Pristine Crystal Research Articles

Structurally modified CuFe2O4/persulfate process for acetaminophen scavenging: high efficiency with low catalyst addition

AbstractBACKGROUNDIron (Fe)–copper (Cu) bimetallic catalysts such as CuFe2O4, CuFeO2 and CuO/Fe3O4 have been widely applied in persulfate oxidization process. Among these catalysts, CuFe2O4 has shown excellent performance in catalyzing peroxymonosulfate. However, because the catalytic effect of CuFe2O4 on persulfate (PS) is not obvious, the application of CuFe2O4 to activate persulfate has been investigated only rarely. Hence, structural modification has been applied in order to improve the catalytic activity of CuFe2O4 on persulfate.RESULTIn this study, Oxygen (O)‐deficient CuFe2O4 was synthesized via the hydrogen reduction method and first used to activate PS for degrading acetaminophen (APAP) in aqueous solution with low catalyst concentration of 0.3 g L−1. Results reveal that high‐concentration APAP (100 mg L−1) could be efficiently removed by O‐deficient CuFe2O4‐activated PS, and 91% removal rate could be reached in 60 min using 0.8 g L−1 PS and 0.3 g L−1 catalyst under unadjusted pH. Dissolved O2 and Cl−showed inhibitory effects on the degradation process. Radical scavenger experiments, in which methanol, tert‐butyl alcohol (TBA) and nitrobenzene (NB) were used as radical trappers, indicated that SO4− and OH were the active radicals in the reaction, but the main radical was SO4−. Oxygen‐deficient CuFe2O4 showed strong reduction ability and could activate PS efficiently, and the electron transfer capability was remarkably enhanced after this structural modification.CONCLUSIONSResults indicated that compared to the pristine crystal, the catalytic activity of CuFe2O4 could be improved through structural modification. Additionally, the structurally modified catalyst showed high potential to treat wastewater with high antibiotic content under mild conditions. © 2018 Society of Chemical Industry

On the presence of antisite defect in monoclinic Li2FeSiO4 – A combined X-Ray diffraction and DFT study

Li2FeSiO4 material, which was prepared by a solid state method, crystallized as monoclinic P21/n polymorph. X-ray diffraction analysis with Rietveld structural refinement indicates specific occupation of Li2 crystallographic site by Fe2+ cation in the amount of 6 atom percents as a result of an antisite defect formation. The exclusive occupation of Li2 position, out of two crystallographic positions Li1 and Li2, by Fe2+ was discussed in relation to the differences that exist in the crystal environment of these positions and further investigated by DFT calculations. It was confirmed that Fe-Li2 substitution is energetically favorable compared to both Fe-Li1 substitution and the pristine crystal. In addition, changes of lattice geometry upon antisite defect formation were analyzed, and the obtained result is discussed in light of various factors (electronic, geometrical and enthropic) that contribute to the overall stability of the system.

Extreme Energy Density Confined Inside a Transparent Crystal: Status and Perspectives of Solid-Plasma-Solid Transformations

It was demonstrated during the past decade that an ultra-short intense laser pulse tightly-focused deep inside a transparent dielectric generates an energy density in excess of several MJ/cm. Such an energy concentration with extremely high heating and fast quenching rates leads to unusual solid-plasma-solid transformation paths, overcoming kinetic barriers to the formation of previously unknown high-pressure material phases, which are preserved in the surrounding pristine crystal. These results were obtained with a pulse of a Gaussian shape in space and in time. Recently, it has been shown that the Bessel-shaped pulse could transform a much larger amount of material and allegedly create even higher energy density than what was achieved with the Gaussian beam (GB) pulses. Here, we present a succinct review of previous results and discuss the possible routes for achieving higher energy density employing the Bessel beam (BB) pulses and take advantage of their unique properties.

High-Field Magneto-Conductivity Analysis of Bi2Se3 Single Crystal

We report the high field (up to 14Tesla) magneto-conductivity analysis of Bi2Se3 topological insulator grown via the self flux method. The detailed experimental investigations including crystal growth as well as the electrical, thermal and spectroscopic characterizations of the resultant Bi2Se3 single crystal are already reported by some of us. The current letter deals with high field magneto-conductivity analysis in terms of Hikami Larkin Nagaoka (HLN) model, which revealed that the electronic conduction is dominated by both surface states driven weak anti localization (WAL), as well the bulk WL (weak localization) states. Further, by applying the HLN equation we have extracted the fitting parameters i.e., phase coherence length and the pre-factor. The HLN equation exhibited values of [pre factor close to -1.0, indicating both WAL and WL contributions. On the other hand, the extracted phase coherence length is seen to decrease from 11.125 nm to 5.576 nm as the temperature is increased from 5K to 200K respectively. Summarily, the short letter discusses primarily the temperature dependent magneto-conductivity analysis of pristine Bi2Se3 single crystal by the HLN model.

Patching of Lattice Defects in Two-Dimensional Diffusion Barriers

Two-dimensional crystals offer promise as diffusion barriers that can also facilitate electronic conduction through the barrier plane via tunneling. We present barriers in which crystal imperfections are patched, leaving the pristine regions of the crystal exposed and able to both prevent diffusion and allow electronic conduction. This is accomplished by atomic layer deposition, where nucleation of patch material is inhibited on the pristine crystal and promoted elsewhere. Demonstrations of the effectiveness of this technique are performed in the contexts of sulfur diffusion control in photovoltaic kesterite devices and oxygen diffusion control in oxide-based resistive switching devices.

Optical and electronic properties of niobium oxynitrides with various N/O ratios: insights from first-principles calculations

The electronic and optical properties of niobium oxynitride (NbON) complexes as a function of the N/O ratio were examined using the Perdew–Burke–Ernzerhof exchange–correlation functional of density functional theory. The investigated NbON complexes (i.e., pristine NbON crystal and Nb16O16N16, Nb16O15N17, Nb16O14N18, Nb16O17N15, and Nb16O18N14 super crystals) were found to be indirect bandgap semiconductors. Varying the N/O ratio reallocates the band edges, giving rise to redshifts in the absorption spectra at higher N/O ratios. Partial density of states calculations showed valence band dependency on the N 2p orbital energy, with the conduction band predominantly composed of Nb 4d states. The dielectric constant and refractive index of pristine NbON are found to be comparable to those of isostructural TaON, and varying the N/O ratio leads to a significant improvement in the optical properties of the studied systems.

Piezofluorochromism of triphenylamine-based triphenylacrylonitrile derivative with intramolecular charge transfer and aggregation-induced emission characteristics

New triphenylacrylonitrile derivative (DPPA) with triphenylamine moiety as electron donor group has been synthesized. Its emission wavelengths were strongly affected by solvent polarity, indicating intramolecular charge transfer (ICT) transitions. It was found that DPPA was almost non-emissive in tetrahydrofuran (THF), and the emission could be intensified obviously when a great amount of H2O was added, illustrating aggregation induced emission property. It is interesting that the pristine crystal of DPPA emitted green light, and the ground made its emitting color to change into orange, which could be recovered under fumed with dichloromethane (DCM) vapor. The piezofluorochromic behavior might be switched reversibly under the stimulus of external force because of crystalline-amorphous phase transformation, which could be confirmed from the results of PXRD patterns and DSC curves in different solid states. This work might open a new strategy to provide a broad perspective for the development of AIE PFC materials.

How and Why Does Helium Permeate Nonporous Arsenolite Under High Pressure?

Investigations into the helium permeation of arsenolite, the cubic, molecular arsenic(III) oxide polymorph As4 O6 , were carried out to understand how and why arsenolite helium clathrate As4 O6 ⋅2 He is formed. High-pressure synchrotron X-ray diffraction experiments on arsenolite single crystals revealed that the permeation of helium into nonporous arsenolite depends on the time for which the crystal is subjected to high pressure and on the crystal history. The single crystal was totally transformed into As4 O6 ⋅2 He within 45 h under 5 GPa. After release of the pressure, arsenolite was recovered and a repeated increase in pressure up to 3 GPa led to practically instant As4 O6 ⋅2 He formation. However, when a pristine arsenolite single crystal was quickly subjected to a pressure of 13 GPa, no helium permeation was observed at all. No neon permeation was observed in analogous experiments. Quantum mechanical computations indicate that there are no specific attractive interactions between He atoms and As4 O6 molecules at the distances observed in the As4 O6 ⋅2 He crystal structure. Detailed analysis of As4 O6 molecular structure changes has shown that the introduction of He into the arsenolite crystal lattice significantly reduces molecular deformations by decreasing the anisotropy of stress exerted on the As4 O6 molecules. This effect and the pΔV term, rather than any specific As⋅⋅⋅He binding, are the driving forces for the formation As4 O6 ⋅2 He.

Ferromagnetism in CVT grown tungsten diselenide single crystals with nickel doping

Two dimensional (2D) single crystal layered transition materials have had extensive consideration owing to their interesting magnetic properties, originating from their lattices and strong spin–orbit coupling, which make them of vital importance for spintronic applications. Herein, we present synthesis of a highly crystalline tungsten diselenide layered single crystal grown by chemical vapor transport technique and doped with nickel (Ni) to tailor its magnetic properties. The pristine WSe2 single crystal and Ni-doped crystal were characterized and analyzed for magnetic properties using both experimental and computational aspects. It was found that the magnetic behavior of the 2D layered WSe2 crystal changed from diamagnetic to ferromagnetic after Ni-doping at all tested temperatures. Moreover, first principle density functional theory (DFT) calculations further confirmed the origin of room temperature ferromagnetism of Ni-doped WSe2, where the d-orbitals of the doped Ni atom promoted the spin moment and thus largely contributed to the magnetism change in the 2D layered material.

The nanoscale effects on the morphology, microstructure and electrochemical performances of the cathodic deposited α-Ni(OH)2

In this study, α-Ni(OH)2 with controllable pristine crystal size is directly electrodeposited on a substrate of Ti wire mesh to fabricate the integrated electrode. The nanoscale effects on morphology, microstructure and electrochemical performance of the cathodic deposited α-Ni(OH)2 are studied. The results show that the morphology of α-Ni(OH)2 varies from irregular honeycomb-like nanopieces, ball-shaped particles to oval nanoplates as the cathodic deposition current density increases. The nanostructure diversity of the cathodic deposited α-Ni(OH)2 is due to the different nanosize which directly depends on the cathodic deposition current density. The electrochemical performances of the cathodic deposited α-Ni(OH)2 increase with the decrease of the pristine crystal size of α-Ni(OH)2. The oval α-Ni(OH)2 nanoplates consisting of nanosheets with a pristine crystal size of 3 ∼ 5 nm × 5 ∼ 7 nm show the ultrahigh specific capacities of ∼348 mAh g−1 and ∼312.5 mAh g−1 at charge/discharge current density of 5 A g−1 and 100 A g−1, respectively, and over 70% specific capacity still remains after 1000 cycles, while the irregular honeycomb-like α-Ni(OH)2 consisting of nanosheet with a pristine crystal size of 10 ∼ 15 nm × 15 ∼ 20 nm shows only ∼260 mAh g−1 specific capacity at 5 A g−1 and ∼150 mAh g−1 at 100 A g−1. The ultrahigh electrochemical performances are attributed to the nanoscale and the defective nanostructure of the cathodic deposited α-Ni(OH)2.

High‐Quality GaSb and GaInSb Crystals Prepared by Vertical Bridgman Method

AbstractHigh‐quality GaSb and Ga1‐xInxSb (x = 0.14) crystals were grown via the vertical Bridgman (VB) method. The lattice structure, morphology, optical, and transport properties of the GaSb and GaInSb crystals were characterized. The influence of the indium doping on the physical properties of the GaSb crystal was also investigated. The results demonstrate that the indium doping maintains the zinc‐blende lattice structure of the GaSb crystal. The segregation of indium is very low, with the radial and axial concentration variation of 2.32% and 4.84%, respectively. The indium doping significantly reduces the dislocation density down to 1.275 × 103 cm−2. The band gap of the indium‐doped GaSb is reduced to 0.549 eV, consistent with the decreased infrared transmission measured by FTIR. Surprisingly, the indium doping changes the majority carrier type of the crystal, from p‐type in the pristine GaSb crystal to n‐type in the GaInSb crystal. Compared to the GaSb crystal, the GaInSb crystal shows enhanced transport properties, with carrier mobility increased to 2.512 × 103 cm2/(V•s) and resistivity reduced to 0.521 × 10−3 ohm•cm.

Ionic Intercalation in Two-Dimensional van der Waals Materials: In Situ Characterization and Electrochemical Control of the Anisotropic Thermal Conductivity of Black Phosphorus.

Two-dimensional van der Waals materials have shown novel fundamental properties and promise for wide applications. Here, we report for the first time an experimental demonstration of the in situ characterization and highly reversible control of the anisotropic thermal conductivity of black phosphorus. We develop a novel platform based on lithium ion batteries that integrates ultrafast optical spectroscopy and electrochemical control to investigate the interactions between lithium ions and the lattices of the black phosphorus electrode. We discover a strong dependence of the thermal conductivity on battery charge states (lithium concentrations) during the discharge/charge process. The thermal conductivity of black phosphorus is reversibly tunable over a wide range of 2.45-3.86, 62.67-85.80, and 21.66-27.58 W·m-1·K-1 in the cross-plan, zigzag, and armchair directions, respectively. The modulation in thermal conductivity is attributed to phonon scattering introduced by the ionic intercalation in between the interspacing layers and shows anisotropic phonon scattering mechanism based on semiclassical model. At the fully discharged state (x ∼ 3 in LixP), a dramatic reduction of thermal conductivity by up to 6 times from that of the pristine crystal has been observed. This study provides a unique approach to explore the fundamental energy transport involving lattices and ions in the layered structures and may open up new opportunities in controlling energy transport based on novel operation mechanisms and the rational design of nanostructures.

Melamine-assisted to fabricate pure α-Fe2O3 polyhedron with high-index facet exposed as an effective photoelectrode

Introducing high-index facet into crystals is a promising way to provide additional catalytically active sites for boosting intrinsic activity. This work presents a simple one-pot annealing way to fabricate highly photoactive pristine polyhedral α-Fe2O3 single crystal, using melamine as solvent and coordination agent. The HR-TEM results realized that the as-prepared sample was enclosed by high-index {116} facet, which was always not presented in traditional hydrothermal method. The photoelectrochemical (PEC) measurements have been carried out and showed that the polyhedron samples exhibited significantly enhancement in the photocurrent density, which is nearly 28 times higher than that of the α-Fe2O3 prepared without melamine under the same conditions. Our work may guide future designs for high-index crystal facet exposed of metal oxides and suggest paths for further improvements to allow technological development and use.

Travelling-solvent floating-zone growth of the dilutely Co-doped spin-ladder compound Sr14(Cu, Co)24O41

We present here crystal growth of dilutely Co-doped spin-ladder compounds Sr14(Cu 1−x, Cox)24O41 (x = 0, 0.01, 0.03, 0.05, 0.1) using the Travelling Solvent Floating Zone (TSFZ) technique associated with an image furnace. We carried out detailed microstructure and compositional analysis. The microstructure of the frozen-in FZ revealed two bands: a lower band consisting of well-aligned single-crystalline stripes of the phase Sr14(Cu, Co)24O41 embedded in the eutectic mixture of composition SrO 18% and (Cu, Co)O 82%; and an upper band consisting of a criss-crossed pattern of these stripes. These analyses were also employed to determine the distribution coefficient of the dopants in Sr14Cu24O41. The distribution coefficient turned out to be close to 1, different from Sr2CuO3 reported previously where Co tend to accumulate in the molten zone. Direct access to the composition of the frozen-in zone eliminated any previous ambiguities associated with the composition of the peritectic point of Sr14Cu24O41; and also the eutectic point in the binary SrO–CuO phase diagram. The lattice parameters show an anisotropic variation upon Co-doping with parameters a and b increasing, c decreasing; and with an overall decrease of the unit cell volume. Magnetic susceptibility measurements were carried out on the pristine and the Co-doped crystals along the principal crystallographic axes. The spin susceptibility of the x = 0.01 crystal exhibits a strong anisotropy, which is in stark contrast with the isotropic behaviour of the pristine crystal. This anisotropy seems to arise from the intradimer exchange interaction as inferred from the anisotropy of the dimer contribution to the susceptibility of the Co-doped crystal. The Curie-tail in the magnetic susceptibility of Sr14(Cu 1−x, Cox)24O41 (x = 0, 0.01, 0.03, 0.05, 0.1) crystals (field applied parallel to the ladder) was found to scale with Co-doping – the scaling is employed to confirm a homogeneous distribution of Co in a x = 0.1 crystal boule.

Femtosecond laser-induced confined microexplosion: tool for creation high-pressure phases

ABSTRACTNew material phases formed under non-equilibrium conditions at pressures above 100 GPa and temperatures exceeding 104K, the conditions of the warm dense matter (WDM), have become accessible using micro-explosions triggered by ultra-short sub-1 ps pulses tightly focused into micro-volume with cross sections comparable with the wavelength of light. Laser-induced micro-explosions convert a material in a focal volume into a non-equilibrium disordered plasma state confined inside the bulk of pristine crystal. Ultra-high quenching rates overcome kinetic barriers to the formation of new metastable high pressure phases, which are preserved in the surrounding pristine crystal for following recovery and exploitation. Direct laser writing was used to pattern large areas by closely packed arrays of the microexplosion modified sites for structural characterisation of the minute volumes of nano-materials with transmission electron microscopy, diffraction and synchrotron X-ray diffraction. The method of ultrafast-laser induced confined microexplosion is demonstrated for modification and creation of new phases in case of bcc-Al inside sapphire, valence change of Fe-ions in olivine, formation of new tetragonal bt8 and st12 phases of silicon, Ge and O separation in GeO2 glass and molecular oxygen formation inside voids at the site of microexplosion inside glasses.

Characterization of the recovery of mechanical properties of ion-implanted diamond after thermal annealing

Due to their outstanding mechanical properties, diamond and diamond-like materials find significant technological applications ranging from well-established industrial fields (cutting tools, coatings, etc.) to more advanced mechanical devices as micro- and nano-electromechanical systems. The use of energetic ions is a powerful and versatile tool to fabricate three-dimensional micro-mechanical structures. In this context, it is of paramount importance to have an accurate knowledge of the effects of ion-induced structural damage on the mechanical properties of this material, primarily to predict potential undesired side-effects of the ion implantation process, and possibly to tailor the desired mechanical properties of the fabricated devices. We present an Atomic Force Microscopy (AFM) characterization of free-standing cantilevers in single-crystal diamond obtained by a FIB-assisted lift-off technique, which allows the determination of the Young's modulus of the diamond crystal after the MeV ion irradiation process concurrent to the fabrication of the microstructures, and subsequent thermal annealing. The AFM measurements were performed with the beam-bending technique and show that the thermal annealing process allows for an effective recovery of the mechanical properties of the pristine crystal.

Valley Hall effect in disordered monolayerMoS2from first principles

Electrons in certain two-dimensional crystals possess a pseudospin degree of freedom associated with the existence of two inequivalent valleys in the Brillouin zone. If, as in monolayer ${\mathrm{MoS}}_{2}$, inversion symmetry is broken and time-reversal symmetry is present, equal and opposite amounts of $k$-space Berry curvature accumulate in each of the two valleys. This is conveniently quantified by the integral of the Berry curvature over a single valley---the valley Hall conductivity. We generalize this definition to include contributions from disorder described with the supercell approach, by mapping (``unfolding'') the Berry curvature from the folded Brillouin zone of the disordered supercell onto the normal Brillouin zone of the pristine crystal, and then averaging over several realizations of disorder. We use this scheme to study from first principles the effect of sulfur vacancies on the valley Hall conductivity of monolayer ${\mathrm{MoS}}_{2}$. In dirty samples the intrinsic valley Hall conductivity receives gating-dependent corrections that are only weakly dependent on the impurity concentration, consistent with side-jump scattering and the unfolded Berry curvature can be interpreted as a $k$-space resolved side jump. At low impurity concentrations skew scattering dominates, leading to a divergent valley Hall conductivity in the clean limit. The implications for the recently observed photoinduced anomalous Hall effect are discussed.

Quantum Spin Liquid Emerging from Antiferromagnetic Order by Introducing Disorder.

Quantum spin liquids, which are spin versions of quantum matter, have been sought after in systems with geometrical frustration. We show that disorder drives a classical magnet into a quantum spin liquid through conducting NMR experiments on an organic Mott insulator, κ-(ET)_{2}Cu[N(CN)_{2}]Cl. Antiferromagnetic ordering in the pristine crystal, when irradiated by x rays, disappears. Spin freezing, spin gap, and critical slowing down are not observed, but gapless spin excitations emerge, suggesting a novel role of disorder that brings forth a quantum spin liquid from a classical ordered state.

Mechanofluorochromism of 1-Alkanoylaminopyrenes.

To create a new series of mechanofluorochromic materials and to elucidate the mechanism of the phenomenon of mechanofluorochromism, 1-alkanoylaminopyrenes including 1-acetylaminopyrene (AAPy), 1-octanoylaminopyrene (OAPy), and 1-stearoylaminopyren (SAPy) were prepared. It was found that these materials exhibited mechanofluorochromism with emission colors in the crystalline samples changing reversibly from bluish purple to yellowish green, which could be induced by mechanical grinding. X-ray crystal structure analysis, electronic absorption, and fluorescence spectroscopies, as well as fluorescence lifetime analysis and powder X-ray diffraction analysis of AAPy suggested that the present mechanofluorochromism was caused by developing crystal defects through grinding. Intermolecular hydrogen bonds were suggested to play an important role in the occurrence of mechanofluorochromism, suppressing the face-to-face overlapping of pyrene moieties to form excimers in the pristine crystal.

Experimental evidence of new tetragonal polymorphs of silicon formed through ultrafast laser-induced confined microexplosion.

Ordinary materials can transform into novel phases at extraordinary high pressure and temperature. The recently developed method of ultrashort laser-induced confined microexplosions initiates a non-equilibrium disordered plasma state. Ultra-high quenching rates overcome kinetic barriers to the formation of new metastable phases, which are preserved in the surrounding pristine crystal for subsequent exploitation. Here we demonstrate that confined microexplosions in silicon produce several metastable end phases. Comparison with an ab initio random structure search reveals six energetically competitive potential phases, four tetragonal and two monoclinic structures. We show the presence of bt8 and st12, which have been predicted theoretically previously, but have not been observed in nature or in laboratory experiments. In addition, the presence of the as yet unidentified silicon phase, Si-VIII and two of our other predicted tetragonal phases are highly likely within laser-affected zones. These findings may pave the way for new materials with novel and exotic properties.