In the frame of my diploma work, I studied Chemical Solution Deposition (CSD) of barium titanate-based thin films, namely (Ba(Zr$_{0,2}$Ti$_{0,8}$)O$_3$, BZT) and ((Ba$_{0,7}$Ca$_{0,3}$)TiO$_3$, BCT) solid solutions. BZT and BCT are the end-members of BZT-BCT ceramic, which is one of the environment-friendly alternatives to the commercially most widespread lead-based piezolectric ceramics. The BZT and BCT precursor solutions with the 0.1 M concentration were prepared by mixing the solutions of alkaline-earth acetates in ethyleneglycol and transition-metal butoxides in ethanol in stoichiometric ratios at room temperature. BZT and BCT thin films on platinised silicon substrates were prepared by repeating ten times the deposition by spin-coating, drying at 250 °C, pyrolysis at 350 °C and rapid thermal annealing at 850 °C.
Thermal decompositions of BZT and BCT xerogels obtained by drying the precursor solutions at 200 °C were followed by thermal analysis. In both cases, the organic groups mainly decomposed between 300 °C and 450 °C, while the carbonaceous residues remained upon heating to 720 °C for BZT and to about 780 °C for BCT. Thermal decomposition of the layers deposited on platinised silicon substrates was followed by Fourier transform infrared spectroscopy. Bands of carboxylic groups were detected in the layers heated to about 500 °C, and carbonate groups to about 650 °C (BZT) or 700 °C (BCT). Metal-oxygen bands could be detected in the spectra of the samples heated to 700 °C (BZT) or 750 °C (BCT).
BZT and BCT thin films, prepared by multistep annealing at 850 °C crystallise in the perovskite phase. The surface microstructure, analysed by scanning electron microscopy, consists of grains of a few 10 nm across. The film thickness is about 120 nm.
|
