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Structural and electrical properties of Gd-doped BiFeO3:BaTiO3 (3:2) multiferroic ceramic materials
摘要： Gadolinium doped BiFeO3:BaTiO3 (3:2) polycrystalline multiferroic ceramics have been prepared by high-temperature solid state reaction technique. X-ray diffraction (XRD) analysis at room temperature of the prepared materials confirmed the formation of the compounds with rhombohedral crystal structure. The average particle size of as prepared samples have been found in the range of 35 nm to 55 nm for different doping concentrations. The average grain size of as prepared samples are less than 100 nm which is confirmed from SEM study. The SEM of annealed compounds showed the uniform distribution of grains and the formation of dense ceramic with average grain size in the order of 4 μm. Dielectric studies of the materials reveals that the dielectric constant ( εr ) and tangent loss (tan δ) decreases with doping concentrations at room temperature. The variation of εr and tan δ with temperature was explained on the basis of Maxwell–Wagner mechanism. The values of grain resistance ( Rb ) and grain capacitance (Cb) were obtained from Nyquist plots for the different doping concentrations at 300 °C. The activation energy ( Ea ) was calculated from the curve of frequency dependent ac conductivity ( σac ) within the range 0.19 eV to 0.45 eV. The remnant polarization of the samples (0.53 μC/cm2) was measured from polarization versus electric field (P–E) hysteresis curves. The ferromagnetic behaviour of the Gd-doped BiFeO3:BaTiO3 (3:2) sample has been studied by SQUID for the lowest doping concentration. The value of remnant magnetization was found 0.0235 emu/g at room temperature.
关键词： multiferroic ceramics,dielectric properties,ferroelectric properties,Gd-doped BiFeO3:BaTiO3,ferromagnetic properties
更新于2025-09-09 09:28:46
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Reference Module in Materials Science and Materials Engineering || Liquid Crystals Under High Pressure
摘要： From a historical perspective, the first high pressure experiments were carried out soon after the discovery of liquid crystals, although the field became more active much later. Despite being considered as equivalent thermodynamic variables, temperature (T) and pressure (P) act differently on liquid crystals (LC), with the former affecting the rotational and vibration energy dependent parameters, and the latter altering the intermolecular distances. This feature, in combination with the fact that relatively low pressures bring about significant changes in the properties of LCs, has provided impetus for the studies described here. These investigations have not only augmented the knowledge on LCs obtained at atmospheric pressure, but have provided valuable insights into the understanding of complex fluids (Chandrasekhar and Shashidhar, 1979; Pollmann, 1999; Urban, 2014); the studies have been carried out using apparatus such as optical transmission, DTA, calorimetry, dielectric, NMR, XRD, volumetry, and Raman, detailed in these articles. For the description of the structures of the LC mesophases, numbering more than 40, the reader may refer to the article.
关键词： ferroelectric properties,mesomorphism,liquid crystals,nematic-isotropic transition,high pressure
更新于2025-09-09 09:28:46
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Unveiling the dual role of chemically synthesized copper doped zinc oxide for resistive switching applications
摘要： In this study, efforts were devoted to unveiling the dual role of single crystalline Cu (5%) doped ZnO (Cu:ZnO) synthesized by a simple and low-cost chemical process and to investigate its efficacy on resistive switching (RS) applications. It was found that when Cu:ZnO was annealed at a lower temperature of 450 °C and integrated onto ITO/glass for RS applications, only oxygen mediated vacancies were responsible for its resistive switching. However, ferroelectric properties have been observed when the same Cu:ZnO was annealed at a higher temperature of 800 °C and integrated onto Nb doped SrTiO3. X-ray diffraction, high resolution transmission electron microscope, x-ray photoelectron spectroscopy, UV-VIS-near infrared spectrometer, and piezoelectric force microscopy (PFM) were employed to study the crystallinity, interfaces, chemical compositions, bandgap, and domains in Cu:ZnO thin films, respectively. The bandgap of Cu:ZnO was found to be 3.20 eV. PFM study exhibits the domain inversion with 180° polarization inversion by applying an external bias, evidencing its effectiveness for memory applications. When the electrical characteristics were concerned, the RS device based on this ferroelectric Cu:ZnO offers better performance, such as lower SET/RESET voltages (～1.40 V), higher retention (up to 106 s) without distortion, and higher ON/OFF ratio (2.20 × 103), as compared to the former lower temperature annealed Cu:ZnO devices. A band-diagram was proposed, and transport studies were developed to understand the operational mechanism of these devices. This study explains both the limits and scopes of Cu:ZnO RS devices and formulates an idea which may accelerate the design of future generation devices.
关键词： copper doped zinc oxide,memory applications,band-diagram,resistive switching,ferroelectric properties
更新于2025-09-09 09:28:46
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Effect of strain on the modifications in electronic structure and resistive switching in Ca-doped BiFeO <sub/>3</sub> films
摘要： Strain-induced modifications in the structure, electronic structure, electrical, and ferroelectric properties of the Bi0.90Ca0.10FeO3 (BCFO)/Nb-doped SrTiO3 (100) films have been systematically studied in light of variation in film thickness. X-ray diffraction and ?-scan measurements confirm the single phase, (100) oriented epitaxial growth of all films. Room temperature absorption spectra show the presence of asymmetric broad peak around ～2.5 eV, which is indicative of the presence of defect states inside the bandgap and is attributed to the oxygen vacancies. Improvement in the bipolar resistive switching behavior with a decrement in oxygen vacancies and improvement in ferroelectric properties with increasing film thickness suggest the crucial role of oxygen vacancies and strain in modifying the electrical properties of the BCFO films. Improvement in the ferroelectric behavior is attributed to the increment in the Fe 3d-O 2p hybridization, localization of Fe 3deg/Bi 6s-O 2p orbitals, and reduction in the oxygen vacancies with an increase in the film thickness. Observed stable retention and large ON/OFF switching ratio in BCFO films make them a promising candidate for application in the non-volatile memory device.
关键词： Ca-doped BiFeO3 films,resistive switching,ferroelectric properties,strain,electronic structure
更新于2025-09-04 15:30:14
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Structure evolution and ferroelectric properties in stoichiometric Bi0.5+xNa0.5?xTi1?0.5xO3
摘要： The influence of B-site deficiency on the stability of electrically induced long-range ferroelectric order of Bi0.5+xNa0.5-xTi1-0.5xO3 (BNT-xVTi) (''h'' denotes vacancies) ceramics is studied. The depolarization and ferroelectric to relaxor transition are identified as separate and discrete processes in BNT-based materials. For BNT-0.02VTi, the resonance and anti-resonance peaks on dielectric permittivity-frequency curves indicate dominating ferroelectric phase at room temperature. The depolarization temperature, determined by thermally stimulated depolarization current, is * 65 °C. However, the ferroelectric to relaxor transition temperature is absent, as no distinct frequency-independent anomalies for the dielectric permittivity exist. This depolarization process can be ascribed to nanoscale ferroelectric domain at room temperature for BNT-0.02VTi, which is induced by chemical disorder and strong random field as VTi generated. Hence, the results imply that the B-site deficiency in BNT is a very effective route to tailor the stability of electrically induced long-range ferroelectric order.
关键词： depolarization,B-site deficiency,Bi0.5Na0.5TiO3,ferroelectric properties,relaxor transition
更新于2025-09-04 15:30:14
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Ferroelectric properties of Ag doped PbZr0.53Ti0.47O3 thin film deposited by sol–gel process
摘要： To suppress the generation of oxygen vacancy during the PbZr0.53Ti0.47O3 (PZT) film synthesis process, herein, the 0–3 type Ag/PZT film is chosen as a prototype to systematically investigate the mechanisms of oxygen vacancy decrease and the relationship of ferroelectric properties. The uniform and dense films were successfully fabricated on fluorine tin oxide glasses (FTO) by facile sol–gel processes. It is confirmed the existence of silver nanoparticles in the film, indicating the composite ferroelectric films are of 0–3 type. When Ag doping mole concentration is 0.010 in the sol, a large remnant polarization (Pr) of ~ 50.7 μΧ/cm2 is got, which is 37.9 μΧ/cm2 for pure PZT. UV–vis spectrum confirms the generation of Ag2O in the process of mixing the sol. Furthermore, the oxygen vacancies caused by natural evaporation of lead specie are effectively reduced because of the decomposition of Ag2O, confirmed by X-ray photoelectron spectroscopy. This work points out the generated Ag2O as the intermediate product is the key to achieve high remnant polarization in Ag/PZT based film and make it as a promising candidate for memory applications.
关键词： remnant polarization,oxygen vacancy,Ag doped PbZr0.53Ti0.47O3,sol–gel process,Ferroelectric properties
更新于2025-09-04 15:30:14