Solid-state Phase Transition Research Articles

C5 H12 N]SnCl3 : A Tin Halide Organic-Inorganic Hybrid as an Above-Room-Temperature Solid-State Nonlinear Optical Switch.

Nonlinear optical (NLO) switches driven by a solid-state structural phase transition have attracted extensive attention; however, above-room-temperature solid-state NLO switch materials are still sparse. Herein, we report an above-room-temperature tin halide organic-inorganic hybrid quadratic NLO switchable material, N-methylpyrrolidinium trichloride stannite ([C5 H12 N]SnCl3 , MPSC). The MPSC crystal exhibits a phase-matchable NLO property that is 1.1 times that of KH2 PO4 (KDP) and NLO switching behavior, changing from a high second harmonic generation (SHG) response to a low SHG response at 383 K, thereby demonstrating its prospective applications in the field of nonlinear optics. Variable-temperature crystal structural analysis combined with theoretical calculations revealed that the large NLO response stems from the inorganic SnCl3 moiety, whereas the high-performance NLO switching properties mainly originate from the order/disorder transformation of the N-methylpyrrolidinium. This work provides a new approach to designing and exploring new high-performance quadratic NLO switches involving tin halide organic-inorganic hybrids.

A new criterion for the prediction of solid-state phase transition in TMDs.

The classical thermodynamic criterion for phase transition predicts whether the phase transition will occur according to whether the nth derivative of the state parameter is discontinuous, and the continuity verification of multi-order derivatives increases the difficulty and complexity of judgment for phase transition to a certain extent. Based on the reverse shifts of the DOS curves near the Fermi level, we propose a new criterion for solid-state phase transition named Conch Criterion, which has been verified in the TMD system. The new criterion can observe the occurrence of phase transition from another perspective besides the thermodynamic properties while mutually confirming the thermodynamic criterion.

Тепловой эффект перехода моноклинной фазы в орторомбическую в сверхвысокомолекулярном полиэтилене

AbstractWe analyze heat effects associated with the solid-state phase transition in ultrahigh molecular weight polyethylene from the unstable monoclinic phase into thermodynamically stable orthorhombic phase. The model proposed here for the structure of supramolecular formations of monoclinic phase does not contradict to earlier X-ray diffraction data for this polymer.

High-throughput thermodynamic computation and experimental study of solid-state phase transitions in organic multicomponent orientationally disordered phase change materials for thermal energy storage

Understanding the behavior of solid-solid phase transformation in phase change materials is crucial to design advanced thermal energy storage materials. It is however challenging to study the complex solid-solid phase transition and predict the optimal composition with reliable performances (such as high energy storage at invariant phase transition temperature) in multi-component systems based on traditional empirical rules. Therefore, the high-throughput computational framework by coupling thermodynamic calculation via CALPHAD (CALculation of PHAse Diagrams) methodology with key experimental validation is firstly proposed for ternary Pentaglycerine-Tris-(hydroxymethyl)-aminomethane-2-amino-2-methyl-1,3-propanediol (PG-TRIS-AMPL) system. A self-consistent thermodynamic database of PG-TRIS-AMPL ternary system has been firstly assessed and validated by experimental measurements from in-situ X-Ray-Diffraction (XRD) and Differential Scanning Calorimetry (DSC). Using this thermodynamic database via CALPHAD method, the high-throughput calculation has been performed to seek the optimal composition in PG-TRIS-AMPL ternary system. It is found that two optimal ternary compositions in PG-TRIS-AMPL ternary system are designed as PG0.33TRIS0.07AMPL0.60 (ΔHmax = 137.5 kJ/kg) during the 1st invariant reaction αAMPL-rich+βPG-rich→δTRIS-rich+γAMPL-rich at 326.5 K (53.35 °C) and PG0.58TRIS0.069AMPL0.351 (ΔHmax = 52.44 kJ/kg) during the 2nd invariant reaction γAMPL-rich+βPG-rich→δTRIS-rich+γ’PG-rich at 338.4 K (65.25 °C), respectively. This finding shows the good balance between high latent heat storage and low invariant phase transition temperature at mid-temperature (20–100 °C) application. Also, the present high-throughput computation approach can be extended into other multicomponent systems for various temperature range.

Solid-Phase Epitaxial Growth of an Alumina Layer Having a Stacking-Mismatched Domain Structure of the Intermediate γ-Phase.

Solid-phase epitaxy (SPE), a solid-state phase transition of materials from an amorphous to a crystalline phase, is a convenient crystal growing technique. In particular, SPE can be used to grow α-Al2O3 epitaxially with a novel structure that provides an effective substrate for improved performance of light-emitting diodes (LEDs). However, the inevitable two-step phase transformation through the γ-Al2O3 phase hinders the expected improved crystallinity of α-Al2O3, and thereby further enhancement of LED performance. Herein, we provide a fundamental understanding of the SPE growth mechanism from amorphous to metastable γ-Al2O3 using transmission electron microscopy (TEM) and density functional theory (DFT) calculations. The nanobeam precession electron diffraction technique enabled clear visualization of the double-positioning domain distribution in the SPE γ-Al2O3 film and emphasized the need for careful selection of the viewing directions for any investigation of double-positioning domains. Void and stacking fault defects further investigated by high-resolution scanning TEM (STEM) analyses revealed how double-positioning domains and other SPE growth behaviors directly influence the crystallinity of SPE films. Additionally, DFT calculations revealed the origins of SPE growth behavior. The double-positioning γ-Al2O3 domains randomly nucleate from the α-Al2O3 substrate regardless of the α-Al2O3 termination layer, but the large energy requirement for reversal of the γ-Al2O3 stacking sequence prevents it from switching the domain type during the crystal growth. We expect that this study will be useful to improve the crystallinity of SPE γ- and α-Al2O3 films.

Crystallization characteristics and local grain abnormal growth of amorphous Ge2Sb2Te5 films induced by a Gaussian picosecond laser

In this paper, crystallization characteristics of amorphous Ge2Sb2Te5 (a-GST) films induced by a Gaussian picosecond laser with different laser fluence were carried out using transmission electron microscopy (TEM), Raman spectra and ab initio molecular dynamics (AIMD) simulations. TEM observations presented a solid-state phase transition with nanocrystalline microstructure at lower fluence, while a liquid-solid phase transition accompanied by an ingot-like crystalline microstructure was found at higher fluence, including a central coarse and an outer fine equiaxed regions as well as a columnar crystal region between them. In spite of the remarkable difference in microstructure, the composition of different regions kept constant from the Energy Dispersive Spectrometer (EDS) measurements. Different phase change behavior and laser fluence affected the shift of Raman peaks due to the phase change stress and thermal stress. A laser irradiation coupled AIMD simulation was then developed to study the preferential nucleation possibility. AIMD simulation results indicated that a thermal process in the central coarse equiaxed regions, with a higher cooling rate (10 k/ps) generated by the Gaussian picosecond laser irradiation, reduced the nucleation rate remarkably, causing crystal nucleus have enough space to grow up even to the micrometer scale. This is different from the morphology induced by nano- or femtosecond pulsed laser.

Study of phase transition and ultimate mechanical properties of orthorhombic polyoxymethylene based on the refined crystal structure

The crystal structure of the orthorhombic polyoxymethylene (POM) has been refined by analyzing the synchrotron X-ray diffraction data measured for a micrometer-size single crystal of moth-type morphology. The 3-dimensional elastic and compliance constants tensors were calculated for both the trigonal and orthorhombic phases on the basis of the thus-obtained accurate structure information. The crystal structure information allowed us also to discuss the solid-state phase transition behavior from the orthorhombic to the trigonal phase occurring at around 78 °C. For this purpose, we have performed the temperature-dependent synchrotron X-ray scattering measurement for a tiny moth-type single crystal and revealed the geometrical relation between these two crystals. The free energy was calculated as a function of temperature for these two accurately-analyzed crystal forms using a density functional theory (DFT). The result showed that the orthorhombic phase is thermodynamically more stable than the trigonal phase in a low temperature region, and the stability was reversed at about 225 K. This temperature corresponds to the phase transition point from the orthorhombic to trigonal phase, which is however considerably lower compared with the actually-observed transition point. The large discrepancy might be ascribed to the additional contribution of the entropy term due to the structural disorder and/or the thermal motion of chains with a large amplitude, which was not taken into account in the DFT calculation.

Light control of the nanoscale phase separation in heteroepitaxial nickelates

Strongly correlated materials show unique solid-state phase transitions with rich nanoscale phenomenology that can be controlled by external stimuli. Particularly interesting is the case of light–matter interaction in the proximity of the metal–insulator transition of heteroepitaxial nickelates. In this work, we use near-infrared laser light in the high-intensity excitation regime to manipulate the nanoscale phase separation in NdNiO3. By tuning the laser intensity, we can reproducibly set the coverage of insulating nanodomains, which we image by photoemission electron microscopy, thus semipermanently configuring the material state. With the aid of transport measurements and finite element simulations, we identify two different timescales of thermal dynamics in the light–matter interaction: a steady-state and a fast transient local heating. These results open interesting perspectives for locally manipulating and reconfiguring electronic order at the nanoscale by optical means.

Relationship between polymerization kinetics and microstructure in reactive polymer blends: An Avrami-Erofeev study

It’s well known that the microstructure in the thermoset/thermoplastic blends is difficult to predict as it depends on many factors like compatibility, viscosity, crosslinking density. In this study, we investigated the relationship between polymerization kinetics and microstructure in bisphenol-A polycarbonate/diallyl phathalate (BAPC/DAP) blends via Avrami-Erofeev equation, which has been widely used to describe the phase transition in solid state. When the values of the exponent n in Avrami-Erofeev equation were greater than 1.73, between 1 and 1.73, and less than 1, the poly(DAP)-rich phases possessed fiber-like three-dimensional network with a relatively small diameter of ∼20 nm, partially connected nodule-like crosslinking structure, and perfect nodule-like three-dimensional network, separately. The results showed that Avrami-Erofeev method could be used to well correlate the polymerization kinetics with the final microstructure in reactive polymer blends.

Thermal transport through the magnetic martensitic transition in MnxMGe(M=Co,Ni)

We report on changes in the thermal conductivity of solid-state synthesized $\mathrm{M}{\mathrm{n}}_{x}M\mathrm{Ge}$ ($M=\mathrm{Co}$, Ni, $0.98lxl1.02$) alloys through their temperature-induced martensitic structural transition. The thermal conductivity is measured by time-domain thermoreflectance. $\mathrm{M}{\mathrm{n}}_{1.014}\mathrm{NiGe}$ exhibits an increase in thermal conductivity from 11 to $15.5\phantom{\rule{0.16em}{0ex}}\mathrm{W}\phantom{\rule{0.16em}{0ex}}{\mathrm{m}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ from approximately 575 to 625 K, and $\mathrm{M}{\mathrm{n}}_{1.007}\mathrm{CoGe}$ exhibits an increase in thermal conductivity from 7 to $8.5\phantom{\rule{0.16em}{0ex}}\mathrm{W}\phantom{\rule{0.16em}{0ex}}{\mathrm{m}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ from 500 to 550 K. In $\mathrm{M}{\mathrm{n}}_{x}\mathrm{NiGe}$, the transition temperature and the magnitude of the change in thermal conductivity are strongly dependent on the alloy composition. Our study advances the fundamental understanding of the thermal transport properties in the $\mathrm{M}{\mathrm{n}}_{x}M\mathrm{Ge}(M=\mathrm{Co},\phantom{\rule{0.16em}{0ex}}\mathrm{Ni})$ family of alloys and opens a new direction in the search for solid-state phase transition materials with potential applications as thermal regulators.

Microstructure evolution of the crystallization of amorphous Ge2Sb2Te5 thin films induced by single picosecond pulsed laser

Phase-change materials (PCMs) have been widely used in optical and electronic applications for their extraordinary properties. However, the procedure of fast transition about PCMs is still not clear for the time limit. Pulse laser, especially ultra-short pulse laser, is an excellent tool to study the crystallization characteristics of PCMs for its high heating rate. In this paper, picosecond pulsed laser was employed to study the crystallization of amorphous Ge2Sb2Te5 (a-GST) thin films via the evolution of morphology and microstructure. The threshold for inducing crystallization was 7.9 mJ/cm2 and amorphization occured at 17.2 mJ/cm2. With the aid of high-resolution transmission electron microscopy (HRTEM), the growth of grains were observed to own a preferable growth direction of [100]. The grain size and laser fluence showed an exponential relationship under the ps laser pulse, and the maximal grain reached to ~5 μm when approaching the melting point. The morphology and grain distribution of GST film under 18.8 mJ/cm2 indicated a solid-state phase transition. Besides, the matrix of a-GST film changed into crystalline state even though the surface melted into amorphous state when irradiated by high laser pulse. Finally, the reason for fast transition of a-GST film under ultra-short laser pulse was discussed in terms of heating rate and temperature. The present study is fundamental for the understanding of the fast phase transition of PCMs.

Study on the crystallization mechanism of amorphous Ge2Sb2Te5 thin films induced by a short single pulsed laser

The crystallization mechanism in an amorphous Ge2Sb2Te5 (a-GST) thin film induced by a single pulsed laser was investigated in this paper. The finite element simulation and x-ray diffraction analysis showed that two kinds of crystallization mechanisms performed for the laser-induced phase transition of a-GST, that is, the solid-state phase transition took place at a lower laser fluence while the liquid–solid phase transition occurred at a relatively high laser fluence. Transmission electron microscopy observations showed that the microstructure in the liquid–solid phase transition was more uniform as compared to that in the solid-state phase transition because of poor atom diffusion. Crystallization characteristics at different laser fluences and film thickness were elucidated. It was found that at a lower laser fluence a thinner film had the better crystallinity owing to thermal convection, while at a higher laser fluence a thicker film showed the better crystallinity due to the release of latent heat in the liquid–solid phase transition. These findings enable a deep understanding of ultra-fast phase transition induced by laser irradiation.

Solid State Phase Transitions in Poly(ethylene oxide) Crystals Induced by Designed Chain Defects

We have used Cu(I)-catalyzed azide–alkyne cycloaddition to synthesize a new series of poly(ethylene oxide)s having in the center of their chains two 1,2,3-triazole (TR) rings separated by (CH2)n spacers with 2 ≤ n ≤ 4 (PEO11-TR-(CH2)n-TR-PEO11). The degree of crystallinity obtained by temperature-dependent WAXS measurements indicates that only one out of the two PEO11 chains of the three polymers forms a 72 helix upon cooling to −10 °C and crystallizes into a monoclinic unit cell known from PEO homopolymer. A solid-state phase transition occurs for all samples during heating below their melting temperature. Solid-state 13C MAS cross-polarization and single-pulse NMR spectroscopy indicate the complete incorporation of the chain defects into the PEO crystals (PEO-TR phase) during this transition. The 2D WAXS pattern of an oriented PEO11-TR-(CH2)2-TR-PEO11 sample generates a structural model where the crystal lattice of the initial PEO phase becomes highly distorted during the solid-state phase transition du...

Experimental and theoretical thermodynamic properties of RS-(±)- and S-(+)-mandelic acids

The enthalpies of formation of RS-(±)- and S-(+)-mandelic acids were measured using high-precision combustion calorimetry. Vapor pressures of the acids were measured using the transpiration method. The enthalpies of sublimation of these compounds at 298.15 K were derived from vapor pressure temperature dependencies. Molar enthalpies of the solid state phase transitions were measured by the DSC. Thermodynamic data on mandelic acids available from the published sources were collected and combined with our experimental results. Thermochemical properties of studied compounds were evaluated and tested for internal and external consistency with different approaches. The methods of quantum chemistry and statistical physics were used to calculate thermodynamic functions of compounds in the ideal gas state in temperature range 298.15 K–1500 K.

Compositional heterogeneity near the base of the mantle transition zone beneath Hawaii

Global seismic discontinuities near 410 and 660 km depth in Earth’s mantle are expressions of solid-state phase transitions. These transitions modulate thermal and material fluxes across the mantle and variations in their depth are often attributed to temperature anomalies. Here we use novel seismic array analysis of SS waves reflecting off the 410 and 660 below the Hawaiian hotspot. We find amplitude–distance trends in reflectivity that imply lateral variations in wavespeed and density contrasts across 660 for which thermodynamic modeling precludes a thermal origin. No such variations are found along the 410. The inferred 660 contrasts can be explained by mantle composition varying from average (pyrolitic) mantle beneath Hawaii to a mixture with more melt-depleted harzburgite southeast of the hotspot. Such compositional segregation was predicted, from petrological and numerical convection studies, to occur near hot deep mantle upwellings like the one often invoked to cause volcanic activity on Hawaii.

Cations controlled growth of β-MnO2 crystals with tunable facets for electrochemical energy storage

Engineering crystal facets to enhance their functionalities often require complex processing routes to suppress the growth of surfaces with the lowest thermodynamic energies. Herein, we report a unique method to control the morphologies of β-MnO2 crystals with different occupancy of {100}/{111} facets through the effect of K+ cations. Combining aberration-corrected scanning transmission electron microscopy (STEM), ultramicrotomy, and dynamic functional theory (DFT) simulation, we clarified that the β-MnO2 crystals were formed through a direct solid-state phase transition process. Increasing the concentration of K+ cations in the precursor gradually changed the morphology of β-MnO2 from bipyramid prism ({100}+{111} facets) to an octahedron structure ({111} facets). The K+ cations controlled the morphology of β-MnO2 by affecting the formation of α-K0.5Mn4O8 intermediate phase and the subsequent phase transition. Utilizing the β-MnO2 crystals as the cathode for Li-ion batteries showed that highly exposed {111} facets offered β-MnO2 crystal better rate performance, with ~70% capacity retention when the charge-discharge rate increased from 20 mA/g to 200 mA/g. Our work revealed a new mechanism to tune the morphology of this earth-abundant metal oxide crystal, which could be used to adjust its electrochemical performance for different applications, such as supercapacitors and catalysts for metal-air batteries and fuel cells.

Rotator side chains trigger cooperative transition for shape and function memory effect in organic semiconductors

Martensitic transition is a solid-state phase transition involving cooperative movement of atoms, mostly studied in metallurgy. The main characteristics are low transition barrier, ultrafast kinetics, and structural reversibility. They are rarely observed in molecular crystals, and hence the origin and mechanism are largely unexplored. Here we report the discovery of martensitic transition in single crystals of two different organic semiconductors. In situ microscopy, single-crystal X-ray diffraction, Raman and nuclear magnetic resonance spectroscopy, and molecular simulations combined indicate that the rotating bulky side chains trigger cooperative transition. Cooperativity enables shape memory effect in single crystals and function memory effect in thin film transistors. We establish a molecular design rule to trigger martensitic transition in organic semiconductors, showing promise for designing next-generation smart multifunctional materials.

Твердотельный фазовый переход наноалмаза при нагреве и облучении

Твердотельный фазовый переход наноалмаза при нагреве и облучении

Exploring the solid state phase transition in dl-norvaline with terahertz spectroscopy.

dl-Norvaline is a molecular crystal at room temperature and it undergoes a phase transition when cooled below 190 K. This phase transition is believed to be Martensitic, thus making it of particular interest for molecular machines. In this paper we investigate this phase transition by measuring its terahertz (THz) spectrum over a range of temperatures. Temperature-dependent THz time-domain spectroscopy (THz-TDS) measurements reveal that the transition temperature (Tβ→α) is 190 K. The influence of nucleation seeds was analyzed by determining the Tβ→α of molecular crystals with varying grain size. Grains of 5 μm or less result in a lower transition temperature (Tβ→α = 180 K) compared to larger grains of 125-250 μm (Tβ→α = 190 K). Additionally, we gain insight into the physical process of the phase transition via temperature-dependent THz-TDS spectra of doped and mixed molecular crystals. The addition of molecular dopants, which differ from dl-norvaline only at the end of the side chain which resides in the hydrophobic layers of the crystal, decreases Tβ→α. This is consistent with a solid-solid phase transition in which the unit cell shifts along this hydrophobic layer, and it leads us to believe that the phase transition in dl-norvaline is Martensitic in nature.

Atomistic modelling of entropy driven phase transitions between different crystal modifications in polymers: the case of poly(3-alkylthiophenes).

Polymorphism and related solid-state phase transitions affect the structure and morphology and hence the properties of materials, but they are not-so-well understood. Atomistic computational methods can provide molecular-level insights, but they have rarely proven successful for transitions between polymorphic forms of crystalline polymers. In this work, we report atomistic molecular dynamics (MD) simulations of poly(3-alkylthiophenes) (P3ATs), widely used organic semiconductors to explore the experimentally observed, entropy-driven transition from form II to more common form I type polymorphs, or, more precisely, to form I mesophases. The transition is followed continuously, also considering X-ray diffraction evidence, for poly(3-hexylthiophene) (P3HT) and poly(3-butylthiophene) (P3BT), evidencing three main steps: (i) loss of side chain interdigitation, (ii) partial disruption of the original stacking order and (iii) reorganization of polymer chains into new, tighter, main-chain stacks and new layers with characteristic form I periodicities, substantially larger than those in the original form II. The described approach, likely applicable to other important transitions in polymers, provides previously inaccessible insight into the structural organization and disorder features of form I structures of P3ATs, not only in their development from form II structures but also from melts or solutions.