Structure matters: A synchrotron study reveals how crystallite structure influences the deposition mechanism for the powder aerosol deposition method

Powder aerosol deposition (PAD or ADM) is a coating technique to produce ceramic films at room temperature. Although the deposition mechanism has been clarified in some respects, unanswered questions remain. The present work reports films of titanium oxide, which forms a typical PAD microstructure, and films of incom-mensurate misfit-layered calcium cobalt oxide (Ca$_3$Co$_4$O$_9$-δ, CCO-349), which forms a atypical film. For this
work, films made of these two materials were examined using X-ray diffraction with synchrotron radiation and a scanning electron microscopy. It turned out that due to its aperiodic crystal structure, CCO-349 can be deformed more easily than conventional technical ceramics like TiO$_2$. The deformation occurs when the layers in the crystal slide in the direction of the misfit. As a result, it is unnecessary to break the crystals, and a larger crystallite size remains in the film. Therefore, PAD films of CCO-349 have a different microstructure.