Papers by Author: X.A. Mei

Abstract: Bi_3.3Tb_0.6Ti₃O₁₂(BTT), Bi_3.3Tb_0.6Ti_2.97V_0.03O₁₂(BTTV), and pure Bi₄Ti₃O₁₂ (BIT) 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 Tb doping into BIT also result in a remarkable improvement in ferroelectric property. The remanent polarization (Pr) and coercive field (Ec) of the BTT film were 25 μC/cm² and 85 kV/cm, respectively. Furthermore, V substitution improves the Pr value of the BTVT film up to 35 μC/cm², which is much larger than that of the BTT film.

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: The electrical properties of Gd₂O₃-bismuth titanate (Bi_4-xGd_xTi₃O₁₂) prepared by a conventional ceramic technique have been investigated. At applied d.c. field below 200V/mm, the current-voltage curve of Gd-doped sample exhibits a simple ohmic behavior. The impedance spectrum of Gd-doped sample indicates that consist of semiconducting grain and moderately insulating grain boundary regions. XRD, SEM and EPMA analyses reveal crystalline phase characterized by a Bi-layered perovskite structure of Bi₄Ti₃O₁₂ and the distribution of every element is uniform. Gd-doped sample exhibit randomly oriented and plate-like morphology.

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.