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698 results on '"Hoffmann, Michael J."'

1. Consequences of hydroxyl generation by the silica/water reaction

Author

Fett, Theo, Schell, Karl G., Bucharsky, Ethel C., Rizzi, Gabriele, Hettich, Pascal, Wagner, Susanne, and Hoffmann, Michael J.

Subjects
Quarzglas, Hydroxylbildung, Schwellen, Diffussion, Wasser/Quarzglas Reaktion, silica, silica/water reaction, swelling, diffusion, bic Book Industry Communication::T Technology, engineering, agriculture::TG Mechanical engineering & materials
Abstract

Water diffusing into silica surfaces gives rise for several effectson diffusion behaviour and mechanical properties. Water added to silica glass increases its specific volume so that the silica expands near the surface. Mechanical boundary conditions give rise for compressive “swelling stresses”. This fact provides a tool for the interpretation of many experimental observations from literature.

Published
2022
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2. Defect redistribution along grain boundaries in SrTiO3 by externally applied electric fields

Author

Qu, Boyi, Eiteneer, Daria, Hughes, Lauren A, Preusker, Jan-Helmut, Wood, Joseph, Rheinheimer, Wolfgang, Hoffmann, Michael J, and van Benthem, Klaus

Subjects
Affordable and Clean Energy, Grain boundary, Electric field, STEM, Oxygen vacancy migration, Materials Engineering, Materials
Abstract

During thermal annealing at 1425 °C nominal electric field strengths of 50 V/mm and 150 V/mm were applied along the grain boundary planes of a near 45° (100) twist grain boundary in SrTiO3. Electron microscopy characterization revealed interface expansions near the positive electrode around 0.8 nm for either field strength. While the interface width decreased to roughly 0.4 nm after annealing at 50 V/mm, the higher field strength caused decomposition of the boundary structure close to the negative electrode. Electron energy-loss and X-ray photoelectron spectroscopies demonstrated an increased degree of oxygen sublattice distortion at the negative electrode side, and enhanced concentrations of Ti3+ and Ti2+ compared to bulk for both single crystals and bicrystals annealed with an external electric field, respectively. Oxygen migration due to the applied electric field causes the observed alteration of grain boundary structures. At sufficiently high field strength the agglomeration of anion vacancies may lead to the decomposition of the grain boundary.

Published
2023

4. Materials Based Lifetime Assessment of Porcelain Insulators

Author

Schulte-Fischedick, Jan, Singh, Prashant, Lehretz, Fabian, Hettich, Pascal, Bucharsky, Claudia, Schell, Günter, Hoffmann, Michael J., Marthen, Wolfgang, Wekenborg, Heinrich, Pohlmann, Heinrich, Angrisani, Leopoldo, Series Editor, Arteaga, Marco, Series Editor, Panigrahi, Bijaya Ketan, Series Editor, Chakraborty, Samarjit, Series Editor, Chen, Jiming, Series Editor, Chen, Shanben, Series Editor, Chen, Tan Kay, Series Editor, Dillmann, Rüdiger, Series Editor, Duan, Haibin, Series Editor, Ferrari, Gianluigi, Series Editor, Ferre, Manuel, Series Editor, Hirche, Sandra, Series Editor, Jabbari, Faryar, Series Editor, Jia, Limin, Series Editor, Kacprzyk, Janusz, Series Editor, Khamis, Alaa, Series Editor, Kroeger, Torsten, Series Editor, Liang, Qilian, Series Editor, Martin, Ferran, Series Editor, Ming, Tan Cher, Series Editor, Minker, Wolfgang, Series Editor, Misra, Pradeep, Series Editor, Möller, Sebastian, Series Editor, Mukhopadhyay, Subhas, Series Editor, Ning, Cun-Zheng, Series Editor, Nishida, Toyoaki, Series Editor, Pascucci, Federica, Series Editor, Qin, Yong, Series Editor, Seng, Gan Woon, Series Editor, Speidel, Joachim, Series Editor, Veiga, Germano, Series Editor, Wu, Haitao, Series Editor, Zhang, Junjie James, Series Editor, and Németh, Bálint, editor

Published
2020
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18. Materials Based Lifetime Assessment of Porcelain Insulators

Author

Schulte-Fischedick, Jan, primary, Singh, Prashant, additional, Lehretz, Fabian, additional, Hettich, Pascal, additional, Bucharsky, Claudia, additional, Schell, Günter, additional, Hoffmann, Michael J., additional, Marthen, Wolfgang, additional, Wekenborg, Heinrich, additional, and Pohlmann, Heinrich, additional

Published
2019
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24. Uncovering the symmetry of the induced ferroelectric phase transformation in polycrystalline barium titanate.

Author

Lemos da Silva, Lucas, Lee, Kai-Yang, Petrick, Simon, Etter, Martin, Schökel, Alexander, Chaves, Cesar Giovanni, Oliveira da Silva, Nilson, Lalitha, K. V., Picht, Gunnar, Hoffmann, Michael J., and Hinterstein, Manuel

Subjects
BARIUM titanate, PHASE transitions, ELECTROMECHANICAL effects, PIEZOELECTRICITY, PARTICLE size distribution, ELECTRIC field effects, CHARGE carrier mobility
Abstract

Microstructural design is a widespread approach to tailor the properties of functional materials with the size effect being an effective constraint that modifies physical phenomena. In this work, we investigate the grain size effect on the properties and the electric field induced phase transformation behavior in barium titanate. A broad range of unimodal average grain size distribution between 0.4 and 15 μm was successfully sintered avoiding abnormal grain growth. Samples with a grain size close to the range of 1–2 μm, balancing microstructural strain, presence, and mobility of domain walls to allow the field induced crystal phase transformation, showed optimal electromechanical and dielectric properties. By means of in situ high energy x-ray diffraction and a high-resolution multianalyzer detector, we distinguish and quantify a tetragonal–orthorhombic phase transformation induced by an electric field, providing unambiguous proof of this induced phase transformation. These results contribute to the understanding of fundamental questions about the piezoelectric effect in barium titanate and consequently other similar systems. [ABSTRACT FROM AUTHOR]

Published
2021
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37. Grain size effects in donor doped lead zirconate titanate ceramics.

Author

Picht, Gunnar, Khansur, Neamul H., Webber, Kyle G., Kungl, Hans, Hoffmann, Michael J., and Hinterstein, Manuel

Subjects
LEAD zirconate titanate, GRAIN size, STRAINS & stresses (Mechanics), ZIRCONIUM boride, X-rays, DIELECTRIC properties, CERAMICS
Abstract

The ferroelectric, ferroelastic, and dielectric properties as well as the crystal structure were investigated for polycrystalline donor doped lead zirconate titanate (PZT) with grain sizes ranging from 0.25 to 5 μm, which were prepared using a novel zirconium titanium hydrate precursor (ZTH) with a specific surface area of 310 m2/g. Piezoforce microscopy was used to investigate the change in the domain structure, revealing a change in the domain configuration from a complex 3D structure to a simple lamellar domain formation at a 1 μm grain size that corresponded to a rapidly increasing internal mechanical stress observed with in situ synchrotron x-ray experiments. The correlation between the change in domain configuration, increasing internal stresses, effects of poling on the crystal structure, and the macroscopic ferroelectric and ferroelastic properties are discussed in detail, allowing a deeper understanding of size effects in polycrystalline donor doped PZT ceramics. [ABSTRACT FROM AUTHOR]

Published
2020
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