ORCID Profile
0000-0001-9546-8463
Current Organisation
Friedrich-Alexander-Universität Erlangen-Nürnberg
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Publisher: Wiley
Date: 07-05-2021
Abstract: Na 1/2 Bi 1/2 TiO 3 ‐based relaxor ferroelectrics are extensively investigated for use in transduction applications because of their relatively large electromechanical properties. Integration of these materials into devices, however, requires better temperature stability in addition to electromechanical properties. This work demonstrates a novel approach to enhance the temperature stability of the long‐range ferroelectric order as well as to enhance electromechanical properties in a non‐ergodic relaxor 0.93(Na 1/2 Bi 1/2 )TiO 3 ‐0.07BaTiO 3 (NBT‐7BT) without changing the chemical composition through, for ex le, chemical substitutions or second phase particles. The approach involves the room temperature deposition of copper electrodes directly on the relaxor ceramic substrate using the aerosol deposition (AD) method. The collision of solid‐state particles with the substrate surface during AD results in large impact and residual stresses, inherent to the AD process, which are shown with piezo‐response force microscopy to induce long‐range ferroelectric domain ordering in non‐ergodic relaxor NBT‐7BT. Using Raman spectroscopy, the magnitude and depth profile of the stress‐induced transformation are determined. It is demonstrated that deposition‐induced stresses significantly increase the temperature stability of the electromechanical properties, where long‐range ferroelectric ordering is observed up to 150 °C, which is approximately 41 °C higher than NBT‐7BT s les without the AD processed electrode. Moreover, the AD treatment also facilitates ferroelectric domain switching at a lower electric field, enabling maximum polarization at a relatively lower field and an enhancement in the piezoelectric response. It is shown that the deposition‐induced stress is responsible for such an enhancement. Importantly, this impact‐stress‐driven tailoring of electromechanical properties can potentially be utilized for other functional ceramic materials as well, where internal residual stress can result in enhanced functional properties.
Publisher: Elsevier BV
Date: 06-2022
Publisher: Springer Science and Business Media LLC
Date: 07-2022
DOI: 10.1007/S10853-022-07467-3
Abstract: The room temperature aerosol deposition method is especially promising for the rapid deposition of ceramic thick films, making it interesting for functional components in energy, mobility, and telecommunications applications. Despite this, a number of challenges remain, such as an enhanced electrical conductivity and internal residual stresses in as-deposited films. In this work, a novel technique that integrates a sacrificial water-soluble buffer layer was used to fabricate freestanding ceramic thick films, which allows for direct observation of the film without influence of the substrate or prior thermal treatment. Here, the temperature-dependent chemical and structural relaxation phenomena in freestanding BaTiO 3 films were directly investigated by characterizing the thermal expansion properties and temperature-dependent crystal structure as a function of oxygen partial pressure, where a clear nonlinear, hysteretic contraction was observed during heating, which is understood to be influenced by lattice defects. As such, aliovalent doping and atmosphere-dependent annealing experiments were used to demonstrate the influence of local chemical redistribution and oxygen vacancies on the thermal expansion, leading to insight into the origin of the high room temperature conductivity of as-deposited films as well as greater insight into the influence of the induced chemical, structural, and microstructural changes in room temperature deposited functional ceramic thick films. Graphical abstract
Publisher: Elsevier BV
Date: 03-2022
Publisher: Elsevier BV
Date: 10-2018
Publisher: Royal Society of Chemistry (RSC)
Date: 2023
DOI: 10.1039/D3TA00808H
Abstract: The annealing temperature and cooling rate influence on the structure and functional properties in K 1/2 Bi 1/2 TiO 3 .
Publisher: AIP Publishing
Date: 16-03-2020
DOI: 10.1063/1.5134554
Abstract: The influence of uniaxial compressive stress on small-signal relative permittivity and direct piezoelectric coefficient of polycrystalline Li-modified (K0.5Na0.5)NbO3 (0, 2, and 4 mol. % Li) was characterized as a function of temperature from 25 to 450 °C. These data reveal corresponding anomalies in both the dielectric and piezoelectric properties near the well-known structural phase transitions in (KxNa1 − x)NbO3. In particular, increasing stress was found to shift the orthorhombic–tetragonal (TO−T) and tetragonal–cubic (TC) phase boundaries to higher temperatures, thereby stabilizing the lower symmetry phases. Experimental results also show that stress up to a critical value flattens the piezoelectric response below TO−T, above which a monotonic decrease is observed. In contrast, permittivity is increased below TO−T with increasing stress. These results are used to construct a stress–temperature phase diagram of Li-modified (K0.5Na0.5)NbO3.
Publisher: Elsevier BV
Date: 08-2023
Publisher: Wiley
Date: 27-02-2022
DOI: 10.1111/JACE.18377
Abstract: Aerosol deposition (AD) is a room‐temperature film deposition method for the fabrication of scalable ferroelectric ceramic films on different substrates, which is particularly appealing for thick film energy storage applications. However, the electrical and mechanical properties of AD ferroelectric films are not yet satisfactorily understood. Here, we report the dielectric, energy storage, and mechanical properties of aerosol‐deposited BaTiO 3 (AD‐BT) thick films with nanosized grains by combining macroscopic electric measurements with indentation tests. We find that thermal annealing is an effective way to improve dielectric permittivity and polarization of the AD‐BT film, as well as to increase the hardness and Young's modulus of the film. However, crack formation in the annealed AD‐BT film is promoted in comparison to the as‐processed s le, suggesting that the interplay between the nanosized grains and release of the internal stress during annealing may have major consequences for the mechanical properties and hence should be taken into consideration in application.
Publisher: IOP Publishing
Date: 04-2022
Abstract: The miniaturization of electronic devices and power systems requires the fabrication of functional components in the form of micrometer-sized thick films. A major challenge is the integration of functional ceramics with metals, which are considered incompatible with high-temperature ceramic processing. To overcome the integration barrier, an aerosol deposition (AD) spray-coating method based on room temperature deposition can be used. By employing the AD method, we were able to deposit relaxor-ferroelectric 0.65Pb(Mg 1/3 Nb 2/3 )O 3 –0.35PbTiO 3 ceramic thick films on low-cost stainless-steel substrates. The as-deposited films were dense, with ∼97% of the theoretical density. Moreover, the post-deposition annealing at 500 °C did not result in any microstructural changes. Compared to the as-deposited films, the annealed films exhibit improved energy storage and electromechanical properties. The annealed thick films achieve a recoverable energy density of 15.1 J⋅cm −3 at an electric field of 1350 kV⋅cm −1 and an electric-field cycling stability of 5 million cycles. A piezoelectric response was detected through the entire film thickness by piezoelectric force microscopy. Macroscopic displacement measurements revealed a maximum relative strain of 0.38% at 1000 kV⋅cm −1 , corresponding to inverse effective piezoelectric coefficient of ∼40 pm⋅V −1 . In this study, we overcame the integration challenges and demonstrated the multifunctionalization of future ceramic-metal structures, as the deposited thick films on stainless steel exhibit energy storage capability and piezoelectric properties.
Publisher: Elsevier BV
Date: 11-2022
Publisher: Elsevier BV
Date: 09-2022
Publisher: Wiley
Date: 06-09-2019
DOI: 10.1111/JACE.16772
Abstract: A novel technique for the rapid room‐temperature deposition of porous ceramic, glass, or metal thick films using the aerosol deposition (AD) method is presented. The process is based on the co‐deposition of the desired film material and a second water‐soluble constituent, resulting in a ceramic‐ceramic composite. Following the subsequent removal of water‐soluble end member, a network of pores is retained. To demonstrate the process, porous BaTiO 3 thick films were fabricated through co‐deposition with NaCl. Microstructural images show the clear development of a porous structure, which was found to enhance the dielectric properties over dense thick films, possibly related to the lower extent of internal residual stress. This simple but highly effective porous structure fabrication can be applied to any film and substrate material stable in water and is promising for the application of AD‐processed films in gas sensors, solid oxide fuel cells, and humidity sensors.
Publisher: Wiley
Date: 17-12-2021
DOI: 10.1111/JACE.18269
Abstract: External thermal, electrical, and mechanical fields can induce structural phase transitions in lead‐free Li‐modified Na 0.5 K 0.5 NbO 3 ferroelectrics, which significantly influence the macroscopic electromechanical response. In particular, the relative stability of the polar monoclinic (or orthorhombic) and tetragonal phases under temperature and stress is critical to realize the ferroelectric and piezoelectric response. In this study, the effect of mechanical and thermal fields on the local structure in the vicinity of the monoclinic‐tetragonal (M‐T) phase boundary was investigated using a novel in situ combined uniaxial compressive stress‐ and temperature‐dependent Raman spectroscopy experimental arrangement. Experiments were performed up to 300°C and −200 MPa, clearly demonstrating stress‐induced M‐T phase transition in Li‐modified Na 0.5 K 0.5 NbO 3 . A stress‐temperature phase diagram has been established based on the change in vibrational modes. It was possible to correlate the relative permittivity singularities previously observed to a given stage of the M‐T phase transition using ratio between characteristic Raman band areas. In addition, the measurement method reported here can be applied to other functional ceramics to investigate the influence of mechanical fields on local structure.
Publisher: Elsevier BV
Date: 12-2021
Location: No location found
No related grants have been discovered for Udo Eckstein.