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The influence of external stress/strain on the phase transitions and dielectric properties of potassium niobate crystal
摘要： We investigated the effects of one-dimensional shock wave compression on the structural, dielectric, and ferroelectric properties of a potassium niobate ferroelectric crystal using Landau–Ginsburg–Devonshire phenomenological theory. Our results show that the cubic to tetragonal and tetragonal to orthorhombic phase transition temperatures increase with increasing shock compression and the derivative of the phase transition temperatures with respect to stain induced by shock compression was estimated to be 21.9 °C/10?3. Additionally, the orthorhombic to rhombohedral phase transition temperature decreased with increasing shock compression and the derivative of the phase transition temperatures with respect to stain induced by shock compression was estimated to be ?144.3 °C/10?3. This result represents a 15.3% increase in the remnant polarization of the tetragonal KNbO3 crystal when the stain induced by shock compression increased from 0 to 4×10?3 at 400 °C. The dielectric susceptibilities ε33 and ε22 were calculated to decrease by approximately 20% and 40%, respectively, when the stain induced by shock compression increased from 0 to 1.6×10?3 at 350 °C. The increase in the remnant polarization and the decrease in the dielectric properties induced by shock compression provide an effective way to improve the power output capacity of a ferroelectric-pulsed power supply.
关键词： phase transition,lead-free ferroelectric crystal,ferroelectric properties,dielectric properties,shock compression
更新于2025-09-09 09:28:46
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Strain induced enhancement of erasable domain wall current in epitaxial BiFeO <sub/>3</sub> thin films
摘要： The characteristic of electronic transport at the ferroelectric domain boundary is intensively studied for the potential application in random access memory due to its unique resistance switching mechanism along with polarization reversal. Such high conductivity in artificially created domain walls is not only affected by the material defect chemistry, such as oxygen vacancies, but also pertinent to the multiple polarization states of the sample. Here, we show the enhanced domain wall current in BiFeO3 thin films that could be obtained by the optimization of epitaxial strains from substrates. The leakage current analysis reveals the electronic transport of domain wall current in line with the space-charge-limited conduction mechanism. It is believed that the uncompensated polarization charge arouses the band bending at the domain boundary, which profoundly affects the wall current. Free carriers are easily concentrated in the domain boundary region for the compensation of the enhanced polarization by the strain, resulting in an abrupt increase of the conductivity.
关键词： ferroelectric domain boundary,BiFeO3 thin films,space-charge-limited conduction,epitaxial strains,electronic transport
更新于2025-09-09 09:28:46
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Impact of electrodes on the extraction of shift current from a ferroelectric semiconductor SbSI
摘要： Noncentrosymmetric bulk crystals generate photocurrent without any bias voltage. One of the dominant mechanisms, shift current, comes from the quantum interference of electron wave functions being distinct from the classical current caused by electrons’ drift or diffusion. The dissipation-less nature of shift current, however, has not been fully veri?ed, presumably due to the premature understanding of the role of electrodes. Here, we show that the photocurrent dramatically enhanced by choosing electrodes with large work functions for a p-type ferroelectric semiconductor SbSI. An optimized device shows a nearly constant zero-bias photocurrent despite the signi?cant dependence of photocarrier mobility on temperature, which could be a clear hallmark for the dissipation-less nature of shift current. Distinct from conventional photovoltaic devices, the shift current generator operates as a majority carrier device. The present study provides fundamental design principles for energy-harvesting and photo-detecting devices with novel architectures optimal for the shift current photovoltaic effect.
关键词： SbSI,electrodes,ferroelectric semiconductor,photocurrent,shift current
更新于2025-09-09 09:28:46
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High Ferroelectricities and High Curie Temperature of BiInO <sub/>3</sub> PbTiO <sub/>3</sub> Thin Films Deposited by RF Magnetron Sputtering Method
摘要： Properties of ferroelectric ??BiInO3-(1 ? ??)PbTiO3 (??BI-(1 ? ??)PT) thin films deposited on (101) SrRuO3/(200) Pt/(200) MgO substrates by rf magnetron sputtering method and effects of deposition conditions are investigated. The structures of the ??BI-(1???)PT films are characterized by x-ray diffraction and scanning electron microscopy. The results indicate that the thin films are grown with mainly (001) orientation. The chemical compositions of the films are analyzed by scanning electron probe and the results indicate that the loss phenomena of Pb and Bi elements depend on the pressure and temperature during the sputtering process. The sputtering parameters including target composition, substrate temperature, and gas pressure are adjusted to obtain optimum sputtering conditions. To decrease leakage currents, 2 mol% La2O3 is doped in the targets. The ?? –?? hysteresis loops show that the optimized ??BI-(1 ? ??)PT (?? = 0.24) film has high ferroelectricities with remnant polarization 2??r = 80 ??C/cm2 and coercive electric field 2??c = 300 kV/cm. The Curie temperature is about 640°C. The results show that the films have optimum performance and will have wide applications.
关键词： ferroelectric,rf magnetron sputtering,BiInO3-PbTiO3,thin films,Curie temperature
更新于2025-09-09 09:28:46
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Photostriction properties of PLZT (4/52/48) ceramics sintered by SPS
摘要： In this paper, the preparation and sintering process of Lanthanum-modi?ed lead zirconate titanate ceramics (PLZT 4/52/48) powders and ceramics were investigated. The PLZT powders were prepared by co-precipitation and sol-gel methods. It is con?rmed that PLZT powders synthesized by sol-gel method had smaller grains and better dispersion. The atmosphere sintering and spark plasma sintering（SPS）technique were used to sinter the PLZT ceramics separately. After sintering, the physical, electrical, and optical properties of the PLZT ceramics sintered by di?erent methods were tested. The results show that the SPS sintering can increase the densi?cation degree (reaching 99.5%)of the PLZT ceramics, which improved the transparency, ferroelectric, piezoelectric and optical properties of PLZT ceramics. It is found that when the light intensity reached 600 mW/cm2, the max- ?3, which was almost 1.4 imum photo-induced strain of the SPS sintered ceramic was as high as 10. 84 × 10 times larger than that of the atmosphere-sintered sample. Obviously, the sol-gel method and SPS process can enhance the comprehensive performance of PLZT ceramics.
关键词： Photo-induced strain,Ferroelectric/piezoelectric property,Sol-gel method,PLZT,SPS
更新于2025-09-09 09:28:46
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Structure development and dielectric properties of Zn-doped Pb([Mg,Fe],W)O <sub/>3</sub> perovskite ceramics
摘要： Ceramic samples of a pseudo-binary system Pb(Mg1/2W1/2)O3-Pb(Fe2/3W1/3)O3 (PMW-PFW) were prepared by solid-state reaction. In addition, their compositions were modified by 20 mol% Pb(Zn1/2W1/2)O3 (PZW) doping in order to investigate the role of zinc in the perovskite formation and dielectric properties. The perovskite contents were ≥95.1% at the overall composition range, except for a significantly low value of 79.0% at 0.8PFW-0.2PZW. The extension of sintering time for PMW accelerated superstructure formation, resulting in the ordering factor increased up to 0.40 after 12 h heat treatment. The maximum dielectric constant values increased with increasing PFW fractions. In comparison, the phase transition temperatures decreased sharply (by up to 161 ℃) at low concentrations of PFW, followed by mild changes (by up to 47 ℃) afterwards. The dielectric constant spectra were analyzed in terms of diffuseness characteristics, which reflected the phase transition modes quite well.
关键词： dielectric materials/properties,perovskites,ferroelectricity/ferroelectric materials,reaction
更新于2025-09-09 09:28:46
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A Comparative Analysis of BaTiO3/(Ba,Sr)TiO3 and BaTiO3/(Ba,Sr)TiO3/SrTiO3 Artificial Superlattices via Raman Spectroscopy
摘要： BaTiO3/Ba50Sr50TiO3 and BaTiO3/Ba50Sr50TiO3/SrTiO3 superlattices are characterized via Raman spectroscopy. Special attention is paid to a comprehensive analysis of their polarized Raman spectra, especially, within a soft mode (E(1TO)) range. The shift of E(1TO) soft mode is found to be more pronounced for BaTiO3/Ba50Sr50TiO3/SrTiO3 sample than for BaTiO3/Ba50Sr50TiO3, presumably owing to stronger 2D compression of BT layers and abruptly increased temperature of transition from ferroelectric to paraelectric phase.
关键词： BaTiO3/Ba50Sr50TiO3/SrTiO3 ferroelectric superlattices,Raman spectroscopy,soft mode,strain,BaTiO3/Ba50Sr50TiO3
更新于2025-09-09 09:28:46
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Structural transformations and physical properties of (1-x) Na<sub>0.5</sub>Bi<sub>0.5</sub>TiO<sub>3-x</sub> BaTiO<sub>3</sub> solid solutions near morphotropic phase boundary
摘要： Piezoelectric and other physical properties are significantly enhanced at (or near) a morphotropic phase boundary (MPB) in ferroelectrics. MPB materials have attracted significant attention owing to both fundamental physics as well as the possibility of well-regulated energy and information storage devices which are dominated by lead (Pb)-based materials. Here, we report the crystal structure, Raman spectra, dielectric constant and polarization near the MPB of lead free (1-x) Na0.5Bi0.5TiO3 - x BaTiO3 (NBT - BT) (0.00 ≤ x ≤ 0.10) solid-solution, prepared by sol-gel auto combustion technique and sintered by microwave sintering technique. With the addition of BaTiO3 into Na0.5Bi0.5TiO3, it induces a structural phase transition from R3c (a single phase) to R3c+P4mm (a dual phase) close to x = 0.06 and 0.07 and transform to a high symmetry tetragonal phase P4mm at higher compositions (x = 0.08 to 0.10) as evident from our X-ray Rietveld refinement and Raman spectroscopic results. In the prepared solid solution, an anomalous enhancement of remnant polarization (2Pr0) was observed for x = 0.06 and 0.07, which has been explained based on the existence of the MPB. On the other hand, the value of coercive field EC0 was found to be decreased linearly from x = 0.00 to 0.06; it is constant for higher compositions. Further details of the ferroelectric properties on the electric field poled samples have been studied and compared with the as-grown (unpoled) samples. We perform first-principles calculations based on density functional theory that confirm a structural transition from a rhombohedral to a tetragonal phase under increasing x.
关键词： First-principles calculations,Crystal structure,Morphotropic Phase Boundary,Microwave sintering,Lead-free ferroelectric materials,Electrical properties,NBT-BT solid solution
更新于2025-09-09 09:28:46
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The effect of the length of terminal n-alkyl carboxylate chain on self-assembling and photosensitive properties of chiral lactic acid derivatives
摘要： A new series of photosensitive azo materials possessing a chiral alkyl lactate moiety and terminal n-alkyl carboxylate unit close to the azo group has been synthesised and studied. The length of the n-alkyl carboxylate chain has been systematically varied in order to establish the effect of the molecular structure on the self-assembling behaviour. Two series of materials possessing hexyl and dodecyl alkyl chains in the chiral part of the molecule have been studied. It has been shown that the length of both the alkyl chains strongly influences the mesomorphic behaviour, however, each chiral/achiral chain has different utility to tune the mesomorphic properties. With exception of the compound with the longest chains, all studied compounds exhibited the chiral tilted ferroelectric smectic C* phase. Based on the combination of terminal alkyl chains, chiral nematic, orthogonal smectic A*, and twist grain boundary smectic A* phases have been detected on cooling beyond the SmC* phase. The presence of the photosensitive functional N=N group in the molecular core allowed further tuning of the material properties by UV light illumination. The E-to-Z photoisomerization of the azo group and subsequent thermal back-isomerisation have been studied in solution by nuclear magnetic resonance and most importantly in the mesophases on bulk samples. We report on UV-induced isothermal switching from chiral smectic and nematic mesophases directly into the isotropic phase, respectively, and differences in the textures of mesophase upon restoration of the ordered liquid.
关键词： E-Z isomerisation,ferroelectric phase,photosensitive liquid crystals,azo group,chiral liquid crystals,NMR spectroscopy,optical switches
更新于2025-09-09 09:28:46
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CHARACTERIZATION OF NEW NON-STOICHIOMETRIC FERROELECTRIC (Li0.95Cu0.15)Ta0.76Nb0.19O3 AND COMPARATIVE STUDY WITH (Li0.95Cu0.15)Ta0.57Nb0.38O3 AS PHOTOCATALYSTS IN MFCs
摘要： This work investigates the photocatalytic activity of new ferroelectric material with formula (Li0.95Cu0.15)Ta0.76Nb0.19O3 (LT76) in a single chamber microbial fuel cell (MFC) and compare its performance with the similar photocatalyst (Li0.95Cu0.15)Ta0.57Nb0.38O3 (LT57). The photocatalysts LT76 and LT57 were synthesized by ceramic route under the same conditions, with the same starting materials. The ratio Ta/Nb was fixed at 4.0 and 1.5 for LT76 and LT57 respectively. These phases were characterized by different techniques including X-Ray diffraction (XRD), transmission electronic microscopy (TEM), particle size distribution (PSD), differential scanning calorimetric (DSC) and UV-Vis. The new photocatalyst LT76 presents specific surface area about 0.791m2/g and Curie temperature of 1197°C. The photocatalytic efficiency of this material is evaluated in terms of wastewater treatment and electricity generation by power density and removal rate of chemical oxygen demand (COD) in the presence of a light source. The values of the maximum power densities and COD removal were 19.77 mW/m3 and 93% respectively for LT76.
关键词： microbial fuel cell,non-stoichiometry,ferroelectric,Lithium niobate-tantalate,photocatalyst
更新于2025-09-09 09:28:46