Effect of B-site isovalent doping on electrical and ferroelectric properties of lead free bismuth titanate ceramics

In the present work, zirconium modified bismuth titanate ceramics have been studied as potential lead-free ferroelectric materials over a broad temperature range (RT – 800 °C). Polycrystalline samples of Bi₄Ti_3−xZr_xO₁₂ (x=0.2, 0.4, 0.6) (BZrT) with high electrical resistivity were prepared using the solution combustion technique. The effect of Zr doping on the crystalline structure, ferroelectric properties and electrical conduction characteristics of BZrT ceramics were explored. Addition of zirconium to bismuth titanate enhances its dielectric constant and reduces the loss factor as it introduces orthorhombic distortion in bismuth titanate lattice which is exhibited by the growth along (0010) lattice plane. Activation energy due to relaxation is found to be greater than that due to conduction thus confirming that electrical conduction in these ceramics is not due to relaxation of dipoles. Remanent polarization of the doped samples increases as the Zirconium content increases.     

Dynamic behaviors of ferroelectric liquid crystal molecules under an applied electric field

The dynamic changes in ferroelectric liquid crystal (FLC) molecular alignments under an applied electric field are examined by observing the formation of conoscopic figures with a time resolution of 0.1 ms. Close agreements between observed and simulated conoscopic figures under low voltage (30 V) were obtained. Under high voltage (120 V), however, the observed conoscopic figures became blurred between 0.8 ms and 1.1 ms after reversal of the electric field. The light scattering producing the blurriness occurred due to the development of fast transient molecular alignments during the switching transition above the applied voltage 70 V.     

Structural and electrical properties of Nd ion modified lead zirconate titanate nanopowders and ceramics

A modified sol-gel method is used for synthesizing Nd ion doped lead zirconate titanate nanopowders Pb_{1 - 3x}/2Nd_xZr₀.52Ti₀.48O₃ (PNZT) in an ethylene glycol system with zirconium nitrate as zirconium source. The results show that it is critical to add lead acetate after the reaction of zirconium nitrate with tetrabutyl titanate in the ethylene glycol system for preparing PNZT with an exact fraction of titanium content. It has been observed that the dopant of excess Nd ions can effectively improve the sintered densification and activity of the PNZT ceramics. Piezoelectric, dielectric and ferroelectric properties of the PNZT ceramics are remarkably enhanced as compared with those of monolithic lead zirconate titanate (PZT). Especially, the supreme values of piezoelectric constant (d₃₃) and dielectric constant (\it ε) for the PNZT are both about two times that of the monolithic PZT and moreover, the remnant polarization (P_r) also increases by 30%. According to the analysis of the structures and properties, we attribute the improvement in electrical properties to the lead vacancies caused by the doping of Nd ions.     

Effect of Zr:Sn ratio in the lead lanthanum zirconate stannate titanate ceramics on microstructure and electric properties

The effect of variations of the Zr:Sn ratio on the microstructure and electric properties of lead lanthanum zirconate stannate titanate (PLZST) antiferroelectric ceramics were investigated. The precursor powders were synthesized by the modified coprecipitation method and all the samples were pure perovskite phase in the XRD patterns. The ceramics sintered at 1100 °C exhibited the highest relative density. With the increasing of Sn⁴⁺ content, the grain size of the ceramics was decreased in the SEM and the maximum dielectric constant and the corresponding temperature were decreased. The P-E hysteresis loops indicated that it is helpful to steady the antiferroelectric phase by increasing Sn⁴⁺ content.     

掺杂钛酸钡薄膜的合成及性能研究

通过化学溶液沉积法制备的BiFeO3-BaTiO3薄膜在室温下能够同时显现铁电性及铁磁性。在600-700℃的条件下,以Pt/TiOx/SiO2/Si为载体,能够成功得到钙钛矿单相0.7BiFeO3-0.3BaTiO3薄膜。随着结晶温度上升,晶粒持续增长,最终在700℃到达更高的结晶度。由于0.7BiFeO3-0.3BaTiO3薄膜的绝缘电阻较低,它所显现的极化（P）-电场（E）磁滞回线较弱。尽管如此,由于在0.7BiFeO3-0.3BaTiO3薄膜铁的位置上添加锰,高作用场的漏电流有效地减少,最终铁电性质得到了提高。在室温下,添加了摩尔分数5%的锰的0.7BiFeO3-0.3BaTiO3薄膜同时显现铁电极化和铁磁磁化磁滞回线。     

Influences of compressive stress and aging on dielectric properties of sodium bismuth titanate ceramics

The influences of compressive stress and aging on dielectric properties of undoped and Fe-doped sodium bismuth titanate (NBT) ceramics were investigated. The dielectric properties were decreased significantly with the compressive stress applied parallel to the electric field direction, while the changes were reversed with the stress applied perpendicularly. In addition, lower changes of the dielectric properties with stress were observed in Fe-NBT ceramics, likely caused by an enhanced relaxor characteristic with the acceptor doping, which also reduced the aging rate in the ceramics. Finally, the aging behavior of the NBT and Fe-NBT ceramics followed the slightly stretched exponential law, and the aging rate in both ceramics was found to decrease with frequency, a result of the pinning of the polarization components. These observations clearly confirmed the role of the acceptor dopant in enhancing the relaxor ferroelectric characteristics in the NBT-based ceramics.     

Synthesis of bismuth titanate with urea as fuel by solution combustion route and its dielectric and ferroelectric properties

Preparation of ferroelectric bismuth titanate (Bi₄Ti₃O₁₂) is carried out by solution combustion route with urea as fuel at much lower calcinations temperatures. The single phase bismuth titanate was obtained after calcinations at 800 °C. SEM micrographs of the calcined powders show agglomerated, flaky and foamy morphology, which is typical of combustion synthesis and that of sintered ceramics shows the grain formation. Behavior of dielectric constant and dielectric loss as a function of temperature of as-prepared sample are reported in this communication. Ferroelectric to paraelectric phase transition occurs at the temperature T_c ∼ 660 °C. Its remnant polarization (2P_r) is very less of the order of 0.012 μC/cm².     

Behavior of a lead scandium tantalate ferroelectric in an ac electric field

The behavior of an incompletely ordered lead scandium tantalate ferroelectric (the degree of ordering s=0.8) in the region of the spontaneous ferroelectric transition is studied in ac electric fields by dielectric and optical methods. Dielectric nonlinearity of two types is observed. In fields above 2 kV/cm, the nonlinearity is caused by induced polarization effects and macrohysteresis behavior, whereas in weak fields, it is most probably associated with the dynamics of domain walls and/or phase boundaries.     

Reversible polarization of ferroelectric ceramics in a rapid-growing electric field

The complex permittivity of ferroelectric PZT ceramics with different compositions was measured in a pulsed rapid-growing electric field. The time dependence of the real component exhibits three peaks. The dips between them correlate with imaginary component peaks. Domain mechanisms that contribute to the ferroelectric polarization and are responsible for the time dependences are considered.     

电场中三层铁电超晶格的物理性质研究

基于微分算符技术的相关有效场理论研究用伊辛模型描述的铁电三层超晶格的物理性质。讨论了电场对电极矩、电极化率、热电系数等物理性质的影响。     

静水压下锆锡钛酸铅铁电陶瓷相变和介电性能研究

研究了铌掺杂锆锡钛酸铅铁电陶瓷Pb_0.99Nb_0.02[(Zr_0.90Sn_0.10)_0.96Ti_0.04]_0.98O₃(PZST 90/10-4-2Nb)在静水压(0-300 MPa)下的电荷释放量和介电性能. 对压力诱导的低温铁电三方(F_R(LT))→反铁电正交(A_O)相变进行了研究. PZST 90/10-4-2Nb铁电陶瓷分为未极化、极化和压力去极化三种. 极化PZST 90/10-4-2Nb陶瓷F_R(LT)→A_O相变过程中,电荷释放量为29.3 μC/cm²,相变压力为140 MPa. 介电性能表明:极化PZST 90/10-4-2Nb陶瓷相变压力为136 MPa,而未极化陶瓷相变压力为104 MPa,压力去极化陶瓷未表现出明显的相变特征. 关键词： 静水压 铁电陶瓷 相变 介电     

Electronic and transport properties of zigzag-edge monolayer/bilayer phosphorene nanoribbon junctions under a perpendicular electric field

We study the electronic and transport properties of monolayer/bilayer/bilayer (ML/BL/BL) and monolayer/bilayer/monolayer (ML/BL/ML) zigzag-edge phosphorene nanoribbon (ZPNR) junctions modulated by a perpendicular electric field (PEF). Within the tight-binding model Hamiltonian and by adopting the nonequilibrium Green's function, it is demonstrated that some oscillating conductance plateaus appear for the junctions, and the conductances are suppressed by the applied PEF. Interestingly, the direction of the PEF has different influence on the conductance of both junctions. We further present separately the band structures of the left lead, the central region and right lead, to reveal the reason for different conductance behavior in detail. Our results show that the ML/BL/BL ZPNR junction may be more suitable for the usage of field effect transistor than the ML/BL/ML ZPNR one under a PEF. Moreover, a PEF can be applied to distinguish the bottom−bottom and bottom−up configurations for the ML/BL/ML ZPNR junction.     

NMR study of triglycine sulphate (TGS) in electric field perpendicular to the ferroelectric axis

The electric field applied perpendicular to the ferroelectric axis bHOP (in Hoshino, Okaya, Pepinsky notation) of the TGS crystal, results new domain structure-striped domains with walls parallel to the cHOP axis. The process is accompanied by changes of the dielectric properties. We present the results of NMR study of TGS crystal with electric field applied parallel to the cHOP or to the cHOP x bHOP directions. After 12 h application of the DC field, a decrease in amplitude of the 1H NMR central line is observed.     

Influence of sintering conditions on structural,thermal, electric and ferroelectric properties of Na0.5Bi0.5TiO3 ceramics

Na_0.5Bi_0.5TiO₃ ceramics were prepared by a conventional solid-state reaction method and by a hot-pressing route. The influence of sintering conditions on structural, thermal, dielectric and ferroelectric properties of these ceramics was investigated. All obtained samples exhibited a single perovskite phase. It was shown that the sintering conditions significantly influence the properties under investigation. This includes changes in the value of the electric permittivity ? and dielectric loss tanδ, a shift of T_m and T_d and change of the ferroelectric properties. These effects are mainly related to volatility of the Na and Bi components during the sintering process along with formation of their compensating charge defects, which leads to local structure change.     

Effect of sintering temperature on the structural, dielectric and ferroelectric properties of tungsten substituted SBT ceramics

Structural, dielectric and ferroelectric properties of tungsten (W) substituted SrBi₂(Ta_1−xW_x)₂O₉ (SBTW) [x=0.0, 0.025, 0.05, 0.075, 0.1 and 0.2] have been studied as a function of sintering temperature (1100-1250 °C). X-ray diffraction patterns confirm the single-phase layered perovskite structure formation up to x=0.05 at all sintering temperatures. The present study reveals an optimum sintering temperature of 1200 °C for the best properties of SBTW samples. Maximum T_c of ∼390 °C is observed for x=0.20 sample sintered at 1200 °C. Peak-dielectric constant (ε_r) increases from ∼270 to ∼700 on increasing x from 0.0 to 0.20 at 1200 °C sintering temperature. DC conductivity of the SBTW samples is nearly two to three orders lower than that of the pristine sample. Remnant polarization (P_r) increases with the W content up to x≤0.075. A maximum 2P_r (∼25 μC/cm²) is obtained with x=0.075 sample sintered at 1200 °C. The observed behavior is explained in terms of improved microstructural features, contribution from the oxygen and cationic vacancies in SBTW. Such tungsten substituted samples sintered at 1200 °C exhibiting enhanced dielectric and ferroelectric properties should be useful for memory applications.     

Nonlinear optical properties of an off-center donor in a quantum dot under applied magnetic field

The nonlinear optical properties of an off-center hydrogenic donor in a two-dimensional quantum dot under applied magnetic field are investigated in detail by using the matrix diagonalization method. Based on the computed energies and wave functions, the linear, third-order and total optical absorption coefficients as well as the refractive index changes have been examined between the ground state (L=0) and the first excited state (L=1). The results show that the ion position, the applied magnetic field, the confinement frequency, and the incident optical intensity have an important influence on the nonlinear optical properties of off-center donors.     

Effect of compressive stress on cavitation erosion-corrosion behavior of nickel-aluminum bronze alloy

The effect of compressive stress on cavitation erosion-corrosion behavior of nickel-aluminum bronze alloy was investigated, and the results showed that the alloy exhibited selective phase corrosion of eutectoid “α + κ_iii” and its destruction was aggravated with more cavitation mass loss up to 1.74 times of the specimen without stress. It was mainly owing to the enhanced corrosion-induced erosion caused by compressive stress, which led to lattice distortion of the alloy and the resulting accelerated selective phase corrosion with increasing surface roughness, and then intensified the synergistic effect of electrochemical corrosion and mechanical erosion.