Sluggish Transition Research Articles

Carbon Nanotube Supported Fluorine Substituted Iron Phthalocyanine Enabling Boosted Polysulfide Redox Conversion Kinetics and Cyclic Stability.

The sluggish transition and shuttle of polysulfides (LiPS) significantly hinder the application and commercialization of Li-S batteries. Herein, carbon nanotubes (CNTs) supported 10 nm sized iron Hexadecafluorophthalocyanine (FePcF16/CNTs) are prepared using a solid synthesis approach. The well-exposed FePcF16 molecular improve the LiPS capture efficiency and redox kinetics by its central Fe-N4 units and F functional groups. The strong electron withdraw F groups significantly promote the conjugate effect and decrease the steric hindrance during mass migration procedure. Distribution of relaxation time (DRT) analysis shows that the Fe-N4 units exhibit strong affinity towards LiPS and the F groups further improve the Li+ diffusion rate in Li2S nucleation and oxidation procedure, accomplishing a porous surface on cathode. As a result, the FePcF16/CNTs separator exhibits a high initial capacity of 1136.2 mAh g-1 at 0.2 C, outstanding rate capacity of 624.9 mAh g-1 at 5 C and superior long-term stability at 2 C surviving 300 cycles with a low capacity decay of 0.43 ‰ per cycle.

Inert structural transition in 4H and 6H SiC at high pressure and temperature: a Raman spectroscopy study

We conducted Raman spectroscopy measurements of 4H-SiC and 6H-SiC up to 69 GPa and 1023 K to assess the stability and bonding of SiC at high pressure and temperature. Both optic and acoustic modes were observed at wide pressure and temperature ranges. The temperature shifts of the Raman frequencies were fitted by the equation with the Bose–Einstein distribution function, and we found that the shifts were almost insensitive to the pressure. The mode Grüneisen coefficients weakly depend on the pressure and temperature, suggesting the sluggish transition of the crystal structure, unlike the previous experiments showing the transition or decomposition of SiC at high pressure and temperature conditions. Inert transitions are confirmed by Raman measurements and annealing experiments using multiple high-pressure apparatuses. The crystallinity may be a hidden critical parameter in the experiments to determine the stable polytypes of SiC under high pressure and temperature.

Theoretical and experimental investigations of vanadium pentoxide–based electrocatalysts for the hydrogen evolution reaction in alkaline media

A key approach towards better realization of intermittent renewable energy resources, namely, solar and wind, is green electrochemical hydrogen production from water electrolysis. In recent years, there have been increasing efforts aimed at developing noble metal-free electrocatalysts that are earth-abundant and electroactive towards hydrogen evolution reaction (HER) in alkaline electrolytes, wherein an initial water dissociation step is followed by a two-electron transfer cathodic reaction. Although relatively earth-abundant, vanadium-based electrocatalysts have been sparsely reported due to subpar electroactivity and kinetics towards water electrolysis in general and alkaline electrolysis in specific. Herein, we investigate the fine-tuning of orthorhombic V2O5-based electrocatalysts as candidates for HER through a scalable two-step sol–gel calcination procedure. Briefly, surface-induced anionic oxygen deficiencies and cationic dopants are synergistically studied experimentally and theoretically. To that end, first-principle facet-dependent density function theory (DFT) calculations were conducted and revealed that the coupling of certain dopants on V2O5 and co-induction of oxygen vacancies can enhance the catalytic HER performance by the creation of new electronic states near the Fermi level (EF), enhancing conductivity, and modulating surface binding of adsorbed protons, respectively. This was reflected experimentally through kinetically non-ideal alkaline electrochemical HER using Zn0.4V1.6O5 whereby − 194 mV of overpotential was required to attain − 10 mA/cm2 of current density, as opposed to pristine V2O5 which required 32% higher overpotential requirement at the same conditions. The disclosed work can be extended to other intrinsically sluggish transition metal (TM)–based oxides via the presented systematic tuning of surface and bulk microenvironment modulation.Graphical

Structural transitions at high pressure and metastable phase in Si0.8Ge0.2

The high-pressure behaviour of Si0.8Ge0.2 alloy is explored using in situ Raman spectroscopy, X-ray diffraction techniques and density functional theory (DFT) simulations. High pressure experiments revealed a pressure-induced transition from the stable cubic semiconducting phase (dc- Si0.8Ge0.2) to the tetragonal β-tin metallic phase (β-Si0.8Ge0.2) during compression. This sluggish transition is significantly accelerated at moderate temperature (<300 °C). Upon decompression, successive transitions towards metastable phases are observed. A first transition from the metallic β-Si0.8Ge0.2 toward the rhombohedral r8-Si0.8Ge0.2 phase is observed at 10.3 GPa followed by a partial transition to the body-centered cubic bc8-Si0.8Ge0.2 phase at 2.2 GPa. After releasing the pressure, r8 and bc8 phases coexist at ambient conditions. This transition pathway is similar to that followed by pure silicon and is consistent with the ab initio enthalpy calculations. This phase transition sequence is confirmed by in situ Raman spectroscopy, where signatures of r8 and bc8 phases are observed in the Raman spectra at decompression. An ab initio simulation method is proposed to assign the Raman spectrum of Si0.8Ge0.2 alloy using group theory and projection operators. The exploration of metastable states in these alloys is of major interest both in terms of applications (e.g. optoelectronics) and from a fundamental point of view to better understand the effects of alloying on the physical properties (e.g. vibrational).

A New Approach Determining a Phase Transition Boundary Strictly Following a Definition of Phase Equilibrium: An Example of the Post-Spinel Transition in Mg2SiO4 System

The Clapeyron slope is the slope of a phase boundary in P–T space and is essential for understanding mantle dynamics and evolution. The phase boundary is delineating instead of balancing a phase transition’s normal and reverse reactions. Many previous high pressure–temperature experiments determining the phase boundaries of major mantle minerals experienced severe problems due to instantaneous pressure increase by thermal pressure, pressure drop during heating, and sluggish transition kinetics. These complex pressure changes underestimate the transition pressure, while the sluggish kinetics require excess pressures to initiate or proceed with the transition, misinterpreting the phase stability and preventing tight bracketing of the phase boundary. Our recent study developed a novel approach to strictly determine phase stability based on the phase equilibrium definition. Here, we explain the details of this technique, using the post-spinel transition in Mg2SiO4 determined by our recent work as an example. An essential technique is to observe the change in X-ray diffraction intensity between ringwoodite and bridgmanite + periclase during the spontaneous pressure drop at a constant temperature and press load with the coexistence of both phases. This observation removes the complicated pressure change upon heating and kinetic problem, providing an accurate and precise phase boundary.

Phase behaviour of ammonium bromide-d 4 under high pressure and low temperature; an average and local structure study

We revisit the pressure-induced order–disorder transition between phases II and IV in ammonium bromide-d 4 using neutron diffraction measurements to characterise both the average and local structures. We identify a very sluggish transition that does not proceed to full conversion and local structure correlations indicate a slight preference for ammonium cation ordering along ⟨110⟩ crystallographic directions, as pressure is increased. Simultaneous cooling below ambient temperature appears to facilitate the pressure-induced transition. Variable-temperature, ambient-pressure measurements across the IV → III → II transitions show slower conversion than previously observed, and that phase III exhibits metastability above ambient temperature.

Influence of Polymorphism on the Electrochemical Behavior of Dilithium (2,3-Dilithium-oxy)-terephthalate vs. Li

Organic electrode materials offer obvious opportunities to promote cost-effective and environmentally friendly rechargeable batteries. Over the last decade, tremendous progress has been made thanks to the use of molecular engineering focused on the tailoring of redox-active organic moieties. However, the electrochemical performance of organic host structures relies also on the crystal packing, like the inorganic counterparts, which calls for further efforts in terms of crystal chemistry to make a robust redox-active organic center electrochemically efficient in the solid state. Following our ongoing research aiming at elaborating lithiated organic cathode materials, we report herein on the impact of polymorphism on the electrochemical behavior of dilithium (2,3-dilithium-oxy-)terephthalate vs. Li. Having isolated dilithium (3-hydroxy-2-lithium-oxy)terephthalate through an incomplete acid-base neutralization reaction, its subsequent thermally induced decarboxylation mechanism led to the formation of a new polymorph of dilithium (2,3-dilithium-oxy-)terephthalate referred to as Li4-o-DHT (β-phase). This new phase is able to operate at 3.1 V vs. Li+/Li, which corresponds to a positive potential shift of +250 mV compared to the other polymorph formerly reported. Nevertheless, the overall electrochemical process characterized by a sluggish biphasic transition is impeded by a large polarization value limiting the recovered capacity upon cycling.

Spin-glass behavior and magnetocaloric properties of high-entropy perovskite oxides

The high-entropy concept has been recently proposed to be a promising paradigm to enhance the magnetocaloric properties of materials. Motivated by this, the magnetic properties and the magnetocaloric performance of two high-entropy perovskites (Dy1/4Ho1/4Er1/4Tb1/4)FeO3 and (Gd1/5Dy1/5Ho1/5Er1/5Tb1/5)FeO3 have been investigated. The magnetic measurements indicate that a spin-glass phase occurs at low temperatures in the high-entropy compounds, which is induced by the strong compositional disorder of rare-earth sublattice. The glassy state can lead to a sluggish magnetic transition and consequently a potential improvement in the magnetocaloric performance. Due to the increase in configurational entropy, large refrigerant capacity of 247 and 203 J/kg for a magnetic field change of 70 kOe is obtained in the (Gd1/5Dy1/5Ho1/5Er1/5Tb1/5)FeO3 and (Dy1/4Ho1/4Er1/4Tb1/4)FeO3 compounds, respectively. Our findings highlight the availability of spin order control through tuning the configurational entropy and demonstrate the key role of high-entropy design in enhancing the magnetocaloric properties of materials.

Schizophrenia induces abnormal frequency-dependent patterns of dynamic brain network reconfiguration during an auditory oddball task

Objective. Schizophrenia is a psychiatric disorder that has been shown to disturb the dynamic top-down processing of sensory information. Various imaging techniques have revealed abnormalities in brain activity associated with this disorder, both locally and between cerebral regions. However, there is increasing interest in investigating dynamic network response to novel and relevant events at the network level during an attention-demanding task with high-temporal-resolution techniques. The aim of the work was: (i) to test the capacity of a novel algorithm to detect recurrent brain meta-states from auditory oddball task recordings; and (ii) to evaluate how the dynamic activation and behavior of the aforementioned meta-states were altered in schizophrenia, since it has been shown to impair top-down processing of sensory information. Approach. A novel unsupervised method for the detection of brain meta-states based on recurrence plots and community detection algorithms, previously tested on resting-state data, was used on auditory oddball task recordings. Brain meta-states and several properties related to their activation during target trials in the task were extracted from electroencephalography data from patients with schizophrenia and cognitively healthy controls. Main results. The methodology successfully detected meta-states during an auditory oddball task, and they appeared to show both frequency-dependent time-locked and non-time-locked activity with respect to the stimulus onset. Moreover, patients with schizophrenia displayed higher network diversity, and showed more sluggish meta-state transitions, reflected in increased dwell times, less complex meta-state sequences, decreased meta-state space speed, and abnormal ratio of negative meta-state correlations. Significance. Abnormal cognition in schizophrenia is also reflected in decreased brain flexibility at the dynamic network level, which may hamper top-down processing, possibly indicating impaired decision-making linked to dysfunctional predictive coding. Moreover, the results showed the ability of the methodology to find meaningful and task-relevant changes in dynamic connectivity and pathology-related group differences.

Pressure-Induced Insulator–Metal Transition in Two-Dimensional Mott Insulator NiPS3

The pressure-induced insulator to metal transition (IMT) of layered magnetic nickel phosphorous tri-sulfide NiPS3 was studied in-situ under quasi-uniaxial conditions by means of electrical resistance (R) and X-ray diffraction (XRD) measurements. This sluggish transition is shown to occur at 35 GPa. Transport measurements show no evidence of superconductivity to the lowest measured temperature (~ 2 K). The structure results presented here differ from earlier in-situ work that subjected the sample to a different pressure state, suggesting that in NiPS3 the phase stability fields are highly dependent on strain. It is suggested that careful control of the strain is essential when studying the electronic and magnetic properties of layered van der Waals solids.

Globalization, Trade Imbalances and Labor Market Adjustment

&amp;amp;lt;ns2:p&amp;amp;gt;We study the role of global trade imbalances in shaping the adjustment dynamics in response to trade shocks. We build and estimate a general equilibrium, multi-country, multi-sector model of trade with two key ingredients: (a) Consumption-saving decisions in each country commanded by representative households, leading to endogenous trade imbalances; (b) labor market frictions across and within sectors, leading to unemployment dynamics and sluggish transitions to shocks. We use the estimated model to study the behavior of labor markets in response to globalization shocks, including shocks to technology, trade costs, and inter-temporal preferences (savings gluts). We find that modeling trade imbalances changes both qualitatively and quantitatively the short- and long-run implications of globalization shocks for labor reallocation and unemployment dynamics. In a series of empirical applications, we study the labor market effects of shocks accrued to the global economy, their implications for the gains from trade, and we revisit the "China Shock" through the lens of our model. We show that the US enjoys a 2.2 percent gain in response to globalization shocks. These gains would have been 73 percent larger in the absence of the global savings glut, but they would have been 40 percent smaller in a balanced-trade world.&amp;amp;lt;/ns2:p&amp;amp;gt;

Selective Adsorption and Electrocatalysis of Polysulfides through Hexatomic Nickel Clusters Embedded in N-Doped Graphene toward High-Performance Li-S Batteries.

The shuttle effect hinders the practical application of lithium-sulfur (Li-S) batteries due to the poor affinity between a substrate and Li polysulfides (LiPSs) and the sluggish transition of soluble LiPSs to insoluble Li2S or elemental S. Here, we report that Ni hexatomic clusters embedded in a nitrogen-doped three-dimensional (3D) graphene framework (Ni-N/G) possess stronger interaction with soluble polysulfides than that with insoluble polysulfides. The synthetic electrocatalyst deployed in the sulfur cathode plays a multifunctional role: (i) selectively adsorbing the polysulfides dissolved in the electrolyte, (ii) expediting the sluggish liquid-solid phase transformations at the active sites as electrocatalysts, and (iii) accelerating the kinetics of the electrochemical reaction of multielectron sulfur, thereby inhibiting the dissolution of LiPSs. The constructed S@Ni-N/G cathode delivers an areal capacity of 9.43 mAh cm−2 at 0.1 C at S loading of 6.8 mg cm−2, and it exhibits a gravimetric capacity of 1104 mAh g−1 with a capacity fading rate of 0.045% per cycle over 50 cycles at 0.2 C at S loading of 2.0 mg cm−2. This work opens a rational approach to achieve the selective adsorption and expediting of polysulfide transition for the performance enhancement of Li-S batteries.

The impact of Bi3+ substitution for Y3+ cation on structural, topographical, electrical and thermal behaviour of YFeO3

Bismuth Substituted Yttrium orthoferrite nano powders have been prepared by Sol-Gel route by setting the pH value at 9 on pH scale. The room temperature X-ray diffraction patterns confirm the single-phase orthorhombic symmetry with space group Pnma. The Rietveld Refinement fitting through FullProf program provided various geometrical and lattice parameters with moderate value of χ2 and GOF. The particle size (D) has been measured using Scherrer and Williamson Hall methods. 2 and 3-Dimensional surface morphology have been measured using atomic force microscopy (AFM) which also supports the particle size to be of the order of nano meter size. The thermal behaviour has been studied using DTA-TGA techniques in the temperature range from RT to 1223 K which shows sluggish transition near Neel Temperature (644 K) in heating as well as in cooling cycle. These sluggish transitions were also verified using MDSC measurement technique in the temperature range from RT to 773 K which is coherent with DTA curve and clarifying the magnetic transition. The activation energies have been calculated from DC conductivity measurement which lie in the semiconducting zone. The response of current with voltage (I–V characteristics) reflects almost Ohmic nature of the prepared samples. The results are discussed in detail.

Long-Range Antiferromagnetic Order in a Rocksalt High Entropy Oxide

We report for the first time the magnetic structure of the high entropy oxide (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)O using neutron powder diffraction. This material exhibits a sluggish magnetic transition but possesses a long-range ordered antiferromagnetic ground state, as revealed by direct current and alternating current magnetic susceptibility, neutron diffraction, and spectroscopy. The magnetic propagation wavevector is k = (1/2, 1/2, 1/2) based on the cubic structure Fm3̅m, and the magnetic structure consists of ferromagnetic sheets in the (111) planes with spins antiparallel between two neighboring planes. Neutron spectroscopy reveals strong magnetic excitations at 100 K that survive up to room temperature. This work demonstrates that entropy-stabilized oxides represent a unique platform to study long-range magnetic order with an extreme chemical disorder.

Aberrant cortical excitability reflects the loss of hand dexterity in musician's dystonia.

Dystonia is a movement disorder characterized by abnormalities at multifaceted aspects of motor dexterity and neural functions. Evidence bridging between pathophysiology and movement abnormalities is limited. A novel finding was that in focal task-specific dystonia (FTSD), an aberrantly reduced inhibition at the motor cortex was related to the temporal imprecision of the dexterous finger movements, whereas an elevated facilitation was associated with an abnormally sluggish transition of finger movements from flexion to extension. We newly identified two sets of behavioural-physiological covariations as hallmarks of hand FTSD, which is clinically significant because these findings provide novel evidence connecting distinct types of malfunctions within the motor cortex at rest with distinct aspects of motor dexterity degradation in FTSD patients. Focal task-specific dystonia (FTSD) compromises dexterous movements. A proposed pathophysiological mechanism of FTSD involves malfunction of the motor cortex (M1). However, no evidence is yet available regarding whether and how malfunctions of M1 are responsible for the loss of motor dexterity. Here, we addressed this issue by assessing both M1 excitability and detailed movement parameters, as well as their relationships. Transcranial magnetic stimulation was applied over M1 in 20 pianists with FTSD, 20 healthy pianists and 20 non-musicians. The patients demonstrated both reduced short-interval intracortical inhibition (SICI) and elevated intracortical facilitation (ICF) compared with the healthy controls. This indicates that the abnormal cortical excitability reflects pathophysiology but not current skills. Hand motor dexterity was evaluated by position sensors during piano playing at two tempi. The patients showed delayed transition from finger flexion to extension at the fastest tempo and greater timing variability of the finger movements. Furthermore, multivariate analyses identified distinct sets of covariation between cortical excitability and dexterity measures. Namely, the SICI measure and ICF measure were associated with the temporal variability of the movements and the quickness of the transition from flexion to extension, respectively. Specifically, the reduced inhibition and elevated facilitation at M1 in pianists was related to the temporal imprecision and impairment of quick transitions in the sequential finger movements. The present study provides novel evidence associating M1 malfunctions with dexterity loss.

Interstitial effects of B addition on the metamagnetic transition and magnetocaloric effect in tetragonal Cu2Sb-type Mn1.95Cu0.05Sb alloys

Mn1.95Cu0.05SbBx (x = 0, 0.06 and 0.1) alloys had been prepared and B interstitial effects on metamagnetic transition were studied. The metamagnetic transition temperature was reduced and thermal hysteresis was widened by higher B concentration. The saturation magnetization and the magnetic entropy change were increased by moderate amount of B addition. However, too high B composition led into the sluggish metamagnetic transition. By relating with crystallographic structure, our results further indicated that the electron density of the atoms at MnⅡ position plays critical role on influencing the metamagnetic transition in tetragonal Cu2Sb-type Mn1.95Cu0.05Sb alloys.

A Critical Sociology’s New Question in an Age of Sluggish Economy and Industrial Transition

A Critical Sociology’s New Question in an Age of Sluggish Economy and Industrial Transition

Deviatoric stress-induced phase transitions in diamantane.

The high-pressure behavior of diamantane was investigated using angle-dispersive synchrotron x-ray diffraction (XRD) and Raman spectroscopy in diamond anvil cells. Our experiments revealed that the structural transitions in diamantane were extremely sensitive to deviatoric stress. Under non-hydrostatic conditions, diamantane underwent a cubic (space group Pa3) to a monoclinic phase transition at below 0.15 GPa, the lowest pressure we were able to measure. Upon further compression to 3.5 GPa, this monoclinic phase transformed into another high-pressure monoclinic phase which persisted to 32 GPa, the highest pressure studied in our experiments. However, under more hydrostatic conditions using silicone oil as a pressure medium, the transition pressure to the first high-pressure monoclinic phase was elevated to 7-10 GPa, which coincided with the hydrostatic limit of silicone oil. In another experiment using helium as a pressure medium, no phase transitions were observed to the highest pressure we reached (13 GPa). In addition, large hysteresis and sluggish transition kinetics were observed upon decompression. Over the pressure range where phase transitions were confirmed by XRD, only continuous changes in the Raman spectra were observed. This suggests that these phase transitions are associated with unit cell distortions and modifications in molecular packing rather than the formation of new carbon-carbon bonds under pressure.

Polymorphism in Li2MSiO4 (M = Fe, Mn): A Variable Temperature Diffraction Study

AbstractLithium transition metal silicates, Li2MSiO4 (M = Fe, Mn, Co), have attracted much interest as positive electrodes for Li‐ion batteries due to their high theoretical capacities and their rich crystal chemistry. Low (β) and high (γ) temperature forms of these tetrahedral structures differ in the ordering/distribution of cations within tetrahedral sites of an hcp based packing of oxygen. We have carried out VT powder neutron and X‐ray diffraction on Li2MSiO4 (M = Fe, Mn) to characterize the rich polymorphism observed across the Li2MSiO4 (M = Fe, Mn) system as a function of temperature. For Li2FeSiO4 below 500 °C a βII phase was observed with slight Li/Fe disorder. Above this temperature there was a sluggish transition to the γs phase, which was observed up to ca. 820 °C, with the γII polymorph seen at highest temperatures. Excellent agreement with phases obtained by quenching was observed, except that the γ phases exhibit a statistical distribution of Li/Fe, in contrast to the well‐ordered structures of quenched phases. The Li2MnSiO4 polymorphism is less complex, the βII phase is stable from room temperature to 750 °C, at which temperature it transforms to the γ structure with disordered Li/Mn.

Scale-Invariant Locomotor Activity Patterns in Children with SAD

Seasonal Affective Disorder (SAD) is a recurring mood disorder with symptoms of fatigue and diminished energy. A prominent characteristic of patients with SAD is disturbance in circadian and hemi-circadian rhythms. The purpose of this study is to investigate whether there are alterations in fluctuations within shorter time scales. Locomotor activity has scale invariant characteristics within a range of minutes and previous studies found alterations in these parameters for psychiatric disorders. In this study, we investigated the scale-invariant features of actigraph recordings of children with SAD. Fourteen children with SAD (11.0±3.3 years) and 12 age matched healthy controls (11.6±3.7 years) were recruited for the study. Wavelet analysis was used to calculate the scaling exponent of daytime and night-time activities. Scaling exponents for periods with higher (maxima) and lower levels (minima) of activities were calculated separately. Children with SAD had larger scaling exponents compared to controls during daytime for periods with higher and lower activities (daytime maxima: p<0.01, minima p<0.05). This means that healthy controls have more abrupt activity bursts and dips while children with SAD have more sluggish transitions in their activity levels. These findings were consistent in night-time activities.