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Crystal structure, optical and electrical properties of metal-halide compound [C7H16N2][ZnCl4]
摘要： A new organic–inorganic hybrid compound [C7H16N2][ZnCl4] was synthesized by hydrothermal method and characterized by single-crystal X-ray diffraction, IR and Raman spectroscopy, optical absorption, differential scanning calorimetry and dielectric measurements. Single crystal diffraction results showed that [C7H16N2][ZnCl4] crystallizes in the monoclinic system, space group P21/c at room temperature. In the molecular arrangement, the tetrachlorozincate anions are connected to organic cations through N-H...Cl hydrogen bonds. The Raman and IR analyses confirm the presence of the organic groups and the anionic entities. UV–Visible absorption spectrum revealed the energy of the optical band gap. DSC measurements indicated that [C7H16N2][ZnCl4] undergoes three sequential phase transitions at 287, 338 and 356 K. The dielectric study proved the ferroelectric properties below the 338K and indicates their classical character for this compound. The analysis of Nyquist plots revealed the contribution of the bulk mechanism and the grain boundaries.
关键词： Phase transitions,Hybrid material,Crystal structure,Optical absorption,Ferroelectric properties,Conduction mechanism
更新于2025-09-23 15:23:52
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Ferroelectric Origin and Distortion Modes in Doped BiFeO <sub>3</sub> by Crystallography Approach
摘要： There are conflicts about the ferroelectric origin and the relationship of two distortion modes, namely, the ferroelectric (FE) mode and antiferrodistortive (AFD) mode. Here the two distortion modes and enhanced ferroelectric properties (Pr=89.5 μC cm-2) are observed in BiFeO3 thin films doped with small radius Mg2+ (A-site) deposited on (111) Pt/Ti/SiO2/Si substrates by a sol-gel method, the relationship of the two distortion modes turns from cooperative to competitive as the FE mode strengthens. A new explanation of ferroelectric origin and distortion modes in doped BiFeO3 by the Defect Dipoles Driven Distortions Theory (abbreviate DDD) from crystallography is reported. Meanwhile, the crystal structure regulation mechanism of doped BiFeO3 thin films with substantially enhanced ferroelectric properties is also put forward. The distances of the positive and negative charge center in [FeO6] octahedrons evidently increase by Mg2+ doping compared with that in the Bi0.9Sm0.1Fe0.95Mn0.05O3 (BSFMO). The change of distances is contributed to the law of the atomic migration from the move of oxygen vacancies and the attraction of defect dipoles. A positive effect on ferroelectric properties of the appropriate increase in oxygen vacancies is explored, which is explained by "the probability of possible position that oxygen vacancies occurred" and "the relationship between the leakage current and the overlapping oxygen positions". The potential structure and more suitable doping ions are successfully predicted by the crystal structure regulation mechanism. In addition, it brings a new direction for the search of other structure regulation ions so as to realize the perfect ferroelectric properties for practical application, which will become an important beginning of ferroelectric materials design.
关键词： ferroelectric properties,structural distortions,crystallography,ferroelectric origin,defect dipoles
更新于2025-09-23 15:22:29
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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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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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Grain boundary effects on piezoelectric properties of the core–shell-structured BaTiO <sub/>3</sub> @TiO <sub/>2</sub> ceramics
摘要： Grain boundary effect on BaTiO3 has been widely investigated for several decades. However, all of them tailored the grain boundary by grain size of BaTiO3. In this case, a direct way was introduced to modify the grain boundary by coating technique to investigate the role of grain boundary in ferroelectric materials. Nonferroelectric phase TiO2 was employed to investigate grain boundary effects on the electrical properties of BaTiO3 piezoelectric ceramics. TiO2 coating can result in the reduction of piezoelectric and ferroelectric properties and the annealing process in oxygen can increase piezoelectric behavior of pure BaTiO3 due to valence state of Ti ions while that remains for Ti-modified composition possibly due to the increased grain boundary effect by impedance analysis. Compared with ferroelectric grain, grain boundary plays a critical role to impact the electrical properties of perovskite-type ferroelectric materials.
关键词： defects.,Piezoelectric properties,ferroelectric properties,BaTiO3 and titanates
更新于2025-09-19 17:15:36
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Origin of enhanced piezoelectric properties revealed through electric field driven studies in 0.94(Na <sub/>0.5</sub> Bi <sub/>0.5</sub> TiO <sub/>3</sub> )a??0.06(Ba <sub/>0.85</sub> Ca <sub/>0.15</sub> Ti <sub/>0.9</sub> Zr <sub/>0.1</sub> O <sub/>3</sub> ) ceramics
摘要： A single phase 0.94(Na0.5Bi0.5TiO3)–0.06(Ba0.85Ca0.15Ti0.9Zr0.1O3) solid solution (i.e., BCZT-0.06) is prepared using a conventional solid-state sintering route with enhanced piezo and ferroelectric properties as compared to Na0.5Bi0.5TiO3 (NBT). In the context of understanding the origin of enhanced piezoelectric properties in a BCZT-0.06 specimen, electric field driven studies on different length scales, viz., global, local, and electronic structure, are carried out using x-ray/neutron diffraction, Raman scattering, and UV–Vis spectroscopic techniques. An analysis on different length scales of the electric field-driven BCZT-0.06 specimen displays minimum rhombohedral lattice distortion (δ r), reduced homogeneous lattice strain (δ), octahedral strain (ζ), and pronounced Ti-cation displacement along the polar [111] direction as compared to parent NBT. The enhanced ferro and piezoelectric responses observed in the BCZT-0.06 specimen have been attributed to the ease of non-180° domain re-orientation, domain switching, and domain wall motion due to reduced strain coupled with a polarization extension mechanism.
关键词： ferroelectric properties,electric field driven studies,solid solution,domain re-orientation,piezoelectric properties
更新于2025-09-19 17:13:59
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Preparation and characterization of pyrochlore-free 0.655Pb(Mg <sub/>1/3</sub> Nb <sub/>2/3</sub> )O <sub/>3</sub> -0.345PbTiO <sub/>3</sub> piezoelectric ceramics by tape-casting process
摘要： Piezoelectric ceramics of the perovskite solid solution 0.655Pb(Mg1/3Nb2/3)O3-0.345PbTiO3 (0.655PMN-0.345PT) were synthesized by tape-casting process. Highly dense ceramics lacking parasitic pyrochlore phases were fabricated by using precursor method and adding moderate PbO. The influences from sintering temperature on the physical and electrical properties of the 0.655PMN-0.345PT ceramics were initially investigated by phase and microstructure analyses. High piezoelectric, dielectric and ferroelectric properties of d33?700 pC/N, kp?0.605, er?4770, tand ? 0.016, Pr?30.68 lC/cm2 were obtained for the specimens sintered at 1200 (cid:2)C. Compared with the traditional solid-state sintering method, the performance of ceramics formed by tape-casting achieved an improvement.
关键词： tape-casting,PMN-PT,ferroelectric properties,dielectric properties,piezoelectric properties
更新于2025-09-11 14:12:44
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Structural, bulk permittivity and impedance spectra of electronic material: Bi(Fe0.5La0.5)O3
摘要： In the present paper, fabrication and characterization (structural, electrical and ferroelectric properties) of a lead-free lanthanum (La) modified bismuth ferrite electroceramic having composition Bi(Fe0.5La0.5)O3 (BFLO) using various experimental techniques have been reported. BFLO has been synthesized by means of a high-temperature inter-diffusion of oxides method. This investigation mainly aims to correlate the phase formation and physical properties while the Fe-site of bismuth ferrite has partially been replaced by La. The surface micrograph shows the formation of the high dense ceramic sample. Analysis of data of various complex spectroscopies related to modulus and impedance exhibits the relaxation mechanism in this sample is of non-Debye type. The combined effect of grains and grain boundaries has been depicted from the Nyquist plot through the least-squares fitting of suitable circuit model along with the experimental data. The remnant polarization and coercive field decreases as temperature rises which was discerned from the ferroelectric loop obtained at different temperatures. The existence of ferroelectric nature in the sample was postulated from the polarization versus electric field plot.
关键词： Ferroelectric properties,Non-Debye relaxation,Lanthanum modification,Bismuth ferrite,Electroceramic
更新于2025-09-10 09:29:36
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The enhanced magnetoelectric effect and piezoelectric properties in the lead-free Bi3.15Nd0.85Ti3O12/La0.7Ca0.3MnO3 nano-multilayers composite thin films
摘要： The lead-free multiferroic nano-multilayers composite thin films were fabricated on basis of ferroelectric (FE) Bi3.15Nd0.85Ti3O12 (BNT) and ferromagnetic (FM) La0.7Ca0.3MnO3 (LCMO) parents with 8 nm/6 nm periodicity, respectively. The crystal structure, switching of polarization, magnetization and temperature dependence of magnetoelectric coupling (ME) effect for the multiferroic BNT/LCMO composite thin films were investigated in detail, respectively. Ferroelectric behavior along with an enhanced remnant polarization (2Pr) of 42 mC/cm2, saturated magnetization around 151 emu/cm3, the enhanced piezoelectric coefficient d33 of 263 pm/V and the enhanced magnetoelectric effect voltage coefficient of 72.1 mV/cm*Oe were obtained. The results show that the lead-free multiferroic films exhibit both good ferroelectric, dielectric and magnetic properties, as well as the enhanced ME effects, indicating that the coupling effects of electric and magnetic field exist in the fabricated Bi3.15Nd0.85Ti3O12/La0.7Ca0.3MnO3 (BNT/LCMO) nano-multilayer thin films, and the strong ME effect originating from the magnetic-mechanical-electric interaction and interface coupling were demonstrated. These results can be particularly important for developing nano-composite multiferroic devices.
关键词： Temperature dependence of ME effect,Lead-free BNT/LCMO nano-multilayers,Ferroelectric properties,Magnetization
更新于2025-09-10 09:29:36
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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