Ferroelectricity in Aurivillius-Type Structure Ceramics with n = 2 and (SrBi2Nb2O9)0.35(Bi3TiNbO9)0.65 Composition

Aurivillius-type structure compounds are good candidates for their use as high temperature piezoelectrics, due to their high ferro-paraelectric phase transition temperature. However, this characteristic correlates with a high coercive field that makes difficult the poling process, necessary to have piezoelectric activity. The electric properties, specially conductivity, limit the maximum poling field. On the other hand, piezoelectric properties are directly related to the ferroelectric remanent polarization. Thus, the study of both characteristics is towards improving the piezoelectric properties of these materials. In this work, ceramics with nominal composition (SrBi₂Nb₂O₉)_0.35(Bi₃TiNbO₉)_0.65 (T_C∼ 760^∘C), prepared by hot pressing of mechanically activated precursors, have been studied. The electrical properties (permittivity, dielectric loss factor and d.c. conductivity) as a function of frequency and temperature have been measured, up to temperatures higher than the ferro-paraelectric phase transition, and their anisotropy explained in terms of the ceramic texture. Well-saturated ferroelectric hysteresis loops at 250^∘C have been obtained, with values of P_r = 21.4 μ C/cm² and E_c = 70.4 kV/cm.     

Effects of O2 rapid thermal annealing on themicrostructural properties and reliability of RF-sputteredTa2O5 films

The microstructural properties and reliability of sputtered Ta₂O₅ films treated by various temperatures of rapid thermal annealing (RTA) in O₂ atmosphere have been systematically investigated. Analytical results revealed that whenever the RTA temperature was >650°C, the noncrystallinity of as-grown Ta₂O₅ film would be effectively improved from an amorphous phase to the β-Ta₂O₅ phase. Leakage current measurement indicated that leakage current decreases with increasing annealing temperature in a low RTA temperature range (⩽650°C) and, contrarily, increases with increasing annealing temperature in a high RTA temperature range (650 to 950°C). The former result was asserted in that reducing pinholes and oxygen vacancies played key factors. However, the latter result arose due to significant Si diffusion into the Ta₂O₅ film, causing a leaky transition layer distributed along the grain boundary to form the leakage path. Finally, the time-dependent dielectric-breakdown experiments revealed that 950°C O₂ RTA treated Ta₂ O₅ film possessed the superior crystallinity, creating less interfacial hole trap states at the junction of Ta₂O₅/Si and exhibiting the best long-term reliability     

Dy2O3掺杂LiDyxMn2-xO4的合成及性能

采用类似溶胶-凝胶法合成稀土金属氧化物Dy2O3掺杂LiDyxMn2-xO4(x=0,0.01,0.02,0.05).通过XRD和恒流充放电测试了稀土金属元素Dy的掺杂对正极材料的结构以及电化学性能的影响.研究结果表明当掺杂量x=0.02时,材料LiDy0.02Mn1.98O4具有较高的初始比容量(109mAh/g)和循环性能,50次循环后,容量保持率为95%.     

Studies on Electrical Properties and Magnetoelectric Effect of (x)Ni0.8Cu0.2Fe2O4 + (1?x)Ba0.8Pb0.2Ti0.8Zr0.2O3 Composites

Materials consisting of piezomagnetic and piezoelectric phases viz. Ni_0.8Cu_0.2Fe₂O₄ and Ba_0.8Pb_0.2 Ti_0.8Zr_0.2O₃ have been prepared by standard ceramic method. The presence of two phases in the composites has been confirmed by XRD. Variation of the dielectric constant with frequency in the range 100–1 MHz has been studied at room temperature and the variation of dielectric constant with temperature at set frequencies (1 kHz, 10 kHz, 100 kHz and 1 MHz) has been studied. The dielectric relaxation was observed for the compositions with tetragonal structure whereas normal behaviour was observed for cubic structure. All the samples have shown linear magnetoelectric conversion in the presence of a static magnetic field. The dc resistivity (ρ_DC) was studied as a function of temperature in the range 300–773^∘K. The variation of resistivity with temperature shows metal/seconductor behaviour.     

Current Instability, Permittivity Variation With Frequency, and Their Relationship in Ta2O5 Capacitor

In this paper, Ta₂O₅ current instability in MIM and MIS capacitors is studied over several sample thicknesses with a current-versus-time measurement and low-frequency dielectric spectroscopy. Three types of phenomena are identified. The first one is attributed to polarization current correlated to flat loss behavior. The second mechanism corresponds to the conduction current identified as a steady state: a unique mechanism, probably a Poole-Frenkel one, is observed on the whole investigated voltage range. Finally, a resistance degradation phenomenon occurs that has been attributed to ionic diffusion in dielectric and follows the space-charge-limited theory. According to physical characterization, a model based on oxygen vacancies migration in the dielectric is suggested. Moreover, according to low-frequency dielectric spectroscopy measurements, it has been identified that the low-frequency loss peak is created by the same defects and is well modeled by the Maxwell-Wagner approach.