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Paulus, Daniel ; Schneider, Jürgen ; Schönauer-Kamin, Daniela ; Moos, Ralf:
Revealing a new room temperature deposition mechanism for materials with layered-type crystal structure by a synchrotron study.
2025
Veranstaltung: International Symposium on Green Processing for Advanced Ceramics - IGPAC 2025
, 5.10.-9.10.2025
, Ise-Shima/Mie, Japan.
(Veranstaltungsbeitrag: Kongress/Konferenz/Symposium/Tagung
,
Poster
)
Abstract
The powder aerosol deposition method (PAD or ADM) is a novel coating technique that facilitates the deposition of dense ceramic films at room temperature. In this study, an anomaly of the deposition mechanism is presented, which forms a microstructure in the films that is atypical for PAD in materials with layer-like crystal structures (shown here on misfit-layered calcium cobalt oxide). The results of several studies are summarized and put into context with each other.
Calcium cobalt oxide (Ca3Co4O9-δ, CCO) was deposited on aluminum oxide and thermoelectrically characterized. In addition, films were deposited on a silicon wafer with (9 1 1) orientation to characterize the microstructure of the CCO film by lab XRD in Bragg-Brentano geometry. The cross-sectional area of the films on alumina was also investigated as a fracture surface using scanning electron microscopy. SEM revealed much coarser structures on the fracture surface of the CCO films than on the fracture surfaces of typical PAD films, which typically have small and grainy morphologies. The XRD pattern shows only (0 0 l) reflexes due to the strong fiber texture of the film. Although this shows a fiber texture, it makes it impossible to evaluate the data using Rietveld refinement.
In order to investigate this anomaly in more detail, a further study was carried out. In this study, films of titanium oxide (TiO2, rutile phase) and calcium cobalt oxide (Ca3Co4O9-δ, CCO) were deposited on soda lime glass substrates. While the anomaly of the microstructure was to be investigated on CCO, titanium oxide was to serve as a reference for a material that forms a typical PAD film. In addition, the behavior of the films during heat treatment was investigated. One third of the samples were left untreated, one third were heat-treated at 300 °C for one hour and one third were heat-treated at 600 °C. The samples were characterized using X-ray diffraction (XRD) at the German Electron Synchrotron (DESY) in transmission geometry and the cross-section of the fracture surface was examined using scanning electron microscopy (SEM). The XRD data were analyzed employing full-profile methods in the software “TOPAS Academic” to derive lattice parameters, crystallite size, and microstrain.
In these investigations, titanium oxide shows a microstructure typical for PAD. The material is nanocrystalline with a crystallite size in the range of 10 to 20 nm. There is only a slight texture and the fracture surface shows fine granular structures. In contrast, the fracture surface of the CCO-films shows angular, layered structures in the 1 μm size range. The evaluation of the synchrotron XRD data using Rietveld refinement suggests a crystallite size of at least 1 μm. In contrast, a crystallite size of 19 nm was determined for the titanium oxide films, which is in the typical range for PAD films. This can already be seen qualitatively in the diffraction patterns. The reflections of the CCO are significantly narrower than those of the TiO2. The crystallite size broadening therefore occurs much more strongly in the TiO2 films.
In contrast to TiO2, CCO has a very unusual crystal structure. It is a misfit-layered structure, in which layers of pseudo hexagonal cobalt oxide alternate with layers of calcium cobalt oxide in rock salt type. It is also a so-called incommensurate structure. This means that the translational symmetry of the layers has a difference in length in one direction and the ratio of the lengths of these layers is an irrational number. This, of course, fundamentally changes the fracture and deformation behavior of CCO-crystals compared to TiO2.
For TiO2, we expect typical ceramic behavior and, therefore, the typical RTIC mechanism as described by Akedo should occur. Polycrystalline ceramic particles with a size of about 1 μm hit a substrate surface or existing layer at high speed and break into fragments of a few 10 nm in size. Subsequent particles then “hammer” these fragments and break them down further (hammering effect).
The microstructure of the CCO films indicates a different deposition mechanism. The crystal structure can be imagined as corrugated plates that can be moved very easily in the direction of the misfit. Accordingly, an impact on a substrate or an existing film is more likely to result in a deformation that is similar to the deformation of a stack of paper placed on an uneven surface (paper pile model). The deformation of the CCO crystals is energetically favored by their structure compared to the break-up. The direct deposition mechanism or the adhesion of the crystals is achieved by positive locking with the existing surface.
As the deposition of a large proportion of the particles means that more material is deposited at the same time, the deposition rate increases. Higher film thicknesses are also possible due to the lower intrinsic compressive film stress that occurs with this deposition mechanism.
The principle that materials with a layer-like crystal structure can be deposited significantly better with the PAD can also be transferred to other materials with a layer-like crystal structure and can be demonstrated using films with an extraordinary thickness that were deposited in a very short time.
Weitere Angaben
| Publikationsform: | Veranstaltungsbeitrag (Poster) |
|---|---|
| Begutachteter Beitrag: | Ja |
| Institutionen der Universität: | Fakultäten > Fakultät für Ingenieurwissenschaften Fakultäten > Fakultät für Ingenieurwissenschaften > Lehrstuhl Funktionsmaterialien > Lehrstuhl Funktionsmaterialien - Univ.-Prof. Dr.-Ing. Ralf Moos Profilfelder > Advanced Fields > Neue Materialien Forschungseinrichtungen > Zentrale wissenschaftliche Einrichtungen > Bayreuther Materialzentrum - BayMAT |
| Titel an der UBT entstanden: | Ja |
| Themengebiete aus DDC: | 600 Technik, Medizin, angewandte Wissenschaften > 620 Ingenieurwissenschaften |
| Eingestellt am: | 13 Okt 2025 07:07 |
| Letzte Änderung: | 13 Okt 2025 07:07 |
| URI: | https://eref.uni-bayreuth.de/id/eprint/94873 |