Theoretical Modeling and Experimental Verification of Electrochemical Equilibria in the Ba−Ti−C−H₂O System

Abstract

The thermodynamic principles controlling the electrochemical synthesis of barium titanate (BaTiO 3 ) films are discussed and explored. a variety of E h -pH diagrams were generated for the Ba-Ti-C-H 2 O system as a function of temperature and whether CO 2 was in the system. Barium titanate is predicted to form at 25 °C and higher temperatures under alkaline conditions. It is demosnstrated that the phase field for BaTiO 3 enlarges as a function of pH with increasing temperature in the absence of CO 2 . The role of CO 2 , although still important in controlling the phase stability of BaTiO 3 via the formation of BaCO 3 , becomes less important under solution pH conditions greater than pH ∼13 and temperatures greater than 100 °C. The theoretical E h -pH predictions compare favorably with experimentally determined regimes, where BaTiO 3 and films in the Ba-Ti-C-H 2 O system form through electrochemical reactions.

Microstructure and permittivity of sintered BaTiO3: influence of particle surface chemistry in an aqueous medium

“…1 (inset (C)), with a BaTiO 3 core surrounded by an Ti-excess layer surrounded by a precipitated Ba-rich phase. Thermodynamic considerations [4] and previous XPS results [8] indicate that the precipitate phase in this case likely consists of BaCO 3 and/or Ba(OH) 2 . It has not been possible to resolve the surface composition or precipitation reaction further, since CO 2 is ubiquitous and carbonates are always detected on BaTiO 3 surfaces, and can easily result from sample preparation artifacts prior to analysis.…”

“…Aqueous forming methods, though environmentally friendly and cost-effective, are more difficult to control due to reactions between the solid and liquid phases. The incongruent dissolution of BaTiO 3 in aqueous media at room temperature as a result of poor thermodynamic stability is well documented [2][3][4][5], and results in the leaching of Ba 2þ . Dissolution at the BaTiO 3 surface in contact with water occurs according to the following reaction [3] Under acidic conditions, the reaction can be written [4]: BaTiO 3 ðsÞ þ 2H þ ðaqÞ ¼ Ba 2þ ðaqÞ þ TiO 2 ðrutileÞ þ H 2 O; pK ¼ À20:37 ð25 CÞ where K is the thermodynamic solubility constant.…”

“…The dissolution and subsequent adsorption/precipitation of Ba 2þ also create substantial problems for the control and reproducibility of dielectric properties in aqueous-based tape casting. There are a number of reports where the effects of bulk Ba/Ti ratio on sintering behavior and dielectric properties of BaTiO 3 have been described [11][12][13][14][15][16][17][18]. Although variations of Ba/Ti ratio within distinct surface layers on BaTiO 3 , as a result of Ba 2þ dissolution/precipitation, should therefore be of significant concern, this has been studied far less than the effect of bulk variations.…”

Influence of Solids Concentration on the Isoelectric Point of Aqueous Barium Titanate

“…Titania (rutile) is relatively insoluble over the pH range used in the present study. 14 In the second stage of dissolution, BaTiO 3 continues to be consumed by reaction (1), but the rate becomes mass transport limited because Ba 2ϩ must diffuse out through a growing reactive surface layer. This process should result in a parabolic (square root of time) rate law.…”

Surface modification of BaTiO3 with yttrium, and dissolution and adsorption/precipitation behaviors of BaTiO3

“…Although the non-aqueous system has some advantages, including a faster drying rate, lower capillary forces, and typically a higher green strength of tapes [2], there has been a recent push towards aqueous-based tape-casting for cost-related and environmental benefits. However, a critical shortcoming associated with aqueous-based systems is the incongruent dissolution of BaTiO 3 and the resulting accumulation of Ba 2+ in solution [3][4][5][6][7]. As recent investigations [8,9] have shown, the dispersion stability of colloidal BaTiO 3 is closely tied to changes in the surface chemistry that result from Ba 2+ leaching.…”