers and further suppress their recombination to enhance the photocatalytic reactivity.
Heterojunction of zinc Blende/Wurtzite in Zn1-xCdxS solid solution for efficient solar hydrogen generation: X-ray absorption/diffraction spectroscopy approach
(2016-03-13)
Hsu, Ying-Ya
;
Suen, Nian-Tzu
;
Hong, Song-Fu
;
Chan, Ting-Shan
;
Chen, San-Yuan
Plasmon Inducing Effects for Enhanced Photoelectrochemical Water Splitting: X-ray Absorption Approach to Electronic Structures
(2012-08-01)
Chen, Hao Ming
;
Chen, Chih Kai
;
Chen, Chih-Jung
;
Cheng, Liang-Chien
;
Wu, Pin Chieh
Artificial photosynthesis using semiconductors has been investigated for more than three decades for the purpose of transferring solar energy into chemical fuels. Numerous studies have revealed that the introduction of plasmonic materials into photochemical reaction can substantially enhance the photo response to the solar splitting of water. Until recently, few systematic studies have provided clear evidence concerning how plasmon excitation and which factor dominates the solar splitting of water in photovoltaic devices. This work demonstrates the effects of plasmons upon an Au nanostructure-ZnO nanorods array as a photoanode. Several strategies have been successfully adopted to reveal the mutually independent contributions of various plasmonic effects under solar irradiation. These have clarified that the coupling of hot electrons that are formed by plasmons and the electromagnetic field can effectively increase the probability of a photochemical reaction in the splitting of water. These findings support a new approach to investigating localized plasmon-induced effects and charge separation in photoelectrochemical processes, and solar water splitting was used herein as platform to explore mechanisms of enhancement of surface plasmon resonance.
Reversible adapting layer produces robust single-crystal electrocatalyst for oxygen evolution
(2015-08-01)
Tung, Ching-Wei
;
Hsu, Ying-Ya
;
Shen, Yen-Ping
;
Zheng, Yixin
;
Chan, Ting-Shan
Electrochemically converting water into oxygen/hydrogen gas is ideal for high-density renewable energy storage in which robust electrocatalysts for efficient oxygen evolution play crucial roles. To date, however, electrocatalysts with long-term stability have remained elusive. Here we report that single-crystal Co3O4 nanocube underlay with a thin CoO layer results in a high-performance and high-stability electrocatalyst in oxygen evolution reaction. An in situ X-ray diffraction method is developed to observe a strong correlation between the initialization of the oxygen evolution and the formation of active metal oxyhydroxide phase. The lattice of skin layer adapts to the structure of the active phase, which enables a reversible facile structural change that facilitates the chemical reactions without breaking the scaffold of the electrocatalysts. The single-crystal nanocube electrode exhibits stable, continuous oxygen evolution for 41,000 h. This robust stability is attributed to the complementary nature of defect-free single-crystal electrocatalyst and the reversible adapting layer.
Semiconducting BiOCuSe Thermoelectrics and Its Metallic Derivative Bi2YO4Cu2Se2
(2015-05-01)
Chou, Ta-Lei
;
Tewari, Girish C.
;
Chan, Ting-Shan
;
Hsu, Ying-Ya
;
Chen, Jin-Ming
ZrCuSiAs-type mixed-anion oxychalcogenides and oxypnictides form a massive family of functional materials readily tailored to host diverse transport properties. Here we investigate semiconducting BiOCuSe, which has been considered as a promising candidate for intermediate-temperature thermoelectric applications, and its intergrowth derivative Bi2YO4Cu2Se2, by using X-ray absorption spectroscopy. Stronger anisotropy and bond covalency are revealed for the latter phase, and in contrast to the simple charge-balance scenario of [Bi3+O2-](+)[Cu+Se2-](-) in the former phase, mixed-valence Cu+/Cu2+ with a single coordination sphere is seen in the selenide block of Bi2YO4Cu2Se2, which gives rise to a metallic electrical conductivity.
The synergistic effect of a well-defined Au@Pt core-shell nanostructure toward photocatalytic hydrogen generation: interface engineering to improve the Schottky barrier and hydrogen-evolved kinetics
(2016)
Hung, Sung-Fu
;
Yu, Ya-Chu
;
Suen, Nian-Tzu
;
Tzeng, Guan-Quan
;
Tung, Ching-Wei
A well-defined co-catalyst system TiO2 nanotube-Au (core)-Pt (shell) was demonstrated to be the combination of the localized surface plasmon effect of gold and excellent proton reduction nature of platinum. Furthermore, surface engineering by the descending Fermi energies of gold and platinum was beneficial to electron transfer.
Thermoelectric misfit-layered cobalt oxides with interlayers of hydroxide and peroxide species
(2013-12-01)
Chou, Ta-Lei
;
Lybeck, Jenni
;
Chan, Ting-Shan
;
Hsu, Ying-Ya
;
Tewari, Girish C.
Among the thermoelectric misfit-layered cobalt oxides, [M(m)A(2)O(m+2)]qCoO(2), the parent m=0 phases exhibit divergent chemical features but are less understood than the more common m>0 members of the series. Here we synthesize Sr-for-Ca substituted [(Ca(1-x)Sr(x)c)(z)(O,OH)(2)](q)CoO2 zero phases up to x=0.2 through low-temperature hydrothermal conversion of precursor powders of the m=1 misfit system, [Co(Ca1-xSrx)(2)O-3](q)CoO2. In the zero-phase [(Ca1-xSrx)(z)(O,OH)(2)](q)CoO2 system, as the Sr content x increases the lattice expands anisotropically along the c axis such that the ab-plane dimension and the misfit parameter q remain essentially constant. X-ray absorption spectroscopy data suggest the presence of peroxide-type oxygen species in the (Ca1-xSrx)(z)(O,OH)(2) rock-salt block and together with infrared spectroscopy, thermogravimetric and low-temperature resistivity and thermopower measurements evidence that the isovalent Sr-for-Ca substitution controls the balance between the peroxide and hydroxide species in the (Ca1-x,Sr-x)(z)(O,OH)(2) block but leaves the valence of Co essentially intact in the CoO2 block. The higher electrical conductivity of the Sr-substituted phases is explained as a consequence of increased carrier mobility. (C) 2013 Elsevier Inc. All rights reserved.
Valence- and element-dependent water oxidation behaviors: in situ X-ray diffraction, absorption and electrochemical impedance spectroscopies
(2017-04-07)
Hsu, Chia-Shuo
;
Suen, Nian-Tzu
;
Hsu, Ying-Ya
;
Lin, Hsuan-Yu
;
Tung, Ching-Wei
Metal oxides of the spinel family have shown great potential towards the oxygen evolution reaction (OER), but the fundamental OER mechanism of spinel oxides is still far from being completely understood, especially for the role of the metal ions. Owing to various coordinated sites of divalent/trivalent metals ions and surface conditions (morphology and defects), it is a great challenge to have a fair assessment of the electrocatalytic performance of spinel systems. Herein, we demonstrated a series of MFe2O4 (M = Fe, Co, Ni, Zn) with a well-controlled morphology to achieve a comprehensive study of electrocatalytic activity toward OER. By utilizing several in situ analyses, we could conclude a universal rule that the activities for OER in the metal oxide systems were determined by the occurrence of a phase transformation, and this structural transformation could work well in both crystallographic sites (Td and Oh sites). Additionally, the divalent metal ion significantly dominated the formation of oxyhydroxide through an epitaxial relationship, which depended on the atomic arrangement at the interface of spinel and metal oxyhydroxide, while trivalent metal ions remained unchanged as a host lattice. The metal oxyhydroxide was formed during a redox reaction rather than being formed during OER. The occurrence of the redox reaction seems to accompany a remarkable increase in resistance and capacitance might result from the structural transformation from spinel to metal oxyhydroxide. We believe that the approaching strategies and information obtained in the present study can offer a guide to designing a promising electrocatalytic system towards the oxygen evolution reaction and other fields.