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Crystal structure and ferroelectric polarization of tetragonal (Bi <sub/>1/2</sub> Na <sub/>1/2</sub> )TiO <sub/>3</sub> –12BaTiO <sub/>3</sub>
摘要： We have investigated the crystal structure and ferroelectric polarization of (Bi1/2Na1/2)TiO3–12%BaTiO3 by high-resolution neutron powder di?raction Rietveld analysis and density-functional theory calculations. It is revealed that the sample has a ferroelectric distortion in tetragonal P4mm symmetry along with a large tetragonality c/a of 1.022. The A- and B-site atoms exhibit a cooperative o?-center displacement along the polar c-axis, which results in a large spontaneous polarization of 54 μC/cm2.
关键词： crystal structure,neutron powder diffraction,tetragonal (Bi1/2Na1/2)TiO3–12BaTiO3,density-functional theory,ferroelectric polarization
更新于2025-09-23 15:21:01
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Direct Observation of Core-Shell Structures in Individual Lead Titanate Ferroelectric Nanostructures by Tip-Enhanced Refractive Index Mapping
摘要： Ferroelectrics undergo a size-driven phase transition at the nanoscale below which the spontaneous polarization, their defining property, irrevocably ceases. This threshold often referred to as the superparaelectric limit has tremendous technological relevance in an era of progressing integration. Just as the balance of short-range elastic and long-range electrostatic ordering in bulk, the critical size depends on temperature. Room-temperature tip-enhanced Raman spectroscopy (TERS) imaging of individual lead titanate (PbTiO3) nanoislands is reported with a spatial resolution of ≈3 nm. Monitoring the spectral shift of the gold-tip enhanced luminescence, which depends on the local refractive index, images grains composing the nanoislands. The wavelength of the enhanced luminescence shifts between the grains and their boundaries indicating the predicted core–shell structure of ferroelectric and paraelectric phase. The shear force configuration rules out the distance dependence of capacitive plasmonic coupling between tip and substrate as the origin of the observed shift. As the reported temperature-changes in nonresonant TERS do not account for noticeable thermal effects, the underlying, even though weak, tip-enhanced Raman spectrum of the grain core reflects PbTiO3 close to the ferroelectric-to-paraelectric phase transition which is primarily related to the finite size of the grains.
关键词： ferroelectric,tip-enhanced Raman spectroscopy,core–shell structure,local refractive index imaging,lead titanate
更新于2025-09-23 15:21:01
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Nd-Cr co-doped BiFeO3 thin films for photovoltaic devices with enhanced photovoltaic performance
摘要： BiFeO3 films and Nd-Cr co-doped BiFeO3 films were prepared by sol-gel method followed by spinning process on fluorine-doped tin oxide glass substrates. By testing the ultraviolet-visible absorption spectra, it was found that Nd-Cr co-doping will increase the light absorption rate of the film and reduce the optical band gap. The reduced bandgap can facilitate the transport of carriers. After Nd-Cr co-doping, the leakage current of the film is effectively reduced, which is near four orders of magnitude lower than the leakage current density of the pristine BiFeO3 film. The reduction of leakage current will enhance the ferroelectric polarization. The enhancement of ferroelectric polarization is more favorable for the separation of photogenerated carriers. Compared with the pristine BiFeO3 film, the short circuit photocurrent density, open circuit photovoltage and power conversion efficiency of Nd-Cr co-doped BiFeO3 film are all clearly improved. The Nd-Cr co-doped BiFeO3 films exhibited largely enhanced photovoltaic property, which favored the practical application of BiFeO3-based films in photovoltaic devices.
关键词： Element doping,Thin films,Ferroelectric property,Photovoltaic property,Bismuth ferrite,Leakage current
更新于2025-09-23 15:19:57
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Polar coupling enabled nonlinear optical filtering at MoS2/ferroelectric heterointerfaces
摘要： Complex oxide heterointerfaces and van der Waals heterostructures present two versatile intrinsically different platforms for exploring emergent quantum phenomena and designing new functionalities. The rich opportunity offered by the synergy between these two classes of materials, however, is yet to be charted. Here, we report an unconventional nonlinear optical filtering effect resulting from the interfacial polar alignment between monolayer MoS2 and a neighboring ferroelectric oxide thin film. The second harmonic generation response at the heterointerface is either substantially enhanced or almost entirely quenched by an underlying ferroelectric domain wall depending on its chirality, and can be further tailored by the polar domains. Unlike the extensively studied coupling mechanisms driven by charge, spin, and lattice, the interfacial tailoring effect is solely mediated by the polar symmetry, as well explained via our density functional theory calculations, pointing to a new material strategy for the functional design of nanoscale reconfigurable optical applications.
关键词： nonlinear optical filtering,second harmonic generation,MoS2/ferroelectric heterointerfaces,density functional theory,polar symmetry
更新于2025-09-23 15:19:57
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Ferroelectric properties and phase transitions of high performance vertically aligned KNN nanowire-arrays grown by pulsed laser deposition
摘要： Pulsed laser deposition (PLD) was used to synthesize piezoelectric nanowire-arrays of K0.5Na0.5NbO3 (KNN) on Pt/TiO2/SiO2/Si substrates. These arrays were successfully prepared by using two different deposition conditions than the previously reported for KNN. KNN with orthorhombic structure and minority secondary phases were identified by XRD. Ferroelectric and Piezoelectric properties were confirmed by piezoresponse force microscopy, and showed that nanowire-arrays have an improvement in their effective piezoelectric coefficient of d33eff = 94.6 pm/V and 133.6 pm/V, higher than previously reported coefficients. Pulsed laser photoacoustic technique was used to analyze the phase transition temperatures and they showed a phase transition (O-T) at ～170 ?C and a phase transition (T-C) at ～360 ?C, lower temperatures than those found for bulk ceramics. Furthermore, it was identified the presence of minor amount of secondary ferroelectric phase (K4Nb6O17).
关键词： Phase transitions,KNN nanowire-arrays,Ferroelectric properties,Pulsed laser deposition,Piezoelectric coefficient
更新于2025-09-23 15:19:57
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Two-dimensional series connected photovoltaic cells defined by ferroelectric domains
摘要： Recently, a large amount of effort has been devoted to bringing p- and n-type two-dimensional (2D) materials in close contact to promise a p–n junction for photodetectors and photovoltaic devices. However, all solar cells based on 2D materials are single p–n junctions so far, where the open circuit voltage is usually limited by the bandgap of semiconductor materials. Here, by using a scanning-probe domain patterning method to polarize the ferroelectric ?lm, we demonstrate a series connected MoTe2 photovoltaic cell with an additive open circuit voltage and output electrical power. The nonvolatile MoTe2 p–n diodes exhibit a recti?cation ratio of 100. As a photodetector, the device presents a responsivity of 220 mA/W and an external quantum ef?ciency of 41% without any gate or bias voltages. The open circuit voltage increases linearly with the number of series connected p–n junctions and can be beyond the bandgap of the multilayer MoTe2.
关键词： photovoltaic cells,MoTe2,open circuit voltage,two-dimensional materials,ferroelectric domains
更新于2025-09-23 15:19:57
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Mechanical writing of in-plane ferroelectric vortices by tip-force and their coupled chirality
摘要： Recent experiments have demonstrated the existence of vortex or flux-closure domains in ferroelectric nanostructures, which are attractive to develop high-density data storage and novel configurable electronic devices. However, it remains challenging to stabilize in-plane vortex or flux-closure domains in ferroelectric film for the absence of a lateral geometry confinement. Based on a 3D phase field model, here we show that stabilization of isolated or interacting in-plane vortices in ferroelectric film can be achieved via applying a mechanical tip-force. The formation of such dipole vortices is caused by a conjoint effect of the tip-force-induced depolarization effect and in-plane strain. The effects of factors like film thickness, misfit strain, tip force and temperature on the vortex formation are systematically revealed and summarized as phase diagrams. The interaction between tip-induced vortices is also investigated. It is found that as the two tips get closer than the critical distance, the two initially isolated vortices become coupled, with identical or opposite chirality, depending on the distance between the two tips. A maximum data storage density of isolated in-plane vortices in ferroelectric thin film is estimated to be ~1 Tb in?2. Our work thus demonstrates a mechanical strategy to stabilize dipole vortices, and provides a comprehensive insight into the characteristics of ferroelectric film under a mechanical tip force.
关键词： flexoelectricity,ferroelectric,mechanical force,domain structure,vortex
更新于2025-09-23 15:19:57
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Domain Wall Conduction in Calcium-Modified Lead Titanate for Polarization Tunable Photovoltaic Devices
摘要： By virtue of the domain wall conduction and polarization tunable charge transport properties of ferroelectrics, Qian et al. theoretically demonstrate evidence of electric conduction in domain walls. They successfully fabricate Pb0.8Ca0.2TiO3-based photovoltaic devices with tunable photovoltaic performance by external poling.
关键词： Pb0.8Ca0.2TiO3,Photovoltaic devices,Polarization tunable,Domain wall conduction,Ferroelectric
更新于2025-09-23 15:19:57
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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
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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