Papers by Author: J. Liu

Abstract: Bi₂WTi₃O₁₂ ceramics are fabricated by conventional solid-state reaction process. XRD analysis reveals that Bi₂WO₆ is the main phase and Bi₄Ti₃O₁₂ is the second phase. With increasing temperature the sample first appears metallic behavior, then strong electrical fluctuations above 100°C, and finally exhibits stable nonlinear properties characterized by semiconductivity above 300°C at low field (E ≤ 100V/mm). The Arrhenius law for electrical conductivity by thermal activation is not suitable to explain the anomalous results. Based on the phase transition of tungsten trioxide from room temperature to about 300°C, the electrical properties of Bi₂WTi₃O₁₂ ceramics can be explained.

Abstract: Ferroelectric Bi₄Ti₃O₁₂ ceramics are fabricated by conventional solid-state reaction process. The current-voltage characteristic of Bi₄Ti₃O₁₂ sample exhibits a voltage-controlled negative differential resistance behavior at low field (E≤100V/mm), and an obvious PTC effect appears at around 100°C on the resistance-temperature curve. Based on conducting filament model about electrical transport, instead of Heywang-Jonker model, the experimental results of Bi₄Ti₃O₁₂ ceramics are suitably explained.

Abstract: The ferroelectricity of Bi_3.25Eu_0.75Ti₃O₁₂ (BET), and Bi_3.25Eu_0.75Ti_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 (P_r) and coercive field (E_c) of the BET ceramics are 16 µC/cm² and 62kV/cm, respectively. Furthermore, V substitution improves the P_r value of the BET ceramics up to 25 μC/cm² which is larger than that of the BET ceramics. Therefore, co-sustitution of Eu and V in Bi₄Ti₃O12 (BIT) ceramic is effective for the improvement of its ferroelectricity.

Abstract: Bi_3.25Gd_0.75Ti_2.97V_0.03O₁₂ (BGTV)ceramic 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. BGTV caused a large shift of the Curie temperature ( T_C ) of Bi₄Ti₃O₁₂ (BIT) from 675°C to 398°C. The remanent polarization and the coercive field of the BGTV were 30μC/cm² and 52kV/cm at an electric field of 87kV/cm, respectively. Furthermore, the dielectric permittivity and dissipation factor were 300 and 0.003 at 1MHz, at 1V and at room temperature, 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: Dy₂O₃-doped bismuth titanate (Bi_4-xDy_xTi₃O₁₂: BDT) thin films with random orientation were fabricated on Pt/Ti/SiO₂/Si substrates by rf magnetron sputtering technique, and the structures and ferroelectric properties of the films were investigated. XRD studies indicated that all of BDT films consisted of single phase of a bismuth-layered structure with well-developed rod-like grains. The remanent polarization (P_r) and coercive field (E_c) of the BDT Film with x = 0.8 were 20 μC/cm² and 60 KV/cm, respectively. After 3 × 10¹⁰ switching cycles, 20% degradation of P_r is observed in the film.

Abstract: Pr6O11-doped bismuth titanate (BixPryTi3O12 BPT) thin films were fabricated on Pt/Ti/SiO2/Si substrates by rf magnetron sputtering technique, and the microstructures and ferroelectric properties of the films were investigated. Microstructure studies indicate that all of BPT films with well-developed rod-like grains consist of single phase of a bismuth-layered structure without preferred orientation. Pr doping into Bi4Ti3O12 (BIT) causes a large shift of the Curie temperature (TC) of paraelectric-ferroelectric phase transition of BIT from 675°C to lower temperature and improvement in dielectric properties. The experimental results indicate that Pr doping into Bi4Ti3O12 results in a remarkable improvement in ferroelectric properties. The remanent polarization ( Pr ) and coercive field (Ec) of the BPT film with y=0.9 were 35 μC/cm2 and 80 kV/cm, respectively. After 3  1010 switching cycles, 20% degradation of Pr is observed in the film.

Abstract: Eu2O3-doped bismuth titanate (Bi1-xEuxTi3O12: BET) thin films with random oriention were fabricated on Pt/Ti/SiO2/Si substrates by rf magnetron sputtering technique, and the structures and ferroelectric properties of the films were investigated. XRD studies indicated that all of BET films consisted of single phase of a bismuth-layered structure with well-developed rod-like grains. For samples with x=0.0 , 0.25, 1.0 and 1.25, I-E characteristics exhibited negative differential resistance behaviors and their ferroelectric hysteresis loops were characterized by large leakage current, whereas for samples with x=0.5 and 0.75, I-E characteristics were simple ohmic behaviors and their ferroelectric hysteresis loops were the saturated and undistorted hysteresis loops. The remanent polarization (Pr) and coercive field (Ec) of the BET Film with x=0.75 were above 30μC/cm2 and 85KV/cm , respectively.

Abstract: Pr6O11-doped bismuth titanate (BixPryTi3O12: BPT) thin films with random oriention were fabricated on Pt/Ti/SiO2/Si substrates by rf magnetron sputtering technique, and the structures and ferroelectric properties of the films were investigated. XRD studies indicated that all of BPT films consisted of single phase of a bismuth-layered structure with well-developed rod-like grains. For samples with y=0.06, 0.3, 1.2 and 1.5, ferroelectric hysteresis loops were characterized by large leakage current, whereas for samples with y=0.6 and 0.9, ferroelectric hysteresis loops were the saturated and undistorted hysteresis loops. The remanent polarization ( Pr ) and coercive field (Ec) of the BPT Film with y=0.9 were above 35μC/cm2 and 80KV/cm , respectively. After 3×1010 switching cycles, 20% degradation of 2Pr is observed in the film with y=0.9.

Abstract: The electrical properties and Microstructures of Tb-doped bismuth titanate (Bi3.3Tb0.6Ti3O12) ceramic were investigated. XRD analyses revealed that the sample had Bi-layered perovskite structure. SEM micrographs showed randomly oriented and plate-like morphology. The remanent polarization (Pr) and coercive field (Ec) of Bi3.3Tb0.6Ti3O12 ceramic are above 25 μC/cm2 and 80 KV/cm, respectively.

Abstract: The electrical properties of Bi3.25Dy0.75Ti3O12 (BDT) and Bi3.25Gd0.75Ti3O12 (BGT) ceramics were investigated. The current-voltage curve of the BGT sample exhibits a negative differential resistance behavior, whereas that of the BDT sample exhibits a simple ohmic behavior. The impedance spectrum of the BDT and BGT samples indicate that both 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. Both BDT and BGT samples exhibit randomly oriented and plate-like morphology.