Abstract
A series of La/Mn, Sm/Mn and Dy/Mn codoped BaTiO3 samples were prepared by the conventional solid state procedure with dopant concentrations ranging from 0.1 up to 2.0 at%. The specimens were sintered at 1320?C and 1350?C in an air atmosphere for two hours. The low doped samples demonstrated a mainly uniform and homogeneous microstructure with average grain sizes ranging from 0.3 ?m to 5.0 ?m. The appearance of secondary abnormal grains in the fine grain matrix and core-shell structure were observed in highly doped La/BaTiO3 and Dy/BaTiO3 sintered at 1350?C. The low doped samples, sintered at 1350?C, display a high value of dielectric permittivity at room temperature, 6800 for Sm/BaTiO3, 5900 for Dy/BaTiO3 and 3100 for La/BaTiO3. A nearly flat permittivity-response was obtained in specimens with 2.0 at% additive content. Using a modified Curie-Weiss law the Curie-like constant C? and a critical exponent ? were calculated. The obtained values of ? pointed out the diffuse phase transformation in heavily doped BaTiO3 samples.
Highlights
Rare earth oxides are widely used as doping materials for BaTiO3 ceramics in order to achieve a high dielectric performance and low dissipation factor of the capacitors [1,2,3]
The relative density of doped samples ranged from 70-80 % of theoretical density (TD) for La/BT, 90 %TD for Dy/BT and up to 93%TD for Sm-doped ceramics, being lower for higher dopant additive and low sintering temperature
The homogeneous and completely fine-grained microstructure with grain size ranged from 1.0-3.0 μm, of fairly narrow size distribution, are the main characteristics of La-doped samples, sintered at 1320°C (Fig.1a and 1b)
Summary
Rare earth oxides are widely used as doping materials for BaTiO3 ceramics in order to achieve a high dielectric performance and low dissipation factor of the capacitors [1,2,3]. The incorporation of trivalent rare-earth cations such as La3+, Dy3+, Sm3+, Er3+ and Ho3+ in the perovskite lattice of BaTiO3, modifies the microstructural and electrical properties of doped BaTiO3. The larger ionic size rare-earth ions (La, Sm) predominantly dissolve in A-sites, and act as donors, and the intermediate ionic size rare-earth ions (Dy, Ho, Er), depending on their concentration, dissolve in both A and B- cationic lattice sites in BaTiO3 structure, and may act as donors or/and acceptors. There are three possible compensation mechanisms: barium vacancies (VBa′′), titanium vacancies (VTi′′′′) and electrons (e′). For samples sintered in air atmosphere, which are electrical insulators, the principal doping mechanism is the ionic compensation mechanism. The controversy remains concerning whether the dominant ionic mechanism is through the creation of barium or titanium vacancies [4,5]
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