scispace - formally typeset
Search or ask a question

Showing papers on "Phase (matter) published in 2008"


Journal ArticleDOI
31 Jan 2008-Nature
TL;DR: This work shows that even a pure compound, in this case lead titanate, can display a morphotropic phase boundary under pressure, and finds that complex microstructures or compositions are not necessary to obtain strong piezoelectricity.
Abstract: A piezoelectric material is one that generates a voltage in response to a mechanical strain (and vice versa). The most useful piezoelectric materials display a transition region in their composition phase diagrams, known as a morphotropic phase boundary, where the crystal structure changes abruptly and the electromechanical properties are maximal. As a result, modern piezoelectric materials for technological applications are usually complex, engineered, solid solutions, which complicates their manufacture as well as introducing complexity in the study of the microscopic origins of their properties. Here we show that even a pure compound, in this case lead titanate, can display a morphotropic phase boundary under pressure. The results are consistent with first-principles theoretical predictions, but show a richer phase diagram than anticipated; moreover, the predicted electromechanical coupling at the transition is larger than any known. Our results show that the high electromechanical coupling in solid solutions with lead titanate is due to tuning of the high-pressure morphotropic phase boundary in pure lead titanate to ambient pressure. We also find that complex microstructures or compositions are not necessary to obtain strong piezoelectricity. This opens the door to the possible discovery of high-performance, pure-compound electromechanical materials, which could greatly decrease costs and expand the utility of piezoelectric materials.

741 citations


Journal ArticleDOI
TL;DR: In this paper, the role of the additive in the mixture solvent and how the optimized nanoscale phase separation develops laterally and vertically during the non-equilibrium spin-coating process was investigated.
Abstract: The mixed solvent approach has been demonstrated as a promising method to modify nanomorphology in polymer solar cells. This work aims to understand the unique role of the additive in the mixture solvent and how the optimized nanoscale phase separation develops laterally and vertically during the non-equilibrium spin-coating process. We found the donor/acceptor components in the active layer can phase separate into an optimum morphology with the additive. Supported by AFM, TEM and XPS results, we proposed a model and identified relevant parameters for the additive such as solubility and vapor pressures. Other additives are discovered to show the ability to improve polymer solar cell performance as well.

683 citations


Journal ArticleDOI
TL;DR: In this paper, the authors report on extensive experimental studies on thin film, single crystal, and ceramics of multiferroic bismuth ferrite BiFeO3 using differential thermal analysis, high-temperature polarized light microscopy, hightemperature x-ray diffraction, dc conductivity, optical absorption and reflectivity, and domain imaging.
Abstract: We report on extensive experimental studies on thin film, single crystal, and ceramics of multiferroic bismuth ferrite BiFeO3 using differential thermal analysis, high-temperature polarized light microscopy, high-temperature and polarized Raman spectroscopy, high-temperature x-ray diffraction, dc conductivity, optical absorption and reflectivity, and domain imaging, and show that epitaxial (001) thin films of BiFeO3 are clearly monoclinic at room temperature, in agreement with recent synchrotron studies but in disagreement with all other earlier reported results. We report an orthorhombic order-disorder beta phase between 820 and 925 (±5) °C, and establish the existence range of the cubic gamma phase between 925 (±5) and 933 (±5) °C, contrary to all recent reports. We also report the refined Bi2O3-Fe2O3 phase diagram. The phase transition sequence rhombohedral-orthorhombic-cubic in bulk [monoclinic-orthorhombic-cubic in (001)BiFeO3 thin film] differs distinctly from that of BaTiO3. The transition to the cubic gamma phase causes an abrupt collapse of the band gap toward zero (insulator-metal transition) at the orthorhombic-cubic beta-gamma transition around 930 °C. Our band structure models, high-temperature dc resistivity, and light absorption and reflectivity measurements are consistent with this metal-insulator transition.

561 citations


Journal ArticleDOI
TL;DR: It is described for the first time how the entire write/erase cycle for the Ge(2)Sb-Te composition can be reproduced using ab initio molecular-dynamics simulations, and the microscopic insight provided on crystal nucleation should open up new ways to develop superior phase-change memory materials.
Abstract: Ge-Sb-Te materials are used in optical DVDs and non-volatile electronic memories (phase-change random-access memory). In both, data storage is effected by fast, reversible phase changes between crystalline and amorphous states. Despite much experimental and theoretical effort to understand the phase-change mechanism, the detailed atomistic changes involved are still unknown. Here, we describe for the first time how the entire write/erase cycle for the Ge(2)Sb(2)Te(5) composition can be reproduced using ab initio molecular-dynamics simulations. Deep insight is gained into the phase-change process; very high densities of connected square rings, characteristic of the metastable rocksalt structure, form during melt cooling and are also quenched into the amorphous phase. Their presence strongly facilitates the homogeneous crystal nucleation of Ge(2)Sb(2)Te(5). As this simulation procedure is general, the microscopic insight provided on crystal nucleation should open up new ways to develop superior phase-change memory materials, for example, faster nucleation, different compositions, doping levels and so on.

481 citations


Journal ArticleDOI
TL;DR: Although structural distortions are robust to changes in particle size, what is affected is the coherency of the distortions, which is decreased in the smaller particles, in contrast to the sharp transition that is found for the bulk sample.
Abstract: We have investigated the paraelectric-to-ferroelectric phase transition of various sizes of nanocrystalline barium titanate (BaTiO3) by using temperature-dependent Raman spectroscopy and powder X-ray diffraction (XRD). Synchrotron X-ray scattering has been used to elucidate the room temperature structures of particles of different sizes by using both Rietveld refinement and pair distribution function (PDF) analysis. We observe the ferroelectric tetragonal phase even for the smallest particles at 26 nm. By using temperature-dependent Raman spectroscopy and XRD, we find that the phase transition is diffuse in temperature for the smaller particles, in contrast to the sharp transition that is found for the bulk sample. However, the actual transition temperature is almost unchanged. Rietveld and PDF analyses suggest increased distortions with decreasing particle size, albeit in conjunction with a tendency to a cubic average structure. These results suggest that although structural distortions are robust to cha...

480 citations


Journal ArticleDOI
11 Sep 2008-Nature
TL;DR: The design and operation of a microfluidic system formed in a synthetic hydrogel captures the main attributes of transpiration in plants: transduction of subsaturation in the vapour phase of water into negative pressures in the liquid phase, stabilization and flow of liquid water at large negative pressures.
Abstract: Plant scientists believe that transpiration-the motion of water from the soil, through a vascular plant, and into the air-occurs by a passive, wicking mechanism. This mechanism is described by the cohesion-tension theory: loss of water by evaporation reduces the pressure of the liquid water within the leaf relative to atmospheric pressure; this reduced pressure pulls liquid water out of the soil and up the xylem to maintain hydration. Strikingly, the absolute pressure of the water within the xylem is often negative, such that the liquid is under tension and is thermodynamically metastable with respect to the vapour phase. Qualitatively, this mechanism is the same as that which drives fluid through the synthetic wicks that are key elements in technologies for heat transfer, fuel cells and portable chemical systems. Quantitatively, the differences in pressure generated in plants to drive flow can be more than a hundredfold larger than those generated in synthetic wicks. Here we present the design and operation of a microfluidic system formed in a synthetic hydrogel. This synthetic 'tree' captures the main attributes of transpiration in plants: transduction of subsaturation in the vapour phase of water into negative pressures in the liquid phase, stabilization and flow of liquid water at large negative pressures (-1.0 MPa or lower), continuous heat transfer with the evaporation of liquid water at negative pressure, and continuous extraction of liquid water from subsaturated sources. This development opens the opportunity for technological uses of water under tension and for new experimental studies of the liquid state of water.

459 citations


Journal ArticleDOI
TL;DR: In this article, the phase-field approach is applied to inhomogeneous systems containing domain structures and it is demonstrated that using a set of independently measured thermodynamic parameters for the corresponding bulk single crystals, the phase field approach is able to quantitatively predict not only the strain effect on phase transition temperatures but also the correct ferroelectric domain structures for a given strain and temperature.
Abstract: This article briefly reviews recent applications of phase-field method to ferroelectric phase transitions and domain structures in thin films. It starts with a brief introduction to the thermodynamics of coupled electromechanical systems and the Landau description of ferroelectric transitions in homogeneous ferroelectric single crystals. The thermodynamic potentials of a homogeneous crystal under different mechanical boundary conditions are presented, including the thin-film boundary conditions. The phase-field approach to inhomogeneous systems containing domain structures is then outlined. It describes a domain structure using the spatial distribution of spontaneous polarization. The evolution of a domain structure towards equilibrium is driven by the reduction in the total-free energy of an inhomogeneous domain structure including the chemical driving force, domain wall energy, electrostatic energy as well as elastic energy. A number of examples are discussed, including phase transitions and domain stability in ferroelectric thin films and superlattices. It is demonstrated that using a set of independently measured thermodynamic parameters for the corresponding bulk single crystals, the phase-field approach is able to quantitatively predict not only the strain effect on phase transition temperatures but also the correct ferroelectric domain structures for a given strain and temperature.

416 citations


Journal ArticleDOI
TL;DR: The ability of different crystal phases of TiO2 nanoparticles to generate ROS was highest for amorphous, followed by anatase, and then anatase/rutile mixtures, and lowest for rutile samples, and important dose metrics for ROS generation are established.
Abstract: A method to investigate the dependence of the physicochemical properties of nanoparticles (e.g. size, surface area and crystal phase) on their oxidant generating capacity is proposed and demonstrated for TiO(2) nanoparticles. Gas phase synthesis methods that allow for strict control of size and crystal phase were used to prepare TiO(2) nanoparticles. The reactive oxygen species (ROS) generating capacity of these particles was then measured. The size dependent ROS activity was established using TiO(2) nanoparticles of 9 different sizes (4 - 195 nm) but the same crystal phase. For a fixed total surface area, an S-shaped curve for ROS generation per unit surface area was observed as a function of particle size. The highest ROS activity per unit area was observed for 30 nm particles, and observed to be constant above 30 nm. There was a decrease in activity per unit area as size decreased from 30 nm to 10 nm; and again constant for particles smaller than 10 nm. The correlation between crystal phase and oxidant capacity was established using TiO(2) nanoparticles of 11 different crystal phase combinations but similar size. The ability of different crystal phases of TiO(2) nanoparticles to generate ROS was highest for amorphous, followed by anatase, and then anatase/rutile mixtures, and lowest for rutile samples. Based on evaluation of the entire dataset, important dose metrics for ROS generation are established. Their implications of these ROS studies on biological and toxicological studies using nanomaterials are discussed.

399 citations


01 Jan 2008
TL;DR: In this article, the commercial TiO2 nanopowder and micropowder of anatase phase and rutile phase have been characterized by x-ray diffraction and transmission electron microscopy (TEM).
Abstract: In this study, the commercial TiO2 nanopowder and micropowder of anatase phase and rutile phase have been characterized by x-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD patterns of nano-TiO2 in rutile and anatase phases exhibit broad peaks whereas both phases of micro-TiO2 demonstrate very sharp peaks. TEM images show that the grain size of TiO2 micropowders and TiO2 nanopowders are 0.3-0.7 ∝m and 10 nm, respectively. The selected-area electron diffraction patterns of TiO2 nanopowders in rutile and anatase phases are consistent with XRD results.

390 citations


Journal ArticleDOI
TL;DR: In this article, the shape of the interface between the immiscible liquids was controlled by a competition between the viscous forces and the local interfacial tension, and the mass transfer coefficients for parallel and slug flow were determined using instantaneous eutralisation (acidbase) reaction.

376 citations


Patent
20 Aug 2008
TL;DR: In this article, the authors proposed a liquid crystal display element which satisfies at least one property selected from a high upper-limit temperature in a nematic phase, a low lower limit temperature in the nematic phases, and a low viscosity, high optical anisotropic, high dielectric anisotropy, a high specific resistivity, high stability to ultraviolet ray, and the like.
Abstract: Disclosed are: a liquid crystal composition, which satisfies at least one property selected from a high upper-limit temperature in a nematic phase, a low lower-limit temperature in a nematic phase, a low viscosity, high optical anisotropy, high dielectric anisotropy, a high specific resistivity, high stability to ultraviolet ray, high stability to heat and the like, or which has an adequate balance between at least two properties selected from the above-mentioned properties; and an AM element having a short response time, a high voltage holding ratio, a high contrast ratio, a long service life and the like. Specifically disclosed are: a liquid crystal composition which comprises a specific pentacyclic compound having high optical anisotropy and high dielectric anisotropy as the first component, a specific compound having a low viscosity as the second component, and a specific tetracyclic compound having a high upper-limit temperature as the third component, and which has a nematic phase; and a liquid crystal display element comprising the composition.

Journal ArticleDOI
TL;DR: In this paper, the precipitate phases in a creep-resistant Mg-1Gd-0.4Zn−0.2Zr alloy aged isothermally at 250 and 200°C have been examined using a three-dimensional atom probe and high-angle annular dark-field scanning transmission electron microscopy.

Journal ArticleDOI
TL;DR: In this article, it was shown that the rhombohedral to tetragonal phase transition in Na0.5Bi 0.5TiO3 (NBT) is a two-step process.
Abstract: This study shows for the first time that the rhombohedral to tetragonal phase transition in Na0.5Bi0.5TiO3 (NBT) is a two step phase transition. The transformation begins by a first order phase transition involving the reconstructive transformation of the rhombohedral phase into an orthorhombic one, through the formation of an intermediate modulated phase. This phase transition begins slightly over 200 °C by the disappearance of the ferroelectric−ferroelastic domains. The intermediate modulated phase is then formed from 230 to 300 °C, the temperature at which it disappears. The modulated phase corresponds to an intergrowth of rhombohedral perovskite blocks in which Pnma orthorhombic sheets are formed by a microtwinning process of the rhombohedral phase. The intermediate orthorhombic phase is then formed at 300 °C and immediately turns to the tetragonal one. A model is presented explaining the formation of the modulated phase and the origin of the antiferroelectric and relaxor behaviors of NBT.

Journal ArticleDOI
TL;DR: In this article, the depolarization temperature Td, rhombohedral-tetragonal phase transition temperature TR-T, and the temperature Tm of the maximum dielectric constant were determined from the temperature dependence of the dielectrics and piezoelectric properties.
Abstract: (1-x)(Bi0.5Na0.5)TiO3–xSrTiO3 (abbreviated as BNST100x) was prepared by a conventional ceramic fabrication process. The depolarization temperature Td, rhombohedral-tetragonal phase transition temperature TR-T, and the temperature Tm of the maximum dielectric constant were determined from the temperature dependence of the dielectric and piezoelectric properties. It is revealed that BNST100x forms a morphotropic phase boundary of rhombohedral ferroelectric and pseudocubic (tetragonal) paraelectric at x=0.26–0.28 for BNST100x, and a very large strain and normalized strain d33* of 0.29% and 488pm∕V, respectively, were obtained at x=0.28. In addition, it was clarified that the intermediate phase between TR-T (⩾Td) and Tm shows relaxor behavior.

Journal ArticleDOI
TL;DR: In this paper, a general continuum theory is developed for ion intercalation dynamics in a single crystal of rechargeable-battery composite electrode material, based on an existing phase-field formulation of the bulk free energy and incorporating two crucial effects: (i) anisotropic ionic mobility in the crystal and (ii) surface reactions governing the flux of ions across the electrode/electrolyte interface, depending on the local free energy difference.

Journal ArticleDOI
TL;DR: High Internal Phase Emulsions (HIPEs) are important for a wide range of applications in the food, cosmetic, pharmaceutical and petroleum industries and can be used as templates for the synthesis of highly porous polymers with potential applications as low weight structures or scaffolds in tissue engineering.
Abstract: High Internal Phase Emulsions (HIPEs) are important for a wide range of applications in the food, cosmetic, pharmaceutical and petroleum industries. If the continuous phase is polymerizable, HIPEs can be used as templates for the synthesis of highly porous polymers with potential applications as low weight structures or scaffolds in tissue engineering. HIPEs are characterized by a minimum internal phase volume ratio of 0.74 but Lissant first defined this minimum as 0.7. HIPEs consisting of a continuous organic phase and an internal aqueous phase (w/o emulsion), are commonly stabilized by large amounts of surfactants. Particle-stabilized emulsions also known as Pickering-emulsions have recently attracted much interest. Unlike surfactants, particles irreversibly adsorb at the interface of emulsions due to their high energy of attachment which makes them good emulsifiers. The ability of particles to adsorb at the interface between the two phases is primarily dependent on the wettability of the particles. Hydrophilic particles such as metal oxides tend to stabilize o/w emulsion while hydrophobic particles such as carbon tend to stabilize w/o emulsions. Nevertheless, it is possible to modify the wettability of particles by adsorbing surfactant molecules onto the particle surfaces or by silanation. All reports on particle-stabilized emulsions deal with emulsions having internal phase levels elow 70 vol.-%. Kralchevsky et al. developed a thermodynamic model, which predicts that

Journal ArticleDOI
TL;DR: In this paper, the authors focus on the determination of phase diagrams by computer simulation, with particular attention to the fluid-solid and solid-solid equilibria, and the methodology to compute the free energy of solid phases is discussed.
Abstract: In this review we focus on the determination of phase diagrams by computer simulation, with particular attention to the fluid–solid and solid–solid equilibria. The methodology to compute the free energy of solid phases will be discussed. In particular, the Einstein crystal and Einstein molecule methodologies are described in a comprehensive way. It is shown that both methodologies yield the same free energies and that free energies of solid phases present noticeable finite size effects. In fact, this is the case for hard spheres in the solid phase. Finite size corrections can be introduced, although in an approximate way, to correct for the dependence of the free energy on the size of the system. The computation of free energies of solid phases can be extended to molecular fluids. The procedure to compute free energies of solid phases of water (ices) will be described in detail. The free energies of ices Ih, II, III, IV, V, VI, VII, VIII, IX, XI and XII will be presented for the SPC/E and TIP4P models of water. Initial coexistence points leading to the determination of the phase diagram of water for these two models will be provided. Other methods to estimate the melting point of a solid, such as the direct fluid–solid coexistence or simulations of the free surface of the solid, will be discussed. It will be shown that the melting points of ice Ih for several water models, obtained from free energy calculations, direct coexistence simulations and free surface simulations agree within their statistical uncertainty. Phase diagram calculations can indeed help to improve potential models of molecular fluids. For instance, for water, the potential model TIP4P/2005 can be regarded as an improved version of TIP4P. Here we will review some recent work on the phase diagram of the simplest ionic model, the restricted primitive model. Although originally devised to describe ionic liquids, the model is becoming quite popular to describe the behavior of charged colloids. Moreover, the possibility of obtaining fluid–solid equilibria for simple protein models will be discussed. In these primitive models, the protein is described by a spherical potential with certain anisotropic bonding sites (patchy sites). (Some figures in this article are in colour only in the electronic version)

Journal ArticleDOI
TL;DR: In this article, a theoretical model for the growth of semiconductor nanowires is developed, which enables one to determine the growth conditions under which the formation of semiconductors is possible.
Abstract: Theoretical model for the growth of semiconductor nanowires is developed, which enables one to determine the growth conditions under which the formation of nanowires is possible. General expression for the nanowire growth rate as function of its radius and the growth conditions is obtained and analyzed. The model also describes the transformation from cubic to hexagonal crystal phase of nanowires. It is shown that the observed crystal structure is controlled mainly by the growth kinetics. Structural diagrams and probabilities of cubic and hexagonal phase formation are calculated as functions of supersaturation and nanowire radius within the plausible range of material parameters. Numerical estimates for the domains of phase mixing and phase purity are presented and analyzed.

Journal ArticleDOI
TL;DR: In this paper, the surface phase structure of TiO2 nanoparticles calcined at different temperatures was studied using FT-IR spectroscopy with CO and CO2 as probe molecules and the results showed that the surface Lewis acidity of anatase phase is stronger than that of rutile phase.
Abstract: Surface phases of TiO2 nanoparticles (30 ∼ 200 nm) were studied by UV Raman spectroscopy and FT-IR spectroscopy with CO and CO2 as probe molecules. UV Raman spectroscopy can differentiate the surface phase structure of TiO2 calcined at different temperatures. IR spectra of adsorbed CO and CO2 on TiO2 calcined at different temperatures are in good agreement with the results from UV Raman spectra. IR results evidently confirm that UV Raman spectroscopy is a surface-sensitive technique for TiO2. Both UV Raman and IR spectra indicate that the crystalline phase of TiO2 in the surface region is usually different from that in the bulk which is characterized by XRD. CO is weakly adsorbed on Ti4+ ions of anatase phase but is hardly adsorbed on those of rutile phase at room temperature. Adsorbed CO2 on anatase phase produces mainly bidentate carbonate, while on rutile phase produces mainly bicarbonate species. These results suggest that the surface Lewis acidity of anatase phase is stronger than that of rutile phas...

Journal ArticleDOI
Xiaodi Yang1, Linjun Wang1, Caili Wang1, Wei Long1, Zhigang Shuai1 
TL;DR: In this paper, first-principles calculations within the Marcus electron transfer theory coupled with random walk simulation for room temperature charge diffusion constants were performed to find that the hole mobility of the HT phase is about 3-4 times larger than that of the LT phase.
Abstract: Both crystal packing and molecular size have strong influences on the charge mobility for organic semiconductors. The crystal structures for oligothiophene (nT) can be roughly classified into two types: the Z = 2 (two molecules in one unit cell) or high temperature (HT) phase and the Z = 4 or low temperature (LT) phase. Through first-principles calculations within the Marcus electron transfer theory coupled with random walk simulation for room temperature charge diffusion constants, we found that the hole mobility of the HT phase is about 3–4 times larger than that of the LT phase because the molecular packing in the HT phase favors the hole transfer (i.e., the frontier orbital wave function phases of the dimer are constructive, which tends to maximize the overlap), while for the LT phase, the molecules are packed in a position that reduces the intermolecular orbital overlap due to phase cancellation. As the molecular size increases from 2T to 8T, the hole mobility tends to increase because the reorganiza...

Journal ArticleDOI
TL;DR: In this article, a numerical simulation of the boiling flow of R141B in a horizontal coiled tube was performed using the VOF multiphase flow model, and the corresponding experiments were conducted to investigate the boiling flows.

Journal ArticleDOI
TL;DR: It is shown that superconducting Cs(3)C(60) can be reproducibly isolated by solvent-controlled synthesis and has the highest Tc of any molecular material at 38 K, and the observed Tc maximum is attributed to the role of strong electronic correlations near the metal-insulator transition onset.
Abstract: C60-based solids are the archetypal molecular superconductors, reaching transition temperatures as high as 33 K. Now, Cs3C60 solids, having a transition temperature of 38 K, have been isolated. Both face-centred-cubic and body-centred-cubic phases were synthesized, and, uniquely among C60 solids, the superconducting phase was found to be body-centred cubic.

Journal ArticleDOI
TL;DR: The great enhancement of red upconversion emission in NaYF4:Yb3+, Er3+ nanocrystals at low doping level is described, which is ascribed to the effectiveness of the multiphonon relaxation process due to the existence of citrate as a chelator and cross relaxation between Er3+, as well as long hydrothermal time.
Abstract: Strong red upconversion luminescence of rare-earth ions doped in nanocrystals is desirable for the biological/biomedical applications. In this paper, we describe the great enhancement of red upconversion emission (4F9/2 → 4I15/2 transition of Er3+ ion) in NaYF4:Yb3+, Er3+ nanocrystals at low doping level, which is ascribed to the effectiveness of the multiphonon relaxation process due to the existence of citrate as a chelator and cross relaxation between Er3+ ions. The dissolution−recrystallization transformation, governing both the intrinsic crystalline phase (cubic and/or hexagonal phase) and the growth regime (thermodynamic vs kinetic), is responsible for the phase control of the NaYF4 crystals. The possible formation mechanism of the NaYF4 crystals and the role of trisodium citrate which acts as a chelating agent and shape modifier are discussed in detail. It is also found that the α → β phase transition is favored by the high molar ratio of fluoride to lanthanide and high hydrothermal temperature as ...

Journal ArticleDOI
TL;DR: Based on density functional methods, relative stabilities between monoclinic, tetragonal, and cubic phases with cation dopants or oxygen vacancies are investigated in this article, where it is found that dopants such as Si, Ge, Sn, P, Al or Ti with ionic radii smaller than Hf stabilize the tetragonal phase but destabilize the cubic phase.
Abstract: Based on density functional methods, relative stabilities between monoclinic, tetragonal, and cubic phases of ${\text{HfO}}_{2}$ with cation dopants or oxygen vacancies are investigated. It is found that dopants such as Si, Ge, Sn, P, Al or Ti with ionic radii smaller than Hf stabilize the tetragonal phase but destabilize the cubic phase. In contrast, larger dopants such as Y, Gd or Sc favor the cubic phase. The ionized oxygen vacancies compensating trivalent dopants greatly stabilize both cubic and tetragonal phases. Microscopic explanations on the results are also given. The metastable phase favored by each dopant is in good agreement with experimental data. Our results can serve as a useful guide in selecting dopants to stabilize a specific phase.

Journal ArticleDOI
TL;DR: In this article, phase equilibria between the y and y' phases at 900°C in the Co-Ni-Al-W system were determined by electron probe microanalysis (EPMA) and X-ray diffractometry (XRD).
Abstract: Phase equilibria between the y and y' phases at 900°C in the Co-(10-70)Ni-Al-W system were determined by electron probe microanalysis (EPMA) and X-ray diffractometry (XRD). It was found that the "/ phase with L1 2 structure continuously exists from the Co side to the Ni side in Co-Ni-Al-W system and that it widens to the low W region with increasing Ni content. The partition of Al into the y' phase increased with Ni content, while the W changed from a y' former to a y former by increase of Ni content. Differential scanning calorimetry (DSC) measurements also revealed that the y' solvus temperature increases with Ni content, while the solidus temperature is hardly affected by such content. The lattice parameter of the y and y' phases and the mismatch decreased with increasing Ni content, which caused the morphologic change of the γ' precipitates from cubes to spheres.

Journal ArticleDOI
TL;DR: In this paper, the flux pinning properties of BaZrO3-doped YBa2Cu3O7−x and BaSnO3doped yBa2C3O 7−x films were studied.
Abstract: We studied the flux pinning properties of BaZrO3-doped YBa2Cu3O7−x and BaSnO3-doped YBa2Cu3O7−x films. We found that BaSnO3-doped films showed very high global pinning forces, Fp, of 28.3 GN m−3 (77 K, ) and 103 GN m−3 (65 K, ), twice that of BaZrO3-doped films. Transmission electron microscopy analysis showed that, in both films, nanorods of the dopant phase were incorporated. The BaSnO3 nanorods were nearly straight but the BaZrO3 nanorods became curved with the increasing film thickness.

Journal ArticleDOI
23 Sep 2008-Polymer
TL;DR: In this paper, the effect of inorganic silica nanoparticles on the morphology and viscoelastic properties of polypropylene/poly(ethylene- co-vinyl acetate) (PP/EVA) immiscible blends has been investigated.

Journal ArticleDOI
TL;DR: In this article, a coarse-grained (CG) molecular model for nonionic surfactants is presented, which is designed to reproduce several key properties including surface/interfacial tension, bulk density, compressibility, hydration/transfer free energy as well as distribution functions obtained by all-atom molecular dynamics simulations.
Abstract: A coarse-grained (CG) molecular model for nonionic surfactants is presented. The transferability and versatility are demonstrated by applying the model to the bulk aqueous solution as well as to the air–water and oil–water interfacial systems. The model is designed to reproduce several key properties including surface/interfacial tension, bulk density, compressibility, hydration/transfer free energy as well as distribution functions obtained by all-atom molecular dynamics simulations. The CG surfactants are demonstrated to spontaneously organize into micelles, and either hexagonal or lamellar bulk structures, respectively, at the corresponding concentration and thermodynamic conditions for those phases. Moreover, even a hexagonal-to-lamellar phase transformation is attainable using the present CG model. The experimental surface pressure–area (π–A) curve for a representative surfactant monolayer at the air–water interface is well reproduced. Micelle budding is observed from an overly compressed monolayer; a phenomenon that is likely to be a reasonable finding because the hydration/transfer free energy is a fitted parameter in the model. The correct molecular partitioning together with a relatively rapid relaxation of the CG model system towards equilibrium enables the computation of self-assembled surfactant behavior at the mesoscale regime.

Journal ArticleDOI
TL;DR: Investigating protein salting-out in ammonium sulfate and sodium chloride for six proteins reveals that the formation of aggregates can be interpreted, in light of theoretical results from mode-coupling theory, as a kinetically trapped state or a gel phase that occurs through the intermediate of a gas-liquid phase separation.

Journal ArticleDOI
TL;DR: In this article, the electromechanical behavior of (1−x)Bi0.5Na 0.5TiO3-xK0.4NbO3 (BNT-KNN) lead free piezoelectric ceramics is investigated for 0⩽x⩾0.12 to gain insight into the antiferroelectric-ferroelectric (AFE-FE) phase transition on the basis of the giant strain recently observed in BNT-based systems.
Abstract: The electromechanical behavior of (1−x)Bi0.5Na0.5TiO3–xK0.5Na0.5NbO3 (BNT-KNN) lead free piezoelectric ceramics is investigated for 0⩽x⩽0.12 to gain insight into the antiferroelectric-ferroelectric (AFE-FE) phase transition on the basis of the giant strain recently observed in BNT-based systems. At x≈0.07, a morphotropic phase boundary (MPB) between a rhombohedral FE phase and a tetragonal AFE phase is found. While the piezoelectric coefficient is largest at this MPB, the total strain further increases with increasing KNN content, indicating the field-induced AFE-FE transition as the main reason for the large strain.