Sabi William Konsago

Understanding the thermal decomposition and perovskite phase crystallization enables the design of the desired micro structure of BaTiO3-based thin films prepared by chemical solution deposition. We prepared xerogels from (Ba0.7Ca0.3) TiO3 (BCT) and Ba(Zr0.2Ti0.8)O3 (BZT) coating solutions, as well as BCT and BZT thin films, to investigate their thermal decomposition. The oxycarbonates, formed during the heating of BCT and BZT xerogels, are fully decomposed at 780 °C and 720 °C, respectively. The thermal decomposition of carbonate residues in BCT and BZT thin films is completed at 750 °C and 700 °C, respectively. The approximately 120 nm thick BCT and BZT films annealed at 850 °C crystallize in the perovskite phase.

Manganese-doped 0.5Ba(Zr_0.2Ti_0.8)O₃–0.5(Ba_0.7Ca_0.3)TiO₃ (BZT–BCT) ferroelectric thin films deposited on platinized sapphire substrates by chemical solution deposition and multistep-annealed at 850 °C, are investigated.

Lead-free ferroelectric 0.5Ba(Ti_0.8Zr_0.2)O₃-0.5(Ba_0.7Ca_0.3)TiO₃ (BZT-BCT) thin films on platinized silicon substrates are prepared by chemical solution deposition route. The solution chemistry involves ethylene glycol and ethanol as solvents for alkaline earth acetates and transition metal alkoxides, respectively. The thermal decompositions of BZT-BCT xerogel, the crystallization process of BZT-BCT thin films, and their homogeneity are investigated. In xerogel, the decomposition of the organic residues occurs between 290 °C and 514 °C, followed by the formation of carbonate groups and their decomposition between 580 °C and 775 °C. In the thin films, the sequence of drying and pyrolysis steps, and the concentration of the coating solution influence the formation of carbonate groups and their decomposition upon annealing. Extending the drying and pyrolysis times from 2 minutes to 15 minutes and lowering the concentration of the coating solution from 0.2 M to 0.1 M contribute to an easier thermal decomposition of the carbon residues. Time-of-Flight Secondary Ion Mass Spectrometry analysis reveals that upon rapid thermal annealing, the decomposition of the carbonate residues in a few 10 nm thick BZT-BCT film proceeds from top downwards, resulting in pure perovskite phase faster in the thinner films than in thicker ones. The about 100 nm thick BZT-BCT film annealed at 850 °C exhibits a columnar microstructure with a homogeneous distribution of elements across the thickness of the film.

Linear Thermal Expansion of 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 Bulk Ceramic

Chemical solution deposition (CSD) of BaTiO₃ (BT) or BT-based thin films relies on using a carboxylic acid and alcohol as the solvents for alkaline-earth carboxylate and transition-metal alkoxide, respectively; however, the esterification reaction of the solvents may lead to in-situ water formation and precipitation. To avoid such an uncontrolled reaction, we developed a route in which ethylene glycol (EG) is used as the solvent for Ba-acetate. The EG-based BT coating solutions are stable for at least a few months. The thermal decomposition of the BT xerogel obtained by drying the EG-based solutions depends on the choice of the solvent for the Ti-alkoxide as well: in the case of EG and 2-methoxyethanol solvents carbon residues are removed at only about 1100 °C, while in the case of ethanol it is concluded at about 700 °C. About 100 nm thick BT films derived from the EG-ethanol solution deposited on platinized silicon reveal dense, crack-free columnar microstructure. They exhibit local ferro- and piezoelectric properties. The macroscopic polarization-electric field loops were obtained up to a quite high electric field of about 2.4 MV/cm. The EG-ethanol based CSD route is a viable alternative to the established acetic acid–alcohol route for BT and BT-based films.