High-temperature Solid Phases Research Articles

Deep machine learning, molecular dynamics and experimental studies of liquid Al-Cu-Co alloys

Understanding the correlations between liquids and solids opens the way to predict by investigating liquids, the domains of thermodynamic parameters favoring intriguing solid phases. This approach is especially urgent for the design of multicomponent systems working with a continuous array of component concentrations (most modern materials of practical interest are multicomponent). Here we address an Al-Cu-Co system experimentally and theoretically using molecular dynamics and machine learning interaction potentials on top of the first-principles training data in a composition range of 15 at.% Co and 10 to 30 at.% Cu, and 25 at.% Cu and 2.5 to 20 at.% Co. The selected concentration sections contain different high-temperature solid phases. Differential thermal analysis has uncovered the features of solid phase formation at slow cooling and normal pressure. The boundaries of different phase regions correlate with the extrema on the one hand in undercooling and on the other hand in viscosity in the concentration area. The theoretical calculations have uncovered the correlations between the extrema and the readjustment of the chemical short-range order in the liquid, with the nonmonotonicity of the concentration dependence of the glass transition temperature and the specific volume.

Ferroelectricity and Phase Change Memory of Bis(tetradecylamide)-Substituted Benzene Derivatives

Interplay between intermolecular interactions including hydrogen bonding, halogen–halogen, and van der Waals interactions in molecular crystals leads to diverse phase transition behaviors and physical properties. Bis(tetradecylamide)-substituted benzene derivatives, terephthalamide (C14-TPA), isophthalamide (C14-IPA), and phthalamide (C14-PA), were examined, and the electric field–polarization curves of the former two crystals indicated ferroelectric hysteresis behavior in high-temperature solid phases. C14-XIPA derivatives where X = CH3, Cl, Br, or I at the 5-position of the IPA molecule were synthesized, and the effects of substituent X on the molecular assembly structure and physical properties were investigated. H- and CH3-substituted C14-IPA and C14-MeIPA formed a crystalline phase in which intermolecular amide-type N–H···O═ hydrogen-bonding interactions were dominant, whereas halogen-substituted C14-XIPAs formed a metastable glass phase upon cooling from the isotropic liquid. The formation of the glass phase is associated with energy competition between hydrogen bonding, halogen–halogen, and van der Waals interactions among the −CONH–, −X, and −CnH2n+1 units. The glass-crystal phase transition of C14-XIPAs (X = Cl, Br, or I) changes the refractive index under polarized optical microscopic observation, which can be utilized for phase-change memory.

High-Throughput Computation of Thermal Conductivity of High-Temperature Solid Phases: The Case of Oxide and Fluoride Perovskites

Using finite-temperature phonon calculations and machine-learning methods, we calculate the mechanical stability of about 400 semiconducting oxides and fluorides with cubic perovskite structures at 0 K, 300 K and 1000 K. We find 92 mechanically stable compounds at high temperatures -- including 36 not mentioned in the literature so far -- for which we calculate the thermal conductivity. We demonstrate that the thermal conductivity is generally smaller in fluorides than in oxides, largely due to a lower ionic charge, and describe simple structural descriptors that are correlated with its magnitude. Furthermore, we show that the thermal conductivities of most cubic perovskites decrease more slowly than the usual $T^{-1}$ behavior. Within this set, we also screen for materials exhibiting negative thermal expansion. Finally, we describe a strategy to accelerate the discovery of mechanically stable compounds at high temperatures.

Electrical conductivity, differential scanning calorimetry, X-ray diffraction, and 7Li nuclear magnetic resonance studies of n-C x H(2x+1)OSO3Li (x = 12, 14, 16, 18, and 20)

Electrical conductivity (σ), differential scanning calorimetry (DSC), and X-ray diffraction (XRD) measurements of n-C xH(2x+1)OSO3Li (x= 12, 14, 16, 18, and 20) crystals were performed as a function of temperature. In addition, σ, DSC, and XRD observations of n-C xH(2x+1)OSO3Na and n-C xH(2x+1)OSO3K (x= 12, 14, 16, 18, and 20) crystals were carried out for comparison. DSC results of the salts revealed several solid-solid phase transitions with large entropy changes (ΔS). For n-C 18H37OSO3Li and n-C 20H41OSO3Li salts, each melting point produced a small ΔSmp value compared with the total entropy change in the solid phases (ΔStr1+ΔStr2). Additionally, Li + ion diffusion was detected in the highest temperature solid phases. For K salts, larger σ values were detected for potassium alkylsulfates compared with those reported for alkyl carboxylate. 7Li NMR spectra of n-C 18H37OSO3Li crystals recorded in the low-temperature phase showed large asymmetry parameters, suggesting the Li + ions are localized at asymmetric sites in the crystals.

Competing Intermolecular Interactions in the High‐Temperature Solid Phases of Even Saturated Carboxylic Acids (C10H19O2H to C20H39O2H)

Structural knowledge of the high-temperature phases of saturated carboxylic acids (C(n)H(2n-1)O(2)H) from C(6)H(11)O(2)H to C(23)H(45)O(2)H is now complete. Crystal structures of the high-temperature phases of even acids from decanoic (C(10)H(19)O(2)H) to eicosanoic (C(20)H(39)O(2)H) are reported. The crystal structures of the six compounds were determined from powder X-ray diffraction data following direct space methods and refined by the Rietveld method combined with force field geometry optimization. The combination proved to be a valuable approach to obtain structures that are chemically sensible and in close agreement with the powder pattern. At the end of the process solid-state DFT calculations were applied to improve the overall accuracy of the system but in this case DFT did not render better structures. The high-temperature solid phases of even carboxylic acids are all P2(1)/c with Z=4, the molecules are united into dimers via strong hydrogen bonds. Two major types of interactions govern the crystal packing of carboxylic acids, hydrogen bonds and van der Waals interactions. A survey of the intermolecular interactions has revealed that hydrogen bonds are the dominant interaction for acids with less than 23 carbon atoms in the alkyl chain while van der Waals interactions dominate the packing for acids with more than 23 carbon atoms.

Structures of the High‐Temperature Solid Phases of the Odd‐Numbered Fatty Acids from Tridecanoic Acid to Tricosanoic Acid

Crystal structures of the high-temperature phases of odd-numbered fatty acids (C(n)H(2n-1)OOH) from tridecanoic acid (C(13)H(25)OOH) to tricosanoic acid (C(23)H(45)OOH) are presented in this article. They have been determined from high-quality X-ray powder-diffraction patterns. Two types of high-temperature phases are adopted: one monoclinic A2/a with Z=8 for the fatty acids with n=13 and n=15, denoted as C'', and one monoclinic P2(1)/a with Z=4 for the longer-chain fatty acids, denoted as C'. It appears that the packing arrangement of the alkyl chains and of the carboxyl groups is similar in all of the structures. However, the arrangement at the methyl-group interface differs between the C' and C'' forms. A survey of the intermolecular interactions involved in these polymorphs coupled with a study of the effects of temperature on the structures have led us to a better understanding of the arrangement of the molecules within the high-temperature solid phases of odd-numbered fatty acids.

Property Measurements and Solidification Studies by Electrostatic Levitation

The National Space Development Agency of Japan has recently developed several electrostatic levitation furnaces and implemented new techniques and procedures for property measurement, solidification studies, and atomic structure research. In addition to the contamination-free environment for undercooled and liquid metals and semiconductors, the newly developed facilities possess the unique capabilities of handling ceramics and high vapor pressure materials, reducing processing time, and imaging high luminosity samples. These are exemplified in this paper with the successful processing of BaTiO(3). This allowed measurement of the density of high temperature solid, liquid, and undercooled phases. Furthermore, the material resulting from containerless solidification consisted of micrometer-size particles and a glass-like phase exhibiting a giant dielectric constant exceeding 100,000.

DSC studies on structural phase transitions and molecular motions in some A2MCl4 compounds

Structural phase transitions and molecular motions in (CH3NH3)2CoCl4, (C5H5NH)2ZnCl4, and [(CH3)3CNH3]2ZnCl4 were investigated by differential scanning calorimetry (DSC) between about 130 K and the melting points. All of the compounds showed at least one structural phase transition over the temperature region investigated. The values of the transition entropies obtained suggest that most of the transitions are of the order-disorder type. From these entropy values, thermal motions of the molecules in the highest-temperature solid phases were inferred. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Simulated behavior of krypton/argon mixtures confined between two graphite slabs: new terrain for familiar systems

We present the results of ( N, ρ, T) molecular-dynamics simulations of krypton/argon mixtures confined between two graphite slabs with varying spacing. Structural, thermodynamic and bond-orientational quantities indicate a group of new phases and phase transitions for these already well-explored systems, and they also further delineate the close cooperation of vertical atomic motion and melting in adsorbed systems. For pure argon and systems with a high argon fraction we observe commensurate and rotated phases. Commensurate argon is stabilized over a wide temperature range for certain slab spacings, and high-temperature solid phases exist for all mixture fractions studied. For all systems explored two phenomena are observed: (1) the melting temperature T m of the system may be controlled to a fairly precise degree within a certain range by only the slab spacing, and (2) competing effects of confinement and heightened room for in-plane atomic fluctuations due to enhanced vertical fluctuations causes T m to reach a minimum value as the slab spacing is varied. The effects of varying the mixture fraction are also explored and, although emphasis is placed on melting, evidence of confinement-induced and composition-induced phase transitions is given and briefly discussed.

Predicted Effects of Confinement on the Melting Transition in Krypton-Argon Adlayers

We report the results of (N,ρ,T) Molecular-Dynamics computer simulations of krypton-argon mixtures physisorbed between two graphite sheets. Three novel aspects of the system’s behavior emerge from this study. To begin with, new high-temperature commensurate solid phases for both argon and krypton as a result of confinement are predicted, as well as a family of confinement-induced solid-liquid phase transitions. In addition, we observe that the melting temperature of the system can be adjusted within a given range by the graphite sheet spacing. Finally, in the case of argon-krypton mixtures, certain temperatures and sheet spacings result in almost complete impurity extraction.

Local structure of liquid and solid silver halides probed by XAFS.

Investigation of the local structure of the high-temperature liquid and solid phases in the 300-725 K range of AgBr has been performed using the x-ray absorption spectroscopy (XAS). Structural results are compared with existing diffraction studies and computer simulations demonstrating the reliability of the XAS technique in determining the short-range structure. Present results on solid AgBr are in agreement with known thermal expansion data. The short-range g(r) of liquid AgBr is reconstructed showing the unique insight provided by the XAS technique in measuring short-range atom-atom correlations in liquids.

Molecular Motions in Highly Disordered Solid Phases of [(CH3)3NCH2CH3]X (X = ClO4, PF6, NO3) Studied by 1H, 19F, and 14N NMR, Powder X-Ray Diffraction, and Differential Scanning Calorimetry

Abstract 1H, 19F, and 14N NMR, powder X-ray diffraction, and differential scanning calorimetry (DSC) were measured in trimethylethylammonium perchlorate, hexafluorophosphate and nitrate, [(CH3)3NCH2CH3]X (X = ClO4, PF6, NO3). Three, four and four solid phases were obtained for perchlorate, hexafluorophosphate, and nitrate, respectively, in the temperature ranges from 77 K to their decomposition temperatures. X-Ray powder patterns showed that the highest-temperature solid phases of perchlorate and hexafluorophosphate are CsCl-type cubic, while that of nitrate is NaCl-type cubic. The second highest-temperature phases of perchlorate and hexafluorophosphate form tetragonal lattices. The NMR study revealed that the cations perform isotropic rotation as well as self-diffusion in the CsCl-type cubic and tetragonal phases of perchlorate. In the cubic phase of hexafluorophosphate, isotropic rotation and self-diffusion of both anion and cation were observed. In the NaCl-type cubic phase of nitrate, isotropic rotation of both ions was detected. The structures in the highest- and second highest-temperature phases of the three salts were found to be dynamically disordered. Especially, the highest-temperature phases of perchlorate and hexafluorophosphate can be classified into the ionic plastic phase of the CsCl-type structure. Activation energies of the ionic motions in these phases were evaluated. Motional modes of the ions in the lower temperature phases were also deduced.

Crystal Structure of the High-temperature Solid Phases of Choline Tetrafluoroborate and Iodide

Abstract The crystal structure of the highest-and second highest-temperature solid phases of choline tetrafluoroborate and iodide was determined by X-ray powder diffraction. The structure in the highest-temperature phase of both salts is NaCl-type cubic (a = 10.16(2) Å, Z = 4 for tetrafluorobo-rate; a = 10.08(2) Å, Z = 4 for iodide). The second highest-temperature phase of tetrafluoroborate and iodide is CsCl-type cubic (a = 6.198(6) Å and Z = 1) and tetragonal (a = 8.706(2) Å, c = 6.144(6) Å, and Z = 2), respectively. DSC was carried out for the iodide, where the presence of three solid-solid phase transitions was confirmed. Enthalpy and entropy changes of these transitions were evaluated.

Physics in the fast lane: rotors, fast ions and mobile fermions

Dynamic disorder in the high-temperature solid phases of the Zintl compounds CsPb and NaSn is characterized by fast orientational motions of the polyanions and coupled motions of the cations. Melting is characterized by slow translational motions of the centres of mass of the polyanions. The dynamic behaviour of the ions is associated with dramatic increases in electrical conductivity characteristic of the behaviour expected of a mixed conductor.

Rotor phases in compound semiconductors

Quasielastic neutron scattering is used to study the disordering processes in two classes of semiconductors: I–IV Zintl compounds and the phosphorous—selenium system. Two alkali-metal-polyvalent metal Zintl compounds, CsPb and NaSn, exhibit a two-stage melting process with high-temperature solid phases characterized by rapid dynamical disorder. In CsPb this disorder is clearly associated with rapid reorientations of polyanions with the cations participating in the dynamical disorder on the same time scale. In NaSn the disorder is associated with fast reorientations of the polyanions closely coupled to a slower migration of the cations. The two high-temperature solid phases of the molecular crystal P 4Se 3 are confirmed to be rotor phases with small but significant differences in the reorientational motions in the two phases.

Orientational and translational disorder in semiconducting Zintl compounds.

Two alkali-metal--polyvalent-metal Zintl compounds, NaSn and CsPb, exhibit a two-stage melting process with high-temperature solid phases characterized by rapid dynamical disorder. In NaSn this disorder is associated with fast reorientations of the Sn{sub 4}{sup 4{minus}} polyanions closely coupled to a slower migration of the Na{sup +} cations. In CsPb it is associated with rapid reorientations of Pb{sub 4}{sup 4{minus}} polyanions with the Cs{sup +} cations participating in the dynamical disorder on the same time scale. In both cases the disordering has dramatic effects on the electronic and ionic transport and thermodynamic properties.

Inter- and Intramolecular Reorientations in Liquid Crystals

Abstract Data of dielectric relaxation measurements so far obtained for isotropic, nematic and solid phases of seven members of di-n-alkoxyazoxybenzene (n-OAOB) homologous series have been reanalysed in order to discuss the influence of the end chains on the molecular reorientations. The relaxation times characterizing the intermolecular reorientations show odd-even alternation in the temperature range both below and above the clearing points. Below the melting temperatures dielectric relaxation processes have been observed for high-temperature solid phases of two substances with n = 4 and 5. The specific behaviour of reorientational dynamics at both clearing and melting points may be related to the corresponding behaviour of thermodynamic quantities.

The thermodynamics of the solid oxides of vanadium

The available thermodynamic data have been critically reviewed and extended to provide values of S 298 and Δ H 298, and analytical equations for -( G- H 289)/ T as a function of temperature for 14 of the high-temperature solid phases of the V-O system.

ChemInform Abstract: NONPLANAR CONFORMERS AND THE PHASE BEHAVIOR OF SOLID N‐ALKANES

Solidsolid phase transitions of the odd n-alkanes n-C17H36 through n-C29H60 were studied by using differential scanning calorimetry (DSC) and infrared (IR) spectroscopy. Two phase transitions were found in C25, C2,, and C29 in addition to the previously reported highest-temperature solid-solid transition (the so-called rotator transition). IR spectra revealed that, as the temperature is raised, the concentration of nonplanar conformers successively increases through each phase transition. Three types of nonplanar have been identified in the highest-temperature phase of all the n-alkanes: (gt ...), kink (...gtg'...), and (...gg...). The end-gauche defect was observed in the lower-temperature phases as well. Kink conformers, however, were observed only in the highest-temperature phase while double-gauche were found in measurable concentrations only within a few degrees of the melting point. The concentrations of nonplanar conformers in the highest-temperature phases increase with increasing chain length. For example, roughly 70% of C29 molcules are nonplanar prior to melting, in contrast to 5-10% for C17. The relationship between the existence of nonplanar conformers and the various distinct solid phases presents a major puzzle. Normal alkanes undergo a remarkable series of solidsolid phase transitions prior to melting. Analogous premelting transitions are also found in a number of more complex systems which contain hydrocarbon chains as major constituents. These systems include polyethylene,' variously substituted alkanes,2 and biological ~nembranes.~ In the latter cases, the phase changes are believed to be intimately related to the state of the hydrocarbon component. For example, current models of the lipid bilayer phase transitions require detailed consideration of the changes in conformation of the alkane chains4 Since the n-alkanes themselves are the sim- plest of these chain-molecule solids, they are a natural starting point for understanding the premelting transitions exhibited by all of these systems. The phase behavior of even the n-alkanes is complex. All odd n-alkanes between C9 and C45 undergo at least one premelting phase transition, and the longer members show no less than four high-temperature solid phases in addition to the low-temperature crystalline phases5 The nature of these phases is not well un- derstood although it is clear that the higher-temperature phases involve increasing degrees of disorder. By here we mean any deviation from the regular arrangement of all-trans chains found in the low-temperature solid. In this paper we focus mainly on one aspect of the disordering processes occurring in these solids-that involving conformational changes. We show that infrared spectroscopy is sensitive to the presence of various nonplanar (not all-trans) conformers and to some types of intermolecular order. We will find that disorder occurs in a series of apparently solid phases. The question then arises how can the apparent short-range implied by these nonplanar conformations be reconciled with the existence of a series of phases showing long-range order? This question which is fundamental to the understanding of the more complex systems such as biolipid bilayers will be taken up again in the Conclusion. The body of this paper presents the infrared spectra of the alkanes as a function of temperature with an analysis of the conformational defects seen in the various phases.

Nonplanar conformers and the phase behavior of solid n-alkanes

Solidsolid phase transitions of the odd n-alkanes n-C17H36 through n-C29H60 were studied by using differential scanning calorimetry (DSC) and infrared (IR) spectroscopy. Two phase transitions were found in C25, C2,, and C29 in addition to the previously reported highest-temperature solid-solid transition (the so-called rotator transition). IR spectra revealed that, as the temperature is raised, the concentration of nonplanar conformers successively increases through each phase transition. Three types of nonplanar have been identified in the highest-temperature phase of all the n-alkanes: (gt ...), kink (...gtg'...), and (...gg...). The end-gauche defect was observed in the lower-temperature phases as well. Kink conformers, however, were observed only in the highest-temperature phase while double-gauche were found in measurable concentrations only within a few degrees of the melting point. The concentrations of nonplanar conformers in the highest-temperature phases increase with increasing chain length. For example, roughly 70% of C29 molcules are nonplanar prior to melting, in contrast to 5-10% for C17. The relationship between the existence of nonplanar conformers and the various distinct solid phases presents a major puzzle. Normal alkanes undergo a remarkable series of solidsolid phase transitions prior to melting. Analogous premelting transitions are also found in a number of more complex systems which contain hydrocarbon chains as major constituents. These systems include polyethylene,' variously substituted alkanes,2 and biological ~nembranes.~ In the latter cases, the phase changes are believed to be intimately related to the state of the hydrocarbon component. For example, current models of the lipid bilayer phase transitions require detailed consideration of the changes in conformation of the alkane chains4 Since the n-alkanes themselves are the sim- plest of these chain-molecule solids, they are a natural starting point for understanding the premelting transitions exhibited by all of these systems. The phase behavior of even the n-alkanes is complex. All odd n-alkanes between C9 and C45 undergo at least one premelting phase transition, and the longer members show no less than four high-temperature solid phases in addition to the low-temperature crystalline phases5 The nature of these phases is not well un- derstood although it is clear that the higher-temperature phases involve increasing degrees of disorder. By here we mean any deviation from the regular arrangement of all-trans chains found in the low-temperature solid. In this paper we focus mainly on one aspect of the disordering processes occurring in these solids-that involving conformational changes. We show that infrared spectroscopy is sensitive to the presence of various nonplanar (not all-trans) conformers and to some types of intermolecular order. We will find that disorder occurs in a series of apparently solid phases. The question then arises how can the apparent short-range implied by these nonplanar conformations be reconciled with the existence of a series of phases showing long-range order? This question which is fundamental to the understanding of the more complex systems such as biolipid bilayers will be taken up again in the Conclusion. The body of this paper presents the infrared spectra of the alkanes as a function of temperature with an analysis of the conformational defects seen in the various phases.