First-order Phase Change Research Articles

High strain rate constitutive modeling of aluminum nitride including a first-order phase transformation

This work presents a computational constitutive model for materials exhibiting a first-order phase transition. The model can represent both recoverable and non-recoverable volume loss characterized by first-order phase transitions. Aluminum Nitride (A1N) is used to demonstrate the model. A1N has a first-order phase transition from the wurtzite (hexagonal) structure to the rock salt (cubic) structure. This phase transformation has been observed under static high pressure testing and inferred to be occurring under high strain rate shock wave loading. The phase transition begins at an approximate hydrostatic pressure of 16GPa where a 20% volume loss commences. The volume loss has been inferred to be non-recoverable. The model used for this study was previously developed for crushable materials, but is demonstrated herein that it can be straightforwardly applied to materials that exhibit a first-order phase change. Constants are obtained for the model using A1N test data Plate impact experiments are simulated using the model, demonstrating the ability of the model to capture the material behavior. The model is also used to evaluate the recoverability of the volume loss and implies that the volume loss is non-recoverable.

A Calorimetric Study of Phospholipid Hydration. Simultaneous Monitoring of Enthalpy and Free Energy

We present a novel method for monitoring isothermal lipid hydration using a sorption microcalorimeter. A measuring cell of the double-twin calorimeter consists of two vessels connected by a stainless steel tube. The upper vessel contains pure water, and the bottom vessel is loaded with the lipid sample. This calorimeter allows for simultaneous measurement of the partial molar enthalpy and the chemical potential (or the partial molar free energy) of the water. The versatility of the method is demonstrated by studies of the hydration of the phospholipids dipalmitoyl phosphatyl choline (DPPC), dimyristoyl phosphatidyl choline (DMPC), and dilauroyl phosphatidyle choline (DLPC) at 25 and 27 °C. The measurements provide a relation between water content and water chemical potential, which, in these lamellar systems, is often recast as a force−distance relation and has been called the hydration force. Through the simultaneously monitored calorimetric values, the partial molar enthalpy of water is also obtained. The method consequently provides a rather unique combination of information on both partial molar enthalpy and partial molar free energy and thus also the partial molar entropy of the process. We find that the incorporation of the first three to four water molecules per lipid is exothermic. These water molecules presumably interact directly with oxygen atoms on the phosphate of the lipid headgroup. When the first waters have been added, the remaining ones are incorporated endothermically. This applies to the water molecules taken up both in the gel phase and in the liquid crystalline state. We also observe that the sorption process triggers a first-order phase change from a gel (Lβ‘) to a liquid crystalline (Lα) phase. For DLPC, this occurs at 25 °C at a relative humidity of 0.79 with an endothermic transition enthalpy of 42 ± 2 kJ/mol (DLPC) and, for DMPC, at 27 °C at 0.93 relative humidity with ΔH = 56 ± 5 kJ/mol (DMPC). We use a previously established model to quantitatively interpret these phase transitions. Furthermore, the observed endothermic nature of the sorption process above three to four waters per lipid is fully consistent with the suggestion that the negative free energy of the sorption (swelling) is due to increased thermal excitations and thus a positive entropy. It is more problematic to reconcile the data with models proposing structuring effects in the water as the main cause of the swelling.

Evidence that the Induction Time in the Surface Pressure Evolution of Lysozyme Solutions Is Caused by a Surface Phase Transition

Induction periods have been reported in the surface pressure evolution of a wide variety of proteins. In this work, this induction period is shown to be caused by a first-order phase change from a surface gaseous to a liquid-expanded state as the protein lysozyme adsorbs and decreases the mean area per molecule. The evolution of this transition is studied using concomitant fluorescence microscopy and surface pressure measurements. The fluorescent images are obtained by using spread films of the dye NBD-HDA at the air−liquid interface. This dye fluoresces when in contact with hydrophobic moieties and is quenched when in contact with water. The hydrophobic liquid-expanded domains therefore appear bright on a dark background. Lysozyme initially adsorbs to establish a surface gaseous phase, and the interface appears dark. The surface tension is fairly insensitive to changes in area per molecule in this state. Once the adsorbed concentration of lysozyme reaches the surface gaseous binodal, protein interactions drive a first-order phase change. Domains of liquid expanded phase grow at the interface at the expense of the surface gaseous phase. During this phase change, the surface tension remains constant. Only after the interface is covered in the bright, liquid-expanded phase does the surface tension decrease from the clean interface value. These results are discussed in terms of the surface coverage and orientation of lysozyme.

Convection in the presence of a first-order phase change.

We report experimental and theoretical results for two-phase convection in a thin horizontal layer of a fluid with a first-order phase change and heated from below. A top layer of the nematic phase of a liquid crystal is located above the bottom layer of the isotropic phase of the same substance. A horizontal field of 1000 G is applied in order to align the director of the nematic phase. Over some ranges of the thickness of the isotropic phase, and in sufficiently large thermal gradients, the more dense nematic phase can be stably stratified above the less dense isotropic one, with a stable interface between them. Based on the equations of motion derived for this problem by Busse and Schubert [J. Fluid Mech. 46, 801 (1971)], we evaluate the bifurcation lines between the quiescent and convecting states and the corresponding critical wave vectors as a function of the interface position. We report experimental measurements based on Nusselt-number determinations for the locations of the bifurcation lines. They are in good agreement with the theoretical results. We also report approximate determinations of the critical wave numbers which are semiquantitatively consistent with the theory. A great diversity of patterns is observed in the convecting states, including normal and parallel rolls, rolls with defects and disorder, target patterns and spirals, and cellular flow with upflow or downflow at the cell center. These patterns are discussed in terms of the breaking of the mirror symmetry at the horizontal midplane by the interface, and in terms of the orienting effects of the magnetic field.

High Pressure Behavior of Sr3(VO4)2and Ba3(VO4)2

We have studied pressure-induced transitions and structural changes in isostructural strontium and barium orthovanadates, Sr3(VO4)2and Ba3(VO4)2, via Raman spectroscopy. The spectral changes in Ba3(VO4)2can be interpreted as being due to condensation of VO3−4units into edge- or corner-shared octahedra with little or no hysteresis on decompression. For Sr3(VO4)2, there is a pressure-induced first-order phase change at about 150 kbar, with large hysteresis on decompression, which can be rationalized as a transition into a spinelloid series of structures, retaining the tetrahedral coordination of the V atoms.

First-Order Transitions and Hexatic Ordering in the Aerogel-Confined Liquid Crystal 650BC

In the liquid-crystal material 650BC confined in a silica aerogel, synchrotron x-ray diffraction shows two distinct kinds of first-order phase change behavior, depending on $r\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ensuremath{\lambda}(T)/〈p〉$, the ratio of the two-phase interface thickness at the transition, $\ensuremath{\lambda}(T)$, to the pore size $〈p〉$. For $r<1$, intrapore phase coexistence is observed, whereas for $r>1$, order in the aerogel nucleates on a scale larger than the mean pore size and grows simultaneously in pores of all sizes. We also find that in all phases translational in-plane order is short ranged and limited in the aerogel host to dimension much smaller than the pore (smectic domain) size and bulk values.

Graphics simulation of a soap film catastrophe model

A soap film model is described that demonstrates catastrophic changes of the film pattern caused by continuous changes in configuration. The scope of the model is extended by the use of computer graphics both to animate the pattern changes of the films and to plot the corresponding movement on energy-configuration and other curves. Such energy-configuration curves are identical to those of systems that experience first-order and second-order phase changes.

A Low-Temperature Amorphous Phase in a Fragile Glass-Forming Substance

We have observed what appears to be a first-order phase change from deeply supercooled liquid triphenyl phosphite at 1 atm to a rigid, “apparently” amorphous phase which we denote as the “glacial phase”. This is a new, crisper, and rather different addition to the examples of polyamorphism that have recently been studied. In order to “deeply” supercool the liquid, it must be quick-quenched to a low temperature: if heated slowly, but immediately, it crystallizes; if allowed to stand for several hours at low temperature, it transforms to the glacial phase; and if subsequently heated it, too, crystallizes, but at a higher temperature than that for liquid crystallization. The glacial phase can be clearly distinguished from both the normal crystal and the ordinary glass. We propose a model for the formation of this “apparently” amorphous glacial phase.

Magnetic studies of some orthovanadates.

The perovskites L${\mathrm{VO}}_{3}$ (L=La, Lu, or Y) are canted-spin antiferromagnets. Magnetic susceptibility measurements made on cooling from room temperature in a field of 1 kOe or on heating after cooling in 1 kOe give rise to a sample magnetization M that is oriented in opposition to the magnetizing field below 138 K in ${\mathrm{LaVO}}_{3}$, but in the direction of the magnetizing field in ${\mathrm{LuVO}}_{3}$ and ${\mathrm{YVO}}_{3}$. Orientation of the M in ${\mathrm{LaVO}}_{3}$ in opposition to the magnetizing field H occurs on cooling through a first-order magneto- strictive transition at 138 K${\mathit{T}}_{\mathit{N}}$\ensuremath{\approxeq}142 K that enhances the ${\mathit{V}}^{3+}$ ion orbital angular momentum. In ${\mathrm{YVO}}_{3}$, a first-order magnetic-order phase change at 78 K ${\mathit{T}}_{\mathit{N}}$\ensuremath{\approxeq}114 K shows no evidence of a discontinuous change in the ${\mathrm{V}}^{3+}$ ion orbital angular momentum. The same is true for a phase change in ${\mathrm{LuVO}}_{3}$ at 83 K${\mathit{T}}_{\mathit{N}}$\ensuremath{\approxeq}105 K that leaves the magnetic order unchanged. A high-pressure (P\ensuremath{\ge}8 kbar) ${\mathrm{LaVO}}_{3}$ phase metastable below 250 \ifmmode^\circ\else\textdegree\fi{}C is antiferromagnetic without spin canting. The ``anomalous diamagnetism'' previously reported for field-cooled ${\mathrm{LaVO}}_{3}$ is interpreted to reflect the first observation of a change in the direction of the persistent currents at an ion associated with a discontinuous change in an unquenched orbital angular momentum contribution to the atomic moment; a spin-orbit coupling stronger than the Zeemann coupling of the spin to the magnetizing field reverses the entire atomic moment ${\mathrm{\ensuremath{\mu}}}_{\mathit{J}}$=gJ${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$. Substitution of La by Lu or Y applies a chemical pressure that suppresses the first-order magnetostrictive distortion responsible for the anomalous diamagnetism.

LaCoO 3 Revisited

Homogeneous samples of LaCoO 3 were prepared from coprecipitated precursors; they reveal that single-phase samples are restricted to a narrow range of the [La]/[Co] ratio of about 1.0. A first-order phase change near 1200 K only appears where Co 3O 4 is present as an impurity phase. Evolution with temperature from all low-spin Co(III) at T = 0 K to 50% high-spin Co 3+ and 50% intermediate-spin Co(III) above 650 K is monitored with magnetic susceptibility, resistance, and thermopower measurements. Evidence is found for a dynamic ordering of high-spin Co 3+ and low-spin Co(III) in the intermediate-temperature interval 110 K < T < 350 K. The lifetime of a Co 3+ ion decreases with increasing temperature to a τ < 10 -8 sec for T > 200 K. The intermediate-temperature phase is semiconductive with an E g ≈ 0.14 eV for excitations of hole-electron pairs. The holes are mobile; the electrons are trapped as Co 2+ on high-spin sites until they recombine with a mobile hole. The metallic high-temperature phase for T > 650 K is nucleated and grows with increasing temperature in the interval 350 K < T < 650 K.

Filling Dependence of Magnetoresistance in Perovskite-type Manganese Oxide Films

AbstractFilling dependence of magnetotransport properties was investigated in Ndl−xSrxMnO3 films. Hysteretic behavior was observed in temperature dependencies of resistivity for restricted filling of x-0.35 and 0.50, indicating the occurrence of a first-order phase transition at low temperatures. The transition gives rise to a high-resistivity state which collapses to low-resistivity state under an external magnetic field. Change in resistivity by applying magnetic field was more than a order of magnitude. Origin of colossal magnetoresistance (CMR) is briefly discussed in terms of such a first-order phase change induced by a magnetic field.

Melting of square crystals in two dimensions.

A 2500-particle molecular-dynamics simulation has been carried out for a two-dimensional continuum model whose classical ground state is a crystal with square symmetry. The interaction potential comprises two-body and three-body contributions. Evidence from both heating and cooling sequences indicates that the crystal-liquid transition is a conventional first-order phase change. Inherent structures (potential-energy minima) have been constructed for the homogeneous liquid over a wide temperature range, for the crystal-liquid coexistence state, and for a defective crystalline state. Liquid-phase inherent structures display a vivid polycrystalline character that is strongly obscured by equilibrium thermal motions.

High-pressure liquid-liquid phase change in carbon.

The likelihood of a first-order liquid-liquid phase change in carbon from a mostly graphitic configuration to one that is more tetrahedral in character is explored. Liquid-phase changes in other materials are noted. Pertinent data on liquid carbon are reviewed and the model is briefly described. The model is consistent with a positive diamond-melting-line slope. Constraints on the strain energy between graphitic and diamondlike liquid clusters allow a phase diagram with a liquid-liquid transition and a graphite-liquid-liquid triple point. An upper limit on the strain energy is the constraint that the graphite melting line should have a reasonable curvature that agrees with melting-line data. The transformation of liquid structure from graphitic to diamondlike under compression significantly increases the compressibility.

Thermal convection in the presence of a first-order phase change.

We report experimental results for convection in a thin horizontal layer of a fluid which is heated from below and which undergoes a first-order phase change. For some parameter ranges the denser layer may be stably stratified above the lighter one, as predicted by Busse and Schubert. Over various parameter ranges we observed hexagonal, inverted-hexagonal, and roll flow. Interesting interactions between two-phase convection and Rayleigh-Benard convection are observed near two codimension-two points.

Thermodynamic aspects of extended inflation.

Extended inflation has recently been proposed as a way of allowing inflation to proceed via a first-order phase change while avoiding the graceful exit problem. We examine the constraints imposed on such models by the need to establish a thermal initial state using the formalism developed in a previous paper. We conclude that, despite the extra free parameters extended inflation enjoys, the difficulties of generating a thermal state are just as great as they are for conventional inflation

Oxygen-deficiency-based anomalies in the ultrasonic properties of Bi(2212) crystals

Ultrasonic velocity and internal friction measurements on a single crystal of Bi2Sr2Ca1Cu2Ox grown by directional solidification have shown a number of anomalous features and instabilities which correlate well with annealing treatments designed to change the oxygen concentration. It is suggested that a first-order phase change occurs close to 150 K in crystals annealed under vacuum conditions.

Phase transition in Pb5Al3F19

Abstract A study of the PbF2-AlF3 system has resulted in a new material Pb5Al3F19 with a tetragonal structure at room temperature closely related to that of Pb5Cr3F19. A phase transition in Pb5Al3F19 has been detected by means of X-ray diffraction, calorimetric and dielectric measurements. The coexistence of the high and low-temperature Pb5Al3F19 phases over the range 270 to 300 K and the abrupt 0.7% increase in the a-axis and 1.5% decrease in the c-axis, on heating through the phase transition, are characteristic of a first-order phase change. The increase in symmetry from point group 4 below to point group 4/m above the phase transition is consistent with a ferroelectric to paraelectric transition, as found previously in Pb5Cr3F19.

Origin of the first-order phase change at the Curie temperature in KNbO3

As judged by the difference between Curie temperature Tc and Curie-Weiss temperature Θ (Tc−Θ∼53 °C) KNbO3 goes through a very strongly first-order phase change at Tc into a tetragonal ferroelectric phase. For BaTiO3, it is known that the weaker first-order change at Tc (Tc−Θ∼10 °C) derives from the electrostrictive coupling and that the strain-free crystal would go directly to rhombohedral symmetry by a second-order transition. It is the purpose of this note to point up the fact that in spite of the much stronger first-order change in KNbO3, the origin is again in the electrostrictive coupling, and that the cubically clamped crystal would go through a second-order phase change.

Observation of a topological transition in the 3He-A vortices.

Vortices in {sup 3}He-{ital A} in low magnetic fields ({ital H}{le}20 mT) have been studied by ultrasonics. A first-order phase change between two vortex types, with dissimilar sound absorption, has been found. The magnetic field at the transition is on the order of the dipolar field {ital H}{sub {ital d}}. The observed change occurs between continuous vortex textures with different topological charges in the {bold {cflx d}} field (where {bold {cflx d}} is the magnetic anisotropy vector).

Composition-dependent ferroelectric Curie temperature of Pb5(Cr1−xAlx)3F19 from 555 to 280 K and of Pb5 (Cr1−xFex)3F19 from 555 to 725 K for 0≤x≤1

Ferroelectric Pb5Cr3F19 forms a complete series of solid solutions both with Pb5Al3F19 and Pb5Fe3F19. The end and intermediate compositions are isostructural with the ferroelectric A5M3F19 family previously reported [J. Appl. Phys. 62, 4299 (1987)]. The a and c axial lengths in Pb5(Cr0.2Al0.8)3F19 undergo discontinuities of +0.5% and −0.8%, respectively on heating through the Curie temperature (Tc =325 K), and exhibit a hysteresis of about 40 K between the phase transition temperature on heating and on cooling, characteristic of a first-order phase change. The value of Tc may be varied continuously between 555 and 280 K for the solid solution Pb5(Cr1−xAlx) 3F19, and between 555 and 725 K for Pb5(Cr1−xFex) 3F19, by increasing x from 0 to 1. The entropy change at the phase transition in Pb5Fe3F19, Pb5Cr3F19, and Pb5(Cr0.8Al0.2)3 F19 is high, at about Rln8. The maximum dielectric permittivity in Pb5Cr3F19 is about 2000.