The multiferroic properties of Bi(Fe0.95Co0.05)O3 films

Bi(Fe_0.95Co_0.05)O₃ films were prepared on conductive indium tin oxide (ITO)/glass substrates by chemical solution deposition. Well saturated polarization hysteresis loop has been observed with a remnant polarization value of about 22 μC/cm² at room temperature. Weak ferromagnetism with saturation magnetization of about 3 emu/cm³ was observed at room temperature. The clear observation of both room temperature ferroelectric and ferromagnetic properties suggests the potential multiferroic applications of Bi(Fe_0.95Co_0.05)O₃.     

Effect of electric-field-assisted thermal treatment on the strain and ferroelectric properties of (100)-oriented ferroelectric Pb(Zr0.52Ti0.48)O3 thin films

Ferroelectric Pb(Zr_0.52Ti_0.48)O₃ thin films were deposited on the Pt/Ti/SiO₂/Si substrate by a sol-gel method. As a direct electric field was applied on the films during thermal treatment, strain behavior and ferroelectric properties have been investigated. X-ray diffraction patterns show that great tensile strain exists nearby the interface of the 250 nm thin film while thermal treatment assisted with direct electric field can obviously relax it. The analysis of hysteresis loops indicates that the remnant polarization increases with the thermal treatment time. These results suggest that electric-field-assisted thermal treatment is an effective way to reduce films' tensile strain through the local plastic deformation in Pt layer and enhance the remnant polarization.     

Electrical characteristics of BaTiO3/ Bi0.5K0.5TiO3 multilayered thin films synthesized via metalloorganic decomposition

Multilayered BaTiO₃(BTO)/Bi_0.5K_0.5TiO₃ (BKT) thin films have been fabricated on Pt/Ti/SiO₂/Si substrates using a metalloorganic decomposition process. XRD investigation of the resultant BTO/BKT multilayered thin films shows that they retain a perovskite-related structure type. They also exhibit a well-defined, polarization–electric field hysteresis loop with a measured remnant polarization (2P_r) of 5 µC/cm² at an applied electric field of 250 kV/cm. The measured dielectric constant and dielectric loss at 10 kHz is 470 and 0.07 respectively. These multilayer BTO/BKT films maintain an excellent fatigue-free character even after 10⁹ switching cycles. The mechanism associated with the enhancement of the electrical properties of the synthesized BTO/BKT films is also discussed.     

溶胶-凝胶法制备Sr2Bi4Ti5O18薄膜及其铁电性能研究

采用溶胶-凝胶法,在氧气氛中和层层晶化的工艺条件下,成功地制备了沉积在Pt/Ti/SiO₂/Si(100)衬底上的铁电性能优良的Sr₂Bi₄Ti₅O₁₈ (SBTi)薄膜,并研究了SBTi薄膜的微结构、表面形貌、铁电性能和疲劳特性.研究表明：薄膜具有单一的层状钙钛矿结构，且为随机取向；薄膜表面光滑，无裂纹，厚度约为725nm；铁电性能测试显示较饱和、方形的电滞回线，当外电场强度为275kV/cm时 关键词： 溶胶-凝胶法 铁电薄膜 2Bi₄Ti₅O₁₈')" href="#">Sr₂Bi₄Ti₅O₁₈     

Influence of cycling electric polarization on multiferroic behaviors in heterostructural films composed of ferroelectric and ferromagnetic oxides

The CoFe₂O₄/Pb(Zr_0.52Ti_0.48)O₃ bilayer films were prepared by a sol–gel process, and the influence of cycling electric polarization on the multiferroic behaviors of the bilayer films was studied. The ferroelectric polarization hysteresis loops under various choices of magnetic bias were measured by an integrating current method. The results showed that after undergoing cycling electric polarization the ferroelectric polarization of the bilayer films enhanced and the suppression of ferroelectric polarization by external magnetic bias remarkably weakened. Based on the measurements of activation energy and leakage current, we confirmed that the oxygen vacancy migration in the bilayer films occurred during cycling electric polarization. Furthermore, we analyzed the mechanism of the influence of cycling electric polarization on the multiferroic behaviors of the bilayer films and attributed it to the oxygen vacancy migration, which could cause a part of ferroelectric domains to be unpinned from the oxygen vacancies and become more active under electric field and magnetic bias.     

Multiferroic properties of Bi0.8La0.2FeO3/CoFe2O4 multilayer thin films

Bi_0.8La_0.2FeO₃/CoFe₂O₄ (BLFO/CFO) multilayer thin films (totally 20 layers BLFO and 19 layers CFO) were prepared on Pt/Ti/SiO₂/Si substrates by pulsed laser deposition. X-ray diffraction and transmission electron microscope measurements show that the films are polycrystalline and consisted of multilayered structure. Ferroelectric hysteresis loops with remnant polarization and saturated polarization of 4.2 and 13.3 μC/cm², respectively, were observed. On the other hand, the films show well-shaped magnetization hysteresis loops with saturated and remnant magnetization of 34.7 and 11.4 emu/cm³, respectively, which are significantly larger than pure BLFO thin films deposited under the same conditions. These results indicate that constructing epitaxial superlattice might be a promising way to fabricate multiferroics with improved properties.     

Synthesis and characterizations of BNT–BT–KNN ceramics for energy storage applications

Dielectric, ferroelectric and piezoelectric properties of the (0.94–x) Bi_0.5Na_0.5TiO₃–0.06BaTiO₃–xK_0.5Na_0.5NbO₃/BNT–BT–KNN ceramics with x = 0.02 and 0.05 (2KNN and 5KNN) were studied in detail. Dielectric study and temperature-dependent polarization hysteresis loops indicated a ferroelectric-to-antiferroelectric transition at depolarization temperature (T_d). The low T_d in both the ceramic samples suggested the dominant antiferroelectric ordering at room temperature (RT), which was also confirmed by RT polarization and strain hysteresis loops studies. Antiferroelectric-to-paraelectric phase transition temperature (T_m) was nearly same for both systems. The 5KNN ceramic samples showed the relaxor behaviour. The values of the dielectric constant, T_d, and maximum strain percentage increased, whereas the coercive field and remnant polarization decreased with the increase of the KNN percentage in the BNT–BT–KNN system. High-energy storage density ～0.5 J/cm³ at RT hinted about the suitability of the 5KNN system for energy storage applications.     

Ferroelectric properties of Pb(Zr1/2Ti1/2)O3–Pb(Zn1/3Nb2/3)O3 ceramics under compressive stress

Effects of compressive stress on the ferroelectric properties of ceramics in PZT–PZN system were investigated. The ceramics with a formula (1−x)Pb(Zr_1/2Ti_1/2)O₃–xPb(Zn_1/3Nb_2/3)O₃ or (1−x)PZT–(x)PZN (x = 0.1–0.5) were prepared by a conventional mixed-oxide method. The ferroelectric properties under the compressive stress of the PZT–PZN ceramics were observed at the stress levels up to 170 MPa using a compressometer in conjunction with a modified Sawyer–Tower circuit. It was found that with increasing compressive stress the area of the ferroelectric hysteresis (P–E) loops, the saturation polarization (P_sat), the remnant polarization (P_r), and the coercive field (E_c) decreased. These results were interpreted through the non-180° ferroelastic domain switching processes.     

Voltage control of millimeter-wave ferromagnetic resonance in multiferroic heterostructures thin films

Multiferroic heterostructures thin films, SrBi₂Ta₂O₉/BaFe₁₂O₁₉ (SBT/BaM), were grown on Pt/TiO₂/SiO₂/Si substrates by using magnetron sputtering and Sol-gel ways. X-ray diffractometer (XRD) analysis showed that only SBT and BaM phases appeared in the multiferroic heterostructures. Magnetic hysteresis loops revealed that the saturated magnetization was 3.7 kG and the M-H characteristics of SBT/BaM were not influenced by the presence of the SBT layer. Ferromagnetic resonance (FMR) measurement showed the lowest FMR linewidth of 205 Oe at 50 GHz. Additionally, when direct-current electric field was applied to SBT layer, as a result of which mechanical deformation of the ferromagnetic layer occurred that leads to a frequency shift in ferromagnetic resonance and the magnetoelectric coupling effect (α) is 1.8 MHz*cm/kV. Our findings indicate that these SBT/BaM thin films have a significant potential for the usage in millimeter wave tunable devices.     

Simulation of hysteresis loops for polycrystalline ferroelectrics by an extensive Landau-type model

Landau-type phenomenological theory is extended to the polycrystalline ferroelectrics by defining a volume fraction of polarization to simulate polarization hysteresis loops. Using this simple model, polarization hysteresis loops of a model Pb(Zr_0.52Ti_0.48)O₃ ceramic at different fields or temperatures are simulated, it is found that our results are in very good agreement with the experimental data for the saturated as well as the unsaturated loops. Moreover, this model can accurately predict the coercive fields and remnant polarizations under arbitrary applied fields.     

Temperature‐dependent ferroelectric dynamic hysteresis properties of modified PMN–PZT relaxor ceramics

Temperature‐dependent ferroelectric dynamic hysteresis properties of modified Pb(Mg_1/3Nb_2/3)O₃–Pb(Zr,Ti)O₃ (PMN–PZT) ceramics have been investigated in a wide range from 298 to 433 K. Interestingly, it was found that back‐switching polarization P_bc increased while the hysteresis area 〈A 〉, coercive field E_c, saturation polarization P_s, and remnant polarization P_r all decreased linearly with temperature below 398 K (close to the macro–micro domain transition temperature T_nr). A set of simple linear temperature scaling relations was established, which is different from the power‐law scaling relations for soft and hard PZT ceramics. At further increased temperature, double‐loop features appeared and the ferroelectric properties varied nonlinearly due to the reversible macro–micro domain transition in the T > T_nr region. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Asymmetric electrical properties in Pt/Ba0.5Sr0.5Ti0.99Co0.01O3/Nb-doped SrTiO3 capacitors

Ba_0.5Sr_0.5Ti_0.99Co_0.01O₃ (BSTC) thin films have been fabricated with pulsed laser deposition on Nb-doped SrTiO₃ (STN) substrate. In Pt/BSTC/STN capacitor, we systematically investigated the capacitance, leakage current and polarization versus bias voltage characteristics, and found that curves of capacitance versus voltage and leakage current versus voltage were not symmetric, and polarization hysteresis loop exhibited large relaxation of the remnant polarization at negatively poled state. A detailed analysis of capacitance data demonstrated a difference of the built-in voltage between top Pt/BSTC interface (V_b,t=2.5 V) and bottom BSTC/STN interface (V_b,b=1.1 V). Such different built-in voltages lead to the presence of an internal electric field, which results in asymmetric electric characteristics in Pt/BSTC/STN capacitor.     

Ferroelectric and phase transition studies in cesium nitrate: poly(vinyl?alcohol)?composite films

The composite films of cesium nitrate (CsNO₃) and poly(vinyl alcohol) (PVA) with varying composition were prepared using the solvent cast method. The hysteresis loop characteristics show optimum remnant polarization (P _r ) of 2.75 μC/cm² at 50 wt.% composition. The field emission scanning electron microscope images show a nearly homogeneous distribution of CsNO₃ grains in the 50 wt.% composite film. The temperature dependence of the remnant polarization shows a diffused transition temperature range from the ferroelectric to the paraelectric phase and this has been attributed to the reduced enthalpy. The butterfly features of the dielectric constant–voltage (ε–V) characteristics have been attributed to polarization switching.     

脉冲电容器用细电滞回线铁电陶瓷材料的研究

采用低锆区的Pb(Zr_0.42Sn_0.40Ti_0.18)O₃(PZST42/40/18)铁电陶瓷为基, 通过少量La和Ba取代Pb同时Nb取代(Zr, Sn, Ti)复合取代的方法得到掺杂PZST42/40/18细电滞回线铁电陶瓷, 其最大极化强度P_max≈20.66μC/cm², 剩余极化强度P_r≈0.55μC/cm^{关键词： 细电滞回线 铁电陶瓷 PZST 脉冲电容器}     

Dielectric and ferroelectric properties of 0.8PZT–0.2PCN ceramics under sintering conditions variation

The influences of sintering conditions on electrical properties of the 0.8Pb(Zr_1/2Ti_1/2)O₃–0.2Pb(Co_1/3Nb_2/3)O₃ ceramics have been investigated with sintering temperatures of 1175, 1200, 1225, and 1250 °C and dwell times for 2, 6, and 10 h. The crystal structure of dense specimens showed coexistence between tetragonal, rhombohedral and pseudo cubic phases in all sintering temperatures, while tetragonal-rich phase appeared with increasing dwell times. A maximum dielectric constant was observed at sintering condition of 1200 °C for 2 h, while the transition temperature slightly increased with increasing dwell time. All ceramics also showed diffused phase transition behaviors with a minimum diffusivity at sintering condition of 1200 °C for 2 h. In addition, the polarization–electric field (P–E) hysteresis loops of the ceramic systems also changed significantly with sintering conditions. Interestingly, the ferroelectric parameters; remnant polarization (P_r) and loop squareness (R_sq) tended to increase with increasing sintering temperatures and dwell times.     

Phase compositions and ferroelectric properties of Pb(Zr0.52,Ti0.48)O3 thin films with different highly orientations prepared by a sol-gel route

It is shown that different highly oriented Pb(Zr_0.52,Ti_0.48)O₃ films can be obtained on Pt/Ti/SiO₂/Si substrate using a sol-gel technique. The effects of pyrolysis temperature on the orientation, phase composition and ferroelectric properties of the films are investigated. It is found the ferroelectric hysteresis loops of (1 1 1)-oriented film, (1 1 1) and (1 0 0) mix-oriented film can both be saturated when the external electric field is large enough, whereas the hysteresis loop of (1 0 0)-oriented film is difficult to saturate. The analysis of X-ray diffraction indicated the possibility of different phase composition in different oriented films under large film residual stress. Higher remnant polarization (53 μC/cm²) for (1 0 0)-oriented film can be attributed to its more tetragonal phase composition, which results in that the in-plane domain switching can continuously occur with external electric field increasing.     

Processing,Structure, Properties,and Applications of PZT Thin Films

There has been a resurgence of complex oxides of late owing to their ferroelectric and ferromagnetic properties. Although these properties had been recognized decades ago, the renewed interest stems from modern deposition techniques that can produce high quality materials and attractive proposed device concepts. In addition to their use on their own, the interest is building on the use of these materials in a stack also. Ferroelectrics are dielectric materials that have spontaneous polarization in certain temperature range and show nonlinear polarization–electric field dependence called a hysteresis loop. The outstanding properties of the ferroelectrics are due to non-centro-symmetric crystal structure resulting from slight distortion of the cubic perovskite structure. The ferroelectric materials are ferroelastic also in that a change in shape results in a change in the electric polarization (thus electric field) developed in the crystal and vice versa. Therefore they can be used to transform acoustic waves to electrical signal in sonar detectors and convert electric field into motion in actuators and mechanical scanners requiring fine control. In a broader sense the ferroelectric materials can be used for pyroelectric and piezoelectric sensors, voltage tunable capacitors, infrared detectors, surface acoustic wave (SAW) devices, microactuators, and nonvolatile random-access memories (NVRAMs), including the potential production of one transistor memory cells, and applications requiring nonlinear optic components. Another set of potential applications seeks to exploit the ferroelastic properties in stacked templates where they are juxtaposed to ferromagnetic materials. Doing so would allow the control of magnetic properties with electric field, which is novel. Such templates taking advantage two or more properties acquired a new name and now goes by multiferroics. After a brief historical development, this article discusses technological issues such as growth and processing, electrical and optical properties, piezo, pyro, and ferroelectric properties, degradation, measurements methods, and application of mainly lead-zirconate-titanate (PZT = PbZr_1?xTi_xO₃). The focus on PZT stems from its large electromechanical constant, large saturation polarization and large dielectric constant.     

Simultaneous measurement of X‐ray diffraction and ferroelectric polarization data as a function of applied electric field and frequency

The characteristics of a new ferroelectric measurement system at the European Synchrotron Radiation Facility are presented. The electric‐field‐induced phase transitions of Pb(Mg_1/3Nb_2/3)O₃–xPbTiO₃ are determined viain situ measurements of electric polarization within the synchrotron diffraction beamline. Real‐time data collection methods on single‐crystal samples are employed as a function of frequency to determine the microstructural origin of piezoelectric effects within these materials, probing the dynamic ferroelectric response.     

Ferroelectric polarization and resistive switching characteristics of ion beam assisted sputter deposited BaTiO3 thin films

In this work, 150 nm thick polycrystalline BaTiO₃ (BTO) films were deposited on Pt/TiO₂/SiO₂/Si substrate by ion beam assisted sputter deposition technique. The bias voltage dependent resistive switching (RS) and ferroelectric polarization characteristics of Au/BTO/Pt devices are investigated. The devices display the stable bipolar RS characteristics without an initial electroforming process. Fittings to current–voltage (I–V) curves suggest that low and high resistance states are governed, respectively, by filamentary model and trap controlled space charge limited conduction mechanism, where the oxygen vacancies act as traps. Presence of oxygen vacancies is evidenced from the photoluminescence spectrum. The devices also display P–V loops with remnant polarization (P_r) of 5.7 μC/cm² and a coercive electric field (E_c) of 173.0 kV/cm. The coupling between the ferroelectric polarization and RS effect in BTO films is demonstrated.     

Influence of magnetic impurities on superconducting property of polycrystalline iron-based NdFeAsO0.88F0.12

Polycrystalline iron-based superconducting NdFeAsO_0.88F_0.12 was prepared via solid-state reaction in ambient pressure. Small amounts of ferromagnetic impurities were detected by Scanning Electron Microscopy (SEM) analysis. To study the influence of magnetism on superconducting properties of the sample, magnetization M(T, H) measurements were performed in fields up to 1.5 T and in the temperature range of 5-60 K. The abnormal behavior was observed in the χ(T) curves, and the magnetization hysteresis loops (MHLs) can be described by a sum of the contributions of superconductive hysteresis, ferromagnetic hysteresis of the impurities and the paramagnetic background of the isolated Nd³⁺ ions. The influence of the ferromagnetic impurities and the paramagnetic background were investigated and discussed. After the corrections of the magnetism contributions, the intrinsic superconductive MHLs as well as the critical current density were obtained.