Showing papers on "Ferroelectricity published in 2004"
TL;DR: Thermodynamic analyses show that the magnetoelectric coupling in a nanostructured BaTiO3-CoFe2O4 ferroelectromagnet can be understood on the basis of the strong elastic interactions between the two phases.
Abstract: We report on the coupling between ferroelectric and magnetic order parameters in a nanostructured BaTiO3-CoFe2O4 ferroelectromagnet. This facilitates the interconversion of energies stored in electric and magnetic fields and plays an important role in many devices, including transducers, field sensors, etc. Such nanostructures were deposited on single-crystal SrTiO3 (001) substrates by pulsed laser deposition from a single Ba-Ti-Co-Fe-oxide target. The films are epitaxial in-plane as well as out-of-plane with self-assembled hexagonal arrays of CoFe2O4 nanopillars embedded in a BaTiO3 matrix. The CoFe2O4 nanopillars have uniform size and average spacing of 20 to 30 nanometers. Temperature-dependent magnetic measurements illustrate the coupling between the two order parameters, which is manifested as a change in magnetization at the ferroelectric Curie temperature. Thermodynamic analyses show that the magnetoelectric coupling in such a nanostructure can be understood on the basis of the strong elastic interactions between the two phases.
2,005 citations
TL;DR: A striking interplay between ferroelectricity and magnetism in the multiferroic TbMn2O5 is reported, demonstrated by a highly reproducible electric polarization reversal and permanent polarization imprint that are both actuated by an applied magnetic field.
Abstract: Ferroelectric and magnetic materials are a time-honoured subject of study and have led to some of the most important technological advances to date. Magnetism and ferroelectricity are involved with local spins and off-centre structural distortions, respectively. These two seemingly unrelated phenomena can coexist in certain unusual materials, termed multiferroics1,2,3,4,5,6,7,8,9,10,11. Despite the possible coexistence of ferroelectricity and magnetism, a pronounced interplay between these properties has rarely been observed6,12. This has prevented the realization of multiferroic devices offering such functionality13. Here, we report a striking interplay between ferroelectricity and magnetism in the multiferroic TbMn2O5, demonstrated by a highly reproducible electric polarization reversal and permanent polarization imprint that are both actuated by an applied magnetic field. Our results point to new device applications such as magnetically recorded ferroelectric memory.
1,912 citations
TL;DR: It is shown that epitaxial strain from a newly developed substrate can be harnessed to increase Tc by hundreds of degrees and produce room-temperature ferro electricity in strontium titanate, a material that is not normally ferroelectric at any temperature.
Abstract: Systems with a ferroelectric to paraelectric transition in the vicinity of room temperature are useful for devices. Adjusting the ferroelectric transition temperature (T(c)) is traditionally accomplished by chemical substitution-as in Ba(x)Sr(1-x)TiO(3), the material widely investigated for microwave devices in which the dielectric constant (epsilon(r)) at GHz frequencies is tuned by applying a quasi-static electric field. Heterogeneity associated with chemical substitution in such films, however, can broaden this phase transition by hundreds of degrees, which is detrimental to tunability and microwave device performance. An alternative way to adjust T(c) in ferroelectric films is strain. Here we show that epitaxial strain from a newly developed substrate can be harnessed to increase T(c) by hundreds of degrees and produce room-temperature ferroelectricity in strontium titanate, a material that is not normally ferroelectric at any temperature. This strain-induced enhancement in T(c) is the largest ever reported. Spatially resolved images of the local polarization state reveal a uniformity that far exceeds films tailored by chemical substitution. The high epsilon(r) at room temperature in these films (nearly 7,000 at 10 GHz) and its sharp dependence on electric field are promising for device applications.
1,861 citations
TL;DR: This work demonstrates a route to a lead-free ferroelectric for nonvolatile memories and electro-optic devices.
Abstract: Biaxial compressive strain has been used to markedly enhance the ferroelectric properties of BaTiO 3 thin films. This strain, imposed by coherent epitaxy, can result in a ferroelectric transition temperature nearly 500°C higher and a remanent polarization at least 250% higher than bulk BaTiO 3 single crystals. This work demonstrates a route to a lead-free ferroelectric for nonvolatile memories and electro-optic devices.
1,672 citations
TL;DR: In this paper, a synchrotron x-ray study of lead titanate as a function of temperature and film thickness for films as thin as a single unit cell was performed.
Abstract: Understanding the suppression of ferroelectricity in perovskite thin films is a fundamental issue that has remained unresolved for decades. We report a synchrotron x-ray study of lead titanate as a function of temperature and film thickness for films as thin as a single unit cell. At room temperature, the ferroelectric phase is stable for thicknesses down to 3 unit cells (1.2 nanometers). Our results imply that no thickness limit is imposed on practical devices by an intrinsic ferroelectric size effect.
1,055 citations
TL;DR: This work identifies the nature of the ferroelectric phase transition in the hexagonal manganite, YMnO3, using a combination of single-crystal X-ray diffraction, thorough structure analysis and first-principles density-functional calculations, and suggests an avenue for designing novel magnetic ferroelectrics.
Abstract: Understanding the ferroelectrocity in magnetic ferroelectric oxides is of both fundamental and technological importance. Here, we identify the nature of the ferroelectric phase transition in the hexagonal manganite, YMnO3, using a combination of single-crystal X-ray diffraction, thorough structure analysis and first-principles density-functional calculations. The ferroelectric phase is characterized by a buckling of the layered MnO5 polyhedra, accompanied by displacements of the Y ions, which lead to a net electric polarization. Our calculations show that the mechanism is driven entirely by electrostatic and size effects, rather than the usual changes in chemical bonding associated with ferroelectric phase transitions in perovskite oxides. As a result, the usual indicators of structural instability, such as anomalies in Born effective charges on the active ions, do not hold. In contrast to the chemically stabilized ferroelectrics, this mechanism for ferroelectricity permits the coexistence of magnetism and ferroelectricity, and so suggests an avenue for designing novel magnetic ferroelectrics.
1,042 citations
TL;DR: In this article, the authors reviewed the literature in this field, with an emphasis on the factors that impact the magnitude of the available piezoelectric response for non-ferroelectric materials such as ZnO and AlN.
Abstract: Thin film piezoelectric materials offer a number of advantages in microelectromechanical systems (MEMS), due to the large motions that can be generated, often with low hysteresis, the high available energy densities, as well as high sensitivity sensors with wide dynamic ranges, and low power requirements This paper reviews the literature in this field, with an emphasis on the factors that impact the magnitude of the available piezoelectric response For non-ferroelectric piezoelectrics such as ZnO and AlN, the importance of film orientation is discussed The high available electrical resistivity in AlN, its compatibility with CMOS processing, and its high frequency constant make it especially attractive in resonator applications The higher piezoelectric response available in ferroelectric films enables lower voltage operation of actuators, as well as high sensitivity sensors Among ferroelectric films, the majority of the MEMS sensors and actuators developed have utilized lead zirconate titanate (PZT) films as the transducer Randomly oriented PZT films show piezoelectric e(31, f) coefficients of about - 7 C/m(2) at the morphotropic phase boundary In PZT films, orientation, composition, grain size, defect chemistry, and mechanical boundary conditions all impact the observed piezoelectric coefficients The highest achievable piezoelectric responses can be observed in {001} oriented rhombohedrally-distorted perovskites For a variety of such films, e(31,f) coefficients of - 12 to - 27 C/m(2) have been reported
1,016 citations
TL;DR: In this article, a single-phased ferroelectromagnet BiFeO3 ceramics with high resistivity were synthesized by a rapid liquid phase sintering technique.
Abstract: Single-phased ferroelectromagnet BiFeO3 ceramics with high resistivity were synthesized by a rapid liquid phase sintering technique. Saturated ferroelectric hysteresis loops were observed at room temperature in the ceramics sintered at 880 °C for 450 s. The spontaneous polarization, remnant polarization, and the coercive field are 8.9 μC/cm2, 4.0 μC/cm2, and 39 kV/cm, respectively, under an applied field of 100 kV/cm. It is proposed that the formation of Fe2+ and an oxygen deficiency leading to the higher leakage can be greatly suppressed by the very high heating rate, short sintering period, and liquid phase sintering technique. The latter was also found effective in increasing the density of the ceramics. The sintering technique developed in this work is expected to be useful in synthesizing other ceramics from multivalent or volatile starting materials.
970 citations
TL;DR: The relationships among magnetism, lattice modulation, and dielectric properties have been investigated for RMnO3 and it was found that the IC-C transition is accompanied by a ferroelectric transition, associated with a lattices modulation in the C phase.
Abstract: The relationships among magnetism, lattice modulation, and dielectric properties have been investigated for RMnO3 (R=Eu, Gd, Tb, and Dy). These compounds show a transition to an incommensurate lattice structure below their Neel temperature, and subsequently undergo an incommensurate-commensurate (IC-C) phase transition. For TbMnO3 and DyMnO3 it was found that the IC-C transition is accompanied by a ferroelectric transition, associated with a lattice modulation in the C phase. DyMnO3 shows a gigantic magnetocapacitance with a change of dielectric constant up to Deltaepsilon/epsilon approximately 500%.
827 citations
TL;DR: Not only can the necessary high-quality ferroelectric films now be grown for new device capabilities, but ferroelectrics can be combined with other functional oxides, such as high-temperature superconductors and magnetic oxide, to create multifunctional materials and devices.
Abstract: Ferroelectric oxide materials have offered a tantalizing potential for applications since the discovery of ferroelectric perovskites more than 50 years ago. Their switchable electric polarization is ideal for use in devices for memory storage and integrated microelectronics, but progress has long been hampered by difficulties in materials processing. Recent breakthroughs in the synthesis of complex oxides have brought the field to an entirely new level, in which complex artificial oxide structures can be realized with an atomic-level precision comparable to that well known for semiconductor heterostructures. Not only can the necessary high-quality ferroelectric films now be grown for new device capabilities, but ferroelectrics can be combined with other functional oxides, such as high-temperature superconductors and magnetic oxides, to create multifunctional materials and devices. Moreover, the shrinking of the relevant lengths to the nanoscale produces new physical phenomena. Real-space characterization and manipulation of the structure and properties at atomic scales involves new kinds of local probes and a key role for first-principles theory.
808 citations
TL;DR: This work performs ab initio studies of ferroelectric nanoscale disks and rods of technologically important Pb(Zr,Ti)O3 solid solutions, and demonstrates the existence of previously unknown phase transitions in zero-dimensional ferroElectric nanoparticles.
Abstract: Bulk ferroelectrics undergo structural phase transformations at low temperatures, giving multi-stable (that is, multiple-minimum) degenerate states with spontaneous polarization. Accessing these states by applying, and varying the direction of, an external electric field is a key principle for the operation of devices such as non-volatile ferroelectric random access memories (NFERAMs). Compared with bulk ferroelectrics, low-dimensional finite ferroelectric structures promise to increase the storage density of NFERAMs 10,000-fold. But this anticipated benefit hinges on whether phase transitions and multi-stable states still exist in low-dimensional structures. Previous studies have suggested that phase transitions are impossible in one-dimensional systems, and become increasingly less likely as dimensionality further decreases. Here we perform ab initio studies of ferroelectric nanoscale disks and rods of technologically important Pb(Zr,Ti)O3 solid solutions, and demonstrate the existence of previously unknown phase transitions in zero-dimensional ferroelectric nanoparticles. The minimum diameter of the disks that display low-temperature structural bistability is determined to be 3.2 nm, enabling an ultimate NFERAM density of 60 x 10(12) bits per square inch-that is, five orders of magnitude larger than those currently available. Our results suggest an innovative use of ferroelectric nanostructures for data storage, and are of fundamental value for the theory of phase transition in systems of low dimensionality.
TL;DR: In this paper, dramatic enhanced polarization has been found for (001, (101), and (111) films relative to that of BiFeO3 crystals, and the easy axis of spontaneous polarization lies close to (111).
Abstract: Dramatically enhanced polarization has been found for (001), (101), and (111) films, relative to that of BiFeO3 crystals. The easy axis of spontaneous polarization lies close to (111), for the various oriented films. BiFeO3 films grown on (111) have a rhombohedral structure, identical to that of single crystals; whereas films grown on (101) or (001) are monoclinically distorted from the rhombohedral structure, due to the epitaxial constraint.
TL;DR: It is shown that in charge-ordered and orbitally ordered perovskites it is possible to make use of the coupling between magnetic and charge ordering to obtain ferroelectric magnets.
Abstract: Transition metal oxides with a perovskite-type structure constitute a large group of compounds with interesting properties. Among them are materials such as the prototypical ferroelectric system BaTiO(3), colossal magnetoresistance manganites and the high-T(c) superconductors. Hundreds of these compounds are magnetic, and hundreds of others are ferroelectric, but these properties very seldom coexist. Compounds with an interdependence of magnetism and ferroelectricity could be very useful: they would open up a plethora of new applications, such as switching of magnetic memory elements by electric fields. Here, we report on a possible way to avoid this incompatibility, and show that in charge-ordered and orbitally ordered perovskites it is possible to make use of the coupling between magnetic and charge ordering to obtain ferroelectric magnets. In particular, in manganites that are less than half doped there is a type of charge ordering that is intermediate between site-centred and bond-centred. Such a state breaks inversion symmetry and is predicted to be magnetic and ferroelectric.
TL;DR: The dislocation-induced polarization instability of (001)-oriented Pb(Zr0.52Ti0.48)O3 (PZT) nanoislands is reported, suggesting that misfit engineering is indispensable for obtaining nanostructured ferroelectrics with stable polarization.
Abstract: Defects exist in almost all materials and defect engineering at the atomic level is part of modern semiconductor technology Defects and their long-range strain fields can have a negative impact on the host materials In materials with confined dimensions, the influence of defects can be even more pronounced due to the enhanced relative volume of the 'defective' regions Here we report the dislocation-induced polarization instability of (001)-oriented Pb(Zr(052)Ti(048))O(3) (PZT) nanoislands, with an average height of approximately 9 nm, grown on compressive perovskite substrates Using quantitative high-resolution electron microscopy, we visualize the strain fields of edge-type misfit dislocations, extending predominantly into a PZT region with a height of approximately 4 nm and width of approximately 8 nm The lattice within this region deviates from the regular crystal structure Piezoresponse force microscopy indicates that such PZT nanoislands do not show ferroelectricity Our results suggest that misfit engineering is indispensable for obtaining nanostructured ferroelectrics with stable polarization
TL;DR: In this article, the authors measured the largest ever measured in ferroelectrics and obtained a well-saturated remarkably giant saturation polarization of 158 µC/cm2 and a remanent polarization of 146 µC /cm2 for a maximum applied voltage of 20 V at 90 K.
Abstract: Ferroelectric BiFeO3 thin films have been deposited on Pt/TiO2/SiO2/Si substrate by pulsed-laser deposition. From the X-ray diffraction analysis, the BiFeO3 thin film consists of perovskite single-phase, and the crystal structure shows the tetragonal structure (c/a = 1.018) with a space group P4mm. It is obtained that the BiFeO3 thin film shows a well-saturated remarkably giant saturation polarization of 158 µC/cm2 and a remanent polarization of 146 µC/cm2 for a maximum applied voltage of 20 V at 90 K. These values of polarization are largest ever-measured in ferroelectrics.
TL;DR: In this paper, the detailed magnetic field dependence of the electric polarization and dielectric constant in (Tb,Dy,Ho)Mn2O5 where magnetic and ferroelectric transitions are intimately coupled was investigated.
Abstract: We have investigated the detailed magnetic field dependence of the electric polarization and dielectric constant in (Tb,Dy,Ho)Mn2O5 where magnetic and ferroelectric transitions are intimately coupled. Our fundamental discovery is the unprecedented large change of the dielectric constant with magnetic field, particularly in DyMn2O5, associated with an unusual commensurate-incommensurate magnetic transition. This extraordinary effect appears to originate from the high sensitivity of the incommensurate state to external perturbation.
TL;DR: In this article, a polymer-assisted deposition (PAD) was proposed to grow metal-oxide films in large areas at low cost using a homogeneous distribution of metal precursors in the solution.
Abstract: Metal oxides are emerging as important materials for their versatile properties such as high-temperature superconductivity, ferroelectricity, ferromagnetism, piezoelectricity and semiconductivity. Metal-oxide films are conventionally grown by physical and chemical vapour deposition. However, the high cost of necessary equipment and restriction of coatings on a relatively small area have limited their potential applications. Chemical-solution depositions such as sol-gel are more cost-effective, but many metal oxides cannot be deposited and the control of stoichiometry is not always possible owing to differences in chemical reactivity among the metals. Here we report a novel process to grow metal-oxide films in large areas at low cost using polymer-assisted deposition (PAD), where the polymer controls the viscosity and binds metal ions, resulting in a homogeneous distribution of metal precursors in the solution and the formation of uniform metal-organic films. The latter feature makes it possible to grow simple and complex crack-free epitaxial metal-oxides.
TL;DR: In this article, the effects of amount of BKT on the electrical properties and crystal structure of lead-free piezoelectric ceramics have been studied, and the results showed that incorporated BKT diffuses into the BNT lattice to form a solid solution during sintering, but changes the crystal structure from rhombohedral to tetragonal symmetry at higher BKT amounts.
Abstract: Lead-free piezoelectric ceramics (095−x)(Bi1∕2Na1∕2)TiO3–x(Bi1∕2K1∕2)TiO3–005BaTiO3 (abbreviated as BNT–BKT–BT100x, with x ranged from 0 to 20mol%) have been studied Effects of amount of BKT on the electrical properties and crystal structure were examined BNT–BKT–BT5 ceramics give good performances with piezoelectric constant d33=148pC∕N, electromechanical coupling factor kp=34%, kt=492%, free permittivity e33T∕e0=700, and dissipation factor tanδ=2% at 1kHz Accordingly, the sample shows larger remanent polarization and lower coercive field than 095BNT–005BT ceramics X-ray diffraction analysis shows that incorporated BKT diffuses into the BNT–BT lattice to form a solid solution during sintering, but changes the crystal structure from rhombohedral to tetragonal symmetry at higher BKT amounts
TL;DR: In this paper, a phase-field model based on the time-dependent Ginzburg-Landau equation was used to simulate the polarization switching in a ferroelectric subjected to an electric field or a stress field.
TL;DR: In this article, the effects of deposition pressure on their crystal structure and multiferroic properties have been investigated at room temperature, showing that the surface roughness and grain size of the films depend dramatically on oxygen pressure.
Abstract: BiFeO3 thin films have been prepared on Pt∕TiO2∕SiO2∕Si substrates under various oxygen pressures of 0.15–0.005Torr at a temperature of 450°C by pulsed-laser deposition. The effects of deposition pressure on their crystal structure and multiferroic properties have been investigated at room temperature. X-ray diffraction analysis (θ-2θ scans and 2-dimensional scans) shows that the BiFeO3 thin films consist of perovskite single phase with tetragonal crystal structure and space group P4mm. The c-axis lattice constant decreases (4.062–4.006A) and c∕a ratio of the films decreases from 1.032 to 1.014 with a decrease in the oxygen pressure. The surface roughness and grain size of the films depend dramatically on oxygen pressures. The dielectric constant of the films decreases with decreasing oxygen pressure. The film deposited at 0.05Torr shows a stable current density and well-saturated hysteresis loop with twice the remanent polarization (2Pr) of 136μC∕cm2 and coercive field (2Ec) of 109kV∕cm. The BiFeO3 thin ...
TL;DR: In this paper, the effect of grain size and dc field on the dielectric properties of BZT ceramics was investigated, and the fine-grained sample showed a relaxor-like ferroelectric behavior.
TL;DR: In this paper, a review of the origins of high permittivity in two groups of materials, La-doped BaTiO3 and a new barrier layer capacitor material, CaCu3Ti4O12, is given.
Abstract: A review is given of the origins of high permittivity in two groups of materials, La-doped BaTiO3 and a new barrier layer capacitor material, CaCu3Ti4O12. Factors that influence permittivity include: dopant, doping mechanism, processing conditions and grain size. La-doped BaTiO3 has high permittivity due to its ferroelectric nature at low temperatures and a novel doping mechanism: A-site substitution linked to the creation of B-site vacancies for charge compensation. Permittivities of 25,000 have been achieved, which can be increased further to ∼36,000 by additional doping with Zr. The value of impedance spectroscopy to characterize materials that have heterogeneous electrical microstructures is illustrated with the example of CaCu3Ti4O12; the high permittivity is not a bulk effect, as widely stated in the literature, but is a thin layer effect typical of a barrier layer capacitor. By attention to processing conditions to achieve large grain sizes, effective permittivities as high as 300,000 have been obtained.
TL;DR: In this paper, a phenomenological model of the effect of flexoelectricity on the dielectric constant, polarization, Curie temperature, and temperature of the onset of reversible polarization for ferroelectric thin films subject to substrate-induced epitaxial strains that are allowed to relax with thickness is presented.
Abstract: Recent experimental measurements of large flexoelectric coefficients in ferroelectric ceramics suggest that strain gradients can affect the polarization and permittivity behaviour of inhomogeneously strained ferroelectrics. Here we present a phenomenological model of the effect of flexoelectricity on the dielectric constant, polarization, Curie temperature (TC), temperature of maximum dielectric constant (Tm) and temperature of the onset of reversible polarization (Tferro) for ferroelectric thin films subject to substrate-induced epitaxial strains that are allowed to relax with thickness, and the qualitative and quantitative predictions of the model are compared with experimental results for (Ba0.5Sr0.5)TiO3 thin films on SrRuO3 electrodes. It is shown that flexoelectricity can play an important role in decreasing the maximum dielectric constant of ferroelectric thin films under inhomogeneous in-plane strain, regardless of the sign of the strain gradient.
TL;DR: In this article, BaTiO3 diffuses into the lattice of (Na 0.5K0.5)NbO3 to form a solid solution, in which orthorhombic symmetry changes to tetragonal symmetry at x≈0.06, and cubic symmetry changes at x=0.20 or higher.
Abstract: (Na0.5K0.5)NbO3 with 0–20 mol% BaTiO3 has been prepared following the conventional mixed oxide process. High-density samples were obtained through the addition of BaTiO3 into (Na0.5K0.5)NbO3 because of an increase in grain size. X-ray diffraction analysis revealed that, during sintering, all of the BaTiO3 diffuses into the lattice of (Na0.5K0.5)NbO3 to form a solid solution, in which orthorhombic symmetry changes to tetragonal symmetry at x≈0.06, and tetragonal symmetry changes to cubic symmetry at x=0.20 or higher. It was found that the samples with a low content of BaTiO3 exhibit relatively good ferroelectric and piezoelectric properties. For 0.98(Na0.5K0.5)NbO3-0.02 BaTiO3 ceramics, the remanent polarization (Pr) is 7.5 µC/cm2 with a coercive field (Ec) of 12 kV/cm. The piezoelectric constant d33 reaches 104 pC/N. The electromechanical coupling coefficients of the planar mode kp and the thickness mode kt reach ~29% and ~38%, respectively. Our results show that (Na0.5K0.5)NbO3-BaTiO3 is a good lead-free piezoelectric ceramic.
TL;DR: A first-principles-derived approach is developed to study the effects of depolarizing electric fields on the properties of Pb(Zr,Ti)O3 ultrathin films for different mechanical boundary conditions, finding a rich variety of ferroelectric phases and polarization patterns.
Abstract: A first-principles-derived approach is developed to study the effects of depolarizing electric fields on the properties of Pb(Zr,Ti)O3 ultrathin films for different mechanical boundary conditions. A rich variety of ferroelectric phases and polarization patterns is found, depending on the interplay between strain and the amount of screening of surface charges. Examples include triclinic phases, monoclinic states with in-plane and/or out-of-plane components of the polarization, homogeneous and inhomogeneous tetragonal states, as well as peculiar laminar nanodomains.
TL;DR: In this paper, an investigation was carried out on barium and strontium-modified Na 0.5Bi0.5TiO3 (NBT) ceramics.
Abstract: In search of lead-free ferroelectric ceramics with improved properties, an investigation was carried out on barium and strontium-modified Na0.5Bi0.5TiO3 (NBT) ceramics. Many compositions among the Ba and Sr-modified ceramic materials exhibit diffuse phase transition and are characterised by a strong temperature and frequency dispersion of the permittivity which would be connected with the cation disorder in the A site of the perovskite unit cell.
TL;DR: In this article, the dielectric property complemented by the mechanical measurement (internal friction) in the doped Bi4Ti3O12 [Bi4−xLaxTi3 O12] and Bi4−y/3Ti3−yNbyO12] was systematically investigated from room temperature to 350°C.
Abstract: The dielectric property complemented by the mechanical measurement (internal friction) in the doped Bi4Ti3O12 [Bi4−xLaxTi3O12 (x=0.5,0.75,1) and Bi4−y/3Ti3−yNbyO12 (y=0.015,0.03,0.06)] was systematically investigated from room temperature to 350 °C. In the plot of dielectric loss versus temperature for Bi4Ti3O12 (BiT), a relaxation peak was confirmed to be associated with the motion of the oxygen vacancy. It is found that the La doping at site A is in favor of improvement of the fatigue property, in contrast, the Nb doping at site B can mainly enhance the remanent polarization. Appropriate La doping at site A of perovskite-type unit in BiT enhances the chemical stability of oxygen vacancy by improving the height of the potential barrier for hopping and enhances the mobility of domain by the changing of domain structures. While the Nb doping at site B could induce the distortion of oxygen octahedral and reduce the oxygen vacancy concentration by a compensating effect so that it results in an enhancement of...
TL;DR: The current status of ferroelectric random access memory (FeRAM) technology is reviewed in this article, in which the memory cells are composed of Ferroelectric capacitors to store the data and cell-selection transistors to access the selected capacitors.
Abstract: The current status of ferroelectric random-access memory (FeRAM) technology is reviewed in this article Presented first is the status of conventional FeRAM, in which the memory cells are composed of ferroelectric capacitors to store the data and cell-selection transistors to access the selected capacitors Discussed next are recent developments in the field Pb(Zr X ,Ti 1 - X )O 3 (PZT) and SrBi 2 Ta 2 O 9 (SBT) films are being used to produce 013 μm and 018 μm FeRAM cells, respectively, with a stacked capacitor configuration; these cells are easily embedded into logic circuits A new class of FeRAM called 6T4C-containing static RAM (SRAM) cells composed of six transistors (6T) and four ferroelectric capacitors (4C)-has been commercially produced This type of FeRAM features a nondestructive readout operation, unlimited read/write cycling, and a fast access time of less than 10 ns Lastly, the status of field-effect-transistor (FET)-type FeRAM is reviewed, emphasizing that the data retention time of a ferroelectric-gate FET has been improved to more than a month in recent studies
TL;DR: A reentrant novel phase is observed in the hexagonal ferroelectric HoMnO3 in the presence of magnetic fields in the temperature range defined by a plateau of the dielectric constant anomaly.
Abstract: A reentrant novel phase is observed in the hexagonal ferroelectric HoMnO3 in the presence of magnetic fields in the temperature range defined by a plateau of the dielectric constant anomaly. The plateau evolves with fields from a narrow dielectric peak at the Mn-spin rotation transition at 32.8 K in zero field. The anomaly appears both as a function of temperature and as a function of magnetic field without detectable hysteresis. This is attributed to the indirect coupling between the ferroelectric (FE) and antiferromagnetic (AFM) orders, arising from an FE-AFM domain wall effect.