Crystal Transition Research Articles

Large-scale assembly of isotropic nanofiber aerogels based on columnar-equiaxed crystal transition

Ice-templating technology holds great potential to construct industrial porous materials from nanometers to the macroscopic scale for tailoring thermal, electronic, or acoustic transport. Herein, we describe a general ice-templating technology through freezing the material on a rotating cryogenic drum surface, crushing it, and then re-casting the nanofiber slurry. Through decoupling the ice nucleation and growth processes, we achieved the columnar-equiaxed crystal transition in the freezing procedure. The highly random stacking and integrating of equiaxed ice crystals can organize nanofibers into thousands of repeating microscale units with a tortuous channel topology. Owing to the spatially well-defined isotropic structure, the obtained Al2O3·SiO2 nanofiber aerogels exhibit ultralow thermal conductivity, superelasticity, good damage tolerance, and fatigue resistance. These features, together with their natural stability up to 1200 °C, make them highly robust for thermal insulation under extreme thermomechanical environments. Cascading thermal runaway propagation in a high-capacity lithium-ion battery module consisting of LiNi0.8Co0.1Mn0.1O2 cathode, with ultrahigh thermal shock power of 215 kW, can be completely prevented by a thin nanofiber aerogel layer. These findings not only establish a general production route for nanomaterial assemblies that is conventionally challenging, but also demonstrate a high-energy-density battery module configuration with a high safety standard that is critical for practical applications.

Spatial localization of high-frequency particle oscillations in a complex plasma monolayer

We study the spatial distribution of dynamical properties in a strongly coupled confined experimental dust monolayer with a dense central region and a rarefied periphery. We show that the dust particle oscillations spectrum shifts into the low-frequency range from the center of the structure toward its periphery. Correspondingly, the high-frequency particle oscillations are localized in the central region of the system. This effect is quantitatively described within the framework of the model system of trapped screened Coulomb charges. Such spatial localization has a significant effect on the spatial distribution of dynamical parameters, such as the amplitude of particle oscillations and the coupling parameter. The obtained results might be useful for the theory of crystal formation, instabilities and phase transitions in complex (dusty) plasmas, colloidal suspensions, and Coulomb crystals.

Standard molar enthalpies of formation of 3-methylglutaric and 3,3-dimethylglutaric anhydrides

In this research, both the standard molar enthalpy of formation in the crystalline phase and in the gas phase of 3-methylglutaric anhydride was calculated from experimental data. The temperature and enthalpy of fusion, as well as the molar heat capacity in solid phase was calculated by differential scanning calorimetry; the molar enthalpy of sublimation at 298.15 K by the Knudsen effusion method, the molar enthalpy of vaporization at 298.15 K by thermogravimetric analysis, and the standard massic combustion energy by combustion adiabatic calorimetry. Since 3,3-dimethylglutaric anhydride presented crystal transitions (with endothermic points at 352.76 K, 356.98 K and 397.15 K), some of its thermochemical properties were estimated from the functional group-contribution methods proposed by Benson, Gani and Naef and from application of Machine Learning based models.

Structural phase transition driven dielectric and optical properties with reduction in band gap in Sr2+ modified BaTiO3 ceramics

Ferroelectric materials with crystal symmetry transition from single phase to multiphase coexistence exhibit anomalous photosensitive properties. The optical properties (optical band gap and photosensitive) found on non-centrosymmetric and centrosymmetric systems achieved research interest because of their interesting behavior. In this regard, the lead-free polycrystalline Ba1−x Sr x TiO3 (BSTO, 0 ) has been synthesized to explore its crystal structure, dielectric, light absorption, and photocurrent sensing properties for various applications. Both experimental and theoretical studies on BSTO (0 ceramics confirm the crystal symmetry transition with the reduction of band gap as compared to pristine BaTiO3. This crystal symmetry transition plays an important role in varying the various physical properties as it involves the transition from the polar phase to the non-polar phase. The optical band gap has been estimated experimentally by the Tauc plot method and found that there is a small variation of energy band gap from 3.615 eV to 3.212 eV with Sr substitution. The highest dielectric constant was found to be 5327 at lower frequency on Ba0.76Sr0.24TiO3 after that for further increase in Sr concentration the dielectric constant decreases because of the introduction of the non-polar phase. A strong correlation between crystal structure and physical properties (dielectric, optical, etc.) has been observed. The photocurrent of the samples is significant which reveals that the sample is influenced by the photons. In a nutshell, the present study deepens the understanding of the correlation between crystal structure and various physical properties of BSTO and, hence provides an idea of required design parameters to construct a ferroelectric system for better photosensitive nature suitable for device applications.

(Digital Presentation) Phase-Field Modeling of the Reduction Process in Solid Oxide Fuel Cell Anode

It is well-known that the reduction process of nickel oxide-yttria-stabilized zirconia (NiO-YSZ) composite anode influences the initial performances and durability of solid oxide fuel cell. In this work, phase field method is used to simulate the reduction process of nickel oxide (NiO) in anode-supporting solid oxide fuel cell (SOFC), which captures the competition effects among diffusion, crystal phase transition of NiO to Ni, and sintering. A real three-dimensional microstructure of NiO-YSZ composite anode reconstructed using focused ion beam-scanning electron microscopy (FIB-SEM) technique is used to initialize the simulation. The simulation results are qualitatively compared to experimental results under different reduction conditions. The results reveal that the stress distribution in SOFC anode can be largely influenced by the interactions between the residual stress in yttria-stabilized zirconia (YSZ) and the reduction process. The results explain the phenomena of mechanical damage formed in SOFC single cell during reduction. Figure 1

Uniaxial - biaxial lyotropic cholesteric phase transition of lyotropic liquid crystals

ABSTRACT A Landau model is proposed to describe the uniaxial – biaxial lyotropic cholesteric phase transition of lyotropic liquid crystals (LLC). The model free energy is based on a mixture of rod-shaped and disc-shaped micelles. The possibility of the existence of two biaxial lyotropic cholesteric phases and two uniaxial lyotropic cholesteric phases of LLC is discussed. The phase transitions between two biaxial lyotropic cholesteric phases and two uniaxial lyotropic cholesteric phases are explored. Qualitative comparisons between theoretical predictions and recent experimental results are discussed.

High-pressure phase transitions in diamondoid molecular crystals observed by in situ Raman spectroscopy

High-pressure phase transitions in diamondoid molecular crystals observed by <i>in situ</i> Raman spectroscopy

Machine learning-based molecular screening of solid–solid transition of molecular crystals

Machine learning-based molecular screening of solid–solid transition of molecular crystals

Locations of the energy levels of lanthanide ions in Gd2O3 single crystals

Large-sized, high optical quality Gd2O3 single crystals were grown from a solution at T = 1145 °C using Czochralski method. XRD analysis showed that the crystal structure is characterized by a single cubic (bixbyite) phase (c-phase). The absorption spectra and luminescence properties of Gd2O3 doped with Eu3+ and Tb3+ impurity ions were studied. The absorption spectrum of Gd2O3:Eu in the short wavelength region is mainly due to charge transfer transitions from O2− to Eu3+ (240–290 nm), which overlap with the Urbach tail of the host-absorption. Additionally, electronic transitions in Eu3+ (320–540 nm) and Gd3+ (245–315 nm) lanthanide ions contribute to the absorption spectrum. Intraconfigurational radiative f – f transitions in impurity ions are clearly observed upon both UV- and X-ray excitations. However, 6PJ → 8S7/2 radiative transitions in Gd3+ ions are completely unobservable. Based on the obtained spectroscopic data, the energy positions of the ground state of all di- and trivalent lanthanide ions, as well as the energies of intraconfigurational f – f and interconfigurational f – d electronic transitions in Gd2O3 crystals with a cubic structure, are calculated. The proposed electronic energy diagram is used to discuss efficient energy transfer between lanthanide ions.

Investigation on nano-grinding process of GaN using molecular dynamics simulation: Nano-grinding parameters effect

Nano-grinding is an essential step in ultra-precision machining for brittle material semiconductor workpieces in order to improve the surface quality and preserve strength prior to practical application. This study utilizes molecular dynamics (MD) method to conduct single-crystal gallium nitride (GaN) nano-grinding simulations under varying parameters. The damage mechanism of the surface/subsurface on the nanometer scale is explored through atomic displacement analysis, radial distribution function (RDF), phase transition, dislocation analysis, processing force, temperature distribution, and residual stress distribution. The machined surface quality and crystal structure distribution in the subsurface damage layer (SDL) are also examined, and a strong correlation is found between the parameters in nano-grinding. The nano-grinding speed is closely associated with the post-processing surface morphology, crystal phase transition, and temperature distribution in the GaN workpiece. Additionally, the ambient temperature has a considerable effect on the surface morphology and crystal phase transition. Moreover, the nano-grinding depth has a considerable influence on the surface morphology, phase transition, dislocation, processing force, and the temperature-dependent distribution of the residual stress in the GaN workpiece. This work reveals the relationship between the parameters and the mechanical properties of the machined surface in nano-grinding, and elucidates the damage mechanism of the subsurface, thus providing a helpful guide to the optimization of ultra-precision machining.

Crystal structures and phase transition in a new organic-inorganic hybrid material TEACCl·FeCl4

A new organic-inorganic hybrid material TEACCl·FeCl4 (1, TEACCl+ = Et3NCH2Cl+) with a phase change at 264.3 K was synthesized. 1 was characterized by thermogravimetric, differential scanning calorimetry, single crystal structure determination, dielectric measurement, infrared spectra and ultraviolet-vis spectral measurement. It is worth noting that a reversible phase change appeared near 264.3 K, which is verified by differential scanning calorimetry, single crystal structure determination and dielectric measurement. The corresponding enthalpy change of phase transition equals to 8.17 J·mol−1·K−1 on the heating process and −8.83 J·mol−1·K−1 on the cooling process, indicating 1 can be used as a heat storage material.

Equilibrium solubility, solvation and dissolution thermodynamics, and density functional theory study of albendazole in solutions of acetone/methanol/isopropanol + water

In this work, albendazole was dissolved in mixtures of acetone/methanol/isopropanol + water to examine its solubility, dissolution thermodynamics, solvation behavior, and intermolecular interactions. The shake-flask method was used to conduct solubility tests at a pressure of 101.0 kPa and temperatures from 278.15 to 323.15 K. In water and pure organic solvents, respectively, the lowest and greatest levels of albendazole solubility were found. XRD analysis-based experiments found no evidence of crystal solvation or transition. Jouyban-Acree, modified Wilson, QSPR and modified van't Hoff-Jouyban-Acree models correlated the solubility to solvent composition and temperature with the relative average deviations (RAD) of no more than 8.99 %. The equilibrium solubility at 298.15 K was examined using the approach of extended Hildebrand solubility parameter, which produced an average relative deviation of 3.63 %. The dipolarity-polarizability and solubility parameter of solutions have a considerable impact on the solubility fluctuation, according to the analysis of linear solvation energy relationship. The preferred solvation of albendazole by water and different organic solvents was quantitatively examined with the help of the inverse Kirkwood-Buff integrals. Albendazole was preferentially solvated by the organic solvents in moderate and rich organic solvent compositions in blends, where albendazole served as a Lewis acid. An enthalpy-driven mechanism and an endothermic process were identified by thermodynamic analysis of the entropy-enthalpy compensation and dissolution properties for albendazole dissolving in blends. The electrostatic characteristics of albendazole acidity/basicity were highlighted using analysis of Hirshfeld surface and molecular surface. The primary targets of nucleophilic and electrophilic assault are the –NH and -S-groups. An independent gradient model based on Hirshfeld partition analysis was used to visual the weak interactions between albendazole and different solvents.

Enhancing the equilibrium solubility of salicylic acid in aqueous media by using polyethylene glycols 200, 400 and 600 as cosolvents: Correlation and dissolution thermodynamics

The solubility of salicylic acid in three mixtures of polyethylene glycol (PEG) with different molar masses of 200 to 600 g/mole were experimentally determined by a shake flask method at temperature range of (293.15 to 313.15) K under ambient pressure (≈85 kPa). The experimental results indicated that the solubility of salicylic acid enhanced by the introduction of PEGs to the water, and that could be explained with Hansen’s parameters and like-dissolves-like rule. Based on the results, PEG 600 had the best solubilization power, whereas PEG 200 displayed the lowest solubilization power, and generally the solubility decreased with decreasing molar mass of PEG and also decreasing temperature. Moreover, the equilibrium solid phase crystal of salicylic acid is characterized with X-ray powder diffraction analysis to identify no polymorphic transformation, solvate formation or crystal transition during the whole solvent crystallization process. A number of linear and nonlinear cosolvency models including the Jouyban-Acree based models along with the equations of van’t Hoff, the mixture response surface, the combined nearly ideal binary solvent/Redlich-Kister, λh and the modified Wilson-van’t Hoff were challenged to correlate/predict the solubility of salicylic acid in these mixtures. The computed values of the Jouyban-Acree based models presented a good agreement with the experiment data than the others, as a consequent of a low mean percentage deviation (MPD ≤ 15.7%). According to the enthalpy–entropy compensation analysis, there observed slope changes indicating that two mechanisms, enthalpy or entropy controlled the solubility increment depending on the PEG mass fraction in each solution.

Large-Scale Production and Optical Properties of a High-Quality SnS2 Single Crystal Grown Using the Chemical Vapor Transportation Method

The scientific community believes that high-quality, bulk layered, semiconducting single crystals are crucial for producing two-dimensional (2D) nanosheets. This has a significant impact on current cutting-edge science in the development of next-generation electrical and optoelectronic devices. To meet this ever-increasing demand, efforts have been made to manufacture high-quality SnS2 single crystals utilizing low-cost CVT (chemical vapor transportation) technology, which allows for large-scale crystal production. Based on the chemical reaction that occurs throughout the CVT process, a viable mechanism for SnS2 growth is postulated in this paper. Optical, XRD with Le Bail fitting, TEM, and SEM are used to validate the quality, phase, gross structural/microstructural analyses, and morphology of SnS2 single crystals. Furthermore, Raman, TXRF, XPS, UV–Vis, and PL spectroscopy are used to corroborate the quality of the SnS2 single crystals, as well as the proposed energy level diagram for indirect transition in the bulk SnS2 single crystals. As a result, the suggested method provides a cost-effective method for growing high-quality SnS2 single crystals, which could lead to a new alternative resource for producing 2D SnS2 nanosheets, which are in great demand for designing next-generation optoelectronic and quantum devices.

Charge Storage Mechanism in Electrospun Spinel-Structured High-Entropy (Mn0.2 Fe0.2 Co0.2 Ni0.2 Zn0.2 )3 O4 Oxide Nanofibers as Anode Material for Li-Ion Batteries.

High-entropy oxides (HEOs) have emerged as promising anode materials for next-generation lithium-ion batteries (LIBs). Among them, spinel HEOs with vacant lattice sites allowing for lithium insertion and diffusion seem particularly attractive. In this work, electrospun oxygen-deficient (Mn,Fe,Co,Ni,Zn) HEO nanofibers are produced under environmentally friendly calcination conditions and evaluated as anode active material in LIBs. A thorough investigation of the material properties and Li+ storage mechanism is carried out by several analytical techniques, including ex situ synchrotron X-ray absorption spectroscopy. The lithiation process is elucidated in terms of lithium insertion, cation migration, and metal-forming conversion reaction. The process is not fully reversible and the reduction of cations to the metallic form is not complete. In particular, iron, cobalt, and nickel, initially present mainly as Fe3+ , Co3+ /Co2+ , and Ni2+ , undergo reduction to Fe0 , Co0 , and Ni0 to different extent (Fe < Co < Ni). Manganese undergoes partial reduction to Mn3+ /Mn2+ and, upon re-oxidation, does not revert to the pristine oxidation state (+4). Zn2+ cations do not electrochemically participate in the conversion reaction, but migrating from tetrahedral to octahedral positions, they facilitate Li-ion transport within lattice channels opened by their migration. Partially reversible crystal phase transitions are observed.

Cryoablation combined with a clinical Chinese medicine for the treatment of lung cancer

Cryoablation has been clinically applied to the treatment of lung cancer, but cryoablation has the problem of incomplete tumor killing when the freezing dose is not enough, which may lead to tumor recurrence or metastasis. Therefore, cryoablation combined with other therapeutic options is usually suggested to achieve a complete cure for lung cancer. Clinical practices have shown that traditional Chinese medicine (TCM) treatment can improve the quality of life of patients with advanced lung cancer and prolong the postoperative survival time. However, the mechanism of the synergistic effect of Chinese medicine and cryotherapy, and the optimal treatment plan have not been clarified so far. Therefore, the effect of TCM particles on ice crystal growth and phase transition during cooling was investigated. In addition, we explored the optimized concentration and combination treatment sequence of TCM (lung care formula) and validated the optimal treatment protocol by establishing a mouse model of non-small cell lung cancer (NSCLC). In general, cryoablation combined with TCM is a useful treatment for lung cancer, which can effectively solve the problem of tumor recurrence after cryoablation.

Ab initio investigations of crystal transition for graphite intercalation compounds during aluminum electrolysiss

This paper studies the crystal transition of graphite intercalation compounds during aluminum electrolysis. Transmission electron microscopy (TEM) analysis demonstrates that the transition induces the structural degradation of carbon cathodes. Buckling of basal planes in the hexagonal compounds contributes to the crystal transition of intercalation compounds from hexagonal to rhombohedral modification. First-principle techniques are used to calculate the structural and electronic properties of graphite intercalation compounds by density-functional theory using the plane wave Pseudo-potential method. The results have demonstrated a close relationship between lattice mismatch and intercalation compounds. The electronic band structure close to the Fermi level has been investigated. The main effect of intercalation compounds is to transfer charge from alkali metal s electron to the carbon pz orbitals, rendering the system metallic. With a decrease of band gap, the crystal transition induces an increase in the interlayer spacing and C–C bond lengths and deteriorates the structural stability of carbon cathodes. The overwhelming majority of contribution to the bands neighboring the Fermi level is from C pz orbital in both intercalation compounds. These findings provide new insights into the mechanisms of carbon cathodes deformation, damage and fracture behavior.

Analysis of crystal structure transition of polycrystalline 3C-SiC in nanocrystalline grinding based on molecular dynamics simulation

In order to study the grain/grain boundary crossing mechanism of polycrystalline 3C-SiC materials under nano-grinding, molecular dynamics(MD) method was used to simulate the grinding process of polycrystalline 3C-SiC materials under diamond abrasive particles. Through the coupling method of Voronoi construction of polycrystalline 3C-SiC workpiece model and MD construction process, the nano-grinding process of polycrystalline 3C-SiC material was established, the potential function field parameters were optimized, and the residual stress in polycrystalline 3C-SiC was eliminated. The energy transition equation is modified to reduce the time for the system to enter dynamic equilibrium. The crystal structure and dislocation generation of polycrystalline 3C-SiC were analyzed by post-processing methods such as defect analysis and crystal structure recognition. The results found that: there are cubic lattice, simple cubic lattice, hexagonal lattice and graphene mechanism type atoms at the grain boundary. During the machining process, the cubic lattice type atoms are converted to other types atoms, and other types structure atoms are converted to each other. The internal structure atoms of grains are converted to the grain boundary structure atoms during the machining process, and the crystal atoms near the grain boundary have low structural stability. The grinding force mainly acts on the forward direction and just below the grinding grain, and also has a small amount of distribution at the grain boundary, but it is relatively weak. The dislocation caused by grinding mainly occurs at grain boundaries. The resulting debris was monolithic, and a few were granular. The interconversion between grains and different structural atoms at the grain boundary is mainly from the crystal lattice atoms in grains to other atoms at the grain boundary. The force is transferred to the grain through the grain boundary, which hinders the transboundary transfer of force and protects the grains. The shearing force plays a dominant role in the grinding process.

Effect of CH2 run length on the crystallization kinetics of sustainable long-spaced aliphatic polyesters

We have studied the isothermal overall crystallization rates and linear growth rates of four symmetric long-spaced aliphatic polyesters (LSAPEs) with 12, 18, 32, or 48 carbons in both the diol and the diacid monomers. With increasing crystallization temperature (Tc) these LSAPEs display discrete rate minima in a number and depth that depend on the length of the methylene spacer between esters. Two rate minima are observed for PE-48,48 and for PE-32,32; one for PE-18,18 and none for PE-12,12. The rate minima are not associated with a change in the mechanism of nucleation and growth or with a change in crystal packing, but occur at Tc where the crystal thickness transitions from a non-integer to a quantized integer number of monomer units. We explain such rate minima based on the self-poisoning feature used earlier to explain similar findings in n-alkanes and other types of precision polyethylene-like systems. In LSAPEs, metastable non-integer crystals attach to the growth front of stable integer crystals retarding their growth until the non-integer segments thicken to complete the layer. Lack of rate minima in the shortest-spaced symmetric polyester is explained by a small difference in lamellar thickness between non-integer and integer layered crystals which favors the formation of integer crystals at any Tc.

Structural transition in a ferroelectric nano-dispersed cholesteric liquid crystal

ABSTRACT We present a theoretical study of the orientational and electrical behaviors of a cholesteric liquid crystal dispersed with ferroelectric nanoparticles. We assume a soft planar coupling between the liquid crystal molecules and the nanoparticles. We consider two spiral structures in the ferroelectric nano-dispersed system under an external electric field. This assumption is due to the fact that the director and the polarization vector would have different pitches of spiral structure. We study the behavior of the average polarization and the pitch of the helical structure as a function of the field strength. The impact of ferroelectric nanoparticles on cholesteric-nematic phase transition is investigated by calculating the critical electric field. The influence of field strength and material parameters on the phase transition is also discussed. The calculations are based on a developed continuum theory and a modified form of free energy for the helical supramolecular structure. The influence of nanoparticle volume fraction on the helix unwinding of both spiral structures is studied. It is found that an electric field with a sufficiently high strength causes an increase in the pitch of the helical structure of polarization. We obtain a critical volume fraction of nanoparticles, after which the pitch of the polarization helical structure differs from the director pitch.