Tzu-Wen Huang

Empa - Swiss Federal Laboratories for Materials Science and Technology, Duebendorf, Zurich, Switzerland

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Publications (5)23.68 Total impact

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    ABSTRACT: In this work, we applied various measurement techniques in order to evaluate the possibility of the introduction of Al and its actual level at Li site in LiFePO4 positive electrode material for Li-ion batteries. Rietveld refinement of neutron diffraction data indicated that Al is incorporated into Li site, however, in lower amount than expected, and that lithium content is substantially depressed. The observed trends were qualitatively supported by results of ICP OES analysis. In addition, the oxygen content in Li1–3xAlxFePO4 was found to decrease with Al doping. The introduction of relatively small amount of dopant could be an effective route to produce single-phase, highly lithium-deficient lithium iron phosphate.
    Solid State Ionics 02/2015; 270. DOI:10.1016/j.ssi.2014.12.004 · 2.11 Impact Factor
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    ABSTRACT: Anodization of α-Fe(2)O(3) (hematite) electrodes in alkaline electrolyte under constant potential conditions the electrode surface in a way that an additional current wave occurs in the cyclic voltammogram. The energy position of this current wave is closely below the potential of the anodization treatment. Continued cycling or exchanging of the electrolyte causes depletion of this new feature. The O 1s and Fe 2p core-level X-ray photoelectron spectra (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectra of such conditioned hematite exhibit a chemical shift towards higher binding energies, in line with the general perception that anodization generates oxide species with dielectric properties. The valence band XPS and particularly the iron resonant valence band photoemission spectra, however, are shifted towards the opposite direction, that is, towards the Fermi energy, suggesting that hole doping on hematite has taken place during anodization. Quantitative analysis of the Fe 2p resonant valence band photoemission spectra shows that the spectra obtained at the Fe 2p absorption threshold are shifted by virtually the same energy as the anodization potential towards the Fermi energy. The tentative interpretation of this observation is that anodization forms a surface film on the hematite that is specific to the anodization potential.
    ChemPhysChem 08/2012; 13(12):2937-44. DOI:10.1002/cphc.201200074 · 3.36 Impact Factor
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    ABSTRACT: Substoichiometric tungsten oxide films of approximately 10 nm thickness deposited with pulsed laser ablation on single-crystal TiO2 substrates with (001) and (110) orientation show defect states near the Fermi energy in the valence-band X-ray photoelectron spectroscopy (XPS) spectra. The spectral weight of the defect states is particularly strong for the film grown on the (001) surface. In situ XPS under an oxygen pressure of 100 mTorr shows that the spectral weight of the defect states decreases significantly at 500 K for the film on the (110) substrate, whereas that of the film grown on the (001) substrate remains the same at a temperature up to 673 K. Furthermore, diffusion of titanium from the substrate to the film surface is observed on the (110) substrate, as is evidenced by the sudden appearance of the Ti 2p core level signature above 623 K and below 673 K. The film grown on the (001) surface does not show such an interdiffusion effect, which suggests that the orientation of the substrate can have a significant influence on the high-temperature integrity of the tungsten oxide films. Quantitative analysis of the O Is core level XPS spectra shows that chemisorbed water from sample storage under ambient conditions is desorbed during heating under oxygen exposure.
    Chemistry of Materials 08/2012; 24(17). DOI:10.1021/cm301829y · 8.54 Impact Factor
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    ABSTRACT: The BaCe0.8Y0.2O3-{\delta} proton conductor under hydration and under compressive strain has been analyzed with high pressure Raman spectroscopy and high pressure x-ray diffraction. The pressure dependent variation of the Ag and B2g bending modes from the O-Ce-O unit is suppressed when the proton conductor is hydrated, affecting directly the proton transfer by locally changing the electron density of the oxygen ions. Compressive strain causes a hardening of the Ce-O stretching bond. The activation barrier for proton conductivity is raised, in line with recent findings using high pressure and high temperature impedance spectroscopy. The increasing Raman frequency of the B1g and B3g modes thus implies that the phonons become hardened and increase the vibration energy in the a-c crystal plane upon compressive strain, whereas phonons are relaxed in the b-axis, and thus reveal softening of the Ag and B2g modes. Lattice toughening in the a-c crystal plane raises therefore a higher activation barrier for proton transfer and thus anisotropic conductivity. The experimental findings of the interaction of protons with the ceramic host lattice under external strain may provide a general guideline for yet to develop epitaxial strained proton conducting thin film systems with high proton mobility and low activation energy.
    The Journal of Physical Chemistry C 11/2011; 115(48). DOI:10.1021/jp208525j · 4.84 Impact Factor
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    ABSTRACT: INTRODUCTION The structure and physicochemical properties of tungsten oxide have sparked interest by scientists and engineers for a long time because of its relevance for technological applications as photoelectrochemical cell anodes, gas sensors, and photochro-mic materials, for example. 1,2 On the basis of a study of defect-free and altered WO 3 surfaces with photoelectron spectroscopy, it has been speculated that the properties of WO 3 depend critically on the defect states in the bulk and on the surface, rather than on its intrinsic nature. 3 An early bulk and surface specific electronic structure study of WO 3 is presented in ref 4, where in particular it was found that the perfect (100) surface has no defect states in the band gap. WO 3 belongs to a class of materials that can tolerate deviations from stoichiometry by adjustment of oxygen octahedral using shear mechanisms, without formation of oxygen vacancies. 3 This was already earlier suggested by Matthias' observation that WO 3 single crystals were remarkably soft. 5 In the oxygen octaheder, the e g orbitals (d x 2 Ày 2, d z 2) of W orient directly to the oxygen atoms, whereas the t 2g orbitals (d xy , d yz , d zx) point between the coordinating ligands. 4 The corresponding calculated density of states is illustrated in Figure 3 in ref 4. The defect free (100) surface has a barely noticeable small density of states in the pÀd band gap, but surface states can be induced by creating oxygen Received: March 13, 2011 Revised:
    The Journal of Physical Chemistry C 07/2011; 115(33):16411-16417. DOI:10.1021/jp202375h · 4.84 Impact Factor