Ferroelectric BaTiO3 is widely used in capacitors, but the low Curie temperature limits a further use of BaTiO3. In this work we present an aqueous chemical solution deposition (CSD) route for BaTiO3 thin films, demonstrating that organic solvents are not required for CSD. Textured BaTiO3 thin films were deposited on SrTiO3 substrates. The in-plane dielectric properties were investigated using interdigitated electrodes and ferroelectric switching was observed up to 160±5 °C. The increased Curie temperature is proposed to result from thermal strain due to a mismatch in thermal expansion coefficient between the film and the substrate, and is in good agreement with the theory of strain engineering in BaTiO3. Finally, the decomposition and crystallization of BaTiO3 during thermal treatment were determined by the combination of thermal analysis, IR spectroscopy and X-ray diffraction of powder prepared from the solution.

The prototype piezoelectric material BaTiO 3 is widely used in e.g., capacitators. Chemical solution deposition (CSD) of BaTiO 3 films is a simple and environmentally friendly processing route, but insight in the crystallization process is crucial to tailor the film properties. In this work, the influence of the annealing conditions on the crystallization behavior of BaTiO 3 thin films from aqueous chemical solution deposition is presented. In situ synchrotron X-ray diffraction was used to reveal the phase evolution, crystallization of the films, and to study how the degree of crystallographic texture in the polycrystalline films evolved. Our results revealed that the formation of an intermediate metastable oxycarbonate phase is critical for the formation of BaTiO 3 thin films prepared by aqueous CSD. The pyrolysis products present in the film before crystallization determine the degree of preferential orientation and by tuning the heating program, especially the heating rate through nucleation (<0.2°C/s), control of the microstructure and degree of preferential orientation in the films was demonstrated.

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Carbonate formation is a prevailing challenge in synthesis of BaTiO 3 , especially through wet chemical synthesis routes. In this work, we report the phase evolution during thermal annealing of an aqueous BaTiO 3 precursor solution, with a particular focus on the structures and role of intermediate phases forming prior to BaTiO 3 nucleation. In situ infrared spectroscopy, in situ X-ray total scattering, and transmission electron microscopy were used to reveal the decomposition, pyrolysis, and crystallization reactions occurring during thermal processing. Our results show that the intermediate phases consist of nanosized calcite-like BaCO 3 and BaTi 4 O 9 phases and that the intimate mixing of these along with their metastability ensures complete decomposition to form BaTiO 3 above 600 °C. We demonstrate that the stability of the intermediate phases is dependent on the processing atmosphere, where especially enhanced CO 2 levels is detrimental for the formation of phase pure BaTiO 3 .

Understanding the crystallization process for chemical solution deposition (CSD) processed thin films is key in designing the fabrication strategy for obtaining high-quality devices. Here, an in situ sample environment is presented for studying the crystallization of CSD processed thin films under typical processing parameters using near-grazing-incidence synchrotron X-ray diffraction. Typically, the pyrolysis is performed in a rapid thermal processing (RTP) unit, where high heating rates, high temperatures and atmosphere control are the main control parameters. The presented in situ setup can reach heating rates of 20°C s−1 and sample surface temperatures of 1000°C, comparable with commercial RTP units. Three examples for lead-free ferroelectric thin films are presented to show the potential of the new experimental set-up: high temperature, for crystallization of highly textured Sr0.4Ba0.6Nb2O6 on a SrTiO3 (001) substrate, high heating rate, revealing polycrystalline BaTiO3, and atmosphere control with 25% CO2, for crystallization of BaTiO3. The signal is sufficient to study a single deposited layer (≥10 nm for the crystallized film) which then defines the interface between the substrate and thin film for the following layers. A protocol for processing the data is developed to account for a thermal shift of the entire setup, including the sample, to allow extraction of maximum information from the refinement, e.g. texture. The simplicity of the sample environment allows for the future development of even more advanced measurements during thin-film processing under non-ambient conditions.