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Tailoring properties of hybrid perovskites by domain-width engineering with charged walls
摘要： Charged ferroelectric domain walls are fascinating electrical topological defects that can exhibit unusual properties. Here, in the search for novel phenomena, we perform and analyze first-principles calculations to investigate the effect of domain width on properties of domains with charged walls in the photovoltaic material consisting of methylammonium lead iodide hybrid perovskite. We report that such domains are stable and have rather low domain wall energy for any investigated width (that is, up to 13 lattice constants). Increasing the domain width first linearly decreases the electronic band gap from ?1.4 eV to about zero (which therefore provides an efficient band-gap engineering), before the system undergoes an insulator-to-metal transition and then remains metallic (with both the tail-to-tail and head-to-head domain walls being conductive) for the largest widths. All these results can be understood in terms of: (i) components of polarization along the normal of the domain walls being small in magnitude; (ii) an internal electric field that is basically independent of the domain width; and (iii) rather negligible charge transfer between walls. These findings deepen the knowledge of charged ferroelectric domain walls and can further broaden their potential for applications, particularly in the context of halide perovskites for photovoltaics.
关键词： charged ferroelectric domain walls,hybrid perovskites,photovoltaic materials,band-gap engineering,insulator-to-metal transition
更新于2025-09-23 15:19:57
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Epitaxial Integration on Si(001) of Ferroelectric Hf <sub/>0.5</sub> Zr <sub/>0.5</sub> O <sub/>2</sub> Capacitors with High Retention and Endurance
摘要： Epitaxial ferroelectric Hf0.5Zr0.5O2 films have been successfully integrated in a capacitor heterostructure on Si(001). The orthorhombic Hf0.5Zr0.5O2 phase, [111] out-of-plane oriented, is stabilized in the films. The films present high remnant polarization Pr close to 20 μC/cm2, rivaling with equivalent epitaxial films on single crystalline oxide substrates. Retention time is longer than 10 years for writing field of around 5 MV/cm, and the capacitors show endurance up to 109 cycles for writing voltage of around 4 MV/cm. It is found that the formation of the orthorhombic ferroelectric phase depends critically on the bottom electrode, being achieved on La0.67Sr0.33MnO3 but not on LaNiO3. The demonstration of excellent ferroelectric properties in epitaxial films of Hf0.5Zr0.5O2 on Si(001) is relevant towards fabrication of devices that require homogeneity in the nanometer scale, as well as for better understanding of the intrinsic properties of this promising ferroelectric oxide.
关键词： Oxides thin films.,Oxides on silicon,Ferroelectric HfO2,Ferroelectric oxides,Epitaxial stabilization
更新于2025-09-19 17:15:36
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Complementary Resistive Switching Using Metal-Ferroelectric-Metal Tunnel Junctions
摘要： Complementary resistive switching (CRS) devices are receiving attention because they can potentially solve the current-sneak and current-leakage problems of memory arrays based on resistive switching (RS) elements. It is shown here that a simple anti-serial connection of two ferroelectric tunnel junctions, based on BaTiO3, with symmetric top metallic electrodes and a common, floating bottom nanometric film electrode, constitute a CRS memory element. It allows nonvolatile storage of binary states (“1” = “HRS+LRS” and “0” = “LRS+HRS”), where HRS (LRS) indicate the high (low) resistance state of each ferroelectric tunnel junction. Remarkably, these states have an identical and large resistance in the remanent state, characteristic of CRS. Here, protocols for writing information are reported and it is shown that non-destructive or destructive reading schemes can be chosen by selecting the appropriate reading voltage amplitude. Moreover, this dual-tunnel device has a significantly lower power consumption than a single ferroelectric tunnel junction to perform writing/reading functions, as is experimentally demonstrated. These findings illustrate that the recent impressive development of ferroelectric tunnel junctions can be further exploited to contribute to solving critical bottlenecks in data storage and logic functions implemented using RS elements.
关键词： ferroelectric tunnel junctions,BaTiO3,complementary resistive switching,ferroelectric
更新于2025-09-19 17:15:36
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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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Ferroelectric mesocrystalline BaTiO <sub/>3</sub> /BaBi <sub/>4</sub> Ti <sub/>4</sub> O <sub/>15</sub> nanocomposite: formation mechanism, nanostructure, and anomalous ferroelectric response
摘要： Ferroelectric mesocrystalline nanocomposites are promising materials for the enhancement of ferroelectricity via lattice strain engineering due to their high density of heteroepitaxial interfaces. In the present study, a ferroelectric mesocrystalline BaTiO3/BaBi4Ti4O15 (BT/BBT) nanocomposite was synthesized using the layered titanate H1.07Ti1.73O4 via a facile two-step topochemical process. The BT/BBT nanocomposite is constructed from well-aligned BT and BBT nanocrystals oriented along the [110] and [11?1] crystal-axis directions, respectively. Lattice strain is introduced into the nanocomposite through the formation of a BT/BBT heteroepitaxial interface, which results in a greatly elevated Curie temperature for BBT in the range of 400 °C to 700 °C and an improved piezoelectric response with d*33 = 130 pm V?1. In addition, the BT/BBT nanocomposite is stable up to a high temperature of 1100 °C; therefore, mesocrystalline ceramics can be fabricated as high-performance ferroelectric materials.
关键词： piezoelectric response,nanocomposite,ferroelectric,mesocrystalline,BaBi4Ti4O15,BaTiO3,Curie temperature,lattice strain
更新于2025-09-19 17:15:36
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Electromechanical Properties of Ferroelectric (NaKLi)(NbTa)O <sub/>3</sub> –CaZrO <sub/>3</sub> Ceramics
摘要： Electromechanical Properties of Ferroelectric (NaKLi)(NbTa)O3–CaZrO3 Ceramics. The effect of CaZrO3 to electric and mechanical properties of (Na0.47K0.51Li0.02)(Nb0.8Ta0.2)O3 was investigated. With increment of CaZrO3, the crystal structure of (Na0.47K0.51Li0.02)(Nb0.8Ta0.2)O3 changed from the mixture of ferroelectric orthorhombic and rhombohedral phases to paraelectric pseudo-cubic phase. On the way of transition from ferroelectric to paraelectric phases, the composition range showing the mixture of ferroelectric/paraelectric phases with a structure of core/shell was revealed with an advent of relatively large strain behavior. The shell phase formed via solid-state diffusion of Nb, Ta, Na, K ions between (Na0.47K0.51Li0.02)(Nb0.8Ta0.2)O3 and CaZrO3 particles, followed by its subsequent solution process with mixing a Ta-rich perovskite with Ca and Zr ions. In contrast, the core phase formed via a solution-precipitation process, resulting in a Ta-depleted ferroelectric perovskite. Energy-dispersive X-ray analysis showed that core was a Nb-rich ferroelectric phase and the shell was a Ta-rich paraelectric phase with Ca and Zr ions at room temperature. This structure implies an interaction between straining behaviors in the core and shell phases under an electric field, leading large deformation in macro-scale.
关键词： Piezoelectric Properties,Electrostrain,(NaKLi)(NbTa)O3,CaZrO3,Ferroelectric Material
更新于2025-09-19 17:15:36
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Polarization Properties and Polarization Depth Profiles of (Cd:Zn)S/P(VDF-TrFE) Composite Films in Dependence of Optical Excitation
摘要： The influence of optical excitation intensity on the electrical, ferroelectric and pyroelectric properties of ferroelectric-semiconductor-composites was investigated. For this purpose, composite thin films consisting of poly(vinylidene fluoride-co-trifluoroethylene) and 10 vol % (Cd:Zn)S particles with a thickness of 34 μm were fabricated. The samples were used to measure the absolute pyrocoefficient and to determine the relative pyroelectric depth profile using Laser Intensity Modulated Method. It was shown that a polarization of the samples without an optical excitation at the utilized relatively small peak-to-peak voltages could not be verified by the Sawyer–Tower circuit and the measurement setup of the pyroelectric coefficient, respectively. Both remanent polarization and pyroelectric coefficients increased with increasing optical excitation intensity during poling as well as increasing peak-to-peak voltage. The pyrocoefficient shows a temporal decay in the first hours after poling. The specific heat and thermal conductivity or the thermal diffusivity are required for the calibration of the pyroelectric depth profile. Rule of mixture and photo-acoustic investigations proved that the thermal properties of the utilized composites do not differ significantly from those of the pristine polymer. Based on the pyroelectric depth profile which is proportional to the polarization profile, the existing “three phase model” has been extended to generate a replacement circuit diagram, explaining the local polarization due to the optical excitation dependency for both local resistivity and local field strength.
关键词： composite,optical excitation,ferroelectric polymer,semiconductor
更新于2025-09-19 17:15:36
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Mn-doping composition dependence of the structures, electrical and magnetic properties, and domain structure/switching of Aurivillius Bi5Ti3FeO15 films
摘要： Mn-doped Bi5Ti3FeO15 (BTFO) ?lms were prepared by a chemical solution deposition route. The e?ect of a series of di?erent Mn-doping concentrations from 0.05 to 0.4 on structures, electrical and magnetic properties, and domain structure/switching was systematically studied. Mn-doping into BTFO can avail the grain growth. Ferroelectric and dielectric properties are improved through Mn-doping, and the optimized Mn-doping content is 0.25 with remnant polarization of 17.2 μC/cm2 and permittivity of 371.2 at 10 kHz. Moreover, similar evolution of the permittivity and loss tangent with frequency to that of parent BTFO ?lms appears in the BTFMO ?lms when Mn-doping content is below 0.25, while obvious dispersion phenomena is demonstrated with further increasing Mn-doping content. A 180° domain structure and local ferroelectric switching are observed in all these Mn-doped BTFO thin ?lms, and the piezo-displacement can reach 416 p.m. in 0.15 Mn-doped BTFO ?lm. Finally, ferromagnetic properties appear in all these Mn-doped BTFO thin ?lms. The coercive ?eld shows weak temperature independence on Mn-doping contents, while the remnant magnetization is raised by Mn-doping.
关键词： Domain structure and switching,Dielectric response,Magnetic property,Ferroelectric property,Aurivillius compounds,Element doping
更新于2025-09-19 17:15:36
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Stabilization of anti-ferroelectric Pbcm phase over ferroelectric P2<sub>1</sub>ma phase in intermittent ferroelectric NaNbO<sub>3</sub> by incorporating CaTiO<sub>3 </sub>
摘要： This study focuses on the structural aspect of stabilization of anti-ferroelectric Pbcm phase over ferroelectric P21ma phase by introducing CaTiO3 in NaNbO3 perovskite. For this work, Na1-xCaxNb1-xTixO3 (x= 0.00, 0.03, 0.04, 0.05) ceramic compositions are chosen for investigation. Structural and dielectric studies are performed on these compositions to see the effect of dopants on phase transitions involved. X-ray diffraction and their respective refinement results confirmed orthorhombic structure with Pbcm space group for all the compositions. Structures were performed for all the above-mentioned compositions. Based on PE and structural analysis, high electric field stable anti-ferroelectric phase can be established for x=0.04 composition. Reasons for high electric field stable antiferroelectric phase at x = 0.04 is presented where it is argued that the octahedral tilt distortion of perovskite structure is responsible for the increase in energy barrier required for AFE?FE transformation, thus stabilizing the antiferroelectric phase. To get more insights into the AFE-FE phase transition and stabilization of AFE phase with respect to composition, dielectric permittivity vs temperature and polarization vs electric field studies are generated using refined X-ray diffraction data in order to understand the effect of doping on octahedral tilting, which plays a huge role in increasing the energy gap required for Pbcm to P21ma conversion and is responsible for establishing stable antiferroelectric phase.
关键词： Double hysteresis,octahedral tilting,Anti-ferroelectric
更新于2025-09-19 17:15:36
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Dielectric and Ferroelectric Properties of P(VDF-TrFE) Films with Different Polar Solvents
摘要： We investigated the structural, dielectric, and ferroelectric properties of poly(vinylidene fluoride-co-trifluoroethylene) [P(VDF-TrFE)] films that were grown using dimethylformamide (DMF) and tetrahydrofuran (THF) polar solvents. The DMF solvent has a large dipole moment with a long bond length and evaporates slowly while the THF solvent has a small dipole moment with a short bond length and evaporates rapidly. Because of these differences, a thin film with a rough surface occurs when using DMF while a thick film with a smooth surface is formed when using THF. Compared to DMF solvent, the ferroelectric polarization is not well saturated and the dielectric constant is quite low for the THF solvent, which is possibly due to the residual paraelectric defects in the P(VDF-TrFE) films. For both solvents, the polarization switching can be explained by using the Kolmogorov-Avrami-Ishibashi (KAI) model with similar switching times. Both solvents enable the P(VDF-TrFE) films to have good retention and fatigue resistance for ferroelectric polarization.
关键词： Polar solvents,P(VDF-TrFE),Fatigue resistance,Ferroelectric switching,Retention
更新于2025-09-19 17:15:36