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RISS 인기검색어
- 검색키워드
- 저자 : Wilfried Wunderlich (검색결과 3 건)
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Wilfried Wunderlich,Torsten Oekermann,Lei Miao,Nguyen Thi Hue,Sakae Tanemura,Masaki Tanemura 한양대학교 세라믹연구소 2004 Journal of Ceramic Processing Research Vol.5 No.4
The electronic properties of anatase, rutile and ZnO thin films are of interest for many applications such as photocatalysis, or dye-sensitised solar cells. This paper describes the correlation between microstructure and electronic properties of photoactive TiO2 and ZnO thin films, which are based on experimental data and are interpreted by ab-initio simulations. This study considers the influence of three main factors on the optical and electrical properties: Strain of epitaxially grown thin films, nano-particle- and nano-pore- structures, and finally the interface to adsorbed dye molecules. The first part describes the search for a suitable substrate to grow titania layers with a smaller band-gap and ab-initio simulations showed excellent agreement to the experimental data. A narrow band gap is predicted for strained lattice constants in the a-direction and compressed in the c-direction. The second part describes the fabrication of nano-porous thin films by sol-gel processing using appropriate precursor solutions (titanium-tetra-iso-propanol(TTIP), di-ethanol-amine (DEA)) applied on suitable nanotemplates. Due to the surface curvatures the nano-porous TiO2 has a narrow band gap, while nano-particles of titania show a larger band-gap. In the third part Dvxα ab-initio simulations were applied to dye-sensitized solar cells (DSSC), based on ZnO and TiO2. The results are compared to experimental data obtained for different dyes on nanoporous electrodeposited ZnO films. The ranking in efficiency found experimentally for the different combinations could be explained by the calculation results. This finding is discussed in the view of further optimization of solar cells.
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Calculations on different length scales for improving processing of nanoceramics
Wilfried Wunderlich 한양대학교 세라믹연구소 2004 Journal of Ceramic Processing Research Vol.5 No.1
Advanced processing of nano-ceramic composite materials requires an understanding of physical phenomena on an atomistic scale by ab-initio calculations. This overview continues a previous report and is divided into three parts. After describing the goals and the range of possible applications of such simulations, the needs for simulations of new applications of ceramics, namely for photovoltaic and thermoelectric materials, are briefly summarized. The most challenging subject for ab-initio calculations, however, is an understanding of physical phenomena in aqueous solutions and their present results are described in the third part. Based on experimental results, the simulation of Al-Mg-spinel formation with different methods, the discrete element method (DEM) and Molecular Dynamics (MD) is described. The appropriate approach for the numerical treatment of these many-particle interactions in liquids is the Voronoi- method, for which some new ideas are presented in this paper. For ab-initio calculations the software Vasp with its great facilities is appropriate.
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Microstructure and seebeck voltage of NaTaO3 composite ceramics with additions of Mn, Cr, Fe or Ti
Wilfried Wunderlich,Susumu Soga 한양대학교 세라믹연구소 2010 Journal of Ceramic Processing Research Vol.11 No.2
This paper reports about Seebeck measurements of the perovskite phase NaTaO3. To increase the carrier concentration,specimens including metallic transition metals such as Mn, Cr, Fe, Ti were sintered at 1273 K and 1473 K. Mircostructural characterization by SEM and XRD showed that besides the perovskite phase, transition metal oxides are present. The solubility limit of NaTaO3 increases with the sintering temperature and is about 17% in the case of Fe after sintering at 1473 K for 10 h. For NaTaO3 with 50 mol% Fe2O3 at a temperature difference of 800 K a Seebeck voltage of −320 mV was measured. This is the highest Seebeck voltage among all the specimens and leads to a Seebeck coefficient of −0.45 mV/K. The specific electric resistivity decreases with an increase in the temperature from 50MΩm at room temperature to 5 Ωm at 1273 K. The power factor of this new n-type thermoelectric candidate material is estimated.
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