scholarly journals Distinct pathways of solid-to-solid phase transitions induced by defects: the case of DL-methionine

IUCrJ ◽  
2021 ◽  
Vol 8 (4) ◽  
Author(s):  
Genpei Shi ◽  
Si Li ◽  
Peng Shi ◽  
Junbo Gong ◽  
Mingtao Zhang ◽  
...  
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Molecular Motion ◽  
Defect Density ◽  
Solid Phase ◽  
Nucleation And Growth ◽  
Crystal Defects ◽  
Second Step ◽  
Transition Mechanism ◽  
Step Transition

Understanding of solid-to-solid phase transition mechanisms in polymorphic systems is of critical importance for rigorous control over polymorph purity in the pharmaceutical industry to achieve the desired bioavailability and efficacy of drugs. Ubiquitous defects in crystals may play an important role in the pathways of phase transitions. However, such effects remain poorly understood. Here, the effects of crystal defects on the solid-to-solid phase transformations between DL-methionine polymorphs α and β are investigated by means of experimental and computational approaches. Thermal analyses of polycrystalline powders show two endothermic peaks in the α-to-β phase transition (and two exothermic peaks for the reverse transition), in contrast with one thermal event observed for single crystals. Variable-temperature 1D and 2D Raman spectra, as well as powder X-ray diffraction patterns, reveal the appearance of two peaks that can attributed to a two-step phase transition, and the extent of the second-step phase transition increases with milling time (or defect density). Quantification of transition kinetics unveils a remarkably higher energy barrier in the second-step phase transition than in the first, proceeding by the cooperative molecular motion pathway. The good linear fitting on the kinetic data by the Jeziorny model suggests that the second-step transition follows the nucleation and growth mechanism. Molecular dynamics simulations were also conducted to understand the role of crystal defects in the solid-state phase transition by tracking the atomic distribution and hydrogen bond lifetime during the transition. It was found that the increasing defect density hinders the propagation of cooperative molecular motion, leading to a combined transition mechanism involving both cooperative motion and nucleation and growth. This study highlights the significant impact of crystal defects on solid-state phase transitions, and the two-step transition mechanism postulated may be universal given the ubiquitous presence of defects in crystalline materials.

Mechanics of Growing Solids and Phase Transitions

2013 ◽  
Vol 535-536 ◽  
pp. 89-93 ◽  
Author(s):  
Alexander V. Manzhirov
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Mathematical Theory ◽  
Solid Phase ◽  
Phase Growth ◽  
Main Attention ◽  
Transition Processes

Phase transitions can be usually observed in nature and technology which effectively utilize certain types of these transitions. An approach to modeling phase transition processes on the basis of the mathematical theory of growing solids is developed. Liquid-solid and gas-solid phase transitions are under consideration. Main attention is paid to the processes of solid phase growth and deformation.

Real-Time Dynamical Observation of Lattice Induced Nucleation and Growth in Interfacial Solid–Solid Phase Transitions

2016 ◽  
Vol 16 (12) ◽  
pp. 7256-7262 ◽  
Author(s):  
Junjie Li ◽  
Qiang Li ◽  
Zhongchang Wang ◽  
Francis Leonard Deepak
Keyword(s):  
Phase Transitions ◽  
Real Time ◽  
Solid Phase ◽  
Nucleation And Growth

scholarly journals Phase Transitions and Hysteresis for a Simple Model Liquid Crystal by Replica-Exchange Monte Carlo Simulations

Molecules ◽  
2021 ◽  
Vol 26 (5) ◽  
pp. 1421
Author(s):  
Akie Kowaguchi ◽  
Paul E. Brumby ◽  
Kenji Yasuoka
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Liquid Crystal ◽  
Solid Phase ◽  
Replica Exchange ◽  
Exchange Method ◽  
Model Liquid ◽  
Hexagonal Close Packed ◽  
Crystal Model ◽  
Transition Points

In this work, the advantages of applying the temperature and pressure replica-exchange method to investigate the phase transitions and the hysteresis for liquid-crystal fluids were demonstrated. In applying this method to the commonly used Hess–Su liquid-crystal model, heat capacity peaks and points of phase co-existence were observed. The absence of a smectic phase at higher densities and a narrow range of the nematic phase were reported. The identity of the crystalline phase of this system was found to a hexagonal close-packed solid. Since the nematic-solid phase transition is strongly first order, care must be taken when using this model not to inadvertently simulate meta-stable nematic states at higher densities. In further analysis, the Weighted Histogram Analysis Method was applied to verify the precise locations of the phase transition points.

scholarly journals Ultrafast disordering of vanadium dimers in photoexcited VO2

Science ◽  
2018 ◽  
Vol 362 (6414) ◽  
pp. 572-576 ◽  
Author(s):  
Simon Wall ◽  
Shan Yang ◽  
Luciana Vidas ◽  
Matthieu Chollet ◽  
James M. Glownia ◽  
...  
Keyword(s):  
Phase Transition ◽  
Phase Space ◽  
Vanadium Dioxide ◽  
Solid Phase ◽  
Rapid Evolution ◽  
X Ray ◽  
Transition Mechanism ◽  
Unit Cells ◽  
Phonon Oscillation

Many ultrafast solid phase transitions are treated as chemical reactions that transform the structures between two different unit cells along a reaction coordinate, but this neglects the role of disorder. Although ultrafast diffraction provides insights into atomic dynamics during such transformations, diffraction alone probes an averaged unit cell and is less sensitive to randomness in the transition pathway. Using total scattering of femtosecond x-ray pulses, we show that atomic disordering in photoexcited vanadium dioxide (VO2) is central to the transition mechanism and that, after photoexcitation, the system explores a large volume of phase space on a time scale comparable to that of a single phonon oscillation. These results overturn the current understanding of an archetypal ultrafast phase transition and provide new microscopic insights into rapid evolution toward equilibrium in photoexcited matter.

DSC Investigations of the Phase Transitions of [M(H2O)6](NO3)2 , where M = Mn, Co, Ni, Cu and Zn

1999 ◽  
Vol 54 (10-11) ◽  
pp. 595-598
Author(s):  
E. Mikuli ◽  
A. Migdał-Mikuli ◽  
S. Wróbel ◽  
B. Grad
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Solid Phase ◽  
Melting Process ◽  
Melting Points ◽  
Two Stage ◽  
Two Phase ◽  
Solid Phase Transition ◽  
Cu And Zn

The phase transitions of [M(H2O)6 ](NO3)2 , where M = Mn2+ , Co2+ , Ni2+ , Cu2+ or Zn2+ have been studied at 100 -400 K by DSC. Two phase transitions connected with a two-stage melting process have been found for these five compounds. For the compound with M = Co, besides the two melting points a solid-solid phase transition at 272 K has been found.

scholarly journals Исследование кинетики фазового перехода I рода в тетракозане С-=SUB=-24-=/SUB=-Н-=SUB=-50-=/SUB=- методом ИК-Фурье спектроскопии

2019 ◽  
Vol 61 (10) ◽  
pp. 1831
Author(s):  
В.А. Марихин ◽  
С.А. Гурьева ◽  
Л.П. Мясникова ◽  
Б.З. Волчек ◽  
Д.А. Медведева
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Solid Phase ◽  
First Order ◽  
First Order Phase Transition ◽  
Narrow Temperature Interval ◽  
Solid Phase Transition ◽  
First Order Phase ◽  
Kinetics Of ◽  
Symmetry Change

The kinetics of the structural first order phase transition in the tetracosane С24Н50 monodisperse samples is studied with the help of FTIR spectroscopy. The temperature dependencies of the frequency and intensity of rocking (ν~ 720 cm-1) and bending (ν~ 1470 cm-1) vibrations of СН2-groupes in the methylene trans-sequences in the crystalline cores of the elementary lamellae are investigated. It is shown that the first order solid phase transition is developing on a heterogeneous mechanism in the narrow temperature interval (T~ 2 K) according to the theory of the diffused first order phase transitions and is due to the crystalline cell symmetry change.

Polymorphism and solid-to-solid phase transitions of a simple organic molecule, 3-chloroisonicotinic acid

CrystEngComm ◽  
2015 ◽  
Vol 17 (11) ◽  
pp. 2389-2397 ◽  
Author(s):  
Sihui Long ◽  
Panpan Zhou ◽  
Sean Parkin ◽  
Tonglei Li
Keyword(s):  
Phase Transition ◽  
Thermal Properties ◽  
Phase Transitions ◽  
Organic Molecule ◽  
Solid Phase ◽  
Molecular Symmetry ◽  
Chlorine Substitution ◽  
Solid Phase Transition

Three polymorphs have been discovered for 3-chloroisonicotinic acid. Its thermal properties appear to be eventful, including sublimation, melting and recrystallization, and solid-to-solid phase transition. The polymorphism seemingly results from the disruption of molecular symmetry by chlorine substitution.

PHASE TRANSITIONS IN MULTIMOLECULAR LAYERS OF ADSORBED NITROGEN

1952 ◽  
Vol 30 (11) ◽  
pp. 890-903 ◽  
Author(s):  
J. A. Morrison ◽  
L. E. Drain ◽  
J. S. Dugdale
Keyword(s):  
Phase Transition ◽  
Heat Capacity ◽  
Phase Transitions ◽  
Solid Phase ◽  
Melting Process ◽  
Adsorbed Films ◽  
Adsorbed Nitrogen ◽  
Normal Melting Point ◽  
Solid Phase Transition ◽  
Molecular Layers

The heat capacity of nitrogen adsorbed on titanium dioxide has been measured for amounts adsorbed corresponding to 2.2, 3.1, 4.0, and 4.8 molecular layers in the temperature range 14 ° to 75 °K. The occurrence in the adsorbed films of melting and of the transition in the solid phase of nitrogen is shown by maxima in the heat capacity. The melting process is completely reversible and takes place at temperatures below the normal melting point. The solid phase transition does not occur reversibly, the magnitude of the anomaly in the heat capacity depending upon the extent to which the system has been cooled prior to the measurement of the heat capacity. The experimental results are discussed in terms of current thermodynamic treatments of phase transitions in adsorbed films.

scholarly journals Study of the Phase Transitions in the Binary System NPG-TRIS for Thermal Energy Storage Applications

Materials ◽  
2020 ◽  
Vol 13 (5) ◽  
pp. 1162 ◽  
Author(s):  
Sergio Santos-Moreno ◽  
Stefania Doppiu ◽  
Gabriel A. Lopez ◽  
Nevena Marinova ◽  
Ángel Serrano ◽  
...  
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Transition Temperature ◽  
Energy Storage ◽  
Binary System ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Solid Phase ◽  
High Enthalpy ◽  
Pure Compounds

Neopentylglycol (NPG) and tris(hydroxymethyl)aminomethane (TRIS) are promising phase change materials (PCMs) for thermal energy storage (TES) applications. These molecules undergo reversible solid-solid phase transitions that are characterized by high enthalpy changes. This work investigates the NPG-TRIS binary system as a way to extend the use of both compounds in TES, looking for mixtures that cover transition temperatures different from those of pure compounds. The phase diagram of NPG-TRIS system has been established by thermal analysis. It reveals the existence of two eutectoids and one peritectic invariants, whose main properties as PCMs (transition temperature, enthalpy of phase transition, specific heat and density) have been determined. Of all transitions, only the eutectoid at 392 K shows sufficiently high enthalpy of solid-solid phase transition (150–227 J/g) and transition temperature significantly different from that of the solid-state transitions of pure compounds (NPG: 313 K; TRIS: 407 K). Special attention has also been paid to the analysis of metastability issues that could limit the usability of NPG, TRIS and their mixtures as PCMs. It is proven that the addition of small amounts of expanded graphite microparticles contributes to reduce the subcooling phenomena that characterizes NPG and TRIS and solve the reversibility problems observed in NPG/TRIS mixtures.

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