- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Phase-transition induced giant negative electrocaloric effect in a lead-free relaxor ferroelectric thin film
摘要： Ferroelectric/antiferroelectric thin/thick films with large positive or negative electrocaloric (EC) effects could be very useful in designing commercial refrigeration devices. Here, a giant negative EC effect (maximum ΔT ≈ ?42.5 K with ΔS ≈ ?29.3 J K?1 kg?1) comparable to the best positive EC effects reported so far is demonstrated for 0.5(Ba0.8Ca0.2)TiO3–0.5Bi(Mg0.5Ti0.5)O3 (BCT–BMT) lead-free relaxor ferroelectric thin films prepared on Pt(111)/TiOx/SiO2/Si substrates using a sol–gel method. An electric-field induced structural phase transition (nanoscale tetragonal and orthorhombic to rhombohedral) along the out-of-plane [111] direction plays a very key role in developing the giant negative EC effect. This breakthrough will pave the way for practical applications of next-generation refrigeration devices with high cooling efficiency in one cycle by ingeniously utilizing and combining both the giant negative and positive EC effects. Moreover, a large energy density of 51.7 J cm?3 with a high power density of 1.15 × 1010 W kg?1 at room temperature is also achieved in the thin film, indicating that it is also an attractive multifunctional material for energy storage.
关键词： lead-free,energy storage,electrocaloric effect,phase transition,thin film,relaxor ferroelectric
更新于2025-11-14 17:28:48
-
[IEEE 2018 IEEE 2nd International Conference on Dielectrics (ICD) - Budapest (2018.7.1-2018.7.5)] 2018 IEEE 2nd International Conference on Dielectrics (ICD) - Influence of Composition and Preparation on Crystalline Phases and Morphology in Poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) Relaxor-Ferroelectric Terpolymer
摘要： The influence of chemical composition and crystallisation conditions on the ferroelectric and paraelectric phases and the resulting morphology in Poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) (P(VDF-TrFE-CFE)) terpolymer films with 55.4/37.2/7.3 mol% or with 62.2/29.4/8.4 mol% of VDF/TrFE/CFE was studied. Poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) with 75/25 mol% VDF/TrFE was employed as reference material. Fourier-Transform Infrared Spectroscopy (FTIR) was used to determine the fractions of the relevant terpolymer phases, and X-Ray Diffraction (XRD) was employed to assess the crystalline morphology. The FTIR results show an increase of the fraction of paraelectric phases after annealing. On the other hand, XRD results indicate a more stable paraelectric phase in the terpolymer with higher CFE content.
关键词： P(VDF-TrFE-CFE) terpolymer,Curie transition,relaxor-ferroelectric polymer,ferroelectric and paraelectric phases
更新于2025-09-23 15:22:29
-
Decoupling mesoscale functional response in PLZT across the ferroelectric – relaxor phase transition with contact Kelvin probe force microscopy and machine learning
摘要： Relaxor ferroelectrics exhibit a range of interesting material behavior including high electromechanical response, polarization rotations as well as temperature and electric field-driven phase transitions. The origin of this unusual functional behavior remains elusive due to limited knowledge on polarization dynamics at the nanoscale. Piezoresponse force microscopy and associated switching spectroscopy provide access to local electromechanical properties on the micro- and nanoscale, which can help to address some of these gaps in our knowledge. However, these techniques are inherently prone to artefacts caused by signal contributions emanating from electrostatic interactions between tip and sample. Understanding functional behavior of complex, disordered systems like relaxor materials with unknown electromechanical properties therefore requires a technique that allows to distinguish between electromechanical and electrostatic response. Here, contact Kelvin probe force microscopy (cKPFM) is used to gain insight into the evolution of local electromechanical and capacitive properties of a representative relaxor material lead lanthanum zirconate across the phase transition from a ferroelectric to relaxor state. The obtained multidimensional data set was processed using an unsupervised machine learning algorithm to detect variations in functional response across the probed area and temperature range. Further analysis showed formation of two separate cKPFM response bands below 50°C, providing evidence for polarization switching. At higher temperatures only one band is observed, indicating an electrostatic origin of the measured response. In addition, from the cKPFM data qualitatively extracted junction potential difference, becomes independent of the temperature in the relaxor state. The combination of this multidimensional voltage spectroscopy technique and machine learning allows to identify the origin of the measured functional response and to decouple ferroelectric from electrostatic phenomena necessary to understand the functional behavior of complex, disordered systems like relaxor materials.
关键词： phase transition,machine learning,Relaxor ferroelectric,lead lanthanum zirconium titanate,piezoresponse force microscopy,k-means clustering,contact Kelvin probe force microscopy
更新于2025-09-23 15:21:01
-
Colossal dielectric, relaxor ferroelectric, diamagnetic and weak ferromagnetic properties of NdCrO3 perovskite nanoparticles
摘要： The NdCrO3 perovskite nanoparticles have been successfully synthesized using sol–gel auto-combustion process. Structural and morphological characterizations of the material have been performed at room temperature using XRD and SEM, respectively. Frequency- and temperature-dependent dielectric measurements have been performed in the range of 1 Hz–10 MHz and RT - 300 °C, respectively. The dielectric constant is found to be in the order of e0 > 103 at room temperature, indicating the colossal dielectric constant behaviour. Ferroelectric phase transition temperature has increased with an increase in frequency, suggesting that the material is a relaxor ferroelectric nature. Temperature- and field-dependent magnetization measurements have been carried out in the temperature range (5–400 K) and field up to 5 T. M–T curve exhibited a diamagnetic-like behaviour in low temperature and low fields. Two magnetic transitions were found at TN1 (223 K) and TN2 (33 K) which correspond to para to weak ferromagnetic transition and Nd3+ spin ordering, respectively. Hysteresis loop noticed weak ferromagnetism.
关键词： weak ferromagnetic properties,relaxor ferroelectric,Colossal dielectric,diamagnetic,NdCrO3 perovskite nanoparticles
更新于2025-09-23 15:19:57
-
Propensity for spontaneous relaxor-ferroelectric transition in quenched (Na <sub/>1/2</sub> Bi <sub/>1/2</sub> )TiO <sub/>3</sub> -BaTiO <sub/>3</sub> compositions
摘要： Recently, quenching lead-free non-ergodic relaxor Na1/2Bi1/2TiO3-BaTiO3 (NBT-BT) materials has been reported to increase the thermal depolarization temperature and enhance the lattice distortion. Driven by the conjecture that enhanced lattice distortion is typically associated with the onset of ferroelectric order, two non-ergodic relaxor NBT-BT compositions at the morphotropic phase boundary were investigated. As evident from the temperature-dependent permittivity, both compositions exhibit a stabilization of ferroelectric order upon quenching. An increase in the depolarization temperature by 40–60 °C is observed. Moreover, the composition with higher tetragonality undergoes a spontaneous relaxor-ferroelectric transition upon quenching. Annealing in oxygen atmosphere is shown to revert back the quenching-induced ferroelectric order to the relaxor state.
关键词： relaxor-ferroelectric transition,NBT-BT,quenching,lattice distortion,depolarization temperature
更新于2025-09-23 15:19:57
-
Giant Piezoelectricity of Ternary Perovskite Ceramics at High Temperatures
摘要： Here, novel ferroelectric ceramics of (0.95 ? x)BiScO3-xPbTiO3-0.05Pb(Sn1/3Nb2/3)O3 (BS-xPT-PSN) of complex perovskite structure are reported with compositions near the morphotropic phase boundary (MPB), and which exhibit a piezoelectric coefficient d33 = 555 pC N?1, a large-signal coefficient *d33 ≈ 1200 pm V?1 at room temperature, and a high Curie temperature TC of 408 °C. More interestingly, this ternary system exhibits a giant and stable piezoelectric response at 200 °C with a large-signal *d33 ≈ 2500 pm V?1, matching that of the costly relaxor-based piezoelectric single crystals at room temperature. The mechanisms of such giant piezoelectricity and its characteristic temperature dependence are attributed to the spontaneous polarization rotation and extension under an electric field and the MPB-related phase transition. The findings reveal that the BS-xPT-PSN ceramics constitute a new family of high-performance piezoelectric materials suitable for electromechanical transducers that can be operated at high temperatures (at 200 °C, or higher).
关键词： giant piezoelectricity,relaxor ferroelectric,high temperatures
更新于2025-09-19 17:15:36
-
Structural, piezoelectric and high-density energy storage properties of lead-free BNKT-BCZT solid solution
摘要： A solid solution of lead-free piezoelectric ceramic (1-x)Bi0.50(Na0.80K0.20)0.50TiO3-xBa0.90Ca0.10Ti0.90Zr0.10O3 (with x=0.00, 0.02, 0.04, 0.06, 0.08) was synthesized by conventional solid-state reaction route. The effect of addition of BCZT on BNKT was investigated on structural, microstructural, dielectric, ferroelectric, piezoelectric and high-density energy storage properties experimentally. Modified Curie Weiss law and Vogel-Fulcher law were employed to study the diffusivity and activation energy. The dielectric dispersion with frequency reveals the relaxor behavior for all compositions. The value of Tv (calculated from Vogel-Fulcher relation) decreases while the corresponding value of Ea increases with the BCZT composition. The unipolar curve shows the increased strain of 0.15% and corresponding ? (Smax/Emax =311 pm/V) for x = 0.02 composition among all studied compositions. Furthermore, compositions x = 0.02 and x = 0.04 shows the improved energy storage efficiency ～50% with respect to pure BNKT.
关键词： Relaxor,Ferroelectric,Vogel-Fulcher,Piezoelectric
更新于2025-09-04 15:30:14