Remarkable piezoelectric properties of barium titanate (BaTiO3, BT) based solid solution 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 (BZT-BCT) have stimulated investigations on this material as one of the promising lead-free ferroelectric materials for micro-electro-mechanical applications, especially at ambient temperature [1, 2]. Materials in the form of thin films enable the miniaturization of devices. Chemical Solution Deposition (CSD) offers the possibility to control thin film microstructure (grain size and shape), phase purity, and chemical homogeneity that can influence the functional properties of the films [3, 4].
In our previous work on the CSD of BT thin films using ethylene glycol (EG) and ethanol (EtOH) as solvents for barium acetate and titanium butoxide, respectively, we revealed that the selected combination of solvents not only increased the stability of the coating solution compared to conventional carboxylic acid-based solution route but also contributed to lowering of the temperature of thermal decomposition of carbon residues in BT films [5].
Following the same synthesis procedure as for BT, we prepared BZT-BCT coating solutions using EG and EtOH solvents. The stability of respective solutions increased from 2 weeks for the acetic-acid-based route to at least 6 months. The BZT-BCT films, both undoped and doped with manganese (1 mol%), rapid thermally annealed at or above 850 oC, crystallize in the perovskite phase. The microstructure of about 120 nm thick films depends on the concentration of coating solutions and the associated number of deposited layers: for 0.1 M solution (10 depositions with crystallization after each deposition), the grains are preferentially columnar with a surface size of about 100 nm, while at 0.2 M solution (4 depositions with sequential treatments after each deposition as well), the grain size is finer, about 30-50 nm. We observe a dependence of dielectric and ferroelectric properties of the films on grain size, in agreement with the dielectric grain size effect reported in studies of BT and BT-based films [6]. The macroscopic measurements are supported by piezo-response force microscopy, confirming the ferro- and piezoelectric response of the films. We conclude that EG-based CSD of BZT-BCT thin films is a good alternative to the established carboxylic-acid-based route.

References.
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