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Domain and Switching Control of the Bulk Photovoltaic Effect in Epitaxial BiFeO3 Thin Films
摘要： Absence of inversion symmetry is the underlying origin of ferroelectricity, piezoelectricity, and the bulk photovoltaic (BPV) effect, as a result of which they are inextricably linked. However, till now, only the piezoelectric effects (inverse) have been commonly utilized for probing ferroelectric characteristics such as domain arrangements and resultant polarization orientation. The bulk photovoltaic effect, despite sharing same relation with the symmetry as piezoelectricity, has been mostly perceived as an outcome of ferroelectricity and not as a possible analytical method. in this work, we investigate the development of BpV characteristics, i.e. amplitude and angular dependency of short-circuit current, as the ferroelastic domain arrangement is varied by applying electric fields in planar devices of Bifeo3 films. A rather sensitive co-dependency was observed from measurements on sample with ordered and disordered domain arrangements. Analysis of the photovoltaic response manifested in a mathematical model to estimate the proportion of switched and un-switched regions. the results unravel the potential utility of BPV effect to trace the orientation of the polarization vectors (direction and amplitude) in areas much larger than that can be accommodated in probe-based techniques.
关键词： BiFeO3,ferroelectricity,polarization orientation,domain switching,bulk photovoltaic effect
更新于2025-09-16 10:30:52
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Evidence for Ferroelectricity of All-Inorganic Perovskite CsPbBr3 Quantum Dots
摘要： The ferroelectric-optical combination of properties in halide perovskites has attracted tremendous interests because of its potential for optoelectronic and energy applications. However, very few reports focus on the ferroelectricity of all-inorganic halide perovskites quantum dots. Herein, we report a excellent ferroelectricity in CsPbBr3 quantum dots (QDs) with a saturation polarization of 0.25 μC/cm2. Differential scanning calorimeter (DSC), X-ray diffraction (XRD), transmission electronic microscopy (TEM) revealed that the mechanism of ferroelectric-paraelectric switching of CsPbBr3 QDs can be attributed to the phase transition from cubic phase (????3??) to orthorhombic phase (Pna21). In the orthorhombic CsPbBr3, the distortion of octahedral [PbBr6]4- structural units and the off-center Cs+ generated the slightly separated centres of positive charge and negative charge, resulting in the ferroelectric properties. The variable temperature emission spectrum from 328 K to 78 K exhibits green luminescence and the gradually red shift due to the phase transition. This finding opens up a avenue to explore the ferroelectric-optical properties of inorganolead halide perovskites for high-performance multifunctional materials.
关键词： CsPbBr3 quantum dots,all-inorganic perovskite,phase transition,optoelectronic applications,ferroelectricity
更新于2025-09-16 10:30:52
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Rashba splitting in bilayer transition metal dichalcogenides controlled by electronic ferroelectricity
摘要： Based on ?rst-principles calculations and k · p model analyses, we uncover the coexistence and coupling of Rashba spin splitting with electronic ferroelectricity in bilayer transition metal dichalcogenides MX2 (M = Mo,W; X = S,Se,Te) with certain stacking con?gurations. The reversible spontaneous ferroelectric polarization, along the out-of-plane direction (the preferred direction for applications), totally arises from the interlayer charge transfer, rather than being governed by the ionic displacement as found in conventional ferroelectrics. The spin texture related to the Rashba spin splitting can be reversed upon inversion of the ferroelectric polarization. In particular, by applying a small in-plane compressive strain, the magnitude of Rashba band splitting can be tuned to be as large as 100 meV. These results would open up possibilities for exploring two-dimensional multiferroic physics and developing electrically controlled nanoscale spintronic devices.
关键词： Rashba splitting,bilayer transition metal dichalcogenides,spintronic devices,electronic ferroelectricity
更新于2025-09-11 14:15:04
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Ferroelectricity and stability measurements in perovskite solar cells
摘要： With the ferroelectric nature of modern perovskite solar cells being more and more accepted by the community, new questions arise. How do the microscopic electric fields within the polar domains affect the device performance, and how must measurement routines be adapted to account for the ferroelectric effect within the light-harvesting layer? This becomes particularly important, if devices are measured constantly for a long time as commonly performed in solar cell ageing tests. In this perspective article, we discuss which effects may arise from creeping poling even under low driving voltages or under illumination, as well as effects from phase transitions when crossing the Curie temperature for accelerated ageing at elevated temperatures. We elucidate why ferroelectric effects must be carefully considered when assessing the life-time of perovskite solar cells and where comparability comes to its limits.
关键词： perovskite solar cell,stability,ferroelectricity,characterization
更新于2025-09-11 14:15:04
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Structural aspects of the high-temperature space charge relaxation in ferroelectric VDF/TFE 94/6 copolymer
摘要： Structural changes in isotropic films of ferroelectric vinylidene fluoride (VDF)/tetrafluoroethylene (TFE) 94/6 copolymers in the metastable state have been studied on heating. The metastable state was ascribed to c-crystals. The dielectric relaxation spectroscopy was employed to study space charge relaxation processes. Two relaxations were observed at high temperatures. One of them was attributed to relaxation of space charge accumulated on the Al electrode which may be partially blocked due to new functional groups formed in the polymer surface. Recrystallization of the film from the melt is accompanied by small a-crystals formation. This results in a decrease in activation energy of the space-charge relaxation process.
关键词： Ferroelectricity,dielectric properties,crystallization,fluoropolymers
更新于2025-09-10 09:29:36
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Understanding the Role of Ferroelastic Domains on the Pyroelectric and Electrocaloric Effects in Ferroelectric Thin Films
摘要： Temperature- and electric-field-induced structural transitions in a polydomain ferroelectric can have profound effects on its electrothermal susceptibilities. Here, the role of such ferroelastic domains on the pyroelectric and electrocaloric response is experimentally investigated in thin films of the tetragonal ferroelectric PbZr0.2Ti0.8O3. By utilizing epitaxial strain, a rich set of ferroelastic polydomain states spanning a broad thermodynamic phase space are stabilized. Using temperature-dependent scanning-probe microscopy, X-ray diffraction, and high-frequency phase-sensitive pyroelectric measurements, the propensity of domains to reconfigure under a temperature perturbation is quantitatively studied. In turn, the “extrinsic” contributions to pyroelectricity exclusively due to changes between the ferroelastic domain population is elucidated as a function of epitaxial strain. Further, using highly sensitive thin-film resistive thermometry, direct electrocaloric temperature changes are measured on these polydomain thin films for the first time. The results demonstrate that temperature- and electric-field-driven domain interconversion under compressive strain diminish both the pyroelectric and the electrocaloric effects, while both these susceptibilities are enhanced due to the exact-opposite effect from the extrinsic contributions under tensile strain.
关键词： electrocaloric effect,ferroelastic domains,ferroelectricity,pyroelectric effect,entropy
更新于2025-09-10 09:29:36
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The origin of low bandgap and ferroelectricity of a co-doped BaTiO <sub/>3</sub>
摘要： We recently demonstrated the lowest bandgap ferroelectric, for visible light absorption in BaTi1?x(Mn1/2Nb1/2)xO3, a promising candidate material optoelectronic devices. Using a combination of x-ray spectroscopies and density functional theory (DFT) calculations, we here elucidate this compound’s electronic structure and the modifications induced by Mn doping. In particular, we are able to rationalize how this compound retains its ferroelectricity even through a significant reduction of the optical gap upon Mn doping. The local electronic structure and atomic coordination are investigated using x-ray absorption at the Ti K, Mn K, and O K edges, which suggests only small distortions to the parent tetragonal ferroelectric system, BaTiO3, thereby providing a clue to the substantial retention of ferroelectricity in spite of doping. Features at the Ti K edge, which are sensitive to local symmetry and an indication of Ti off-centering within the Ti-O6 octahedra, show modest changes with doping and strongly corroborates our measured polarization values. Resonant photoelectron spectroscopy results suggest the origin of the reduction of the bandgap in terms of newly created Mn d bands that hybridize with O 2p states. X-ray absorption spectra at the O K edge provide evidence for new states below the conduction band of the parent compound, illustrating additional contributions facilitating bandgap reduction.
关键词： ferroelectricity,Mn doping,x-ray spectroscopies,bandgap,density functional theory,BaTiO3
更新于2025-09-10 09:29:36
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Ferroelectricity mediated by ferroelastic domain switching in HfO <sub/>2</sub> -based epitaxial thin films
摘要： Herein, ferroelastic domain switching from the nonpolar b-axis to the polar c-axis oriented domain in ferroelectric ?lms is demonstrated. Scanning 7%-YO1.5-substituted HfO2 (YHO-7) epitaxial transmission electron microscopy (STEM) indicates that the polarization of a pristine ?lm deposited on a Sn-doped In2O3/(001)YSZ substrate by the pulsed laser deposition method tends to be along the in-plane direction to avoid a strong depolarization ?eld with respect to the out-of-plane direction. Applying an electric ?eld aids in ferroelastic domain switching in YHO-7 ?lms. Such ?lms exhibit ferroelectric characteristics with a relatively large saturated polarization around 30 lC/cm2 by polarization reorientation from the in-plane to the out-of-plane directions and an increased dielectric constant. The synchrotron X-ray diffraction measurements with a focused beam for the pristine and poled area indicate ferroelastic 90(cid:2) domain switching as the odd number re?ection disappears, which is only allowed in the nonpolar b-axis orientation. STEM observations also show a signi?cant increase in the c-axis oriented domain. This observation of ferroelastic domain switching strongly supports the conclusion that the ferroelectricity of HfO2 originates from the non-centrosymmetric orthorhombic phase.
关键词： ferroelectricity,ferroelastic domain switching,epitaxial thin films,HfO2
更新于2025-09-10 09:29:36
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Hydrogen-bonded and supramolecular ferroelectricity in a new hybrid (C<sub>12</sub>H<sub>25</sub>NH<sub>3</sub>)<sub>2</sub>CoCl<sub>4</sub>
摘要： A new organic-inorganic layered halide perovskite ((C12H25NH3)2CoCl4) has been synthesized and characterized by: chemical analysis, X-ray powder diffraction, differential scanning calorimetry, and differential thermal analysis thermographs. The dielectric and ferroelectric properties have been investigated. Analysis of the ac conductivity σac (ω, T) measured in the temperature interval from 110K to 370K and at selected frequencies in the range 1 kHz< f<100 kHz and the results show that the Jonscher universal power law is accurately obeyed. The existence of ferroelectricity has been demonstrated by the hysteresis P-E loop. The collective data evidenced that the hybrid behaves as a proper ferroelectric rather than a relaxor one and undergoes an order-disorder ferroelectric phase transition at the Curie temperature Tc (Tc?360K) accompanied with a structural distortion from an intercalated to non- intercalated state as the other Co and/or Zn hybrids. Since the room temperature space group of the hybrid is centrosymmetric (P21/c), the ferroelectricity should be due to the supramolecular interaction which results from the induced dipoles. The hydrogen bonding system of the type N-H....Cl plays the key role in the mechanism of supramolecular ferroelectricity.
关键词： ac induced conductivity and complex dielectric permittivity,phase transition,Supramolecular ferroelectricity,polarization
更新于2025-09-10 09:29:36
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High-Pressure Synthesis, Crystal Structure, Chemical Bonding, and Ferroelectricity of LiNbO <sub/>3</sub> -Type LiSbO <sub/>3</sub>
摘要： A polar LiNbO3 (LN)-type oxide LiSbO3 was synthesized by a high-temperature heat treatment under a pressure of 7.7 GPa and found to exhibit ferroelectricity. The crystal structural re?nement using the data of synchrotron powder X-ray di?raction and neutron di?raction and the electronic structure calculation of LN-type LiSbO3 suggest a covalent-bonding character between Sb and O. When comparing the distortion of BO6 in LN-type ABO3, the distortions of SbO6 in LiSbO3 and SnO6 in ZnSnO3, which included a B cation with a d10 electronic con?guration, were smaller than those of BO6 in LN-type oxides having the second-order Jahn?Teller active B cation, e.g., LiNbO3 and ZnTiO3. The temperature dependence of the lattice parameters, second harmonic generation, dielectric permittivity, and di?erential scanning calorimetry made it clear that a second-order ferroelectric?paraelectric phase transition occurs at a Curie temperature of Tc = 605 ± 10 K in LN-type LiSbO3. Further, ?rst-principles density functional theory calculation suggested that perovskite-type LiSbO3 is less stable than LN-type LiSbO3 under even high pressure, and the ambient phase of LiSbO3 directly transforms to LN-type LiSbO3 under high pressure. The phase stability of LN-type LiSbO3 and the polar and ferroelectric properties are rationalized by the covalent bonding of Sb?O and the relatively weak Coulomb repulsion between Li+ and Sb5+.
关键词： high-pressure synthesis,LiNbO3-type oxide,covalent bonding,ferroelectricity,second-order Jahn?Teller effect,LiSbO3
更新于2025-09-10 09:29:36