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This paper reports the retention behavior for Al0.93B0.07N thin films, a member of the novel family of wurtzite ferroelectrics. Our experiments suggest that bipolar cycling of metal (Pt/W)/Al0.93B0.07N/W/Al2O3 film stacks first induced wake-up and then a region of constant switchable polarization. The films showed excellent retention of the stored polarization state. As expected, data retention was slightly inferior in the opposite state (OS) measurements. However, it is noted that even after 3.6 × 106 s (1000 h) at 200 °C, the OS signal margin still exceeded 200 μC/cm2. The predicted OS retention is 82% after 10 yr baking at 200 °C. [ABSTRACT FROM AUTHOR]

Bulk or anomalous photovoltaic effect in ferroelectrics has recently sparked interest due to the generation of switchable photovoltages that are not limited by the bandgap of the material. The development of strategies to tune its magnitude is a key for the development of light-driven devices, e.g., photostrictive actuators, photostrictive sensors, or reconfigurable waveguides. In this paper, the bulk photovoltaic effect of polycrystalline solution-deposited bismuth ferrite thin films is studied under different stress conditions induced by different substrates and quantified using a direct strain assessment via x-ray diffraction. An increase in the short-circuit bulk photovoltaic current of 150% is observed with a change from a compressive stress of 0.54 GPa to a tensile stress of 0.93 GPa. This change is attributed to intrinsic piezophotovoltaic effect, demonstrating the potential to strain engineer the bulk photovoltaic effect in thin films. [ABSTRACT FROM AUTHOR]

Multiferroic (MF) composites, in which magnetic and ferroelectric orders coexist, represent a very attractive class of materials with promising applications in areas, such as spintronics, memories, and sensors. One of the most important multiferroics is the perovskite phase of bismuth ferrite, which exhibits weak magnetoelectric properties at room temperature; its properties can be enhanced by doping with other elements such as dysprosium. A recent paper has demonstrated that a thin film of Bi0.7Dy0.3FeO3 shows good magnetoelectric coupling. In separate work it has been shown that a carefully crafted ring connection of N (N odd and N ≥ 3) ferroelectric capacitors yields, past a critical point, nonlinear oscillations that can be exploited for electric (E) field sensing. These two results represent the starting point of our work. In this paper the (electrical) hysteresis, experimentally measured in the MF material Bi0.7Dy0.3FeO3, is characterized with the applied magnetic field (B) taken as a control parameter. This yields a 'blueprint' for a magnetic (B) field sensor: a ring-oscillator coupling of N = 3 Sawyer-Tower circuits each underpinned by a mutliferroic element. In this configuration, the changes induced in the ferroelectric behavior by the external or 'target' B-field are quantified, thus providing a pathway for very low power and high sensitivity B-field sensing. [ABSTRACT FROM AUTHOR]

Metal-nitride layers were used as tungsten (W)-diffusion barriers for ultra-thin (<5 nm) Hf0.5Zr0.5O2 (HZO)-based ferroelectric capacitors with W as the bottom electrode. The influence of various metal nitrides (e.g., TiN, HfN, and ZrN) on the leakage properties, ferroelectricity, and reliability of the HZO capacitors was systematically investigated to identify appropriate materials for use as diffusion barriers in TiN/HZO/W stack capacitors. All the metal-nitrides were observed to significantly suppress W diffusion, resulting in a reduced leakage current. A comparative study between diffusion barriers revealed that the TiN/HZO/W stack capacitor with a ZrN layer exhibited the largest remanent polarization (2Pr) of 23 μC/cm2, as well as the highest reliability. This was attributed to the ZrN forming a ZrO2 interfacial layer, which could contribute to polarization switching and improve reliability. We quantitatively calculated the interfacial capacitance by performing the pulse switching measurement. In addition, crystal structures and diffusion properties with various metal nitrides are evaluated by analyzing grazing-angle incidence x-ray diffraction and x-ray photoelectron spectroscopy. These results provide a guideline for the fabrication of ultrathin HZO-based capacitors with stable ferroelectricity, reduced leakage, and excellent reliability. [ABSTRACT FROM AUTHOR]

The standard "Kittel Law" for the thickness and shape of ferroelectric, ferroelastic, or ferromagnet domains assumes mechanical equilibrium. The present paper shows that such domains may be highly nonequilibrium, with unusual thicknesses and shapes. In lead germanate and multiferroic lead zirconate titanate iron tantalate domain wall instabilities resemble hydrodynamics (Richtmyer-Meshkov and Helfrich-Hurault, respectively). [ABSTRACT FROM AUTHOR]

Nanoparticles embedded in liquid crystals can trap mobile ions and decrease their concentration. In this paper, we generalize the nanoparticles-based approach and, through the quantitative analysis, identify the ferroelectric micro- and nanomaterials as the most promising "ion traps" that ensure close to 100% liquid crystal purification. We demonstrate that the treatment of liquid crystals with ferroelectric materials leads to a two-order of magnitude decrease in their electrical conductivity. This value exceeds previous data reported for similar systems by a factor of 10. Ferroelectric nanoparticles, when dispersed and stabilized in liquid crystals, act as highly efficient permanent ion traps, solve the problem of uncontrolled ionic contaminations, and eliminate the negative effects caused by ions. [ABSTRACT FROM AUTHOR]

This paper presents our work on electrical characterization of metal-ferroelectric-oxidesemiconductor (MFeOS) and metal-ferroelectric-nitride-semiconductor (MFeNS) structures for nonvolatile memory applications. Thin films of lead zirconate titanate (PZT: 35:65) have been used as ferroelectric material on 2.5-5 nm thick thermally grown SiO2 and Si3N4 as buffer layer for MFeOS and MFeNS structures, respectively. Capacitance-Voltage (C-V) and Current-Voltage (I-V) characteristics were used for electrical characterization. Our comparative results reveal that the MFeNS structure with 2.5 nm thick buffer layer has higher memory window of about 3.6V as compared to 3V for similar MFeOS structure. Also superior electrical properties such as lower leakage current and higher dielectric strength were observed in MFeNS structures. Higher nitridation time was observed to deteriorate the polarization characteristics resulting in reduced memory window. The highest memory window of 6.5V was observed for SiO2 buffer layer thickness of 5 nm. We also observed that the annealing temperature influences the leakage current characteristic and memory window of these structures. [ABSTRACT FROM AUTHOR]

We report the demonstration of ferroelectric switching in yttrium (Y)-doped nitride semiconductors. In this study, single-crystalline, wurtzite Y0.07Al0.93N films were epitaxially grown on GaN/sapphire templates by plasma-assisted molecular beam epitaxy. The ferroelectric switching process has been investigated by current density–electric field (J-E) and polarization–electric field (P-E) loops as well as positive-up-negative-down measurements, showing a coercive field of ∼6 MV/cm and a switchable polarization of ∼130 μC/cm2. Ferroelectric switching was further confirmed via butterfly shape capacitance–voltage (C-V) loops and polarity-sensitive wet etching. The realization of ferroelectric, Y-doped AlN films further extends the family of nitride ferroelectrics and unravels a wealth of intriguing opportunities in III-nitride based electronic, piezo-electronic, and optoelectronic devices. [ABSTRACT FROM AUTHOR]

Pulsed power systems require high-performance capacitors with high energy storage density. In this work, (1 − x)BaTiO3-xBi(Mg1/2Sn1/2)O3 ferroelectric ceramics were synthesized in a solid-state solution. The sample of x = 0.12 (0.88BT-0.12BMS) has excellent energy storage density, wide temperature, and wide frequency stability. The excellent energy density of 4.87 J/cm3 at 315 kV/cm and the energy efficiency of 72% at room temperature for 0.88BT-0.12BMS ceramics were achieved. Furthermore, the 0.88BT-0.12BMS ceramics demonstrated well temperature stabilities in the range of 20–100 °C and very good frequency stability in the range of 1–100 Hz. Through pulsed charging–discharging testing, the current density is calculated as 314.01 A/cm2, and the power density is 21.98 MW/cm3. Moreover, the oxygen vacancies' defects and ferroelectric domain mechanism for enhanced breakdown strength as well as high energy density were discussed. These findings broaden the horizon for lead-free dielectrics and show promising applications for pulse power capacitors. [ABSTRACT FROM AUTHOR]

Many ferroelectric solid solutions exhibit enhanced electromechanical properties at the morphotropic boundary separating two phases with different orientations of polarization. The mechanism of properties enhancement is associated with easy paths for polarization rotation in anisotropically flattened free energy profile. Another mechanism of properties enhancement related to free energy flattening is polarization extension. It is best known at temperature-driven ferroelectric-paraelectric phase transitions and may lead to exceedingly large properties. Its disadvantage is temperature instability of the enhancement. In this paper a temperature-composition phase diagram is proposed that exhibits compositionally driven-phase transitions with easy paths for both polarization rotation and polarization extension. [ABSTRACT FROM AUTHOR]

It is well known that first-order ferroelectric to paraelectric transition is a one-step transition and it gives rise to one latent heat peak and one permittivity peak during heating. In the present paper, however, we report an unexpected finding; in Mn-doped Ba(Zr0.01Ti0.98Mn0.01)O3-δ the ferroelectric to paraelectric transition proceeds in two steps, after the sample has experienced a prior aging at the differential scanning calorimetry (DSC) peak temperature and followed by cooling down to a fully ferroelectric state. The two-step transition is evidenced by a split DSC peak as well as a split permittivity peak. These abnormal effects can be explained by considering that aging at DSC peak temperature corresponds to aging in a two-phase state (paraelectric+ferroelectric). Such two-phase aging produces two different defect symmetries, which give rise to different stabilities for the same ferroelectric phase and thus results in different reverse transition temperatures. [ABSTRACT FROM AUTHOR]

CsPbBr3 shows excellent photoelectric properties such as a direct bandgap of 2.25 eV, large optical absorption coefficient, and strong luminescence intensity. Therefore, it is promising to be applied in LED devices. It is important to modulate and enhance photoluminescence (PL) intensity through external stimulus. Here, (001) CsPbBr3 films with nanocrystals were grown on the PMN-PT ferroelectric single crystal substrate, and its PL can be largely modulated by the ferroelectric polarization switching of PMN-PT. The saturated polarization of a 90 nm thick CsPbBr3 film induces a 67% increase in the PL intensity, which is due to piezoelectric strain passivated defects, resulting in decreased nonradiative recombination. However, the upward saturated polarization of the 40 nm thick CsPbBr3 film introduces a 55% decrease in the PL intensity, which can be attributed to the inner electric field separating the light-excited electron–hole pairs, thereby decreasing their radiative combination. This reversible and tunable photoluminescence is important for the development of advanced multifunctional optoelectrical devices. [ABSTRACT FROM AUTHOR]

The utilization of ferroelectrics in forms of ceramics, films, and composites toward energy-storage applications is of great interest recent years. However, the simultaneous achievement of high polarization, high breakdown strength, low energy loss, and weakly nonlinear polarization–electric field (P–E) correlation has been a huge challenge, which impedes progress in energy storage performance. In this work, a vortex domain engineering constructed via the core–shell structure in ferroelectric ceramics is proposed. The formation and the switching characteristics of vortex domains (VDs) were validated through a phase-field simulation based on the time-dependent Ginzburg–Landau kinetic equation. Benefiting from the smaller depth of a potential well in the energy profiles, the switching of VDs was much easier than that of conventional large-sized domains, which was found to be the origin of the lower coercive field, lower remanent polarization, and weaker nonlinear P–E correlation. Choosing BaTiO3 (BT) as a representative of ferroelectric ceramics, the shell fractions and permittivity values were varied in our phase-field simulation to optimize the energy storage performance. As a result, a large discharge energy of 6.5 J/cm3 was obtained in BT ferroelectric ceramics with a shell fraction of 5% and a shell permittivity of 20 under the applied electric field of 100 kV/mm, which is almost 140% higher than that with no shell structure. In general, the vortex domain engineering proposed in this work can serve as a universal method in designing high-performance ferroelectrics with simultaneous high breakdown strength, high discharge energy density, and high energy efficiency. [ABSTRACT FROM AUTHOR]

Scaling of planar HfO2-based ferroelectric capacitors is investigated experimentally by varying the capacitor area within five orders of magnitude, under the scope of a limited thermal budget for crystallization. Both Hf0.5Zr0.5O2 (HZO) and Si-doped HfO2 (HSO)-based metal/ferroelectric/metal capacitors with a 10 nm dielectric film thickness and TiN electrodes are demonstrated to be ferroelectric when integrated in a back-end of line (BEOL) of 130 nm CMOS technology, with a maximum thermal budget below 500 °C. When the area of the ferroelectric capacitors is scaled down from 7850 μm2 to 0.28 μm2, no degradation of the remanent polarization (2·PR > 10 μC/cm2 for HSO, > 30 μC/cm2 for HZO) or of the switching kinetics (down to 100 ns at 3 V) is observed. Significant improvement of the field cycling endurance is demonstrated upon area scaling, consistent with the reduction of the total number of defects when devices are shrunk. The results pave the way for future BEOL demonstrations in 130 nm and more advanced nodes with record endurance similar to perovskite ferroelectrics. [ABSTRACT FROM AUTHOR]

The deployment of ferroelectrics in device concepts such as Ferroelectric Random Access Memory and Ferroelectric Field Effect Transistors requires a good understanding of the polarization switching mechanisms. While several reports already exist involving classical perovskite ferroelectrics, only recently has the switching dynamics in HfO2-based layers started to be addressed. In this work, the Kolmogorov–Avrami–Ishibashi (KAI), the Nucleation Limited Switching (NLS), the Landau–Khalatnikov (LK), and the Inhomogeneous Field Mechanism (IFM) models for polarization switching are surveyed and evaluated with the existing body of literature. Data concerning NLS and IFM are compared to experiments undertaken in this study. After excluding the KAI model because of considerations dealing with film morphology and domain wall energy, we conclude that the NLS, the LK, and the IFM models do not necessarily mutually exclude each other, but rather give a diverse perspective on the switching phenomenon based on thermodynamic, kinetic, statistic, microscopic, and/or macroscopic points of view. [ABSTRACT FROM AUTHOR]

TiN/Gd:HfO2/TiN metal/ferroelectric/metal structures were elaborated in one batch by plasma enhanced atomic layer deposition. The crystal structure and ferroelectric properties of 12-nm-thick Gd-doped HfO2 thin films are investigated. The modulation of the Gd content within the HfO2 layer leads to a subsequent variation of crystalline phases; predominance of the orthorhombic phase correlates with a maximum 2·Pr value of 30 μC/cm2 for 1.8% of Gd doping as well as a ferroelectric polarization switching endurance up to 7 × 109 cycles. These remarkable properties of Gd:HfO2 material compared to previous works are likely the consequence of nonexposure to air of metal/insulator interfaces during stack deposition, preventing their oxidation and/or carbon contamination. [ABSTRACT FROM AUTHOR]

Single-crystal rods of the α-phase of potassium nitrate were grown with [010] uniform crystallographic orientation inside a matrix of aluminum oxide nanopores. The pores were prepared by anodization of polished aluminum substrates. The potassium nitrate single crystals were grown inside the pores from a supersaturated aqueous solution at various temperatures. Dielectric polarization measurements of the porous film filled with the potassium nitrate crystals show an electric field induced reversible transition from the nonferroelectric α-phase to the ferroelectric γ-phase at about 200 kV/cm. The ferroelectric γ-phase has a coercive field of about 169 kV/cm and remnant polarization of about 0.216 μC/cm2. [ABSTRACT FROM AUTHOR]

We report the mechanical properties of [(1-x)%]Pb(Mg[sub 1/3]Nb[sub 2/3])O[sub 3]-x%PbTiO[sub 3] ceramics with PbTiO[sub 3] content changed from 23% to 0% measured at the vibration frequency of about 1 kHz. Two modulus kinks can be observed in any of the samples. The kink appears at higher temperature can be attributed to the stress-induced relaxation of nanodomains. Another modulus kink at a lower temperature appears near the Vogel–Fulcher freezing temperature. An associated internal friction peak can also be observed at this temperature. This kink and the internal friction peak can be explained to be due to a ferroelectric phase transition, which becomes weaker with the decrease of PbTiO[sub 3] content. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A ferroelectric hysteresis depends on the orientation of the applied field with respect to the spontaneous polarization. The ferroelectric switching occurs through correlated domain movements forming avalanches. We tested whether avalanches in single crystals of the prototypic ferroelectric BaTiO3 and the relaxor ferroelectric 0.7Pb(Mg2/3Nb1/3)O3–0.3PbTiO3 show anisotropic field dependences. The anisotropy of the energy exponent of avalanches is very small in BaTiO3 with exponents between 1.53 and 1.6, which is remarkably close to the prediction of mean field theory 5/3. The anisotropy is much stronger in 0.7Pb(Mg2/3Nb1/3)O3–0.3PbTiO3 with one exponent slightly above the typical range of mean field values (4/3–5/3): 1.43 ± 0.02, 1.64 ± 0.03, and 1.79 ± 0.03 for fields along [100], [110], and [111], respectively. This anisotropy indicates a variation of the fractal dimensions of the transient domain patterns depending on the direction of the switching field. [ABSTRACT FROM AUTHOR]

HfO2-based ferroelectrics have dramatically changed the application perspectives of polarization-switching materials for information processing and storage. Their CMOS compatibility and preservation of high reversible polarization down to a few nanometer thickness make them attractive for various device concepts including non-volatile memories and negative-capacitance-enhanced steep-slope transistors. In the context of these applications, the long-standing discussion of intrinsic (thermodynamic) or extrinsic nuclei-limited switching (NLS) in ferroelectrics has recently gained importance. In particular, the negative capacitance effect that is formally described by the Landau–Ginzburg–Devonshire formalism implies the intrinsic polarization switching driven by the thermodynamic coercive field. On the other hand, recent studies reported the nucleation-limited extrinsic switching, which does not result in the hysteresis-free negative capacitance effect. Here, we analyze the polarization response in the nanometer scale on the ferroelectric/dielectric bilayer where the negative capacitance has been previously demonstrated. Our analysis of the two limiting cases of quasi-static switching and the earlier reported ultra-fast polarization response supports the intrinsic polarization reversal scenario. The compatibility of this mechanism with the previously reported NLS region-by-region switching with remarkably low domain wall velocity is addressed. Our results confirm the usability of CMOS-compatible polycrystalline HZO ferroelectric films for gates operating in the negative-capacitance regime. Furthermore, they point towards possible solutions for optimizing their switching properties for applications including memories. [ABSTRACT FROM AUTHOR]

A ferroelectric depolarized by high strain-rates induced by the passage of adiabatic shock waves releases a high-density electric charge, initiating the generation of high voltage and megawatt power levels. Additionally, this depolarization process alters physical and mechanical properties that might cause energy and electric charge losses in the ferroelectric materials. We report, herein, the results of an experimental study of electric charge losses in Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3 and Pb0.99(Zr0.52Ti0.48)0.99Nb0.01O3 ferroelectrics subjected to shock compression. We found that electric charge losses mainly occur in the compressed zone of ferroelectric elements; i.e., shock compression is an essential part of the charge loss mechanism. Based on our analysis of the experimental results, charge losses are explained by the leakage current flowing through microscopic conductive pathways (conductive channels), which are formed due to the effects of high magnitude stress and high electric fields in compressed zones of ferroelectric elements. It is shown that the Joule heating of conductive channels by the leakage current increases their temperature and conductance, eventually short-circuiting the electrodes of the shocked ferroelectric element and causing electric breakdown. The leakage current density, jleak, and breakdown delay time, tcr, can be described by the relationship, j leak 2 t c r = β (where β is the material dependent constant), over a wide range of delay times. The breakdown criterion we propose is based on the integral of specific current action and can be used to characterize the electric breakdown in a broad range of shock-compressed ferroelectric materials. [ABSTRACT FROM AUTHOR]

Photoresponsive ferroelectrics are recently under intense study due to their potential application to photovoltaic devices. Antimony sulfoiodide (SbSI) is a prototypical compound that possesses both ferroelectricity and a strong visible-light-response. However, most of the SbSI films reported so far have a polycrystalline structure with a randomly oriented polarization axis. In this study, we have fabricated c-axis textured SbSI thin films through annealing of amorphous films deposited in a molecular beam epitaxy system, employing Sb2S3 and SbI3 sources. The fabricated films are highly uniform and have the polarization axis ordered vertical to the film plane. We have confirmed that the films show a strong visible-light-response and ferroelectricity in accord with bulk samples. These results will stimulate the development of photovoltaics employing narrow bandgap ferroelectric compounds. [ABSTRACT FROM AUTHOR]

Investigates the influence of the 180-degree domains of the ferroelectric properties of barium titanium trioxide single crystal. Removal of the domain walls of the single crystal; Measurement of the dielectric constant; Variation of the dielectric spectra with the rearrangement of the domain configuration.

In this paper, we report the basic design conditions and the experimental confirmation of a temperature dependent negative capacitance (NC) effect in a ferroelectric field-effect-transistor (Fe-FET). We find that the internal voltage amplification peaks of a metal-ferroelectric-metal-insulator-semiconductor (MFMIS) structure are correlated with the S-shape of the polarization versus electrical field characteristics. The internal voltage amplification is responsible for the subthreshold swing reduction in a Fe-FET; this effect cancels out when the temperature is increased close to the Curie temperature because of the narrowing of the NC region and because of the saturation of the amplification. A counter-clockwise rotation of the P-V loops with an associated increase of the dP/dV slope with the temperature is reported, which corresponds to an increase of the overall ferroelectric capacitance with the temperature. Finally, we theoretically and experimentally demonstrate that an optimum temperature exists at which the amplification gets its maximum. [ABSTRACT FROM AUTHOR]

Relaxor-based ferroelectric crystals of lead magnesium niobate-lead titanate (PMN-PT) are attracting great attention due to their prominent piezoelectric properties. Moreover, an enhancement of the integral properties requires the deep understanding of domain kinetics and domain structure evolution for application of the domain engineering techniques in relaxor-PT materials. Here, we demonstrate the results of studying the domain structure evolution by direct optical imaging during polarization reversal in [111]-oriented rhombohedral PMN-PT single crystals. Three domain types involved in the switching process have been revealed. The following consequent stages of the domain structure evolution have been separated: (I) nucleation and growth of a↑-domains and 2a-CDW and (II) nucleation and growth of c↓-domains. The undesirable effect of the partial backswitching during the electric field decrease was attributed to the clamped switching conditions. [ABSTRACT FROM AUTHOR]

The nonlinear electric susceptibility of a glass ceramic is characterized in the microwave range by measuring intermodulation of two high-power signals. To achieve the necessary sensitivity for dielectric nonlinearities, the setup ensures that the measured intermodulation can be ascribed to the material under test while all other intermodulation sources are suppressed. This is achieved by coupling three dielectric resonators in a cut-off waveguide. The third order nonlinearity of the glass ceramic is found to be χ3/εr = (1.6 ± 0.8) × 10−15 m2/V2 at 950 MHz. The magnitude is comparable to the previously measured high-end sintered ceramics. The power of the intermodulation signal as a function of the input power deviates from the simple 3 dB/dB scaling and can be modeled by linear-nonlinear interaction. [ABSTRACT FROM AUTHOR]

Recently, we have analyzed the complex infrared (IR) and terahertz (THz) response of the relaxor ferroelectric Pb(Mg1/3Nb2/3)O3 (PMN) and suggested a new interpretation of the so-called intermediate temperature T* ≈ 400 K, where the split soft phonon mode undergoes incomplete softening. IR-THz reflectivity was fitted using effective medium approximation, which describes the uniaxially anisotropic response of polar nanodomains (PNDs). It indicated that the response perpendicular to the local polarization undergoes a classical Cochran softening toward T* with the extrapolated low-frequency permittivity obeying the Curie-Weiss (CW) law with TC ≈ T*. In this letter, we report analysis performed in a similar way on the published IR-THz response in closely related relaxor Pb(Mg1/3Ta2/3)O3 and have revealed a similar behavior: The lowest-frequency phonon polarized perpendicularly to the local polarization of PNDs softens below ∼900 K according to the Cochran law and the corresponding low-frequency permittivity obeys the CW law with TC = 340 K ≈ T* and Curie constant C = 1.16 × 105 K. This is comparable to similar parameters for PMN, TC = 380 K ≈ T* and C = 1.7 × 105 K. This explains the high-temperature CW anomaly in the low-frequency dielectric response of both materials and strongly suggests that both relaxors undergo a local ferroelectric phase transition near T* which induces a new polarization component perpendicular to the local random electric field. [ABSTRACT FROM AUTHOR]

We report the effect of the epitaxial strain and deliberate incorporation of anionic/cationic defects on the ferroelectric-like response of CaTiO3 thin films. The role of the defect concentration and TiO6 octahedral rotation in the suppression or promotion of a ferroelectric phase is discussed. We demonstrate that a local electric field and/or mechanical force induce the local accumulation/depletion of oxygen vacancies, which change the surface potential and local volume similar to ferroelectric polarization. Our results demonstrate that reversible bi-stable states can be produced in CaTiO3 by electrical or mechanical means, opening interesting possibilities for ionic-based devices. [ABSTRACT FROM AUTHOR]

Three-dimensional laser Doppler vibrometry is used to quantify the modal composition of the guided plate waves generated by relaxor ferroelectric disk actuators of a ⟨011⟩ poled Mn-Pb(Mg1/3Nb2/3)O-lead zirconate titanate (PZT) single crystal and ⟨100⟩ poled piezoelectric PZT, bonded to an isotropic plate. Disk actuators are excited using a 5.5 cycle Hann-windowed voltage tone-burst at centre frequencies of 100, 200, and 300 kHz. Measured wave fields are processed using a two-dimensional fast Fourier transform to determine the radiation pattern of each contributing mode. For the same applied electric field strength, the single crystal actuators are shown to produce significantly larger wave amplitudes and one additional wave mode, the shear horizontal, as compared with PZT actuators. The wave-mode radiation patterns are shown to be anisotropic, suggesting that the classical theory describing guided-wave modal excitability may need to be revised for these materials. [ABSTRACT FROM AUTHOR]

Topological Hall effect (THE) as one of spin-related effects originates from scalar spin chirality formed by non-coplanar spin structures, being a promising tool for probing the change of electron spin. Single-phase (022) Mn4N films with coplanar spin structures were prepared on unpoled ferroelectric [Pb(Mg1/3Nb2/3)O3]0.67-[PbTiO3]0.33 (PMN-PT) substrates. The transport properties of Mn4N/PMN-PT have been investigated. The decreased magnetization and anomalous resistivity imply that the spin states of Mn4N are influenced by ferroelectric polarization of the substrate. The observation of THE in the Mn4N/PMN-PT heterostructure strongly supports that the spin states of Mn4N are modified. After poling PMN-PT, the enhanced THE peak magnitude verifies that the spin states of Mn4N are tuned by ferroelectric polarization. This study provides a non-magnetic method for manipulation of spin states, which could avoid the external magnetic field perturbations. [ABSTRACT FROM AUTHOR]

The pulsed power supply that generates megawatts of electrical power has drawn important attention for many decades. Despite that the large energy output has been obtained in lead-containing materials such as Pb(Zr0.95Ti0.05)O3 (PZT95/5) ceramics, lead-free ferroelectric candidates are highly desired due to the environmental concerns. In this work, we report the depolarization behavior of lead-free ternary 0.99[0.98(Bi0.5Na0.5)(Ti0.995Mn0.005)O3-0.02BiAlO3]-0.01NaNbO3 ferroelectric ceramics under shock wave compression. A current profile with a maximum value of ∼25 A and a FWHM of ∼2.3 μs was obtained. Particularly, the poled BNT-BA-0.01NN ceramics were almost completely depolarized under high strain rate loading, releasing a high charge density J of 38 μC/cm2. The released J was approximately 96% of thermal-induced charge density (∼40 μC/cm2), which was 18% higher than that of PZT95/5 ceramics. The shock-induced depolarization mechanism can be attributed to the ferroelectric-ergodic relaxor phase transition. These results reveal the BNT-based ceramics as promising candidates for pulsed power applications. [ABSTRACT FROM AUTHOR]

The observation of room temperature sub-60 mV/dec subthreshold slope (SS) in MOSFETs with ferroelectric (FE) layers in the gate stacks or in series with the gate has attracted much attention. Recently, we modeled this effect in the framework of a FE polarization switching model. However, there is a large amount of literature attributing this effect to a stabilization of quasi-static (QS) negative capacitance (NC) in the FE. The technological implications of a stabilized non-switching QSNC model vs a FE switching model are vastly different; the latter precluding applications to sub-60 mV/dec SS scaled CMOS due to speed limitations and power dissipated in switching. In this letter, we provide a thorough analysis assessing the foundations of models of QSNC, identifying which specific assumptions (ansatz) may be unlikely or unphysical, and analyzing their applicability. We show that it is not reasonable to expect QSNC for two separate capacitors connected in series [with a metal plate between dielectric (DE) and FE layers]. We propose a model clarifying under which conditions a QS “apparent NC” for a FE layer in a FE-DE bi-layer stack may be observed, quantifying the requirements of strong interface polarization coupling in addition to capacitance matching. In this regime, our model suggests the FE layer does not behave as a NC layer, simply, the coupling leads to both the DE and FE behaving as high-k DE with similar permittivities. This may be useful for scaled equivalent oxide thickness devices, but does not lead to sub-60 mV/dec SS. [ABSTRACT FROM AUTHOR]

TiO2- δ thin films were epitaxially grown on (001)-oriented 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-PT) ferroelectric single-crystal substrates. By applying electric fields E across the PMN-PT, the TiO2- δ film resistance could be reversibly switched into different stable states at room temperature. The on-off ratio, tuned by the strength of the electric field E, remained at ~1 under the E ≤ 0.6 kV/cm and reached ~3413 with the E increasing to 6 kV/cm, leading to a promising approach for designing nonvolatile multiple-state memory devices. By taking into account the migration of the oxygen vacancies and the ferroelectric ?eld effect induced charge manipulations, the mechanism of the multiple-state resistive switching behaviors was discussed. [ABSTRACT FROM AUTHOR]

High quality ultrathin two-dimensional zinc oxide (ZnO) nanosheets (NSs) are synthesized, and the ZnO NS ferroelectric field effect transistors (FeFETs) are demonstrated based on the P(VDF-TrFE) polymer film used as the top gate insulating layer. The ZnO NSs exhibit a maximum field effect mobility of 588.9 cm2/Vs and a large transconductance of 2.5 lS due to their high crystalline quality and ultrathin two-dimensional structure. The polarization property of the P(VDF-TrFE) film is studied, and a remnant polarization of >100 lC/cm2 is achieved with a P(VDF-TrFE) thickness of 300 nm. Because of the ultrahigh remnant polarization field generated in the P(VDF-TrFE) film, the FeFETs show a large memory window of 16.9V and a high source-drain on/off current ratio of more than 107 at zero gate voltage and a source-drain bias of 0.1 V. Furthermore, a retention time of >3000 s of the polarization state is obtained, inspiring a promising candidate for applications in data storage with non-volatile features. [ABSTRACT FROM AUTHOR]

Domain shape evolution and domain wall motion have been studied in KTiOPO4 (KTP) ferroelectric single crystals using complementary experimental methods. The in situ visualization of domain kinetics has allowed revealing: (1) qualitative change of the domain shape, (2) dependence of the domain wall velocity on its orientation, (3) jump-like domain wall motion caused by domain merging, (4) effect of domain shape stability. The model of domain wall motion driven by generation of elementary steps (kink-pair nucleation) and subsequent kink motion is presented. The decrease in the relative velocity of the approaching parallel domain walls is attributed to electrostatic interaction. The effect of polarization reversal induced by chemical etching is observed. The obtained results are important for the development of domain engineering in the crystals of KTP family. [ABSTRACT FROM AUTHOR]

All scanning probe microscopies are subjected to topographic cross-talk, meaning the topographyrelated contrast in functional images. Here, we investigate the signatures of indirect topographic cross-talk in piezoresponse force microscopy (PFM) imaging and spectroscopy and its decoupling using band excitation (BE) method in ferroelectric BaTiO3 deposited on the Si substrates with free standing nanopillars of diameter 50 nm. Comparison between the single-frequency PFM and BEPFM results shows that the measured signal can be significantly distorted by topography-induced shifts in the contact resonance frequency and cantilever transfer function. However, with proper correction, such shifts do not affect PFM imaging and hysteresis loop measurements. This suggests the necessity of an advanced approach, such as BE-PFM, for detection of intrinsic sample piezoresponse on the topographically non-uniform surfaces. [ABSTRACT FROM AUTHOR]

We demonstrate infrared femtosecond laser-induced inversion of ferroelectric domains. This process can be realised solely by using tightly focused laser pulses without application of any electric field prior to, in conjunction with, or subsequent to the laser irradiation. As most ferroelectric crystals like LiNbO3, LiTaO3, and KTiOPO4 are transparent in the infrared, this optical poling method allows one to form ferroelectric domain patterns much deeper inside a ferroelectric crystal than by using ultraviolet light and hence can be used to fabricate practical devices. We also propose in situ diagnostics of the ferroelectric domain inversion process by monitoring the Čerenkov second harmonic signal, which is sensitive to the appearance of ferroelectric domain walls. [ABSTRACT FROM AUTHOR]

Landau field effect transistors promise to lower the power-dissipation of integrated circuits (ICs) by reducing the subthreshold swing (S) below the Boltzmann limit of 60mV/dec. The key idea is to replace the classical gate insulator with dielectrics that exhibit negative capacitance (NC) associated with double-well energy landscape, for example, ferroelectrics (FE), air-gap capacitors, or a combination thereof. Indeed, S is dramatically reduced, constrained only by the limits of hysteresis-free operation. Unfortunately, the following limitations apply (i) the need for capacitance matching constrains steep S only to the small subthreshold region for FE based negative capacitance field effect transistor (NCFET) and requires an insulator too thick for sub-20nm scaling; (ii) the kinetics of mechanical switching for airgap based NCFET obviate high-speed operation; and (iii) the lattice mismatch between the substrate and the dielectric makes defect-free integration difficult. In this article, we demonstrate that a FET integrated with 10 nm HfO2-based anti-ferroelectric and FE hetero stack would achieve ultralow S with ON-current (Ion) at par with classical transistors at significantly lower voltage and would simplify integration. Our results address the well-known challenges/criticisms of classical Landau transistors, thereby, making them technology relevant for modern ICs. [ABSTRACT FROM AUTHOR]

We present a strong electric-field-induced light scattering phenomenon in relaxor ferroelectrics 75Pb(Mg1/3Nb2/3)-25PbTiO3 transparent ceramics under a weak threshold electric field, which is attributed to the abrupt growth of polar nanoregions above the threshold field with a significant change of local crystal symmetry, dielectric, and Raman response. These results provide further understanding on the electric field-induced domain behaviors and peculiar properties in relaxor ferroelectrics. [ABSTRACT FROM AUTHOR]

Using the advanced spherical aberration-corrected high angle annular dark field scanning transmission electron microscope imaging techniques, we investigated atomic-scale structural features of domain walls and domain patterns in YMnO3 single crystal. Three different types of interlocked ferroelectric-antiphase domain walls and two abnormal topological four-state vortex-like domain patterns are identified. Each ferroelectric domain wall is accompanied by a translation vector, i.e., 1/6[210] or -1/6[210], demonstrating its interlocked nature. Different from the four-state vortex domain patterns caused by a partial edge dislocation, two four-state vortex-like domain configurations have been obtained at atomic level. These observed phenomena can further extend our understanding of the fascinating vortex domain patterns in multiferroic hexagonal rare-earth manganites. [ABSTRACT FROM AUTHOR]

Dielectric barrier discharges (DBD) are commonly used to generate surface plasmas in atmospheric conditions due to their broad operational scope. Yet, high input voltages are typically required to breakdown atmospheric air. Ferroelectric crystals, however, can be used in place of dielectrics in order to reduce the driving voltage required to generate a DBD. Ferroelectrics are unique in that they have spontaneous polarizations that can be reversed by an applied electric field and also typically have very large relative permittivities. By using a ferroelectric with a large permittivity and small coercive fields, the applied voltage required to generate a discharge was reduced to <600 V in atmospheric air, and a visible glow and current filaments consistent with polarization switching were observed. Analysis of the discharge showed that the onset voltage follows a power law relation with its capacitance. Furthermore, poling the ferroelectric with a large DC voltage before use also reduced the onset voltage of the discharge. [ABSTRACT FROM AUTHOR]

It is thought that the proposed new family of multi-functional materials, namely, the ferroelectric thermoelectrics may exhibit enhanced functionalities due to the coupling of the thermoelectric parameters with ferroelectric polarization in solids. Therefore, the ferroelectric thermoelectrics are expected to be of immense technological and fundamental significance. As a first step towards this direction, it is most important to identify the existing high performance thermoelectric materials exhibiting ferroelectricity. Herein, through the direct measurement of local polarization switching, we show that the recently discovered thermoelectric semiconductor AgSbSe2 has local ferroelectric ordering. Using piezo-response force microscopy, we demonstrate the existence of nanometer scale ferroelectric domains that can be switched by external electric field. These observations are intriguing as AgSbSe2 crystalizes in cubic rock-salt structure with centro-symmetric space group (Fm–3m), and therefore, no ferroelectricity is expected. However, from high resolution transmission electron microscopy measurement, we found the evidence of local superstructure formation which, we believe, leads to local distortion of the centro-symmetric arrangement in AgSbSe2 and gives rise to the observed ferroelectricity. Stereochemically active 5S2 lone-pair of Sb may also give rise to local structural distortion thereby creating ferroelectricity in AgSbSe2. [ABSTRACT FROM AUTHOR]

Scattering scanning near-field optical microscopy (s-SNOM) has been established as an excellent tool to probe domains in ferroelectric crystals at room temperature. Here, we apply the s-SNOM possibilities to quantify low-temperature phase transitions in barium titanate single crystals by both temperature-dependent resonance spectroscopy and domain distribution imaging. The orthorhombic- to-tetragonal structural phase transition at 263K manifests in a change of the spatial arrangement of ferroelectric domains as probed with a tunable free-electron laser. More intriguingly, the domain distribution unravels non-favored domain configurations upon sample recovery to room temperature as explainable by increased sample disorder. Ferroelectric domains and topographic influences are clearly deconvolved even at low temperatures, since complementing our s- SNOM nano-spectroscopy with piezoresponse force microscopy and topographic imaging using one and the same atomic force microscope and tip [ABSTRACT FROM AUTHOR]

We observe periodic faceting of 8-nm diameter ferroelectric disks on a 10 s time-scale when thin Pb(Zr0.52Ti0.48)O3 film is exposed to constant high-resolution transmission electron microscopy beams. The oscillation is between circular disk geometry and sharply faceted hexagons. The behavior is analogous to that of spin structure and magnetic domain wall velocity oscillations in permalloy [Bisig et al., Nat. Commun. 4, 2328 (2013)], involving overshoot and de-pinning from defects [Amann et al., J. Rheol. 57, 149-175 (2013)]. [ABSTRACT FROM AUTHOR]

The switchable photovoltaic effect in BiFeO3 thin films capacitors has been studied extensively. However, the origin of the photovoltaic response is still under debate. Both bulk depolarization field and interface effects have been used to explain the observations. In this work, we fabricate BiFeO3 epitaxial films on SrTiO3 substrate with La0.7Sr0.3MnO3 and Pt as electrodes. Much larger switchable photovoltaic response can be observed in the Pt/BiFeO3/La0.7Sr0.3MnO3 samples, as compared with La0.7Sr0.3MnO3/BiFeO3/La0.7Sr0.3MnO3. Moreover, the photovoltaic voltage of the Pt/BiFeO3/La0.7Sr0.3MnO3 samples is nearly independent of the thickness of the La0.7Sr0.3MnO3 bottom electrode. We suggest that the Schottky barrier modulation by ferroelectric polarization at the Pt/BiFeO3 interface is mainly responsible for the photovoltaic effect, with very small contribution from the bulk depolarization field. [ABSTRACT FROM AUTHOR]

In the last several decades, ferroelectrics have attracted much attention as perspective materials for nonlinear optics and data storage devices. Scanning probe microscopy (SPM) has emerged as a powerful tool both for studies of domain structures with nanoscale spatial resolution and for writing the isolated nanodomains by local application of the electric field. Quantitative analysis of the observed behavior requires understanding the role of environmental factors on imaging and switching process. Here, we study the influence of the relative humidity in the SPM chamber on tipinduced polarization switching. The observed effects are attributed to existence of a water meniscus between the tip and the sample surface in humid atmosphere. These results are important for a deeper understanding of complex investigations of ferroelectric materials and their applications and suggest the necessity for fundamental studies of electrocapillary phenomena at the tip-surface junction and their interplay with bias-induced materials responses. [ABSTRACT FROM AUTHOR]

To elucidate the origin of the formation of the ferroelectric phase in Hf0.5Zr0.5O2 films, the effects of film strain and crystallographic orientation on the properties were examined. Using a (111)-textured Pt bottom electrode, Hf0.5Zr0.5O2 films with a (111)-preferred texture inappropriate for transforming their phase from non-ferroelectric tetragonal to ferroelectric orthorhombic phase were deposited. In contrast, randomly oriented Hf0.5Zr0.5O2 films, grown on the TiN electrode, showed feasible ferroelectric properties due to their transformation to the ferroelectric orthorhombic phase. The origin of such transformation is the large in-plane tensile strain for the elongation of the c-axis of the tetragonal phase. [ABSTRACT FROM AUTHOR]

The ferroelectric and tunnel electro- and magnetoresistance properties in La0.6Sr0.4MnO3/ BiFeO3/La0.6Sr0.4MnO3 multiferroic tunnel junctions sandwiched with the antiferromagneticferroelectric BiFeO3 as a tunnel barrier were reported. Besides the four non-volatile resistance states and the interfacial magnetoelectric coupling effect with the tunnel magnetoresistance manipulated by ferroelectric polarizations, one of the most important results is that the exchange bias effect on the tunnel magnetoresistance is observed in this junction due to the magnetic interaction between antiferromagnetic BiFeO3 and ferromagnetic La0.6Sr0.4MnO3 layers. These finds may be helpful for designing exchange bias based multiferroic tunnel junction in next generation random access memory devices [ABSTRACT FROM AUTHOR]

Diffuse scattering and relaxor behavior in Na0.5Bi0.5TiO3 (NBT) and NBT-5.6 at. %BaTiO3 (NBT-5.6%BT) were investigated. X-ray diffraction revealed two types of diffuse scattering in NBT: (i) broad and (ii) asymmetric L-shaped. After modification with 5.6%BT, the broad diffuse scattering patterns became narrow, and the asymmetric L-shaped ones were replaced by symmetric ones. The symmetric diffuse scattering in NBT-5.6%BT disappeared with increasing dc electric field (E) for E ≥ 9.5 kV/cm where the frequency dispersion in the dielectric constant disappeared. These results demonstrate that the relaxor characteristics are directly correlated with the diffuse scattering and the presence polar nano-regions. [ABSTRACT FROM AUTHOR]

Double-loop-like characteristic was detected in acceptor Aurivillius ceramic, (Na,Bi)0.47(Li,Ce)0.03Bi2Ta1.97Sc0.03O8.97 (NBTO-LiCeSc-0.03) due to the restoring force provided by defect polarization (PD). The PD was associated with non-centric distributing defect dipoles [(ScTa″-VO••)×], which was verified by impedance spectroscopy measures. Interestingly, the PD could be reoriented with high external electric field at very low frequency, which contributed to the significant enhancement of the polarization of NBTO-LiCeSc-0.03. Air or O2 annealing led to the degradation of the polarization owing to high leakage current and the strong 'pinning' effects of space charge and charged defect complexes [e.g., (ScTa″-OO•)′]. [ABSTRACT FROM AUTHOR]