Electrical Conductivities and Conduction Mechanism of Lithium-Doped High-Entropy Oxides at Different Temperature and Pressure Conditions.

Li-doped high-entropy oxides (Li-HEO) are promising electrode materials for Li-ion batteries. However, their electrical conduction in a wide range of temperatures and/or at high pressure is unknown, hindering their applications under extreme conditions. Especially, a clear understanding of the conduction mechanism is needed. In this work, we determined the carrier type of several Li-doped (MgCoNiCuZn)O semiconductor compounds and measured their electrical conduction at temperatures 79-773 K and/or at pressures up to 50 GPa. Three optical band gaps were uncovered from the UV-vis-NIR absorption measurements, unveiling the existence of defect energy levels near the valence band of p-type semiconductors. The Arrhenius-like plot of the electrical conductivity data revealed the electronic conduction in three temperature regions, i.e., the ionization region from 79 to 170 K, the extrinsic region from ∼170 to 300 K, and the intrinsic region at ≥300 K. The closeness of the determined electronic band gap and the second optical band gap suggests that the conduction electrons in the intrinsic region originate from a thermal excitation from the defect energy levels to the conduction band, which determines the electronic conductivity. It was also found that at or above room temperature, ionic conduction coexists with electronic conduction with a comparable magnitude at ambient pressure and that the intrinsic conduction mechanism also operates at high pressures. These findings provide us a fundamental understanding of the band structure and conduction mechanism of Li-HEO, which would be indispensable to their applications in new technical areas.

Questing for High-Performance Electrocatalysts for Oxygen Evolution Reaction: Importance of Chemical Complexity, Active Phase, and Surface-Adsorbed Species.

Rational design of advanced electrocatalysts for oxygen evolution reaction (OER) is of vital importance for the development of sustainable energy. Entropy engineering is emerging as a promising approach for the design of efficient OER electrocatalysts. However, other multi-anion/cation electrocatalysts with compositional complexity, particularly the medium-entropy and other non-equimolar cation/anion complex electrocatalysts, have not received noteworthy attention. In this perspective, we review and highlight the importance of compositionally complex catalysts and propose a concept of chemical complexity to correlate the OER catalytic activity with the contributions from the pairwise cation-anion interactions. Then, we offer a new view on the active catalytic sites being the hydroxylated reacting interface in an alkaline solution. Further, we argue that the common discrepancies between computationally predicted OER activities and experimental results stem from lack of considerations of surface-adsorbed species in modeling the active catalytic phases or sites. This perspective would facilitate achieving a renewed and profound understanding of the OER mechanism and promote efficient design of OER electrocatalysts for renewable energy conversion and storage.

Comprehensive investigation of pressure-induced gelatinization of starches using in situ and ex-situ technical analyses.

The pressure-induce gelatinization of pea starch, potato starch and corn starch was investigated by a combination of in situ and ex-situ technical analyses. According to in-situ observation of gelatinization process and the analysis of granular morphology by scanning electronic microscopy (SEM), the pressure that caused potato starch gelatinization was the highest at 600 MPa. This was followed by pea starch, and the pressure that caused the gelatinization of corn starch was the lowest at 400 MPa. In situ Raman spectral analysis revealed the molecular mechanism of starch gelatinization. This indicated that high pressure treatment resulted in the modification of the structure of the double helical polymers and the degree of a double helix of the starch crystalline varied as well. This study dynamically monitors the starch gelatinization process, aiming to better understand the gelatinization mechanism and provide a theoretical basis for the application of pressure in the starch field.

Expediting Oxygen Evolution by Optimizing Cation and Anion Complexity in Electrocatalysts Based on Metal Phosphorous Trichalcogenides.

Purposely changing the rate-determining step (RDS) of oxygen evolution reaction (OER) remains a major challenge for enhancing the energy efficiency of electrochemical splitting of water. Here we show that the OER RDS can be regulated by simply varying the cation and anion complexity in a family of the metal phosphorous trichalcogenide electrocatalysts (MPT3 , where M=Fe, Ni; T=S, Se), achieving an exceptionally high OER activity in (Ni,Fe)P(S,Se)3 , as demonstrated by its ultra-low Tafel slope (34 mV dec-1 ) and a very low overpotential compared to many relevant OER catalysts. This is strongly supported by density functional theory calculations, which showed that this catalyst has a nearly optimal OER activity descriptor value of ΔG(O*)-ΔG(OH*)=1.5 eV. We also found that the activity descriptor is proportional to a newly proposed cation/anion complexity index that consists of pairwise contributions from cation-anion bonds in a catalyst compound, revealing the pivotal role of the cation-anion interactions in determining the catalyst performance and providing a simple way for predicting catalytic activities.

Metallization and Superconductivity in the van der Waals Compound CuP2Se through Pressure-Tuning of the Interlayer Coupling.

Emergent layered Cu-bearing van der Waals (vdW) compounds have great potentials for use in electrocatalysis, lithium batteries, and electronic and optoelectronic devices. However, many of their alluring properties such as potential superconductivity remain unknown. In this work, using CuP2Se as a model compound, we explored its electrical transport and structural evolution at pressures up to ∼60 GPa using both experimental determinations and ab initio calculations. We found that CuP2Se undergoes a semiconductor-to-metal transition at ∼20 GPa at room temperature and a metal-to-superconductor transition at 3.3-5.7 K in the pressure range from 27.0 to 61.4 GPa. At ∼10 and 20 GPa, there are two isostructural changes in the compound, corresponding to, respectively, the emergence of the interlayer coupling and start of interlayer atomic bonding. At a pressure between 35 and 40 GPa, the vdW layers start to slide and then merge, forming a new phase with high coordination numbers. We also found that the Bardeen-Cooper-Schrieffer (BCS) theory describes quite well the pressure dependence of the critical temperature despite occurrence of a possible medium-to-strong electron-phonon coupling, revealing the determinant roles of the enhanced bulk modulus and electron density of states at high pressure. Moreover, nanosizing of CuP2Se at high pressure further increased the critical temperature even at sizes approaching the Anderson limit. These findings would have important implications for developing novel applications of layered vdW compounds through simple pressure tuning of the interlayer coupling.

Ultra-incompressible High-Entropy Diborides.

Transition metal borides are commonly hard and incompressible, offering great opportunities for advanced applications under extreme conditions. Recent studies show that the hardness of high-entropy borides may exceed that of their constituent simple borides due to the "cocktail effect". However, how high-entropy borides deform elastically remains largely unknown. Here, we show that two newly synthesized high-entropy diborides are ultra-incompressible, attaining ∼90% of the incompressibility of single-crystalline diamond and exhibiting a 50-60% enhancement over the density functional theory predictions. This unusual behavior is attributed to a Hall-Petch-like effect resulting from nanosizing under high pressure, which increases the bulk moduli through dynamic dislocation interactions and creation of stacking faults. The exceptionally low compressibility, together with their high phase stabilities, high hardness, and high electric conductance, renders them promising candidates for electromechanics and microelectronic devices that demand strong resistance to environmental impacts, in addition to traditional grinding and abrading.

Association of LDLc to HDLc ratio with carotid plaques in a community-based population with a high stroke risk: A cross-sectional study in China.

BACKGROUND AND AIMS: The association between low-density lipoprotein cholesterol (LDLc) to high-density lipoprotein cholesterol (HDLc) ratio (LDLc/HDLc) and carotid plaques remains controversial. We conducted a cross-sectional study to evaluate whether LDLc/HDLc is associated with carotid plaques in individuals with a high-stroke-risk. METHODS AND RESULTS: The study initially enrolled 5529 residents aged 40 years or older from Yangzhou, China in 2013-2014. All participants received a questionnaire interview, physical examination, and laboratory tests. Risk factors for stroke included hypertension, diabetes mellitus, dyslipidemia, atrial fibrillation, smoking, less exercise, overweight/obesity, and family stroke history. Subjects with at least three of the risk factors or a history of stroke/transient ischemic attack (TIA) were defined as a high-stroke-risk population. Carotid ultrasonography was only conducted for this high-stroke-risk population. Logistic regression was used to examine the association of LDLc/HDLc with the presence of carotid plaques. Final analysis included 839 high-stroke-risk subjects and 40.6% were identified to have carotid plaques. Subjects with the highest tertiles group of LDLc/HDLc had a higher proportion of carotid plaques than the other two groups (47.1% vs. 34.6% and 40.4%, P < 0.001). With each unit increase of LDLc/HDLc, the chance of having carotid plaques increased by 65% (OR 1.65, 95%CI 1.31-2.08) after adjusted for potential confounders. Among most subgroups, a higher LDLc/HDLc was significantly correlated with the presence of carotid plaques. CONCLUSION: Higher LDLc/HDLc was significantly associated with the presence of carotid plaques in the Chinese population with a high risk of stroke.

Relationship between the non-HDLc-to-HDLc ratio and carotid plaques in a high stroke risk population: a cross-sectional study in China.

BACKGROUND: Evidence on the association between the non-high-density lipoprotein cholesterol (non-HDLc)-to-high-density lipoprotein cholesterol (HDLc) ratio (non-HDLc/HDLc) and carotid plaques is still limited. This study aims to assess the relationship between the non-HDLc/HDLc and carotid plaques in a population with a high risk of stroke. METHODS: A cross-sectional study based on the community was conducted in Yangzhou, China. Residents (no younger than 40 years old) underwent questionnaire interviews, physical examinations, and laboratory testing during 2013-2014. The subjects with a high risk of stroke were further selected (at least three of eight risk factors including hypertension, atrial fibrillation, type 2 diabetes mellitus, dyslipidaemia, smoking, lack of exercise, overweight, and family history of stroke) or a transient ischaemic attack (TIA) or stroke history. Carotid ultrasonography was then performed on the high stroke risk participants. Carotid plaque was defined as a focal carotid intima-media thickness (cIMT) ≥1.5 cm or a discrete structure protruding into the arterial lumen at least 50% of the surrounding cIMT. Logistic regression was employed to evaluate the relationship between the non-HDLc/HDLc and carotid plaques. RESULTS: Overall, 839 subjects with a high risk of stroke were ultimately included in the analysis, and carotid plaques were identified in 341 (40.6%) of them. Participants in the highest non-HDLc/HDLc tertile group presented a higher proportion of carotid plaques than did those in the other two groups. After adjustment for other confounders, each unit increase in the non-HDLc/HDLc was significantly associated with carotid plaques (OR 1.55, 95%CI 1.28-1.88). In the subgroup analysis, the non-HDLc/HDLc was positively and significantly associated with the presence of carotid plaques in most subgroups. Additionally, the non-HDLc/HDLc interacted significantly with three stratification variables, including sex (OR 1.31 for males vs. OR 2.37 for females, P interaction = 0.016), exercise (OR 1.18 for subjects without lack of exercise vs. OR 1.99 for subjects with lack of exercise, P interaction = 0.004) and heart diseases (OR 1.40 for subjects without heart diseases vs. OR 3.12 for subjects with heart diseases, P interaction = 0.033). CONCLUSION: The non-HDLc/HDLc was positively associated with the presence of carotid plaques in a Chinese high stroke risk population. A prospective study or randomized clinical trial of lipid-lowering therapy in the Chinese population is needed to evaluate their causal relationship.

High-pressure strengthening in ultrafine-grained metals.

The Hall-Petch relationship, according to which the strength of a metal increases as the grain size decreases, has been reported to break down at a critical grain size of around 10 to 15 nanometres1,2. As the grain size decreases beyond this point, the dominant mechanism of deformation switches from a dislocation-mediated process to grain boundary sliding, leading to material softening. In one previous approach, stabilization of grain boundaries through relaxation and molybdenum segregation was used to prevent this softening effect in nickel-molybdenum alloys with grain sizes below 10 nanometres3. Here we track in situ the yield stress and deformation texturing of pure nickel samples of various average grain sizes using a diamond anvil cell coupled with radial X-ray diffraction. Our high-pressure experiments reveal continuous strengthening in samples with grain sizes from 200 nanometres down to 3 nanometres, with the strengthening enhanced (rather than reduced) at grain sizes smaller than 20 nanometres. We achieve a yield strength of approximately 4.2 gigapascals in our 3-nanometre-grain-size samples, ten times stronger than that of a commercial nickel material. A maximum flow stress of 10.2 gigapascals is obtained in nickel of grain size 3 nanometres for the pressure range studied here. We see similar patterns of compression strengthening in gold and palladium samples down to the smallest grain sizes. Simulations and transmission electron microscopy reveal that the high strength observed in nickel of grain size 3 nanometres is caused by the superposition of strengthening mechanisms: both partial and full dislocation hardening plus suppression of grain boundary plasticity. These insights contribute to the ongoing search for ultrastrong metals via materials engineering.

Large bandgap of pressurized trilayer graphene.

Graphene-based nanodevices have been developed rapidly and are now considered a strong contender for postsilicon electronics. However, one challenge facing graphene-based transistors is opening a sizable bandgap in graphene. The largest bandgap achieved so far is several hundred meV in bilayer graphene, but this value is still far below the threshold for practical applications. Through in situ electrical measurements, we observed a semiconducting character in compressed trilayer graphene by tuning the interlayer interaction with pressure. The optical absorption measurements demonstrate that an intrinsic bandgap of 2.5 ± 0.3 eV could be achieved in such a semiconducting state, and once opened could be preserved to a few GPa. The realization of wide bandgap in compressed trilayer graphene offers opportunities in carbon-based electronic devices.

Mesoporous hollow black TiO2 with controlled lattice disorder degrees for highly efficient visible-light-driven photocatalysis.

Black TiO2 has received tremendous attention because of its lattice disorder-induced reduction in the TiO2 bandgap, which yields excellent light absorption and photocatalytic ability. In this report, a highly efficient visible-light-driven black TiO2 photocatalyst was synthesized with a mesoporous hollow shell structure. It provided a higher specific surface area, more reaction sites and enhanced visible light absorption capability, which significantly promoted the photocatalytic reaction. Subsequently, the mesoporous hollow black TiO2 with different lattice disorder-engineering degrees were designed. The structure disorder in the black TiO2 obviously increased with reduction temperature, leading to improved visible light absorption. However, their visible-light-driven photocatalytic efficiency increased first and then decreased. The highest value can be observed for the sample reduced at 350 °C, which was 2-, 1.4- and 5-fold that of the samples reduced at 320 °C, 380 °C and 400 °C, respectively. This contradiction can be ascribed to the varied functions of the surface defects with different concentrations in the black TiO2 during the catalytic process. In particular, the defects at low concentrations boost photocatalysis but reverse photocatalysis at high concentrations when they act as charge recombination centers. This study provides significant insight for the fabrication of high-efficiency visible-light-driven catalytic black TiO2 and the understanding of its catalysis mechanism.

Nanocrystals in compression: unexpected structural phase transition and amorphization due to surface impurities.

We report an unprecedented surface doping-driven anomaly in the compression behaviors of nanocrystals demonstrating that the change of surface chemistry can lead to an interior bulk structure change in nanoparticles. In the synchrotron-based X-ray diffraction experiments, titania nanocrystals with low concentration yttrium dopants at the surface are found to be less compressible than undoped titania nanocrystals. More surprisingly, an unexpected TiO2(ii) phase (α-PbO2 type) is induced and obvious anisotropy is observed in the compression of yttrium-doped TiO2, in sharp contrast to the compression behavior of undoped TiO2. In addition, the undoped brookite nanocrystals remain with the same structure up to 30 GPa, whereas the yttrium-doped brookite amorphizes above 20 GPa. The abnormal structural evolution observed in yttrium-doped TiO2 does not agree with the reported phase stability of nano titania polymorphs, thus suggesting that the physical properties of the interior of nanocrystals can be controlled by the surface, providing an unconventional and new degree of freedom in search for nanocrystals with novel tunable properties that can trigger applications in multiple areas of industry and provoke more related basic science research.

CRYSTAL GROWTH. Crystallization by particle attachment in synthetic, biogenic, and geologic environments.

Field and laboratory observations show that crystals commonly form by the addition and attachment of particles that range from multi-ion complexes to fully formed nanoparticles. The particles involved in these nonclassical pathways to crystallization are diverse, in contrast to classical models that consider only the addition of monomeric chemical species. We review progress toward understanding crystal growth by particle-attachment processes and show that multiple pathways result from the interplay of free-energy landscapes and reaction dynamics. Much remains unknown about the fundamental aspects, particularly the relationships between solution structure, interfacial forces, and particle motion. Developing a predictive description that connects molecular details to ensemble behavior will require revisiting long-standing interpretations of crystal formation in synthetic systems, biominerals, and patterns of mineralization in natural environments.

Molecular Dynamics Simulation Study of the Early Stages of Nucleation of Iron Oxyhydroxide Nanoparticles in Aqueous Solutions.

Nucleation is a fundamental step in crystal growth. Of environmental and materials relevance are reactions that lead to nucleation of iron oxyhydroxides in aqueous solutions. These reactions are difficult to study experimentally due to their rapid kinetics. Here, we used classical molecular dynamics simulations to investigate nucleation of iron hydroxide/oxyhydroxide nanoparticles in aqueous solutions. Results show that in a solution containing ferric ions and hydroxyl groups, iron-hydroxyl molecular clusters form by merging ferric monomers, dimers, and other oligomers, driven by strong affinity of ferric ions to hydroxyls. When deprotonation reactions are not considered in the simulations, these clusters aggregate to form small iron hydroxide nanocrystals with a six-membered ring-like layered structure allomeric to gibbsite. By comparison, in a solution containing iron chloride and sodium hydroxide, the presence of chlorine drives cluster assembly along a different direction to form long molecular chains (rather than rings) composed of Fe-O octahedra linked by edge sharing. Further, in chlorine-free solutions, when deprotonation reactions are considered, the simulations predict ultimate formation of amorphous iron oxyhydroxide nanoparticles with local atomic structure similar to that of ferrihydrite nanoparticles. Overall, our simulation results reveal that nucleation of iron oxyhydroxide nanoparticles proceeds via a cluster aggregation-based nonclassical pathway.

A unified description of attachment-based crystal growth.

Crystal growth is one of the most fundamental processes in nature. Understanding of crystal growth mechanisms has changed dramatically over the past two decades. One significant advance has been the recognition that growth does not only occur atom by atom, but often proceeds via attachment and fusion of either amorphous or crystalline particles. Results from recent experiments and calculations can be integrated to develop a simple, unified conceptual description of attachment-based crystal growth. This enables us to address three important questions: What are the driving forces for attachment-based growth? For crystalline particles, what enables the particles to achieve crystallographic coalignment? What determines the surface on which attachment occurs? We conclude that the extent of internal nanoparticle order controls the degree of periodicity and anisotropy in the surrounding electrostatic field. For crystalline particles, the orienting force stemming from the electrostatic field can promote oriented attachment events, although solvent-surface interactions modulate this control. In cases where perfect crystallographic alignment is not achieved, misorientation gives rise to structural defects that can fundamentally modify nanomaterial properties.

Investigating processes of nanocrystal formation and transformation via liquid cell TEM.

Recent ex situ observations of crystallization in both natural and synthetic systems indicate that the classical models of nucleation and growth are inaccurate. However, in situ observations that can provide direct evidence for alternative models have been lacking due to the limited temporal and spatial resolution of experimental techniques that can observe dynamic processes in a bulk solution. Here we report results from liquid cell transmission electron microscopy studies of nucleation and growth of Au, CaCO3, and iron oxide nanoparticles. We show how these in situ data can be used to obtain direct evidence for the mechanisms underlying nanoparticle crystallization as well as dynamic information that provide constraints on important energetic parameters not available through ex situ methods.

Analysis of the relationship between different bleeding positions on intraoperative rupture anterior circulation aneurysm and surgical treatment outcome.

BACKGROUND: It is well recognized that intraoperative aneurysm rupture (IAR) is a serious event that is difficult to manage and has a relatively serious influence on a patient's prognosis. The aim of this study was to evaluate the prognostic value of different bleeding positions of IAR in patients, and to describe the technique that the authors have used to clip the ruptured aneurysms. METHODS: From May 2009 to March 2012, a total of 148 aneurysms in 135 consecutive patients in our institution underwent clipping surgeries, and 31 IARs occurred in 30 patients. The clinical data of all patients were retrospectively analyzed. Statistics analysis was performed to analyze possible factors of different bleeding positions of IARs, to assist observation. RESULTS: Outcome was estimated by Glasgow outcome scale via following up or calling back within 1, 3, and 6 months after surgery: 94 patients were 5', 23 patients were 4', nine patients were 3', two patients were 2' and eight patients were 1'. There was no significant difference between the outcome of IAR and that of no intraoperative aneurysm rupture (NIAR) in Hunt-Hess groups 0-III (P = 0.802) and Hunt-Hess groups IV-V (P = 0.229), and the different bleeding positions were shown to be an important factor that significantly influences the patients' prognosis (P = 0.001). CONCLUSIONS: Different bleeding positions of IAR have a significant impact on surgical outcome; IAR of the neck is the most devastating complication. If surgeons take appropriate measures according to different bleeding positions, the efficiency, accuracy and security of the operation will be improved.

Titania nanorods curve to lower their energy.

Spontaneous formation of curved nanorods is generally unexpected, since curvature introduces strain energy. However, electron microscopy shows that under hydrothermal conditions, some nanorods grown by oriented attachment of small anatase particles on {101} surfaces are curved and dislocation free. Molecular dynamics simulations show that the lattice energy of a curved anatase rod is actually lower than that of a linear rod due to more attractive long-range interatomic Coulombic interactions among atoms in the curved rod. The thermodynamic driving force stemming from lattice energy could be harnessed to produce asymmetric morphologies unexpected from classical Ostwald ripening with unusual shapes and properties.

In situ structural characterization of ferric iron dimers in aqueous solutions: identification of µ-oxo species.

The structure of ferric iron (Fe(3+)) dimers in aqueous solutions has long been debated. In this work, we have determined the dimer structure in situ in aqueous solutions using extended X-ray absorption fine structure (EXAFS) spectroscopy. An Fe K-edge EXAFS analysis of 0.2 M ferric nitrate solutions at pH 1.28-1.81 identified a Fe-Fe distance at ∼3.6 Å, strongly indicating that the dimers take the µ-oxo form. The EXAFS analysis also indicates two short Fe-O bonds at ∼1.80 Å and ten long Fe-O bonds at ∼2.08 Å, consistent with the µ-oxo dimer structure. The scattering from the Fe-Fe paths interferes destructively with that from paths belonging to Fe(OH2)6(3+) monomers that coexist with the dimers, leading to a less apparent Fe shell in the EXAFS Fourier transform. This might be a reason why the characteristic Fe-Fe distance was not detected in previous EXAFS studies. The existence of µ-oxo dimers is further confirmed by Mössbauer analyses of analogous quick frozen solutions. This work also explores the electronic structure and the relative stability of the µ-oxo dimer in a comparison to the dihydroxo dimer using density function theory (DFT) calculations. The identification of such dimers in aqueous solutions has important implications for iron (bio)inorganic chemistry and geochemistry, such as understanding the formation mechanisms of Fe oxyhydroxides at molecular scale.