Redox processes at grain boundaries in barium titanate-based polycrystalline ferroelectrics semiconductors

• Published in: Journal of materials science 2008-05, Vol.43 (9), p.3320-3326
• Main Authors: Belous, Antolii, V’yunov, Oleg, Glinchuk, Maya, Laguta, Valentin, Makovez, Darko
• Format: Article
• Language: English
• Subjects: Applied sciences; Barium; barium titanate; Barium titanates; Building materials. Ceramics. Glasses; Ceramic industries; ceramics; Characterization and Evaluation of Materials; Charge exchange; Chemical industry and chemicals; Chemistry and Materials Science; Chromium; Classical Mechanics; Crystallography and Scattering Methods; Dopants; Electrotechnical and electronic ceramics; Exact sciences and technology; Ferroelectric materials; Ferroelectricity; Grain boundaries; Grains; Impurities; ions; iron; Manganese; Manganese ions; Materials Science; Polymer Sciences; Positive temperature coefficient; Potential barriers; Reagents; Semiconductors; Solid Mechanics; Technical ceramics; temperature; Titanium; Yttrium
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1007/s10853-008-2503-7

Barium titanate, which is characterized by a positive temperature coefficient of resistance (PTCR), is widely used in practice. At the same time, it is unknown why only a small percentage of the introduced donor dopant takes part in the formation of PTCR effect, which phases appear at grain boundaries, how the introduced acceptor dopants affect the properties of grains. Elucidation of the above questions is of considerable scientific and practical interest. It has been shown that the phases Bа₆Ti₁₇O₄₀ and Y₂Ti₂O₇ precipitate on grains of barium titanate doped with donor dopant (yttrium). We identified paramagnetic impurities (iron, manganese, chromium) in starting reagents. These impurities can occupy titanium sites. Therefore, the part of the donor dopant that is spent on the charge exchange of acceptor dopants does not participate in the charge exchange of titanium Ti⁴⁺ → Ti³⁺, which is responsible for the appearance of PTCR effect in barium titanate. It has been found that an extra acceptor dopant (manganese) is distributed mainly at grain boundaries and in the grain outer layer. It has been shown that manganese ions introduced additionally (as acceptor dopants) increase the potential barrier at grain boundaries and form a high-resistance outer layer in PTCR ceramics. The resistance of grains, outer layers, and grain boundaries as a function of the manganese content has been investigated.