Sonochemical activation in aqueous medium for solid-state synthesis of BaTiO3 powders

Abstract

BaTiO₃-based oxide compounds are important ceramic materials for multilayer ceramic capacitors. In this paper, we report a sonochemical activation process of BaCO₃ and TiO₂ in an aqueous medium for the synthesis of BaTiO₃ powders through a solid-state process. Owing to the physical and chemical effects of the ultrasonication in aqueous medium on the raw materials, BaTiO₃ powders could be successfully synthesized at relatively low temperatures through a solid-state reaction, which was significantly enhanced as compared to the case in ethanol medium. Detailed investigations on the resulting BaTiO₃ powders and ceramics were performed, and a model to understand the role of aqueous medium on the enhancement of the solid-state reaction was proposed in terms of Ba²⁺ ion leaching and zeta potential of TiO₂, which are strongly affected by the pH of the aqueous medium. Our results are not only helpful for cost-effective synthesis of BaTiO₃ through the highly reliable solid-state reaction process, but they also provide an understanding of the role of aqueous medium for the sonochemical process using raw materials with partial solubility in water.

Keywords: BaTiO(3); Powder; Solid-state synthesis; Sonochemical activation.

Fig. 1

Schematic of the sonochemical activation of raw materials in aqueous medium.

Fig. 2

(a) Average particle size of BaCO₃ after 600 W ultrasonication for 5 min and (b) amount of leached Ba²⁺ ions in aqueous supernatant after the ultrasonication.

Fig. 3

TEM micrographs of (a) pristine TiO₂ and (b-d) ultrasonicated TiO₂ after 600 W ultrasonication in aqueous medium with pH values of 3, 7, and 11, respectively.

Fig. 4

(a) Phase conversion ratio to BaTiO₃ of 600 W ultrasonicated mixtures and (b) zeta potential of TiO₂ with respect to pH in aqueous medium.

Fig. 5

(a-c) Model for the rearrangement of leached Ba²⁺ ions on the surface of TiO₂ particles in aqueous medium under pH = 3, pH = 5, and pH ≥ 7, respectively. (d) No leached Ba²⁺ ions exist in ethanol.

Fig. 6

Phase conversion ratio to BaTiO₃ of (a) 300 and (b) 900 W ultrasonicated mixtures as a function of pH in aqueous medium.

Fig. 7

(a) Lattice constants of BaTiO₃ powders for 900 W ultrasonicated mixtures under different pH conditions with respect to calcination temperature and (b) the corresponding tetragonalities.

Fig. 8

SEM micrographs of 900 °C-calcined powders for 900 W ultrasonicated mixtures (a)–(e) in aqueous medium under pH = 3, 5, 7, 9 and 11, respectively, and (f) in ethanol.

Fig. 9

SEM micrographs of (a–f) BT-3, BT-5, BT-7, BT-9, BT-11, and BT-E, respectively.

Fig. 10

(a) Dielectric constants and dielectric losses (tanδ) of BaTiO₃ ceramics as a function of temperature and (b) P-E hysteresis loops of BaTiO₃ ceramics measured at room temperature.