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Water adsorption energy, Eads, is a key physical quantity in sustainable chemical technologies such as (photo)electrocatalytic water splitting, water desalination, and water harvesting. In many of these applications, the electrode surface is operated outside the point (potential) of zero charge, which attracts counter-ions to form the electric double layer and controls the surface properties. Here, by applying density functional theory-based finite-field molecular dynamics simulations, we have studied the effect of water adsorption energy Eads on surface acidity and the Helmholtz capacitance of BiVO4 as an example of metal oxide electrodes with weakly chemisorbed water. This allows us to establish the effect of Eads on the coordination number, the H-bond network, and the orientation of chemisorbed water by comparing an oxide series composed of BiVO4, TiO2, and SnO2. In particular, it is found that a positive correlation exists between the degree of asymmetry ΔCH in the Helmholtz capacitance and the strength of Eads. This correlation is verified and extended further to graphene-like systems with physisorbed water, where the electric double layers (EDLs) are controlled by electronic charge rather than proton charge as in the oxide series. Therefore, this work reveals a general relationship between water adsorption energy Eads and EDLs, which is relevant to both electrochemical reactivity and the electrowetting of aqueous interfaces. [ABSTRACT FROM AUTHOR]

Polymer flooding technology has become the most widely utilized chemical flooding technology in the world. The polymer structure gradually grows from linear to branched and hyperbranched as reservoir variability increases and polymer flooding technology advances. In this study, the nano-SiO2 was first controllably modified, and subsequently, a series of nano-SiO2 grafted modified polymers (MNSP) were synthesized using homogeneous aqueous solution polymerization with modified nano-SiO2 and another functional monomer. The rheological properties of MNSP were analyzed by using the MCR 301 rheometer; then, the mechanism of the influence of the concentration and the modification degree of nano-SiO2 on the rheological properties of MNSP was explored from the microscopic standpoint. The results demonstrate that at a salinity of 3 × 104 mg/L and temperature of 85 °C, the viscosity of the MNSP polymer is superior to that of the standard amphiphilic polymer APC16 whose synthesized monomers do not include nano-SiO2. When the concentration and the modification degree of nano-SiO2 were increased, the solution viscosity first increased and then decreased, and this is mostly due to the addition of inorganic nanoparticles, which stimulates the creation of a three-dimensional network structure and improves the solution characteristics of MNSP. However, too much modified SiO2 addition will interfere with polymerization between various monomers. The modification degree of the nano-SiO2 mostly influences the density of the polymer-formed network structure, the active sites on the modified nano-SiO2 surface rise as the degree of modification increases, as does spatial site resistance, resulting in inferior polymer characteristics. The findings of the experiments reveal fresh ideas for inorganic particles compounding organic polymers and expand the use area of polymers in the oilfield. [ABSTRACT FROM AUTHOR]

Permeability is a key property in various fields such as membrane technology for chemical separation and transport of substances through cell membranes. At the molecular scale, the counting method uses the number of membrane crossings in a conventional unbiased molecular dynamics simulation to predict the permeability. This contribution investigates under which conditions the counting method has insufficient statistics. An equation is derived for a compartmental model based on the inhomogeneous solubility–diffusion (Smoluchowski) model, giving insight into how the flux correlates with the solubility of permeants. This equation shows that a membrane crossing is a rare event not only when the membrane forms a large free energy barrier but also when the membrane forms a deep free energy well that traps permeants. Such a permeant trap has a high permeability; yet, the counting method suffers from poor statistics. To illustrate this, coarse-grained MD was run for 16 systems of dipalmitoylphosphatidylcholine bilayer membranes with different permeant types. The composition rule for permeability is shown to also hold for fluxes, and it is highlighted that the considered thickness of the membrane causes uncertainty in the permeability calculation of highly permeable membranes. In conclusion, a high permeability in itself is not an effective indicator of the sampling efficiency of the counting method, and caution should be taken for permeants whose solubility varies greatly over the simulation box. A practical consequence relevant in, e.g., drug design is that a drug with high membrane permeability might get trapped by membranes thus reducing its efficacy. [ABSTRACT FROM AUTHOR]

In recent decades, the hot-spot theory of condensed-phase explosives has been a compelling focus of scientific investigation attracting many researchers. The defect in the polymeric binder of the polymer-bonded explosive is called the intergranular defect. In this study, the real polymeric binder was substituted by poly(methyl methacrylate) (PMMA) as it is transparent and has similar thermodynamic properties to some binders. A set of modified split Hopkinson pressure bars equipped with a time-resolved shadowgraph was used to study the process of crack initiation and potential hot-spot formation around a cylindrical defect in PMMA. The new and significant phenomenon that the opening-mode crack emerged earlier than the shearing-mode crack from the cylindrical defect has been published for the first time in this paper. Furthermore, a two-dimensional numerical simulation was performed to show the evolution of both the stress field and the temperature field. The simulation results were in good agreement with the experiment. Finally, the law of potential hot-spot formation is discussed in detail. [ABSTRACT FROM AUTHOR]

We provide an overview of 70 years of evaluated chemical kinetic data published in the Journal of Physical and Chemical Reference Data (dating to 1972), the National Standard Reference Data System series (dating to 1965), as part of the National Bureau of Standards Chemical Kinetics Data Center (dating to 1951), and the National Institute of Standards and Technology Chemical Kinetics Database (SRD 17) (dating to 1990). [ABSTRACT FROM AUTHOR]

Ti alloys have many excellent properties, including low elastic modulus, desired corrosion resistance, nontoxicity, and biocompatibility. Hence, they promise to be major hard-tissue implant biomaterials (HTIBs). However, some properties, like surface hardness, wearability, and cellular activity, need to be enhanced. Moreover, their corrosion resistance in simulated body fluids and biocompatibility also need to be investigated systematically before practical applications. As HTIBs, the primary properties in clinical applications are wearability, corrosion resistance, and biocompatibility. Surface modification is a commonly used effective way to improve the above-mentioned disadvantages. This work is a brief review of the main surface modification technologies of Ti alloys for HTIBs (hereafter referred to as Ti alloys). The main surface modification technologies of Ti alloys are divided into four types, namely, physical technologies, chemical technologies, electrochemical technologies, and surface plastic deformation technologies. The principle and applications of these four types of surface modification technologies on Ti alloys are introduced one by one. Finally, the future directions for the surface modification of Ti alloys are proposed. [ABSTRACT FROM AUTHOR]

It is well known that confining a liquid into a pore strongly alters the liquid behavior. Investigations of the effect of confinement are of great importance for many scientific and technological applications. Here we present a molecular dynamics study of the behavior of cyclohexane confined in carbon slit pores. The local structure and orientational ordering of cyclohexane molecules are investigated. It is shown that the system freezes with decreasing the pore width, and the freezing temperature of nanoconfined cyclohexane is higher than the bulk one. [ABSTRACT FROM AUTHOR]

The alarming rise of indoor pollution and the need to combat the associated negative effects have promoted increasing attention in modernizing the chemical sensing technologies by newly designed materials with rich and tunable functionalities at atomic or molecular levels. With the appealing physical, chemical, optical, and electronic properties for various potential applications, the state-of-art gas-sensing nanomaterials and their future perspectives are well-documented and summarized in this paper. Specifically, the key performance attributes are addressed in detail such as the sensitivity, selectivity, reversibility, operating temperature, response time, and detection limit. As such, this review provides both critical insights in exploring and understanding various gas sensing nanomaterials and points out limitations and opportunities for further developments, such as morphology control, doping and surface alteration, atomic-scale characterization, and applications in different fields. Finally, the challenges and outlooks are discussed on the basis of the current developments. [ABSTRACT FROM AUTHOR]

The speed of sound in high-purity water has been measured in the temperature range (253 to 473) K at pressures up to 400 MPa. The experimental technique used was based on a double-path pulse-echo method with a single 5-MHz ultrasound transducer placed between two unequally spaced reflectors. The cell was calibrated in water at T = 298.15 K and p = 1 MPa against the speed of sound given by the 1995 equation-of-state formulation of the International Association for the Properties of Water and Steam (IAPWS-95) which, for that state point, has an uncertainty of 0.005%. Corrections for the effects of temperature and pressure on the path length difference are considered in detail. The estimated expanded relative uncertainty of the speed of sound determined in this work is shown to be between 0.03% and 0.04% at a confidence level of 95%. The density and isobaric specific heat capacity of water have been obtained in the temperature range (253.15 to 473.15) K at pressure up to 400 MPa by thermodynamic integration of the sound-speed data subject to initial values computed from IAPWS-95 on the isobar at p = 0.1 MPa. The speed of sound, density, and isobaric specific heat capacity were compared with IAPWS-95 with corresponding absolute relative deviations within 0.3%, 0.03%, and 1%, respectively at T ≥ 273.15 K and p ≤ 400 MPa; larger deviations, especially for heat capacity, were found at lower temperatures. The results imply that the uncertainties of properties computed from IAPWS-95 may be significantly reduced over the major part of the region investigated in this work. [ABSTRACT FROM AUTHOR]

The high pressure phase stability of intermetallic PtIn2 at ambient temperature has been investigated using the synchrotron based angle dispersive x-ray diffraction technique, electrical resistance measurements, and first principles electronic structure calculations. The electrical resistance falls continuously up to 5 GPa and then remains almost constant up to 10 GPa. Beyond 10 GPa, the resistance increases and continues to increase up to 21 GPa which is the highest pressure of the present measurements. Consistent with this, the x-ray diffraction measurements show a structural phase transition from the ambient cubic phase to a low symmetry orthorhombic phase beyond 10 GPa. Upon pressure release, the ambient cubic phase is obtained. Ab initio structural relaxations and total energy calculations predict the cubic to orthorhombic phase transitions at 10.5 GPa. [ABSTRACT FROM AUTHOR]

The electric field dependence of the dielectric constant (dc-tunability) as a function of temperature for a few compositions of Ba(Sn,Ti)O3 ceramics was investigated. Dense and homogeneous BaSnxTi1-xO3 ceramics (ferroelectric for x = 0.05 and x = 0.10, relaxor for x = 0.15 and 0.20) with high dielectric constant and low dielectric losses were prepared by solid state reaction. Their dc-tunability characteristics were investigated at a few temperatures from 20-120 °C, including the Curie range. The tunability data were discussed in terms of the Johnson model completed with a Langevin term that describes the 'extrinsic' contribution to the nonlinear &eh;(E) dependences. [ABSTRACT FROM AUTHOR]

Although the origins of the high effective permittivity observed in CaCu3Ti4O12 (CCTO) ceramics and single crystals at ∼100-400 K have been resolved, the relaxorlike temperature- and frequency-dependence of permittivity obtained from fixed frequency capacitance measurements at higher temperatures reported in the literature remains unexplained, especially as CCTO adopts a centrosymmetric cubic crystal structure in the range of ∼35-1273 K. Impedance spectroscopy studies reveal that this type of relaxorlike behavior is an artifact induced mainly by a nonohmic sample-electrode contact impedance. In addition, an instrument-related parasitic series inductance and resistance effect modifies the measured capacitance values as the sample resistance decreases with increasing temperature. This can lead to an underestimation of the sample capacitance and, in extreme cases, to so-called 'negative capacitance.' Such a relaxorlike artifact and negative capacitance behavior are not unique to CCTO and may be expected in other leaky dielectrics whose resistance is low. [ABSTRACT FROM AUTHOR]

The shock initiation process was directly observed in different powder mixtures that produce little or no gas upon reaction. The samples of reactive powder were contained in recovery capsules that permitted the samples to be analyzed after being shocked and that allowed the initiation of reaction to be monitored using three different methods. The microsecond time-scale processes were observed via a fast two-color pyrometer. Light intensity detected from the bottom of reactive samples was slightly greater compared to inert simulants in the first 10 μs after shock arrival. However, this light was much less intense than that which would correspond to the bulk of the material reacting. Thus it seemed that only small, localized zones, or hot spots, had begun to react on a time scale of less than 30 μs. Light emissions were then recorded over longer time scales, and intense light appeared at the bottom of samples a few milliseconds to a few hundreds of milliseconds after shock arrival at the bottom of the test samples. Thus it appeared that the bulk of the material reacted as the hot spots spread via convective/diffusive means. This bulk reaction was also observed using thermocouples for a large number of mixtures and incident shock pressures. The delay time for the onset of bulk reaction was found to be not strongly dependent upon shock pressure but seemed to correlate with the burning speed of the mixtures. The shock initiation process appeared to take place via the initiation and growth of hot spots, as in high explosives, except that burning speeds are much slower in reactive powders that produce little gas. [ABSTRACT FROM AUTHOR]

The structure, electrical properties, and depoling mechanism of the (0.95-x)BiScO3-xPbTiO3-0.05Pb(Zn1/3Nb2/3)O3 (BS-xPT-PZN, x=0.54-0.70) compositions close to the morphotropic phase boundary (MPB) have been systematically investigated as a function of PbTiO3 content (x). The phase approached from the rhombohedral toward the tetragonal phase when the PbTiO3 contents increased. The composition with high PT content exhibited normal ferroelectric behavior while it showed a diffused phase transition characteristic as PT decreased. In the vicinity of the MPB, the ceramics showed enhanced piezoelectric, electromechanical, and ferroelectric properties with piezoelectric constant d33=490 pC/N, planar electromechanical coupling factors kp=57.4%, remnant polarization Pr=40.1 μC/cm2, and coercive field Ec=28.5 kV/cm with a high transition temperature Tm∼417 °C, respectively. The thermal depoling experiments of the polarization for samples with different phase structures were investigated and the possible depoling mechanism was discussed. [ABSTRACT FROM AUTHOR]

The role of oxygen atoms in the growth of magnetron sputter-deposited ZnO films was studied by alternating the deposition of a several-nanometer-thick ZnO layer and the O2/Ar mixture plasma exposure, i.e., layer-by-layer technique. The film crystallization promoted with suppressing the oxygen vacancy and interstitial defects by adjusting the exposure condition of O2/Ar plasma. These findings suggest that the chemical potential of oxygen atom determine the film crystallization as well as the electronic state. The diffusion and effusion of oxygen atoms at the growing surface play a role of thermal annealing, promoted the film crystallization as well as the creation and the annihilation of oxygen and zinc related defects. The role of oxygen atoms reaching at the film-growing surface is discussed in term of chemical annealing. The possible oxygen diffusion mechanism is proposed. [ABSTRACT FROM AUTHOR]

In large explosive and propellant charges, relatively low shock pressures on the order of 1-2 GPa impacting large volumes and lasting tens of microseconds can cause shock initiation of detonation. The pressure buildup process requires several centimeters of shock propagation before shock to detonation transition occurs. In this paper, experimentally measured run distances to detonation for lower input shock pressures are shown to be much longer than predicted by extrapolation of high shock pressure data. Run distance to detonation and embedded manganin gauge pressure histories are measured using large diameter charges of six octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) based plastic bonded explosives (PBX's): PBX 9404; LX-04; LX-07; LX-10; PBX 9501; and EDC37. The embedded gauge records show that the lower shock pressures create fewer and less energetic "hot spot" reaction sites, which consume the surrounding explosive particles at reduced reaction rates and cause longer distances to detonation. The experimental data is analyzed using the ignition and growth reactive flow model of shock initiation in solid explosives. Using minimum values of the degrees of compression required to ignite hot spot reactions, the previously determined high shock pressure ignition and growth model parameters for the six explosives accurately simulate the much longer run distances to detonation and much slower growths of pressure behind the shock fronts measured during the shock initiation of HMX PBX's at several low shock pressures. [ABSTRACT FROM AUTHOR]

In this paper, the effect of the sintering temperature on the low-field dielectric behavior of nonstoichiometric Pb0.95La0.05(Fe2/3W1/3)0.65Ti0.35O3 relaxor ferroelectrics is investigated. The x-ray patterns and the scanning electron microscope images are used to detect the pyrochlore phase and the perovskite structure. The electric properties of the resistivity, the space charge polarization, the temperature-dependent dielectric constant and dielectric loss are discussed. The diffused phase transition and the ordering state are fitted and discussed by using the empirical law and two ordering models. Furthermore, the glassy behavior is determined by using the Curie-Weiss law and the spin-glass model. According to the experimental data and fitting results, the dielectric picture is changed from the short range order relaxorlike behavior to the long range order normal ferroelectric state as increasing the sintering temperature and the glassy behavior is weakened at the lowest and highest sintering temperature at which the pyrochlore phase PWO4 is induced. Therefore, it is suggested that the 1:1 ordered domain is enhanced by increasing the sintering temperature and the glassy behavior is related to not only the ordering degree also the polar defect pairs. For more ordering degree and polar defect pairs, the glassy is weakened and the correlation of neighboring polar microregions is enhanced. [ABSTRACT FROM AUTHOR]

Nominal composition of Ba0.93Bi0.07Ti1-xMnxO3 (x=0, 0.02, and 0.04) ceramics have been prepared by a modified Pechini method. X-ray diffraction analysis reveals that the samples are pure perovskite BaTiO3 (BTO) structure with no trace of impurity phase. The cell volume of the composites increases monotonously with the increase in Mn content, which indicates that Mn ions have been incorporated into the lattice of Ba0.93Bi0.07TiO3. The samples are experimentally confirmed to show ferromagnetic (FM) and ferroelectric behaviors simultaneously at room temperature. The temperature dependent magnetic behaviors show complex magnetic interactions including FM, antiferromagnetic, and paramagnetic. These results suggest that the dopant Bi and Mn help BTO transit from pure ferroelectric to multiferroic materials and the magnetic behaviors can be explained by the bound magnetic polaron model with inhomogeneity of Mn dopant distribution. [ABSTRACT FROM AUTHOR]

In this work we present a unique transmission electron microscopy study of the thermal stability of gas phase synthesized Mg nanoparticles, which have attracted strong interest as high capacity hydrogen storage materials. Indeed, Mg nanoparticles with a MgO shell (∼3 nm thick) annealed at 300 °C show evaporation, void formation, and void growth in the Mg core both in vacuum and under a high pressure gas environment. This is mainly due to the outward diffusion and evaporation of Mg with the simultaneously inward diffusion of vacancies leading to void growth (Kirkendall effect). The rate of Mg evaporation and void formation depends on the annealing conditions. In vacuum, and at T=300 °C, the complete evaporation of the Mg core takes place (within a few hours) for sizes ∼15–20 nm. Void formation and growth has been observed for particles with sizes ∼20–50 nm, while stable Mg nanoparticles were observed for sizes >50 nm. Furthermore, even at relative low temperature annealing (as low as 60 °C), void formation and growth occurs in 15–20 nm sized Mg nanoparticles, indicating that voiding will be even more dominant for nanoparticles smaller than 10 nm. Our findings confirm that Mg evaporation and void formation in nanoparticles with sizes less than 50 nm present formidable barriers for their applicability in hydrogen storage, but also could inspire future research directions to overcome these obstacles. [ABSTRACT FROM AUTHOR]

The dielectric response of hard (Fe-doped) and soft (Nb-doped) rhombohedral Pb(Zr0.58Ti0.42)1-xMexO3 (Me=Fe or Nb) ceramics was studied at subswitching conditions over a wide range of temperatures (50–450 °C) and frequencies (10 mHz to 10 kHz). The results show qualitative differences in the behavior of the acceptor- and donor-doped samples. Hard materials exhibit a steep increase in the complex permittivity with decreasing frequency. The onset of the dispersion is thermally activated with activation energies of about 0.6–0.8 eV and is attributed here to oxygen vacancy hopping. The activation energy for ac conductivity observed in soft materials is estimated to be about 1.7 eV, corresponding to half of the energy gap of Pb(Zr,Ti)O3 and is thus consistent with electronic conduction. The relevance of ionic hopping conductivity in hard materials to ferroelectric aging/deaging and hardening is analyzed. Strong ionic conductivity in hard samples and its absence in soft samples agree well with the dipolar mechanism of aging in hard materials and the absence of significant aging in soft materials. [ABSTRACT FROM AUTHOR]

We investigated the electrical transport of electroformed titanium dioxide memristive switches from liquid helium to room temperatures in order to better understand their internal states. After electroforming, we observed a continuous transition between two distinct limiting behaviors: a nearly Ohmic “ON”-state and an “OFF”-state characterized by conduction through a barrier. We interpret our data in terms of a model in which the electroforming step creates a conducting channel that does not completely bridge the metal contacts on the titanium dioxide film. The switching then occurs as a result of voltage-induced changes in the oxygen vacancy concentration in the gap between the tip of the channel and the adjacent metal contact. We used the metallic resistivity of the conduction channel as an in situ thermometer to measure the local device temperature, thus revealing an important implicit state variable. [ABSTRACT FROM AUTHOR]

High pressure behavior of ZrGeO4 has been investigated using Raman and photoluminescence (PL) spectroscopies up to 25 GPa in a diamond anvil cell. Under the application of pressure, the GeO4 librational mode exhibits softening, suggesting dynamical instability of the scheelite structure. Qualitative changes are noted in the Raman spectrum above 12 GPa, suggesting a possible transition around this pressure. High pressure PL behavior of Eu3+-related crystal field transitions indicates a clear change in the site symmetry of Eu3+ around 12 GPa, strongly supporting structural transition to a lower symmetry phase at this pressure. [ABSTRACT FROM AUTHOR]

We report an in situ high pressure investigation of the structural change in vitreous As2S3 up to 60 GPa using the diamond anvil cell and energy dispersive x-ray absorption spectroscopy. The main finding of the present study is a gradual elongation of the average As–S bond length, which takes place in the pressure range of 15–50 GPa. This change is interpreted as a signature of the coordination number increase around As atoms. The negative shift of the As K absorption edge position confirms the progressive metallization of the glass at high pressure. The observed changes are reversible after pressure release. [ABSTRACT FROM AUTHOR]

New infrared absorbing species are identified in the pulse radiolysis of supercritical Kr at high pressures. The species are believed to be excimers. Their formation and decay rates have been time resolved using the Laser Electron Accelerator Facility. An initial species, formed in less than 1 ns, absorbs at several wavelengths between 790 and 1300 nm; The decay of this species is initially fast, followed by a slower component; the decay rate increases with pressure. As this initial species decays a second excimer is formed absorbing at 830, 890, and 990 nm. The growth and decay rates of this excimer are also pressure dependent. A third excimer, absorbing between 1000 and 1200 nm grows at a rate similar to that of the decay of the second species. The decay rate of the third species is also pressure dependent; the lifetime increases from 9.4 ns at 109 bar to 49 ns at 15 bar. A kinetic mechanism is proposed that satisfactorily reproduces the experimental results. The first species is identified as a higher energy gerade triplet state excimer and the second as the singlet gerade state. [ABSTRACT FROM AUTHOR]

Pyrochlore Bi2(Zn1/3Ta2/3)2O7 (BZT) films were prepared by pulsed laser deposition on Pt/TiO2/SiO2/Si substrates. In contrast to bulk monoclinic BZT ceramics, the BZT films have a cubic structure mediated by an interfacial layer. The dielectric properties of the cubic BZT films [[variant_greek_epsilon]∼177, temperature coefficient of capacitance (TCC) ∼-170 ppm/°C] are much different from those of monoclinic BZT ceramics ([variant_greek_epsilon]∼61, TCC ∼+60 ppm/°C). Increasing the thickness of the BZT films returns the crystal structure to the monoclinic phase, which allows the dielectric properties of the BZT films to be tuned without changing their chemical composition. [ABSTRACT FROM AUTHOR]

The theory developed in our earlier papers is extended to predict dynamical and thermodynamic properties of clathrate structures by accounting for the possibility of multiple filling of cavities by guest molecules. The method is applied to the thermodynamic properties of argon and krypton hydrates, considering both structures I (sI) and II (sII), in which the small cages can be singly occupied and large cages of sII can be singly or doubly occupied. It was confirmed that the structure of the clathrate hydrate is determined by two main factors: intermolecular interaction between guest and host molecules and the configurational entropy. It is shown that for guests weakly interacting with water molecules, such as argon or krypton, the free energy of host lattices without the contribution of entropy is the main structure-determining factor for clathrate hydrates, and it is a cause of hydrate sII formation at low pressure with these guests. Explicit account of the entropy contribution in the Gibbs free energy allows one to determine the stability of hydrate phases and to estimate the line of structural transition from sII to sI in P-T plane. The structural transition between sII and sI in argon and krypton hydrates at high pressure is shown to be the consequence of increasing intermolecular interaction and the degree of occupancy of the large cavities. [ABSTRACT FROM AUTHOR]

We study a simple two patch model of globular protein solutions. The model consists of a hard sphere interaction, together with a weak isotropic attraction, decorated with stronger attractive patch-patch interactions. The isotropic and anisotropic attractions are modeled with square well potentials with an interaction range of 1.2σ, where σ is the hard sphere diameter. We have calculated its phase diagram and found a metastable fluid-fluid phase separation curve. We have also obtained the different stable crystal structures at various temperatures. The orientationally ordered, body-centered crystal (bcc-o) lattice is the crystal structure that has the lowest energy; it is stable at lower temperatures and moderate pressures. The orientationally ordered face-centered crystal (fcc) lattice has a higher energy and becomes stable with respect to bcc-o at high pressures and lower temperatures. Finally, at high temperatures when the entropy effect becomes important, the orientational order is lost and an orientationally disordered fcc lattice becomes stable. [ABSTRACT FROM AUTHOR]

In an unprecedented experimental investigation, a ternary and a four component hydrocarbon mixture at high pressure have been studied in a nearly convection free environment to understand the thermodiffusion process. A binary mixture has also been investigated in this environment. Experimental investigations of the three mixtures have been conducted in space onboard the spacecraft FOTON-M3 thereby isolating the gravity-induced convection that otherwise interferes with thermodiffusion experiments on Earth. The experimental results have also been used to test a thermodiffusion model that has been calibrated based on the results of previous experimental investigations. It was found that with an increase in the number of components in the mixtures, the performance of the thermodiffusion model deteriorated. Computational analysis was also made to estimate the possible sources of errors. Simulations showed that the vibrations of the spacecraft could influence the estimates of thermodiffusion factors. It was also found that they are sensitive to slight variations in the temperature of the mixture. [ABSTRACT FROM AUTHOR]

The phase stability of YbVO4 under pressure has been investigated using synchrotron based angle dispersive x-ray diffraction and Raman spectroscopic techniques up to 34.5 and 26.5 GPa, respectively. The results indicate that the compound transforms from the ambient pressure zircon structure to the scheelite structure above 5.9 GPa with 11.8% volume discontinuity. The coexistence of the two phases is observed over a large pressure range. At 15.8 GPa, the (011) peak of the scheelite phase develops asymmetry, and the pattern at further high pressures could be fitted to a fergusonite-type monoclinic structure. On reducing the pressure, the fergusonite phase reverses back to the scheelite phase; the latter phase could be recovered as a metastable phase at ambient pressure. The refined structural parameters along with the equation of state are given for various phases of YbVO4. Changes in the vibrational properties across these transitions, particularly across the scheelite↔fergusonite transition, have been investigated using Raman spectroscopy. [ABSTRACT FROM AUTHOR]

The effects of high pressure (up to 9 GPa) on the thermal decomposition of ammonia borane, BH3NH3, were studied in situ by Raman spectroscopy in a diamond anvil cell. In contrast with the three-step decomposition at ambient pressure, thermolysis under pressure releases almost the entire hydrogen content of the molecule in two distinct steps. The residual of the first decomposition is polymeric aminoborane, (BH2NH2)x, which is also observed at ambient pressure. The residual after the second decomposition is unique to high pressure. Presumably it corresponds to a precursor to hexagonal BN where macromolecular fragments of planar hexagon layers formed by B and N atoms are terminated by H atoms. Increasing pressure increases the temperature of both decomposition steps. Due to the increased first decomposition temperature it becomes possible to observe a new high pressure, high temperature phase of BH3NH3 which may represent melting. [ABSTRACT FROM AUTHOR]

The effect of direct-current (dc) biasing on the dielectric properties of porous Ba0.6Sr0.4TiO3 with various porosities, pore sizes, and different pore shapes has been studied in the paraelectric state. The existing model did not consider the effect of the change in grain size and pore shape, lead to the theory fitting the fine grained or nonspherical pore ceramics less well. The bias equation used in this literature to predict the electric field dependence of permittivity is modified by introducing a coefficient α. α is the microstructure parameter introduced to depict the influence of grain size and pore shape effect. Taking high porosity samples and nonspherical pore ceramic samples, for example, the modified bias equation gives a better fit to the experimental result in this study. [ABSTRACT FROM AUTHOR]

We report the appearance of two plastic crystal phases of water at high pressure and temperature using computer simulations. In one of them the oxygen atoms form a body centered cubic structure (bcc) and in the other they form a face centered cubic structure (fcc). In both cases the water molecules were able to rotate almost freely. We have found that the bcc plastic crystal transformed into a fcc plastic crystal via a Martensitic phase transition when heated at constant pressure. We have performed the characterization and localization in the phase diagram of these plastic crystal phases for the SPC/E, TIP4P, and TIP4P/2005 water potential models. For TIP4P/2005 model free energy calculations were carried out for the bcc plastic crystal and fcc plastic crystal using a new method (which is a slight variation of the Einstein crystal method) proposed for these types of solid. The initial coexistence points for the SPC/E and TIP4P models were obtained using Hamiltonian Gibbs–Duhem integration. For all of these models these two plastic crystal phases appear in the high pressure and temperature region of the phase diagram. It would be of interest to study if such plastic crystal phases do indeed exist for real water. This would shed some light on the question of whether these models can describe satisfactorily the high pressure part of the phase diagram of water, and if not, where and why they fail. [ABSTRACT FROM AUTHOR]

Lanthanum-doped lead zirconate titanate, PLZT-x/65/35 (x=8.0, 9.0, and 9.4), relaxor ferroelectric ceramics were investigated by the high resolution Brillouin light scattering spectroscopy in the temperature range from ∼870 down to ∼170 K. Broad anomalies were observed in the acoustic phonon mode velocity and related elastic stiffness coefficient showing minimum between ∼320–∼240 K. The deviation in the acoustic mode velocity from the high temperature linearity at the Burns temperature (TB∼720 K) and presence of a broad central peak in the temperature range 200≤T≤540 K were attributed to the dynamics of polar nanoregions with randomly oriented local polarization appearing due to site and/or charge disorder at both A- and B-sites of the ABO3 perovskite lattice. The presence of a new temperature point Td (∼575 K) was conclusively established in PLZT-x/65/35 relaxor ceramics. [ABSTRACT FROM AUTHOR]

The experimental characteristics of polarization fatigue in thin-film, bulk ceramic, and single-crystalline ferroelectrics have been reviewed in detail. Various scenarios and models proposed for fatigue in ferroelectric materials during the past few decades have been discussed, together with our own model developed very recently [Phys. Rev. Lett. 97, 177601 (2006); Phys. Rev. B 75, 244104 (2007)]. Interpretations for the experimental data reviewed in this paper but untreated in our previous work [Phys. Rev. B 75, 244104 (2007)] as well as the methods of improving the fatigue endurance in ferroelectrics are given based on this model. Finally, the results on polarization fatigue in some special classes of ferroelectrics such as multiferroics (e.g., BiFeO3-based materials), ferroelectric polymers, and antiferroelectric thin films and ceramics are discussed and accounted for in light of our model. [ABSTRACT FROM AUTHOR]

We have performed numerical simulations to determine the modulation transfer function for glass ceramic x-ray imaging plates where the image readout is by a scanned laser beam. We focus, in particular, on the role of the effective scattering length in determining the width of the modulation transfer function, covering a range of scattering lengths describing very opaque to very transparent glass ceramics. We find that the shape of the modulation transfer function is, in general, bimodal, with a broad contribution from the laser beam width, and superimposed a narrow one from scattering. The overall width of the modulation transfer function reaches a minimum when the scattering length is comparable with the beam width, and so scattering lengths either much greater or less than the beam width, corresponding to either strongly scattering or highly transparent glass ceramics, give the best expected spatial resolution. However, for a practical range of scattering parameters, transparent glass ceramics are predicted to have a superior resolution compared to very opaque ones. Simulations are included which also demonstrate the effect of particle size, optical absorption, and readout laser power. Stronger optical absorption at the wavelength of the stimulating beam in comparison with that at the wavelength of the emitted light has a markedly beneficial effect on the spatial resolution at the expense of sensitivity. Simulation results are confronted with experimental results for a commercial BaFBr:Eu2+ powder-based imaging plate and a europium-doped fluorozirconate glass ceramic, and good agreement is obtained. [ABSTRACT FROM AUTHOR]