Aerosol Deposition Method: Co-deposition of functional materials and fillers to replace a subsequent thermal treatment

• Applicant: Professor Dr.-Ing. Ralf Moos
• Subject Area: Synthesis and Properties of Functional Materials
• Term: from 2018 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 408251943

• Final Report Year: 2023

Final Report Abstract

The present project dealt with the substitution of a thermal post-treatment step in the production of layers that are produced by the so-called powder aerosol deposition method (PADM or PAD). In the research preceding this project, it had been found that the electronic and ionic conductivity of PAD layers is far below that of the same material in bulk form. It was also found that there is a high intrinsic compressive stress in the layers. Heat treatment could, on the one hand, increase the electrical or ionic conductivity by orders of magnitude and, on the other hand, relax the compressive stress. At the time of the application, it was assumed that there was a correlation between the compressive stress occurring and the low electrical or ionic conductivity. In a subsequent heat treatment, the compressive stress would then be relaxed and consequently the conductivity increased. For this reason, an attempt was made in this project to replace this heat treatment step by adding a soft component. The soft component was intended to absorb a large portion of the strain presumed to produce the compressive stress. However, in the course of the project it was shown that the increase in electronic/ionic conductivity is not due to the intrinsic compressive stress, but is caused by lattice distortions. They can be measured by XRD as a so-called microstrain. Likewise, an equation could be derived at which the maximum conductivity increase is reached. For this purpose, the melting temperature can be used for estimating the ideal annealing temperature. Furthermore, it was shown that the relaxation of the intrinsic compressive stress occurs at lower temperatures than the annealing or degradation of the microstrain. At 200 °C - 350 °C, this phenomenon is actually in a temperature range where no deformation or stress relaxation would be expected. However, this phenomenon could be conclusively explained by the crystallite size of the layers. With a crystallite size of about 25 nm, the material behavior is strongly influenced by the high grain boundary content and the material behaves like a nanomaterial. While the original project objective turned out not to be feasible, the processes that lead to the increase in conductivity of electronically or ionically conductive layers were elucidated instead. Furthermore, the mechanisms leading to the reduction of compressive stress were also clarified. However, the results of the investigations, which disproved that the project could work at all, are more far-reaching and more valuable than the insights that a success of the project would have brought.

Publications

• Laser‐Annealing of Thermoelectric CuFe0.98Sn0.02O2 Films Produced by Powder Aerosol Deposition Method. Advanced Materials Interfaces, 7(22).
  Nazarenus, Tobias; Kita, Jaroslaw; Moos, Ralf & Exner, Jörg
  
• What Happens during Thermal Post‐Treatment of Powder Aerosol Deposited Functional Ceramic Films? Explanations Based on an Experiment‐Enhanced Literature Survey. Advanced Materials, 32(19).
  Exner, Jörg; Nazarenus, Tobias; Hanft, Dominik; Kita, Jaroslaw & Moos, Ralf
  
• Influence of filler materials on the internal stresses and thermal annealing behavior of ceramic films formed by Powder Aerosol Deposition, PACRIM 14 (2021), Vancouver (virtual), Canada (Tagungsvortrag)
  D. Paulus; J. Exner; J. Kita & R. Moos
  
• Posttreatment of powder aerosol deposited oxide ceramic films by high power LED. International Journal of Applied Ceramic Technology, 19(3), 1540-1553.
  Nazarenus, Tobias; Schlesier, Kira; Biberger, Simon; Exner, Jörg; Kita, Jaroslaw; Köhler, Anna & Moos, Ralf
  
• Influence of powder composition on the internal stresses and thermal annealing behavior of ceramic films formed by Powder Aerosol Co- Deposition, Ceramics in Europe (2022), Jena, Germany (Tagungsvortrag)
  D. Paulus; J. Kita & R. Moos
  
• Microstrain release decouples electronic and thermal conductivity in powder aerosol deposited films. Materials Letters, 322, 132461.
  Nazarenus, T.; Schlesier, K.; Lebeda, F.; Retsch, M. & Moos, R.
  
• Intrinsic compressive stress relaxation in ceramic films manufactured by powder aerosol deposition (PAD), 98. DKG-Jahrestagung (2023), Jena, Germany (Tagungsbeitrag)
  D. Paulus; J. Kita & R. Moos
  
• Relaxation behavior of intrinsic compressive stress in powder aerosol co-deposited films: Rethinking PAD films as nanomaterials. Ceramics International, 49(23), 38375-38381.
  Paulus, Daniel; Kita, Jaroslaw & Moos, Ralf