Crystal Phase Transition Research Articles

Electrical monitoring of organic crystal phase transition using MoS2 field effect transistor.

Hybrid van der Waals heterostructures made of 2D materials and organic molecules exploit the high sensitivity of 2D materials to all interfacial modifications and the inherent versatility of the organic compounds. In this study, we are interested in the quinoidal zwitterion/MoS2 hybrid system in which organic crystals are grown by epitaxy on the MoS2 surface and reorganize in another polymorph after thermal annealing. By means of field-effect transistor measurements recorded in situ all along the process, atomic force microscopy and density functional theory calculations we demonstrate that the charge transfer between quinoidal zwitterions and MoS2 strongly depends on the conformation of the molecular film. Remarkably, both the field effect mobility and the current modulation depth of the transistors remain unchanged which opens up promising prospects for efficient devices based on this hybrid system. We also show that MoS2 transistors enable fast and accurate detection of structural modifications that occur during phases transitions of the organic layer. This work highlights that MoS2 transistors are remarkable tools for on-chip detection of molecular events occurring at the nanoscale, which paves the way for the investigation of other dynamical systems.

Unusual single crystal to single crystal phase transition of a nicotine salt monitored using temperature dependent single crystal X-ray diffraction

The organic salt (S)-nicotinium 2,6-dihydroxybenzoate undergoes reversible single crystal to single crystal phase transition at 104 K.

Tailoring the physical properties of hybrid magnetic quinuclidine-based plastic compoundsviaweak interactions

The ketonization of the quinuclidine molecule were used to synthesize and physically characterize two paramagnetic hybrid compounds. The significant increase in the conductivity at HT is related with a crystal to plastic crystal phase transition.

Sacrificial Catalyst of Carbothermal-Shock-Synthesized 1T-MoS2 Layers for Ultralong-Lifespan Seawater Battery.

A Pt-nanoparticle-decorated 1T-MoS2 layer is designed as a sacrificial electrocatalyst by carbothermal shock (CTS) treatment to improve the energy efficiency and lifespan of seawater batteries. The phase transition of MoS2 crystals from 2H to metallic 1T─induced by the simple but potent CTS treatment─improves the oxygen-reduction-reaction (ORR) activity in seawater catholyte. In particular, the MoS2-based sacrificial catalyst effectively decreases the overpotential during charging via edge oxidation of MoS2, enhancing the cycling stability of the seawater battery. Furthermore, Pt nanoparticles are deposited onto CTS-MoS2 via an additional CTS treatment. The resulting specimen exhibits a significantly low charge/discharge potential gap of Δ0.39 V, high power density of 6.56 mW cm-2, and remarkable cycling stability up to ∼200 cycles (∼800 h). Thus, the novel strategy reported herein for the preparation of Pt-decorated 1T-MoS2 by CTS treatment could facilitate the development of efficient bifunctional electrocatalysts for fabricating seawater batteries with long service life.

Atomic-Scale Engineering of CuOx–Au Interfaces over AuCu Single-Nanoparticles

A face-centered tetragonal (fct) AuCu particle with a size of 7.1 nm and an Au/Cu molar ratio of 1/1 was coated by a silica shell of 6 nm thickness. Segregation of Cu atoms from the metal particle under an oxidative atmosphere precisely mediated the CuOx-Au interfacial structure by simply varying the temperature. As raising the temperature from 473 to 773 K, more Cu atoms emigrated from the AuCu particle and were oxidized into CuOx layers that grew up to 0.8 nm in thickness. Simultaneously, the size of the Au-rich particle lowered moderately while the crystalline structure transformed from the fct phase into the face-centered cubic (fcc) phase. The CuOx-Au interface shifted from the CuOx monolayer bound to Au single-atoms to Au@CuOx core-shell geometry, while the catalytic activity for CO oxidation at 433 K decreased dramatically. Moreover, a sharp loss in activity was observed as the crystal-phase transition occurred. This change in catalytic performance was ascribed to the geometrical configuration at the interfacial sites: the synergetic effect between the fct-AuCu particle and CuOx monolayer contributed to the much higher activity, whereas the fcc-AuCu/Au particle weakened its interaction with the thicker CuOx layer and thus decreased the activity.

Effect of Gd3+/Ti4+ heterovalent substitution on the crystal structure, morphology, optical properties, and phase transition behavior of bismuth layer-structured SrBi2Nb2O9

The double-layer Aurivillius compounds Sr1-xGdxBi2Nb2-xTixO9 (x ​= ​0, 0.2, 0.4, 0.6, 0.8, and 1), which have the potential to be developed as a ferroelectric material, have been synthesized using the molten salt method. This study aims to investigate the effect of the simultaneous substitution of Gd3+ and Ti4+ ions in SrBi2Nb2O9 on the phase formation, crystal structure, morphology, and ferroelectric properties. The single-phase product with A21am orthorhombic structure was obtained for all samples by X-ray diffraction analysis. The unit cell becomes more orthorhombic with increasing x as the degree of tetragonality increases. SEM micrographs demonstrate the plate-like grain morphology with an anisotropic growth direction, and the grain is smaller in size with increasing x. FTIR spectra indicate that cation substitution was successful, especially Ti4+ ions at the B-site. With increasing x, the ferroelectric transition temperature (Tc) increases, which has been explained in terms of a reduction in the tetragonality. The open hysteresis loops provide evidence of ferroelectric properties which is consistent with the trend of room-temperature dielectric constant. The optical bandgap value is proportional to the trend of the dielectric characteristics of the samples.

Tunable Luminescence on Indium Halide Hybrid Regulated by Sb3+ Doping Concentration

AbstractSb3+ doping strategy has proved to be an effective way to regulate the band gap and improve the photophysical properties of metal halides. Herein, Sb3+‐doped lead‐free indium halide hybrid InCl6(C4H12N2)2Cl·H2O:xSb3+ (0 ≤ x ≤ 1) is reported. Upon Sb3+‐doping, the weak emission of InCl6(C4H12N2)2Cl experiences a significant enhancement in emission intensity with near‐unity photoluminescence quantum yield (PLQY). The photophysical data fitted by the power‐law equation verifies self‐trapped exciton emission for the broadband emission. Interestingly, the emission experiences a gradual red‐shift with emission color changing from green to yellow and finally to orange as the Sb3+‐doped concentration increases. The single crystal X‐ray diffraction, excitation wavelengths‐dependent emission spectra, and the distortion degree calculation of InCl6(C4H12N2)2Cl·H2O:xSb3+ (0 ≤ x ≤ 1) indicate that the Sb3+ concentration dependent luminescence results from the synergistic effect of crystal phase transition, change of luminescence center, and the distortion of crystal structure. This achievement represents a successful strategy to achieve the photophysical properties modulation of metal halides for versatile optical applications.

Sodium lithium niobate lead-free piezoceramics for high-power applications: Fundamental, progress, and perspective

With the capability of interconversion between electrical and mechanical energy, piezoelectric materials have been revolutionized by the implementation of perovskite-piezoelectric-ceramic-based studies over 70 years. In particular, the market of piezoelectric ceramics has been dominated by lead zirconate titanate for decades. Nowadays, the research on piezoelectric ceramics is largely driven by cutting-edge technological demand as well as the consideration of a sustainable society. Hence, environmental-friendly lead-free piezoelectric materials have emerged to replace lead-based Pb(Zr,Ti)O₃ (PZT) compositions. Owing to the inherent high mechanical quality factor (<i>Q</i>_m) and low energy loss, (Li,Na)NbO₃ (LNN) materials have recently drawn increasing attention and brought advantages to high-power piezoelectric applications. Although the crystallographic structures of LNN materials were intensively investigated for decades, the technical strategies for electrical performance are still limited. As a result, the property enhancement appears to have approached a plateau. This review traces the progress in the development of LNN materials, starting from the polymorphism in terms of the crystal structures, phase transitions, and local structural distortions. Then, the key milestone works on the functional tunability of LNN are reviewed with emphasis on involved engineering approaches. The exceptional performance at a large vibration velocity makes LNN ceramics promising for high-power applications, such as ultrasonic welding (UW) and ultrasonic osteotomes (UOs). The remaining challenges and some strategic insights for synergistically engineering the functional performance of LNN piezoceramics are also suggested.

Parametric decay induced first-order phase transition in two-dimensional Yukawa crystals

The melting process of two-dimensional (2D) Yukawa crystals for dusty plasma medium induced by external perturbations has been explored using molecular dynamics simulations. A 2D monolayer of particles interacting via Yukawa pair potential is formed in the presence of an external confinement potential. The confinement potential is a combined effect of the gravitational force and an externally applied electric force, which mimics the sheath electric field in dusty plasma experiments. The response of the 2D crystalline layer to an external perturbation is investigated. It is shown that transverse surface waves are generated below a particular threshold value of initial perturbation, but the crystalline order remains. However, above a threshold value of initial disturbance, the crystalline order structure of the 2D layer breaks, and it melts. The melting process is shown to be a first-order phase transition. We have demonstrated that the nonlinear amplitude modulation of initial disturbance through the parametric decay instability is responsible for the melting. Our proposed mechanism of first-order phase transition in the context of 2D dusty plasma crystal is distinctly different from the existing theoretical models. This research can provide a deeper understanding of the experimental observations in the context of plasma crystal.

Probing Phase Transitions in Organic Crystals Using Atomistic MD Simulations

Probing Phase Transitions in Organic Crystals Using Atomistic MD Simulations

Elucidating the phase transitions of decanoic-acid crystal by XRD, Raman, group theory and Gibbs energy analyses combined with DFT calculations

This research reports a series of phase transitions in the decanoic-acid (DA) crystal under low-temperature conditions, which were elucidated by XRD, Raman scattering and DFT calculations in a dimer of DA in the C form (monoclinic structure). The first phase change was noticed within the 210–190 K interval duly characterized as a transition of second-order type, as indicated by Gibbs energy behavior, suggesting that the monoclinic structure (P21/c) of the crystal is not changed. The second change was observed nearly 110–90 K, whose transition is first-order type occurring from the C form to an A form (triclinic), possibly belonging to the P1 space group. This new polymorphic phase was duly predicted through DFT calculations. According to Gibbs energy behavior, the third phase change (∼30–10 K) is proposed to be a transition from the A form to a new polymorphic phase that probably is a first-order transition, likely associated with a change from the P1 space group to P-1. Furthermore, group theory and wavenumber vs temperature plots’ analyses corroborated the phase transitions undergone by DA crystal. In addition, anharmonicity effects in several Raman bands’ behavior were noticed during the cooling. A correct assignment for the Raman and IR modes via DFT calculations at room-temperature conditions is also provided herein.

Combined pressure and magnetic field induced caloric effects in Fe7Se8 single crystals doped with Ni and Co ions

The influence of Co and Ni ion doping on the crystal structure, phase transitions, and magnetic properties of the Fe7Se8 system has been investigated. The compounds studied are (Fe0.987Ni0.013)7Se8, (Fe0.955Ni0.045)7Se8, (Fe0.915Ni0.085)7Se8, (Fe0.89Ni0.11)7Se8, (Fe0.79Ni0.21)7Se8, (Fe0.975Co0.025)7Se8, (Fe0.951Co0.049)7Se8, and (Fe0.91Co0.09)7Se8 as well as the parent compound Fe7Se8. The crystals are grown using a modified Bridgman method and exist as a hexagonal NiAs-like structure with an ordered distribution of Fe vacancies that determine their magnetic properties. The substitution effect, inducing a systematic decrease in the unit-cell volume due to the ionic radii of doping ions being smaller than the radii of Fe2+ ions, is a source of chemical pressure, acting on the magnetic subsystem and determining the magnetic ordering temperature TC and the spin-reorientation temperature (TSRT). As the most important result of this paper, it was shown that hydrostatic and chemical pressures are strongly correlated in the investigated system. The character of magnetic phase transitions has been designated in the vicinity of TC and TSRT temperatures, and the magnetic entropy change ΔSm and refrigeration potential magnitudes have been determined for this temperature range. These magnetocaloric parameters were shown to depend strongly on chemical pressure. A phenomenological model developed based on the experimental measurements demonstrated that the magnetic properties of the system depend strongly on the crystal field acting on Fe2+ ions and the ratio of the numbers of Fe2+ and Fe3+ ions.

Enhanced removal of tetracycline over CeMO-7 % nanorods via electronic interaction effect: Degradation, kinetics and mechanism

Although multifarious strategies, including oxygen vacancies or surface defects improvement, morphology modification, crystal phase transition and ion doping, have been developed for improving the catalytic performance of MnO2 in the removal of pollutant substances. As far as we know, there is the first report providing enhanced performance of MnO2 in the removal of pollutant substances by its electronic interaction effect. Herein, this study proposes a facile and high-efficiency method to achieve Ce-doping manganese oxide (CeMO) nanorods for the enhanced tetracycline removal via electronic interaction effect at 30 °C for the first time. The detailed characterizations and anions effect experiment have confirmed that CeMO-7 % nanorods possessed abundant surface reactive oxygen species, which is in favor of PMS activation. Compared to manganese oxide (MO), CeMO-5 % and CeMO-9 %, an obvious left shift has been observed in the Mn 2p of CeMO-7 %, suggesting that some electrons are transferred from Mn atoms to Ce atoms in CeMO-7 %, and implying that the highest degradation efficiency of CeMO-7 % in TC degradation may be due to the strong electronic interaction between Ce and Mn in CeMO-7 %. This study not only offers a facile and high-efficiency methodology for the synthesis of two-dimensional nanomaterial, but also proposes a new idea for enhancing the removal of TC.

Size-Dependent Nucleation in Crystal Phase Transition from Machine Learning Metadynamics.

In this Letter, we present a framework that combines machine learning potential (MLP) and metadynamics to investigate solid-solid phase transition. Based on the spectral descriptors and neural networks regression, we develop a scalable MLP model to warrant an accurate interpolation of the energy surface where two phases coexist. Applying it to the simulation of B4-B1 phase transition of GaN under 50GPa with different model sizes, we observe sequential change of the phase transition mechanism from collective modes to nucleation and growths. When the size is at or below 128 000atoms, the nucleation and growth appear to follow a preferred direction. At larger sizes, the nuclei occur at multiple sites simultaneously and grow to microstructures by passing the critical size. The observed change of the atomistic mechanism manifests the importance of statistical sampling with large system size in phase transition modeling.

Direct Observation of Size-Dependent Phase Transition in Methylammonium Lead Bromide Perovskite Microcrystals and Nanocrystals.

Methylammonium (MA) lead halide perovskites have been widely studied as active materials for advanced optoelectronics. As crystalline semiconductor materials, their properties are strongly affected by their crystal structure. Depending on their applications, the size of MA lead halide perovskite crystals varies by several orders of magnitude. The particle size can lead to different structural phase transitions and optoelectronic properties. Herein, we investigate the size effect for phase transition of MA lead bromide (MAPbBr3) by comparing the temperature-dependent neutron powder diffraction patterns of microcrystals and nanocrystals. The orthorhombic-to-tetragonal phase transition occurs in MAPbBr3 microcrystals within the temperature range from 100 to 310 K. However, the phase transition is absent in nanocrystals in this temperature range. In this work, we offer a persuasive and direct evidence of the relationship between the particle size and the phase transition in perovskite crystals.

Utilization of supercritical CO2 for controlling the crystal phase transition and cell morphology of isotactic polybutene-1 foams

Isotactic polybutene-1 (iPB-1) is a semi-crystalline polymer with multiple crystal forms. In this work, we found a novel method to obtain and adjust the expansion ratio and bimodal cellular structures of iPB-1 foams with annealing and foaming using supercritical CO2. The form I′ can be obtained via the supercritical CO2 annealing, and the ratio of form I and I′ can be adjusted by controlling simply the annealing time. The effects of crystal form ratio on the thermal behavior, rheological behavior and cell morphology of foams were analyzed. Energy storage modulus (G′) and complex viscosity (|η*|) decrease with the increased content of form I. Crystal form I′ has a lower foaming temperature window and bubble growth resistance than form I, resulting in larger cell diameter and expansion ratio. The bimodal cell structure can be observed in the samples with 1:1 form I′/form I, where the average large and small cell size are 122 and 40 µm at 109 °C and 10 MPa CO2, respectively. To regulate the cell distribution, various ratios of mixed crystal phases were applied to investigate their effect on the foaming behavior and bimodal cells structure at different temperatures. Even with a similar expansion ratio, significantly different cell distributions of bimodal cell structure can be easily prepared by simply adjusting the content of form I′, which can broaden the application range of iPB-1 foams.

Effect of polyols on membrane structures of liposomes: A study using small-angle X-ray scattering data and generalized indirect Fourier transformation

This study aimed to evaluate the membrane structure of distearoylphosphatidylcholine (DSPC) liposomes dispersed in water containing various types of polyols with low molecular weight such as glycerin (Gly), 1,3-butandiol (BG), and propylene glycol (PG). To clarify the detailed membrane structure, generalized indirect Fourier transformation (GIFT) analysis, which provides information about the bilayer spacing, bilayer thickness, number of lamellar layers, and membrane flexibility, was applied to small-angle X-ray scattering (SAXS) data of the present system. The GIFT results showed that the bilayer thickness of the DSPC liposomes followed the order Gly>>BG>PG. In addition, the membrane flexibility estimated by the Caille parameter was in the order Gly>>BG>PG; this result was supported by the gel-liquid crystal phase transition temperature (Tc) obtained by differential scanning calorimetry (DSC). These results, together with the Raman spectra, suggest that BG and PG incorporated into the bilayers of DSPC liposomes result in the formation of an interdigitated lamellar structure.

Design and Robustness Evaluation of Valley Topological Elastic Wave Propagation in a Thin Plate with Phononic Structure

Based on the concept of band topology in phonon dispersion, we designed a topological phononic crystal in a thin plate for developing an efficient elastic waveguide. Despite that various topological phononic structures have been actively proposed, a quantitative design strategy of the phononic band and its robustness assessment in an elastic regime are still missing, hampering the realization of topological acoustic devices. We adopted a snowflake-like structure for the crystal unit cell and determined the optimal structure that exhibited the topological phase transition of the planar phononic crystal by changing the unit cell structure. The bandgap width could be adjusted by varying the length of the snow-side branch, and a topological phase transition occurred in the unit cell structure with threefold rotational symmetry. Elastic waveguides based on edge modes appearing at interfaces between crystals with different band topologies were designed, and their transmission efficiencies were evaluated numerically and experimentally. The results demonstrate the robustness of the elastic wave propagation in thin plates. Moreover, we experimentally estimated the backscattering length, which measures the robustness of the topologically protected propagating states against structural inhomogeneities. The results quantitatively indicated that degradation of the immunization against the backscattering occurs predominantly at the corners in the waveguides, indicating that the edge mode observed is a relatively weak topological state.

Crystal structures, dielectric properties, and phase transitions in Sr2ScGaO5-based brownmillerite ceramics

In the present work, the crystal structures and dielectric properties of the Sr2Sc1-xInxGaO5 (x = 0.0, 0.1, 0.2, 0.3) ceramics with the brownmillerite structures were investigated. The ceramics belong to the I2mb polar phases with fully ordered oxygen tetrahedral chains based on the X-ray diffraction and transmission electron microscope results. A typical second-order phase transition from the polar I2mb to non-polar Imma phase is identified by the dielectric properties and Raman analysis. The phase transition temperature increases linearly with the x value in Sr2Sc1-xInxGaO5 ceramics, which is induced by the increased ordering degree of GaO4 tetrahedral chains. The fact that no thermal hysteresis was found in dielectric response during the heating and cooling process along with the Curie-Weiss fitting result confirmed the second-order phase transition in the ceramics. The present work identifies the phase transition temperature in Sr2ScGaO5-based brownmillerite ceramics, and it can be easily adjusted by substituting the cations at the octahedral center in the brownmillerite ceramics.

Partial magnetic ion substitution of BiFeO3 Multiferroic photocatalyst for hydrogen evolution from water splitting

BiFeO 3 as a p-type photocatalyst in BiFeO 3 –CdWO 4 p-n heterojunction was modified by partial substitution of divalent Co 2+ and Ni 2+ at Fe-site to enhance the photocatalytic performance for H 2 evolution from pure water splitting. At high impurity concentrations, XRD and Raman spectroscopy revealed a phase transition from rhombohedral to orthorhombic/tetragonal with higher crystal symmetry due to larger ionic radii of Co 2+ and Ni 2+ relative to that of Fe 3+ . The excess amount of impurities also resulted in the formation of nickel ferrite (NiFe 2 O 4 ), cobalt ferrite (CoFe 2 O 4 ), sillenite (Bi 25 FeO 40 ) and mullite (Bi 2 Fe 4 O 9 ) as secondary phases. The high resolution XPS spectra of O 1s and Fe 2p indicted that the concentration of oxygen vacancy and Fe 2+ : Fe 3+ increased with doping BiFeO 3 , which is due to the structural distortion and defection. Moreover, magnetic property of BiFeO 3 was promoted by Co and Ni doping so that the residual magnetization increased from 0.009 emu/g up to 0.061 and 0.068 emu/g by 9 mol.% doping of Ni and Co, respectively. The enhanced magnetism can be attributed to the net magnetic moment caused by different magnetic moment of Fe 3+ , Co 2+ and Ni 2+ as well as the structural defection that may be a reason for spin spiral suppression. Doping with Co and Ni led to reducing band gap energy, suppression of charge recombination, and increment of charge density and mobility. The efficiency of photocatalytic H 2 evolution increased from 268.9 μmol/h gcat by pure BFO up to 449.6 and 494.7 μmol/h gcat by 9 mol.% Ni and Co doping, respectively. • BiFeO 3 was modified by substitution of Fe 3+ with larger divalent Co 2+ and Ni 2+ . • Crystal distortion and phase transition were revealed by XRD and Raman analyses. • Magnetic property was modified as a result of crystal distortion. • Charge recombination was efficiently suppressed by Co and Ni doping. • Photocatalytic H 2 evolution was boosted by 9 mol.% Co and Ni doping.