Enhancement of polarization and related properties in heteroepitaxially constrained thin films the ferroelectromagnet, BiFeO3, is reported. Structure analysis indicates that crystal structure film monoclinic contrast to bulk, which rhombohedral. The display a room-temperature spontaneous (50 60 microcoulombs per square centimeter) almost an order magnitude higher than bulk (6.1 centimeter). observed enhancement corroborated by first-principles calculations found originate from high...

Boron- and nitrogen-doped graphenes are prepared by the arc discharge between carbon electrodes or transformation of nanodiamond under appropriate atmospheres. Using a combination experiment theories based on first principles, systematic changes in carrier-concentration electronic structure doped demonstrated. Stiffening G-band mode intensification defect-related D-band Raman spectra also observed.

The ground-state structural and electronic properties of ferroelectric $\mathrm{Bi}\mathrm{Fe}{\mathrm{O}}_{3}$ are calculated using density functional theory within the local spin-density approximation (LSDA) $\mathrm{LSDA}+U$ method. crystal structure is computed to be rhombohedral with space group $R3c$, found insulating antiferromagnetic, both in excellent agreement available experiments. A large polarization...

Most of recent research on layered chalcogenides is understandably focused single atomic layers. However, it unclear if single-layer units are the most ideal structures for enhanced gas-solid interactions. To probe this issue further, we have prepared large-area MoS2 sheets ranging from to multiple layers 300 nm SiO2/Si substrates using micromechanical exfoliation method. The thickness and layering were identified by optical microscope, invoking recently reported specific color contrast,...

Strong electron-phonon interaction which limits electronic mobility of semiconductors can also have significant effects on phonon frequencies. The latter is the key to use Raman spectroscopy for nondestructive characterization doping in graphene-based devices. Using in-situ scattering from single layer MoS$_2$ electrochemically top-gated field effect transistor (FET), we show softening and broadening A$_{1g}$ with electron whereas other active E$_{2g}^{1}$ mode remains essentially inert....

Enthused by the fascinating properties of graphene, we have prepared graphene analogues BN a chemical method with control on number layers. The involves reaction boric acid urea, wherein relative proportions two been varied over wide range. Synthesis high proportion urea yields product majority 1−4 surface area increases progressively decreasing layers, and exhibits CO2 adsorption, but negligible H2 adsorption. Few-layer has solubilized interaction Lewis bases. We used first-principles...

Ordering up better conductivity Improving a thermoelectric material's ability to convert heat electricity involves optimizing one property without changing another in detrimental way. Roychowdhury et al. found that cadmium doping of silver antimony telluride enhances cationic ordering, which simultaneously improves electric properties and helpfully decreases thermal (see the Perspective by Liu Ibáñez). This strategy markedly could be used for other materials. Science , this issue p. 722 ;...

The introduction of ferromagnetic order in ZnO results a transparent piezoelectric ferromagnet and further expands its already wide range applications into the emerging field spintronics. Through an analysis density functional calculations we determine nature magnetic interactions for transition metals doped develop physical picture based on hybridization, superexchange, double exchange that captures chemical trends. We identify crucial role defects observed weak preparation sensitive...

The full phonon dispersion relations of lead titanate and zirconate in the cubic perovskite structure are computed using first-principles variational density-functional perturbation theory, with ab initio pseudopotentials a plane-wave basis set. Comparison results previously obtained for barium shows that change single constituent (Ba to Pb, Ti Zr) has profound effects on character unstable modes, significant implications nature phase transitions dielectric piezoelectric responses compounds....

SnTe, a lead-free rock-salt analogue of PbTe, having valence band structure similar to recently has attracted attention for thermoelectric heat electricity generation. However, pristine SnTe is poor material because very high hole concentration resulting from intrinsic Sn vacancies, which give rise low Seebeck coefficient and electrical thermal conductivity. In this report, we show that can be optimized performance power generation by controlling the significantly improving coefficient. Mg...

We report magnetic, dielectric, and magnetodielectric responses of the pure monoclinic bulk phase partially disordered ${\mathrm{La}}_{2}{\mathrm{NiMnO}}_{6}$, exhibiting a spectrum unusual properties establish that this compound is an intrinsically multiglass system with large coupling (8%--20%) over wide range temperatures (150--300 K). Specifically, our results unique way to obtain colossal magnetodielectricity, independent any striction effects, by engineering asymmetric hopping...

Using a combination of Landau theoretical analysis and first-principles calculations, we establish spontaneous symmetry breaking the metallic state 1T monolayer MoS2 that opens up band gap leads to an unexpected yet robust ferroelectricity with ordering electric dipoles perpendicular its plane. Central properties this thinnest known ferroelectric is strong coupling conducting states valley phonons induce effective field. The current in semiconducting 1T-MoS2 channel can, thus, be controlled...

We predict the occurrence of large ferroelectric polarization and piezoelectricity in hypothetical perovskite-structure oxides, bismuth aluminate (BiAlO3) gallate (BiGaO3), using density functional theory within local approximation. show that BiGaO3 will have a similar structure to PbTiO3, although with much stronger tetragonal distortion therefore improved properties. Likewise, BiAlO3 shares structural characteristics antiferrodistortive PbZrO3, but it is also polarization. Therefore, we...

The atomic-scale structure of hafnium oxide explains ferroelectric properties for very thin films.

Abstract We report the temperature‐dependent Raman spectra of single‐ and few‐layer MoSe 2 WSe in range 77–700 K. observed linear variation peak positions widths bands arising from contributions anharmonicity thermal expansion. After characterization using atomic force microscopy high‐resolution transmission electron microscopy, temperature coefficients modes were determined. Interestingly, coefficient A 2u mode is larger than that 1g mode, latter being much smaller corresponding same...

Abstract The d-band center model of Hammer and Nørskov is widely used in understanding predicting catalytic activity on transition metal (TM) surfaces. Here, we demonstrate that this inadequate for capturing the complete magnetically polarized TM surfaces propose its generalization. We validate generalized through comparison adsorption energies NH 3 molecule 3d TMs (V, Cr, Mn, Fe, Co, Ni, Cu Zn) determined with spin-polarized density functional theory (DFT)-based methods predictions our...

Based on earlier results the photocatalytic properties of MoS2, 1T form MoSe2, prepared by lithium intercalation and exfoliation bulk has been employed for visible-light induced generation hydrogen. 1T-MoSe2 is found to be superior both 2H MoS2 as well 2H-MoSe2 in producing hydrogen from water, yield being 60–75 mmol h−1 g−1 range with a turn over frequency 15–19 h−1. First principles calculations reveal that lower work function than 2H-MoS2, making it easier transfer an electron production H2.

Birch reduction of few-layer graphene samples gives rise to hydrogenated containing up 5 wt % hydrogen. Spectroscopic studies reveal the presence sp 3 C-H bonds in graphenes. They, however, decompose readily on heating 500 °C or irradiation with UV laser radiation releasing all hydrogen, thereby demonstrating possible use for chemical storage First-principles calculations throw light mechanism dehydrogenation that appears involve a significant reconstruction and relaxation lattice.

Unprecedented adsorption of chlorpyrifos (CP), endosulfan (ES), and malathion (ML) onto graphene oxide (GO) reduced (RGO) from water is reported. The observed capacities CP, ES, ML are as high ~1200, 1100, 800 mg g(-1) , respectively. Adsorption found to be insensitive pH or background ions. adsorbent reusable can applied in the field with suitable modifications. A first-principles pseudopotential-based density functional analysis graphene-water-pesticide interactions showed that mediated...

Understanding the basis of electronic transport and developing ideas to improve thermoelectric power factor are essential for production efficient materials. Here, we report a significantly large ∼31.4 μW/cm·K2 at 856 K in Ag In co-doped SnTe (i.e., SnAgxInxTe1+2x). This is highest so far reported SnTe-based material, which arises from synergistic effects on structure improved electrical properties SnTe. play different but complementary roles modifying valence band In-doping introduces...

We use a combination of first-principles density functional theoretical analysis and experimental characterization to understand the lattice dynamics, dielectric ferroelectric properties lead-free relaxor Na0.5Bi0.5TiO3 (NBT) system. Vibrational spectrum determined through our calculations agrees well with observed Raman spectrum, allows assignment symmetry labels modes. The calculated Born effective charges reveal (a) two distinct types Ti ions at B-site anomalous dynamical differing by up...

We report superior hydrogen evolution activity of metal-free borocarbonitride (BCN) catalysts.