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Results of switching behavior of the improper ferroelectric LuFeO3 are presented. Using a model set of films prepared under controlled chemical and growth-rate conditions, it is shown that defects can reduce the quasi-static switching voltage by up to 40% in qualitative agreement with first-principles calculations. Switching studies show that the coercive field has a stronger frequency dispersion for the improper ferroelectrics compared to a proper ferroelectric such as PbTiO3 . It is concluded that the primary structural order parameter controls the switching dynamics of such improper ferroelectrics.

Photocatalytic water splitting is a direct and potential approach to generate hydrogen (H2), but it is very difficult to find the ideal semiconducting materials with maximum photocatalytic water splitting efficiency. Herein, we synthesized 2D/2D heterojunction of NiAl-LDH/gC3N4 nanocomposite by in situ hydrothermal method and demonstrated their photocatalytic performance for H2 evolution from water splitting under simulated light irradiation. The optimized NiAl-LDH/gC3N4 nanocomposites showed the H2 evolution rate of 3170 µmol h−1 g−1, the highest value so far reported for NiAl-LDH family. The enhanced photocatalytic efficiency is attributed to the formation of 2D/2D heterojunction in NiAL-LDH/gC3N4 nanocomposite, leading to excellent electron-hole separation under light illumination, which increases the electron conductivity in the composite. Present work provides the new insights for the design of layered double hydroxides based 2D/2D heterojunction as a high-performance photocatalyst for H2 evolution from water splitting.

In this paper, we report the synthesis of spinel CuCo2S4 nanoparticles (NPs) via a one-step hydrothermal method using two kinds of sulfur precursor's thioacetamide-TAA and thiourea-TU separately. The X-ray powder diffraction (XRD) analysis of both samples revealed a cubic phase of spinel CuCo2S4 crystal structure with Fd3m space group. The spherical (19–20 nm) and hexagonal (17–19 nm) shaped NPs were observed by transmission electron microscope (TEM) images. N2 adsorption-desorption results showed the high surface area of TAA-CuCo2S4 (91.03 m2 g-1) than TU-CuCo2S4 (59.82 m2 g-1). XPS spectra exhibited the coexistence of Cu2+ and Cu3+ valence states of spinel cubic CuCo2S4. Electrochemical measurements showed that the TAA based CuCo2S4/Ni foam electrode has high specific capacity (1885 C g−1/523 mA h g−1 at a current density of 2 A g-1 about 5.4 times higher than thiourea based electrodes), ultrahigh capacity retention of 98% after 6000 GCD cycles at high current density of 10 A g-1 and excellent energy density of 41.89 provided with a power density of 318.31 W kg−1. These results suggest that TAA assisted electrode material is suitable for improving electrochemical performance of supercapacitors.

In this present work, a novel heterostructure rGO - SrSnO3 nanocomposites with different weight percentage of reduced graphene oxide were successfully synthesised by hydrothermal method. The formation of crystalline structure, morphology, elemental composition and optical properties were characterized using Powder X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR), Energy dispersive X-ray analysis (EDX), and UV–vis diffuse reflectance spectroscopy (UV DRS) and photoluminescence (PL) spectroscopy techniques. The photocatalytic activity of pure and composite materials was assessed by degradation of aqueous methylene blue dye under UV light irradiation. The highest degradation efficiency of 97 % was obtained for 10 wt.% rGO - SrSnO3 composite. Enhancement in the photocatalytic activity is mainly due to the suppressed photoexcited charge carrier’s recombination rate. Moreover, the reusable and stability of the photocatalyst demonstrated after four consecutive runs of photocatalytic test.

In the present work, photocatalytic activity of cobalt doped bismuth tungstate nanostructures are reported for the first time. Hydrothermal method was adopted for the synthesis of pristine and Co2+ doped Bi2WO6 nanostructures. The synthesized nanostructures were characterized by X-ray diffraction (XRD), Field emission scanning and transmission electron microscopies (FESEM and TEM), ultraviolet–visible diffuse reflectance spectroscopy (UV-DRS) and Fourier-transform infrared spectroscopy (FTIR). XRD pattern reveals the crystal structure to be orthorombic. The incorporation of dopant leads to the destruction of surface morphology of Bi2WO6 nanostructures. From the DRS spectra it is clear that the dopant has shifted the absorbance of nanostructures to lower wavelength. The synthesized nanostructures exhibit excellent photocatalytic activity against the photodegradation of rhodamine B (RhB) under visible light irradiation. Bi2WO6 with 0.15 and 0.20 mol % cobalt possess better photocatalytic activity among the synthesized nanostructures.

Multiferroic BiFeO3 (BFO) shows several phonon modes at infrared (IR) to THz energies, which are expected to carry information on any sample property coupled to crystal lattice vibrations. While macroscopic IR studies of BFO are often limited by single-crystal size, scattering-type scanning near-field optical microscopy (s-SNOM) allows for IR thin film spectroscopy of nanoscopic probing volumes with negligible direct substrate contribution to the optical signal. In fact, polaritons such as phonon polaritons of BFO introduce a resonant tip–sample coupling in s-SNOM, leading to both stronger signals and enhanced sensitivity to local material properties. Here, we explore the near-field response of BFO thin films at three consecutive resonances (centered around 5 THz, 13 THz, and 16 THz), by combining s-SNOM with a free-electron laser. We study the dependence of these near-field resonances on both the wavelength and tip–sample distance. Enabled by the broad spectral range of the measurement, we probe phonon modes connected to the predominant motion of either the bismuth or oxygen ions. Therefore, we propose s-SNOM at multiple near-field resonances as a versatile and very sensitive tool for the simultaneous investigation of various sample properties.

Zinc oxide (ZnO) nanoparticles are emerged as a leading phtocatlyst for organic dye degradation owing to its non-toxicity, low cost and high photochemical reactivity. In the present work, ZnO nanoparticles with different particle size were prepared via hydrothermal assisted phytofabrication method using Aerva lanata and Aerva javanica flower extracts as the reducing agent. The synthesized ZnO nanoparticles were analyzed using different analytical techniques which evidently revealed that phase purity, structural properties, band gap and particle size of the ZnO nanoparticles were considerably influenced by the type of flower extract used as reducing agent under hydrothermal circumstance. The photocatalytic degradation of Rhodamine B was examined in the presence of prepared ZnO nanoparticles under visible light irradiation. Photocatlytic study clearly indicate that ZnO nanoparticles prepared using Aerva lanata flower extract exhibits superior photocatlytic degradation of Rhodamine B dye than ZnO prepared using Aerva javanica flower extract due to its inherent properties. Hence, the synthesized ZnO nanoparticles using hydrothermal assisted phytofabrication can be used as a potential photocatlyst for the removal of Rhodamine B dye from the textile waste water by photocatalytic degradation.

In this work, djembe like ZnO microstructures was successfully synthesized by surfactant-assisted hydrothermal method and its composite with g-C3N4 was prepared by an ethanolic reflux method for the first time. Moreover, the structural, morphological, electrical, optical properties and its photocatalytic activities were studied. The result revealed that the formation heterojunction between djembe like ZnO and g-C3N4, decreased the optical band gap energy thereby the light absorption was shifted towards visible region. The photocatalytic performance was studied by dye degradation experiment under visible light irradiation. The degradation efficiency of the ZnO/g-C3N4 composite for MB and RhB degradation was found to be ~95% and ~97% respectively, which is higher than that of the same for pure ZnO and g-C3N4. The scavenger studies indicated the active role of hydroxyl radicals in the degradation process. Furthermore, djembe like ZnO/g-C3N4 composite was successfully reused for five cycles of photodegradation without any drastic change in its activity and crystalline properties.

Author(s): Lupi, E; Ghosh, A; Saremi, S; Hsu, SL; Pandya, S; Velarde, G; Fernandez, A; Ramesh, R; Martin, LW | Abstract: The ability to produce atomically precise, artificial oxide heterostructures allows for the possibility of producing exotic phases and enhanced susceptibilities not found in parent materials. Typical ferroelectric materials either exhibit large saturation polarization away from a phase boundary or large dielectric susceptibility near a phase boundary. Both large ferroelectric polarization and dielectric permittivity are attained wherein fully epitaxial (PbZr0.8Ti0.2O3)n/(PbZr0.4Ti0.6O3)2n (n = 2, 4, 6, 8, 16 unit cells) superlattices are produced such that the overall film chemistry is at the morphotropic phase boundary, but constitutive layers are not. Long- (n ≥ 6) and short-period (n = 2) superlattices reveal large ferroelectric saturation polarization (Ps = 64 µC cm−2) and small dielectric permittivity (er ≈ 400 at 10 kHz). Intermediate-period (n = 4) superlattices, however, exhibit both large ferroelectric saturation polarization (Ps = 64 µC cm−2) and dielectric permittivity (er = 776 at 10 kHz). First-order reversal curve analysis reveals the presence of switching distributions for each parent layer and a third, interfacial layer wherein superlattice periodicity modulates the volume fraction of each switching distribution and thus the overall material response. This reveals that deterministic creation of artificial superlattices is an effective pathway for designing materials with enhanced responses to applied bias.

Nanoelectronic devices based on ferroelectric domain walls (DWs), such as memories, transistors, and rectifiers, have been demonstrated in recent years. Practical high-speed electronics, on the other hand, usually demand operation frequencies in the gigahertz (GHz) regime, where the effect of dipolar oscillation is important. Herein, an unexpected giant GHz conductivity on the order of 103 S m-1 is observed in certain BiFeO3 DWs, which is about 100 000 times greater than the carrier-induced direct current (dc) conductivity of the same walls. Surprisingly, the nominal configuration of the DWs precludes the alternating current (ac) conduction under an excitation electric field perpendicular to the surface. Theoretical analysis shows that the inclined DWs are stressed asymmetrically near the film surface, whereas the vertical walls in a control sample are not. The resultant imbalanced polarization profile can then couple to the out-of-plane microwave fields and induce power dissipation, which is confirmed by the phase-field modeling. Since the contributions from mobile-carrier conduction and bound-charge oscillation to the ac conductivity are equivalent in a microwave circuit, the research on local structural dynamics may open a new avenue to implement DW nano-devices for radio-frequency applications.

Polar crystals composed of charged ionic planes cannot exist in nature without acquiring surface changes to balance an ever-growing dipole. The necessary changes can manifest structurally or electronically as observed in semiconductors and ferroelectric materials through screening charges and/or domain wall formation. In the case of prototypical polar complex oxides such as the LaAlO3/SrTiO3 system the nature of screening charges for different interface terminations is not symmetric. Electron accumulation is observed near the LaAlO3/TiO2-SrTiO3 interface, while the LaAlO3/SrO-SrTiO3 stack is insulating. Here, we observe evidence for an asymmetry in the surface chemical termination for nominally stoichiometric LaAlO3 films in contact with the two different surface layers of SrTiO3 crystals, TiO2 and SrO. Using several element-specific probes, we find that the surface termination of LaAlO3 remains AlO2 irrespective of the starting termination of SrTiO3 substrate surface. We use a combination of cross-plane tunneling measurements and first-principles calculations to understand the effects of this unexpected termination on band alignments and polarity compensation of LaAlO3/SrTiO3 heterostructures. An asymmetry in LaAlO3 polarity compensation and resulting electronic properties will fundamentally limit atomic level control of oxide heterostructures.

Magnetoelectricity enables a new class of nonvolatile, ultralow-energy computing with quantum materials for AI & Moore’s law., Demonstration of ultralow energy switching mechanisms is imperative for continued improvements in computing devices. Ferroelectric (FE) and multiferroic (MF) order and their manipulation promise an ideal combination of state variables to reach attojoule range for logic and memory (i.e., ~30× lower switching energy than nanoelectronics). In BiFeO3 (BFO), the coupling between the antiferromagnetic (AFM) and FE order is robust at room temperature, scalable in voltage, stabilized by the FE order, and can be integrated into a fabrication process for a beyond-CMOS (complementary metal-oxide semiconductor) era. The presence of the AFM order and a canted magnetic moment in this system causes exchange interaction with a ferromagnet such as Co0.9Fe0.1 or La0.7Sr0.3MnO3. Previous research has shown that exchange coupling (uniaxial anisotropy) can be controlled with an electric field. However, voltage modulation of unidirectional anisotropy, which is preferred for logic and memory technologies, has not yet been demonstrated. Here, we present evidence for electric field control of exchange bias of laterally scaled spin valves that is exchange coupled to BFO at room temperature. We show that the exchange bias in this bilayer is robust, electrically controlled, and reversible. We anticipate that magnetoelectricity at these scaled dimensions provides a powerful pathway for computing beyond modern nanoelectronics by enabling a new class of nonvolatile, ultralow energy computing elements.

The ability to synthesize high-quality, complex-oxide heterostructures has created a veritable playground in which to explore emergent phenomena and exotic phases which arise from the interplay of spin, charge, orbital, and lattice degrees of freedom. Of particular interest is the creation of artificial heterostructures and superlattices built from two or more materials. Through such approaches, it is possible to observe new phases and phenomena that are not present in the parent materials alone. This is especially true in ferroelectric materials where the appropriate choice of superlattice constituents can lead to structures with complex phase diagrams and rich physics. In this article, we review and explore future directions in such ferroic superlattices wherein recent studies have revealed complex emergent polarization topologies, novel states of matter, and intriguing properties that arise from our ability to manipulate materials with epitaxial strain, interfacial coupling and interactions, size effects, and more. We focus our attention on recent work in (PbTiO3)n/(SrTiO3)n superlattices wherein exotic polar-vortex structures have been observed. We review the history of these observations and highlights of recent studies and conclude with an overview and prospectus of how the field may evolve in the coming years.

Electric field control of magnetism ultimately opens up the possibility of reducing energy consumption of memory and logic devices. Electric control of magnetization and exchange bias are demonstrated in all-oxide heterostructures of BiFeO

Electric-field control of magnetism requires deterministic control of the magnetic order and understanding of the magnetoelectric coupling in multiferroics like BiFeO3 and EuTiO3. Despite this critical need, there are few studies on the strain evolution of magnetic order in BiFeO3 films. Here, in (110)-oriented BiFeO3 films, we reveal that while the polarization structure remains relatively unaffected, strain can continuously tune the orientation of the antiferromagnetic-spin axis across a wide angular space, resulting in an unexpected deviation of the classical perpendicular relationship between the antiferromagnetic axis and the polarization. Calculations suggest that this evolution arises from a competition between the Dzyaloshinskii–Moriya interaction and single-ion anisotropy wherein the former dominates at small strains and the two are comparable at large strains. Finally, strong coupling between the BiFeO3 and the ferromagnet Co0.9Fe0.1 exists such that the magnetic anisotropy of the ferromagnet can be effectively controlled by engineering the orientation of the antiferromagnetic-spin axis.

Defects in solids can be broadly classified based on their dimensionality (1). Zero-dimensional defects (point defects) arise as a consequence of entropy considerations (configurational entropy) and thus are thermodynamically required in any material. One-dimensional defects such as dislocations are not required by thermodynamics but arise anyway as a consequence of imperfections in the synthetic environment or due to structural constraints imposed by applied stresses from a variety of sources. Dislocations arise as a consequence of stresses imposed through thermal history, processing, or structural mismatch, as in the case of heteroepitaxial thin films, which are so prevalent in modern technology. Extended defects are known to have a profound influence in achieving or impacting the desired material performance. Complex networks of dislocations are designed into alloys to enhance their mechanical properties, such as the tensile strength in steels and other technologically relevant alloys (2). In many cases, defects, such as dislocations, are harmful to the desired performance of the device (3). Volumetric defects (such as second-phase inclusions, some of which are deliberately designed into materials such as the Guinier–Preston zones in Al–Cu alloys) (4, 5) can arise as a consequence of improper processing or through deliberate materials engineering. The characteristic length scale of such defects will depend on the physical phenomenon in question (e.g., pinning of the movement of dislocations would require second phases that are of a certain size and spacing). We now come to 2D, surface-type defects, the designing of which is the focus of the paper by Wang et al. (6). Two-dimensional defects, such as antiphase boundaries (APBs) and domain walls in certain ferroic materials, arise primarily as a consequence of symmetry mismatch in spatial coordinates, … [↵][1]1Email: rramesh{at}berkeley.edu. [1]: #xref-corresp-1-1

The ultrafast motion of oxygen vacancies in solids is crucial for various future applications, such as oxide electrolytes. Visualization and quantification can offer unforeseen opportunities to probe the collective dynamics of defects in crystalline solids, but little research has been conducted on oxygen vacancy electromigration using these approaches. Here, we visualize electric-field-induced creation and propagation of oxygen-vacancy-rich and -poor competing phases and their interface with optical contrast in Ca-substituted BiFeO3 that contains a high density of mobile oxygen vacancies. We quantitatively determined the drift velocity of collective migration to be on the order of 100 μm s−1 with an activation barrier of 0.79 eV, indicating a significantly large ionic mobility of 2 × 10−6 cm2 s−1 V−1 at a remarkably low temperature of 390 °C. In addition, visualization enables direct observation of fluidic behavior, such as the enhancement of conduction at channel edges, which results in U-shaped viscous propagation of the phase boundary and turbulence under a reverse electric field. All of these results provide new insights into the collective motion of defects. The collective propagation of defects in an oxide material has been visualized by researchers in South Korea and the USA. Most crystalline materials are imperfect. One type of imperfection, known as a vacancy, is the absence of an atom from the crystal lattice. These vacancies move through the material as surrounding atoms shift to fill the empty spot. A better understanding of this motion could aid the development of novel memories, solid oxide fuel cells and batteries. Chan-Ho Yang from the Korea Advanced Institute of Science and Technology, Daejeon, and colleagues recorded the movement of oxygen vacancies in calcium-substituted BiFeO3 because of the color difference between regions of high and low vacancy concentration. This ability to visualize oxygen-vacancies in real-time offers an opportunity to measure their movement and better understand defect-induced material changes. We visualize an electric-field-induced collective propagation of oxygen vacancies spontaneously contained in Ca-substituted BiFeO3 films, using the fact that the oxygen-rich and poor regions have different color contrasts and thus they are optically distinguishable forming a sharp boundary. We quantitatively determine the drift velocity to be of the order of 100 μm s−1 with an activation barrier of 0.79 eV indicating a significantly large ionic mobility 2 × 10−6 cm2 s−1 V−1 at a remarkably low temperature of 390 °C. Furthermore, U-shaped propagation and turbulence under backward electric field provide insights into fluidic defects in crystalline solids.

We map electronic states, band gaps, and interface-bound charges at termination-engineered BiFeO3/La0.7Sr0.3MnO3 interfaces using atomically resolved cross-sectional scanning tunneling microscopy. We identify a delicate interplay of different correlated physical effects and relate these to the ferroelectric and magnetic interface properties tuned by engineering the atomic layer stacking sequence at the interfaces. This study highlights the importance of a direct atomically resolved access to electronic interface states for understanding the intriguing interface properties in complex oxides.

Chirality is a geometrical property by which an object is not super-imposable onto its mirror image, thereby imparting a handedness. Chirality determines many important properties in nature—from the strength of the weak interactions according to the electroweak theory in particle physics to the binding of enzymes with naturally occurring amino acids or sugars, reactions that are fundamental for life. In condensed matter physics, the prediction of topologically protected magnetic skyrmions and related spin textures in chiral magnets has stimulated significant research. If the magnetic dipoles were replaced by their electrical counterparts, then electrically controllable chiral devices could be designed. Complex oxide BaTiO/SrTiO nanocomposites and PbTiO/SrTiO superlattices are perfect candidates, since “polar vortices,” in which a continuous rotation of ferroelectric polarization spontaneously forms, have been recently discovered. Using resonant soft X-ray diffraction, we report the observation of a strong circular dichroism from the interaction between circularly polarized light and the chiral electric polarization texture that emerges in PbTiO/SrTiO superlattices. This hallmark of chirality is explained by a helical rotation of electric polarization that second-principles simulations predict to reside within complex 3D polarization textures comprising ordered topological line defects. The handedness of the texture can be topologically characterized by the sign of the helicity number of the chiral line defects. This coupling between the optical and novel polar properties could be exploited to encode chiral signatures into photon or electron beams for information processing., The Advanced Light Source is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the US Department of Energy under Contract DE-AC02-05CH11231. Electron microscopy of superlattice structures was performed at the Molecular Foundry, Lawrence Berkeley National Laboratory, supported by the Office of Science, Office of Basic Energy Sciences, US Department of Energy under Contract DE-AC02-05CH11231. P.G.-F. recognizes support from Ramón y Cajal Grant RyC-2013-12515. A.R.D. acknowledges support from the Army Research Office under Grant W911NF-14-1-0104 and the US Department of Energy, Office of Basic Energy Sciences under Grant DE-SC0012375 for synthesis and structural study of the materials. A.K.Y. and C.T.N. were supported by the Office of Basic Energy Sciences, US Department of Energy under Contract DE-AC02-05CH11231. S.-L.H. acknowledges support from the National Science Foundation under the Materials Research Science and Engineering Centers program under Grant DMR-1420620. J.Í. acknowledges support from the Luxembourg National Research Fund under Grant C15/MS/10458889 NEWALLS. P.G.-F. and J.J. acknowledge financial support from the Spanish Ministry of Economy and Competitiveness through Grant FIS2015-64886-C5-2-P. R.R. and L.W.M. acknowledge support from the Gordon and Betty Moore Foundation’s Emergent Phenomena in Quantum Systems Initiative, under Grant GBMF5307.

The ultimate challenge for the development of new multiferroics with enhanced properties lies in achieving nanoscale control of the coupling between different ordering parameters. In oxide-based multiferroics, substitutional cation dopants offer the unparalleled possibility to modify both the electric and magnetic properties at a local scale. Herein it is demonstrated the formation of a dopant-controlled polar pattern in BiFeO

Cracks in solid-state materials are typically irreversible. Here we report electrically reversible opening and closing of nanoscale cracks in an intermetallic thin film grown on a ferroelectric substrate driven by a small electric field (~0.83 kV/cm). Accordingly, a nonvolatile colossal electroresistance on–off ratio of more than 108 is measured across the cracks in the intermetallic film at room temperature. Cracks are easily formed with low-frequency voltage cycling and remain stable when the device is operated at high frequency, which offers intriguing potential for next-generation high-frequency memory applications. Moreover, endurance testing demonstrates that the opening and closing of such cracks can reach over 107 cycles under 10-μs pulses, without catastrophic failure of the film., Electric-field-induced cracks are generally detrimental to functionality of ferroelectric ceramics. Liu et al. use an intermetallic alloy and ferroelectric oxide junction to mediate the reversible formation of cracks at nanoscales, resulting in colossal electroresistance modulation for memory applications.

Electric-field control of magnetism requires deterministic control of the magnetic order and understanding of the magnetoelectric coupling in multiferroics like BiFeO

It is well known that one needs an external source of energy to provide voltage amplification. Because of this, conventional circuit elements such as resistors, inductors or capacitors cannot provide amplification all by themselves. Here, we demonstrate that a ferroelectric can cause a differential amplification without needing such an external energy source. As the ferroelectric switches from one polarization state to the other, a transfer of energy takes place from the ferroelectric to the dielectric, determined by the ratio of their capacitances, which, in turn, leads to the differential amplification. {This amplification is very different in nature from conventional inductor-capacitor based circuits where an oscillatory amplification can be observed. The demonstration of differential voltage amplification from completely passive capacitor elements only, has fundamental ramifications for next generation electronics.

Complex oxides provide an ideal playground for exploring the interplay among the fundamental degrees of freedom: structural (lattice), electronic (orbital and charge), and magnetic (spin). In thin films and heterostructures, new states of matter can emerge as a consequence of such interactions. Over the past decade, the ability to synthesize self-assembled nanocomposite thin films of metal oxides has provided another pathway for creating new interfaces and, thus, new physical phenomena. In this article, we describe examples of such materials systems explored to date and highlight the fascinating multifunctional properties achieved. These include enhanced flux pinning in superconductors, strain-enhanced ferroelectricity, strain- and charge-coupled magnetoelectrics, tunable magnetotransport, novel electrical/ionic transport, memristors, and tunable dielectrics.

We report a voltage controlled reversible creation and annihilation of a-axis oriented ∼10 nm wide ferroelastic nanodomains without a concurrent ferroelectric 180° switching of the surrounding c-domain matrix in archetypal ferroelectric Pb(Zr0.2Ti0.8)O3 thin films by using the piezo-response force microscopy technique. In previous studies, the coupled nature of ferroelectric switching and ferroelastic rotation has made it difficult to differentiate the underlying physics of ferroelastic domain wall movement. Our observation of distinct thresholds for ferroelectric and ferroelastic switching allows us investigate the ferroelastic switching cleanly and demonstrate a new degree of nanoscale control over the ferroelastic domains.

Improvement of both solution and vapor-phase synthetic techniques for nanoscale ferroelectrics has fueled progress in fundamental understanding of the polar phase at reduced dimensions, and this physical insight has pushed the boundaries of ferroelectric phase stability and polarization switching to sub-10 nm dimensions. The development and characterization of new ferroelectric nanomaterials has opened new avenues toward future nonvolatile memories, devices for energy storage and conversion, biosensors, and many other applications. This prospective will highlight recent progress on the synthesis, fundamental understanding, and applications of zero- and one-dimensional ferroelectric nanomaterials and propose new directions for future study in all three areas.

Low temperature solution-processed organic-inorganic halide perovskite CH3NH3PbI3 has demonstrated great potential for photovoltaics and light emitting devices. Recent discoveries of long ambipolar carrier diffusion lengths and the prediction of the Rashba effect in CH3NH3PbI3, that possesses large spin-orbit coupling, also point to a novel semiconductor system with highly promising properties for spin-based applications. Through circular pump-probe measurements, we demonstrate that highly polarized electrons of total angular momentum (J) with an initial degree of polarization Pini ~ 90% (i.e., –30% degree of electron spin polarization) can be photogenerated in perovskites. Time-resolved Faraday rotation measurements reveal photo-induced Faraday rotation as large as 10°/μm at 200 K (at wavelength λ = 750 nm) from an ultrathin 70 nm film. These spin polarized carrier populations generated within the polycrystalline perovskite films, relax via intraband carrier spin-flip through the Elliot-Yafet mechanism. Through a simple two-level model, we elucidate the electron spin relaxation lifetime to be ~7 ps and that of the hole is ~1 ps. Our work highlights the potential of CH3NH3PbI3 as a new candidate for spintronics applications such as ultrafast spin switches, spin aligners or filters and possibly spin-polarized light emitters. Accepted version

Hexagonal manganites are among the most intensively studied multiferroics, exhibit unusual geometrically driven ferroelectricity and magnetoelectric couplings, and form domains and domain walls with intriguing functional properties. In order to study these electronic correlation phenomena and develop a comprehensive understanding about the underlying physics, the availability of high-quality single-crystals is crucial. In particular, different members of the R MnO 3 ( R =Sc, Y, In, Dy to Lu) family require different growth condition in order to achieve stoichiometric single-phase crystals. Here, we report on the growth of high-quality ErMnO 3 single crystals with dimensions of 5 mm in diameter and up to 60 mm in length using the pressurized floating-zone technique. We present Laue diffraction, piezoresponse force microscopy, and conductive atomic force microscopy data, reflecting the quality of our single crystals regarding the structure, as well as electronic properties on the level of domains and domain walls.

The manipulation of magnetic properties by an electric field in magnetoelectric multiferroic materials has driven significant research activity, with the goal of realizing their transformative technological potential. Here, we review progress in the fundamental understanding and design of new multiferroic materials, advances in characterization and modelling tools to describe them, and the exploration of devices and applications. Focusing on the translation of the many scientific breakthroughs into technological innovations, we identify the key open questions in the field where targeted research activities could have maximum impact in transitioning scientific discoveries into real applications. Magnetoelectric multiferroics, where magnetic properties are manipulated by electric field and vice versa, could lead to improved electronic devices. Here, advances in materials, characterisation and modelling, and usage in applications are reviewed.

Ferroelectric materials are used in many applications of modern technologies including information storage, transducers, sensors, tunable capacitors, and other novel device concepts. In many of these applications, the ferroelectric properties, such as switching voltages, piezoelectric constants, or stability of nanodomains, are crucial. For any application, even for material characterization, the material itself needs to be interfaced with electrodes. On the basis of the structural, chemical, and electronic properties of the interfaces, the measured material properties can be determined by the interface. This is also true for surfaces. However, the importance of interfaces and surfaces and their effect on experiments are often neglected, which results in many dramatically different experimental results for nominally identical samples. Therefore, it is crucial to understand the role of the interface and surface properties on internal bias fields and the domain switching process. Here, the nanoscale ferroelectric switching process and the stability of nanodomains for Pb(Zr,Ti)O

Systems that exhibit phase competition, order parameter coexistence, and emergent order parameter topologies constitute a major part of modern condensed-matter physics. Here, by applying a range of characterization techniques, and simulations, we observe that in PbTiO>3/SrTiO>3 superlattices all of these effects can be found. By exploring superlattice period-, temperature- and field-dependent evolution of these structures, we observe several new features. First, it is possible to engineer phase coexistence mediated by a first-order phase transition between an emergent, low-temperature vortex phase with electric toroidal order and a high-temperature ferroelectric a>1/a>2 phase. At room temperature, the coexisting vortex and ferroelectric phases form a mesoscale, fibre-textured hierarchical superstructure. The vortex phase possesses an axial polarization, set by the net polarization of the surrounding ferroelectric domains, such that it possesses a multi-order-parameter state and belongs to a class of gyrotropic electrotoroidal compounds. Finally, application of electric fields to this mixed-phase system permits interconversion between the vortex and the ferroelectric phases concomitant with order-of-magnitude changes in piezoelectric and nonlinear optical responses. Our findings suggest new cross-coupled functionalities., A.R.D. acknowledges support from the Army Research Office under grant W911NF-14-1-0104 and the Department of Energy, Office of Science, Office of Basic Energy Sciences under grant no. DE-SC0012375 for synthesis and structural study of the materials. Z.H. acknowledges support from NSF-MRSEC grant number DMR-1420620 and NSF-MWN grant number DMR-1210588. A.K.Y. acknowledges support from the Office of Basic Energy Sciences, US Department of Energy DE-AC02-05CH11231. C.T.N. acknowledge support from the Office of Basic Energy Sciences, US Department of Energy DE-AC02-05CH11231. S.L.H. acknowledges support from the National Science Foundation under the MRSEC programme (DMR-1420620). M.R.M. acknowledges support from the National Science Foundation Graduate Research Fellowship under grant number DGE-1106400. K.-D.P., V.K. and M.B.R. acknowledge support from the US Department of Energy, Office of Basic Sciences, Division of Material Sciences and Engineering, under Award No. DE-SC0008807. A.F. acknowledges support from the Swiss National Science Foundation. P.G.-F. and J.J. acknowledge financial support from the Spanish Ministry of Economy and Competitiveness through grant number FIS2015-64886-C5-2-P. J.I. is supported by the Luxembourg National Research Fund (Grant FNR/C15/MS/10458889 NEWALLS). L.-Q.C. is supported by the US Department of Energy, Office of Basic Energy Sciences under Award FG02-07ER46417. R.R. and L.W.M. acknowledge support from the Gordon and Betty Moore Foundation’s EPiQS Initiative, under grant GBMF5307. The Advanced Light Source is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the US Department of Energy under Contract No. DE-C02-05CH11231. Nanodiffraction measurements were supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division. This research used resources of the Advanced Photon Source, a US Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. Electron microscopy of superlattice structures was performed at the Molecular Foundry at Lawrence Berkeley National Laboratory, supported by the Office of Science, Office of Basic Energy Sciences, US Department of Energy (DE-AC02-05CH11231).

A strain-driven orthorhombic (O) to rhombohedral (R) phase transition is reported in La-doped BiFeO

We demonstrate an electrically induced, non-volatile, metal-insulator phase transition in a MoS$_2$ transistor. A single crystalline, epitaxially grown, PbZr$_{0.2}$Ti$_{0.8}$O$_3$ (PZT) was placed in the gate of a field effect transistor made of thin film MoS$_2$. When a gate voltage is applied to this ferroelectric gated transistor, a clear transition from insulator to metal and vice versa is observed. Importantly, when the gate voltage is turned off, the remnant polarization in the ferroelectric can keep the MoS$_2$ in its original phase, thereby providing a non-volatile state. Thus a metallic or insulating phase can be written, erased or retained simply by applying a gate voltage to the transistor.

To achieve high quality epitaxial thin films and heterostructures of transition metal oxides with atomically controlled interfaces, one critical requirement is the use of atomically flat single terminated oxide substrates since the atomic arrangements and the reaction chemistry of the topmost surface layer of substrates determine the growth and consequent properties of the overlying films. Achieving the atomically flat and chemically single terminated surface state of commercially available substrates, however, requires judicious efforts because the surface of as-received substrates is of chemically mixed nature and also often polar. In this review, we summarize the surface treatment procedures to accomplish atomically flat surfaces with single terminating layer for various metal oxide substrates. We particularly focus on the substrates with lattice constant ranging from 4.00 to 3.70 angstrom, as the lattice constant of most perovskite materials falls into this range. For materials outside the range, one can utilize the substrates to induce compressive or tensile strain on the films and explore new states not available in bulk. The substrates covered in this review, which have been chosen with commercial availability and, most importantly, experimental practicality as a criterion, are KTaO3, REScO3 (RE = Rare-earth elements), SrTiO3, La0.18Sr0.82Al0.59Ta0.41O3 (LSAT), NdGaO3, LaAlO3, SrLaAlO4, and YAlO3. Analyzing all the established procedures, we conclude that atomically flat surfaces with selective A- or B-site single termination would be obtained for most commercially available oxide substrates. We further note that this topmost surface layer selectivity would provide an additional degree of freedom in searching for unforeseen emergent phenomena and functional applications in epitaxial oxide thin films and heterostructures with atomically controlled interfaces., A review article

Electric-field (E-field) control of magnetism enabled by multiferroic materials has the potential to revolutionize the landscape of present memory devices plagued with high energy dissipation. To date, this E-field controlled multiferroic scheme has only been demonstrated at room temperature using BiFeO

We report a giant, ~22%, electroresistance modulation for a metallic alloy above room temperature. It is achieved by a small electric field of 2 kV/cm via piezoelectric strain-mediated magnetoelectric coupling and the resulting magnetic phase transition in epitaxial FeRh/BaTiO3 heterostructures. This work presents detailed experimental evidence for an isothermal magnetic phase transition driven by tetragonality modulation in FeRh thin films, which is in contrast to the large volume expansion in the conventional temperature-driven magnetic phase transition in FeRh. Moreover, all the experimental results in this work illustrate FeRh as a mixed-phase model system well similar to phase-separated colossal magnetoresistance systems with phase instability therein., 6 pages, 3 figures

Ferroelectric domain walls hold great promise as functional two-dimensional materials because of their unusual electronic properties. Particularly intriguing are the so-called charged walls where a polarity mismatch causes local, diverging electrostatic potentials requiring charge compensation and hence a change in the electronic structure. These walls can exhibit significantly enhanced conductivity and serve as a circuit path. The development of all-domain-wall devices, however, also requires walls with controllable output to emulate electronic nano-components such as diodes and transistors. Here we demonstrate electric-field control of the electronic transport at ferroelectric domain walls. We reversibly switch from resistive to conductive behaviour at charged walls in semiconducting ErMnO3 . We relate the transition to the formation—and eventual activation—of an inversion layer that acts as the channel for the charge transport. The findings provide new insight into the domain-wall physics in ferroelectrics and foreshadow the possibility to design elementary digital devices for all-domain-wall circuitry. © 2017. This is the authors' accepted and refereed manuscript to the article. The final authenticated version is available online at: https://www.nature.com/articles/nmat4878#abstract

Ferromagnetic ZnFe2O4 nanoparticles were synthesized by surfactant assisted hydrothermal method using different amount of triethylamine (TEA). The synthesized nanoparticles were characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy (TEM), high-resolution transmission electron microscopy and vibrating sample magnetometer. The formation of single phase ZnFe2O4 was investigated by addition of different amount of TEA. Regular spinel structure was obtained for all synthesized product except for lower amount of TEA, owing to the less alkaline atmosphere. All the synthesized nanoparticles were spherical in shape with a small aggregation. Observed size of the nanoparticles was 10 nm as determined from TEM measurement for the sample synthesized with a higher amount of TEA. Room temperature ferromagnetic behavior was observed in all the samples.

Self-assembled vertical heteroepitaxial nanostructures (VHN) in the complex oxide field have fascinated scientists for decades because they provide degrees of freedom to explore in condensed matter physics and design-coupled multifunctionlities. Recently, of particular interest is the perovskite-spinel-based VHN, covering a wide spectrum of promising applications. In this review, fabrication of VHN, their growth mechanism, control, and resulting novel multifunctionalities are discussed thoroughly, providing researchers a comprehensive blueprint to construct promising VHN. Following the fabrication section, the state-of-the-art design concepts for multifunctionalities are proposed and reviewed by suitable examples. By summarizing the outlook of this field, we are excitedly expecting this field to rise with significant contributions ranging from scientific value to practical applications in the foreseeable future.

Anisotropic electronic conductivity is reported for isosymmetric phase boundaries in highly strained bismuth ferrite, which are the (fully epitaxial) connecting regions between two different structural variants of the same material. Strong correlations between nanoscale phase transition and local electronic conductivity are found. A high degree of control over their electronic properties can be attained through non-local electrical switching.

Superparamagnetic ZnFe2O4 nanoparticles were synthesized by facile hydrothermal method using different amount of diethylamine (DEA) as a precipitating agent. The phase formation, morphological and magnetic properties were investigated using X-ray diffraction, field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy and vibrating sample magnetometer. The amount of DEA required for forming single phase ZnFe2O4 was optimized. For 2 ml of DEA, a mixed phase of α-Fe2O3 and ZnFe2O4 was formed whereas single phase of ZnFe2O4 was formed with high crystalline quality for 4, 6, 8 and 10 ml of DEA. FE-SEM results indicated that all the synthesized products were in spherical shape with small aggregations. Particle size of 9 nm was obtained from TEM image for sample synthesized using 10 ml of DEA. Superparamagnetic property was observed for the samples synthesized using 4, 6, 8, and 10 ml of DEA.

Using epitaxy and the misfit strain imposed by an underlying substrate, it is possible to elastically strain oxide thin films to percent levels—far beyond where they would crack in bulk. Under such strains, the properties of oxides can be dramatically altered. In this article, we review the use of elastic strain to enhance ferroics, materials containing domains that can be moved through the application of an electric field (ferroelectric), a magnetic field (ferromagnetic), or stress (ferroelastic). We describe examples of transmuting oxides that are neither ferroelectric nor ferromagnetic in their unstrained state into ferroelectrics, ferromagnets, or materials that are both at the same time (multiferroics). Elastic strain can also be used to enhance the properties of known ferroic oxides or to create new tunable microwave dielectrics with performance that rivals that of existing materials. Results show that for thin films of ferroic oxides, elastic strain is a viable alternative to the traditional method of chemical substitution to lower the energy of a desired ground state relative to that of competing ground states to create materials with superior properties.

Scaling-up solutions require learning and adapting lessons between locations and at different scales. To accomplish this, common metrics are vital to building a shared language. For California, this has meant careful financial, cradle-to-grave life-cycle assessment methods leading to carbon accounting in many avenues of government (via the Low Carbon Fuel Standard or the Cap and Trade program). These methods themselves interact, such as the use of carbon accounting for the resources needed to manage water and other key resources; the use of criteria air pollution monitoring to identify environmental injustices; and the use of carbon market revenues to address these inequalities, through investment in best available abatement technologies (BACT) and in job creation in disadvantaged communities anticipated in the emerging clean energy sector. Creating interdisciplinary partnerships across the UC Campuses and the National Laboratories to innovate science and technology is critical to scalable carbon neutrality solutions. As an example, we can build coordinated research and development programs across UC and California, with strong partnerships with the Federal government to coordinate and “multiply” resources that accelerate development and deployment. These partnerships should be strongly goal-focused, i.e., they are created to solve specific, large problems, to enable quantitatively measurable outcomes within energy generation, efficiency and CO2 abatement categories. Intersectoral partnerships should be fostered across campuses, laboratories, with state, federal and multi-lateral organizations funding to develop technologies and deploy solutions at scale. Integrated partnerships with industry are required to influence markets, deploy solutions, and create new industries and jobs. Beyond California, we need to establish consortia with industry and foundations to deploy solutions at the regional, state, national, and international scale to create new industries, new jobs, and further UC and California’s leadership position. Significant economic opportunities exist, such as promoting aggressive electric vehicle programs elsewhere in the world, where California-based companies could play a key role on many fronts, via electric vehicles themselves, but also through building-integrated smart meters, inverters, solar and other clean energy generation technologies. All work must include a focus on environmental justice both at home in California and through global partnerships.

Author(s): Nelson, Christopher T; Hong, Zijian; Yadav, Ajay K; Damodaran, Anoop R; Hsu, Shang-Lin; Clarkson, James D; Chen, Long-Qing; Martin, Lane W; Ramesh, Ramamoorthy