Microstructural Changes during the Reduction/Reoxidation Process in Donor‐Doped BaTiO 3 Ceramics

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Abstract
Microstructural changes occurring during oxidation of the reduced form of donor‐doped BaTiO 3 (Ba 1− X D X . Ti 1− X 4+ Ti X 3+ O 3 ) and during reduction of the oxidized form of donor‐doped BaTiO 3 (Ba 1− X D X . Ti 1− X /4 4+ ( V Ti ) X /4 O 3 ) were studied using TEM. Samples of both types of solid solutions, containing different La concentrations (from 2 to 20 mol% La), were prepared by sintering under reducing conditions and in air, respectively. The reduced form of donor‐doped BaTiO 3 was oxidized by annealing at high temperatures (1150° and 1350°C) in air, while the oxidized form was reduced by annealing under reducing conditions. Because of oxidation of the reduced phase of donor‐doped BaTiO 3 , the Ti‐rich phases Ba 6 Ti 17 O 40 and BaLa 2 Ti 4 O 12 were precipitated. Reduction of the oxidized form caused precipitation of the Ba‐rich phase Ba 2 TiO 4 preferentially inside the matrix grains. All precipitates had well‐defined orientational relationships with the perovskite matrix.

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