Photoinduced Phase Transitions in Ferroelectrics.

Ferroic materials naturally exhibit a rich number of functionalities, which often arise from thermally, chemically, or mechanically induced symmetry breakings or phase transitions. Based on density functional calculations, we demonstrate here that light can drive phase transitions as well in ferroelectric materials such as the perovskite oxides lead titanate and barium titanate. Phonon analysis and total energy calculations reveal that the polarization tends to vanish under illumination, to favor the emergence of nonpolar phases, potentially antiferroelectric, and exhibiting a tilt of the oxygen octahedra.

Nanocrystalline Cellulose-Derived Doped Carbonaceous Material for Rapid Mineralization of Nitrophenols under Visible Light.

Nitrophenols (NPs) and related derivatives are industrially important chemicals, used notably to synthesize pharmaceuticals, insecticides, herbicides, and pesticides. However, NPs and their metabolites are highly toxic and mutagenic. They pose a serious threat to human health and ecosystem.

Electric-Field Control of Magnetization, Jahn-Teller Distortion, and Orbital Ordering in Ferroelectric Ferromagnets.

Controlling the direction of the magnetization by an electric field in multiferroics that are both ferroelectric and strongly ferromagnetic will open the door to the design of the next generation of spintronics and memory devices. Using first-principles simulations, we report that the discovery that the PbTiO_{3}/LaTiO_{3} (PTO/LTO) superlattice possesses such highly desired control, as evidenced by the electric-field-induced rotation of 90° and even a possible full reversal of its magnetization in some cases. Moreover, such systems also exhibit Jahn-Teller distortions, as well as orbital orderings, that are switchable by the electric field, therefore making PTO/LTO of importance for the tuning of electronic properties too.

Ferroelectricity with Asymmetric Hysteresis in Metallic LiOsO_{3} Ultrathin Films.

Bulk LiOsO_{3} was experimentally identified as a "ferroelectric" metal where polar distortions coexist with metallicity [Shi et al., Nat. Mater.

Advanced on-site glucose sensing platform based on a new architecture of free-standing hollow Cu(OH) nanotubes decorated with CoNi-LDH nanosheets on graphite screen-printed electrode.

The planned design of nanocomposites combined with manageable production processes, which can offer controllability over the nanomaterial structure, promises the practical applications of functional nanomaterials. Hollow core-shell nanostructure architectures represent an emerging category of advanced functional nanomaterials, whose benefits derived from their notable properties may be hampered by complicated construction processes, especially in the sensing domain. In this regard, we designed a highly porous three-dimensional array of hierarchical hetero Cu(OH)@CoNi-LDH core-shell nanotubes via a quick, very simple, green, and highly controllable three-step in situ method; they were directly grown on a glassy carbon electrode to fabricate an enzyme-free glucose sensor.

Novel Dynamical Magnetoelectric Effects in Multiferroic BiFeO_{3}.

An atomistic effective Hamiltonian scheme is employed within molecular dynamics simulations to investigate how the electrical polarization and magnetization of the multiferroic BiFeO_{3} respond to time-dependent ac magnetic fields of various frequencies, as well as to reveal the frequency dependency of the dynamical (quadratic) magnetoelectric coefficient. We found the occurrence of vibrations having phonon frequencies in both the time dependency of the electrical polarization and magnetization (for any applied ac frequency), therefore making such vibrations of electromagnonic nature, when the homogeneous strain of the system is frozen (case 1). Moreover, the quadratic magnetoelectric coupling constant is monotonic and almost dispersionless in the sub-THz range in this case 1.

Refreshing Piezoelectrics: Distinctive Role of Manganese in Lead-Free Perovskites.

Driven by an ever-growing demand for environmentally compatible materials, the past two decades have witnessed the booming development in the field of piezoelectrics. To maximally explore the potential of lead-free piezoelectrics, chemical doping could be an effective approach, referenced from tactics adopted in lead-based piezoelectrics. Herein, we reveal the distinct role of manganese in a promising lead-free perovskite (K, Na)NbO (denoted by KNN) in comparison to that in market-dominating lead-based counterparts [Pb(Zr, Ti)O, PZT].

Giant resistive switching in mixed phase BiFeOvia phase population control.

Highly-strained coherent interfaces, between rhombohedral-like (R) and tetragonal-like (T) phases in BiFeO3 thin films, often show enhanced electrical conductivity in comparison to non-interfacial regions. In principle, changing the population and distribution of these interfaces should therefore allow different resistance states to be created. However, doing this controllably has been challenging to date.

Intrinsic Origin of Enhancement of Ferroelectricity in SnTe Ultrathin Films.

Previous studies showed that, as ferroelectric films become thinner, their Curie temperature (T_{c}) and polarization below T_{c} both typically decrease. In contrast, a recent experiment [Chang et al., Science 353, 274 (2016)SCIEAS0036-807510.

A rainbow ratiometric fluorescent sensor array on bacterial nanocellulose for visual discrimination of biothiols.

Considering the crucial role of biothiols in many biological processes, which turns them into highly valuable biomarkers for the early diagnosis of various diseases, the development of an affordable, sensitive and portable probe for the identification and discrimination of these compounds is of great importance. Herein, we developed a ratiometric fluorescent (RF) sensor array with a wide color emissive variation, on a bacterial cellulose (BC) nanopaper substrate for the visual discrimination of biothiols. To this aim, RF sensing elements including N-acetyl l-cysteine capped green CdTe quantum dots-rhodamine B (GQDs-RhB) and red CdTe QDs-carbon dots (RQDs-CDs) at two different NaOH concentrations (0 and 5 mM) were utilized as sensor elements for the discrimination of biothiols.

Aptamer immobilization on amino-functionalized metal-organic frameworks: an ultrasensitive platform for the electrochemical diagnostic of Escherichia coli O157:H7.

Herein, we report the development of an electrochemical biosensor for Escherichia coli O157:H7 diagnostic based on amino-functionalized metal-organic frameworks (MOFs) as a new generation of organic-inorganic hybrid nanocomposites. The electrical and morphological properties of MOFs were enhanced by interweaving each isolated MOF crystal with polyaniline (PANI). Subsequent attachment of the amine-modified aptamer to the polyanilinated MOFs was accomplished using glutaraldehyde (GA) as a cross-linking agent.

Cooperative Couplings between Octahedral Rotations and Ferroelectricity in Perovskites and Related Materials.

The structure of ABO_{3} perovskites is dominated by two types of unstable modes, namely, the oxygen octahedral rotation (AFD) and ferroelectric (FE) mode. It is generally believed that such AFD and FE modes tend to compete and suppress each other. Here we use first-principles methods to show that a dual nature of the FE-AFD coupling, which turns from competitive to cooperative as the AFD mode strengthens, occurs in numerous perovskite oxides.

Interface reconstruction with emerging charge ordering in hexagonal manganite.

Multiferroic materials, which simultaneously have multiple orderings, hold promise for use in the next generation of memory devices. We report a novel self-assembled MnO double layer forming at the interface between a multiferroic YMnO film and a -AlO substrate. The crystal structures and the valence states of this MnO double layer were studied by atomically resolved scanning transmission electron microscopy and spectroscopy, as well as density functional theory (DFT) calculations.

Topological Defects with Distinct Dipole Configurations in PbTiO_{3}/SrTiO_{3} Multilayer Films.

Distinct and novel features of nanometric electric topological defects, including dipole waves and dipole disclinations, are presently revealed in the PbTiO_{3} layers of PbTiO_{3}/SrTiO_{3} multilayer films by means of quantitative high-resolution scanning transmission electron microscopy. These original dipole configurations are confirmed and explained by atomistic simulations and have the potential to act as functional elements in future electronics.

Reducing Surface Recombination by a Poly(4-vinylpyridine) Interlayer in Perovskite Solar Cells with High Open-Circuit Voltage and Efficiency.

Identifying and reducing the dominant recombination processes in perovskite solar cells is one of the major challenges for further device optimization. Here, we show that introducing a thin interlayer of poly(4-vinylpyridine) (PVP) between the perovskite film and the hole transport layer reduces nonradiative recombination. Employing such a PVP interlayer, we reach an open-circuit voltage of 1.

Label-free detection of β-amyloid peptides (Aβ40 and Aβ42): a colorimetric sensor array for plasma monitoring of Alzheimer's disease.

Monitoring the ratio of 40- and 42-residue amyloid β peptides (i.e., Aβ40 and Aβ42) in human plasma is considered one of the hallmarks of detection of the early stage of Alzheimer's disease (AD).

2D Intrinsic Ferromagnets from van der Waals Antiferromagnets.

Intrinsically ferromagnetic 2D semiconductors are essential and highly sought for nanoscale spintronics, but they can only be obtained from ferromagnetic bulk crystals, while the possibility to create 2D intrinsic ferromagnets from bulk antiferromagnets remains unknown. Herein on the basis of ab initio calculations, we demonstrate this feasibility with the discovery of intrinsic ferromagnetism in an emerging class of single-layer 2D semiconductors CrOX (CrOCl and CrOBr monolayers), which show robust ferromagnetic ordering, large spin polarization, and high Curie temperature. These 2D crystals promise great dynamical and thermal stabilities as well as easy experimental fabrication from their bulk antiferromagnets.

Photostriction and elasto-optic response in multiferroics and ferroelectrics from first principles.

The present work reviews a series of recent first-principles studies devoted to the description of the interaction of light and strain in ferroelectric and multiferroic materials. Specifically, the modelling schemes used in these works to describe the so-called photostriction and elasto-optic effects are presented, in addition to the results and analysis provided by these ab initio calculations. In particular, the large importance of the piezoelectric effect in the polar direction in the photostriction of ferroelectric materials is stressed.

Nanoscale Bubble Domains and Topological Transitions in Ultrathin Ferroelectric Films.

Observation of a new type of nanoscale ferroelectric domains, termed as "bubble domains"-laterally confined spheroids of sub-10 nm size with local dipoles self-aligned in a direction opposite to the macroscopic polarization of a surrounding ferroelectric matrix-is reported. The bubble domains appear in ultrathin epitaxial PbZr Ti O /SrTiO /PbZr Ti O ferroelectric sandwich structures due to the interplay between charge and lattice degrees of freedom. The existence of the bubble domains is revealed by high-resolution piezoresponse force microscopy (PFM), and is corroborated by aberration-corrected atomic-resolution scanning transmission electron microscopy mapping of the polarization displacements.

Vacancies and holes in bulk and at 180° domain walls in lead titanate.

Domain walls (DWs) in ferroic materials exhibit a plethora of unexpected properties that are different from the adjacent ferroic domains. Still, the intrinsic/extrinsic origin of these properties remains an open question. Here, density functional theory calculations are used to investigate the interaction between vacancies and 180° DWs in the prototypical ferroelectric PbTiO, with a special emphasis on cationic vacancies and released holes.

Luminescent Spectral Conversion to Improve the Performance of Dye-Sensitized Solar Cells.

Relative to the broadband solar spectrum, a narrow range of spectral absorption of photovoltaic (PV) devices is considered an important determinant that the efficiency of light harvesting of these devices is less than unity. Having the narrowest spectral response to solar radiation among all PV devices, dye-sensitized solar cells (DSSCs) suffer severely from this loss. Luminescent spectral conversion provides a mechanism to manipulate and to adapt the incident solar spectrum by converting, through photoluminescence, the energies of solar photons into those that are more effectively captured by a PV device.

Emergent Berezinskii-Kosterlitz-Thouless Phase in Low-Dimensional Ferroelectrics.

Using first-principles-based simulations merging an effective Hamiltonian scheme with scaling, symmetry, and topological arguments, we find that an overlooked Berezinskii-Kosterlitz-Thouless (BKT) phase sustained by quasicontinuous symmetry emerges between the ferroelectric phase and the paraelectric one of BaTiO_{3} ultrathin film, being under tensile strain. Not only do these results provide an extension of BKT physics to the field of ferroelectrics, but they also unveil their nontrivial critical behavior in low dimensions.

Tunable Magnetism and Extraordinary Sunlight Absorbance in Indium Triphosphide Monolayer.

Atomically thin two-dimensional (2D) materials have received considerable research interest due to their extraordinary properties and promising applications. Here we predict the monolayered indium triphosphide (InP) as a new semiconducting 2D material with a range of favorable functional properties by means of ab initio calculations. The 2D InP crystal shows high stability and promise of experimental synthesis.

Microscopic origins of the large piezoelectricity of leadfree (Ba,Ca)(Zr,Ti)O.

In light of directives around the world to eliminate toxic materials in various technologies, finding lead-free materials with high piezoelectric responses constitutes an important current scientific goal. As such, the recent discovery of a large electromechanical conversion near room temperature in (1-x)Ba(ZrTi)O-x(BaCa)TiO compounds has directed attention to understanding its origin. Here, we report the development of a large-scale atomistic scheme providing a microscopic insight into this technologically promising material.

Designing lead-free antiferroelectrics for energy storage.

Dielectric capacitors, although presenting faster charging/discharging rates and better stability compared with supercapacitors or batteries, are limited in applications due to their low energy density. Antiferroelectric (AFE) compounds, however, show great promise due to their atypical polarization-versus-electric field curves. Here we report our first-principles-based theoretical predictions that BiRFeO systems (R being a lanthanide, Nd in this work) can potentially allow high energy densities (100-150 J cm) and efficiencies (80-88%) for electric fields that may be within the range of feasibility upon experimental advances (2-3 MV cm).