Superior Piezo-/Ferro-Electricity in Antiferroelectric AgNbO Thin Films by Nanopillar Local Structure Design.

Antiferroelectrics are fundamental mother compounds critical in developing innovative lead-free piezoelectrics and ferroelectrics and hold great promise for wide-ranging applications in energy conversion and electronic devices. However, harnessing their superior properties presents a significant challenge due to the delicate balance required between their various states. In this study, through the unique design of nanopillar structures to alleviate the local polar heterogeneity, we have achieved significantly improved piezo-/ferro-electricity in classic lead-free antiferroelectric AgNbO ( = 1, 0.

Superfine Nanodomain Engineering Unleashing Ferroelectricity in Incipient Ferroelectrics.

Incipient ferroelectrics have emerged as an attractive class of functional materials owing to their potential to be engineered for exotic ferroelectric behavior, holding great promise for expanding the ferroelectric family. However, thus far, their artificially engineered ferroelectricity has fallen far short of rivaling classic ferroelectrics. In this study, we address this challenge by developing a superfine nanodomain engineering strategy.

Ultrahigh-Efficiency Superior Energy Storage in Lead-Free Films with a Simple Composition.

Dielectric capacitors are highly desired in modern electronic devices and power systems to store and recycle electric energy. However, achieving simultaneous high energy density and efficiency remains a challenge. Here, guided by theoretical and phase-field simulations, we are able to achieve a superior comprehensive property of ultrahigh efficiency of 90-94% and high energy density of 85-90 J cm remarkably in strontium titanate (SrTiO), a linear dielectric of a simple chemical composition, by manipulating local symmetry breaking through introducing Ti/O defects.

High-Temperature Ferroic Glassy States in SrTiO_{3}-Based Thin Films.

Disordered ferroics hold great promise for next-generation magnetoelectric devices because their lack of symmetry constraints implies negligible hysteresis with low energy costs. However, the transition temperature and the magnitude of polarization and magnetization are still too low to meet application requirements. Here, taking the prototype perovskite of SrTiO_{3} as an instance, we realize a coexisting spin and dipole reentrant glass states in SrTiO_{3} homoepitaxial films via manipulation of local symmetry.

Mean inner potential of elemental crystals from density-functional theory calculations: Efficient computation and trends.

The mean inner potential (V) of crystals plays an important role in electron microscopy. In a few cases, it has been measured experimentally, using mostly electron holography; however, it is not uncommon to find reports that disagree by a few volts regarding the mean inner potential of the same material. Different levels of theory have also been used to estimate its value, often by building the crystal as a superposition of isolated atoms or ions-an independent-atom approximation that does not take bonding into account.

The Mean Inner Potential of Hematite α-Fe2O3 Across the Morin Transition.

We measure the mean inner potential (MIP) of hematite, α-Fe2O3, using electron holography and transmission electron microscopy. Since the MIP is sensitive to valence electrons, we propose its use as a chemical bonding parameter for solids. Hematite can test the sensitivity of the MIP as a bonding parameter because of the Morin magnetic phase transition.

Unidirectional rotation of micromotors on water powered by pH-controlled disassembly of chiral molecular crystals.

Biological and synthetic molecular motors, fueled by various physical and chemical means, can perform asymmetric linear and rotary motions that are inherently related to their asymmetric shapes. Here, we describe silver-organic micro-complexes of random shapes that exhibit macroscopic unidirectional rotation on water surface through the asymmetric release of cinchonine or cinchonidine chiral molecules from their crystallites asymmetrically adsorbed on the complex surfaces. Computational modeling indicates that the motor rotation is driven by a pH-controlled asymmetric jet-like Coulombic ejection of chiral molecules upon their protonation in water.

Ferroelectricity in layered bismuth oxide down to 1 nanometer.

Atomic-scale ferroelectrics are of great interest for high-density electronics, particularly field-effect transistors, low-power logic, and nonvolatile memories. We devised a film with a layered structure of bismuth oxide that can stabilize the ferroelectric state down to 1 nanometer through samarium bondage. This film can be grown on a variety of substrates with a cost-effective chemical solution deposition.

Carbon Dioxide Reduction on Transition Metal Dichalcogenides with Ni and Cu Edge Doping: A Density-Functional Theory Study.

Transition-metal dichalcogenides (TMDs) have promising properties for their use as catalysts of CO reduction to methane via the Sabatier reaction. In this article we use density-functional theory calculations to gain insight into the energetics of this reaction for Mo/W-based and S/Se-based TMDs with non-, Ni- and Cu-doping. We show that sulfur-based TMDs with Ni/Cu doping exhibit better indicators for catalytic performance of the CO reduction reaction than non-doped and doped TMDs without active sites.

Measuring the mean inner potential of AlO sapphire using off-axis electron holography.

The mean inner potential (MIP) of a single crystal α-AlO sapphire was measured using off-axis electron holography. To measure the MIP, we use mechanically polished wedge specimens for transmission electron microscopy (TEM). This approach also enabled us to measure the plasmon mean free path for inelastic scattering (IMFP).

Giant polarization in super-tetragonal thin films through interphase strain.

Strain engineering has emerged as a powerful tool to enhance the performance of known functional materials. Here we demonstrate a general and practical method to obtain super-tetragonality and giant polarization using interphase strain. We use this method to create an out-of-plane-to-in-plane lattice parameter ratio of 1.

Multiple structural transitions driven by spin-phonon couplings in a perovskite oxide.

Spin-phonon interactions are central to many interesting phenomena, ranging from superconductivity to magnetoelectric effects. However, they are believed to have a negligible influence on the structural behavior of most materials. For example, magnetic perovskite oxides often undergo structural transitions accompanied by magnetic signatures whose minuteness suggests that the underlying spin-phonon couplings are largely irrelevant.

Mapping Charge Distribution in Single PbS Core - CdS Arm Nano-Multipod Heterostructures by Off-Axis Electron Holography.

We synthesized PbS core-CdS arm nanomultipod heterostructures (NMHs) that exhibit PbS{111}/CdS{0002} epitaxial relations. The PbS-CdS interface is chemically sharp as determined by aberration corrected transmission electron microscopy (TEM) and compared to density functional theory (DFT) calculations. Ensemble fluorescence measurements show quenching of the optical signal from the CdS arms indicating charge separation due to the heterojunction with PbS.

Ferroelectric domains in multiferroic BiFeO3 films under epitaxial strains.

First-principles calculations are performed to investigate energetic and atomistic characteristics of ferroelectric domains walls (DWs) of BiFeO(3) (BFO) films subject to compressive strain. Significantly lower DW energies than those previously reported, and a different energetic hierarchy between the various DW types, are found for small strains. In all investigated cases (corresponding to ideal angles of 71°, 109°, and 180° formed by the domain polarizations), the DW energy reaches its maximum value for misfit strains that are around the critical strain at which the transition between the R-like and T-like phases occurs in single-domain BFO.

Strain engineering magnetic frustration in perovskite oxide thin films.

Our first-principles results show that geometric frustration can be induced in thin films of multiferroic BiFeO(3). We find that competing magnetic interactions occur in the so-called supertetragonal phase of this material, which can be grown on strongly compressive substrates. We show that the frustration level can be tuned by appropriately choosing the substrate; in fact, the phase diagram of the films presents a critical line at which the three-dimensional spin order gets annihilated.

First-principles investigation of morphotropic transitions and phase-change functional responses in BiFeO3-BiCoO3 multiferroic solid solutions.

We present an ab initio study of the BFCO solid solution formed by multiferroics BiFeO(3) (BFO) and BiFeO(3) (BCO). We find that BFCO presents a strongly discontinuous morphotropic transition between BFO-like and BCO-like ferroelectric phases. Further, for all compositions such phases remain (meta)stable and retain well-differentiated properties.

Wannier-based definition of layer polarizations in perovskite superlattices.

In insulators, the method of Marzari and Vanderbilt [Phys. Rev. B 56, 12 847 (1997)] can be used to generate maximally localized Wannier functions whose centers are related to the electronic polarization.

First-principles calculations for insulators at constant polarization.

We develop an exact formalism for performing first-principles calculations for insulators at fixed electric polarization. As shown by Sai, Rabe, and Vanderbilt (SRV) [Phys. Rev.