Crystal Boundaries Research Articles

A Space‐Confined Polymerization Templated by Ice Enables Large‐Scale Synthesis of Two‐Dimensional Polymer Sheets

AbstractDespite significant progress in the preparation and characterization of two‐dimensional (2D) materials, the synthesis of 2D organic materials remains challenging. Here, we report a novel space‐confined polymerization method that enables the large‐scale synthesis of 2D sheets of a functional conjugated polymer, namely, poly(3,4‐ethylenedioxythiophene) (PEDOT). A key step in this method is the confinement of monomer to the boundaries of ice crystals using micelles. This spatial confinement directs the polymerization to form 2D PEDOT sheets with high crystallinity and controlled morphology. Supercapacitors prepared from the 2D PEDOT sheets exhibit outstanding performance metrics. In aqueous electrolyte, a high areal specific capacitance of 898 mF cm−2 at 0.2 mA cm−2 along with an excellent rate capability is achieved (e.g., capacitance retention of 67.6 % at a 50‐fold higher current). Moreover, the 2D PEDOT‐based supercapacitors exhibit outstanding cycling stability (capacitance retention of 98.5 % after 30,000 cycles). Device performance is further improved when an organic electrolyte is used.

A Space-Confined Polymerization Templated by Ice Enables Large-Scale Synthesis of Two-Dimensional Polymer Sheets.

Despite significant progress in the preparation and characterization of many two-dimensional (2D) materials, the synthesis of 2D organic materials remains challenging. Here, we report a novel space-confined polymerization method that enables the large-scale synthesis of 2D sheets of a functional conjugated polymer, namely, poly(3,4-ethylenedioxythiophene) (PEDOT). A key step in this method is the confinement of monomer to the boundaries of ice crystals using micelles. This spatial confinement directs the polymerization to form 2D PEDOT sheets with high crystallinity and controlled morphology. Supercapacitors prepared from the 2D PEDOT sheets exhibit outstanding performance metrics. In aqueous electrolyte, a high areal specific capacitance of 898 mF cm-2 at 0.2 mA cm-2 along with an excellent rate capability is achieved (e.g., capacitance retention of 67.6% at a 50-fold higher current). Moreover, the 2D PEDOT-based supercapacitors exhibit outstanding cycling stability (capacitance retention of 98.5% after 30,000 cycles). Device performance is further improved when an organic electrolyte is used.

Failure transition of shear-to-dilation band of rock salt under triaxial stresses

Great potential of underground gas/energy storage in salt caverns seems to be a promising solution to support renewable energy. In the underground storage method, the operating cycle unfortunately may reach up to daily or even hourly, which generates complicated pressures on the salt cavern. Furthermore, the mechanical behavior of rock salt may change and present distinct failure characteristics under different stress states, which affects the performance of salt cavern during the time period of full service. To reproduce a similar loading condition on the cavern surrounding rock mass, the cyclic triaxial loading/unloading tests are performed on the rock salt to explore the mechanical transition behavior and failure characteristics under different confinement. Experimental results show that the rock salt samples present a diffused shear failure band with significant bulges at certain locations in low confining pressure conditions (e.g. 5 MPa, 10 MPa and 15 MPa), which is closely related to crystal misorientation and grain boundary sliding. Under the elevated confinement (e.g. 20 MPa, 30 MPa and 40 MPa), the dilation band dominates the failure mechanism, where the large-size halite crystals are crushed to be smaller size and new pores are developing. The failure transition mechanism revealed in the paper provides additional insight into the mechanical performance of salt caverns influenced by complicated stress states.

Improvement in piezoelectric performance of the lead-free BiFeO3-BaTiO3 ceramics by synergistic approach

High-piezoelectric properties in lead-free materials have been the pursuit for both industry and scientific research. In this work, the synergistic approaches of phase/domain engineering and novel poling method are adopted for the improvement of piezoelectric performance. The strategically designed lead-free donor-doped BiFeO3-xBaTiO3 ceramics at the crystal structure morphotropic phase boundary (MPB) between the rhombohedral and tetragonal phases exhibited a high Curie temperature (TC ≥ 450 °C). Furthermore, simultaneously enhanced static piezoelectric constant (d33) of 436±5 pC/N and thermally stable dynamic piezoelectric constant (d33*) of 550±10 pm/V were achieved. The high piezoelectric performance is collectively attributed to the crystal structure MPB, thermal quenching effect, local structure heterogeneity induced by donor doping, mesoscale nanodomains, and novel poling method inside a magnetic field. The temperature-insensitive and high piezoelectric performance of the current work is superior to the other lead-free piezoceramics. The synergistic approach for the improvement of piezoelectricity provides a path for the development of lead-free ceramics for high-temperature commercial applications.

Atomic-scale observation of premelting at 2D lattice defects inside oxide crystals

Since two major criteria for melting were proposed by Lindemann and Born in the early 1900s, many simulations and observations have been carried out to elucidate the premelting phenomena largely at the crystal surfaces and grain boundaries below the bulk melting point. Although dislocations and clusters of vacancies and interstitials were predicted as possible origins to trigger the melting, experimental direct observations demonstrating the correlation of premelting with lattice defects inside a crystal remain elusive. Using atomic-column-resolved imaging with scanning transmission electron microscopy in polycrystalline BaCeO3, here we clarify the initiation of melting at two-dimensional faults inside the crystals below the melting temperature. In particular, melting in a layer-by-layer manner rather than random nucleation at the early stage was identified as a notable finding. Emphasizing the value of direct atomistic observation, our study suggests that lattice defects inside crystals should not be overlooked as preferential nucleation sites for phase transformation including melting.

Early hydration characteristics and kinetics model of cement pastes containing internal curing materials with different absorption behaviors

Internal curing with superabsorbent polymer (SAP) has potential effect on the early deformation and hydration of cementitious material. However, there are few studies on the hydration kinetics and hydration characteristics of internal curing cementitious material. Here, the effects of microgel, composite microgel and commercial SAP with different dosage and absorption behaviors on the hydration characteristics of cement paste were studied by the hydration model proposed by Krstulović-Dabić and hydration heat. Results showed that the hydration reaction of paste containing internal curing materials increased as function of the dosage. When nano-silica(NS) incorporated into microgel, 24.5% and 5.6% increase in value of exothermic peak and cumulative heat were observed for paste. The hydration kinetic model showed that the composite microgel promoted the crystal growth and phase boundary reaction process, thus extending the transition point to the diffusion process. For commercial SAP with premature desorption behavior, the hydration rate of cement paste decreases and the appearance of conversion point at each process is delayed. Hydration characteristics are in good agreement with the kinetic model, suggesting that portlandite consumed by pozzolanic reaction promoted the development of hydration reaction and further refined the microstructure of paste.

MP05-07 VALIDATING THE THEORY OF PHASE TRANSITION FROM CALCIUM OXALATE DIHYDRATE TO MONOHYDRATE IN THE STONE FORMATION: THE FIRST ARTIFICIAL IN VIVO EXPERIMENT

You have accessJournal of UrologyCME1 Apr 2023MP05-07 VALIDATING THE THEORY OF PHASE TRANSITION FROM CALCIUM OXALATE DIHYDRATE TO MONOHYDRATE IN THE STONE FORMATION: THE FIRST ARTIFICIAL IN VIVO EXPERIMENT Mihoko Maruyama, Uta Michibata, Yutaro Tanaka, Hiroshi Yoshikawa, Kazufumi Takano, Rie Tajiri, Kazumi Taguchi, Shuzo Hamamoto, Atsushi Okada, Takahiro Yasui, Shigeyoshi Usami, Masayuki Imanishi, Masashi Yoshimura, and Yusuke Mori Mihoko MaruyamaMihoko Maruyama More articles by this author , Uta MichibataUta Michibata More articles by this author , Yutaro TanakaYutaro Tanaka More articles by this author , Hiroshi YoshikawaHiroshi Yoshikawa More articles by this author , Kazufumi TakanoKazufumi Takano More articles by this author , Rie TajiriRie Tajiri More articles by this author , Kazumi TaguchiKazumi Taguchi More articles by this author , Shuzo HamamotoShuzo Hamamoto More articles by this author , Atsushi OkadaAtsushi Okada More articles by this author , Takahiro YasuiTakahiro Yasui More articles by this author , Shigeyoshi UsamiShigeyoshi Usami More articles by this author , Masayuki ImanishiMasayuki Imanishi More articles by this author , Masashi YoshimuraMasashi Yoshimura More articles by this author , and Yusuke MoriYusuke Mori More articles by this author View All Author Informationhttps://doi.org/10.1097/JU.0000000000003216.07AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVE: We have previously reported that the phase transition phenomenon of calcium oxalate (CaOx) makes urinary stones harder. Knowing phase transition velocity helps estimate the change of the patient's stone hardness over time. It affects the decision-making of the fragmentation treatment methods. However, the mechanism of the phase transition has not been clarified. Therefore, we stimulated the phase transition of CaOx dihydrate (COD) stone to CaOx monohydrate (COM), and observed the time course of the internal and surface structure. METHODS: A urinary stone mainly composed of COD, in which the phase transition has not progressed much, was stored in a vial containing CaOx supersaturated solution at 37oC with gentle shaking. We picked up the stone from the solution every week and observed the phase transition process from COD to COM. X-ray micro-CT and scanning electron microscopy were introduced. After completing the phase transition observation, a thin section of the stone was prepared. Then, the phase identification was performed in more detail using polarizing microscopy and Raman microscopy. RESULTS: The dissolution of the COD crystal surface and nucleation of COM crystals co-occurred. The inside of the COD stone underwent a phase transition to COM. After the transition, we found typical mosaic and concentric structures of COM (Figure 1). The extent of the transition from COD to COM strongly depended on the area. An area where crystal defects, cracks, and crystal boundaries exist, transited fast (∼10 μm/h); a few millimeter size COD crystals almost turned into COM structures in only two weeks. The transition ratio was faster than that in the human body. CONCLUSIONS: We have succeeded in the world's first artificial urinary stone phase transition experiment. Once the phase transition starts, rapid progress possibly occurs. Further, transformation velocity strongly depends on COD crystal structure and aggregation state. Our observation showed experimental phase transition of a natural urinary stone is faster than that in the human body, and indicated a potential mechanism enabled to slow down the phase transition of crystals in vivo, which could be useful to prevent stone formation. Source of Funding: JSPS KAKENHI Grant Numbers (JP19K22965, JP20K21658, JP22H00302, JP22H01971) © 2023 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 209Issue Supplement 4April 2023Page: e46 Advertisement Copyright & Permissions© 2023 by American Urological Association Education and Research, Inc.MetricsAuthor Information Mihoko Maruyama More articles by this author Uta Michibata More articles by this author Yutaro Tanaka More articles by this author Hiroshi Yoshikawa More articles by this author Kazufumi Takano More articles by this author Rie Tajiri More articles by this author Kazumi Taguchi More articles by this author Shuzo Hamamoto More articles by this author Atsushi Okada More articles by this author Takahiro Yasui More articles by this author Shigeyoshi Usami More articles by this author Masayuki Imanishi More articles by this author Masashi Yoshimura More articles by this author Yusuke Mori More articles by this author Expand All Advertisement PDF downloadLoading ...

Indicatrix of TE and TM- polarized wave velocities in crystal of classes 4mm, 3m, 6mm with magneto-electric effect

This work is devoted to the theoretical study of the laws of propagation of electromagnetic waves of TE and TM polarization in anisotropic media belonging to classes 4mm, 3m, 6mm, etc. having a magnetoelectric effect. The directions of the vectors of the phase and group velocities of the polarization waves TE and TM at the boundary of a uniaxial crystal with magnetoelectric properties are considered. In the analytical form, the values of the directions of the phase and group velocities of the TE and TM waves are indicated, depending on the direction of the wave vector of the incident wave. The consequences of the obtained results for uniaxial crystals in the absence of magnetoelectric properties are discussed. The solution of the tasks set in this paper is based on the use of the matrix method. On its basis, various problems of wave processes in an isotropic elastic medium, electromagnetic waves in crystals, the distribution of coupled elastic and electromagnetic waves in piezoelectric and piezomagnetic media with a magnetoelectric effect were previously considered. In the presence of a magnetoelectric effect for electromagnetic waves propagating through uniaxial crystals, the parameters of the wave vector, phase and group velocities are determined. The obtained results are analyzed for electromagnetic waves propagating through uniaxial crystals in the absence of a magnetoelectric effect. The indicatrices of the wave vectors propagating in the plane and the phase velocities of the TM polarization waves are limited ( 0 ) x z. Based on the Rayleigh equation, the values of the group velocity are obtained. The density of electromagnetic energy fluxes and their components are determined for TE and TM waves. The energy transfer rate and its direction are determined. It is shown that the group velocities and directions obtained from the Rayleigh equation and the Umov-Poynting vector do not coincide.

A promising composite solid electrolyte of garnet-type LLZTO and succinonitrile in thermal polyurethane matrix for all-solid-state lithium-ion batteries

For solid-state electrolyte in lithium-ion batteries, high crystal boundary impedance leads to tough electrolyte-electrode interfacial issues. Here, we introduce garnet Li6.4La3Zr1.4Ta0.6O12 (LLZTO) nanoparticles and succinonitrile (SN) into thermal polyurethane (TPU) to fabricate a composite solid-state electrolyte (TPU/LLZTO/SN), achieving high ionic conductivity of 6.452 × 10−4 S cm−1. The TPU polymer with specific soft and hard segments allows lithium ions fast transport and holds good mechanical strength as the electrolyte matrix. The ionic conductor LLZTO further improves the ionic conductivity and mechanical property of the composite electrolyte membrane. Additional SN supplies the electrolyte’ wide electrochemical stabilization window, and enhances the metallic lithium compatibility of the TPU matrix. As a result, the as prepared TPU/LLZTO/SN electrolyte presents high lithium ions transference number of 0.64, and also good mechanical property.

COMPUTER SIMULATION OF THE EFFECT OF COHERENT DYNAMICAL DIFFRACTION OF SYNCHROTRON RADIATION IN CRYSTALS OF ARBITRARY SHAPE AND STRUCTURE

A new scheme for the numerical solution of Takagi–Taupin equations, which makes it possible to simulate the effect of synchrotron radiation diffraction in crystals of arbitrary structure, is described in detail. The new scheme is convenient to perform calculations for crystals of arbitrary shape. The rectangular coordinate system and the algorithm for calculating derivatives at half of step have proven their efficiency and are used, but the recurrence equations of this algorithm have been modified towards simplification. The boundary conditions are in no way related to the crystal boundaries. A computer program is developed, and two examples are considered for the cases of diffraction in the Laue and Bragg geometries, for which the analyticl solutions are known. The calculation results are in complete agreement with these solutions.

Classification of EBSD Kikuchi Patterns for Stainless Steel by Unsupervised Learning Methods to Investigate Grain Boundaries

Electron backscatter diffraction (EBSD) indexing based on Kikuchi diffraction patterns, which indicate the types and orientation of the crystal lattice, is effective for characterizing crystals. Most regions in a sample can be indexed due to simulation of diffraction patterns of possible crystal types, orientations, and angles. However, indexing some of the complex regions related to the grain boundaries, dislocations, and strain areas is difficult. Moreover, minor crystal structures are possibly omitted from the index results. To characterize all the regions, including such complicated boundaries, the analysis of raw data, including all Kikuchi patterns, is necessary. By analyzing all the Kikuchi patterns, significant information can be extracted from mixed crystal conditions. Stainless steel was used as the model sample in this study. As hydrogen diffusion in metals strongly depends on the crystal structure and grain boundaries, structural analysis is required to study hydrogen behavior in steel. In this study, all Kikuchi patterns at all pixels in a measurement area of stainless steel were analyzed simultaneously using unsupervised learning methods, such as principal component analysis and multivariate curve resolution, and the pixels of the measurement area were classified based on the Kikuchi patterns to investigate the grain boundaries and dislocations in detail.

Synergistic approach for enhancement of piezoelectricity in the lead-free BiFeO3-BaTiO3 ceramics

Large piezoelectric actuator coefficient (d33*) and enhanced piezoelectric sensor coefficient (d33) with high Curie temperature (TC) are desired for real applications. In this work, a synergistic approach of bipolar cycling and donor doping strategy was applied for the enhancement of piezoelectric performance. An excellent d33 value of 382 pC/N was achieved by the novel (AC-bias and DC-bias) poling method in the lead-free Nb-modified 0.67Bi1.03FeO3-0.33BaTiO3 quenched ceramics. In addition, a large d33* of ∼ 400 pm/V has been obtained under a very low electric field of 25 kV/cm along with a high TC ≈ 473 °C. This enhanced piezoelectric performance is related to the crystal structure morphotropic phase boundary, bipolar cycling, optimum grain size (∼5 µm), maximum lattice distortion, and soft-ferroelectric effect induced by the donor doping. The small strain hysteresis, Hs ≈ 20%, and temperature-insensitive piezoelectric strain, Δd33*(T) = d33*(T)/d33*(RT) ≈ 24% suggest the accurate and precise positioning in the piezoelectric actuator devices. The simultaneously improved d33 and temperature-stable d33* with a high TC are promising results in the lead-free BFBT ceramics.

Optical Steganography via Programmable Anchoring Boundary of Soft Materials

AbstractEngineering the properties of light with multi‐channel planar elements can produce independent spectral response, and has formed the solid basis for image steganography techniques, which holds great promise for applications including information storage, optical encryption, and anti‐counterfeiting. However, most of the recently reported steganography systems suffer from limited size, sophisticated fabrication, and finite degree of freedom in encoding and decoding process. Herein, a versatile image steganography system based on soft material is proposed. The polarization and intensity of transmitted light are modulated by programing the anchoring boundary of liquid crystals, allowing arbitrary independent images multiplexing in single‐size element with high fidelity. Specifically, the stimuli‐responsiveness of liquid crystals endows the platform with a new degree of freedom to manipulate the transmitted spectrum dynamically, further sketching a prospective framework toward a new type of steganography with fascinating tunability. The proposed strategy sheds new light on multifarious display system by harnessing the stimuli‐responsiveness of soft materials, leading to promising applications in information storing, image steganography, anti‐counterfeiting, and multilevel encryption techniques.

Micro-karstification in a stalagmite, Küpeli Cave, southern Turkey

This article deals with micro-karstification forming abundant dissolution features in a stalagmite from Küpeli Cave in southern Turkey. Dissolution occurs when cave water enriched with CO2 from the atmosphere and soil seeps into the stalagmite. Water is transmitted from the surface of the stalagmite to the interior by the roughly vertical or diagonal notch-shaped pores formed by the enlargement of intercrystalline pores by dissolution. These slightly elongated pores appear embedded in different parts of the stalagmite and characterize different stages of dissolution during the stalagmite formation. Later, when this water reaches the relatively more permeable growth layer surfaces, it flows along these surfaces, and diffuse dissolution features form. These features include micro-scale pitted and etched surface structures, rounded and enlarged crystal boundaries and intercrystalline pores, and the breakdown of relatively large crystals into small crystals (micritization). When the percolating water is sufficiently saturated with calcium carbonate in the stalagmite, secondary calcite precipitation occurs as rim and pore-filling cements within the pores formed as a result of dissolution. In general, dissolution and calcite re-precipitation as cement are early diagenetic events and occur at different stages of stalagmite development due to seasonal variation in CO2 and CaCO3 contents of the water in the epikarst zone and within the stalagmite. These conditions were probably provided during the wet season.

Dating individual zones in phenocrysts from the 2016–2017 eruption of Bogoslof volcano provides constraints on timescales of magmatic processes

We investigate the rates of magmatic processes using clinopyroxene diffusion chronometry on volcanic products erupted in August 2017 at the end of the 9-month eruption of Bogoslof volcano. The eruptive products contain plagioclase, clinopyroxene, and amphibole, all of which exhibit sharp chemical boundaries and are occasionally observed in multi-phase crystal clots with shared zoning boundaries across different mineral phases. At the shared boundaries in crystal clots, clinopyroxene and plagioclase continued to grow but abruptly changed composition from Mg# 81.7 ± 5.8 to 72.9 ± 3.0 and An82.5±1.4 to An61.3±5.7, respectively. Additionally, the sharp boundary marks where amphibole became unstable and began forming a reaction rim. Synthesizing these observations, we were able to determine that the shared boundaries formed as a result of rapid decompression during magma ascent, followed by storage in a shallow cryptodome, where magma accumulated prior to erupting.In order to determine the timescales of magma ascent and subsequent crystal residence times, we applied diffusion chronometry on zoned clinopyroxene phenocrysts using Mg# concentrations at 1056 °C determined from FeTi oxide pairs. Our diffusion modeling results show that diffusion began at the stepwise boundaries in clinopyroxenes no more than180 days before the final explosive event.These results were then used to calculate crystal growth rates for shared plagioclase and amphibole rims, as shared zones in crystal clots indicate that the boundaries in all three phases formed contemporaneously. We calculate growth rates of plagioclase crystals (1.7 ± 0.99 × 10−6 um/s) and amphibole reaction rims (2.8 ± 0.47 × 10−6 um/s). The calculated natural growth rate of plagioclase was then used to constrain additional magmatic timescales from growth rate chronometry, results of which support our diffusion timescales.Our results indicate that the distinct boundaries in all three mineral phases formed due to ascent-driven decompression followed by shallow emplacement of mafic magma that occurred continually throughout the course of the eruption. By subtracting diffusion timescales from the date that the samples were erupted, the oldest crystal boundaries correspond to March 2017, seemingly correlating with increases in both seismicity and SO2 emissions. These observations may suggest that our petrochronometric results are supported by interdisciplinary observations.

The roles of microstructural anisotropy in tribo-corrosion performance of one certain laser cladding Fe-based alloy

Because of the microstructural anisotropy for laser cladding materials, the tribo-corrosion performance can vary significantly with different directions. In this study, one certain Fe-based coating was fabricated by laser cladding. To study the effects of anisotropy, three working surfaces (0°, 45°, and 90° to the building direction) were machined from the laser cladding samples; as-cast samples with an approximately homogeneous structure were prepared as controls. The tribo-corrosion tests were conducted in a 3.5 wt% NaCl solution with varying normal loads (5, 10, and 15 N). The results demonstrated that the 45° surface has superior friction stability, corrosion resistance, and wear resistance. This was directly related to the crystal orientation and grain boundary density. In addition, a refined microstructure may enhance tribo-corrosion properties by increasing deformation resistance and decreasing surface activity.

Molecular dynamics study of thermal transport across Ga2O3–diamond interfaces

Integration of β-Ga2O3 with high thermal conductivity materials such as diamond has been considered due to β-Ga2O3's low and anisotropic thermal conductivity, reaching only 27 W m–1 K–1. However, the effect of crystallographic orientation on thermal interface resistance has not been studied extensively, which is relevant for potential device architectures. In this work, we use molecular dynamics simulations to investigate the crystal orientation-dependent thermal boundary resistance (TBR) across van der Waals bonded diamond–β-Ga2O3 and ionicly bonded amorphous Al2O3–β-Ga2O3 interfaces. Al2O3 is often used as interlayer to grow diamond onto Ga2O3. We find that TBR values across the van der Waals interface may vary by up to 70% depending on the orientation of the β-Ga2O3, while the Al2O3–β-Ga2O3 TBR values remain around 0.9 ± 0.3 m2 KGW−1. We, thus, conclude on the optimal direction of β-Ga2O3 to use for reducing the TBR in these heterostructures.

Using acoustic velocities and microimaging to probe microstructural changes caused by thermal shocking of tight rocks

Introduction: Large scale, Earth processes and bulk rock properties are influenced by underpinning, dynamic, microstructures within rocks and geomaterials. Traditionally, the amount of porosity has been considered the primary control on important bulk rock properties like seismic wave velocities (Vp and Vs) and permeability. However, in tight rocks, velocity and permeability (k) can change substantially despite small changes in the amount of porosity during cracking. Therefore, other microstructural features inherent to given lithologies, such as heterogeneity and anisotropy in mineral properties are considered as factors controlling these bulk rock properties. Understanding which microstructural features control Vp, Vs, and permeability in tight rocks is useful in applications like enhanced geothermal systems (EGS), where thermal shocking is used to increase permeability. Thermal shocking involves injecting surface water into the subsurface to cool mineral crystals, induce contraction of crystals, and cause thermal cracking.Methods: We tested three tight lithologies with unique microstructures; granodiorite (SWG), basalt (PTB), and carbonate (MSA). We simulated thermal shocking by slowly heating samples to 350°C and then quenching them. We chose a temperature of 350°C because thermal shocking at this temperature is not well documented in literature, and this temperature is relevant to EGS. Using time-lapse microimaging, we assessed how thermal cracking occurs in each lithology and explored how thermal cracks influence connected porosity, Vp, Vs, and k.Results: Microimaging shows extensive cracking in the SWG and MSA lithologies, and little to no cracking in PTB with thermal shocking treatment. Vp and Vs became more pressure sensitive, and elastic moduli decreased with treatment for all lithologies. This may be caused by reduced stiffness between mineral crystal boundaries with treatment.Discussion: Lithologies with minerals that have anisotropy of or a wide range in thermal conductivity and/or thermal expansion coefficients can have increased thermal cracking. In thermally shocked SWG and MSA, Vp and Vs are good indicators of thermal cracking and k increases, but less so in PTB. Lithologies like PTB may require multiple thermal shock stimulations to increase permeability. Our results highlight how micro-scale changes influence bulk rock properties and when we can monitor permeability increases and microscale thermal cracking with Vp and Vs.

Bulk Incorporation with 4‐Methylphenethylammonium Chloride for Efficient and Stable Methylammonium‐Free Perovskite and Perovskite‐Silicon Tandem Solar Cells

AbstractMethylammonium (MA)‐free perovskite solar cells have the potential for better thermal stability than their MA‐containing counterparts. However, the efficiency of MA‐free perovskite solar cells lags behind due to inferior bulk quality. In this work, 4‐methylphenethylammonium chloride (4M‐PEACl) is added into a MA‐free perovskite precursor, which results in greatly enhanced bulk quality. The perovskite crystal grains are significantly enlarged, and defects are suppressed by a factor of four upon the incorporation of an optimal concentration of 4M‐PEACl. Quasi‐2D perovskites are formed and passivate defects at the grain boundaries of the perovskite crystals. Furthermore, the perovskite surface chemistry is modified, resulting in surface energies more favorable for hole extraction. This facile approach leads to a steady state efficiency of 23.7% (24.2% in reverse scan, 23.0% in forward scan) for MA‐free perovskite solar cells. The devices also show excellent light stability, retaining more than 93% of the initial efficiency after 1000 h of constant illumination in a nitrogen environment. In addition, a four‐terminal mechanically stacked perovskite‐silicon tandem solar cell with champion efficiency of 30.3% is obtained using this MA‐free composition. The encapsulated tandem devices show excellent operational stability, retaining more than 98% of the initial performance after 42 day/night cycles in an ambient atmosphere.

Microscopic mechanisms of coral reef limestone crack propagation

Coral reef limestone (CRL) is a marine sedimentary rock dominated by biogenesis, and its composition as well as internal structure characteristics are different from traditional terrigenous rocks. This article used CT scanning and petrographic thin section observations to visually and quantitatively analyze crack morphological characteristics after triaxial shear failure at a microscopic scale. The analysis revealed the mechanism of crack initiation and propagation from the perspectives of geological genesis and fracture mechanics. Results show that the crack propagation mechanism in the bio-cemented framework includes propagation along crystal boundaries and across crystals. Cracks can be classified as intergranular cracks, transgranular cracks, and bifurcation cracks based on crack morphology. The destruction mode of the specimen is controlled by the pore structure and cemented framework. Based on the pore distribution, the destruction mode can be divided into local tension failure and monoclinic shear failure. Understanding CRL crack propagation mechanisms has important scientific significance and practical engineering value for enriching rock damage theory and long-term stability analysis of island reef engineering foundations.