Papers by Keyword: Ferroelectric

Abstract: Bi_3.25Gd_0.75Ti_2.97V_0.03O₁₂ (BGTV) ceramics were prepared by solid state reaction. These samples had polycrystalline Bi-layered perovskite structure without preferred orientation, and consisted of well developed plate-like grains with random orientation. The remanent polarization and the coercive field of the BGTV were 24μC/cm² and 65kV/cm at an electric field of 100kV/cm, respectively. These ferroelectric properties of BGTV are superior to V-doped Bi₄Ti₃O₁₂ (~20μC/cm² and 80kV/cm) and (Sr, Ta)-doped Bi₄Ti₃O₁₂ (~12μC/cm² and 71kV/cm) ceramics. In addition, the dense ceramics of BGTV could be obtained by sintering at temperatures 100─200°C lower than those of the SrBi₂Ta₂O₉ system.

Abstract: Bi_2.9Pr_0.9Ti_2.97V_0.03O₁₂ (BPTV) ceramics were prepared by solid state reaction. These samples had polycrystalline Bi-layered perovskite structure without preferred orientation, and consisted of well developed plate-like grains with random orientation. BPTV caused a large shift of the Curie temperature ( TC ) of Bi₄Ti₃O₁₂ (BIT) from 675°C to 385°C. The remanent polarization and the coercive field of the BLTV were 31μC/cm² and 60kV/cm at an electric field of 100kV/cm, respectively. Furthermore, the dielectric permittivity and dissipation factor were 300 and 3.3×10-3 at 1MHz, at 1V and at room temperature, respectively. These ferroelectric properties of BPTV are superior to V-doped Bi₄Ti₃O₁₂ (~20μC/cm² and 80kV/cm) and (Sr, Ta)-doped Bi₄Ti₃O₁₂ (~12μC/cm² and 71kV/cm) ceramics. In addition, the dense ceramics of BPTV could be obtained by sintering at temperatures 100─200°C lower than those of the SrBi₂Ta₂O₉ system.

Abstract: Bi_3.25Er_0.75Ti₃O₁₂(BET) and Bi_3.25Er_0.75Ti_2.97V_0.03O₁₂(BETV) thin films with random orientation were fabricated on Pt/Ti/SiO₂/Si substrates by rf magnetron sputtering technique. These samples had polycrystalline Bi-layered perovskite structure without preferred orientation, and consisted of well developed rod-like grains with random orientation. The experimental results indicated that Er doping into Bi₄Ti₃O₁₂ (BIT) also result in a remarkable improvement in ferroelectric property. The remanent polarization (Pr) and coercive field (Ec) of the BET film were 17 μC/cm² and 80 kV/cm, respectively. Furthermore, V substitution improves the Er value of the BETV films up to 28 μC/cm², which is much larger than that of the BET film.

Abstract: The electrical properties of Er₂O₃-doped bismuth titanate，Bi_4-xEr_xTi₃O₁₂ (BET) ceramics prepared by a conventional electroceramic technique were investigated. XRD analyses revealed Bi-layered perovskite structure in all samples. SEM micrographs showed randomly oriented and plate-like morphology. For the samples with x=0.4 and 1.0 the current-voltage characteristics exhibited negative differential resistance behaviors and their P-E hysteresis loops were characterized by large leakage current, whereas for the samples with x=0.6 and 0.8 the current-voltage characteristics showed simple ohmic behaviors and their P-E hysteresis loops were the saturated and undistorted hysteresis loops. The remanent polarization ( Pr ) and coercive field (Ec) of the BET ceramic with x=0.8 were above 20μC/cm² and 65KV/cm , respectively.

Abstract: The ferroelectricity of Bi_3.2Er_0.8Ti₃O₁₂ (BET), and Bi_3.2Er_0.8Ti_2.97V_0.03O₁₂ (BETV) ceramics prepared at 1100°C by a conventional ceramic technique was investigated. These ceramics possess random-oriented polycrystalline structure. The remanent polarization (Pr) and coercive field (Ec) of the BET ceramics are 18 µC/cm² and 64kV/cm, respectively. Furthermore, V substitution improves the Pr value of the BETV ceramics up to 30 μC/cm², which is much larger than that of the BET ceramics. Therefore, co-sustitution of Er and V in Bi₄Ti₃O₁₂ (BIT) ceramic is effective for the improvement of its ferroelectricity.

Abstract: The ferroelectricity of Bi_3.25Nd_0.75Ti₃O₁₂ (BNT), and Bi_3.25Nd_0.75Ti_2.97V_0.03O₁₂ (BNTV) ceramics prepared at 1100°C by a conventional ceramic technique was investigated. These ceramics possess random-oriented polycrystalline structure. The remanent polarization (Pr) and coercive field (Ec) of the BNT ceramics are 16 µC/cm² and 65kV/cm, respectively. Furthermore, V substitution improves the Pr value of the BNTV ceramics up to 23 μC/cm², which is much larger than that of the BNT ceramics. Therefore, co-sustitution of Nd and V in Bi₄Ti₃O₁₂ ceramic is effective for the improvement of its ferroelectricity.

Abstract: The electrical properties of Sm-doped bismuth titanate，Bi_4-xSm_xTi₃O₁₂ (BST) ceramics prepared by a conventional electroceramic technique were investigated. XRD analyses revealed Bi-layered perovskite structure in all samples. The P-V hysteresis loops of samples with x=0.4 and 1.2 were characterized by large leakage current, whereas for samples with x=0.6 and 0.8 the P-E hysteresis loops were the saturated and undistorted hysteresis loops. The remanent polarization ( Pr ) and coercive field (Ec) of the BST ceramic with x=0.8 were above 20μC/cm² and 60KV/cm , respectively.

Abstract: The Ferroelectric properties and Microstructures of Bi_3.3Tb_0.6Ti₃O₁₂ (BTT) and Bi_3.3Tb_0.6Ti_2.97V_0.03O₁₂ (BTTV) ceramics prepared at 1100°C by a conventional ceramic technique were investigated. These ceramics possess random-oriented polycrystalline structure. The remanent polarization (Pr) and coercive field (Ec) of the BTT ceramics are 23µC/cm2 and 80kV/cm, respectively. Furthermore, V substitution improves the Pr value of the BTTV ceramics up to 35μC/cm², which is larger than that of the BTT ceramics. Therefore, co-sustitution of Tb and V in Bi₄Ti₃O₁₂ (BIT) ceramic is effective for the improvement of its ferroelectricity.

Abstract: The electrocaloric effect (ECE) of barium titanate ceramics with hydrothermal synthesized nano-sized starting powders was investigated. The Curie point and latent heat of the phase transition were characterized by a differential scanning calorimeter (DSC). The P-E hysteresis loops were measured in the temperature range from 30-160oC and ECE adiabatic temperature change was obtained according to the Maxwell relation. A double hysteresis loop is observed at the temperature slightly above the Curie point, which indicates a good consistency of phase transition similar to single crystal. It is also proved by the sharp endothermic peak of phase transition in DSC curves. It exhibits a high ECE of ΔTmax=1.3K under a low applied field of 10kV/cm, which is much higher than that of the sample using micron-sized starting powders.

Abstract: Single crystals of K_0.5Na_0.5NbO₃ (KNN) and 5wt%, 10wt%, 15wt% of Sb doped KNN crystals were grown by flux method. The formation of crystalline structure, microstructure, domain structure and the dielectric properties were investigated for both pure and Sb doped KNN single crystals. X-ray diffraction (XRD) pattern shows that pure and doped KNN single crystals have orthorhombic perovskite structure. The doped crystals have slight shrinkage in the unit cell volume. The partial substitution of the B-site ion Nb₅₊ by the Sb₅₊ ion in the KNN single crystal results in decreasing phase transition temperatures T_O-T and Curie temperatures TC of the doped crystals with increasing amount of Sb. The dielectric properties of the doped crystals show significant improvement with doping concentration. The peaks slightly shift towards lower frequencies with increasing dopant concentration.