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: <i>Ab initio</i> and Monte Carlo approaches
摘要： The effects of nonmagnetic impurity doping on magnetic and ferroelectric properties of multiferroic delafossite CuCrO2 are investigated by means of density functional theory calculations and Monte Carlo simulations. Density functional theory calculations show that replacing up to 30% of Cr3+ ions by Ga3+ ones does not significantly affect the remaining Cr-Cr superexchange interactions. Monte Carlo simulations show that CuCr1?xGaxO2 preserves its magnetoelectric properties up to x ≈ 0.15 with a spiral ordering, while it becomes disordered at higher fractions. Antiferromagnetic transition shifts towards lower temperatures with increasing x and eventually disappears at x ≈ 0.2. Our simulations show that Ga3+ doping increases the Curie-Weiss temperature of CuCr1?xGaxO2, which agrees well with experimental observations. Moreover, our results show that the incommensurate ground-state configuration is destabilized by Ga3+ doping under zero applied field associated with an increase of frustration. Finally, coupling between noncollinear magnetic ordering and electric field is reported for x ≤ 0.15 through simulating P -E hysteresis loops, which leads to ferroelectricity in the extended inverse Dzyaloshinskii-Moriya model.
关键词： CuCrO2,multiferroic,Monte Carlo simulations,ferroelectric properties,magnetic properties,density functional theory,delafossite,Ga doping
更新于2025-09-23 15:21:01
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Dielectric and electro-optic studies of a ferroelectric liquid crystal dispersed with different sizes of silica nanoparticles
摘要： The impact of the size of silica nanoparticles (SNPs) on the properties of ferroelectric liquid crystals (KCFLC 10R) has been investigated by electro-optical and dielectric techniques. We have found that the doping of silica nanoparticles in the host ferroelectric liquid crystal strongly affects the various properties of doped systems. Doping of silica nanoparticles shows a small decrease in spontaneous polarisation and faster switching time. An improvement in permittivity and conductivity with the temperature at a constant frequency was also noticed after dispersion. This dependence is stronger for large size particles (,40 nm) and weaker for small size particles (~12 nm). The Goldstone mode (GM) shifts towards the higher relaxation frequency. These results would be useful to manufacture better optical and electronic devices for display, switching and beam steering applications.
关键词： relaxation frequency,Ferroelectric liquid crystals,spontaneous polarisation,silica nanoparticles,goldstone mode,electro-optical,switching time
更新于2025-09-23 15:21:01
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Superior ferroelectric photovoltaic properties in Fe -modified (Pb,La) (Zr,Ti)O3 thin film by improving the remnant polarization and reducing the band gap
摘要： In order to develop ferroelectric photovoltaic devices with high power conversion e?ciency, ferroelectric materials must have simultaneously large remnant polarization and narrow band gap so as to e?ciently separate photo-generated carriers and absorb more sunlight. Based on this idea, in this report, we introduce Fe3+ into Pb0·93La0·07(Zr0·6Ti0.4)0.9825O3 ferroelectric thin ?lm to increase the remnant polarization and decrease the band gap of the thin ?lm. In doing so, we prepare Fe3+ doping Pb0·93La0·07(Zr0·6Ti0.4)0.9825O3 thin-?lm based photovoltaic devices. The experimental results indicate that with increasing the Fe3+ amount, the remnant polarization of the ?lm ?rst improves to the maximum value of 50 μC/cm2 at the 4.8 mol% Fe3+ content and then reduces gradually, while the band gap continuously decreases. In addition, at a negative poling voltage, the device exhibits larger short-circuit current and open-circuit voltage in comparison with those obtained at the positive poling voltage, which is attributed to the depolarization electric ?eld originating from the remnant polarization of ferroelectric thin ?lms in the same direction as the built-in electric ?eld caused by the Schottky barrier. In this report, the most superior photovoltaic performances with the open-circuit voltage of as large as ?0.55 V and short-circuit current of as high as 0.4 μA/cm2 are obtained in the device with 4.8 mol% Fe3+ amount and at ?5 V poling voltage. This is on account of the improved sunlight absorbing properties and photo-generated carriers separation ability of the device. This work provides a novel idea for designing and preparing ferroelectric photovoltaic devices with high power conversion e?ciency.
关键词： Fe3+ doping,Photovoltaic properties,Band gap,Remnant polarization,Ferroelectric thin ?lm
更新于2025-09-23 15:21:01
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Enhanced Ferroelectric Photovoltaic Effect in Semiconducting Single-Wall Carbon Nanotubes/BiFeO <sub/>3</sub> Heterostructure Enabled by Wide-Range Light Absorption and Efficient Charge Separation
摘要： The interfacial electronic band structures of photovoltaic heterostructure devices greatly affect their light absorption and charge-transport properties and thus their photovoltaic performance. In this work, we report an enhanced ferroelectric photovoltaic effect in a semiconducting single-walled carbon nanotube (S-SWCNTs)/ferroelectric BiFeO3 (BFO) heterostructure. A wide range of light absorption was possible in this structure owing to the low bandgaps of the S-SWCNTs (0.2–2.1 eV) and BFO (2.2–2.7 eV). The heterostructure also enabled efficient charge separation owing to the strong built-in electric field resulting from the synergic effect of the formation of p–f–n junctions (p-type S-SWCNTs/ferroelectric (f) BFO/n-type Nb:SrTiO3) and the introduction of a polarization-mediated internal field in the ferroelectric BFO layer. Compared with a single-layer device (Pt/BFO/Nb:SrTiO3), the heterostructure device (Pt/S-SWCNTs/BFO/Nb:SrTiO3) exhibited substantial enhancement of the photovoltaic performance. The open-circuit photovoltage and short-circuit photocurrent density reached up to 0.23 V and ?7.52 mA cm?2 (corresponding to a photo-conversion efficiency of 4.40%) under one-sun illumination, respectively, after optimization of the ferroelectric layer thickness and appropriate interfacial band alignment. Moreover, by applying switchable electric polarization, this heterostructure could be tuned, enabling the development of controllable photovoltaic devices. Our findings demonstrate that the synergistic integration of materials with different functionalities is a promising approach for the design of photovoltaic devices with tunable performance.
关键词： BiFeO3,light absorption,single-walled carbon nanotube,heterostructure,charge separation,ferroelectric photovoltaic effect
更新于2025-09-23 15:21:01
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Determination of 60° polarization nanodomains in a relaxor-based ferroelectric single crystal
摘要： Here, we report a determination of monoclinic nanodomains in PMN-xPT with x ? 31%PT by using scanning convergent beam electron diffraction (SCBED). We show the presence of 60 6 a degree nanodomains with Cm-like symmetry as well as signi?cant variations (a) in local polarization directions across lengths of (cid:3)10 nm. The principle of our technique is general and can be applied for the determination of polarization domains in other ferroelectric materials of different symmetry. VC 2015 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4932955]
关键词： ferroelectric materials,scanning convergent beam electron diffraction,monoclinic nanodomains,PMN-xPT,SCBED
更新于2025-09-23 15:21:01
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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
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Investigation on the structural, multiferroic and magnetoelectric properties of BaTi1-xNixO3 ceramics
摘要： In this paper, we report the influence of Ni doping on the structural, electrical, magnetic and magnetoelectric properties of BaTiO3 (BTO) ceramics. X-ray diffraction (XRD) analysis indicates a phase transition from tetragonal to hexagonal at x = 2.5 mol%. Further, XRD data has been refined using Rietveld method to extract the phase formation, lattice parameters, and the phase fraction of BaTi1-xNixO3 (BTNO)(0 ≤ (cid:129) ≤ 10 mol%) ceramics. The ferroelectric polarization decreases with Ni doping concentration. The relative permittivity of BTNO compositions decreases while the corresponding dielectric loss increases with Ni doping concentration. Room temperature magnetic hysteresis (M-H) loop of all BTNO samples exhibit ferromagnetic nature with a saturated loop except for x = 2.5 mol% Ni doping concentration. At x = 2.5 mol% Ni doping concentration, a small amount of diamagnetism is observed at higher fields along with ferromagnetism. The origin of ferromagnetism is due to the F- center exchange interaction via oxygen vacancies. The highest remnant magnetization (Mr) is 11.76 memu/g for x = 10 mol%. The Magnetodielectric coefficient (MD) and magnetoelectric coefficient (ME) gradually increases with increasing Ni doping concentration, and are 1.72 % and 4.51 mVcm !Oe ! respectively for x = 10 mol%.
关键词： ferroelectric,magnetoelectric,Barium titanate,magnetic,multiferroic,Perovskite
更新于2025-09-23 15:21:01
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Cation Exchange as a Mechanism to Engineer Polarity in Layered Perovskites.
摘要： Cation exchange reactions performed on the n = 2 Dion-Jacobson phases RbNdNb2O7 and RbNdTa2O7, using LiNO3 and NaNO3, yield the corresponding LiNdM2O7 and NaNdM2O7 (M = Nb, Ta) phases. Synchrotron X-ray and neutron powder diffraction data, in combination with second-harmonic generation data and supported by first-principles DFT calculations, reveal that the LiNdM2O7 phases adopt n = 2 Ruddlesden-Popper type structures with an aˉaˉc+/-(aˉaˉc+) distortion described in the polar space group B2cm. In contrast, the NaNdM2O7 phases adopt n = 2 Ruddlesden-Popper type structures with an aˉb0c0/b0aˉc0 distortion, described in the centrosymmetric space group P42/mnm. The differing structures adopted by the LiNdM2O7 and NaNdM2O7 phases are rationalized on the basis of a competition between i) optimizing the size of the Li/Na coordination site via octahedral tilting and ii) ordering the Na/Li cations within the (Li/Na)O2 sheets to minimize cation-cation repulsion – the former appears to be the dominant factor for the Li phases and the latter factor dominates for the Na phases. The strong A’-cation dependence of the tilting distortions adopted by the A’NdM2O7 phases suggests that by careful selection of the substituting cation the tilting distortions of layered perovskite phases can be rationally tuned to adopt polar configurations, and thus new ferroelectric phases can be synthesized.
关键词： Layered perovskites,Cation exchange,Structural distortion,Ferroelectric materials,Polarity engineering
更新于2025-09-23 15:21:01
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Atomic and electronic structure of ferroelectric La-doped HfO<sub>2</sub> films
摘要： The atomic structure and optical properties of ferroelectric La-doped hafnium oxide (La:HfO2) thin films grown by the plasma-assisted atomic layer deposition were investigated. Using high resolution transmission electron microscopy, it was shown that the studied La:HfO2 film has a orthorhombic polar structure with the P mn21 space group. It was found that the film exhibits ferroelectric properties. By means of X-ray photoelectron spectroscopy and specroellipsometry it was established that La:HfO2 consists of the HfO2 and La2O3 phases mixture. The specroellipsometry analysis with the Bruggeman effective medium approximation showed that the investigated La:HfO2 consists of 88% HfO2 and 12% La2O3. It is shown that etching La:HfO2 with argon ions leads to the oxygen vacancies generation in the near-surface region. These vacancies are generated mainly due to the knocking out of oxygen atoms to the interstitial positions, and the following annealing at 700 ℃ in vacuum for 1 hour leads to the annihilation of that Frenkel defects.
关键词： ferroelectric,XPS,electronic structure,plasma-assisted atomic layer deposition,atomic structure,La-doped HfO2,specroellipsometry,HRTEM
更新于2025-09-23 15:21:01
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Thermal properties and remnant state variables of ferroelectric ceramics switched by both electric field and compressive stress at room temperature
摘要： A commercial poled ferroelectric cube specimen is subject to electric ?eld and compressive stress of various magnitudes at the reference temperature 20 °C. After reaching speci?c states of remnant polarization and remnant strains, temperature of the specimen increases under no external load, measuring changes in polarization and strains. Assuming constant values of thermal properties in the temperature range of interest, we estimated pyroelectric and thermal expansion coe?cients for all tested levels of electric and stress ?elds and plotted them versus remnant state variables at 20, 50, 80, and 110 °C. The distributions of thermal properties ?t well into quadratic curves independent of electric and stress ?elds at each of the four temperatures. One could predict successfully the quadratic ?tting curves at high temperatures by using the equations of quadratic ?tting curves at reference temperature. Remnant state variables also seem to have close correlation among themselves, independent of the levels of applied electric ?eld or stress. ? 2018 The Japan Society of Applied Physics
关键词： thermal properties,compressive stress,electric ?eld,ferroelectric ceramics,remnant state variables
更新于2025-09-23 15:21:01