Browsing by Author "Burghard, Zaklina"

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Open Access
Behaviour of glasses and polymer derived amorphous ceramics under contact stress
(2004) Burghard, Zaklina; Aldinger, Fritz (Prof. Dr. rer. nat.)
A Vickers indentation study is presented focusing on the crack opening displacement (COD) method as one new approach for fracture toughness determination. COD measurements over the entire radial indentation crack lengths enable quantitative evaluations of residual stresses at the contact site. An alternative estimation of toughness, without knowledge of the calibration parameter which is required for the indentation crack length (ICL) method, is provided by COD measurements in the vicinity of the crack tip. In addition, this method allows to study slow crack growth which is another important phenomenon. The measurements generally require recourse to high magnification, high accuracy observation techniques like atomic force microscopy (AFM) that has been used in this work. Two different types of glasses, as reference materials, and fully dense, amorphous SiCN ceramics produced from precursor polymers through a casting route are investigated. Soda lime and borosilicate glass have been selected, which are well documented to behave as "normal" and "anomalous" glass under contact stress, respectively. A set of four different pyrolysis temperatures for polymer-derived ceramics differing in pyrolysis temperature (800°C, 900°C, 1000°C, 1100°C), were chosen. Indents for a given load in the investigated materials reveal substantially shorter radial cracks and smaller opening in polymer derived SiCN ceramics. This effect is attributed to the different levels of residual elastic-plastic contact stresses that drive the radial crack formation. In soda-lime glass, the plastic component of contact deformation is shear-driven, with conservation of material volume; in borosilicate, as well as polymer-derived amorphous SiCN ceramics, the plastic component is compression-driven, with resultant material densification. The latter deformation mode is less effective in expanding the surrounding elastic material outward upon removal of the indenter. Hence, the opening and crack lengths are consequently smaller in the amorphous SiCN ceramics which is in agreement with the calculated lowest residual stress level in these materials. A higher toughness in polymer derived amorphous SiCN ceramics relative to the glasses is obtained, and an increase with increasing pyrolysis temperature. The influence of subcritical crack growth on the crack opening profiles was investigated only in case of the glasses since the polymer-derived amorphous SiCN ceramics did not show subcritical crack length growth. The methodology presented in this study should prove useful as a means of characterizing the deformation response of glasses and other brittle materials under contact stress.
Open Access
Binder-free V2O5 cathode for high energy density rechargeable aluminum-ion batteries
(2020) Diem, Achim M.; Fenk, Bernhard; Bill, Joachim; Burghard, Zaklina
Nowadays, research on electrochemical storage systems moves into the direction of post-lithium-ion batteries, such as aluminum-ion batteries, and the exploration of suitable materials for such batteries. Vanadium pentoxide (V2O5) is one of the most promising host materials for the intercalation of multivalent ions. Here, we report on the fabrication of a binder-free and self-supporting V2O5 micrometer-thick paper-like electrode material and its use as the cathode for rechargeable aluminum-ion batteries. The electrical conductivity of the cathode was significantly improved by a novel in-situ and self-limiting copper migration approach into the V2O5 structure. This process takes advantage of the dissolution of Cu by the ionic liquid-based electrolyte, as well as the presence of two different accommodation sites in the nanostructured V2O5 available for aluminum-ions and the migrated Cu. Furthermore, the advanced nanostructured cathode delivered a specific discharge capacity of up to ~170 mAh g-1 and the reversible intercalation of Al3+ for more than 500 cycles with a high Coulomb efficiency reaching nearly 100%. The binder-free concept results in an energy density of 74 Wh kg-1, which shows improved energy density in comparison to the so far published V2O5-based cathodes. Our results provide valuable insights for the future design and development of novel binder-free and self-supporting electrodes for rechargeable multivalent metal-ion batteries associating a high energy density, cycling stability, safety and low cost.
Open Access
Cuttlebone-like V2O5 nanofibre scaffolds - advances in structuring cellular solids
(2017) Knöller, Andrea; Runčevski, Tomče; Dinnebier, Robert E.; Bill, Joachim; Burghard, Zaklina
Open Access
Fast one‐step fabrication of highly regular microscrolls with controllable surface morphology
(2023) Diem, Achim M.; Bill, Joachim; Burghard, Zaklina
Although rolling origami technology has provided convenient access to three-dimensional (3D) microstructure systems, the high yield and scalable construction of complex rolling structures with well-defined geometry without impeding functionality has remained challenging. The straightforward, one-step fabrication that uses external mechanical stress to scroll micrometer thick, flexible planar films with centimeter lateral dimensions into tubular or spiral geometry within a few seconds is demonstrated. The method allows controlling the scrolls’ diameter, number of windings and nanostructured surface morphology, and is applicable to a wide range of functional materials. The obtained 3D structures are highly promising for various applications including sensors, actuators, microrobotics, as well as energy storage and electronic devices.
Open Access
Highly porous free-standing rGO/SnO2 pseudocapacitive cathodes for high-rate and long-cycling Al-ion batteries
(2020) Jahnke, Timotheus; Raafat, Leila; Hotz, Daniel; Knöller, Andrea; Diem, Achim Max; Bill, Joachim; Burghard, Zaklina
Establishing energy storage systems beyond conventional lithium ion batteries requires the development of novel types of electrode materials. Such materials should be capable of accommodating ion species other than Li+, and ideally, these ion species should be of multivalent nature, such as Al3+. Along this line, we introduce a highly porous aerogel cathode composed of reduced graphene oxide, which is loaded with nanostructured SnO2. This binder-free hybrid not only exhibits an outstanding mechanical performance, but also unites the pseudocapacity of the reduced graphene oxide and the electrochemical storage capacity of the SnO2 nanoplatelets. Moreover, the combination of both materials gives rise to additional intercalation sites at their interface, further contributing to the total capacity of up to 16 mAh cm-3 at a charging rate of 2 C. The high porosity (99.9%) of the hybrid and the synergy of its components yield a cathode material for high-rate (up to 20 C) aluminum ion batteries, which exhibit an excellent cycling stability over 10,000 tested cycles. The electrode design proposed here has a great potential to meet future energy and power density demands for advanced energy storage devices.
Open Access
Peptide controlled shaping of biomineralized tin(II) oxide into flower-like particles
(2019) Kilper, Stefan; Jahnke, Timotheus; Wiegers, Katharina; Grohe, Vera; Burghard, Zaklina; Bill, Joachim; Rothenstein, Dirk
The size and morphology of metal oxide particles have a large impact on the physicochemical properties of these materials, e.g., the aspect ratio of particles affects their catalytic activity. Bioinspired synthesis routes give the opportunity to control precisely the structure and aspect ratio of the metal oxide particles by bioorganic molecules, such as peptides. This study focusses on the identification of tin(II) oxide (tin monoxide, SnO) binding peptides, and their effect on the synthesis of crystalline SnO microstructures. The phage display technique was used to identify the 7-mer peptide SnBP01 (LPPWKLK), which shows a high binding affinity towards crystalline SnO. It was found that the derivatives of the SnBP01 peptide, varying in peptide length and thus in their interaction, significantly affect the aspect ratio and the size dimension of mineralized SnO particles, resulting in flower-like morphology. Furthermore, the important role of the N-terminal leucine residue in the peptide for the strong organic-inorganic interaction was revealed by FTIR investigations. This bioinspired approach shows a facile procedure for the detailed investigation of peptide-to-metal oxide interactions, as well as an easy method for the controlled synthesis of tin(II) oxide particles with different morphologies.
Open Access
Piezoelectric templates - new views on biomineralization and biomimetics
(2016) Stitz, Nina; Eiben, Sabine; Atanasova, Petia; Domingo, Neus; Leineweber, Andreas; Burghard, Zaklina; Bill, Joachim
Biomineralization in general is based on electrostatic interactions and molecular recognition of organic and inorganic phases. These principles of biomineralization have also been utilized and transferred to bio-inspired synthesis of functional materials during the past decades. Proteins involved in both, biomineralization and bio-inspired processes, are often piezoelectric due to their dipolar character hinting to the impact of a template’s piezoelectricity on mineralization processes. However, the piezoelectric contribution on the mineralization process and especially the interaction of organic and inorganic phases is hardly considered so far. We herein report the successful use of the intrinsic piezoelectric properties of tobacco mosaic virus (TMV) to synthesize piezoelectric ZnO. Such films show a two-fold increase of the piezoelectric coefficient up to 7.2 pm V−1 compared to films synthesized on non-piezoelectric templates. By utilizing the intrinsic piezoelectricity of a biotemplate, we thus established a novel synthesis pathway towards functional materials, which sheds light on the whole field of biomimetics. The obtained results are of even broader and general interest since they are providing a new, more comprehensive insight into the mechanisms involved into biomineralization in living nature.
Open Access
Strengthening of ceramic-based artificial nacre via synergistic interactions of 1D vanadium pentoxide and 2D graphene oxide building blocks
(2017) Knöller, Andrea; Lampa, Christian P.; Cube, Felix von; Zeng, Tingying Helen; Bell, David C.; Dresselhaus, Mildred S.; Burghard, Zaklina; Bill, Joachim