Enhanced Hydrogen Evolution Catalysis of Pentlandite due to the Increases in Coordination Number and Sulfur Vacancy during Cubic-Hexagonal Phase Transition.

The search for new phases is an important direction in materials science. The phase transition of sulfides results in significant changes in catalytic performance, such as MoS2 and WS2 . Cubic pentlandite [cPn, (Fe, Ni)9 S8 ] can be a functional material in batteries, solar cells, and catalytic fields. However, no report about the material properties of other phases of pentlandite exists. In this study, the unit-cell parameters of a new phase of pentlandite, sulfur-vacancy enriched hexagonal pentlandite (hPn), and the phase boundary between cPn and hPn are determined for the first time. Compared to cPn, the hPn shows a high coordination number, more sulfur vacancies, and high conductivity, which result in significantly higher hydrogen evolution performance of hPn than that of cPn and make the non-nano rock catalyst hPn superior to other most known nanosulfide catalysts. The increase of sulfur vacancies during phase transition provides a new approach to designing functional materials.

Silica-water superstructure and one-dimensional superionic conduit in Earth's mantle.

Water in Earth's deep interior is predicted to be hydroxyl (OH-) stored in nominally anhydrous minerals, profoundly modulating both structure and dynamics of Earth's mantle. Here, we use a high-dimensional neuro-network potential and machine learning algorithm to investigate the weight percent water incorporation in stishovite, a main constituent of the subducted oceanic crust. We found that stishovite and water prefer forming medium- to long-range ordered superstructures, featuring one-dimensional (1D) water channels. Synthesizing single crystals of hydrous stishovite, we verified the ordering of OH- groups in the water channels through optical and nuclear magnetic resonance spectroscopy and found an average H-H distance of 2.05(3) Å, confirming simulation results. Upon heating, H atoms were predicted to behave fluid-like inside the channels, leading to an exotic 1D superionic state. Water-bearing stishovite could feature high ionic mobility and strong electrical anisotropy, manifesting as electrical heterogeneity in Earth's mantle.

Inhibition of defect-induced α-to-δ phase transition for efficient and stable formamidinium perovskite solar cells.

Defects passivation is widely devoted to improving the performance of formamidinium lead triiodide perovskite solar cells; however, the effect of various defects on the α-phase stability is still unclear. Here, using density functional theory, we first reveal the degradation pathway of the formamidinium lead triiodide perovskite from α to δ phase and investigate the effect of various defects on the energy barrier of phase transition. The simulation results predict that iodine vacancies are most likely to trigger the degradation, since they obviously reduce the energy barrier of α-to-δ phase transition and have the lowest formation energies at the perovskite surface. A water-insoluble lead oxalate compact layer is introduced on the perovskite surface to largely suppress the α-phase collapse through hindering the iodine migration and volatilization. Furthermore, this strategy largely reduces the interfacial nonradiative recombination and boosts the efficiency of the solar cells to 25.39% (certified 24.92%). Unpackaged device can maintain 92% of its initial efficiency after operation at maximum power point under simulated air mass 1.5 G irradiation for 550 h.

Interstitial Hydrogen Atom to Boost Intrinsic Catalytic Activity of Tungsten Oxide for Hydrogen Evolution Reaction.

Tungsten oxide (WO3 ) is an appealing electrocatalyst for the hydrogen evolution reaction (HER) owing to its cost-effectiveness and structural adjustability. However, the WO3 electrocatalyst displays undesirable intrinsic activity for the HER, which originates from the strong hydrogen adsorption energy. Herein, for effective defect engineering, a hydrogen atom inserted into the interstitial lattice site of tungsten oxide (H0.23 WO3 ) is proposed to enhance the catalytic activity by adjusting the surface electronic structure and weakening the hydrogen adsorption energy. Experimentally, the H0.23 WO3 electrocatalyst is successfully prepared on reduced graphene oxide. It exhibits significantly improved electrocatalytic activity for HER, with a low overpotential of 33 mV to drive a current density of 10 mA cm-2 and ultra-long catalytic stability at high-throughput hydrogen output (200 000 s, 90 mA cm-2 ) in acidic media. Theoretically, density functional theory calculations indicate that strong interactions between interstitial hydrogen and lattice oxygen lower the electron density distributions of the d-orbitals of the active tungsten (W) centers to weaken the adsorption of hydrogen intermediates on W-sites, thereby sufficiently promoting fast desorption from the catalyst surface. This work enriches defect engineering to modulate the electron structure and provides a new pathway for the rational design of efficient catalysts for HER.

Negative linear compressibility in Se at ultra-high pressure above 120 GPa.

A series of in situ synchrotron X-ray diffraction (XRD) measurements were carried out, combined with first-principles calculations, to study structural phase transitions of selenium at high pressures and room temperature. Several phase transitions were observed, among which an isostructural phase transition was found at around 120 GPa for the first time. Evolved from the rhombohedral (space group R 3 m) structure (Se-V), the new phase (Se-V') exhibited an interesting increase of lattice parameter a at pressures from 120 to 148 GPa, known as negative linear compressibility (NLC). The discovery of NLC behavior observed in this work is mainly attributed to the accuracy and fine steps controlled by the membrane system for in situ XRD data collected with an exposure time of 0.5 s. After 140 GPa, a body-centered cubic (b.c.c.) structure Se-VI (space group Im 3 m) was formed, which remains stable up to 210 GPa, the highest pressure achieved in this study. The bulk moduli of phases Se-V, Se-V' and Se-VI were estimated to be 83 ± 2, 321 ± 2 and 266 ± 7 GPa, respectively, according to the P-V curve fit by the third-order Birch-Murnaghan equation of state. The Se-V' phase shows a bulk modulus almost 4 times larger than that of the Se-V phase, which is mainly due to the effect of its NLC. NLC in a higher pressure range is always more significant in terms of fundamental mechanism and new materials discovery, yet it has barely been reported at pressures above 100 GPa. This will hopefully inspire future studies on potential NLC behaviors in other materials at ultra-high pressure.

Topological Ordering of Memory Glass on Extended Length Scales.

Identifying ordering in non-crystalline solids has been a focus of natural science since the publication of Zachariasen's random network theory in 1932, but it still remains as a great challenge of the century. Literature shows that the hierarchical structures, from the short-range order of first-shell polyhedra to the long-range order of translational periodicity, may survive after amorphization. Here, in a piece of AlPO4, or berlinite, we combine X-ray diffraction and stochastic free-energy surface simulations to study its phase transition and structural ordering under pressure. From reversible single crystals to amorphous transitions, we now present an unambiguous view of the topological ordering in the amorphous phase, consisting of a swarm of Carpenter low-symmetry phases with the same topological linkage, trapped in a metastable intermediate stage. We propose that the remaining topological ordering is the origin of the switchable "memory glass" effect. Such topological ordering may hide in many amorphous materials through disordered short atomic displacements.

Pressure tuned incommensurability and guest structure transition in compressed scandium from machine learning atomic simulation.

Scandium (Sc) is the lightest non-main-group element and transforms to a host-guest (H-G) incommensurate structure under gigapascal (GPa) pressures. While the host structure is stable over a wide pressure range, the guest structure may exist in multiple forms, featuring different incommensurate ratios, and mixing up to generate long-range "disordered" guest structures. Here, we employed the recently developed global neural network (g-NN) potential and the stochastic surface walking (SSW) global optimization algorithm to explore the global potential energy surface of Sc under various pressures. We probe the global minima structure in a system made of hundreds of atoms and revealed that the solid-phase transition between Sc-I and H-G Sc-II phases is fully reconstructive in nature. Above 62.5 GPa, the pressure will further destabilize the face-centered tetragonal (fct, Sc-IIa) guest structure to a body-centered tetragonal phase (bct, Sc-IIb), while sustaining the host structure. The structural transition mechanism of this work will shed light on the nature of the complex H-G structural modifications in compressed metals.

Confronting the Air Instability of Cesium Tin Halide Perovskites by Metal Ion Incorporation.

Tin halide perovskite's potential as a photovoltaic absorber has not been fully realized to date, largely due to its instability in ambient air. Here, we demonstrate by both experiments and simulations that the air instability of black-phase cesium tin iodide perovskite (γ-CsSnI3) could be greatly lessened by a controlled incorporation of bismuth (Bi) ions into the crystal lattice. Hall effect measurements on films of γ-CsSnI3 suggest the unwanted formation of a tin vacancy and p-type self-doping can be effectively suppressed by the Bi incorporation. Structural and optical results indicate that the Bi incorporation markedly enhances the air stability by impeding the direct conversion of γ-CsSnI3 to zero-dimensional Cs2SnI6. By using a stochastic surface walking (SSW) method integrating neural network (NN) potential and density functional theory (DFT), it is revealed that the remarkable enhanced stability could be attributed to a combination of factors originating from lattice-contraction-induced strain, a suppressed tin vacancy, and an increased energy barrier for the transformation of γ-CsSnI3 to Cs2SnI6. This study provides physical insights into the stabilization mechanism of tin perovskites by heterovalent B-site engineering, paving the way for realizing stable and efficient lead-free perovskite photovoltaics.

Unraveling the structural transition mechanism of room-temperature compressed graphite carbon.

The discovery of graphite transition to transparent and superhard carbons under room-temperature compression (Takehiko, et al., Science, 1991, 252, 1542 and Mao, et al., Science, 2003, 302, 425) launched decades of intensive research into carbon's structural polymorphism and relative phase transition mechanisms. Although many possible carbon allotropes have been proposed, experimental observations and their transition mechanisms are far from conclusive. Three longstanding issues are: (i) the speculative structures inferred by amorphous-like XRD peaks, (ii) sp2 and sp3 bonding mixing, and (iii) the controversies of transition reversibility. Here, by utilizing the stochastic surface walking method for unbiased pathway sampling, we resolve the possible atomic structure and the lowest energy pathways between multiple carbon allotropes under high pressure. We found that a new transition pathway, through which graphite transits to a highly disordered phase by shearing the boat architecture line atoms out of the graphite (001) plane upward or downward featuring without the nuclei core, is the most favorable. This transition pathway facilitates the generation of a variety of equally favorable carbon structures that are controlled by the local strain and crystal orientation, resembling structural disordering. Our results may help to understand the nature of graphite under room temperature compression.

Assessing the impact of different distal ureter management techniques during radical nephroureterectomy for primary upper urinary tract urothelial carcinoma on oncological outcomes: A systematic review and meta-analysis.

OBJECTIVES: To assess the oncological outcomes of several distal ureter management techniques in patients administered with radical nephroureterectomy (RNU) for primary upper urinary tract urothelial carcinoma (UTUC). METHODS: A systematic search of PubMed, EMBASE, and the Cochrane Library was conducted to identify studies comparing outcomes following RNU under various surgical methods for bladder cuff management. Standard cumulative analyses of hazard ratios (HRs) with 95% confidence intervals (CIs) were performed using Review Manager (5.3). RESULTS: Nine studies involving 4683 patients were selected based upon eligibility criteria. Meta-analysis of cancer-specific survival (CSS) and overall survival (OS) revealed no significant differences among intravesical incision of the bladder cuff (IVBC), extravesical incision of the bladder cuff (EVBC) and transurethral incision of the bladder cuff (TUBC) techniques. However, the IVBC technique appeared to have better recurrence-free survival (RFS) (HR = 1.37, p < 0.01) and intravesical recurrence-free survival (IRFS) (HR = 1.45, p < 0.01) compared with non-IVBC methods, including both TUBC and EVBC. When studies involving patients with bladder tumour history were excluded, the pooled statistic appeared to confirm that IVBC was associated with improved IRFS (HR = 1.25, p = 0.03) compared with EVBC and TUBC. No significant difference was found between the EVBC and TUBC groups (HR = 1.81, p = 0.32). CONCLUSIONS: The findings suggest that IVBC is associated with improved oncologic outcomes and that it may be recommended for distal ureter management. However, caution must be taken because this recommendation is based upon a very limited number of clinical studies. Further research with enhanced outcome data collection and improved reporting is required to confirm these findings.

Technical Modification of the Terminal Ureter During Total Transperitoneal Laparoscopic Nephroureterectomy for Upper Urinary Tract Urothelial Carcinoma.

Upper tract urothelial carcinoma (UTUC) accounts for 5%-10% of all urothelial tumors. Radical nephroureterectomy is the standard treatment procedure. At present, different choices still exist for treating the ureteral end during laparoscopic ureteral bladder sleeve resection. Our center has adopted a new method for treating the ureteral end. This new method can increase the operating space and reduce the difficulty of the surgery compared with current methods.

Electrides with Dinitrogen Ligands.

Electrides are a class of materials which contain excess electrons occupying the cavities in the crystal and playing the role of anions. To achieve electron-rich conditions, it usually requires a positive total formal charge in electride materials. However, the assignment of charges relies on a detailed analysis on chemical bonding. Herein, we present a survey on potential electrides which may be overlooked if no bonding analysis is performed. By applying various structure sampling techniques in conjunction with first-principles calculation, we predicted two compounds Ba2N2:e- and Li2Ca3N6:2e-, both of which are featured by the presence of dinitrogen ligands [N2], to be potential electrides. While Li2Ca3N6:2e- with [N2]2- ions has been synthesized in the past, its electride nature was discovered for the first time based on our high-throughput screening. On the other hand, Ba2N2:e- with [N2]3- ions is a new compound entirely from first-principles structure prediction. The different valence states of dinitrogen ligands identified in these two compounds suggest a novel route to tune the concentration and anisotropic properties of anionic interstitial electrons. Our discovery does not only establish a new class of inorganic electrides but also demonstrates the predictive power of modern crystal structure sampling techniques toward rational material design.

Structure-Controlled Oxygen Concentration in Fe2O3 and FeO2.

Solid-solid reaction, particularly in the Fe-O binary system, has been extensively studied in the past decades because of its various applications in chemistry and materials and earth sciences. The recently synthesized pyrite-FeO2 at high pressure suggested a novel oxygen-rich stoichiometry that extends the achievable O-Fe ratio in iron oxides by 33%. Although FeO2 was synthesized from Fe2O3 and O2, the underlying solid reaction mechanism remains unclear. Herein, combining in situ X-ray diffraction experiments and first-principles calculations, we identified that two competing phase transitions starting from Fe2O3: (1) without O2, perovskite-Fe2O3 transits to the post-perovskite structure above 50 GPa; (2) if free oxygen is present, O diffuses into the perovskite-type lattice of Fe2O3 leading to the pyrite-type FeO2 phase. We found the O-O bonds in FeO2 are formed by the insertion of oxygen into the Pv lattice via the external stress and such O-O bonding is only kinetically stable under high pressure. This may provide a general mechanism of adding extra oxygen to previous known O saturated oxides to produce unconventional stoichiometries. Our results also shed light on how O is enriched in mantle minerals under pressure.

ROY revisited, again: the eighth solved structure.

X-ray powder diffraction and crystal structure prediction (CSP) algorithms were used in synergy to establish the crystal structure of the eighth polymorph of 5-methyl-2-[(2-nitrophenyl)amino]-3-thiophenecarbonitrile (ROY), form R05. R05 crystallizes in the monoclinic space group P21 with lattice parameters a = 11.479(4) Å, b = 11.030(1) Å, c = 10.840(6) Å, ß = 118.23(1)°. This is both the first acentric ROY polymorph, and the first with Z' > 1. The torsion angles defined by the S-C-N-C atom sequence of each molecule in the asymmetric unit (R05-1 and R05-2) are 44.9° and -34.0°. These values are between those previously determined for the red and orange forms of ROY. The crystal packing and intermolecular interactions in R05 are explained herein through Hirshfeld surface analysis and an updated energy stability ranking is determined using computational methods. Although the application of CSP was critical to the structure solution of R05, energy stability rankings determined using a series of DFT van der Waals (vdW)-inclusive models substantially differ from experiment, indicating that ROY polymorphism continues to be a challenge for CSP.

Photoselective Vaporesection of the Prostate via an End-firing Lithium Triborate Crystal Laser.

The occurrence of lower urinary tract symptoms (LUTS) caused by benign prostatic hyperplasia (BPH) is a common problem with a high incidence in the aging male population. Although it is not a life-threatening disease, BPH causes problems that seriously impact the quality of life. Here, we introduce a new technique called photoselective vaporesection of the prostate (PVRP) in treating BPH, which can be seen as a variation of photoselective vaporization of the prostate (PVP). This procedure presents several advantages compared to the PVP technique including less laser energy loss, less intraoperative complications as well as more tissue resection rate.

Hydrogen-Bond Symmetrization Breakdown and Dehydrogenation Mechanism of FeO2H at High Pressure.

The cycling of hydrogen plays an important role in the geochemical evolution of our planet. Under high-pressure conditions, asymmetric hydroxyl bonds tend to form a symmetric O-H-O configuration in which H is positioned at the center of two O atoms. The symmetrization of O-H bonds improves their thermal stability and as such, water-bearing minerals can be present deeper in the Earth's lower mantle. However, how exactly H is recycled from the deep mantle remains unclear. Here, we employ first-principles free-energy landscape sampling methods together with high pressure-high temperature experiments to reveal the dehydrogenation mechanism of a water-bearing mineral, FeO2H, at deep mantle conditions. Experimentally, we show that ∼50% H is released from symmetrically hydrogen-bonded ε-FeO2H upon transforming to a pyrite-type phase (Py-phase). By resolving the lowest-energy transition pathway from ε-FeO2H to the Py-phase, we demonstrate that half of the O-H bonds in the mineral rupture during the structural transition, leading toward the breakdown of symmetrized hydrogen bonds and eventual dehydrogenation. Our study sheds new light on the stability of symmetric hydrogen bonds during structural transitions and provides a dehydrogenation mechanism for hydrous minerals existing in the deep mantle.

Fractal MTW Zeolite Crystals: Hidden Dimensions in Nanoporous Materials.

Screw dislocation structures in crystals are an origin of symmetry breaking in a wide range of dense-phase crystals. Preparation of such analogous structures in framework-phase crystals is of great importance in zeolites but is still a challenge. On the basis of crystal-structure solving and model building, it was found that the two specific intergrowths in MTW zeolite produce this complex fractal and spiral structure. With the structurally determined parameters (spiral pitch h, screw angle θ, and spatial angle ψ) of Burgers circuit, the screw dislocation structure can be constructed by two different dimensional intergrowth sections. Thus the reported complexity of various dimensions in diverse crystals can be unified.

Photoselective Vaporesection of the Prostate with an End-firing Lithium Triborate Crystal Laser.

BACKGROUND: Photoselective vaporization of the prostate is a technique that is widely used for the treatment of benign prostatic hyperplasia (BPH) and has pronounced advantages compared to the traditional transurethral resection of the prostate. Following the recent introduction of end-firing lithium triborate lasers, we have created a new technique called photoselective vaporesection of the prostate (PVRP). This study described our initial experience using the PVRP technique for the treatment of BPH. METHODS: This prospective study included a total of 35 patients with BPH who underwent PVRP from August 2013 to July 2014. The chief clinical parameters were obtained and evaluated during the perioperative period and follow-up, including the International Prostate Symptom Score (IPSS), quality of life (QoL) score, maximum urinary flow rate, and prostate volume. All variables were evaluated for statistically significant differences compared to baseline values using the analysis of variance. RESULTS: The mean subgroup IPSS and QoL scores significantly improved during follow-up; the respective decreases in IPSS storage score, IPSS voiding score, IPSS nocturia score, and QoL score were 75.3%, 83.6%, 51.4%, and 71.7%, respectively (all P < 0.001 compared with baseline). Three patients were diagnosed with prostate cancer based on postoperative pathological examinations. There were no serious perioperative complications. CONCLUSION: The PVRP technique demonstrates satisfactory short-term clinical outcomes and perioperative safety in the treatment of BPH.

Mechanism and microstructures in Ga2O3 pseudomartensitic solid phase transition.

Solid-to-solid phase transition, although widely exploited in making new materials, challenges persistently our current theory for predicting its complex kinetics and rich microstructures in transition. The Ga2O3α-ß phase transformation represents such a common but complex reaction with marked change in cation coordination and crystal density, which was known to yield either amorphous or crystalline products under different synthetic conditions. Here we, via recently developed stochastic surface walking (SSW) method, resolve for the first time the atomistic mechanism of Ga2O3α-ß phase transformation, the pathway of which turns out to be the first reaction pathway ever determined for a new type of diffusionless solid phase transition, namely, pseudomartensitic phase transition. We demonstrate that the sensitivity of product crystallinity is caused by its multi-step, multi-type reaction pathway, which bypasses seven intermediate phases and involves all types of elementary solid phase transition steps, i.e. the shearing of O layers (martensitic type), the local diffusion of Ga atoms (reconstructive type) and the significant lattice dilation (dilation type). While the migration of Ga atoms across the close-packed O layers is the rate-determining step and yields "amorphous-like" high energy intermediates, the shearing of O layers contributes to the formation of coherent biphase junctions and the presence of a crystallographic orientation relation, (001)α//(201[combining macron])ß + [120]α//[13[combining macron]2]ß. Our experiment using high-resolution transmission electron microscopy further confirms the theoretical predictions on the atomic structure of biphase junction and the formation of (201[combining macron])ß twin, and also discovers the late occurrence of lattice expansion in the nascent ß phase that grows out from the parent α phase. By distinguishing pseudomartensitic transition from other types of mechanisms, we propose general rules to predict the product crystallinity of solid phase transition. The new knowledge on the kinetics of pseudomartensitic transition complements the theory of diffusionless solid phase transition.

Reaction Network of Layer-to-Tunnel Transition of MnO2.

As a model system of 2-D oxide material, layered δ-MnO2 has important applications in Li ion battery systems. δ-MnO2 is also widely utilized as a precursor to synthesize other stable structure variants in the MnO2 family, such as α-, ß-, R-, and γ-phases, which are 3-D interlinked structures with different tunnels. By utilizing the stochastic surface walking (SSW) pathway sampling method, we here for the first time resolve the atomistic mechanism and the kinetics of the layer-to-tunnel transition of MnO2, that is, from δ-MnO2 to the α-, ß-, and R-phases. The SSW sampling determines the lowest-energy pathway from thousands of likely pathways that connects different phases. The reaction barriers of layer-to-tunnel phase transitions are found to be low, being 0.2-0.3 eV per formula unit, which suggests a complex competing reaction network toward different tunnel phases. All the transitions initiate via a common shearing and buckling movement of the MnO2 layer that leads to the breaking of the Mn-O framework and the formation of Mn(3+) at the transition state. Important hints are thus gleaned from these lowest-energy pathways: (i) the large pore size product is unfavorable for the entropic reason; (ii) cations are effective dopants to control the kinetics and selectivity in layer-to-tunnel transitions, which in general lowers the phase transition barrier and facilitates the creation of larger tunnel size; (iii) the phase transition not only changes the electronic structure but also induces the macroscopic morphology changes due to the interfacial strain.