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Variable-range-hopping conduction and polaron dielectric relaxation in Cu and Nb co-doped BaTiO3
摘要： BaTi0.7(Cu0.1Nb0.2)O3 ceramic was prepared using a solid-state method and its structure, valence states, conduction mechanism and dielectric properties were investigated in detail. A fine-grained microstructure and a distorted pseudo-cubic perovskite structure were confirmed by scanning electron microscopy, X-ray diffraction analysis and Raman spectroscopy. X-ray photoelectron spectroscopy analysis suggested that Cu in BaTi0.7(Cu0.1Nb0.2)O3 was polyvalent but the valence states of Ti and Nb were invariable. Mott’s variable-range-hopping (VRH) conduction was observed. The two colossal dielectric constant plateaus in low- and high-temperature ranges were ascribed to the electrode and grain boundary responses, respectively. The VRH model described the low-temperature relaxation well, indicating that the dielectric relaxation was a polaron relaxation rather than Maxwell–Wagner type. Both grain and grain boundary resistances were well fitted by the VRH model, suggesting that the VRH mechanism was tenable in both grain and grain boundaries. The electron paramagnetic resonance signal was ascribed to Cu ions, and the linewidth showed a linear relationship with T?1/4, corresponding to the charge transfer between different valence via Cu+-O-Cu2+ and Cu2+-O-Cu3+ paths. The hopping of carriers was also responsible for the conduction and polaron dielectric relaxations.
关键词： Variable-range-hopping conduction,Electron paramagnetic resonance.,Dielectric relaxation,Cu and Nb co-doped BaTiO3
更新于2025-09-23 15:23:52
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Effect of an electric field on the electrocaloric response of ferroelectrics
摘要： The electrocaloric effect of the model ferroelectric BaTiO3 was investigated using phenomenological theory. The results indicate that the applied electric field strength is a key factor for the induced electrocaloric response and there are two distinguishing electrocaloric responses. When a moderate electric field is applied, the electrocaloric temperature variation is small but the electrocaloric strength is high. In contrast, the electrocaloric temperature variation is large but electrocaloric strength is low when a very high electric field is applied. These results are consistent with the experimental observations on BaTiO3 based bulk and thin film ferroelectric materials.
关键词： BaTiO3,ferroelectrics,electrocaloric effect
更新于2025-09-23 15:23:52
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Fabrication and electromagnetic wave absorption property of quartz ceramics with a gradient distribution of BaTiO3
摘要： Quartz ceramics with a uniform/gradient distribution of BaTiO3 (U/G–SO–BTO) are fabricated by cold pressing a powder blend with BTO followed by sintering and using a combined technique of spreading the powder blends with gradually increased BTO layer–by–layer and sintering. The electromagnetic wave absorption properties of these two ceramics are studied in detail. For U–SO–BTO samples, the primary electromagnetic re?ection is strong due to the aggravated impedance mismatch at their surfaces. The electromagnetic wave re?ectivity of U–SO–BTO could only reach ?7.0 dB when the sample thickness is 6 mm and the BTO content is 8.0 wt%, and it decreases slightly to ?8.1 dB when the sample thickness is increased to 10.0 mm and the BTO content is decreased to 5.0 wt% simultaneously. For G–SO–BTO samples, electromagnetic waves could enter with little re?ection due to the weak surface impedance mismatch, and the electromagnetic waves entering these samples could propagate forward while being absorbed gradually with little re?ection because of the weak impedance mismatch at the interfaces. The G–SO–BTO samples are promising excellent electromagnetic absorbing materials because their electromagnetic wave re?ectivity could reach a level lower than ?12.0 dB and could decrease further from –12.2 to ?13.1 dB as the layer thickness increases from 1.0 to 2.0 mm.
关键词： Impedance mismatch,Electromagnetic wave absorption,Quartz ceramics,Electromagnetic re?ection,Gradient distribution,BaTiO3
更新于2025-09-23 15:22:29
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Tuning optical and magnetic properties of nanocrystalline BaTiO3 films by Fe doping
摘要： Fe-doped BaTiO3 is a promising multiferroics material due to its appealing physical properties and potential applications in sensors, transducers and non-volatile memories and multilayer capacitors. Herein, Fe-doped BaTiO3 nanocrystalline films were deposited on silicon substrates by chemical solution route. The relation between Fe content and the optical and magnetic properties of the samples was analyzed. X-ray diffraction data show that the films are tetragonal with P4mm space group. The atomic force microscopy measurement indicates that the film surface roughness increases with Fe composition. The optical response behavior of the films was investigated by Adachi’s dielectric function model with fitting ellipsometric spectra in the photon energy 1.5–4.13?eV. With increasing Fe content, the real part of dielectric functions gradually decreases in the transparent region. Moreover, EOBG (the optical band gap) is reduced with increasing Fe composition x, and the relationship between them is EOBG = (3.817–1.440 × x) eV. All Fe-doped films show weak ferromagnetism coming from the bound magnetic polarons and exchange interaction between oxygen vacancies and Fe3+ in the films. When iron content x exceeds 0.06, the magnetization values of the samples exhibit an unsaturated characteristic at more than 3000 Oe magnetic fields, which is due to the competition between the ferromagnetism and the antiferromagnetism of two Fe3+ ions superexchange. These results suggest that optical and magnetic properties of Fe-doped BaTiO3 nanocrystalline films can be changed by Fe composition.
关键词： multiferroics,optical properties,Fe-doped BaTiO3,magnetic properties,chemical solution route
更新于2025-09-23 15:21:21
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Strategies to Achieve High Performance Piezoelectric Nanogenerators
摘要： Piezoelectric nanogenerators have attracted much attention in the past decade. In this study, the development of piezoelectric nanogenerators and their progress toward high power generation is discussed. The characteristics and application range of numerous types of piezoelectric nanogenerators are also considered. In addition, several strategies that may improve the performance of piezoelectric nanogenerators are summarized. Here, we compare the open circuit voltages and short circuit currents of various piezoelectric nanogenerators under different factors, and the current problems of piezoelectric nanogenerators are also discussed. Finally, the future prospects and directions of piezoelectric nanogenerators are predicted. Future studies should be focused on the production of high-performance materials, the establishment of working principle and simulation model, the integration of nanogenerator, and the design of the energy harvesting circuit. Hence, it is emergency to search for functional materials with high piezoelectricity and further improve the electromechanical properties of existing piezoelectric materials. Moreover, further research is needed to increase the stability and flexibility of composite materials, to develop wearable and embedded flexible functional devices based on the biocompatibility of inorganic nanoparticles, and to supply power for microelectronic systems.
关键词： BaTiO3,Piezoelectric nanogenerators,Composite thin film materials,PVDF,Chemical doping,Nanostructure
更新于2025-09-23 15:21:01
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Energy storage properties in BaTiO <sub/>3</sub> -Bi <sub/>3.25</sub> La <sub/>0.75</sub> Ti <sub/>3</sub> O <sub/>12</sub> thin films
摘要： Developing lead-free film dielectric capacitors with high-performance of energy storage density, efficiency, fatigue endurance, and thermal stabilities is desirable. Here, we report energy storage properties in (1-x)BaTiO3-xBi3.25La0.75Ti3O12 thin films. It is revealed that a 0.6BaTiO3-0.4Bi3.25La0.75Ti3O12 thin film with a thickness of 280 nm and a crystallization temperature of 650 °C shows a breakdown strength of 3.23 MV/cm with a large polarization value and dielectric constant. An ultrahigh energy storage density of 61.1 J/cm3 and an efficiency of 84.2% are simultaneously achieved at room temperature. Additionally, excellent fatigue endurance after 6 × 109 cycles and good thermal stability up to 150 °C are observed, implying excellent energy storage performance in 0.6BaTiO3-0.4Bi3.25La0.75Ti3O12 thin films.
关键词： energy storage,thin films,BaTiO3-Bi3.25La0.75Ti3O12,dielectric capacitors,lead-free
更新于2025-09-23 15:21:01
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The electronic structures and optical properties of B, C or N doped BaTiO <sub/>3</sub>
摘要： The electronic structures and optical properties of Boron, Carbon or Nitrogen doped BaTiO3 are calculated by the first-principles calculations. The doped atoms decrease the band gap of BaTiO3 significantly, which could increase the host material ability to absorb the visible light. The absorption spectrum calculations confirm that both Boron and Carbon-doped BaTiO3 have a favorable performance in the absorption of visible light. However, Nitrogen-doped BaTiO3 doesn’t present the improvement. BaTiO3 doped with Boron or Carbon is expected to be a new class of perovskite materials for the field of solar energy.
关键词： BaTiO3,doping,optical properties,solar energy,electronic structures
更新于2025-09-23 15:21:01
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Effect of the occupation of Ba and Ti sites on the structural, optical and dielectric properties of Sm-doped BaTiO3 ceramics
摘要： Sm-doped BaTiO3 powders have been synthesized with the help of the sol gel process. X-ray diffraction (XRD) patterns of the obtained powders, heat treated at a relatively low temperature (750 °C/3 h), revealed their crystallization in the pure perovskite structure without the presence of secondary phases. The occupation of the Ba and Ti sites by Sm in the BaTiO3 lattice and the evolution of the crystalline parameters as functions of the dopant content have been discussed based on XRD and Raman results. Dielectric measurements performed on the samples revealed a strong increasing diffuse character of the ferro-to-paraelectric phase transition with increasing Sm content. Moreover, the behavior of the permittivity as a function of frequency indicates that the samples are approaching their resonance frequency. The study of the conductivity showed the existence of a weak positive temperature coefficient of resistivity (PTCR) effect.
关键词： Sm-doped BaTiO3,dielectric properties,PTCR effect,perovskite structure,sol gel process
更新于2025-09-23 15:21:01
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Effects of substrate-controlled-orientation on the electrical performance of sputtered BaTiO <sub/>3</sub> thin films
摘要： In this work, the relationships between bottom electrode/substrate configuration, crystalline microstructure, and electrical performances of BaTiO3 (BTO) thin films were investigated. The films were fabricated via RF magnetron sputtering on (Sr0.5La0.5)CoO3 (LSCO) buffered (110)-, (111)-SrTiO3 (STO) and SrRuO3 (SRO) buffered (110)-, (111)-MgO (MGO) substrates. The x-ray diffractometer results show that the LSCO/STO substrate resulted in films with high-quality epitaxial orientation, whereas the SRO/MGO substrate resulted in films having a strong (110) texture. The electrode/substrate configurations were designed to control the crystalline microstructure, which in turn affects the electrical performances of the films. The electrical performances were studied by employing a metal/ferroelectric/metal model. The J-V characteristics show obvious asymmetry with bias, which is mainly due to the varying transport state of oxygen vacancies. BTO films grown on LSCO/STO substrates exhibit large dielectric frequency dispersion, while those grown on SRO/MGO substrates display a nearly frequency independent response. All electrical parameters of these films were strongly affected by the polarization-tilting angle and the preferred orientation degree. Epitaxial and textured (110)-oriented films show higher permittivity but lower loss tangent, free-carrier concentration, built-in voltage, and leakage current density as compared to the epitaxial (111)-oriented film.
关键词： dielectric properties,electrical performance,substrate-controlled-orientation,BaTiO3 thin films,RF magnetron sputtering
更新于2025-09-23 15:19:57
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Grain boundary effects on piezoelectric properties of the core–shell-structured BaTiO <sub/>3</sub> @TiO <sub/>2</sub> ceramics
摘要： Grain boundary effect on BaTiO3 has been widely investigated for several decades. However, all of them tailored the grain boundary by grain size of BaTiO3. In this case, a direct way was introduced to modify the grain boundary by coating technique to investigate the role of grain boundary in ferroelectric materials. Nonferroelectric phase TiO2 was employed to investigate grain boundary effects on the electrical properties of BaTiO3 piezoelectric ceramics. TiO2 coating can result in the reduction of piezoelectric and ferroelectric properties and the annealing process in oxygen can increase piezoelectric behavior of pure BaTiO3 due to valence state of Ti ions while that remains for Ti-modified composition possibly due to the increased grain boundary effect by impedance analysis. Compared with ferroelectric grain, grain boundary plays a critical role to impact the electrical properties of perovskite-type ferroelectric materials.
关键词： defects.,Piezoelectric properties,ferroelectric properties,BaTiO3 and titanates
更新于2025-09-19 17:15:36