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Sample records for phase diagram calculation

  1. Calculation of Gallium-metal-Arsenic phase diagrams

    NASA Technical Reports Server (NTRS)

    Scofield, J. D.; Davison, J. E.; Ray, A. E.; Smith, S. R.

    1991-01-01

    Electrical contacts and metallization to GaAs solar cells must survive at high temperatures for several minutes under specific mission scenarios. The determination of which metallizations or alloy systems that are able to withstand extreme thermal excursions with minimum degradation to solar cell performance can be predicted by properly calculated temperature constitution phase diagrams. A method for calculating a ternary diagram and its three constituent binary phase diagrams is briefly outlined and ternary phase diagrams for three Ga-As-X alloy systems are presented. Free energy functions of the liquid and solid phase are approximated by the regular solution theory. Phase diagrams calculated using this method are presented for the Ga-As-Ge and Ga-As-Ag systems.

  2. Phase diagram calculation of AIIIBV binary solutions of the eutectic type in the generalized lattice model

    NASA Astrophysics Data System (ADS)

    Panov, G. A.; Zakharov, M. A.

    2015-11-01

    The present work is devoted to the phase diagrams calculation of AIIIBV systems within the framework of the generalized lattice model taking account of volume effects. The theoretically calculated phase diagram is compared with the corresponding experimental diagrams.

  3. Electrochemical phase diagrams for Ti oxides from density functional calculations

    NASA Astrophysics Data System (ADS)

    Huang, Liang-Feng; Rondinelli, James M.

    2015-12-01

    Developing an accurate simulation method for the electrochemical stability of solids, as well as understanding the physics related with its accuracy, is critically important for improving the performance of compounds and predicting the stability of new materials in aqueous environments. Herein we propose a workflow for the accurate calculation of first-principles electrochemical phase (Pourbaix) diagrams. With this scheme, we study the electrochemical stabilities of Ti and Ti oxides using density-functional theory. First, we find the accuracy of an exchange-correlation functional in predicting formation energies and electrochemical stabilities is closely related with the electronic exchange interaction therein. Second, the metaGGA and hybrid functionals with a more precise description of the electronic exchange interaction lead to a systematic improvement in the accuracy of the Pourbaix diagrams. Furthermore, we show that accurate Ti Pourbaix diagrams also require that thermal effects are included through vibrational contributions to the free energy. We then use these diagrams to explain various experimental electrochemical phenomena for the Ti-O system, and show that if experimental formation energies for Ti oxides, which contain contributions from defects owing to their generation at high (combustion) temperatures, are directly used to predict room temperature Pourbaix diagrams then significant inaccuracies result. In contrast, the formation energies from accurate first-principles calculations, e.g., using metaGGA and hybrid functionals, are found to be more reliable. Finally, to facilitate the future application of our accurate electrochemical phase equilibria diagrams, the variation of the Ti Pourbaix diagrams with aqueous ion concentration is also provided.

  4. Highly Accurate Calculations of the Phase Diagram of Cold Lithium

    NASA Astrophysics Data System (ADS)

    Shulenburger, Luke; Baczewski, Andrew

    The phase diagram of lithium is particularly complicated, exhibiting many different solid phases under the modest application of pressure. Experimental efforts to identify these phases using diamond anvil cells have been complemented by ab initio theory, primarily using density functional theory (DFT). Due to the multiplicity of crystal structures whose enthalpy is nearly degenerate and the uncertainty introduced by density functional approximations, we apply the highly accurate many-body diffusion Monte Carlo (DMC) method to the study of the solid phases at low temperature. These calculations span many different phases, including several with low symmetry, demonstrating the viability of DMC as a method for calculating phase diagrams for complex solids. Our results can be used as a benchmark to test the accuracy of various density functionals. This can strengthen confidence in DFT based predictions of more complex phenomena such as the anomalous melting behavior predicted for lithium at high pressures. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. DOE's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  5. Calculation of binary phase diagrams between the actinide elements, rare earth elements, and transition metal elements

    SciTech Connect

    Selle, J E

    1992-06-26

    Attempts were made to apply the Kaufman method of calculating binary phase diagrams to the calculation of binary phase diagrams between the rare earths, actinides, and the refractory transition metals. Difficulties were encountered in applying the method to the rare earths and actinides, and modifications were necessary to provide accurate representation of known diagrams. To calculate the interaction parameters for rare earth-rare earth diagrams, it was necessary to use the atomic volumes for each of the phases: liquid, body-centered cubic, hexagonal close-packed, and face-centered cubic. Determination of the atomic volumes of each of these phases for each element is discussed in detail. In some cases, empirical means were necessary. Results are presented on the calculation of rare earth-rare earth, rare earth-actinide, and actinide-actinide diagrams. For rare earth-refractory transition metal diagrams and actinide-refractory transition metal diagrams, empirical means were required to develop values for the enthalpy of vaporization for rare earth elements and values for the constant (C) required when intermediate phases are present. Results of using the values determined for each element are presented.

  6. The phase diagram of solid hydrogen at high pressure: A challenge for first principles calculations

    NASA Astrophysics Data System (ADS)

    Azadi, Sam; Foulkes, Matthew

    2015-03-01

    We present comprehensive results for the high-pressure phase diagram of solid hydrogen. We focus on the energetically most favorable molecular and atomic crystal structures. To obtain the ground-state static enthalpy and phase diagram, we use semi-local and hybrid density functional theory (DFT) as well as diffusion quantum Monte Carlo (DMC) methods. The closure of the band gap with increasing pressure is investigated utilizing quasi-particle many-body calculations within the GW approximation. The dynamical phase diagram is calculated by adding proton zero-point energies (ZPE) to static enthalpies. Density functional perturbation theory is employed to calculate the proton ZPE and the infra-red and Raman spectra. Our results clearly demonstrate the failure of DFT-based methods to provide an accurate static phase diagram, especially when comparing insulating and metallic phases. Our dynamical phase diagram obtained using fully many-body DMC calculations shows that the molecular-to-atomic phase transition happens at the experimentally accessible pressure of 374 GPa. We claim that going beyond mean-field schemes to obtain derivatives of the total energy and optimize crystal structures at the many-body level is crucial. This work was supported by the UK engineering and physics science research council under Grant EP/I030190/1, and made use of computing facilities provided by HECTOR, and by the Imperial College London high performance computing centre.

  7. Determining the phase diagram of lithium via ab initio calculation and ramp compression

    NASA Astrophysics Data System (ADS)

    Shulenburger, Luke; Seagle, Chris; Haill, Thomas; Harding, Eric

    2015-06-01

    Diamond anvil cell experiments have shown elemental lithium to have an extraordinarily complex phase diagram under pressure exhibiting numerous solid phases at pressures below 1 Mbar, as well as a complicated melting behavior. We explore this phase diagram utilizing a combination of quantum mechanical calculations and ramp compression experiments performed on Sandia National Laboratories' Z-machine. We aim to extend our knowledge of the high pressure behavior to moderate temperatures at pressures above 50 GPa with a specific focus on the melt line above 70 GPa. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the US Dept of Energy's Natl. Nuclear Security Administration under Contract DE-AC04-94AL85000.

  8. Phase Diagram Calculation and Analyze on Cast High-Boron High-Speed Steel

    NASA Astrophysics Data System (ADS)

    Yang, Yong-wei; Fu, Han-guang; Lei, Yong-ping; Wang, Kai-ming; Zhu, Li-long; Jiang, Liang

    2016-02-01

    The equilibrium phases of high-boron high-speed steel whose compositions are 0-3.0% B, 0.2-0.8% C, 4.0-8.0% Cr, 2.0-4.0% Mo, 0.5-1.5% Al, 0.5-1.5% Si, 0-1.0% Mn, and 0.5-1.5% V were calculated and vertical section pseudo-binary phase diagrams were drawn by Thermo-Calc software. The phase transformation and carbides precipitation temperatures were measured by using differential scanning calorimetry. The type of carbides and matrix of the as-cast specimens were determined by using x-ray diffraction. Meanwhile, the shape and the number of carbides in the different specimens were detected by using optical microscope and scanning electron microscope. The influence of boron, carbon, aluminum, and chromium elements on equilibrium phase diagrams was discussed. The calculation results obtained from Thermo-Calc software are agreed with the ones from experiments. This work provides a practical method for engineers and researchers in related areas.

  9. γ- and α-Ce phase diagram: First-principle calculation

    NASA Astrophysics Data System (ADS)

    Lin, Zhang; Ying-Hua, Li; Xue-Mei, Li; Zu-Gen, Zhang; Xiang-Ping, Ye; Ling-Cang, Cai

    2016-03-01

    Controversies about the phase diagram for the isostructural γ ↔ α phase transition of cerium have long been standing out for several decades. To seek insight into the problems, high-precision equations of state (EOS) for γ- and α-cerium are constructed based on first-principle calculation. Versus previous works, the strong anharmonic effects of ion vibration and the variation of magnetism of γ-cerium are stressed. The new EOS generally agrees well with experimental data regarding thermodynamics, phase diagrams, and phase transitions. However, new EOS predicts that another part of phase boundary in pressure-temperature space may exist except for the commonly known boundary. In addition, the well-known critical point seems to be a critical point for γ-cerium to translate from a stable state to an unstable state. Project supported by the National Natural Science Foundation of China (Grant Nos. 11272293 and U1230201), the Defense Industrial Technology Development Program (Grant No. B1520132001), and the Foundation of National Key Laboratory of Shock Wave and Detonation Physics of China (Grant No. 9140C670301140C67283).

  10. The Role of the Cluster Variation Method in the First Principles Calculation of Phase Diagrams

    NASA Astrophysics Data System (ADS)

    Sanchez, J. M.; Becker, J. D.

    The Cluster Variation Method (CVM) proposed by Professor Kikuchi to study cooperative phenomena in solids has played a major role in the development of phenomenological and first principles theories of phase equilibrium. The CVM provides an accurate and rigorous framework for the study of the configurational thermodynamics of alloys. As such, the method has been a powerful tool in the quest for insight into the main contributions to alloy phase stability and in the interpretation of complex and extensive experimental data. The early successes of the CVM have also been instrumental in the development of ab-initio methods for the reliable description of phase equilibrium and, in particular, of phase diagrams. These new developments have relied heavily on the CVM and on the theoretical ideas put forth over 40 years ago by Professor Kikuchi. Here, we review the use of the CVM in the first-principles computation of phase diagrams, and present results for the Zr-Nb system. The theory that emerges is one that incorporates the calculation of total energies in the local density approximation, configurational entropies using the CVM, and vibrational modes in the Debye-Grüneisen approximation.

  11. Ab initio calculation of the thermodynamic properties and phase diagram of gallium nitride

    NASA Astrophysics Data System (ADS)

    Zhou, Ying; Wang, Shaofeng; Wang, Rui; Jiang, Na

    2013-12-01

    The thermodynamic properties of gallium nitride (GaN) with wurtzite (WZ) and rocksalt (RS) phases have been investigated by carrying out the first principles-calculations, in which the density-functional theory (DFT) and density-functional perturbation theory (DFPT) have been employed. The quasiharmonic approximation (QHA) has been utilized to estimate the free energies. The phonon dispersion, thermal expansion coefficients, bulk modulus, and heat capacities are presented and provided good agreement with the previous calculation and experimental data. Furthermore, the pressure-temperature (P-T) diagram of WZ-RS phase transition of GaN is predicted and the values of transition pressure range from 32.2 GPa at 0 K to about 21 GPa at 2480 K.

  12. PHASEGO: A toolkit for automatic calculation and plot of phase diagram

    NASA Astrophysics Data System (ADS)

    Liu, Zhong-Li

    2015-06-01

    The PHASEGO package extracts the Helmholtz free energy from the phonon density of states obtained by the first-principles calculations. With the help of equation of states fitting, it reduces the Gibbs free energy as a function of pressure/temperature at fixed temperature/pressure. Based on the quasi-harmonic approximation (QHA), it calculates the possible phase boundaries among all the structures of interest and finally plots the phase diagram automatically. For the single phase analysis, PHASEGO can numerically derive many properties, such as the thermal expansion coefficients, the bulk moduli, the heat capacities, the thermal pressures, the Hugoniot pressure-volume-temperature relations, the Grüneisen parameters, and the Debye temperatures. In order to check its ability of phase transition analysis, I present here two examples: semiconductor GaN and metallic Fe. In the case of GaN, PHASEGO automatically determined and plotted the phase boundaries among the provided zinc blende (ZB), wurtzite (WZ) and rocksalt (RS) structures. In the case of Fe, the results indicate that at high temperature the electronic thermal excitation free energy corrections considerably alter the phase boundaries among the body-centered cubic (bcc), face-centered cubic (fcc) and hexagonal close-packed (hcp) structures.

  13. First-Principles Calculations of Thermodynamic Properties and Phase Diagrams of Binary Substitutional Alloys

    NASA Astrophysics Data System (ADS)

    Asta, Mark David

    In this dissertation it is shown how quantum and statistical mechanical computational techniques can be combined in order to make possible the calculation of thermodynamic properties for solid-state binary substitutional alloy phases from first principles, i.e., from a knowledge of only basic crystallographic information and the atomic numbers of the alloy constituents. The framework which is discussed here for performing such calculations is based on the formalism of cluster expansions. Using this formalism the statistical mechanical problem of computing substitutional alloy thermodynamic properties can be reduced to that of solving a generalized Ising model. It is shown how the parameters describing atomic interactions in such an Ising model can be derived with the structure inversion method from the results of quantum mechanical calculations of zero-temperature total energies for a number of ordered stoichiometric alloy compounds sharing a common underlying parent structure. Once the parameters in the generalized Ising model have been derived, alloy thermodynamic properties can be calculated by a variety of statistical mechanical techniques. In the work presented here the quantum and statistical mechanical calculations have been performed using the linear muffin-tin orbital and cluster variation methods, respectively. These computational methods are both described in some detail. The formalism and computational techniques mentioned in the previous paragraph are applied to the study of alloy phase stability in the Ti-Al and Cd-Mg systems. For Cd -Mg an effort is made to determine the relative magnitudes of the contributions to the alloy free energy arising from configurational disorder, structural relaxations, as well as vibrational and electronic excitations. It is shown that when all of these different contributions to the free energy are included, the calculated solid-state portion of the composition-temperature phase diagram for the Cd -Mg system is in

  14. Phase Equilibria Diagrams Database

    National Institute of Standards and Technology Data Gateway

    SRD 31 NIST/ACerS Phase Equilibria Diagrams Database (PC database for purchase)   The Phase Equilibria Diagrams Database contains commentaries and more than 21,000 diagrams for non-organic systems, including those published in all 21 hard-copy volumes produced as part of the ACerS-NIST Phase Equilibria Diagrams Program (formerly titled Phase Diagrams for Ceramists): Volumes I through XIV (blue books); Annuals 91, 92, 93; High Tc Superconductors I & II; Zirconium & Zirconia Systems; and Electronic Ceramics I. Materials covered include oxides as well as non-oxide systems such as chalcogenides and pnictides, phosphates, salt systems, and mixed systems of these classes.

  15. Misfit strain-temperature phase diagrams and domain stability of asymmetric ferroelectric capacitors: Thermodynamic calculation and phase-field simulation

    SciTech Connect

    Chen, W. J.; Zheng, Yue Wu, C. M.; Wang, B. Ma, D. C.

    2014-03-07

    Thermodynamic calculation and phase-field simulation have been conducted to investigate the misfit strain-temperature phase diagrams, dielectric property, and domain stability of asymmetric ferroelectric capacitors (FCs), with considering the effects of dissimilar screening properties and work function steps at the two interfaces. The distinct features of asymmetric FCs from their symmetric counterparts have been revealed and discussed. Polar states with nonzero out-of-plane polarization in parallel with the built-in field are found preferential to form in asymmetric FCs. Meanwhile, the built-in field breaks the degeneracy of states with out-of-plane polarization in anti-directions. This leads to the necessity of redefining phases according to the bistability of out-of-plane polarization. Moreover, the phase stability as well as the dielectric behavior can be significantly controlled by the properties of electrodes, misfit strain, and temperature. The phase-field simulation result also shows that polydomain instability would happen in asymmetric FCs as the equivalence of domain stability in anti-directions is destroyed.

  16. Ab-initio calculations and phase diagram assessments of An-Al systems (An = U, Np, Pu)

    NASA Astrophysics Data System (ADS)

    Sedmidubský, D.; Konings, R. J. M.; Souček, P.

    2010-02-01

    The enthalpies of formation of binary intermetallic compounds AnAl n(n=2,3,4, An=U,Np,Pu) were assessed from first principle calculations of total energies performed using full potential APW + lo technique within density functional theory ( WIEN2k). The substantial contribution to entropies, S298°, arising from lattice vibrations was calculated by direct method within harmonic crystal approximation ( Phonon software + VASP for obtaining Hellmann-Feynman forces). The electronic heat capacity and the corresponding contribution to entropy were estimated from the density of states at Fermi level obtained from electronic structure calculations. The phase diagrams of the relevant systems An-Al were calculated based on the thermodynamic data assessed from ab-initio calculations, known equilibrium and calorimetry data by employing the FactSage program.

  17. Misfit strain-misfit strain diagram of epitaxial BaTiO3 thin films: Thermodynamic calculations and phase-field simulations

    NASA Astrophysics Data System (ADS)

    Sheng, G.; Zhang, J. X.; Li, Y. L.; Choudhury, S.; Jia, Q. X.; Liu, Z. K.; Chen, L. Q.

    2008-12-01

    The effect of anisotropic strains on the phase transitions and domains structures of BaTiO3 thin films was studied using both thermodynamic calculations and phase-field simulations. The misfit strain-misfit strain domain stability diagrams were predicted. The similarity and significant differences between the diagrams from thermodynamic calculations assuming single domains and from phase-field simulations were analyzed. Typical domain structures as a result of anisotropic misfit strains are presented.

  18. The neptunium-iron phase diagram

    NASA Astrophysics Data System (ADS)

    Gibson, J. K.; Haire, R. G.; Beahm, E. C.; Gensini, M. M.; Maeda, A.; Ogawa, T.

    1994-08-01

    The phase relations in the Np-Fe alloy system have been elucidated using differential thermal analysis. A phase diagram for this system is postulated based upon the experimental results, regular-solution model calculations, and an expected correspondence to the U-Fe and Pu-Fe diagrams. The postulated Np-Fe diagram is characterized by limited terminal solid solubilities, two intermetallic solid phases, NpFe 2 and Np 6Fe, and two eutectics.

  19. Lattice and Phase Diagram in QCD

    SciTech Connect

    Lombardo, Maria Paola

    2008-10-13

    Model calculations have produced a number of very interesting expectations for the QCD Phase Diagram, and the task of a lattice calculations is to put these studies on a quantitative grounds. I will give an overview of the current status of the lattice analysis of the QCD phase diagram, from the quantitative results of mature calculations at zero and small baryochemical potential, to the exploratory studies of the colder, denser phase.

  20. Self-consistent field theory and numerical scheme for calculating the phase diagram of wormlike diblock copolymers.

    PubMed

    Jiang, Ying; Chen, Jeff Z Y

    2013-10-01

    This paper concerns establishing a theoretical basis and numerical scheme for studying the phase behavior of AB diblock copolymers made of wormlike chains. The general idea of a self-consistent field theory is the combination of the mean-field approach together with a statistical weight that describes the configurational properties of a polymer chain. In recent years, this approach has been extensively used for structural prediction of block copolymers, based on the Gaussian-model description of a polymer chain. The wormlike-chain model has played an important role in the description of polymer systems, covering the semiflexible-to-rod crossover of the polymer properties and the highly stretching regime, which the Gaussian-chain model has difficulties to describe. Although the idea of developing a self-consistent field theory for wormlike chains could be traced back to early development in polymer physics, the solution of such a theory has been limited due to technical difficulties. In particular, a challenge has been to develop a numerical algorithm enabling the calculation of the phase diagram containing three-dimensional structures for wormlike AB diblock copolymers. This paper describes a computational algorithm that combines a number of numerical tricks, which can be used for such a calculation. A phase diagram covering major parameter areas was constructed for the wormlike-chain system and reported by us, where the ratio between the total length and the persistence length of a constituent polymer is suggested as another tuning parameter for the microphase-separated structures; all detailed technical issues are carefully addressed in the current paper. PMID:24229202

  1. Misfit strain-misfit strain diagram of epitaxial BaTiO(3) thin films: thermodynamic calculations and phase-field simulations

    SciTech Connect

    Jia, Quanxi; Sheng, G; Zhang, J X; Li, Y L; Choudhury, S; Liu, Z K; Chen, L Q

    2009-01-01

    The effect of anisotropic strains on the phase transitions and domains structures of BaTi03 thin films was studied using both thermodynamic calculations and phase-field simulations. The misfit strain -misfit strain domain stability diagrams, i.e. the graphical representations of stable ferroelectric phases and domain structures as a function of strains, were predicted. The similarity and significant differences between the diagrams from thermodynamic calculations assuming single domains and from phase-field simulations were analyzed. Typical domain structures as a result of anisotropic misfit strains are presented.

  2. The theoretical calculation of the phase diagram of infrared detector materials (Hg,Zn)Te and (Cd,Zn)Te

    NASA Astrophysics Data System (ADS)

    Li, Chi; Huang, Xingliang

    1989-05-01

    A technique for constructing the phase diagrams of Te-based pseudobinary IR detector materials on the basis of thermodynamics theory is described and demonstrated. The fundamental principles of the segregation-coefficient and shape-statement methods are reviewed; the computational procedure is explained; and results are presented for HgTe-ZnTe and CdTe-ZnTe. The temperatures in the diagrams are found to be within 0.6 and 15 C, respectively, of the experimentally measured values.

  3. Compression and phase diagram of lithium hydrides at elevated pressures and temperatures by first-principles calculation

    NASA Astrophysics Data System (ADS)

    Chen, Yang M.; Chen, Xiang R.; Wu, Qiang; Geng, Hua Y.; Yan, Xiao Z.; Wang, Yi X.; Wang, Zi W.

    2016-09-01

    High pressure and high temperature properties of AB (A  =  6Li, 7Li; B  =  H, D, T) are comprehensively investigated with first-principles methods. It is found that H‑sublattice features in the low-pressure electronic structure near the Fermi level of LiH are shifted to that dominated by the Li+ sublattice under compression. The lattice dynamics are studied in quasi-harmonic approximation, from which the phonon contribution to the free energy and the isotopic effects are accurately modelled with the aid of a parameterized double-Debye model. The equation of state (EOS) obtained matches perfectly with available static experimental data. The calculated principal Hugoniot is also in accordance with that derived from shock wave experiments. Using the calculated principal Hugoniot and the previous theoretical melting curve, we predict a shock melting point at 56 GPa and 1923 K. In order to establish the phase diagram for LiH, the phase boundaries between the B1 and B2 solid phases are explored. The B1–B2-liquid triple point is determined at about 241 GPa and 2413 K. The remarkable shift in the phase boundaries with isotopic effect and temperature reveal the significant role played by lattice vibrations. Furthermore, the Hugoniot of the static-dynamic coupling compression is assessed. Our EOS suggests that a precompression of the sample to 50 GPa will allow the shock Hugoniot to pass through the triple point and enter the B2 solid phase. This transition leads to a discontinuity with 4.6% volume collapse—about four times greater than the same B1–B2 transition at zero temperature.

  4. Simple method for the calculation and use of CVD phase diagrams with applications to the Ti-B-Cl-H system, 1200 to 800/sup 0/K

    SciTech Connect

    Randich, E.; Gerlach, T. M.

    1980-03-01

    A simple method for calculating multi-component gas-solid equilibrium phase diagrams for chemical vapor deposition (CVD) systems is presented. The method proceeds in three steps: dtermination of stable solid assemblages, evaluation of gas-solid stability relations, and calcuation of conventional phase diagrams using a new free energy minimization technique. The phase diagrams can be used to determine (1) bulk compositions and phase fields accessible by CVD techniques; (2) expected condensed phases for various starting gas mixtures; and (3) maximum equilibrium yields for specific CVD process variables. The three step thermodynamic method is used to calcuate phase diagrams for the example CVD system Ti-B-Cl-H at 1200 and 800/sup 0/K. Examples of applications of the diagrams for yield optimization and experimental accessibility studies are presented and discussed. Experimental verification of the TiB/sub 2/ + Gas/Gas phase field boundary at 1200/sup 0/K, H/Cl = 1 confirms the calculated boundary and indicates that equilibrium is nearly and rapidly approached under laboratory conditions.

  5. Phase diagram of the CulnSe{sub 2}-CuGaSe{sub 2} pseudobinary system studied by combined ab initio density functional theory and thermodynamic calculation

    SciTech Connect

    Xue, H. T.; Tang, F. L.; Lu, W. J.; Li, X. K.; Zhang, Y.; Feng, Y. D.

    2014-08-07

    The phase diagram of the CuInSe{sub 2}-CuGaSe{sub 2} pseudobinary system was determined using a combination of special quasirandom structure approach, ab initio density functional theory calculations, and thermodynamic modelling. It is shown that the CuIn{sub 1−x}Ga{sub x}Se{sub 2} solution phase has a tendency to phase separation at low temperature. The calculated consolute temperature is 485 K. It is found that both the binodal and spinodal curves are significantly asymmetric and on both curves there are a local maximum and a local minimum, which have not been reported in the previous studies. Our phase diagram can well explain the finding that the inhomogeneity of CuIn{sub 0.25}Ga{sub 0.75}Se{sub 2} is higher than that of CuIn{sub 0.75}Ga{sub 0.25}Se{sub 2} at the same temperature, while the previous phase diagrams cannot. Hence, our phase diagram should be more reliable and applicable.

  6. Phase diagram of a truncated tetrahedral model.

    PubMed

    Krcmar, Roman; Gendiar, Andrej; Nishino, Tomotoshi

    2016-08-01

    Phase diagram of a discrete counterpart of the classical Heisenberg model, the truncated tetrahedral model, is analyzed on the square lattice, when the interaction is ferromagnetic. Each spin is represented by a unit vector that can point to one of the 12 vertices of the truncated tetrahedron, which is a continuous interpolation between the tetrahedron and the octahedron. Phase diagram of the model is determined by means of the statistical analog of the entanglement entropy, which is numerically calculated by the corner transfer matrix renormalization group method. The obtained phase diagram consists of four different phases, which are separated by five transition lines. In the parameter region, where the octahedral anisotropy is dominant, a weak first-order phase transition is observed. PMID:27627273

  7. Prediction of boron carbon nitrogen phase diagram

    NASA Astrophysics Data System (ADS)

    Yao, Sanxi; Zhang, Hantao; Widom, Michael

    We studied the phase diagram of boron, carbon and nitrogen, including the boron-carbon and boron-nitrogen binaries and the boron-carbon-nitrogen ternary. Based on the idea of electron counting and using a technique of mixing similar primitive cells, we constructed many ''electron precise'' structures. First principles calculation is performed on these structures, with either zero or high pressures. For the BN binary, our calculation confirms that a rhmobohedral phase can be stablized at high pressure, consistent with some experimental results. For the BCN ternary, a new ground state structure is discovered and an Ising-like phase transition is suggested. Moreover, we modeled BCN ternary phase diagram and show continuous solubility from boron carbide to the boron subnitride phase.

  8. Phase diagram of superconductor-ferromagnet superlattices

    SciTech Connect

    Radovic, Z.; Dobrosavljevic-Grujic, L.

    1994-12-31

    Recent progress in the proximity effect theory of superconductor-ferromagnet superlattices is reviewed. The phase diagram calculations, transition temperature {Tc} and upper critical fields H{sub c2}, are presented. Characteristic features in {Tc} and H{sub c2}(T) dependence on layers thicknesses, including the predicted unusual oscillatory variations and new inhomogeneous superconducting state with nontrivial phase difference between neighboring superconducting layers, are discussed and compared with experimental data for V/Fe and Nb/Gd superlattices.

  9. Phase diagram and dynamics of Yukawa systems

    NASA Astrophysics Data System (ADS)

    Robbins, Mark. O.; Kremer, Kurt; Grest, Gary S.

    1988-03-01

    The phase diagram and dynamical properties of systems of particles interacting through a repulsive screened Coulomb (Yukawa) potential have been calculated using molecular and lattice dynamics techniques. The phase diagram contains both a melting transition and a transition from fcc to bcc crystalline phases. These phase transitions have been studied as a function of potential shape (screening length) and compared to phenomenological criteria for transition temperatures such as those of Lindemann and of Hansen and Verlet. The transition from fcc to bcc with increasing temperature is shown to result from a higher entropy in the bcc phase because of its softer shear modes. Even when the stable solid phase below the melting temperature is fcc, bcc-like local order is found in the liquid phase. This may substantially slow crystallization. The calculated phase diagram and shear modulus are in good agreement with experiments on colloidal suspensions of polystyrene spheres. The single particle dynamics of Yukawa systems show several unusual features. There is a pronounced subdiffusive regime in liquids near and below the melting temperature. This regime reflects the existence of two time scales: a typical phonon period, and the time for a particle to feel a new environment. The second time scale becomes longer as the temperature is lowered or the range of interaction (screening length) increases.

  10. Phase Coexistence in a Dynamic Phase Diagram.

    PubMed

    Gentile, Luigi; Coppola, Luigi; Balog, Sandor; Mortensen, Kell; Ranieri, Giuseppe A; Olsson, Ulf

    2015-08-01

    Metastability and phase coexistence are important concepts in colloidal science. Typically, the phase diagram of colloidal systems is considered at the equilibrium without the presence of an external field. However, several studies have reported phase transition under mechanical deformation. The reason behind phase coexistence under shear flow is not fully understood. Here, multilamellar vesicle (MLV)-to-sponge (L3 ) and MLV-to-Lα transitions upon increasing temperature are detected using flow small-angle neutron scattering techniques. Coexistence of Lα and MLV phases at 40 °C under shear flow is detected by using flow NMR spectroscopy. The unusual rheological behavior observed by studying the lamellar phase of a non-ionic surfactant is explained using (2) H NMR and diffusion flow NMR spectroscopy with the coexistence of planar lamellar-multilamellar vesicles. Moreover, a dynamic phase diagram over a wide range of temperatures is proposed. PMID:26083451

  11. Phase Diagrams of Nuclear Pasta

    NASA Astrophysics Data System (ADS)

    Caplan, Matthew; Horowitz, Chuck; Berry, Don; da Silva Schneider, Andre

    2016-03-01

    In the inner crust of neutrons stars, where matter is near the saturation density, protons and neutrons arrange themselves into complex structures called nuclear pasta. Early theoretical work predicted a simple graduated hierarchy of pasta phases, consisting of spheres, cylinders, slabs, and uniform matter with voids. Previous work has simulated these phases with a simple classical model and has shown that the formation of these structures is dependent on the temperature, density, and proton fraction. However, previous work only studied a limited range of these parameters due to computational limitations. Thanks to recent advances in computing it is now possible to survey the structure of nuclear pasta for a larger range of parameters. By simulating nuclear pasta with constant temperature and proton fraction in an expanding simulation volume we are able to study the phase transitions in nuclear pasta, and thus produce a set of phase diagrams. We report on these phase diagrams as well as newly identified phases of nuclear pasta and discuss their implications for neutron star observables.

  12. Application of computer methods for calculation of multicomponent phase diagrams of high-temperature structural ceramics. Final report, August 1984-July 1987

    SciTech Connect

    Kaufman, L.

    1987-07-31

    A data base is being developed for calculation of quasi-binary and quasi-ternary phase diagrams of ceramic systems. Previous segments of this base cover combinations of Cr/sub 2/O/sub 3/, MgO, A1/sub 2/O/sub 3/, SiO/sub 2/, CaO, Si/sub 3/N/sub 4/, A1N, BeO, Y/sub 2/O/sub 3/ and Ce/sub 2/O/sub 3/. Sixty -six quasi binary and nineteen quasi ternary systems have been calculated. Current work extends the base to cover GeO/sub 2/, HfO3, ZrO/sub 2/ and TiO/sub 2/ which are of interest in applications requiring toughness and structural performance at high temperatures. This has been effected by employing available source of thermochemical and phase-diagram data. Recently it has been shown that by alloying GeO/sub 2/ with SiO/sub 2/ a whole range of glasses can be synthesized with tailor-made coefficients of expansion. Utilization of such compositions offers the possibility of enhancing the high temperature oxidation resistance of ceramic composites in which a mixed GeO/sub 2/-SiO/sub 2/ phase which a desired CTE would replace the conventional SiO/sub 2/ as a filler.

  13. Phase diagram of ammonium nitrate

    NASA Astrophysics Data System (ADS)

    Dunuwille, M.; Yoo, C. S.

    2014-05-01

    Ammonium Nitrate (AN) has often subjected to uses in improvised explosive devices, due to its wide availability as a fertilizer and its capability of becoming explosive with slight additions of organic and inorganic compounds. Yet, the origin of enhanced energetic properties of impure AN (or AN mixtures) is neither chemically unique nor well understood -resulting in rather catastrophic disasters in the past1 and thereby a significant burden on safety in using ammonium nitrates even today. To remedy this situation, we have carried out an extensive study to investigate the phase stability of AN at high pressure and temperature, using diamond anvil cells and micro-Raman spectroscopy. The present results confirm the recently proposed phase IV-to-IV' transition above 17 GPa2 and provide new constraints for the melting and phase diagram of AN to 40 GPa and 400 °C.

  14. Effect of external mechanical constraints on the phase diagram of epitaxial PbZr1-xTixO3 thin films—thermodynamic calculations and phase-field simulations

    NASA Astrophysics Data System (ADS)

    Li, Y. L.; Choudhury, S.; Liu, Z. K.; Chen, L. Q.

    2003-08-01

    The phase diagram of a PbZr1-xTixO3 (PZT) film constrained by a much thicker substrate was studied using both thermodynamic calculations and phase-field approach. It was found that the ferroelectric transition temperature is increased with substrate constraint regardless of the nature of the constraint, i.e., tensile or compressive. The maximum increase in the transition temperature occurs near x=0.5, and the morphotropic phase boundary is shifted considerably by the substrate constraint. It is shown that the orthorhombic phase (|P1|=|P2|≠0,P3=0) that does not exist in the bulk becomes stable under a tensile constraint, and the rhombohedral phase (|P1|=|P2|=|P3|≠0) in the bulk is distorted in the constrained film, i.e., |P1|=|P2|≠0,|P3|≠0. The phase diagrams obtained by the phase-field approach indicated that the stability region for the tetragonal phase is much wider than that obtained from the thermodynamic calculations assuming a single-domain, especially under tensile substrate constraint. The discrepancy between the two methods becomes larger as substrate constraint changes from compressive to tensile, implying that thermodynamic calculations are unreliable for constructing stability diagram of PZT, particularly under a tensile constraint.

  15. Non-equilibrium phases and phase diagrams

    SciTech Connect

    Massalski, T.B.; Rizzo, H.F.

    1988-03-01

    In this paper we consider the degree of usefulness of the phase diagram and the related thermodynamics in predicting and understanding the formation of metastable phases during quenching, or during low-temperature solid-state interdiffusion, or during co-deposition. Recent research has demonstrated that many of such metastable phases are formed because the more stable intermediate phases that are favored thermodynamically are nevertheless bypassed kinetically. The kinetic elimination of intermediate phases provides conditions where a metastable equilibrium can be established at low temperatures between the supercooled liquid and the terminal solid solutions, leading to metastable partitioned two-phase regions. Alternatively, the range of the metastable phases may be governed by the T/sub 0/ principle related to the crossover of the respective free energy curves, or may be controlled mainly by kinetic considerations. Which particular thermodynamic conditions apply appears to depend on the initial form of the phase diagram and the specific technique used. The occurrence of massive transformations also is discussed. 34 refs., 10 figs.

  16. Generic Phase Diagram of Binary Superlattices

    NASA Astrophysics Data System (ADS)

    Tkachenko, Alexei

    Emergence of a large variety of self-assembled superlattices is a dramatic recent trend in the fields of nanoparticle and colloidal sciences. Motivated by this development, we propose a model that combines simplicity with a remarkably rich phase behavior, applicable to a wide range of such self-assembled systems. Those include nanoparticle and colloidal assemblies driven by DNA-mediated interactions, electrostatics, and possibly, by controlled drying. In our model, a binary system of Large and Small hard sphere (L and S)interact via selective short-range (''sticky'') attraction. In its simplest version, this Binary Sticky Sphere model features attraction only between 'S' and 'L' particles, respectively. We demonstrate that in the limit when this attraction is sufficiently strong compared to kT, the problem becomes purely geometrical: the thermodynamically preferred state should maximize the number of S-L contacts. A general procedure for constructing the phase diagram as a function of system composition f, and particle size ratio r, is outlined. In this way, the global phase behavior can be calculated very efficiently, for a given set of plausible candidate phases. Furthermore, the geometric nature of the problem enables us to generate those candidate phases through a well defined and intuitive construction. We calculate the phase diagrams both for 2D and 3D systems, and compare the results with existing experiments. Most of the 3D superlattices observed to date are featured in our phase diagram, while several more are yet to be discovered. The research was carried out at the CFN, DOE Office of Science Facility, at BNL, under Contract No. DE-SC0012704.

  17. Phase diagram of ammonium nitrate

    SciTech Connect

    Dunuwille, Mihindra; Yoo, Choong-Shik

    2013-12-07

    Ammonium Nitrate (AN) is a fertilizer, yet becomes an explosive upon a small addition of chemical impurities. The origin of enhanced chemical sensitivity in impure AN (or AN mixtures) is not well understood, posing significant safety issues in using AN even today. To remedy the situation, we have carried out an extensive study to investigate the phase stability of AN and its mixtures with hexane (ANFO–AN mixed with fuel oil) and Aluminum (Ammonal) at high pressures and temperatures, using diamond anvil cells (DAC) and micro-Raman spectroscopy. The results indicate that pure AN decomposes to N{sub 2}, N{sub 2}O, and H{sub 2}O at the onset of the melt, whereas the mixtures, ANFO and Ammonal, decompose at substantially lower temperatures. The present results also confirm the recently proposed phase IV-IV{sup ′} transition above 17 GPa and provide new constraints for the melting and phase diagram of AN to 40 GPa and 400°C.

  18. Phase Diagram of Ammonium Nitrate

    NASA Astrophysics Data System (ADS)

    Dunuwille, Mihindra; Yoo, Choong-Shik

    2013-06-01

    Ammonium Nitrate (AN) has often been subjected to uses in improvised explosive devices, due to its wide availability as a fertilizer and its capability of becoming explosive with slight additions of organic and inorganic compounds. Yet, the origin of enhanced energetic properties of impure AN (or AN mixtures) is neither chemically unique nor well understood - resulting in rather catastrophic disasters in the past1 and thereby a significant burden on safety, in using ammonium nitrates even today. To remedy this situation, we have carried out an extensive study to investigate the phase stability of AN, in different chemical environments, at high pressure and temperature, using diamond anvil cells and micro-Raman spectroscopy. The present results confirm the recently proposed phase IV-to-IV' transition above 15 GPa2 and provide new constraints for the melting and phase diagram of AN to 40 GPa and 673 K. The present study has been supported by the U.S. DHS under Award Number 2008-ST-061-ED0001.

  19. Calculation of the LiF-CeF{sub 3}-BeF{sub 2} and LiF-PuF{sub 3}-BeF{sub 2} ternary phase diagrams

    SciTech Connect

    Mulford, R.N.R.

    1993-07-01

    The LiF-CeF{sub 3}-BeF{sub 2} and LiF-PuF{sub 3}-BeF{sub 2} ternary phase diagrams were calculated from optimized binary diagrams using computer programs developed by Lukas and coworkers. The approximate overall diagrams were calculated without the use of ternary interaction terms, but inclusion of ternary terms was necessary to reproduce the experimental data for solubilities of CeF{sub 3} and PuF{sub 3} which are considerably less soluble in LiF-BeF{sub 2} liquid than predicted without ternary interaction terms.

  20. Calculation of phase diagrams for the FeCl2, PbCl2, and ZnCl2 binary systems by using molecular dynamics simulation

    NASA Astrophysics Data System (ADS)

    Seo, Won-Gap; Matsuura, Hiroyuki; Tsukihashi, Fumitaka

    2006-04-01

    Recently, molecular dynamics (MD) simulation has been widely employed as a very useful method for the calculation of various physicochemical properties in the molten slags and fluxes. In this study, MD simulation has been applied to calculate the structural, transport, and thermodynamic properties for the FeCl2, PbCl2, and ZnCl2 systems using the Born—Mayer—Huggins type pairwise potential with partial ionic charges. The interatomic potential parameters were determined by fitting the physicochemical properties of iron chloride, lead chloride, and zinc chloride systems with experimentally measured results. The calculated structural, transport, and thermodynamic properties of pure FeCl2, PbCl2, and ZnCl2 showed the same tendency with observed results. Especially, the calculated structural properties of molten ZnCl2 and FeCl2 show the possibility of formation of polymeric network structures based on the ionic complexes of ZnCl{4/2-}, ZnCl{3/-}, FeCl{4/2-}, and FeCl{3/-}, and these calculations have successfully reproduced the measured results. The enthalpy, entropy, and Gibbs energy of mixing for the PbCl2-ZnCl2, FeCl2-PbCl2, and FeCl2-ZnCl2 systems were calculated based on the thermodynamic and structural parameters of each binary system obtained from MD simulation. The phase diagrams of the PbCl2-ZnCl2, FeCl2-PbCl2, and FeCl2-ZnCl2 systems estimated by using the calculated Gibbs energy of mixing reproduced the experimentally measured ones reasonably well.

  1. Critical point analysis of phase envelope diagram

    SciTech Connect

    Soetikno, Darmadi; Siagian, Ucok W. R.; Kusdiantara, Rudy Puspita, Dila Sidarto, Kuntjoro A. Soewono, Edy; Gunawan, Agus Y.

    2014-03-24

    Phase diagram or phase envelope is a relation between temperature and pressure that shows the condition of equilibria between the different phases of chemical compounds, mixture of compounds, and solutions. Phase diagram is an important issue in chemical thermodynamics and hydrocarbon reservoir. It is very useful for process simulation, hydrocarbon reactor design, and petroleum engineering studies. It is constructed from the bubble line, dew line, and critical point. Bubble line and dew line are composed of bubble points and dew points, respectively. Bubble point is the first point at which the gas is formed when a liquid is heated. Meanwhile, dew point is the first point where the liquid is formed when the gas is cooled. Critical point is the point where all of the properties of gases and liquids are equal, such as temperature, pressure, amount of substance, and others. Critical point is very useful in fuel processing and dissolution of certain chemicals. Here in this paper, we will show the critical point analytically. Then, it will be compared with numerical calculations of Peng-Robinson equation by using Newton-Raphson method. As case studies, several hydrocarbon mixtures are simulated using by Matlab.

  2. Critical point analysis of phase envelope diagram

    NASA Astrophysics Data System (ADS)

    Soetikno, Darmadi; Kusdiantara, Rudy; Puspita, Dila; Sidarto, Kuntjoro A.; Siagian, Ucok W. R.; Soewono, Edy; Gunawan, Agus Y.

    2014-03-01

    Phase diagram or phase envelope is a relation between temperature and pressure that shows the condition of equilibria between the different phases of chemical compounds, mixture of compounds, and solutions. Phase diagram is an important issue in chemical thermodynamics and hydrocarbon reservoir. It is very useful for process simulation, hydrocarbon reactor design, and petroleum engineering studies. It is constructed from the bubble line, dew line, and critical point. Bubble line and dew line are composed of bubble points and dew points, respectively. Bubble point is the first point at which the gas is formed when a liquid is heated. Meanwhile, dew point is the first point where the liquid is formed when the gas is cooled. Critical point is the point where all of the properties of gases and liquids are equal, such as temperature, pressure, amount of substance, and others. Critical point is very useful in fuel processing and dissolution of certain chemicals. Here in this paper, we will show the critical point analytically. Then, it will be compared with numerical calculations of Peng-Robinson equation by using Newton-Raphson method. As case studies, several hydrocarbon mixtures are simulated using by Matlab.

  3. Understanding the reentrant superconducting phase diagram of the iron pnictide Ca4Al2O6Fe2(As1-xPx)2: First-principles calculations

    NASA Astrophysics Data System (ADS)

    Usui, Hidetomo; Suzuki, Katsuhiro; Kuroki, Kazuhiko; Takeshita, Nao; Shirage, Parasharam Maruti; Eisaki, Hiroshi; Iyo, Akira

    2013-05-01

    Recently, a very rich phase diagram has been obtained for an iron-based superconductor Ca4Al2O6Fe2(As1-xPx)2. It has been revealed that nodeless (x˜0) and nodal (x=1) superconductivity are separated by an antiferromagnetic phase. Here we study the origin of this peculiar phase diagram using a five orbital model constructed from first-principles band calculation, and applying the fluctuation exchange approximation assuming spin-fluctuation-mediated pairing. At x=1, there are three hole Fermi surfaces, but the most inner one around the wave vector (0,0) has strong dX2-Y2 orbital character, unlike in LaFeAsO, where the most inner Fermi surface has dXZ/YZ character. Since the Fermi surfaces around (0,0), (π,0), and (π,π) all have dX2-Y2 orbital character, the repulsive pairing interaction mediated by the spin fluctuations gives rise to a frustration in momentum space, thereby degrading superconductivity despite the bond angle being close to the regular tetrahedron angle. As x decreases and the bond angle is reduced, the inner hole Fermi surface disappears, but the frustration effect still remains because the top of the band with dX2-Y2 character lies close to the Fermi level. On the other hand, the loss of the Fermi surface itself gives rise to a very good nesting of the Fermi surface because the number of electron and hole Fermi surfaces are now the same. The pairing interaction frustration and the good nesting combined favors antiferromagnetism over superconductivity. Finally for x close to 0, the band sinks far below the Fermi level, reducing the frustration effect, so that superconductivity is enhanced. There, the Fermi surface nesting is also lost to some extent, once again favoring superconductivity over antiferromagnetism. To see whether the present theoretical scenario is consistent with the actual nature of the competition between superconductivity and antiferromagnetism, we also perform hydrostatic pressure experiment for Ca4Al2O6Fe2(As1-xPx)2. In the

  4. Fluctuations and the QCD phase diagram

    SciTech Connect

    Schaefer, B.-J.

    2012-06-15

    In this contribution the role of quantum fluctuations for the QCD phase diagram is discussed. This concerns in particular the importance of the matter back-reaction to the gluonic sector. The impact of these fluctuations on the location of the confinement/deconfinement and the chiral transition lines as well as their interrelation are investigated. Consequences of our findings for the size of a possible quarkyonic phase and location of a critical endpoint in the phase diagram are drawn.

  5. The Phase Diagram of Superionic Ice

    NASA Astrophysics Data System (ADS)

    Sun, Jiming; Clark, Bryan; Car, Roberto

    2014-03-01

    Using the variable cell Car-Parrinello molecular dynamics method, we study the phase diagram of superionic ice from 200GPa to 2.5TPa. We present evidence that at very high pressure the FCC structure of the oxygen sublattice may become unstable allowing for a new superionic ice phase, in which the oxygen sublattice takes the P21 structure found in zero-temperature total energy calculations. We also report on how the melting temperature of the hydrogen sublattice is affected by this new crystalline structure of the oxygen sublattice. This work was supported by the NSF under grant DMS-1065894(J.S. and R.C.) and PHY11-25915(B.C.).

  6. Phase diagram for passive electromagnetic scatterers.

    PubMed

    Lee, Jeng Yi; Lee, Ray-Kuang

    2016-03-21

    With the conservation of power, a phase diagram defined by amplitude square and phase of scattering coefficients for each spherical harmonic channel is introduced as a universal map for any passive electromagnetic scatterers. Physically allowable solutions for scattering coefficients in this diagram clearly show power competitions among scattering and absorption. It also illustrates a variety of exotic scattering or absorption phenomena, from resonant scattering, invisible cloaking, to coherent perfect absorber. With electrically small core-shell scatterers as an example, we demonstrate a systematic method to design field-controllable structures based on the allowed trajectories in this diagram. The proposed phase diagram and inverse design can provide tools to design functional electromagnetic devices. PMID:27136839

  7. Shock dynamics of phase diagrams

    SciTech Connect

    Moro, Antonio

    2014-04-15

    A thermodynamic phase transition denotes a drastic change of state of a physical system due to a continuous change of thermodynamic variables, as for instance pressure and temperature. The classical van der Waals equation of state is the simplest model that predicts the occurrence of a critical point associated with the gas–liquid phase transition. Nevertheless, below the critical temperature theoretical predictions of the van der Waals theory significantly depart from the observed physical behaviour. We develop a novel approach to classical thermodynamics based on the solution of Maxwell relations for a generalised family of nonlocal entropy functions. This theory provides an exact mathematical description of discontinuities of the order parameter within the phase transition region, it explains the universal form of the equations of state and the occurrence of triple points in terms of the dynamics of nonlinear shock wave fronts. -- Highlights: •A new generalisation of van der Waals equation of state. •Description of phase transitions in terms of shock dynamics of state curves. •Proof of the universality of equations of state for a general class of models. •Interpretation of triple points as confluence of classical shock waves. •Correspondence table between thermodynamics and nonlinear conservation laws.

  8. [New diagrams for quick calculation of refrigerating machines (author's transl)].

    PubMed

    Palla, L; Sellerio, U

    1974-01-01

    The present edition is a re-elaboration and an extension of a previous one and takes into account the data meanwhile brought up to date--concerning the characteristics of saturated vapours--as well as the opportuneness of an easier consultation. In fact, by introducing logarithmic scales and by an appropriate choice of the logarithmic modulus, it has been possible to summarize the characteristics of each fluid in one diagram only, whereas, in the first edition, the extension of the metric scales of the abcissas imposed to divide each diagram in two parts. Besides, more units have been introduced, namely: m3/kcal, m3/kj and ft3/Btu for volumes; oF and oC degrees for temperatures. These new diagrams have heen developed for the following refrigerant fluids: R 11, R 12, R 13, R 13 B1, R 22, R 114, R 502, NH3 and CH3Cl. Known the temperature before the throttling device, the evaporating temperature and the one of the eventual superheating, they enable to promptly calculate the volume of the refrigerant in the gaseous phase, both as dry saturated vapour and superheated vapour; besides, they allow the quick calculation of the speed of the fluid inside thepiping system, the performance of the compressor under different working conditions and with different refrigerants, and so on. A number of practical examples illustrate even more clearly what stated about quickness and possibilities of calculation. PMID:4470993

  9. Phase diagram of a single lane roundabout

    NASA Astrophysics Data System (ADS)

    Echab, H.; Lakouari, N.; Ez-Zahraouy, H.; Benyoussef, A.

    2016-03-01

    Using the cellular automata model, we numerically study the traffic dynamic in a single lane roundabout system of four entry/exit points. The boundaries are controlled by the injecting rates α1, α2 and the extracting rate β. Both the system with and without Splitter Islands of width Lsp are considered. The phase diagram in the (α1 , β) space and its variation with the roundabout size, Pagg (i.e. the probability of aggressive entry), and Pexit (i.e. the probability of preferential exit) are constructed. The results show that the phase diagram in both cases consists of three phases: free flow, congested and jammed. However, as Lsp increases the free flow phase enlarges while the congested and jammed ones shrink. On the other hand, the short sized roundabout shows better performance in the free flow phase while the large one is more optimal in the congested phase. The density profiles are also investigated.

  10. B-Fe-U Phase Diagram

    NASA Astrophysics Data System (ADS)

    Dias, Marta; Carvalho, Patrícia Almeida; Mardolcar, Umesh Vinaica; Tougait, Olivier; Noël, Henri; Gonçalves, António Pereira

    2014-04-01

    The liquidus projection of the U-rich corner of the B-Fe-U phase diagram is proposed based on X-ray powder diffraction measurements, differential thermal analysis, and scanning electron microscopy observations complemented with energy- and wavelength-dispersive X-ray spectroscopies. Two ternary reactions in this U-rich region were observed and their approximate temperatures were established. In addition, an overview of the complete phase diagram is given, including the liquidus projection; isothermal sections at 1053 K, 1223 K, and 1373 K (780 °C, 950 °C, and 1100 °C); and a U:(Fe,B) = 1:5 isopleth.

  11. First Principles Phase Diagram Calculaions with the Maps Package

    NASA Astrophysics Data System (ADS)

    Burton, B. P.

    2003-12-01

    The MAPS, MIT ab initio software package (http://cms.northwestern.edu/Group.html) was used to perform first principles phase diagram calculations (FPPD) for the mineral systems: CaCO3}-MgCO{3; CdCO3}-MgCO{3; CaCO3}-MgCO{3; and NaCl-KCl. General characteristics of FPPD calculations will be reviewed and details of specific calculations will be discussed. Particular attention will be given to: the prediction of new stable ordered phases; metastable ordered phases; and the role of vibrational entropy in phase stability.

  12. On phase diagrams of magnetic reconnection

    SciTech Connect

    Cassak, P. A.; Drake, J. F.

    2013-06-15

    Recently, “phase diagrams” of magnetic reconnection were developed to graphically organize the present knowledge of what type, or phase, of reconnection is dominant in systems with given characteristic plasma parameters. Here, a number of considerations that require caution in using the diagrams are pointed out. First, two known properties of reconnection are omitted from the diagrams: the history dependence of reconnection and the absence of reconnection for small Lundquist number. Second, the phase diagrams mask a number of features. For one, the predicted transition to Hall reconnection should be thought of as an upper bound on the Lundquist number, and it may happen for considerably smaller values. Second, reconnection is never “slow,” it is always “fast” in the sense that the normalized reconnection rate is always at least 0.01. This has important implications for reconnection onset models. Finally, the definition of the relevant Lundquist number is nuanced and may differ greatly from the value based on characteristic scales. These considerations are important for applications of the phase diagrams. This is demonstrated by example for solar flares, where it is argued that it is unlikely that collisional reconnection can occur in the corona.

  13. Fog Machines, Vapors, and Phase Diagrams

    ERIC Educational Resources Information Center

    Vitz, Ed

    2008-01-01

    A series of demonstrations is described that elucidate the operation of commercial fog machines by using common laboratory equipment and supplies. The formation of fogs, or "mixing clouds", is discussed in terms of the phase diagram for water and other chemical principles. The demonstrations can be adapted for presentation suitable for elementary…

  14. Complexities of One-Component Phase Diagrams

    ERIC Educational Resources Information Center

    Ciccioli, Andrea; Glasser, Leslie

    2011-01-01

    For most materials, the solid at and near the triple-point temperature is denser than the liquid with which it is in equilibrium. However, for water and certain other materials, the densities of the phases are reversed, with the solid being less dense. The profound consequences for the appearance of the "pVT" diagram of one-component materials…

  15. Phase diagram of spiking neural networks

    PubMed Central

    Seyed-allaei, Hamed

    2015-01-01

    In computer simulations of spiking neural networks, often it is assumed that every two neurons of the network are connected by a probability of 2%, 20% of neurons are inhibitory and 80% are excitatory. These common values are based on experiments, observations, and trials and errors, but here, I take a different perspective, inspired by evolution, I systematically simulate many networks, each with a different set of parameters, and then I try to figure out what makes the common values desirable. I stimulate networks with pulses and then measure their: dynamic range, dominant frequency of population activities, total duration of activities, maximum rate of population and the occurrence time of maximum rate. The results are organized in phase diagram. This phase diagram gives an insight into the space of parameters – excitatory to inhibitory ratio, sparseness of connections and synaptic weights. This phase diagram can be used to decide the parameters of a model. The phase diagrams show that networks which are configured according to the common values, have a good dynamic range in response to an impulse and their dynamic range is robust in respect to synaptic weights, and for some synaptic weights they oscillates in α or β frequencies, independent of external stimuli. PMID:25788885

  16. The Binary Temperature-Composition Phase Diagram

    ERIC Educational Resources Information Center

    Sanders, Philip C.; Reeves, James H.; Messina, Michael

    2006-01-01

    The equations for the liquid and gas lines in the binary temperature-composition phase diagram are derived by approximating that delta(H)[subscript vap] of the two liquids are equal. It is shown that within this approximation, the resulting equations are not too difficult to present in an undergraduate physical chemistry lecture.

  17. Equilibrium phase diagrams of alloys using nested sampling

    NASA Astrophysics Data System (ADS)

    Bernstein, Noam; Baldock, Robert J. N.; Bartók-Partáy, Livia; Csányi, Gábor

    Temperature-pressure-composition phase diagrams describe the structures of materials in thermal equilibrium, and are an essential tool in understanding material properties. Predicting phase diagrams is challenging, even given a description of the interatomic interactions, because of the need to sample a very large configuration space. Nested sampling (NS) has been shown to be an efficient tool for calculating the partition function, and therefore all thermodynamic properties and ensemble averages, by systematically sampling the configuration space of isolated and periodic systems. Its effectiveness comes from sampling starting from high energy, where barriers are relatively low and equilibration is relatively fast, and iteratively eliminating a fixed fraction of the remaining configuration space. We present an application of NS at constant pressure to the phase diagram of a model binary alloy, CuAu, using an embedded atom method potential. We identify phase transitions indicated by peaks in the calculated specific heat, and the dominant phase at each temperature from ensemble-averaged structural ordering, as represented by quantities such as the radial distribution function. These results demonstrate the power of NS as a method for calculating complete phase diagrams.

  18. Direct Measurement of the Fluid Phase Diagram.

    PubMed

    Bao, Bo; Riordon, Jason; Xu, Yi; Li, Huawei; Sinton, David

    2016-07-19

    The thermodynamic phase of a fluid (liquid, vapor or supercritical) is fundamental to all chemical processes, and the critical point is particularly important for supercritical chemical extraction. Conventional phase measurement methods require hours to obtain a single datum on the pressure and temperature diagram. Here, we present the direct measurement of the full pressure-temperature phase diagram, with 10 000 microwells. Orthogonal, linear, pressure and temperature gradients are obtained with 100 parallel microchannels (spanning the pressure range), each with 100 microwells (spanning the temperature range). The phase-mapping approach is demonstrated with both a pure substance (CO2) and a mixture (95% CO2 + 5% N2). Liquid, vapor, and supercritical regions are clearly differentiated, and the critical pressure is measured at 1.2% error with respect to the NIST standard. This approach provides over 100-fold improvement in measurement speed over conventional methods. PMID:27331613

  19. Analysis of the heat capacity for pure CH4 and CH4/CCl4 on graphite near the melting point and calculation of the T-X phase diagram for (CH3)CCl3 + CCl4

    NASA Astrophysics Data System (ADS)

    Yurtseven, Hamit; Yılmaz, Aygül

    2016-06-01

    We study the temperature dependence of the heat capacity Cp for the pure CH4 and the coadsorbed CH4/CCl4 on graphite near the melting point. The heat capacity peaks are analyzed using the experimental data from the literature by means of the power-law formula. The critical exponents for the heat capacity are deduced below and above the melting point for CH4 (Tm = 104.8 K) and CH4/CCl4 (Tm = 99.2 K). Our exponent values are larger as compared with the predicted values of some theoretical models exhibiting second order transition. Our analyses indicate that the pure methane shows a nearly second order (weak discontinuity in the heat capacity peak), whereas the transition in coadsorbed CH4/CCl4 is of first order (apparent discontinuity in Cp). We also study the T – X phase diagram of a two-component system of CH3CCl3+CCl4 using the Landau phenomenological model. Phase lines of the R+L (rhombohedral+liquid) and FCC+L (face-centred cubic + liquid) are calculated using the observed T – X phase diagram of this binary mixture. Our results show that the Landau mean field theory describes the observed behavior of CH3CCl3+CCl4 adequately. From the calculated T – X phase diagram, critical behavior of some thermodynamic quantities can be predicted at various temperatures and concentrations (CCl4) for a binary mixture of CH3CCl3+CCl4.

  20. Size Dependent Phase Diagrams of Nickel-Carbon Nanoparticles

    NASA Astrophysics Data System (ADS)

    Magnin, Y.; Zappelli, A.; Amara, H.; Ducastelle, F.; Bichara, C.

    2015-11-01

    The carbon rich phase diagrams of nickel-carbon nanoparticles, relevant to catalysis and catalytic chemical vapor deposition synthesis of carbon nanotubes, are calculated for system sizes up to about 3 nm (807 Ni atoms). A tight binding model for interatomic interactions drives the grand canonical Monte Carlo simulations used to locate solid, core shell and liquid stability domains, as a function of size, temperature, and carbon chemical potential or concentration. Melting is favored by carbon incorporation from the nanoparticle surface, resulting in a strong relative lowering of the eutectic temperature and a phase diagram topology different from the bulk one. This should lead to a better understanding of the nanotube growth mechanisms.

  1. Phase diagrams of bosonic ABn chains

    NASA Astrophysics Data System (ADS)

    Cruz, G. J.; Franco, R.; Silva-Valencia, J.

    2016-04-01

    The A B N - 1 chain is a system that consists of repeating a unit cell with N sites where between the A and B sites there is an energy difference of λ. We considered bosons in these special lattices and took into account the kinetic energy, the local two-body interaction, and the inhomogenous local energy in the Hamiltonian. We found the charge density wave (CDW) and superfluid and Mott insulator phases, and constructed the phase diagram for N = 2 and 3 at the thermodynamic limit. The system exhibited insulator phases for densities ρ = α/ N, with α being an integer. We obtained that superfluid regions separate the insulator phases for densities larger than one. For any N value, we found that for integer densities ρ, the system exhibits ρ + 1 insulator phases, a Mott insulator phase, and ρ CDW phases. For non-integer densities larger than one, several CDW phases appear.

  2. Lattice dynamics and phase diagram of aluminum at high temperatures

    SciTech Connect

    Kudasov, Yu. B. Surdin, O. M.; Korshunov, A. S.; Pavlov, V. N.; Frolova, N. V.; Kuzin, R. S.

    2013-10-15

    The dispersion of phonons in the fcc, hcp, and bcc phases of aluminum is calculated at ultrahigh pressures by the method of small displacements in a supercell. The stability of the phonon subsystem is studied. The thermodynamic characteristics are calculated in the quasi-harmonic approximation, and a phase diagram of aluminum is plotted. As compared to the Debye model, the use of a phonon spectrum calculated in the quasi-harmonic approximation significantly broadens the hcp phase field and strongly shifts the phase boundary between the fcc and bcc phases. The normal isentrope is calculated at megabar pressures. It is shown to intersect the fcc-hcp and hcp-bcc phase boundaries. The sound velocity along the normal isentrope is calculated. It is shown to have a nonmonotonic character.

  3. Equations of state and phase diagrams of hydrogen isotopes

    SciTech Connect

    Urlin, V. D.

    2013-11-15

    A new form of the semiempirical equation of state proposed for the liquid phase of hydrogen isotopes is based on the assumption that its structure is formed by cells some of which contain hydrogen molecules and others contain hydrogen atoms. The values of parameters in the equations of state of the solid (molecular and atomic) phases as well as of the liquid phase of hydrogen isotopes (protium and deuterium) are determined. Phase diagrams, shock adiabats, isentropes, isotherms, and the electrical conductivity of compressed hydrogen are calculated. Comparison of the results of calculations with available experimental data in a wide pressure range demonstrates satisfactory coincidence.

  4. Toward a phase diagram for stocks

    NASA Astrophysics Data System (ADS)

    Ivanova, K.

    1999-08-01

    A display of the tentatively basic parameters of stocks, i.e. the daily closing price and the daily transaction volume is presented eliminating the time variable between them. The “phase diagram” looks like a triangular region similar to the two-phase region of traffic diagrams. The data is taken for two companies (SGP and OXHP) which present different long-range correlations in the closing price value as examined by the linearly Detrended Fluctuation Analysis (DFA) statistical method. Substructures are observed in the “phase diagram” as due to changes in management policy, e.g. stock splits.

  5. The stable and metastable Ti-Nb phase diagrams

    NASA Astrophysics Data System (ADS)

    Moffat, D. L.; Kattner, U. R.

    1988-10-01

    The phase transformations which occur in the Ti-Nb binary alloy system have been discussed in two recent papers. The phase relationships were investigated by varying alloy composition and thermal history. In this paper, these results are summarized in complete and thermodynamically consistent calculations of the stable and metastable phase diagrams. The calculations of the metastable equilibria are relevant to the Ti-V and Ti-Mo systems, as well as to several other titanium and zirconium-based transition metal alloy systems.

  6. Phase diagram of Mo at high pressure and temperature

    SciTech Connect

    Ross, M

    2008-10-01

    We report values of the Poisson Ratios for shock compressed Mo, calculated from the sound speed measurements, which provide evidence that the 210 GPa ({approx}4100K) transition cannot be a bcc-hcp transition, as originally proposed. Instead, we find the transition is from the bcc to a noncrystalline phase. For pressures above 210 GPa, the Poisson Ratio increases steadily with increasing temperature, approaching the liquid value of 0.5 at 390 GPa({approx}10,000K), suggesting the presence of a noncrystalline solid-liquid mixture. Free energy model calculations were used to show that the low melting slope of Mo, and the phase diagram, can be explained by the presence of local liquid structures. A new phase diagram is proposed for Mo that is constrained by the experimental evidence.

  7. Phase diagrams of disordered Weyl semimetals

    NASA Astrophysics Data System (ADS)

    Shapourian, Hassan; Hughes, Taylor L.

    2016-02-01

    Weyl semimetals are gapless quasitopological materials with a set of isolated nodal points forming their Fermi surface. They manifest their quasitopological character in a series of topological electromagnetic responses including the anomalous Hall effect. Here, we study the effect of disorder on Weyl semimetals while monitoring both their nodal/semimetallic and topological properties through computations of the localization length and the Hall conductivity. We examine three different lattice tight-binding models which realize the Weyl semimetal in part of their phase diagram and look for universal features that are common to all of the models, and interesting distinguishing features of each model. We present detailed phase diagrams of these models for large system sizes and we find that weak disorder preserves the nodal points up to the diffusive limit, but does affect the Hall conductivity. We show that the trend of the Hall conductivity is consistent with an effective picture in which disorder causes the Weyl nodes move within the Brillouin zone along a specific direction that depends deterministically on the properties of the model and the neighboring phases to the Weyl semimetal phase. We also uncover an unusual (nonquantized) anomalous Hall insulator phase which can only exist in the presence of disorder.

  8. Phase stabilities at a glance: Stability diagrams of nickel dipnictides

    NASA Astrophysics Data System (ADS)

    Bachhuber, F.; Rothballer, J.; Söhnel, T.; Weihrich, R.

    2013-12-01

    In the course of the recent advances in chemical structure prediction, a straightforward type of diagram to evaluate phase stabilities is presented based on an expedient example. Crystal structures and energetic stabilities of dipnictides NiPn2 (Pn = N, P, As, Sb, Bi) are systematically investigated by first principles calculations within the framework of density functional theory using the generalized gradient approximation to treat exchange and correlation. These dipnictides show remarkable polymorphism that is not yet understood systematically and offers room for the discovery of new phases. Relationships between the concerned structures including the marcasite, the pyrite, the arsenopyrite/CoSb2, and the NiAs2 types are highlighted by means of common structural fragments. Electronic stabilities of experimentally known and related AB2 structure types are presented graphically in so-called stability diagrams. Additionally, competing binary phases are taken into consideration in the diagrams to evaluate the stabilities of the title compounds with respect to decomposition. The main purpose of the stability diagrams is the introduction of an image that enables the estimation of phase stabilities at a single glance. Beyond that, some of the energetically favored structure types can be identified as potential new phases.

  9. Phase stabilities at a glance: stability diagrams of nickel dipnictides.

    PubMed

    Bachhuber, F; Rothballer, J; Söhnel, T; Weihrich, R

    2013-12-01

    In the course of the recent advances in chemical structure prediction, a straightforward type of diagram to evaluate phase stabilities is presented based on an expedient example. Crystal structures and energetic stabilities of dipnictides NiPn2 (Pn = N, P, As, Sb, Bi) are systematically investigated by first principles calculations within the framework of density functional theory using the generalized gradient approximation to treat exchange and correlation. These dipnictides show remarkable polymorphism that is not yet understood systematically and offers room for the discovery of new phases. Relationships between the concerned structures including the marcasite, the pyrite, the arsenopyrite/CoSb2, and the NiAs2 types are highlighted by means of common structural fragments. Electronic stabilities of experimentally known and related AB2 structure types are presented graphically in so-called stability diagrams. Additionally, competing binary phases are taken into consideration in the diagrams to evaluate the stabilities of the title compounds with respect to decomposition. The main purpose of the stability diagrams is the introduction of an image that enables the estimation of phase stabilities at a single glance. Beyond that, some of the energetically favored structure types can be identified as potential new phases. PMID:24320392

  10. Phase stabilities at a glance: Stability diagrams of nickel dipnictides

    SciTech Connect

    Bachhuber, F.; Rothballer, J.; Weihrich, R.; Söhnel, T.

    2013-12-07

    In the course of the recent advances in chemical structure prediction, a straightforward type of diagram to evaluate phase stabilities is presented based on an expedient example. Crystal structures and energetic stabilities of dipnictides NiPn{sub 2} (Pn = N, P, As, Sb, Bi) are systematically investigated by first principles calculations within the framework of density functional theory using the generalized gradient approximation to treat exchange and correlation. These dipnictides show remarkable polymorphism that is not yet understood systematically and offers room for the discovery of new phases. Relationships between the concerned structures including the marcasite, the pyrite, the arsenopyrite/CoSb{sub 2}, and the NiAs{sub 2} types are highlighted by means of common structural fragments. Electronic stabilities of experimentally known and related AB{sub 2} structure types are presented graphically in so-called stability diagrams. Additionally, competing binary phases are taken into consideration in the diagrams to evaluate the stabilities of the title compounds with respect to decomposition. The main purpose of the stability diagrams is the introduction of an image that enables the estimation of phase stabilities at a single glance. Beyond that, some of the energetically favored structure types can be identified as potential new phases.

  11. Phase diagram of quantum square ice

    NASA Astrophysics Data System (ADS)

    Henry, Louis-Paul; Holdsworth, Peter; Mila, Frederic; Roscilde, Tommaso

    2013-03-01

    We have investigated the ground-state and finite-temperature phase diagram of quantum square ice - realized by the transverse-field Ising model on a checkerboard lattice - using both linear spin-wave (LSW) theory and quantum Monte Carlo (QMC). We generalize the model with different couplings between nearest (J1) and next-to-nearest (J2) neighbors on the checkerboard lattice. Our QMC approach generalizes the loop algorithm - very efficient in the study of constrained classical systems - to a ``brane algorithm'' for quantum systems. At the LSW level the vast degeneracy of the ground-state for J1 =J2 and J2 >J1 remains intact; moreover LSW theory breaks down in extended regions of the phase diagram, pointing at non-classical states. Our QMC study goes beyond perturbative schemes and addresses directly the nature of the low-temperature phases. We have critically examined the possibility of a resonating-plaquette state for J1 =J2 , suggested by degenerate perturbation theory on the ice-rule manifold for weak fields. Our QMC results for finite fields confirm the absence of Néel or collinear order, but they do not confirm the presence of resonating-plaquette order, pointing at a possibly more complex non-classical state.

  12. Revisiting the phase diagram of hard ellipsoids.

    PubMed

    Odriozola, Gerardo

    2012-04-01

    In this work, the well-known Frenkel-Mulder phase diagram of hard ellipsoids of revolution [D. Frenkel and B. M. Mulder, Mol. Phys. 55, 1171 (1985)] is revisited by means of replica exchange Monte Carlo simulations. The method provides good sampling of dense systems and so, solid phases can be accessed without the need of imposing a given structure. At high densities, we found plastic solids and fcc-like crystals for semi-spherical ellipsoids (prolates and oblates), and SM2 structures [P. Pfleiderer and T. Schilling, Phys. Rev. E 75, 020402 (2007)] for x : 1-prolates and 1 : x-oblates with x ≥ 3. The revised fluid-crystal and isotropic-nematic transitions reasonably agree with those presented in the Frenkel-Mulder diagram. An interesting result is that, for small system sizes (100 particles), we obtained 2:1- and 1.5:1-prolate equations of state without transitions, while some order is developed at large densities. Furthermore, the symmetric oblate cases are also reluctant to form ordered phases. PMID:22482570

  13. Revisiting the phase diagram of hard ellipsoids

    NASA Astrophysics Data System (ADS)

    Odriozola, Gerardo

    2012-04-01

    In this work, the well-known Frenkel-Mulder phase diagram of hard ellipsoids of revolution [D. Frenkel and B. M. Mulder, Mol. Phys. 55, 1171 (1985), 10.1080/00268978500101971] is revisited by means of replica exchange Monte Carlo simulations. The method provides good sampling of dense systems and so, solid phases can be accessed without the need of imposing a given structure. At high densities, we found plastic solids and fcc-like crystals for semi-spherical ellipsoids (prolates and oblates), and SM2 structures [P. Pfleiderer and T. Schilling, Phys. Rev. E 75, 020402 (2007)] for x : 1-prolates and 1 : x-oblates with x ≥ 3. The revised fluid-crystal and isotropic-nematic transitions reasonably agree with those presented in the Frenkel-Mulder diagram. An interesting result is that, for small system sizes (100 particles), we obtained 2:1- and 1.5:1-prolate equations of state without transitions, while some order is developed at large densities. Furthermore, the symmetric oblate cases are also reluctant to form ordered phases.

  14. Reentrant Phase Diagram of Network Fluids

    NASA Astrophysics Data System (ADS)

    Russo, J.; Tavares, J. M.; Teixeira, P. I. C.; Telo da Gama, M. M.; Sciortino, F.

    2011-02-01

    We introduce a microscopic model for particles with dissimilar patches which displays an unconventional “pinched” phase diagram, similar to the one predicted by Tlusty and Safran in the context of dipolar fluids [Science 290, 1328 (2000)SCIEAS0036-807510.1126/science.290.5495.1328]. The model—based on two types of patch interactions, which account, respectively, for chaining and branching of the self-assembled networks—is studied both numerically via Monte Carlo simulations and theoretically via first-order perturbation theory. The dense phase is rich in junctions, while the less-dense phase is rich in chain ends. The model provides a reference system for a deep understanding of the competition between condensation and self-assembly into equilibrium-polymer chains.

  15. Phase diagram in the entanglement PNJL model

    NASA Astrophysics Data System (ADS)

    Friesen, A.; Kalinovsky, Y.; Toneev, V.

    2016-01-01

    Effects of the vector interaction in the Nambu-Jona-Lasinio model with Polyakov loop are studied in combination with the entanglement interaction between the quark and pure gauge sectors. We investigate the QCD phase diagram and find that the first order chiral phase transition at finite baryon chemical potentials and its critical endpoint disappear for sufficiently large values of the vector interaction constant Gv. The presence of an entanglement interaction between quark and pure gauge sectors leads to an increase of the value Gv for which the first order transition disappears. The influence of a nonzero Gv on the curvature of the crossover boundary in the T - μ plane nearby μ= 0 is also examined for both cases.

  16. The effective QCD phase diagram and the critical end point

    NASA Astrophysics Data System (ADS)

    Ayala, Alejandro; Bashir, Adnan; Cobos-Martínez, J. J.; Hernández-Ortiz, Saúl; Raya, Alfredo

    2015-08-01

    We study the QCD phase diagram on the temperature T and quark chemical potential μ plane, modeling the strong interactions with the linear sigma model coupled to quarks. The phase transition line is found from the effective potential at finite T and μ taking into account the plasma screening effects. We find the location of the critical end point (CEP) to be (μCEP /Tc, TCEP /Tc) ∼ (1.2, 0.8), where Tc is the (pseudo)critical temperature for the crossover phase transition at vanishing μ. This location lies within the region found by lattice inspired calculations. The results show that in the linear sigma model, the CEP's location in the phase diagram is expectedly determined solely through chiral symmetry breaking. The same is likely to be true for all other models which do not exhibit confinement, provided the proper treatment of the plasma infrared properties for the description of chiral symmetry restoration is implemented. Similarly, we also expect these corrections to be substantially relevant in the QCD phase diagram.

  17. Size Dependent Phase Diagrams of Nickel-Carbon Nanoparticles.

    PubMed

    Magnin, Y; Zappelli, A; Amara, H; Ducastelle, F; Bichara, C

    2015-11-13

    The carbon rich phase diagrams of nickel-carbon nanoparticles, relevant to catalysis and catalytic chemical vapor deposition synthesis of carbon nanotubes, are calculated for system sizes up to about 3 nm (807 Ni atoms). A tight binding model for interatomic interactions drives the grand canonical Monte Carlo simulations used to locate solid, core shell and liquid stability domains, as a function of size, temperature, and carbon chemical potential or concentration. Melting is favored by carbon incorporation from the nanoparticle surface, resulting in a strong relative lowering of the eutectic temperature and a phase diagram topology different from the bulk one. This should lead to a better understanding of the nanotube growth mechanisms. PMID:26613451

  18. Phase diagram of a Schelling segregation model

    NASA Astrophysics Data System (ADS)

    Gauvin, L.; Vannimenus, J.; Nadal, J.-P.

    2009-07-01

    The collective behavior in a variant of Schelling’s segregation model is characterized with methods borrowed from statistical physics, in a context where their relevance was not conspicuous. A measure of segregation based on cluster geometry is defined and several quantities analogous to those used to describe physical lattice models at equilibrium are introduced. This physical approach allows to distinguish quantitatively several regimes and to characterize the transitions between them, leading to the building of a phase diagram. Some of the transitions evoke empirical sudden ethnic turnovers. We also establish links with ‘spin-1’ models in physics. Our approach provides generic tools to analyze the dynamics of other socio-economic systems.

  19. Global Phase Diagram in Layered Organic Conductors

    NASA Astrophysics Data System (ADS)

    Chen, Yan; Guo, Yaowu

    2014-03-01

    Layered organic superconductors serve as model systems for Mott physics with geometrical frustration. The global phase diagram of such system is obtained by using Gutzwiller variational method to study a Hubbard model including a spin exchange coupling term. Five possible candidates of ground state are obtained respectively, including a spin liquid insulating state at large on-site Coulomb repulsion U and large lattice frustration t'/t, an antiferromagnetic state at large U and small t'/t , two Gossamer superconducting states at medium U with either gapless dx 2 - y 2-wave (small t'/t) or gapped d +id-wave symmetry (large t'/t) , and a metallic Fermi liquid state at small U. Moreover, we study the evolution of double occupancy number d in terms of different U and t'/t parameters mimicking the pressure effect. Our results are qualitatively consistent with main experimental results in organic superconductors. -/abstract- Billing ID: 814549 Member I

  20. Phase diagram and critical properties of Yukawa bilayers

    NASA Astrophysics Data System (ADS)

    Travěnec, Igor; Šamaj, Ladislav

    2015-08-01

    We study the ground-state Wigner bilayers of pointlike particles with Yukawa pairwise interactions, confined to the surface of two parallel hard walls at dimensionless distance η . The model involves as limiting cases the unscreened Coulomb potential and hard spheres. The phase diagram of Yukawa particles, studied numerically by Messina and Löwen [Phys. Rev. Lett. 91, 146101 (2003), 10.1103/PhysRevLett.91.146101], exhibits five different staggered phases as η varies from 0 to intermediate values. We present a lattice summation method using the generalized Misra functions which permits us to calculate the energy per particle of the phases with a precision much higher than usual in computer simulations. This allows us to address some tiny details of the phase diagram. Going from the hexagonal phase I to phase II is shown to occur at η =0 . All second-order phase transitions are proved to be of mean-field type. We also derive the asymptotic shape of critical lines close to the Coulomb and hard-spheres limits. In and close to the hard-spheres limit, the dependence of the internal parameters of the present phases on η is determined exactly.

  1. Modelling of phase diagrams of nanoalloys with complex metallic phases: application to Ni-Sn.

    PubMed

    Kroupa, A; Káňa, T; Buršík, J; Zemanová, A; Šob, M

    2015-11-14

    A method for modelling of size-dependent phase diagrams was developed by combining the semiempirical CALPHAD method and ab initio calculations of surface stresses for intermetallic phases. A novel approach was devised for the calculation of surface energy, free of systematic errors from the selection of different parameters of the software (e.g. number of the k-points) and for handling layered structures and off-stoichiometric slabs. Our approach allows the determination of complex size-dependent phase diagrams of systems with intermetallic phases, which was not possible up to now. The method was verified for the modelling of the phase diagram of the Ni-Sn system and basic comparison with rare experimental results was shown. There is reasonable agreement between the calculated and experimental results. The modelling of size-dependent phase diagrams of real systems allows the prediction of phase equilibria existing in nanosystems and possible changes in material properties. There is a need for such knowledge and the existence of reliable data for simpler systems is crucial for further application of this approach. This should motivate future experimental work. PMID:25824490

  2. Phase diagram for inertial granular flows.

    PubMed

    DeGiuli, E; McElwaine, J N; Wyart, M

    2016-07-01

    Flows of hard granular materials depend strongly on the interparticle friction coefficient μ_{p} and on the inertial number I, which characterizes proximity to the jamming transition where flow stops. Guided by numerical simulations, we derive the phase diagram of dense inertial flow of spherical particles, finding three regimes for 10^{-4}≲I≲10^{-1}: frictionless, frictional sliding, and rolling. These are distinguished by the dominant means of energy dissipation, changing from collisional to sliding friction, and back to collisional, as μ_{p} increases from zero at constant I. The three regimes differ in their kinetics and rheology; in particular, the velocity fluctuations and the stress ratio both display nonmonotonic behavior with μ_{p}, corresponding to transitions between the three regimes of flow. We rationalize the phase boundaries between these regimes, show that energy balance yields scaling relations between microscopic properties in each of them, and derive the strain scale at which particles lose memory of their velocity. For the frictional sliding regime most relevant experimentally, we find for I≥10^{-2.5} that the growth of the macroscopic friction μ(I) with I is induced by an increase of collisional dissipation. This implies in that range that μ(I)-μ(0)∼I^{1-2b}, where b≈0.2 is an exponent that characterizes both the dimensionless velocity fluctuations L∼I^{-b} and the density of sliding contacts χ∼I^{b}. PMID:27575203

  3. Phase diagram for inertial granular flows

    NASA Astrophysics Data System (ADS)

    DeGiuli, E.; McElwaine, J. N.; Wyart, M.

    2016-07-01

    Flows of hard granular materials depend strongly on the interparticle friction coefficient μp and on the inertial number I , which characterizes proximity to the jamming transition where flow stops. Guided by numerical simulations, we derive the phase diagram of dense inertial flow of spherical particles, finding three regimes for 10-4≲I ≲10-1 : frictionless, frictional sliding, and rolling. These are distinguished by the dominant means of energy dissipation, changing from collisional to sliding friction, and back to collisional, as μp increases from zero at constant I . The three regimes differ in their kinetics and rheology; in particular, the velocity fluctuations and the stress ratio both display nonmonotonic behavior with μp, corresponding to transitions between the three regimes of flow. We rationalize the phase boundaries between these regimes, show that energy balance yields scaling relations between microscopic properties in each of them, and derive the strain scale at which particles lose memory of their velocity. For the frictional sliding regime most relevant experimentally, we find for I ≥10-2.5 that the growth of the macroscopic friction μ (I ) with I is induced by an increase of collisional dissipation. This implies in that range that μ (I ) -μ (0 ) ˜I1 -2 b , where b ≈0.2 is an exponent that characterizes both the dimensionless velocity fluctuations L ˜I-b and the density of sliding contacts χ ˜Ib .

  4. Water, Water Everywhere: Phase Diagrams of Ordinary Water Substance

    ERIC Educational Resources Information Center

    Glasser, L.

    2004-01-01

    The full phase diagram of water in the form of a graphical representation of the three-dimensional (3D) PVT diagram using authentic data is presented. An interesting controversy regarding the phase behavior of water was the much-touted proposal of a solid phase of water, polywater, supposedly stable under atmospheric conditions.

  5. Cu-Zn binary phase diagram and diffusion couples

    NASA Technical Reports Server (NTRS)

    Mccoy, Robert A.

    1992-01-01

    The objectives of this paper are to learn: (1) what information a binary phase diagram can yield; (2) how to construct and heat treat a simple diffusion couple; (3) how to prepare a metallographic sample; (4) how to operate a metallograph; (5) how to correlate phases found in the diffusion couple with phases predicted by the phase diagram; (6) how diffusion couples held at various temperatures could be used to construct a phase diagram; (7) the relation between the thickness of an intermetallic phase layer and the diffusion time; and (8) the effect of one species of atoms diffusing faster than another species in a diffusion couple.

  6. Superconducting phase diagram of itinerant antiferromagnets

    NASA Astrophysics Data System (ADS)

    Rømer, A. T.; Eremin, I.; Hirschfeld, P. J.; Andersen, B. M.

    2016-05-01

    We study the phase diagram of the Hubbard model in the weak-coupling limit for coexisting spin-density-wave order and spin-fluctuation-mediated superconductivity. Both longitudinal and transverse spin fluctuations contribute significantly to the effective interaction potential, which creates Cooper pairs of the quasiparticles of the antiferromagnetic metallic state. We find a dominant dx2-y2-wave solution in both electron- and hole-doped cases. In the quasi-spin-triplet channel, the longitudinal fluctuations give rise to an effective attraction supporting a p -wave gap, but are overcome by repulsive contributions from the transverse fluctuations which disfavor p -wave pairing compared to dx2-y2. The subleading pair instability is found to be in the g -wave channel, but complex admixtures of d and g are not energetically favored since their nodal structures coincide. Inclusion of interband pairing, in which each fermion in the Cooper pair belongs to a different spin-density-wave band, is considered for a range of electron dopings in the regime of well-developed magnetic order. We demonstrate that these interband pairing gaps, which are nonzero in the magnetic state, must have the same parity under inversion as the normal intraband gaps. The self-consistent solution to the full system of five coupled gap equations gives intraband and interband pairing gaps of dx2-y2 structure and similar gap magnitude. In conclusion, the dx2-y2 gap dominates for both hole and electron doping inside the spin-density-wave phase.

  7. An Introductory Idea for Teaching Two-Component Phase Diagrams

    ERIC Educational Resources Information Center

    Peckham, Gavin D.; McNaught, Ian J.

    2011-01-01

    The teaching of two-component phase diagrams has attracted little attention in this "Journal," and it is hoped that this article will make a useful contribution. Current physical chemistry textbooks describe two-component phase diagrams adequately, but do so in a piecemeal fashion one section at a time; first solid-liquid equilibria, then…

  8. Dynamic phase diagram of soft nanocolloids.

    PubMed

    Gupta, Sudipta; Camargo, Manuel; Stellbrink, Jörg; Allgaier, Jürgen; Radulescu, Aurel; Lindner, Peter; Zaccarelli, Emanuela; Likos, Christos N; Richter, Dieter

    2015-09-01

    We present a comprehensive experimental and theoretical study covering micro-, meso- and macroscopic length and time scales, which enables us to establish a generalized view in terms of structure-property relationship and equilibrium dynamics of soft colloids. We introduce a new, tunable block copolymer model system, which allows us to vary the aggregation number, and consequently its softness, by changing the solvophobic-to-solvophilic block ratio (m : n) over two orders of magnitude. Based on a simple and general coarse-grained model of the colloidal interaction potential, we verify the significance of interaction length σint governing both structural and dynamic properties. We put forward a quantitative comparison between theory and experiment without adjustable parameters, covering a broad range of experimental polymer volume fractions (0.001 ≤ϕ≤ 0.5) and regimes from ultra-soft star-like to hard sphere-like particles, that finally results in the dynamic phase diagram of soft colloids. In particular, we find throughout the concentration domain a strong correlation between mesoscopic diffusion and macroscopic viscosity, irrespective of softness, manifested in data collapse on master curves using the interaction length σint as the only relevant parameter. A clear reentrance in the glass transition at high aggregation numbers is found, recovering the predicted hard-sphere (HS) value in the hard-sphere like limit. Finally, the excellent agreement between our new experimental systems with different but already established model systems shows the relevance of block copolymer micelles as a versatile realization of soft colloids and the general validity of a coarse-grained approach for the description of the structure and dynamics of soft colloids. PMID:26219628

  9. Phase stability in nanoscale material systems: extension from bulk phase diagrams.

    PubMed

    Bajaj, Saurabh; Haverty, Michael G; Arróyave, Raymundo; Goddard, William A; Shankar, Sadasivan

    2015-06-01

    Phase diagrams of multi-component systems are critical for the development and engineering of material alloys for all technological applications. At nano dimensions, surfaces (and interfaces) play a significant role in changing equilibrium thermodynamics and phase stability. In this work, it is shown that these surfaces at small dimensions affect the relative equilibrium thermodynamics of the different phases. The CALPHAD approach for material surfaces (also termed "nano-CALPHAD") is employed to investigate these changes in three binary systems by calculating their phase diagrams at nano dimensions and comparing them with their bulk counterparts. The surface energy contribution, which is the dominant factor in causing these changes, is evaluated using the spherical particle approximation. It is first validated with the Au-Si system for which experimental data on phase stability of spherical nano-sized particles is available, and then extended to calculate phase diagrams of similarly sized particles of Ge-Si and Al-Cu. Additionally, the surface energies of the associated compounds are calculated using DFT, and integrated into the thermodynamic model of the respective binary systems. In this work we found changes in miscibilities, reaction compositions of about 5 at%, and solubility temperatures ranging from 100-200 K for particles of sizes 5 nm, indicating the importance of phase equilibrium analysis at nano dimensions. PMID:25965301

  10. Octahedral tilting, monoclinic phase and the phase diagram of PZT

    NASA Astrophysics Data System (ADS)

    Cordero, F.; Trequattrini, F.; Craciun, F.; Galassi, C.

    2011-10-01

    Anelastic and dielectric spectroscopy measurements on PbZr1-xTixO3 (PZT) close to the morphotropic (MPB) and antiferroelectric boundaries provide new insight into some controversial aspects of its phase diagram. No evidence is found of a border separating monoclinic (M) from rhombohedral (R) phases, in agreement with recent structural studies supporting a coexistence of the two phases over a broad composition range x < 0.5, with the fraction of M increasing toward the MPB. It is also discussed why the observed maximum of elastic compliance appears to be due to a rotational instability of the polarization linearly coupled to shear strain. Therefore it cannot be explained by extrinsic softening from finely twinned R phase alone, but indicates the presence also of M phase, not necessarily homogeneous. A new diffuse transition is found within the ferroelectric phase near x ˜ 0.1, at a temperature TIT higher than the well established boundary TT to the phase with tilted octahedra. It is proposed that around TIT the octahedra start rotating in a disordered manner and finally become ordered below TT. In this interpretation, the onset temperature for octahedral tilting monotonically increases up to the antiferroelectric transition of PbZrO3, and the depression of TT(x) below x = 0.18 would be a consequence of the partial relief of the mismatch between the average cation radii with the initial stage of tilting below TIT.

  11. Using a Spreadsheet To Explore Melting, Dissolving and Phase Diagrams.

    ERIC Educational Resources Information Center

    Goodwin, Alan

    2002-01-01

    Compares phase diagrams relating to the solubilities and melting points of various substances in textbooks with those generated by a spreadsheet using data from the literature. Argues that differences between the diagrams give rise to new chemical insights. (Author/MM)

  12. Equations of State and Phase Diagrams of Ammonia

    ERIC Educational Resources Information Center

    Glasser, Leslie

    2009-01-01

    We present equations of state relating the phases and a three-dimensional phase diagram for ammonia with its solid, liquid, and vapor phases, based on fitted authentic experimental data and including recent information on the high-pressure solid phases. This presentation follows similar articles on carbon dioxide and water published in this…

  13. Temperature-field phase diagram of extreme magnetoresistance.

    PubMed

    Fallah Tafti, Fazel; Gibson, Quinn; Kushwaha, Satya; Krizan, Jason W; Haldolaarachchige, Neel; Cava, Robert Joseph

    2016-06-21

    The recent discovery of extreme magnetoresistance (XMR) in LaSb introduced lanthanum monopnictides as a new platform to study this effect in the absence of broken inversion symmetry or protected linear band crossing. In this work, we report XMR in LaBi. Through a comparative study of magnetotransport effects in LaBi and LaSb, we construct a temperature-field phase diagram with triangular shape that illustrates how a magnetic field tunes the electronic behavior in these materials. We show that the triangular phase diagram can be generalized to other topological semimetals with different crystal structures and different chemical compositions. By comparing our experimental results to band structure calculations, we suggest that XMR in LaBi and LaSb originates from a combination of compensated electron-hole pockets and a particular orbital texture on the electron pocket. Such orbital texture is likely to be a generic feature of various topological semimetals, giving rise to their small residual resistivity at zero field and subject to strong scattering induced by a magnetic field. PMID:27274081

  14. Low-pressure phase diagram of crystalline benzene from quantum Monte Carlo

    NASA Astrophysics Data System (ADS)

    Azadi, Sam; Cohen, R. E.

    2016-08-01

    We studied the low-pressure (0-10 GPa) phase diagram of crystalline benzene using quantum Monte Carlo and density functional theory (DFT) methods. We performed diffusion quantum Monte Carlo (DMC) calculations to obtain accurate static phase diagrams as benchmarks for modern van der Waals density functionals. Using density functional perturbation theory, we computed the phonon contributions to the free energies. Our DFT enthalpy-pressure phase diagrams indicate that the Pbca and P21/c structures are the most stable phases within the studied pressure range. The DMC Gibbs free-energy calculations predict that the room temperature Pbca to P21/c phase transition occurs at 2.1(1) GPa. This prediction is consistent with available experimental results at room temperature. Our DMC calculations give 50.6 ± 0.5 kJ/mol for crystalline benzene lattice energy.

  15. Calculation of the phase diagrams of ferrimagnetic alloys A cB 1- c and application to transition metal-rare-earth Fe cGd 1- c and Fe cTb 1- c materials

    NASA Astrophysics Data System (ADS)

    Fresneau, M.; Virlouvet, A.; Khater, A.

    1999-07-01

    A theoretical model is presented for the calculation of the magnetic properties of generalised spin ferrimagnetic random substitutional alloys A cB 1- c with antiferromagnetic coupling between the A and B spin species. In particular, we study in an effective field method the phase diagrams of these systems as a function of the alloy concentration c, for given magnetic exchange constants. The model is applied with no adjustable parameters to the transition metal-rare-earth Fe cGd 1- c and Fe cTb 1- c alloys, using the appropriate spins for the Fe, Gd and Tb ions. We report a coherent and an overall qualitative agreement between theory and experiment in the complete range of concentrations 1⩾ c⩾0, for the first time to our knowledge, and determine consequently for these materials a set of ionic exchange constants that are invariant with respect to the alloy concentration. To our knowledge this is the first time that approximate but seemingly reliable exchange constants for the two alloys have been derived.

  16. Water Mediated Interactions and the Protein Folding Phase Diagram in the Temperature-Pressure Plane.

    PubMed

    Sirovetz, Brian J; Schafer, Nicholas P; Wolynes, Peter G

    2015-08-27

    The temperature-pressure behavior of two proteins, ubiquitin and λ-repressor, is explored using a realistically coarse-grained physicochemical model, the associative memory, water mediated, structure and energy model (AWSEM). The phase diagram across the temperature-pressure plane is obtained by perturbing the water mediated interactions in the Hamiltonian systematically. The phase diagrams calculated with direct simulations along with an extended bridge sampling estimator show the main features found experimentally, including both cold- and pressure-denaturation. The denatured ensembles in different parts of the phase diagram are characterized and found to be structurally distinct. The protein energy landscape is found to be funneled throughout the phase diagram, but modest changes in the entropy and free energy of the water are found to drive both cold and pressure induced denaturation. PMID:26102155

  17. Phase diagram studies on the Na-Mo-O system

    NASA Astrophysics Data System (ADS)

    Gnanasekaran, T.; Mahendran, K. H.; Kutty, K. V. G.; Mathews, C. K.

    1989-06-01

    The phase diagram of the Na-Mo-O ternary system is of interest in interpreting the behaviour of structural materials in the sodium circuits of fast breeder reactors and sodium-filled heat pipes. Experiments involving heating of sodium oxide with molybdenum metal under vacuum, selective removal of oxygen from polymolybdates by reducing them under hydrogen and confirmation of the coexistence of various phase mixtures were conducted in the temperature range of 673 to 923 K. Phase fields involving molybdenum metal, dioxide of molybdenum and ternary compounds were derived from these results. The ternary phase diagram of the Na-Mo-O system was constructed and isothermal cross sections of the phase diagram are presented.

  18. Phase diagram of the three-dimensional axial next-nearest-neighbor Ising model

    NASA Astrophysics Data System (ADS)

    Gendiar, A.; Nishino, T.

    2005-01-01

    The three-dimensional axial next-nearest-neighbor Ising model is studied by a modified tensor product variational approach. A global phase diagram is constructed with numerous commensurate and incommensurate magnetic phases. The devil’s stairs behavior for the model is confirmed. The wavelength of the spin modulated phases increases to infinity at the boundary with the ferromagnetic phase. Widths of the commensurate phases are considerably narrower than those calculated by mean-field approximations.

  19. Entanglement interaction and the phase diagram of strongly interacting matter

    NASA Astrophysics Data System (ADS)

    Shao, G. Y.; Tang, Z. D.; Di Toro, M.; Colonna, M.; Gao, X. Y.; Gao, N.; Zhao, Y. L.

    2015-12-01

    The entanglement interactions between the Polyakov loop and chiral condensate have been recently studied in the entangled Polyakov-loop Nambu-Jona-Lasinio model (EPNJL). The calculation shows that such an interaction plays an important role in the pseudocritical temperatures of deconfinement and chiral symmetry restoration. As a further study, here we construct a hadron-quark two-equation-of-state (two-EoS) model, based on the Walecka-quantum hadrodynamics and the EPNJL pictures, in order to study the equilibrium transition between hadronic and quark matter in heavy-ion collisions at finite densities and temperatures. We can explore the phase diagram of strongly interacting matter and the transition boundaries from nuclear to quark matter. We discuss the influence of the entanglement interaction on the critical point of the expected first-order phase transition in the two-EoS model. In particular, for charge asymmetric matter, we analyze the local asymmetry of the u , d quarks as a function of quark concentration in the hadron-quark mixed phase during the phase transition. We finally propose some related observables that are possibly measurable in heavy-ion collision experiments.

  20. Phase stability in nanoscale material systems: extension from bulk phase diagrams

    NASA Astrophysics Data System (ADS)

    Bajaj, Saurabh; Haverty, Michael G.; Arróyave, Raymundo; Goddard Frsc, William A., III; Shankar, Sadasivan

    2015-05-01

    Phase diagrams of multi-component systems are critical for the development and engineering of material alloys for all technological applications. At nano dimensions, surfaces (and interfaces) play a significant role in changing equilibrium thermodynamics and phase stability. In this work, it is shown that these surfaces at small dimensions affect the relative equilibrium thermodynamics of the different phases. The CALPHAD approach for material surfaces (also termed ``nano-CALPHAD'') is employed to investigate these changes in three binary systems by calculating their phase diagrams at nano dimensions and comparing them with their bulk counterparts. The surface energy contribution, which is the dominant factor in causing these changes, is evaluated using the spherical particle approximation. It is first validated with the Au-Si system for which experimental data on phase stability of spherical nano-sized particles is available, and then extended to calculate phase diagrams of similarly sized particles of Ge-Si and Al-Cu. Additionally, the surface energies of the associated compounds are calculated using DFT, and integrated into the thermodynamic model of the respective binary systems. In this work we found changes in miscibilities, reaction compositions of about 5 at%, and solubility temperatures ranging from 100-200 K for particles of sizes 5 nm, indicating the importance of phase equilibrium analysis at nano dimensions.Phase diagrams of multi-component systems are critical for the development and engineering of material alloys for all technological applications. At nano dimensions, surfaces (and interfaces) play a significant role in changing equilibrium thermodynamics and phase stability. In this work, it is shown that these surfaces at small dimensions affect the relative equilibrium thermodynamics of the different phases. The CALPHAD approach for material surfaces (also termed ``nano-CALPHAD'') is employed to investigate these changes in three binary systems by

  1. Sphingomyelin/Phosphatidylcholine/Cholesterol Phase Diagram: Boundaries and Composition of Lipid Rafts

    PubMed Central

    de Almeida, Rodrigo F. M.; Fedorov, Aleksandre; Prieto, Manuel

    2003-01-01

    The ternary system palmitoylsphingomyelin (PSM)/palmitoyloleoylphosphatidylcholine (POPC)/cholesterol is used to model lipid rafts. The phase behavior of the three binary systems PSM/POPC, PSM/cholesterol, and POPC/cholesterol is first experimentally determined. Phase coexistence boundaries are then determined for ternary mixtures at room temperature (23°C) and the ternary phase diagram at that temperature is obtained. From the diagram at 23°C and the binary phase diagrams, a reasonable expectation is drawn for the ternary phase diagram at 37°C. Several photophysical methodologies are employed that do not involve detergent extraction, in addition to literature data (e.g., differential scanning calorimetry) and thermodynamic rules. For the ternary phase diagrams, some tie-lines are calculated, including the one that contains the PSM/POPC/ cholesterol 1:1:1 mixture, which is often used in model raft studies. The diagrams here described are used to rationalize literature results, some of them apparently discrepant, and to discuss lipid rafts within the framework of liquid-ordered/liquid-disordered phase coexistence. PMID:14507704

  2. Short-range order and phase diagram of a three-dimensional granular superconductor

    SciTech Connect

    Fazio, R.; Giaquinta, G.

    1986-10-01

    The phase diagram of a three-dimensional granular superconductor is explored by calculation of the charge-charge correlation function in the Oguchi approximation. A charge-fluctuation--dominated regime is found, not previously accounted for into the literature. The relevance of phase and/or charge fluctuations is discussed.

  3. Thermodynamic modeling of the UO2-ThO2 phase diagram

    NASA Astrophysics Data System (ADS)

    Kim, Jinwon; Kim, Sung S.

    2016-02-01

    The phase diagram in the UO2-ThO2 system has been assessed by thermodynamic modeling with existing data from the literature. The subregular solution model was used to represent the Gibbs free energies of the liquid and the solid phases. By considering the liquidus, solidus and miscibility gap data, the interaction parameters of the liquid and the solid phases were optimized through a multiple linear regression method. A consistent set of interaction parameters were derived for describing the miscibility gap as well as the liquidus/solidus. The phase diagram calculated in the present work is in good agreement with experimental data in the literature.

  4. Phase diagrams for the blue phases of highly chiral liquid crystals

    NASA Astrophysics Data System (ADS)

    Bowling, Miriam B.; Collings, Peter J.; Booth, Christopher J.; Goodby, John W.

    1993-11-01

    Polarizing microscopy and optical-activity measurements are used to determine the phase diagram for the blue phases of chiral-racemic mixtures of terephthaloyloxy-bis-4-(2'-methylbutyl) benzoate. Contrary to an earlier report, it is the second blue phase (BP II) rather than the first blue phase (BP I) that is not stable relative to the other blue phases at high chirality. With this development, all phase diagrams for the blue phases reported to date have the same topology. Using similar data for two other highly chiral systems, it is found that a simple scaling of the temperature and chiral-fraction axes produces phase diagrams in quantitative agreement with the present results. Thus, in spite of differences in molecular structure, the number of chiral centers, and phase-transition temperatures, these three systems possess remarkably similar phase diagrams and lend evidence for a universal phase diagram for the blue phases.

  5. Stability of metal/GaAs-lnterfaces: A phase diagram survey

    NASA Astrophysics Data System (ADS)

    Schmid-Fetzer, Rainer

    1988-03-01

    Calculated phase diagrams of ternary Ga-As-metal systems for the metals Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Re, Os, Rh, Ir, Ni, Pd, Pt, Cu, Ag and Au are presented. The predictive calculations are based on the following simplifications: Ternary phases and solid solubilities are disregarded and the Gibbs energy of formation of binary compounds is estimated by the enthalpy of formation and calculated from Miedema’s model. The predicted diagrams agree surprisingly well with experimental data and they may be useful for the many cases where data are lacking or fragmentary. The phase diagrams and the thermodynamic data are shown to be a powerful tool for the understanding of interface reactions of metallic contacts to GaAs and hence for the development of improved contact materials.

  6. Phase diagram of the disordered Bose-Hubbard model

    SciTech Connect

    Gurarie, V.; Pollet, L.; Prokof'ev, N. V.; Svistunov, B. V.; Troyer, M.

    2009-12-01

    We establish the phase diagram of the disordered three-dimensional Bose-Hubbard model at unity filling which has been controversial for many years. The theorem of inclusions, proven by Pollet et al. [Phys. Rev. Lett. 103, 140402 (2009)] states that the Bose-glass phase always intervenes between the Mott insulating and superfluid phases. Here, we note that assumptions on which the theorem is based exclude phase transitions between gapped (Mott insulator) and gapless phases (Bose glass). The apparent paradox is resolved through a unique mechanism: such transitions have to be of the Griffiths type when the vanishing of the gap at the critical point is due to a zero concentration of rare regions where extreme fluctuations of disorder mimic a regular gapless system. An exactly solvable random transverse field Ising model in one dimension is used to illustrate the point. A highly nontrivial overall shape of the phase diagram is revealed with the worm algorithm. The phase diagram features a long superfluid finger at strong disorder and on-site interaction. Moreover, bosonic superfluidity is extremely robust against disorder in a broad range of interaction parameters; it persists in random potentials nearly 50 ({exclamation_point}) times larger than the particle half-bandwidth. Finally, we comment on the feasibility of obtaining this phase diagram in cold-atom experiments, which work with trapped systems at finite temperature.

  7. Bi-phase transition diagrams of metallic thin multilayers

    SciTech Connect

    Li, J.C.; Liu, W.; Jiang, Q. . E-mail: jiangq@jlu.edu.cn

    2005-02-01

    Phase transitions of metallic multilayers induced by differences in interface energy are considered thermodynamically, based on a thermodynamic model for interface energy and the Goldschmidt premise for lattice contraction. Bi-phase transition diagrams of Co/Cr, Zr/Nb, Ti/Nb and Ti/Al multilayers are constructed, which are in agreement with experimental results.

  8. On the phase diagram of 2d Lorentzian Quantum Gravity

    NASA Astrophysics Data System (ADS)

    Ambjørn, Jan; Anagnostopoulos, K. N.; Loll, R.

    The phase diagram of 2d Lorentzian quantum gravity (LQG) coupled to conformal matter is studied. A phase transition is observed at c = c crit ( {1}/{2} < c crit < 4) which can be thought of as the analogue of the c = 1 barrier of Euclidean quantum gravity (EQG). The non-trivial properties of the quantum geometry are discussed.

  9. Stripes and phase diagram of d-p model

    NASA Astrophysics Data System (ADS)

    Yanagisawa, T.; Koike, S.; Yamaji, K.

    2001-02-01

    We study the ground state of the two-dimensional d-p model in the oxide superconductors by using the variational Monte Carlo method. We employ the Gutzwiller-projected BCS and SDW wave functions in search for possible ground states with respect to dependence on parameters included in the d-p model. Near half-filling the strong antiferromagnetic correlations exist and the SDW phase extends up to 20 percent doping. It is shown that the d-wave state is possible away from half-filling for both the hole and electron doping cases. Overall structure of the phase diagram obtained by our calculations coincides with experimental indications. The superconducting condensation energy agrees well with the experimental value obtained from specific heat and critical magnetic field measurements. A possibility of stripe phase is also examined by using the SDW wave functions with incommensurate spin structures. The distance between stripes depends on the hole concentration in the underdoped region. We show that a stability of the stripe state is dependent on the transfer parameter tpp between oxygen sites.

  10. Phase diagram of the lattice superconductor

    SciTech Connect

    Shenoy, S.R.; Gupte, N.

    1988-08-01

    In a mean-field approximation the phase transition of a lattice superconductor is understood in terms of an orientation of its topological excitations (vortex loops and magnetic field loops). The loops are obtained through a duality transformation of the original variables. The phase boundary T/sub c/(e/sup 2/,b/sup -1/) is found as a function of the charge e and a Ginzburg-Landau quartic term coefficient b. Second-order behavior is found for a region b>b/sub c/(e/sup 2/) and a tricritical point with first-order behavior appears for bphase boundary T/sub HLM/(e/sup 2/,b/sup -1/)>T/sub c/(e/sup 2/, b/sup -1/) is also found, consistent with the early continuum results of Halperin, Lubensky, and Ma (HLM). T/sub HLM/(e/sup 2/,b/sup -1/) is associated with ordering within a superconducting grain, while T/sub c/(e/sup 2/,b/sup -1/) involves phase locking between grains.

  11. Phase diagrams: a graphical representation of linkage relations.

    PubMed

    Rösgen, Jörg; Hinz, Hans-Jürgen

    2003-04-18

    It is shown here that phase diagrams of ligand-binding biological macromolecules provide a powerful tool for the analysis of reaction mechanisms. The present study provides simple rules for the construction and interpretation of such phase diagrams. We give examples for the derivation of reaction schemes for macromolecules that can bind two different kinds of ligands. By sampling one dimension of a phase diagram it is possible to reconstruct the second dimension, including the correct stoichiometry, positive and negative linkage between the ligands and equilibrium binding constants for the complete series of reactions. The discussion is generalised to temperature and pressure-dependent phase diagrams. To exemplify the new diagram method we analyse the pH-dependent binding of trans-beta-indole acrylic acid to apo-Trp repressor, the pH-dependent thermal denaturation of alpha-chymotrypsinogen A, calcium binding and denaturation of annexin I, high affinity zinc binding to a metallo-beta-lactamase and high-pressure and temperature denaturation of RNase A and staphylococcal nuclease. PMID:12684012

  12. A redetermination of the succinonitrile-water phase diagram

    NASA Technical Reports Server (NTRS)

    Smith, J. E., Jr.; Frazier, D. O.; Kaukler, W. F.

    1984-01-01

    The phase diagram of the water/succinonitrile system often used in modeling binary metallic alloys is determined experimentally using a laser scattering method. Triply distilled and zone-refined succinonitrile is placed in a jacketed water-cooled vessel with a magnetic mixer and a copper-constantan thermocouple, and the melting point is determined under vacuum and under Ar by observing the response of a photodiode placed opposite a laser source as the chamber is cooled and reheated. Then water is added, and the eutectic and monotectic temperatures and the entire phase diagram are determined under Ar. The results are presented in a table and graph and compared to those of Schreinemakers (1897): significant discrepancies are noted and attributed to impurities in the succinonitrile used by Schreinemakers. The importance of accurate phase diagrams for modeling binary alloys is stressed.

  13. The Phase Diagram of Crystalline Surfaces

    NASA Astrophysics Data System (ADS)

    Anagnostopoulos, K.; Bowick, M. J.; Catterall, S. M.; Falcioni, M.; Thorleifsson, G.

    1996-03-01

    We report the status of a high-statistics Monte Carlo simulation of non-self-avoiding crystalline surfaces with extrinsic curvature on lattices of size up to 128 2 nodes. We impose free boundary conditions. The free energy is a gaussian spring tethering potential together with a normal-normal bending energy. Particular emphasis is given to the behavior of the model in the cold phase where we measure the decay of the normal-normal correlation function.

  14. Phase diagram of two interacting helical states

    NASA Astrophysics Data System (ADS)

    Santos, Raul A.; Gutman, D. B.; Carr, Sam T.

    2016-06-01

    We consider two coupled time-reversal-invariant helical edge modes of the same helicity, such as would occur on two stacked quantum spin Hall insulators. In the presence of interaction, the low-energy physics is described by two collective modes, one corresponding to the total current flowing around the edge and the other one describing relative fluctuations between the two edges. We find that quite generically, the relative mode becomes gapped at low temperatures, but only when tunneling between the two helical modes is nonzero. There are two distinct possibilities for the gapped state depending on the relative size of different interactions. If the intraedge interaction is stronger than the interedge interaction, the state is characterized as a spin-nematic phase. However, in the opposite limit, when the interaction between the helical edge modes is strong compared to the interaction within each mode, a spin-density wave forms, with emergent topological properties. First, the gap protects the conducting phase against localization by weak nonmagnetic impurities; second, the protected phase hosts localized zero modes on the ends of the edge that may be created by sufficiently strong nonmagnetic impurities.

  15. Phase diagram of softly repulsive systems: the Gaussian and inverse-power-law potentials.

    PubMed

    Prestipino, Santi; Saija, Franz; Giaquinta, Paolo V

    2005-10-01

    We redraw, using state-of-the-art methods for free-energy calculations, the phase diagrams of two reference models for the liquid state: the Gaussian and inverse-power-law repulsive potentials. Notwithstanding the different behaviors of the two potentials for vanishing interparticle distances, their thermodynamic properties are similar in a range of densities and temperatures, being ruled by the competition between the body-centered-cubic (bcc) and face-centered-cubic (fcc) crystalline structures and the fluid phase. We confirm the existence of a reentrant bcc phase in the phase diagram of the Gaussian-core model, just above the triple point. We also trace the bcc-fcc coexistence line of the inverse-power-law model as a function of the power exponent n and relate the common features in the phase diagrams of such systems to the softness degree of the interaction. PMID:16238377

  16. Phase diagram of the Gaussian-core model.

    PubMed

    Prestipino, Santi; Saija, Franz; Giaquinta, Paolo V

    2005-05-01

    We trace with high numerical accuracy the phase diagram of the Gaussian-core model, a classical system of point particles interacting via a Gaussian-shaped, purely repulsive potential. This model, which provides a reliable qualitative description of the thermal behavior of interpenetrable globular polymers, is known to exhibit a polymorphic fcc-bcc transition at low densities and reentrant melting at high densities. Extensive Monte Carlo simulations, carried out in conjunction with accurate calculations of the solid free energies, lead to a thermodynamic scenario that is partially modified with respect to previous knowledge. In particular, we find that: (i) the fluid-bcc-fcc triple-point temperature is about one third of the maximum freezing temperature; (ii) upon isothermal compression, the model exhibits a fluid-bcc-fcc-bcc-fluid sequence of phases in a narrow range of temperatures just above the triple point. We discuss these results in relation to the behavior of star-polymer solutions and of other softly repulsive systems. PMID:16089510

  17. Phase diagram of a model of the protein amelogenin.

    PubMed

    Haaga, Jason; Pemberton, Elizabeth; Gunton, J D; Rickman, J M

    2016-08-28

    There has been considerable recent interest in the self-assembly and phase behavior of models of colloidal and protein particles with anisotropic interactions. One example of particular interest is amelogenin, an important protein involved in the formation of dental enamel. Amelogenin is primarily hydrophobic with a 25-residue charged C-terminus tail. This protein undergoes a hierarchical assembly process that is crucial to mineral deposition, and experimental work has demonstrated that the deletion of the C-terminus tail prevents this self-assembly. A simplified model of amelogenin has been proposed in which the protein is treated as a hydrophobic sphere, interacting via the Asakura-Oosawa (AO) potential, with a tethered point charge on its surface. In this paper, we examine the effect of the Coulomb interaction between the point charges in altering the phase diagram of the AO model. For the parameter case specific to amelogenin, we find that the previous in vitro experimental and model conditions correspond to the system being near the low-density edge of the metastable region of the phase diagram. Our study illustrates more generally the importance of understanding the phase diagram for proteins, in that the kinetic pathway for self-assembly and the resulting aggregate morphology depends on the location of the initial state in the phase diagram. PMID:27586954

  18. Phase shifts of the paired wings of butterfly diagrams

    NASA Astrophysics Data System (ADS)

    Li, Ke-Jun; Liang, Hong-Fei; Feng, Wen

    2010-11-01

    Sunspot groups observed by the Royal Greenwich Observatory/US Air Force/NOAA from 1874 May to 2008 November and the Carte Synoptique solar filaments from 1919 March to 1989 December are used to investigate the relative phase shift of the paired wings of butterfly diagrams of sunspot and filament activities. Latitudinal migration of sunspot groups (or filaments) does asynchronously occur in the northern and southern hemispheres, and there is a relative phase shift between the paired wings of their butterfly diagrams in a cycle, making the paired wings spatially asymmetrical on the solar equator. It is inferred that hemispherical solar activity strength should evolve in a similar way within the paired wings of a butterfly diagram in a cycle, demonstrating the paired wings phenomenon and showing the phase relationship between the northern and southern hemispherical solar activity strengths, as well as a relative phase shift between the paired wings of a butterfly diagram, which should bring about almost the same relative phase shift of hemispheric solar activity strength.

  19. Phase diagram of compressively strained nickelate thin films

    SciTech Connect

    Disa, Ankit S; Kumah, D.; Ngai, J H; Specht, Eliot D; Arena, D.A.; Walker, Frederick J.; Ahn, Charles H.

    2013-01-01

    The complex phase diagrams of strongly correlated oxides arise from the coupling between physical and electronic structure. This can lead to a renormalization of the phase boundaries when considering thin films rather than bulk crystals due to reduced dimensionality and epitaxial strain. The well-established bulk RNiO3 phase diagram shows a systematic dependence between the metal-insulator transition and the perovskite A-site rare-earth ion, R. Here, we explore the equivalent phase diagram for nickelate thin films under compressive epitaxial strain. We determine the metalinsulator phase diagram for the solid solution of Nd1-yLayNiO3 thin films within the range 0 y 1. We find qualitative similarity between the films and their bulk analogs, but with an overall renormalization in the metal-insulator transition to lower temperature. A combination of x-ray diffraction measurements and soft x-ray absorption spectroscopy indicates that the renormalization is due to increased Ni O bond hybridization for coherently strained thin films.

  20. Phase Diagram of the Bose Hubbard Model with Weak Links

    NASA Astrophysics Data System (ADS)

    Hettiarachchilage, Kalani; Rousseau, Valy; Tam, Ka-Ming; Moreno, Juana; Jarrell, Mark; Sheehy, Daniel

    2012-02-01

    We study the ground state phase diagram of strongly interacting ultracold Bose gas in a one-dimensional optical lattice with a tunable weak link, by means of Quantum Monte Carlo simulation. This model contains an on-site repulsive interaction (U) and two different near-neighbor hopping terms, J and t, for the weak link and the remainder of the chain, respectively. We show that by reducing the strength of J, a novel intermediate phase develops which is compressible and non-superfluid. This novel phase is identified as a Normal Bose Liquid (NBL) which does not appear in the phase diagram of the homogeneous bosonic Hubbard model. Further, we find a linear variation of the phase boundary of Normal Bose Liquid (NBL) to SuperFluid (SF) as a function of the strength of the weak link. These results may provide a new path to design advanced atomtronic devices in the future.

  1. Phase diagram of the two-dimensional extended Hubbard model

    NASA Astrophysics Data System (ADS)

    Onari, Seiichiro; Arita, Ryotaro; Aoki, Hideo; Kuroki, Kazuhiko

    2004-03-01

    In order to explore how superconductivity arises when charge fluctuations and spin fluctuations coexist, we have obtained a phase diagram against the off-site repulsion V and charge density n for the extended, repulsive Hubbard model on the square lattice with the fluctuation exchange approximation. We have found the existence of (i) a quantum phase transition between d_xy and d_x^2-y^2 pairing symmetries, (ii) f-pairing phase in between the d_x^2-y^2 and CDW phases for intermediate 0.5phase diagram". All these are consequences of the structure in the charge and spin susceptibilities, which can have peaks habitating at common or segregated positions in k space.

  2. Phase Diagrams and Electronic Structure of II-VI Alloys

    NASA Astrophysics Data System (ADS)

    de Gironcoli, Stefano

    1998-03-01

    Among II-VI wide-gap semiconductor solid solutions, Zn_xMg_1-xS_ySe_1-y alloy is the most studied for its potential applications in the blue-green light-emitter technology. In spite of this enormous technological interest little is known about its fundamental thermodynamical and structural properties. In this work the structural and thermodynamical properties of the Zn_xMg_1-xS_ySe_1-y solid solutions are determined by a combination of the computational alchemy (S. de Gironcoli, P. Giannozzi, and S. Baroni, Phys. Rev. Lett. 66), 2116 (1991); N. Marzari, S. de Gironcoli, and S. Baroni, Phys. Rev. Lett. 72, 4001 (1994). and the cluster expansion (S.-H. Wei, L. G. Ferreira, and A. Zunger, Phys. Rev. B 41), 8240 (1990). methods with Monte Carlo simulations. We determine the phase diagram of the alloy and show that the system is completely mixible at the tipical growth temperatures and phase separates at lower temperatures into two or three phases. The homogeneous phase is characterized by a large amount of short-range order occurring among first-nearest neighbors. Electronic-structure calculations, performed extending the special quasi-random structures approach (A. Zunger, S.-H. Wei, L. G. Ferreira, and J. E. Bernard, Phys. Rev. Lett. 65), 353 (1990). to the quaternary alloy case, indicate that the energy gap of the alloy is rather sensitive to this short-range order.

  3. Using Nuclear Magnetic Resonance Spectroscopy for Measuring Ternary Phase Diagrams

    ERIC Educational Resources Information Center

    Woodworth, Jennifer K.; Terrance, Jacob C.; Hoffmann, Markus M.

    2006-01-01

    A laboratory experiment is presented for the upper-level undergraduate physical chemistry curriculum in which the ternary phase diagram of water, 1-propanol and n-heptane is measured using proton nuclear magnetic resonance (NMR) spectroscopy. The experiment builds upon basic concepts of NMR spectral analysis, typically taught in the undergraduate…

  4. Computer-Generated Phase Diagrams for Binary Mixtures.

    ERIC Educational Resources Information Center

    Jolls, Kenneth R.; And Others

    1983-01-01

    Computer programs that generate projections of thermodynamic phase surfaces through computer graphics were used to produce diagrams representing properties of water and steam and the pressure-volume-temperature behavior of most of the common equations of state. The program, program options emphasizing thermodynamic features of interest, and…

  5. Phase diagram and thermal properties of strong-interaction matter

    NASA Astrophysics Data System (ADS)

    Gao, Fei; Chen, Jing; Liu, Yu-Xin; Qin, Si-Xue; Roberts, Craig D.; Schmidt, Sebastian M.

    2016-05-01

    We introduce a novel method for computing the (μ , T )-dependent pressure in continuum QCD, from which we obtain a complex phase diagram and predictions for thermal properties of the dressed-quark component of the system, providing the in-medium behavior of the related trace anomaly, speed of sound, latent heat, and heat capacity.

  6. Zero and finite temperature phase diagram of the spinless fermion model in infinite dimensions

    NASA Astrophysics Data System (ADS)

    Uhrig, G. S.; Vlaming, R.

    The phase diagram of the model of spinless fermions with repulsive nearest neighbour interaction is calculated analytically on a hypercubic lattice in infinite dimensions (d ). In spite of its simplicity the model displays a rich phase diagram depending on the doping , the interaction U and the temperature T. The system can be in the homogeneous phase (HOM), the nonsegregated AB charge density wave (AB-CDW), the AB phase separation region (PS-AB/HOM; coexistence of AB-CDW and HOM), the incommensurate phase (IP) or the IP phase separation region (PS-AB/IP; coexistence of AB-CDW and IP). We identify three important values of the interaction UIPL = 0.572 < UIPH = 1.914 < UIP/PS = 4.212 which distinguish four intervals of U. These imply four different types of phase diagrams. In all the three phase diagrams with U below UIP/PS the IP appears. We propose a new general ansatz for the order parameter of this phase. A competition between the IP, the PS-AB/IP and the PS-AB/HOM is found. The relevance of our findings for the phase scenario of the Hubbard model is shown.

  7. Molecular Complexation and Phase Diagrams of Urea/PEG Mixtures

    NASA Astrophysics Data System (ADS)

    Fu, Guoepeng; Kyu, Thein

    2014-03-01

    Polyethylene glycol (PEG) and urea complexation has been known to form a stable crystal due to molecular complexation. The effect of molecular weight of PEG on the phase diagrams of its blends with urea has been explored. In the case of high molecular weight PEG8k/urea, the observed phase diagram is azeotrope, accompanied by eutectoid reactions in the submerged phases such as induced stable ``alpha'' phase crystals and metastable ``beta'' phase crystals. The metastable crystal can transform to stable crystal under a certain thermal annealing condition. However, the phase diagram of PEG1k/urea is of coexistence loop, whereas PEG400/urea exhibits eutectic character. Subsequently, the change of azeotrope to eutectic behavior with PEG molecular weight is analyzed in the context of the combined Flory-Huggins theory of liquid-liquid demixing and phase field theory of crystal solidification. Of particular interest is that only a very small urea amount (2 wt%) is needed to form a stable inclusion crystal via complexation with PEG. Potential application in lithium battery is discussed based on AC impedance spectroscopy and cyclic voltammetry. Supported by NSF-DMR 1161070.

  8. Determination of the quaternary phase diagram of the water-ethylene glycol-sucrose-NaCl system and a comparison between two theoretical methods for synthetic phase diagrams

    PubMed Central

    Han, Xu; Liu, Yang; Critser, John K.

    2010-01-01

    Characterization of the thermodynamic properties of multi-solute aqueous solutions is of critical importance for biological and biochemical research. For example, the phase diagrams of aqueous systems, containing salts, saccharides, and plasma membrane permeating solutes, are indispensible in the field of cryobiology and pharmacology. However, only a few ternary phase diagrams are currently available for these systems. In this study, an auto-sampler differential scanning calorimeter (DSC) was used to determine the quaternary phase diagram of the water-ethylene glycol-sucrose-NaCl system. To improve the accuracy of melting point measurement, a “mass redemption” method was also applied for the DSC technique. Base on the analyses of these experimental data, a comparison was made between the two practical approaches to generate phase diagrams of multi-solute solutions from those of single-solute solutions: the summation of cubic polynomial melting point equations versus the use of osmotic virial equations with cross coefficients. The calculated values of the model standard deviations suggested that both methods are satisfactory for characterizing this quaternary system. PMID:20447385

  9. Phase Diagrams of Electrostatically Self-Assembled Amphiplexes

    SciTech Connect

    V Stanic; M Mancuso; W Wong; E DiMasi; H Strey

    2011-12-31

    We present the phase diagrams of electrostatically self-assembled amphiplexes (ESA) comprised of poly(acrylic acid) (PAA), cetyltrimethylammonium chloride (CTACl), dodecane, pentanol, and water at three different NaCl salt concentrations: 100, 300, and 500 mM. This is the first report of phase diagrams for these quinary complexes. Adding a cosurfactant, we were able to swell the unit cell size of all long-range ordered phases (lamellar, hexagonal, Pm3n, Ia3d) by almost a factor of 2. The added advantage of tuning the unit cell size makes such complexes (especially the bicontinuous phases) attractive for applications in bioseparation, drug delivery, and possibly in oil recovery.

  10. Protein phase diagrams: The physics behind their elliptic shape

    NASA Astrophysics Data System (ADS)

    Lesch, Harald; Hecht, Christoph; Friedrich, Josef

    2004-12-01

    We relate the condition for the elliptic shape of the phase diagram of proteins to the degree of correlation in the fluctuations of the changes of enthalpy and volume at the denaturing-refolding transition. Since this degree cannot be larger than 1, hyperbolically shaped diagrams are not likely to exist. Experiments show that the correlation factor is actually quite low for proteins implying that one-order parameter is not enough to describe the folding-denaturing transition. These findings seem to be the thermodynamic manifestation of the glasslike properties of proteins despite the fact that the transition itself is of first order.

  11. Alloy Phase Diagrams for III-P Semiconductor Crystal Growth

    NASA Astrophysics Data System (ADS)

    Gennett, Adam

    and error experimentation to determine said condition would be time consuming and costly. To reduce the amount of experimentation that must be done equilibrium phase diagram are constructed using the CALPHAD method. Calculations are performed using Gibbs free energy minimization software commercially available from Thermo-Calc Software, Inc., and databases containing thermochemical data on binary III-V material systems. Diagrams were calculated for temperatures between 530 °C and 1475 °C, thus providing coverage of the entire temperature range where both a segregated liquid and solid phase exist and liquid phase solution growth is possible. Data from these phase diagrams were used to establish conditions of temperature and melt composition for growth of any solid composition of GaxIn1-xP, as well as theoretical Scheil solidification profiles for various starting charge compositions. Additionally, equilibrium phase data was used to create models for rates at which the depleted phosphide components (GaP and InP) must be replenished in the melt solution in order to grow bulk crystals of uniform axial compositions. It was also determined from the Scheil solidification curves that it is theoretically possible for self-grading of the solid composition to occur followed by growth of a solid with uniform axial composition simply by cooling a system with sufficiently high atom fractions of phosphorus and sufficiently low atom fractions of gallium. Experiments were carried out to test conditions for growth given by the phase diagrams, as well as validate the Scheil solidification profiles and the possibility of compositional grading to high-GaP compositions through feed of GaP. Growth of different GaxIn1-xP compositions from this melt and compositional grading toward high-GaP compositions was demonstrated to feasible. In addition, the extent of the solubility of GaP and InP as well as their low diffusion rates in InSb was demonstrated. Finally, high sensitivity of the solid

  12. CALCULATING ASTEROSEISMIC DIAGRAMS FOR SOLAR-LIKE OSCILLATIONS

    SciTech Connect

    White, Timothy R.; Bedding, Timothy R.; Stello, Dennis; Huber, Daniel; Christensen-Dalsgaard, Jorgen; Kjeldsen, Hans

    2011-12-20

    With the success of the Kepler and CoRoT missions, the number of stars with detected solar-like oscillations has increased by several orders of magnitude; for the first time we are able to perform large-scale ensemble asteroseismology of these stars. In preparation for this golden age of asteroseismology we have computed expected values of various asteroseismic observables from models of varying mass and metallicity. The relationships between these asteroseismic observables, such as the separations between mode frequencies, are able to significantly constrain estimates of the ages and masses of these stars. We investigate the scaling relation between the large frequency separation, {Delta}{nu}, and mean stellar density. Furthermore we present model evolutionary tracks for several asteroseismic diagrams. We have extended the so-called C-D diagram beyond the main sequence to the subgiants and the red giant branch. We also consider another asteroseismic diagram, the {epsilon} diagram, which is more sensitive to variations in stellar properties at the subgiant stages and can aid in determining the correct mode identification. The recent discovery of gravity-mode period spacings in red giants forms the basis for a third asteroseismic diagram. We compare the evolutionary model tracks in these asteroseismic diagrams with results from pre-Kepler studies of solar-like oscillations and early results from Kepler.

  13. Liquid-vapor phase diagram of metals using EAM potential

    NASA Astrophysics Data System (ADS)

    Bhattacharya, Chandrani

    2013-02-01

    Pair-wise additive potentials are not adequate to describe the properties of metallic systems since many body effects are completely ignored in that approximation. In this regard, the embedded atom method is more appropriate because, in addition to the pair interaction, the total energy includes an embedding energy which is the energy required to add an impurity atom to the host electron fluid. Thus EAM takes into account the many body effects to some extent. We use the Cai and Ye's EAM potential to predict the liquid vapor phase diagram and critical constants of Aluminum and Copper within a perturbation theory approach. In this method, free energy of a fluid molecule, trapped in a cage formed by its nearest neighbors, is expanded about a hard sphere reference system. The first order correction term is calculated in terms of the zero temperature isotherm of the solid obtained using the EAM potential. Higher order correction terms are added to account for the deviation of the behavior of the real fluid from the reference hard sphere fluid.

  14. Magnetic phase diagram of ν=2 quantum Hall systems

    NASA Astrophysics Data System (ADS)

    Yoshizawa, Kanako; Takayanagi, Kazuo

    2009-03-01

    We present the magnetic phase diagram of the ν=2 quantum Hall system on the whole (rs,EZ) plane. We fix the phase boundaries of the paramagnetic and ferromagnetic states by looking for a softening of spin-density excitations in the time-dependent Hartree-Fock theory. A nontrivial phase is obtained in the self-consistent Hartree-Fock theory for rs˜2 and EZ≲0.06ℏωc , where both the paramagnetic and ferromagnetic states show spin instability. We show that the obtained phase is the spin-density wave (SDW) state, and explain the mechanism how the SDW stabilizes.

  15. Exploring the magnetic phase diagram of dysprosium with neutron diffraction

    NASA Astrophysics Data System (ADS)

    Yu, J.; LeClair, P. R.; Mankey, G. J.; Robertson, J. L.; Crow, M. L.; Tian, W.

    2015-01-01

    With one of the highest intrinsic magnetic moments (10.6 μB/atom ) among the heavy rare-earth elements, dysprosium exhibits a rich magnetic phase diagram, including several modulated magnetic phases. Aided by the Ruderman-Kittel-Kasuya-Yosida interaction, the magnetic modulations propagate coherently over a long range. Neutron diffraction experiments were performed to determine the microscopic magnetic origin of the field induced phases in bulk Dy as a function of temperature, covering regions of the well-known ferromagnetic, helical antiferromagnetic, fan phases, and several possible new phases suggested by previous studies. A short-range ordered fan phase was identified as the intermediate state between ferromagnetism and long-range ordered fan. In a field of 1 T applied along the a axis, the temperature range of a coexisting helix/fan phase was determined. The magnetic phase diagram of Dy was thus refined to include the detailed magnetic origin and the associated phase boundaries. Based on the period of the magnetic modulation and the average magnetization, the evolution of the spin arrangement upon heating was derived quantitatively for the modulated magnetic phases.

  16. The phase diagram and Bose metal in superconducting nanowires

    NASA Astrophysics Data System (ADS)

    Morgan-Wall, Tyler; Hughes, Hannah; Hartman, Nikolaus; Markovic, Nina

    We experimentally investigated the transport properties of thin, narrow superconducting aluminum nanowires as a function of magnetic field and temperature. We characterized the full superconducting phase diagram with respect to magnetic field and temperature, and show the onset of a flux-flow phase for certain values of temperature and magnetic field. The flux-flow resistance follows the Bardeen-Stephen model and it is shown that the resistance increases linearly with respect to magnetic field in this region of the phase diagram. In addition, we show the saturation to a non-zero finite resistance state below the normal state resistance for certain magnetic fields as the temperature decreases to zero. This work is supported by NSF DMR-1507782.

  17. Poly(N-isopropylacrylamide) Phase Diagrams: Fifty Years of Research.

    PubMed

    Halperin, Avraham; Kröger, Martin; Winnik, Françoise M

    2015-12-14

    In 1968, Heskins and Guillet published the first systematic study of the phase diagram of poly(N-isopropylacrylamide) (PNIPAM), at the time a "young polymer" first synthesized in 1956. Since then, PNIPAM became the leading member of the growing families of thermoresponsive polymers and of stimuli-responsive, "smart" polymers in general. Its thermal response is unanimously attributed to its phase behavior. Yet, in spite of 50 years of research, a coherent quantitative picture remains elusive. In this Review we survey the reported phase diagrams, discuss the differences and comment on theoretical ideas regarding their possible origins. We aim to alert the PNIPAM community to open questions in this reputably mature domain. PMID:26612195

  18. Global phase diagram and single particle excitations in Kondo insulators

    NASA Astrophysics Data System (ADS)

    Si, Qimiao; Pixley, Jedediah; Yu, Rong; Paschen, Silke

    Motivated by quantum criticality in Kondo insulators tuned by pressure or doping we study the effects of magnetic frustration and the properties of the single particle excitations in a Kondo lattice model. Focusing on the Kondo insulating limit we study the Shastry-Sutherland Kondo lattice and determine the zero temperature phase diagram, which incorporates a valence bond solid, antiferromagnet, and Kondo insulating ground states, with metal-to-insulator quantum phase transitions. We argue that this phase diagram is generic and represents a ``global'' phase diagram of Kondo insulators in terms of quantum fluctuations and the Kondo interaction. We then focus on the momentum distribution of single particle excitations within the Kondo insulating ground state. We show how features of the Fermi-surface of the underlying conduction electrons appear in the Kondo insulating phase. Lastly, we discuss the implications of our results for quantum criticality in Kondo insulators as well as for the recent de Haas-von Alphen measurements in the Kondo insulator SmB6.

  19. Phase Diagrams of Electric-Fduced Aggregation in Conducting Colloids

    NASA Technical Reports Server (NTRS)

    Khusid, B.; Acrivos, A.

    1999-01-01

    Under the application of a sufficiently strong electric field, a suspension may undergo reversible phase transitions from a homogeneous random arrangement of particles into a variety of ordered aggregation patterns. The surprising fact about electric-field driven phase transitions is that the aggregation patterns, that are observed in very diverse systems of colloids, display a number of common structural features and modes of evolution thereby implying that a universal mechanism may exist to account for these phenomena. It is now generally believed that this mechanism emanates from the presence of the long-range anisotropic interactions between colloidal particles due to their polarization in an applied field. But, in spite of numerous applications of the electric-field-driven phenomena in biotechnology, separation, materials engineering, chemical analysis, etc. our understanding of these phenomena is far from complete. Thus, it is the purpose of the proposed research to develop a theory and then test experimentally, under normal- and low-gravity conditions, the accuracy of the theoretical predictions regarding the effect of the synergism of the interparticle electric and hydrodynamic interactions on the phase diagram of a suspension. The main results from our theoretical studies performed to-date enable one to trace how the variations of the electrical properties of the constituent materials influence the topology of the suspension phase diagram and then, by using an appropriate phase diagram, to evaluate how the electric-field-induced transformations will depend on the frequency and the strength of the applied field.

  20. Application of quaternary phase diagrams to compound semiconductor processing. Progress report, April 1, 1988--December 31, 1988

    SciTech Connect

    Schwartzman, A.

    1988-12-31

    This paper considers the application of quaternary phase diagrams to understanding and predicting the behavior of II-VI thin film interfaces in photovoltaic devices under annealing conditions. Examples, listed in a table, include semiconductor/insulator/semiconductor (SIS) layered structures, II-VI/II-VI and III-V/II-VI epitaxial heterojunctions and oxidation of ternary compounds. Solid solubility is taken into account for quaternary phase diagrams of semiconductor systems. Using free energies of formation, a method to calculate the quaternary phase diagrams was developed. The Ga-As-II-VI and Cd-Te-Zn-O phase diagrams are reviewed as examples of quaternary phase diagrams without and with solid solubility.

  1. Phase diagram of a reentrant gel of patchy particles

    SciTech Connect

    Roldán-Vargas, Sándalo; Smallenburg, Frank; Sciortino, Francesco; Kob, Walter

    2013-12-28

    We study the phase diagram of a binary mixture of patchy particles which has been designed to form a reversible gel. For this we perform Monte Carlo and molecular dynamics simulations to investigate the thermodynamics of such a system and compare our numerical results with predictions based on the analytical parameter-free Wertheim theory. We explore a wide range of the temperature-density-composition space that defines the three-dimensional phase diagram of the system. As a result, we delimit the region of thermodynamic stability of the fluid. We find that for a large region of the phase diagram the Wertheim theory is able to give a quantitative description of the system. For higher densities, our simulations show that the system is crystallizing into a BCC structure. Finally, we study the relaxation dynamics of the system by means of the density and temperature dependences of the diffusion coefficient. We show that there exists a density range where the system passes reversibly from a gel to a fluid upon both heating and cooling, encountering neither demixing nor phase separation.

  2. Determining pressure-temperature phase diagrams of materials

    NASA Astrophysics Data System (ADS)

    Baldock, Robert J. N.; Pártay, Lívia B.; Bartók, Albert P.; Payne, Michael C.; Csányi, Gábor

    2016-05-01

    We extend the nested sampling algorithm to simulate materials under periodic boundary and constant pressure conditions, and show how it can be used to determine the complete equilibrium phase diagram for a given potential energy function, efficiently and in a highly automated fashion. The only inputs required are the composition and the desired pressure and temperature ranges, in particular, solid-solid phase transitions are recovered without any a priori knowledge about the structure of solid phases. We benchmark and showcase the algorithm on the periodic Lennard-Jones system, aluminum, and NiTi.

  3. Retrieval phase diagrams of non-monotonic Hopfield networks

    NASA Astrophysics Data System (ADS)

    Inoue, Jun-ichi

    1996-08-01

    We investigate the retrieval phase diagrams of an asynchronous fully connected attractor network with non-monotonic transfer function by means of a mean-field approximation. We find for the noiseless zero-temperature case that this non-monotonic Hopfield network can store more patterns than a network with monotonic transfer function investigated by Amit et al. Properties of retrieval phase diagrams of non-monotonic networks agree with the results obtained by Nishimori and Opris who treated synchronous networks. We also investigate the optimal storage capacity of the non-monotonic Hopfield model with state-dependent synaptic couplings introduced by Zertuche et al. We show that the non-monotonic Hopfield model with state-dependent synapses stores more patterns than the conventional Hopfield model. Our formulation can be easily extended to a general transfer function.

  4. Phase diagram of the ground states of DNA condensates.

    PubMed

    Hoang, Trinh X; Trinh, Hoa Lan; Giacometti, Achille; Podgornik, Rudolf; Banavar, Jayanth R; Maritan, Amos

    2015-12-01

    The phase diagram of the ground states of DNA in a bad solvent is studied for a semiflexible polymer model with a generalized local elastic bending potential characterized by a nonlinearity parameter x and effective self-attraction promoting compaction. x=1 corresponds to the wormlike chain model. Surprisingly, the phase diagram as well as the transition lines between the ground states are found to be a function of x. The model provides a simple explanation for the results of prior experimental and computational studies and makes predictions for the specific geometries of the ground states. The results underscore the impact of the form of the microscopic bending energy at macroscopic observable scales. PMID:26764619

  5. Global Phase Diagram of the High-Tc Cuprates

    NASA Astrophysics Data System (ADS)

    Chen, Han-Dong; Zhang, Shou-Cheng

    2006-02-01

    We propose a bosonic effective quantum Hamiltonian based on the projected SO(5) model with extended interactions, which can be derived from the microscopic models of the cuprates. The global phase diagram of this model is obtained using mean-field theory and the quantum Monte Carlo simulation. We show that this single quantum model can account for most salient features observed in the high-Tc cuprates, with different families of the cuprates attributed to different traces in the global phase diagram. A particular prediction of this theory is the checkerboard state of the d-wave hole pairs formed at certain magic filling fractions. We shall describe various properties of this state and present evidence that this novel state has been detected in recent STM and transport experiments.

  6. Magnetic structures in the magnetic phase diagram of Ho2RhIn8

    NASA Astrophysics Data System (ADS)

    Čermák, Petr; Prokeš, Karel; Ouladdiaf, Bachir; Boehm, Martin; Kratochvílová, Marie; Javorský, Pavel

    2015-04-01

    The magnetic phase diagram of the tetragonal Ho2RhIn8 compound has similar features to many related systems, revealing a zero magnetic field AF1 and a field-induced AF2 phases. Details of the magnetic order in the AF2 phase were not reported yet for any of the related compounds. In addition, only the Ho2RhIn8 phase diagram contains a small region of the incommensurate zero-field AF3 phase. We have performed a number of neutron diffraction experiments on single crystals of Ho2RhIn8 using several diffractometers including experiments in both horizontal and vertical magnetic fields up to 4 T. We present details of the magnetic structures in all magnetic phases of the rich phase diagram of Ho2RhIn8 . The Ho magnetic moments point along the tetragonal c axis in every phase. The ground-state AF1 phase is characterized by propagation vector k =(1 /2 ,0 ,0 ) . The more complex ferrimagnetic AF2 phase is described by four propagation vectors k0=(0 ,0 ,0 ) ,k1=(1 /2 ,0 ,0 ) ,k2=(0 ,1 /2 ,1 /2 ) ,k3=(1 /2 ,1 /2 ,1 /2 ) . The magnetic structure in the AF3 phase is incommensurate with kA F 3=(0.5 ,δ ,0 ) . Our results are consistent with theoretical calculations based on crystal field theory.

  7. Spent Nuclear Fuel (SNF) Project Canister Storage Building (CSB) Process Flow Diagram Mass Balance Calculations

    SciTech Connect

    KLEM, M.J.

    2000-05-11

    The purpose of these calculations is to develop the material balances for documentation of the Canister Storage Building (CSB) Process Flow Diagram (PFD) and future reference. The attached mass balances were prepared to support revision two of the PFD for the CSB. The calculations refer to diagram H-2-825869.

  8. Crystalline condensates in the chiral symmetry breaking phase diagram

    SciTech Connect

    Dunne, Gerald V.

    2010-07-27

    The existence of crystalline condensates in the temperature and chemcial potential phase diagram of the Gross-Neveu models can be traced to intricate symmetries of the associated inhomogeneous gap equation, which in turn reflect the form of chiral symmetry (discrete or continuous) that is broken. The gap equation based on the Ginzburg-Landau expansion is precisely the mKdV or AKNS hierarchy of integrable nonlinear equations for the Gross-Neveu model with discrete or continuous chiral symmetry, respectively.

  9. Magnetic phase diagrams of barcode-type nanostructures

    NASA Astrophysics Data System (ADS)

    Leighton, B.; Suarez, O. J.; Landeros, P.; Escrig, J.

    2009-09-01

    The magnetic configurations of barcode-type magnetic nanostructures consisting of alternate ferromagnetic and nonmagnetic layers arranged within a multilayer nanotube structure are investigated as a function of their geometry. Based on a continuum approach we have obtained analytical expressions for the energy which lead us to obtain phase diagrams giving the relative stability of characteristic internal magnetic configurations of the barcode-type nanostructures.

  10. Phase diagram of dipolar hard and soft spheres: manipulation of colloidal crystal structures by an external field.

    PubMed

    Hynninen, Antti-Pekka; Dijkstra, Marjolein

    2005-04-01

    Phase diagrams of hard and soft spheres with a fixed dipole moment are determined by calculating the Helmholtz free energy using simulations. The pair potential is given by a dipole-dipole interaction plus a hard-core and a repulsive Yukawa potential for soft spheres. Our system models colloids in an external electric or magnetic field, with hard spheres corresponding to uncharged and soft spheres to charged colloids. The phase diagram of dipolar hard spheres shows fluid, face-centered-cubic (fcc), hexagonal-close-packed (hcp), and body-centered-tetragonal (bct) phases. The phase diagram of dipolar soft spheres exhibits, in addition to the above mentioned phases, a body-centered-orthorhombic (bco) phase, and it agrees well with the experimental phase diagram [Nature (London) 421, 513 (2003)]. Our results show that bulk hcp, bct, and bco crystals can be realized experimentally by applying an external field. PMID:15904046

  11. Phase diagram for bilayer quantum Hall effect at total filling νT=5

    NASA Astrophysics Data System (ADS)

    Shi, Chuntai; Jolad, Shivakumar; Regnault, Nicolas; Jain, Jainendra K.

    2008-04-01

    We evaluate the phase diagram of the bilayer quantum Hall effect at total filling νT=5 , which is a bilayer phase coherent state at small separations and two uncoupled 5/2 states at large separations. Based on a combination of variational and exact calculations, we estimate that the transition between these states occurs at a layer separation of approximately one magnetic length. The composite fermion Fermi sea is not found to be relevant for any parameters.

  12. Phase diagram of KHF2 and non-equilibrium effects

    NASA Technical Reports Server (NTRS)

    Hobson, M. C.; Kellner, J. D.

    1978-01-01

    The equilibrium diagram for the KHF2-H2O system was constructed from cooling and heating curves for the compositions between 5 wt% and 40 wt% KHF2 and the results are shown. The phase diagrams shown is typical of that of a two component system with miscible liquid phases and whole solid phases consist of pure components. A eutectic point was found at approximately 15% KHF2 which remains completely liquid down to a temperature of -9.0 C. No hydrate formation was observed and no anomalous behavior such as the occurrence of solid transitions or metastable states was observed. The effect of rapid freezing on the equilibrium diagram did not appear, and cooling curves exhibited only one halt. Also, at rapid freezing rates, the supercooling of the solutions was smaller than those observed at the slow cooling rates. The existence of a eutectic composition and the slow rate of dissolution of the salt are used to interpret heat absorption behavior in practical applications of the KHF2-H2O system.

  13. The coupling of thermochemistry and phase diagrams for group III-V semiconductor systems. Final report

    SciTech Connect

    Anderson, T.J.

    1998-07-21

    The project was directed at linking the thermochemical properties of III-V compound semiconductors systems with the reported phase diagrams. The solid-liquid phase equilibrium problem was formulated and three approaches to calculating the reduced standard state chemical potential were identified and values were calculated. In addition, thermochemical values for critical properties were measured using solid state electrochemical techniques. These values, along with the standard state chemical potentials and other available thermochemical and phase diagram data, were combined with a critical assessment of selected III-V systems. This work was culminated with a comprehensive assessment of all the III-V binary systems. A novel aspect of the experimental part of this project was the demonstration of the use of a liquid encapsulate to measure component activities by a solid state emf technique in liquid III-V systems that exhibit high vapor pressures at the measurement temperature.

  14. Phase diagram of the composite fermion Wigner crystals

    NASA Astrophysics Data System (ADS)

    Archer, Alex; Park, Kwon; Jain, Jainendra

    2013-03-01

    The energies of the Wigner crystal (WC) phase and the fractional quantum Hall (FQH) liquid have been compared in the past at some special filling factors. We deduce in this work the phase diagram of the WC phase as a function of the general filling factor by considering: (i) the WC of electrons; (ii) WCs of composite fermions (CFs) carrying 2 p vortices; and (iii) FQH states supporting WC of CF quasiparticles or CF quasiholes. In particular, we find that the re-entrant insulating phase between 1/5 and 2/9 is a WC of composite fermions carrying two vortices. To distinguish the CF Wigner crystal from the electron WC, we compute a number of properties, including shear modulus, magnetophonon and magnetoplasmon dispersions, and melting temperatures. The width dependence of the phase diagram is also studied. A technical innovation that makes these comparisons feasible is to model the WC as the thermodynamic limit of the Thomson crystal on the surface of a sphere, which minimizes the Coulomb energy of classical charged particles.

  15. Ternary Phase Diagrams that Relate to the Plutonium Immobilization Ceramic

    SciTech Connect

    Ebbinghaus, B b; Krikorian, O H; Vance, E R; Stewart, M W

    2001-01-01

    The plutonium immobilization ceramic consists primarily of a pyrochlore titanate phase of the approximate composition Ca{sub 0.97}Hf{sub 0.17}Pu{sub 0.22}U{sub 0.39}Gd{sub 0.24} Ti{sub 2}O{sub 7}. In this study, a series of ternary phase diagrams was constructed to evaluate the relationship of various titanate phases (e.g., brannerite, zirconolite-2M, zirconolite-4M, and perovskite) to pyrochlore titanates, usually in the presence of excess TiO{sub 2} (rutile), and at temperatures in the vicinity of 1350 C. To facilitate the studies, U, Th, and Ce were used as surrogates for Pu in a number of the phase diagrams in addition to the use of Pu itself. The effects of impurity oxides, Al{sub 2}O{sub 3} and MgO, were also studied on pyrochlore (Gd{sub 2}Ti{sub 2}O{sub 7}) and zirconolite (CaHfTi{sub 2}O{sub 7}) mixtures. Either electron microprobe (at Lawrence Livermore National Laboratory) or quantitative SEM-EDS (at Australian Nuclear Science and Technology Organization) were used to evaluate the compositions of the phases.

  16. First-principles pressure-temperature phase diagrams in metals

    SciTech Connect

    Moriarty, J.A.

    1993-07-01

    Using interatomic potentials derived from first-principles generalized pseudopotential theory, finite-temperature phase transitions in both simple and transition metals can be studied through a combination of analytic statistical methods and molecular-dynamics simulation. In the prototype simple metal-Mg, where volume and pair forces adequately describe the energetics, a complete and accurate phase diagram has thereby been obtained to 60 GPa. A rapidly temperature-dependent hcp-bcc phase line is predicted which ends in a triple point on the melting curve near 4 GPa. In central transition metals such as Mo or Fe, on the other hand, the energetics are complicated by d-state interactions which give rise to both many-body angular forces and enhanced electron-thermal contributions. We have made a detailed study of these phenomena and their impact on melting in the prototype case of Mo and a full melting curve to 2 Mbar has been obtained. In the case of Fe, we are examining the high-pressure phase diagram and the question of whether or not there exists a high-pressure, high-temperature solid bcc phase, as has been speculated. To date, we have shown that the bcc structure is both thermodynamically and mechanically unstable at high pressure and zero temperature, with a large and increasing bcc-hcp energy difference under compression.

  17. Phase diagram and entanglement of two interacting topological Kitaev chains

    NASA Astrophysics Data System (ADS)

    Herviou, Loïc; Mora, Christophe; Le Hur, Karyn

    2016-04-01

    A superconducting wire described by a p -wave pairing and a Kitaev Hamiltonian exhibits Majorana fermions at its edges and is topologically protected by symmetry. We consider two Kitaev wires (chains) coupled by a Coulomb-type interaction and study the complete phase diagram using analytical and numerical techniques. A topological superconducting phase with four Majorana fermions occurs until moderate interactions between chains. For large interactions, both repulsive and attractive, by analogy with the Hubbard model, we identify Mott phases with Ising-type magnetic order. For repulsive interactions, the Ising antiferromagnetic order favors the occurrence of orbital currents spontaneously breaking time-reversal symmetry. By strongly varying the chemical potentials of the two chains, quantum phase transitions towards fully polarized (empty or full) fermionic chains occur. In the Kitaev model, the quantum critical point separating the topological superconducting phase and the polarized phase belongs to the universality class of the critical Ising model in two dimensions. When increasing the Coulomb interaction between chains, then we identify an additional phase corresponding to two critical Ising theories (or two chains of Majorana fermions). We confirm the existence of such a phase from exact mappings and from the concept of bipartite fluctuations. We show the existence of negative logarithmic corrections in the bipartite fluctuations, as a reminiscence of the quantum critical point in the Kitaev model. Other entanglement probes such as bipartite entropy and entanglement spectrum are also used to characterize the phase diagram. The limit of large interactions can be reached in an equivalent setup of ultracold atoms and Josephson junctions.

  18. QCD Phase Diagram According to the Center Group

    SciTech Connect

    Delgado Mercado, Ydalia; Gattringer, Christof; Evertz, Hans Gerd

    2011-06-03

    We study an effective theory for QCD at finite temperature and density which contains the leading center symmetric and center symmetry breaking terms. The effective theory is studied in a flux representation where the complex phase problem is absent and the model becomes accessible to Monte Carlo techniques also at finite chemical potential. We simulate the system by using a generalized Prokof'ev-Svistunov worm algorithm and compare the results to a low temperature expansion. The phase diagram is determined as a function of temperature, chemical potential, and quark mass. The shape and quark mass dependence of the phase boundaries are as expected for QCD. The transition into the deconfined phase is smooth throughout, without any discontinuities or critical points.

  19. Evaluating the phase diagram of superconductors with asymmetric spin populations

    SciTech Connect

    Mannarelli, Massimo; Nardulli, Giuseppe; Ruggieri, Marco

    2006-09-15

    The phase diagram of a nonrelativistic fermionic system with imbalanced state populations interacting via a short-range S-wave attractive interaction is analyzed in the mean-field approximation. We determine the energetically favored state for different values of the mismatch between the two Fermi spheres in the weak- and strong-coupling regimes considering both homogeneous and nonhomogeneous superconductive states. We find that the homogeneous superconductive phase persists for values of the population imbalance that increase with increasing coupling strength. In the strong-coupling regime and for large population differences the energetically stable homogeneous phase is characterized by one gapless mode. We also find that the inhomogeneous superconductive phase characterized by the condensate {delta}(x){approx}{delta} exp(iq{center_dot}x) is energetically favored in a range of values of the chemical-potential mismatch that shrinks to zero in the strong-coupling regime.

  20. The phase diagram of hydrogen in ultra thin films

    SciTech Connect

    Jisrawi, N.M.; Ruckman, M.W.; Reisfeld, G.; Wiesmann, H.; Loeb, F; Gallego, E.; Gorelik, Y.; Thurston, T.R.; Strongin, M.

    1995-12-31

    This paper, we discuss changes in the phase diagram of hydrogen in both bilayer (i.e. 200-2000 {Angstrom} Nb/100 {Angstrom} Pd on glass) and multilayer configurations. Comparison of x-ray diffraction, electrical resistivity and volumetric measurements of the films before and after hydrogen charging indicate that the phase equilibria between a correlated (high concentration) and a dilute phase of hydrogen in Nb is not sensitive to the number of layers in the films. On the other hand, the experimental methods show different behavior for 200 {Angstrom} thick Nb films and thicker (>400 {Angstrom}) Nb layers. The diffraction results also show that, while charging with hydrogen, the Nb layers mainly expand along the surface normal of the films, while the Pd layers expand in all directions equally, and transform to the bulk {alpha} phase.

  1. Misfit strain phase diagrams of epitaxial PMN-PT films

    NASA Astrophysics Data System (ADS)

    Khakpash, N.; Khassaf, H.; Rossetti, G. A.; Alpay, S. P.

    2015-02-01

    Misfit strain-temperature phase diagrams of three compositions of (001) pseudocubic (1 - x).Pb (Mgl/3Nb2/3)O3 - x.PbTiO3 (PMN-PT) thin films are computed using a phenomenological model. Two (x = 0.30, 0.42) are located near the morphotropic phase boundary (MPB) of bulk PMN-PT at room temperature (RT) and one (x = 0.70) is located far from the MPB. The results show that it is possible to stabilize an adaptive monoclinic phase over a wide range of misfit strains. At RT, the stability region of this phase is much larger for PMN-PT compared to barium strontium titanate and lead zirconate titanate films.

  2. Misfit strain phase diagrams of epitaxial PMN–PT films

    SciTech Connect

    Khakpash, N.; Khassaf, H.; Rossetti, G. A.; Alpay, S. P.

    2015-02-23

    Misfit strain–temperature phase diagrams of three compositions of (001) pseudocubic (1 − x)·Pb (Mg{sub l/3}Nb{sub 2/3})O{sub 3} − x·PbTiO{sub 3} (PMN–PT) thin films are computed using a phenomenological model. Two (x = 0.30, 0.42) are located near the morphotropic phase boundary (MPB) of bulk PMN–PT at room temperature (RT) and one (x = 0.70) is located far from the MPB. The results show that it is possible to stabilize an adaptive monoclinic phase over a wide range of misfit strains. At RT, the stability region of this phase is much larger for PMN–PT compared to barium strontium titanate and lead zirconate titanate films.

  3. Non-ionic surfactant phase diagram prediction by recursive partitioning.

    PubMed

    Bell, Gordon

    2016-07-28

    A model has been designed to predict the phase which forms in water for a non-ionic surfactant, at a given concentration and temperature. The full phase diagram is generated by selecting enough data points to cover the region of interest. The model estimates the probability for each one of 10 possible phases and selects the one with the highest likelihood. The probabilities are based on the recursive partitioning of a dataset of 10 000 known observations. The model covers alkyl chain length and branching, ethoxylate head length and number, and end capping of one or more of the ethoxylate chains. The relationship between chemical structure, shape and phase behaviour is discussed.This article is part of the themed issue 'Soft interfacial materials: from fundamentals to formulation'. PMID:27298439

  4. Phase diagrams of scalemic mixtures: A Monte Carlo simulation study

    NASA Astrophysics Data System (ADS)

    Vlot, Margot J.; van Miltenburg, J. Cornelis; Oonk, Harry A. J.; van der Eerden, Jan P.

    1997-12-01

    In this paper, a simplified model was used to describe the interactions between the enantiomers in a scalemic mixture. Monte Carlo simulations were performed to determine several thermodynamic properties as a function of temperature and mole fraction of solid, liquid, and gas phase. Phase diagrams were constructed using a macroscopic thermodynamic program, PROPHASE. The model consists of spherical D and L molecules interacting via modified Lennard-Jones potentials (σDD=σLL, ɛDD=ɛLL, ɛDL=eɛDD, and σDL=sσDD.) The two heterochiral interaction parameters, e and s, were found to be sufficient to produce all types of phase diagrams that have been found for these systems experimentally. Conglomerates were found when the heterochiral interaction strength was smaller than the homochiral value, e<1. A different heterochiral interaction distance, s≠1, led to racemic compounds, with an ordered distribution of D and L molecules. The CsCl-structured compound was found to be stable for short DL interactions, s<1 (e=1), with an enantiotropic transition to a solid solution for s=0.96. Longer heterochiral distances, s>1, result in the formation of layered fcc compounds. The liquid regions in the phase diagram become larger for s≠1, caused by a strong decrease of the melting point for s<1 and s>1, in combination with only a small effect on the boiling point for s<1, and even an increase of the boiling point for s>1. Segregation into two different solid solutions, one with low mole fraction and the other one close to x=0.25, was obtained for these mixtures as well.

  5. Phase diagram of two-dimensional hard ellipses

    NASA Astrophysics Data System (ADS)

    Bautista-Carbajal, Gustavo; Odriozola, Gerardo

    2014-05-01

    We report the phase diagram of two-dimensional hard ellipses as obtained from replica exchange Monte Carlo simulations. The replica exchange is implemented by expanding the isobaric ensemble in pressure. The phase diagram shows four regions: isotropic, nematic, plastic, and solid (letting aside the hexatic phase at the isotropic-plastic two-step transition [E. P. Bernard and W. Krauth, Phys. Rev. Lett. 107, 155704 (2011)]). At low anisotropies, the isotropic fluid turns into a plastic phase which in turn yields a solid for increasing pressure (area fraction). Intermediate anisotropies lead to a single first order transition (isotropic-solid). Finally, large anisotropies yield an isotropic-nematic transition at low pressures and a high-pressure nematic-solid transition. We obtain continuous isotropic-nematic transitions. For the transitions involving quasi-long-range positional ordering, i.e., isotropic-plastic, isotropic-solid, and nematic-solid, we observe bimodal probability density functions. This supports first order transition scenarios.

  6. Phase diagram of two-dimensional hard ellipses.

    PubMed

    Bautista-Carbajal, Gustavo; Odriozola, Gerardo

    2014-05-28

    We report the phase diagram of two-dimensional hard ellipses as obtained from replica exchange Monte Carlo simulations. The replica exchange is implemented by expanding the isobaric ensemble in pressure. The phase diagram shows four regions: isotropic, nematic, plastic, and solid (letting aside the hexatic phase at the isotropic-plastic two-step transition [E. P. Bernard and W. Krauth, Phys. Rev. Lett. 107, 155704 (2011)]). At low anisotropies, the isotropic fluid turns into a plastic phase which in turn yields a solid for increasing pressure (area fraction). Intermediate anisotropies lead to a single first order transition (isotropic-solid). Finally, large anisotropies yield an isotropic-nematic transition at low pressures and a high-pressure nematic-solid transition. We obtain continuous isotropic-nematic transitions. For the transitions involving quasi-long-range positional ordering, i.e., isotropic-plastic, isotropic-solid, and nematic-solid, we observe bimodal probability density functions. This supports first order transition scenarios. PMID:24880296

  7. Quantum Monte Carlo study of the phase diagram of solid molecular hydrogen at extreme pressures.

    PubMed

    Drummond, N D; Monserrat, Bartomeu; Lloyd-Williams, Jonathan H; López Ríos, P; Pickard, Chris J; Needs, R J

    2015-01-01

    Establishing the phase diagram of hydrogen is a major challenge for experimental and theoretical physics. Experiment alone cannot establish the atomic structure of solid hydrogen at high pressure, because hydrogen scatters X-rays only weakly. Instead, our understanding of the atomic structure is largely based on density functional theory (DFT). By comparing Raman spectra for low-energy structures found in DFT searches with experimental spectra, candidate atomic structures have been identified for each experimentally observed phase. Unfortunately, DFT predicts a metallic structure to be energetically favoured at a broad range of pressures up to 400 GPa, where it is known experimentally that hydrogen is non-metallic. Here we show that more advanced theoretical methods (diffusion quantum Monte Carlo calculations) find the metallic structure to be uncompetitive, and predict a phase diagram in reasonable agreement with experiment. This greatly strengthens the claim that the candidate atomic structures accurately model the experimentally observed phases. PMID:26215251

  8. Glass and liquid phase diagram of a polyamorphic monatomic system.

    PubMed

    Reisman, Shaina; Giovambattista, Nicolas

    2013-02-14

    We perform out-of-equilibrium molecular dynamics (MD) simulations of a monatomic system with Fermi-Jagla (FJ) pair potential interactions. This model system exhibits polyamorphism both in the liquid and glass state. The two liquids, low-density (LDL) and high-density liquid (HDL), are accessible in equilibrium MD simulations and can form two glasses, low-density (LDA) and high-density amorphous (HDA) solid, upon isobaric cooling. The FJ model exhibits many of the anomalous properties observed in water and other polyamorphic liquids and thus, it is an excellent model system to explore qualitatively the thermodynamic properties of such substances. The liquid phase behavior of the FJ model system has been previously characterized. In this work, we focus on the glass behavior of the FJ system. Specifically, we perform systematic isothermal compression and decompression simulations of LDA and HDA at different temperatures and determine "phase diagrams" for the glass state; these phase diagrams varying with the compression/decompression rate used. We obtain the LDA-to-HDA and HDA-to-LDA transition pressure loci, P(LDA-HDA)(T) and P(HDA-LDA)(T), respectively. In addition, the compression-induced amorphization line, at which the low-pressure crystal (LPC) transforms to HDA, P(LPC-HDA)(T), is determined. As originally proposed by Poole et al. [Phys. Rev. E 48, 4605 (1993)] simulations suggest that the P(LDA-HDA)(T) and P(HDA-LDA)(T) loci are extensions of the LDL-to-HDL and HDL-to-LDL spinodal lines into the glass domain. Interestingly, our simulations indicate that the P(LPC-HDA)(T) locus is an extension, into the glass domain, of the LPC metastability limit relative to the liquid. We discuss the effects of compression/decompression rates on the behavior of the P(LDA-HDA)(T), P(HDA-LDA)(T), P(LPC-HDA)(T) loci. The competition between glass polyamorphism and crystallization is also addressed. At our "fast rate," crystallization can be partially suppressed and the glass

  9. Glass and liquid phase diagram of a polyamorphic monatomic system

    NASA Astrophysics Data System (ADS)

    Reisman, Shaina; Giovambattista, Nicolas

    2013-02-01

    We perform out-of-equilibrium molecular dynamics (MD) simulations of a monatomic system with Fermi-Jagla (FJ) pair potential interactions. This model system exhibits polyamorphism both in the liquid and glass state. The two liquids, low-density (LDL) and high-density liquid (HDL), are accessible in equilibrium MD simulations and can form two glasses, low-density (LDA) and high-density amorphous (HDA) solid, upon isobaric cooling. The FJ model exhibits many of the anomalous properties observed in water and other polyamorphic liquids and thus, it is an excellent model system to explore qualitatively the thermodynamic properties of such substances. The liquid phase behavior of the FJ model system has been previously characterized. In this work, we focus on the glass behavior of the FJ system. Specifically, we perform systematic isothermal compression and decompression simulations of LDA and HDA at different temperatures and determine "phase diagrams" for the glass state; these phase diagrams varying with the compression/decompression rate used. We obtain the LDA-to-HDA and HDA-to-LDA transition pressure loci, PLDA-HDA(T) and PHDA-LDA(T), respectively. In addition, the compression-induced amorphization line, at which the low-pressure crystal (LPC) transforms to HDA, PLPC-HDA(T), is determined. As originally proposed by Poole et al. [Phys. Rev. E 48, 4605 (1993)], 10.1103/PhysRevE.48.4605 simulations suggest that the PLDA-HDA(T) and PHDA-LDA(T) loci are extensions of the LDL-to-HDL and HDL-to-LDL spinodal lines into the glass domain. Interestingly, our simulations indicate that the PLPC-HDA(T) locus is an extension, into the glass domain, of the LPC metastability limit relative to the liquid. We discuss the effects of compression/decompression rates on the behavior of the PLDA-HDA(T), PHDA-LDA(T), PLPC-HDA(T) loci. The competition between glass polyamorphism and crystallization is also addressed. At our "fast rate," crystallization can be partially suppressed and the

  10. Phase diagram of chiral quark matter: From weakly to strongly coupled Fulde-Ferrell phase

    SciTech Connect

    Sedrakian, Armen; Rischke, Dirk H.

    2009-10-01

    We calculate the phase diagram of two-flavor quark matter within the Nambu-Jona-Lasinio (NJL) model in the temperature-flavor asymmetry plane in the case where there are three competing phases: the homogeneous Bardeen-Cooper-Schrieffer (BCS) phase, the unpaired phase, and a phase with broken spatial symmetry, which is here taken to be the counterpart of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase in condensed matter physics. The system belongs to the universality class of paramagnetic-ferromagnetic-helical systems, and therefore contains a tricritical Lifshitz point in its phase diagram, where the momentum scale characterizing the breaking of translational invariance has a critical exponent of 1/2 to leading order. Upon varying the coupling constant of the theory we find that in weak coupling, the FFLO phase is favored at arbitrary flavor asymmetries for sufficiently low temperatures; at intermediate coupling its occupancy domain is shifted towards larger asymmetries. Strong coupling features a new regime of an inhomogeneous FF state, which we identify with a current-carrying Bose-Einstein condensate of tightly bound up and down quarks. The temperature and asymmetry dependence of the gap function is studied. It is shown that the anomalous temperature dependence of the gap in the homogeneous, flavor-asymmetric phase is transformed into a normal dependence (self-similar to the BCS phase) at arbitrary coupling, once the FF phase is allowed for. We analyze the occupation numbers and the Cooper-pair wave function and show that when the condensate momentum is orthogonal to the particle momentum the minority component contains a blocking region (breach) around the Fermi sphere in the weak-coupling limit, which engulfs more low-momentum modes as the coupling is increased, and eventually leads to a topological change in strong coupling, where the minority Fermi sphere contains either two occupied strips or an empty sphere. For nonorthogonal momenta, the blocking

  11. QCD Phase Diagram and the Constant Mass Approximation

    NASA Astrophysics Data System (ADS)

    Ahmad, A.; Ayala, A.; Bashir, A.; Gutiérrez, E.; Raya, A.

    2015-11-01

    Dynamical generation of quark masses in the infrared region of QCD plays an important role to understand the peculiar nature of the physics of hadrons. As it is known, the solution of QCD gap equation for the quark mass function is flat for low momentum, but smoothly evolves to the perturbative behavior at high momentum. In this work, we use an effective truncation of QCD gap equation valid up to 1 GeV, and implement it at finite temperature and chemical potential to understand the QCD phase diagram for chiral symmetry breaking-chiral symmetry restoration, and confinement-deconfinement phase transitions from the Schwinger-Dysin equations point of view. Our effective kernel contains a gluon dressing function with two light quark flavors Nf = 2, with current quark mass 0.0035 GeV. An effective coupling, adjusted to reproduce the behavior of the chiral condensate at finite T complements our truncation. We find the critical end point of the phase diagram located at the temperature TE = 0.1245 GeV and the baryonic chemical potential μEB = 0.211 GeV.

  12. Edge states and phase diagram for graphene under polarized light

    NASA Astrophysics Data System (ADS)

    Wang, Yi-Xiang; Li, Fuxiang

    2016-07-01

    In this work, we investigate the topological phase transitions in graphene under the modulation of circularly polarized light, by analyzing the changes of edge states and its topological structures. A full phase diagram, with several different topological phases, is presented in the parameter space spanned by the driving frequency and light strength. We find that the high-Chern number behavior is very common in the driven system. While the one-photon resonance can create the chiral edge states in the π-gap, the two-photon resonance will induce the counter-propagating edge modes in the zero-energy gap. When the driving light strength is strong, the number and even the chirality of the edge states may change in the π-gap. The robustness of the edge states to disorder potential is also examined. We close by discussing the feasibility of experimental proposals.

  13. Edge states and phase diagram for graphene under polarized light

    DOE PAGESBeta

    Wang, Yi -Xiang; Li, Fuxiang

    2016-03-22

    In this paper, we investigate the topological phase transitions in graphene under the modulation of circularly polarized light, by analyzing the changes of edge states and its topological structures. A full phase diagram, with several different topological phases, is presented in the parameter space spanned by the driving frequency and light strength. We find that the high-Chern number behavior is very common in the driven system. While the one-photon resonance can create the chiral edge states in the π-gap, the two-photon resonance will induce the counter-propagating edge modes in the zero-energy gap. When the driving light strength is strong, themore » number and even the chirality of the edge states may change in the π-gap. The robustness of the edge states to disorder potential is also examined. We close by discussing the feasibility of experimental proposals.« less

  14. Surface phase diagram for Cr_2O_3(0001)

    NASA Astrophysics Data System (ADS)

    Wang, Xiao-Gang; Smith, John R.

    2004-03-01

    Surface phases of Cr_2O3 (0001) as a function of ambient oxygen pressure and temperature were computed by ab initio density-functional theory for a solid surface^1. The surface can be (1×1) or (√3×√3) Cr-terminated, (1×1) O-terminated, and (1×1) or (√3×√3) (O=Cr)-terminated. This is the first theory of the chromyl (O=Cr) termination. The terminations critically depend on the environment, i.e., on the temperature and on the ambient oxygen partial pressure. The first-principles phase diagram is compared with a substantial number of experimental observations of surface phases. 1. Xiao-Gang Wang and John R. Smith, Phys. Rev. B 68, 201402(R) (2003).

  15. The High Field Phase Diagram of (2) Perchlorate Tetramethyltetraselenafulvalene

    NASA Astrophysics Data System (ADS)

    McKernan, Steffen Keleher

    1995-11-01

    We have established the magnetic phase diagram of (TMTSF)_2ClO_4 to fields of 30 tesla at temperatures above 0.5 K. The phase diagram is derived from a wealth of data amassed on six physical parameters, rho_ {xx}, rho_{yy }, rho_{zz} , rho_{xy}, S_{xx} (thermopower) and magnetization. The cascade of field induced spin density waves produced by fields along the crystalline c-axis and known to exist below 8 T, saturates to a maximum transition temperature of 5.5 K at approximately 15 T. This second order phase boundary persists at 5.5 K to 30 T. Wholly contained within this upper phase boundary, there is a newly discovered first order phase line which begins in an apparent critical point at 3.5 K and 22 T. This lower phase boundary continues at constant temperature to ~26 T, where it begins to decrease in temperature, falling below our measurement range at approximately 27 T. The previously reported high field reentrance to the normal state, is not found. (TMTSF)_2ClO_4 is formed by stacking the planar tetramethyltetraselenafulvalene (TMTSF) molecules along the crystalline a-axis. These stacks are separated along the c-axis by the perchlorate anions. At 24 K, the pyramidal anions order with wave vector (0, 1over 2, 0), thus distinguishing alternate chains and giving rise to two distinct Fermi surfaces. The high field spin density wave states are tentatively interpreted in terms of separate, weakly coupled transitions on these Fermi surfaces.

  16. Study of charge-phase diagrams for coupled system of Josephson junctions

    NASA Astrophysics Data System (ADS)

    Hamdipour, M.; Shukrinov, Y. U. M.

    2010-11-01

    Dynamics of stacked intrinsic Josephson junctions (IJJ) in the high-Tc superconductors is theoretically investigated. We calculate the current-voltage characteristics (CVC) of IJJ and study the breakpoint region on the outermost branch of the CVC for the stacks with 9 IJJ. A method for investigation of the fine structure in CVC of IJJ based on the recording the "phase-charge" diagrams is suggested. It is demonstrated that this method reflects the main features of the breakpoint region.

  17. Investigation of new phases in the Ba-Si phase diagram under high pressure using ab initio structural search.

    PubMed

    Shi, Jingming; Cui, Wenwen; Flores-Livas, José A; San-Miguel, Alfonso; Botti, Silvana; Marques, Miguel A L

    2016-03-01

    Barium silicides are versatile materials that have attracted attention for a variety of applications in electronics and optoelectronics. Using an unbiased structural search based on a particle-swarm optimization algorithm combined with density functional theory calculations, we investigate systematically the ground-state phase stability and the structural diversity of Ba-Si binaries under high pressure. The phase diagram turns out to be quite intricate, with several compositions stabilizing/destabilizing as a function of pressure. In particular, we identify novel phases of BaSi, BaSi2, BaSi3, and BaSi5 that might be synthesizable experimentally over a wide range of pressures. Our results not only clarify and complete the previously known structural phase diagram, but also provide new insights for understanding the Ba-Si binary system. PMID:26923068

  18. State diagram of magnetostatic coupling phase-locked spin-torque oscillators

    SciTech Connect

    Zhang, Mengwei; Wang, Longze; Wei, Dan; Gao, Kai-Zhong

    2015-05-07

    The state diagram of magnetostatic coupling phase-locked spin torque oscillator (STO) with perpendicular reference layer and planar field generation layer (FGL) is studied by the macrospin model and the micromagnetic model. The state diagrams of current densities are calculated under various external fields. The simulation shows that there are two phase-lock current density regions. In the phase-locked STOs in low current region I, the spin configuration of FGL is uniform; in high current region II, the spin configuration of FGL is highly nonuniform. In addition, the results with different STOs separation L{sub s} are compared, and the coupling between two STOs is largely decreased when L{sub s} is increased from 40 nm to 60 nm.

  19. Invariants in the Yukawa system's thermodynamic phase diagram

    NASA Astrophysics Data System (ADS)

    Veldhorst, Arno A.; Schrøder, Thomas B.; Dyre, Jeppe C.

    2015-07-01

    This paper shows that several known properties of the Yukawa system can be derived from the isomorph theory, which applies to any system that has strong correlations between its virial and potential-energy equilibrium fluctuations. Such "Roskilde-simple" systems have a simplified thermodynamic phase diagram deriving from the fact that they have curves (isomorphs) along which structure and dynamics in reduced units are invariant to a good approximation. We show that the Yukawa system has strong virial potential-energy correlations and identify its isomorphs by two different methods. One method, the so-called direct isomorph check, identifies isomorphs numerically from jumps of relatively small density changes (here 10%). The second method identifies isomorphs analytically from the pair potential. The curves obtained by the two methods are close to each other; these curves are confirmed to be isomorphs by demonstrating the invariance of the radial distribution function, the static structure factor, the mean-square displacement as a function of time, and the incoherent intermediate scattering function. Since the melting line is predicted to be an isomorph, the theory provides a derivation of a known approximate analytical expression for this line in the temperature-density phase diagram. The paper's results give the first demonstration that the isomorph theory can be applied to systems like dense colloidal suspensions and strongly coupled dusty plasmas.

  20. Invariants in the Yukawa system's thermodynamic phase diagram

    SciTech Connect

    Veldhorst, Arno A. Schrøder, Thomas B.; Dyre, Jeppe C.

    2015-07-15

    This paper shows that several known properties of the Yukawa system can be derived from the isomorph theory, which applies to any system that has strong correlations between its virial and potential-energy equilibrium fluctuations. Such “Roskilde-simple” systems have a simplified thermodynamic phase diagram deriving from the fact that they have curves (isomorphs) along which structure and dynamics in reduced units are invariant to a good approximation. We show that the Yukawa system has strong virial potential-energy correlations and identify its isomorphs by two different methods. One method, the so-called direct isomorph check, identifies isomorphs numerically from jumps of relatively small density changes (here 10%). The second method identifies isomorphs analytically from the pair potential. The curves obtained by the two methods are close to each other; these curves are confirmed to be isomorphs by demonstrating the invariance of the radial distribution function, the static structure factor, the mean-square displacement as a function of time, and the incoherent intermediate scattering function. Since the melting line is predicted to be an isomorph, the theory provides a derivation of a known approximate analytical expression for this line in the temperature-density phase diagram. The paper's results give the first demonstration that the isomorph theory can be applied to systems like dense colloidal suspensions and strongly coupled dusty plasmas.

  1. The phase diagram and hardness of carbon nitrides

    SciTech Connect

    Dong, Huafeng; Oganov, Artem R.; Zhu, Qiang; Zhu, Qiang; Qian, Guang-Rui

    2015-05-06

    Novel superhard materials, especially those with superior thermal and chemical stability, are needed to replace diamond. Carbon nitrides (C-N), which are likely to possess these characteristics and have even been expected to be harder than diamond, are excellent candidates. Here we report three new superhard and thermodynamically stable carbon nitride phases. Based on a systematic evolutionary structure searches, we report a complete phase diagram of the C-N system at 0–300 GPa and analyze the hardest metastable structures. Surprisingly, we find that at zero pressure, the earlier proposed graphitic-C3N4 structure (P6-bar m2) is dynamically unstable, and we find the lowest-energy structure based on s-triazine unit and s-heptazine unit.

  2. The phase diagram and hardness of carbon nitrides

    PubMed Central

    Dong, Huafeng; Oganov, Artem R.; Zhu, Qiang; Qian, Guang-Rui

    2015-01-01

    Novel superhard materials, especially those with superior thermal and chemical stability, are needed to replace diamond. Carbon nitrides (C-N), which are likely to possess these characteristics and have even been expected to be harder than diamond, are excellent candidates. Here we report three new superhard and thermodynamically stable carbon nitride phases. Based on a systematic evolutionary structure searches, we report a complete phase diagram of the C-N system at 0–300 GPa and analyze the hardest metastable structures. Surprisingly, we find that at zero pressure, the earlier proposed graphitic-C3N4 structure () is dynamically unstable, and we find the lowest-energy structure based on s-triazine unit and s-heptazine unit. PMID:25943072

  3. The phase diagram and hardness of carbon nitrides

    DOE PAGESBeta

    Dong, Huafeng; Oganov, Artem R.; Zhu, Qiang; Qian, Guang-Rui

    2015-05-06

    Novel superhard materials, especially those with superior thermal and chemical stability, are needed to replace diamond. Carbon nitrides (C-N), which are likely to possess these characteristics and have even been expected to be harder than diamond, are excellent candidates. Here we report three new superhard and thermodynamically stable carbon nitride phases. Based on a systematic evolutionary structure searches, we report a complete phase diagram of the C-N system at 0–300 GPa and analyze the hardest metastable structures. Surprisingly, we find that at zero pressure, the earlier proposed graphitic-C3N4 structure (P6-bar m2) is dynamically unstable, and we find the lowest-energy structuremore » based on s-triazine unit and s-heptazine unit.« less

  4. On the Cu-Nb Phase Diagram and Solidified Microstructures

    NASA Technical Reports Server (NTRS)

    Li, D.; Robinson, M. B.; Rathz, T. J.; Williams, G.

    1998-01-01

    Container and containerless processing was employed to determine liquidus temperatures and to examine microstructural development in the Cu-Nb system. The Cu-Nb phase diagram of an S-shaped, near-horizontal liquidus, has been confirmed by both the temperature-time profiles and resultant microstructures with only Nb dendrites in a Cu matrix, which were obtained from crucible experiments under clean conditions. However, the microstructural pathways of Cu-Nb alloys are particularly sensitive to processing variables. By the addition of oxygen impurities or rapid solidification, droplet-shaped morphology was observed for some compositions, implying occurrence of a liquid-phase separation. The effects of impurities and cooling rates are analyzed in connection with a stable and metastable liquid miscibility gap, respectively.

  5. The Iron-Iron Carbide Phase Diagram: A Practical Guide to Some Descriptive Solid State Chemistry.

    ERIC Educational Resources Information Center

    Long, Gary J.; Leighly, H. P., Jr.

    1982-01-01

    Discusses the solid state chemistry of iron and steel in terms of the iron-iron carbide phase diagram. Suggests that this is an excellent way of introducing the phase diagram (equilibrium diagram) to undergraduate students while at the same time introducing the descriptive solid state chemistry of iron and steel. (Author/JN)

  6. Experimental Investigation of the Cd-Pr Phase Diagram

    PubMed Central

    Reichmann, Thomas L.; Effenberger, Herta S.; Ipser, Herbert

    2014-01-01

    The complete Cd-Pr equilibrium phase diagram was investigated with a combination of powder-XRD, SEM and DTA. All intermetallic compounds within this system, already reported in literature, could be confirmed: CdPr, Cd2Pr, Cd3Pr, Cd45Pr11, Cd58Pr13, Cd6Pr and Cd11Pr. The corresponding phase boundaries were determined at distinct temperatures. The homogeneity range of the high-temperature allotropic modification of Pr could be determined precisely and a limited solubility of 22.1 at.% Cd was derived. Additionally, single-crystal X-ray diffraction was employed to investigate structural details of Cd2Pr; it is isotypic to the AlB2-type structure with a z value of the Cd site of 0.5. DTA results of alloys located in the adjacent two-phase fields of Cd2Pr suggested a phase transformation between 893 and 930°C. For the phase Cd3Pr it was found that the lattice parameter a changes linearly with increasing Cd content, following Vegard’s rule. The corresponding defect mechanism could be evaluated from structural data collected with single-crystal XRD. Introduction of a significant amount of vacancies on the Pr site and the reduction in symmetry of one Cd position (8c to 32f) resulted in a noticeable decrease of all R-values. PMID:24718502

  7. Experimental investigation of the Cd-Pr phase diagram.

    PubMed

    Reichmann, Thomas L; Effenberger, Herta S; Ipser, Herbert

    2014-01-01

    The complete Cd-Pr equilibrium phase diagram was investigated with a combination of powder-XRD, SEM and DTA. All intermetallic compounds within this system, already reported in literature, could be confirmed: CdPr, Cd2Pr, Cd3Pr, Cd45Pr11, Cd58Pr13, Cd6Pr and Cd11Pr. The corresponding phase boundaries were determined at distinct temperatures. The homogeneity range of the high-temperature allotropic modification of Pr could be determined precisely and a limited solubility of 22.1 at.% Cd was derived. Additionally, single-crystal X-ray diffraction was employed to investigate structural details of Cd2Pr; it is isotypic to the AlB2-type structure with a z value of the Cd site of 0.5. DTA results of alloys located in the adjacent two-phase fields of Cd2Pr suggested a phase transformation between 893 and 930°C. For the phase Cd3Pr it was found that the lattice parameter a changes linearly with increasing Cd content, following Vegard's rule. The corresponding defect mechanism could be evaluated from structural data collected with single-crystal XRD. Introduction of a significant amount of vacancies on the Pr site and the reduction in symmetry of one Cd position (8c to 32f) resulted in a noticeable decrease of all R-values. PMID:24718502

  8. Phase diagram of the uniaxial and biaxial soft-core Gay-Berne model

    NASA Astrophysics Data System (ADS)

    Berardi, Roberto; Lintuvuori, Juho S.; Wilson, Mark R.; Zannoni, Claudio

    2011-10-01

    Classical molecular dynamics simulations have been used to explore the phase diagrams for a family of attractive-repulsive soft-core Gay-Berne models [R. Berardi, C. Zannoni, J. S. Lintuvuori, and M. R. Wilson, J. Chem. Phys. 131, 174107 (2009)] and determine the effect of particle softness, i.e., of a moderately repulsive short-range interaction, on the order parameters and phase behaviour of model systems of uniaxial and biaxial ellipsoidal particles. We have found that isotropic, uniaxial, and biaxial nematic and smectic phases are obtained for the model. Extensive calculations of the nematic region of the phase diagram show that endowing mesogenic particles with such soft repulsive interactions affect the stability range of the nematic phases, and in the case of phase biaxiality it also shifts it to lower temperatures. For colloidal particles, stabilised by surface functionalisation, (e.g., with polymer chains), we suggest that it should be possible to tune liquid crystal behaviour to increase the range of stability of uniaxial and biaxial phases (by varying solvent quality). We calculate second virial coefficients and show that they are a useful means of characterising the change in effective softness for such systems. For thermotropic liquid crystals, the introduction of softness in the interactions between mesogens with overall biaxial shape (e.g., through appropriate conformational flexibility) could provide a pathway for the actual chemical synthesis of stable room-temperature biaxial nematics.

  9. Phase diagram of the uniaxial and biaxial soft-core Gay-Berne model.

    PubMed

    Berardi, Roberto; Lintuvuori, Juho S; Wilson, Mark R; Zannoni, Claudio

    2011-10-01

    Classical molecular dynamics simulations have been used to explore the phase diagrams for a family of attractive-repulsive soft-core Gay-Berne models [R. Berardi, C. Zannoni, J. S. Lintuvuori, and M. R. Wilson, J. Chem. Phys. 131, 174107 (2009)] and determine the effect of particle softness, i.e., of a moderately repulsive short-range interaction, on the order parameters and phase behaviour of model systems of uniaxial and biaxial ellipsoidal particles. We have found that isotropic, uniaxial, and biaxial nematic and smectic phases are obtained for the model. Extensive calculations of the nematic region of the phase diagram show that endowing mesogenic particles with such soft repulsive interactions affect the stability range of the nematic phases, and in the case of phase biaxiality it also shifts it to lower temperatures. For colloidal particles, stabilised by surface functionalisation, (e.g., with polymer chains), we suggest that it should be possible to tune liquid crystal behaviour to increase the range of stability of uniaxial and biaxial phases (by varying solvent quality). We calculate second virial coefficients and show that they are a useful means of characterising the change in effective softness for such systems. For thermotropic liquid crystals, the introduction of softness in the interactions between mesogens with overall biaxial shape (e.g., through appropriate conformational flexibility) could provide a pathway for the actual chemical synthesis of stable room-temperature biaxial nematics. PMID:21992294

  10. Stereoscopic Diagrams Prepared by a Desk Calculator and Plotter

    ERIC Educational Resources Information Center

    Hayman, H. J. G.

    1977-01-01

    Describes the use of a Hewlett-Packard 9810A programmable desk calculator with plotter for drawing ball-and-line stereopairs as well as three-dimensional structural formulas which are useful for teaching stereochemical principles and molecular structure. (MLH)

  11. Gd5(SixGe1-x)4 system - updated phase diagram

    NASA Astrophysics Data System (ADS)

    Melikhov, Yevgen; Hadimani, R. L.; Raghunathan, Arun

    2015-12-01

    Gd5(SixGe1-x)4 for 0.41phase transition between the two. In this range, the magnetic moment vs. magnetic field (MH) isotherms measured just above the first order transition temperature carry information about all magnetic and structural transitions. Here, the Curie-Weiss law was applied to the paramagnetic portions of the MH isotherms which allowed identification of the second order magnetic phase transition temperature of the monoclinic phase, a region where the second order transition does not occur due to the existence of the first order transition. The calculated second order phase transition temperatures of the monoclinic phase were added to the existing phase diagram. The completed magnetic-structural phase diagram carries now all the information including the magnetic transition temperatures of both monoclinic and orthorhombic phases. It was also found that the magnetic transition temperature of the monoclinic phase and the first order transition temperature are interrelated.

  12. Ab Initio Construction of Magnetic Phase Diagrams in Alloys: The Case of Fe(1-x)Mn(x)Pt.

    PubMed

    Pujari, B S; Larson, P; Antropov, V P; Belashchenko, K D

    2015-07-31

    A first-principles approach to the construction of concentration-temperature magnetic phase diagrams of metallic alloys is presented. The method employs self-consistent total energy calculations based on the coherent potential approximation for partially ordered and noncollinear magnetic states and is able to account for competing interactions and multiple magnetic phases. Application to the Fe(1-x)Mn(x)Pt "magnetic chameleon" system yields the sequence of magnetic phases at T=0 and the c-T magnetic phase diagram in good agreement with experiment, and a new low-temperature phase is predicted at the Mn-rich end. The importance of non-Heisenberg interactions for the description of the magnetic phase diagram is demonstrated. PMID:26274437

  13. Phase Diagram of Inhomogeneous Percolation with a Defect Plane

    NASA Astrophysics Data System (ADS)

    Iliev, G. K.; Janse van Rensburg, E. J.; Madras, N.

    2015-01-01

    Let be the -dimensional hypercubic lattice and let be an -dimensional sublattice, with . We consider a model of inhomogeneous bond percolation on at densities and , in which edges in are open with probability , and edges in open with probability . We generalize several classical results of (homogeneous) bond percolation to this inhomogeneous model. The phase diagram of the model is presented, and it is shown that there is a subcritical regime for and (where is the critical probability for homogeneous percolation in ), a bulk supercritical regime for , and a surface supercritical regime for and . We show that is a strictly decreasing function for , with a jump discontinuity at . We extend the Aizenman-Barsky differential inequalities for homogeneous percolation to the inhomogeneous model and use them to prove that the susceptibility is finite inside the subcritical phase. We prove that the cluster size distribution decays exponentially in the subcritical phase, and sub-exponentially in the supercritical phases. For a model of lattice animals with a defect plane, the free energy is related to functions of the inhomogeneous percolation model, and we show how the percolation transition implies a non-analyticity in the free energy of the animal model. Finally, we present simulation estimates of the critical curve.

  14. Extended phase diagram of the three-dimensional phase field crystal model.

    PubMed

    Jaatinen, A; Ala-Nissila, T

    2010-05-26

    We determine the phase diagram of the phase field crystal model in three dimensions by using numerical free energy minimization methods. Previously published results, based on single mode approximations, have indicated that in addition to the uniform (liquid) phase, there would be regions of stability of body-centered cubic, hexagonal and stripe phases. We find that in addition to these, there are also regions of stability of face-centered cubic and hexagonal close packed structures in this model. PMID:21393705

  15. Quantum path-integral study of the phase diagram and isotope effects of neon.

    PubMed

    Ramírez, R; Herrero, C P

    2008-11-28

    The phase diagram of natural neon has been calculated for temperatures in the range of 17-50 K and pressures between 10(-2) and 2 x 10(3) bar. The phase coexistence between solid, liquid, and gas phases has been determined by the calculation of the separate free energy of each phase as a function of temperature. Thus, for a given pressure, the coexistence temperature was obtained by the condition of equal free energy of coexisting phases. The free energy was calculated by using nonequilibrium techniques such as adiabatic switching and reversible scaling. The phase diagram obtained by classical Monte Carlo simulations has been compared to that obtained by quantum path-integral simulations. Quantum effects related to the finite mass of neon cause that coexistence lines are shifted toward lower temperatures when compared to the classical limit. The shift found in the triple point amounts to 1.5 K, i.e., about 6% of the triple-point temperature. The triple-point isotope effect has been determined for (20)Ne, (21)Ne, (22)Ne, and natural neon. The simulation data show satisfactory agreement to previous experimental results, which report a shift of about 0.15 K between triple-point temperatures of (20)Ne and (22)Ne. The vapor pressure isotope effect has been calculated for both solid and liquid phases at triple-point conditions. The quantum simulations predict that this isotope effect is larger in the solid than in the liquid phase, and the calculated values show nearly quantitative agreement to available experimental data. PMID:19045868

  16. Phase diagram of the isovalent phosphorous-substituted 122-type iron pnictides

    DOE PAGESBeta

    Zhao, YuanYuan; Tai, Yuan -Yen; Ting, C. S.

    2015-05-11

    Recent experiments demonstrated that the isovalent doping system gives a similar phase diagram as the heterovalent doped cases. For example, with the phosphorous (P) doping, the magnetic order in BaFe2(As1–xPx)2 compound is first suppressed, then the superconductivity dome emerges to an extended doping region but eventually it disappears at large x. With the help of a minimal two-orbital model for both BaFe2As2 and BaFe2P2, together with the self-consistent lattice Bogoliubov-de Gennes (BdG) equation, we calculate the phase diagram against the P content x in which the doped isovalent P atoms are treated as impurities. Furthermore, we show that our numericalmore » results can qualitatively compare with the experimental measurements.« less

  17. Phase diagram of the isovalent phosphorous-substituted 122-type iron pnictides

    SciTech Connect

    Zhao, YuanYuan; Tai, Yuan -Yen; Ting, C. S.

    2015-05-11

    Recent experiments demonstrated that the isovalent doping system gives a similar phase diagram as the heterovalent doped cases. For example, with the phosphorous (P) doping, the magnetic order in BaFe2(As1–xPx)2 compound is first suppressed, then the superconductivity dome emerges to an extended doping region but eventually it disappears at large x. With the help of a minimal two-orbital model for both BaFe2As2 and BaFe2P2, together with the self-consistent lattice Bogoliubov-de Gennes (BdG) equation, we calculate the phase diagram against the P content x in which the doped isovalent P atoms are treated as impurities. Furthermore, we show that our numerical results can qualitatively compare with the experimental measurements.

  18. Phase diagrams of orientational transitions in absorbing nematic liquid crystals

    SciTech Connect

    Zolot’ko, A. S. Ochkin, V. N.; Smayev, M. P.; Shvetsov, S. A.

    2015-05-15

    A theory of orientational transitions in nematic liquid crystals (NLCs), which employs the expansion of optical torques acting on the NLC director with respect to the rotation angle, has been developed for NLCs with additives of conformationally active compounds under the action of optical and low-frequency electric and magnetic fields. Phase diagrams of NLCs are constructed as a function of the intensity and polarization of the light field, the strength of low-frequency electric field, and a parameter that characterizes the feedback between the rotation of the NLC director and optical torque. Conditions for the occurrence of first- and second-order transitions are determined. The proposed theory agrees with available experimental data.

  19. Phase diagram of hopping conduction mechanisms in polymer nanofiber network

    SciTech Connect

    Li, Jeng-Ting; Lu, Yu-Cheng; Jiang, Shiau-Bin; Zhong, Yuan-Liang; Yeh, Jui-Ming

    2015-12-07

    Network formation by nanofiber crosslinking is usually in polymer materials as application in organic semiconductor devices. Electron hopping transport mechanisms depend on polymer morphology in network. Conducting polymers morphology in a random network structure is modeled by a quasi-one-dimensional system coupled of chains or fibers. We observe the varying hopping conduction mechanisms in the polyaniline nanofibers of the random network structure. The average diameter d of the nanofibers is varied from approximately 10 to 100 nm. The different dominant hopping mechanisms including Efros-Shklovskii variable-range hopping (VRH), Mott VRH, and nearest-neighbor hopping are dependent on temperature range and d in crossover changes. The result of this study is first presented in a phase diagram of hopping conduction mechanisms based on the theories of the random network model. The hopping conduction mechanism is unlike in normal semiconductor materials.

  20. Topological excitations and the phase diagram of the superconducting cuprates

    NASA Astrophysics Data System (ADS)

    Marino, Eduardo C.; Silva Neto, Marcello B.

    2002-03-01

    We study the destruction of long-range antiferromagnetic order in the high-Tc superconductors La2-xSrxCuO4 and YBa2Cu3O6+x, within the framework of the CP1-nonlinear sigma model coupled to Dirac fermions that describe the doped holes. Skyrmion topological defects are shown to be introduced by doping and their energy is used as an order parameter for the antiferromagnetic state. We obtain analytic expressions for the skyrmion energy as a function of doping which allow us to plot the curves TN(xc)×xc and M(x)×x, for the two compounds, in good quantitative agreement with the experimental data. We also discuss stripes formation and analyse its effects on the curves of the phase diagram.

  1. Magnetic quantum phase diagram of magnetic impurities in two-dimensional disordered electron systems

    NASA Astrophysics Data System (ADS)

    Lee, Hyun Yong; Kettemann, Stefan

    2014-04-01

    The quantum phase diagram of disordered electron systems as a function of the concentration of magnetic impurities nm and the local exchange coupling J is studied in the dilute limit. We take into account the Anderson localization of the electrons by a nonperturbative numerical treatment of the disorder potential. The competition between Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction JRKKY and the Kondo effect, as governed by the temperature scale TK, is known to give rise to a rich magnetic quantum phase diagram, the Doniach diagram. Our numerical calculations show that in a disordered system both the Kondo temperature TK and JRKKY as well as their ratio JRKKY/TK is widely distributed. However, we find a sharp cutoff of that distribution, which allows us to define a critical density of magnetic impurities nc below which Kondo screening wins at all sites of the system above a critical coupling Jc, forming the Kondo phase [see Fig. 3(b)]. As disorder is increased, Jc increases and a spin coupled phase is found to grow at the expense of the Kondo phase. From these distribution functions we derive the magnetic susceptibility which show anomalous power-law behavior. In the Kondo phase that power is determined by the wide distribution of the Kondo temperature, while in the spin coupled phase it is governed by the distribution of JRKKY. At low densities and small J phase (LM). We also report results on a honeycomb lattice, graphene, where we find that the spin coupled phase is more stable against Kondo screening, but is more easily destroyed by disorder into a LM phase.

  2. Phase diagram of the Pr-Mn-O system in composition-temperature-oxygen pressure coordinates

    NASA Astrophysics Data System (ADS)

    Vedmid', L. B.; Yankin, A. M.; Fedorova, O. M.; Kozin, V. M.

    2016-05-01

    The phase relations in the Pr-Mn-O system were studied by the static method at lowered oxygen pressure in combination with thermal analysis and high-temperature X-ray diffraction. The equilibrium oxygen pressure in dissociation of PrMn2O5 and PrMnO3 was measured, and the thermodynamic characteristics of formation of these compounds from elements were calculated. The P- T- x phase diagram of the Pr-Mn-O system was constructed in the "composition-oxygen pressure-temperature" coordinates.

  3. Pressure-temperature phase diagram for the Allende meteorite

    NASA Astrophysics Data System (ADS)

    Agee, C. B.; Li, J.; Shannon, M. C.; Circone, S.

    1995-09-01

    Piston cylinder and multianvil experiments from 1 to 27 GPa have been performed on the Allende CV3 meteorite to establish a pressure-temperature phase diagram that includes major phase boundaries and the silicate-oxide-sulfide melting intervals. Olivine is the liquidus phase up to ~14 GPa, followed by garnet up to ~25 GPa. Near 26 GPa a cotectic exists where garnet and magnesiowüstite are liquidus phases. Magnesiowüstite is likely to be a lower mantle liquidus phase in both chondritic and peridotitic (see also Zhang and Herzberg, 1994) compositions. Hence element partitioning tests that neglect the role of liquidus magnesiowüstite may be incomplete for describing planetary differentiation at pressures >25 GPa. Allende shows immiscibility between (Fe,Ni)-sulfide melt and FeO-rich silicate melt. (Fe,Ni)-sulfide is the lower temperature melt phase and is present at all experimental pressures and temperatures investigated. It is concluded that a terrestrial planet with a radius of ~3000 km (maximum internal pressure of ~30 GPa), and a bulk composition of carbonaceous chondrite, will upon magmatic differentiation form an FeO-rich silicate mantle with an Fe-Ni-S core. The silicate fraction of Allende in our high-pressure experiments is too rich in FeO to be a good match for the composition of peridotite xenoliths from Earth's upper mantle. However, the major elements of a peridotite upper mantle may be derived from an Allende-like bulk Earth by a combination of lower mantle magnesiowüstite, perovskite, and sulfide fractionation and by upper mantle olivine flotation.

  4. Relationship between grain/interphase boundary energies and phase diagrams

    NASA Astrophysics Data System (ADS)

    Hiraga, T.; Matsuzaki, T.; Tsurekawa, S.; Watanabe, T.; Kohlstedt, D. L.

    2004-12-01

    We have examined the relationship between the type of phase diagram and relative grain boundary to interphase boundary energy in order to answer a long-term unsolved question: Why do crystals prefer different neighbors? For minerals as well as metals and ceramics, dihedral angles formed at triple grain junctions involving two different crystalline phases (A and B) are commonly <120° . Based on the interface tension balance equation 2cos(θ /2) = γ gb/γ int (Eq. 1) -- where \\theta is dihedral angle and γ is either grain or interphase boundary energy -- a value of θ <120° indicates that the interphase boundary energy is lower than of the grain boundary energy. Grain boundary energies of metals correlate linearly with latent heat of fusion and/or melting temperature. Systems composed of two crystalline phases often have a eutectic point at a lower temperature than the melting points of pure phases; accordingly, the latent heat of fusion is lower for the two-phase system than for the individual component phases. Therefore, we predict that the interphase boundary energy is lower than that of the grain boundaries in the case of a eutectic system; however, the opposite holds for monotectic systems. We examined grain boundary versus phase boundary energies for binary systems in which one phase is Ag and the other is Fe, Co, Ni, Cu, Ge, or Si. The systems formed from Ag and any of the former three elements are monotectics, while the systems composed of Ag and any of the latter three elements are eutectics. To obtain binary polycrystalline materials, we sintered the powders of 5-10 μ m of Ag plus either Fe, Co, Ni or Cu at vacuum conditions. We also made amorphous ribbons of Ag-Si and Ag-Ge by the rapid rolling technique, which we then annealed for 10-15 h to cause crystallization and grain growth. After surface etching, we measured dihedral angles with a field emission SEM. Also, we used dihedral angle data for synthetic and natural mineral assemblages of quartz

  5. Equation of state and phase diagram of FeO

    SciTech Connect

    Fischer, Rebecca A.; Campbell, Andrew J.; Shofner, Gregory A.; Lord, Oliver T.; Dera, Przemyslaw; Prakapenka, Vitali B.

    2012-04-11

    Wuestite, Fe{sub 1-x}O, is an important component in the mineralogy of Earth's lower mantle and may also be a component in the core. Therefore the high pressure, high temperature behavior of FeO, including its phase diagram and equation of state, is essential knowledge for understanding the properties and evolution of Earth's deep interior. We performed X-ray diffraction measurements using a laser-heated diamond anvil cell to achieve simultaneous high pressures and temperatures. Wuestite was mixed with iron metal, which served as our pressure standard, under the assumption that negligible oxygen dissolved into the iron. Our data show a positive slope for the subsolidus phase boundary between the B1 and B8 structures, indicating that the B1 phase is stable at the P-T conditions of the lower mantle and core. We have determined the thermal equation of state of B1 FeO to 156 GPa and 3100 K, finding an isothermal bulk modulus K{sub 0} = 149.4 {+-} 1.0 GPa and its pressure derivative K'{sub 0} = 3.60 {+-} 0.4. This implies that 7.7 {+-} 1.1 wt.% oxygen is required in the outer core to match the seismologically-determined density, under the simplifying assumption of a purely Fe-O outer core.

  6. Sub-monolayer Strontium Phase Diagram on Silicon (100)

    NASA Astrophysics Data System (ADS)

    Reiner, James; Garrity, Kevin; Walker, Fred; Ismail-Beigi, Sohrab; Ahn, C. H.

    2008-03-01

    Crystalline oxides manifest a number of important phenomena, including magnetism, ferroelectricity, superconductivity, and colossal magnetoresistance. Recently, it has become possible to integrate these materials onto a silicon platform in a fully epitaxial structure. These crystalline oxide-silicon heterostructures bring the promise of integrating the rich functionality present in crystalline oxides with modern silicon device technology. The most successful fully epitaxial oxide-silicon (100) heterostructures have been achieved through a deposition recipe that involves manipulating substrate temperature and oxygen pressure on a layer by layer basis during the deposition of an alkaline earth metal. Motivated by a desire to develop a fundamental understanding of this important transition layer between silicon and oxide, we have mapped out the phase diagram of strontium on silicon as a function of temperature and coverage. In particular, recent work on sub-monolayer strontium deposition on the silicon surface suggests the conventional picture of this structure, upon which the entire crystalline oxides on silicon framework is built, is only a low-temperature phase which plays no role in enabling epitaxial oxide growth. Instead, there is strong evidence that a different high temperature phase is the crucial template for epitaxial oxide growth on silicon.

  7. Predicted phase diagram of boron-carbon-nitrogen

    NASA Astrophysics Data System (ADS)

    Zhang, Hantao; Yao, Sanxi; Widom, Michael

    2016-04-01

    Noting the structural relationships between phases of carbon and boron carbide with phases of boron nitride and boron subnitride, we investigate their mutual solubilities using a combination of first-principles total energies supplemented with statistical mechanics to address finite temperatures. Thus we predict the solid-state phase diagram of boron-carbon-nitrogen (B-C-N). Owing to the large energy costs of substitution, we find that the mutual solubilities of the ultrahard materials diamond and cubic boron nitride are negligible, and the same for the quasi-two-dimensional materials graphite and hexagonal boron nitride. In contrast, we find a continuous range of solubility connecting boron carbide to boron subnitride at elevated temperatures. An electron-precise ternary compound B13CN consisting of B12 icosahedra with NBC chains is found to be stable at all temperatures up to melting. It exhibits an order-disorder transition in the orientation of NBC chains at approximately T =500 K. We also propose that the recently discovered binary B13N2 actually has composition B12.67N2 .

  8. Phase diagram of oxygen adsorbed on Ni(111) and thermodynamic properties from first-principles

    NASA Astrophysics Data System (ADS)

    Lazo, C.; Keil, F. J.

    2009-06-01

    The thermodynamic properties and the surface phase diagram of O/Ni(111) have been calculated from Metropolis and Wang-Landau Monte Carlo simulations based on lateral interactions derived from density-functional theory (DFT) calculations. The DFT energies were mapped onto an Ising-like Hamiltonian according to the cluster expansion technique formalism. Both fcc and hcp adsorption sites were included in the Hamiltonian. Different criteria were used to evaluate competing parameter sets: cross-validation score CV, Mallow’s Cp statistics, and adjusted R2 statistics. The parameter space was searched using genetic algorithms in order to find optimum parameter sets. The different parameter sets obtained from different criteria lead essentially to the same transition temperatures. Excellent agreement is found when comparing the shape and the stability regions of the theoretical and the experimental (from the literature) phase diagrams. We investigate the nature of the p(2×2) and (3×3)R30° phase transitions at Θ=1/4 and 1/3 ML, respectively. Differences arise when comparing the values of the calculated and the experimental transition temperatures owing to imprecision in present-day DFT calculations.

  9. Ab initio construction of magnetic phase diagrams in alloys: The case of Fe1-xMnxPt

    DOE PAGESBeta

    Pujari, B. S.; Larson, P.; Antropov, V. P.; Belashchenko, K. D.

    2015-07-28

    A first-principles approach to the construction of concentration-temperature magnetic phase diagrams of metallic alloys is presented. The method employs self-consistent total energy calculations based on the coherent potential approximation for partially ordered and noncollinear magnetic states and is able to account for competing interactions and multiple magnetic phases. The application to the Fe1–xMnxPt “magnetic chameleon” system yields the sequence of magnetic phases at T = 0 and the c-T magnetic phase diagram in good agreement with experiment, and a new low-temperature phase is predicted at the Mn-rich end. The importance of non-Heisenberg interactions for the description of the magnetic phasemore » diagram is demonstrated.« less

  10. Using Fluid Inclusions to Bring Phase Diagrams to Life in a Guided Inquiry Instructional Setting

    NASA Astrophysics Data System (ADS)

    Farver, J. R.; Onasch, C.

    2011-12-01

    selected sample. Using a fluorite sample (Denton Mine) yields excellent results and a meaningful extension activity. Each student collects Th and Tm data that are then combined and class histograms are generated and interpreted. At this point, a general explanation of fluid inclusions is provided to bring together the student's observations and to assess their understanding. The extension activity involves using the Th, Te, and Tm data obtained for primary inclusions to constrain the true trapping temperature (Tt). The isochore is calculated and plotted on a P-T plot. Using the geothermal gradient for the sample locale, students calculate the hydrostatic and lithostatic gradients for the region and plot these on the P-T diagram in order to constrain the possible range in Tt. Finally, based upon the salinity and Tt range, students determine what ore fluid type is represented (MVT). The evaluation includes observation of participation, answers to questions posed during the engagement activity, and a written report that includes answers to refining and open-ended questions as well as a reflection on their learning. This activity strengthens student's understanding of phase diagrams while introducing them to the importance of fluids in the crust.

  11. Evaluation of the Current Status of the Combinatorial Approach for the Study of Phase Diagrams

    PubMed Central

    Wong-Ng, W.

    2012-01-01

    This paper provides an evaluation of the effectiveness of using the high throughput combinatorial approach for preparing phase diagrams of thin film and bulk materials. Our evaluation is based primarily on examples of combinatorial phase diagrams that have been reported in the literature as well as based on our own laboratory experiments. Various factors that affect the construction of these phase diagrams are examined. Instrumentation and analytical approaches needed to improve data acquisition and data analysis are summarized. PMID:26900530

  12. Phase diagram of the half-filled ionic Hubbard model

    NASA Astrophysics Data System (ADS)

    Bag, Soumen; Garg, Arti; Krishnamurthy, H. R.

    2015-06-01

    We study the phase diagram of the ionic Hubbard model (IHM) at half filling on a Bethe lattice of infinite connectivity using dynamical mean-field theory (DMFT), with two impurity solvers, namely, iterated perturbation theory (IPT) and continuous time quantum Monte Carlo (CTQMC). The physics of the IHM is governed by the competition between the staggered ionic potential Δ and the on-site Hubbard U . We find that for a finite Δ and at zero temperature, long-range antiferromagnetic (AFM) order sets in beyond a threshold U =UA F via a first-order phase transition. For U smaller than UA F the system is a correlated band insulator. Both methods show a clear evidence for a quantum transition to a half-metal (HM) phase just after the AFM order is turned on, followed by the formation of an AFM insulator on further increasing U . We show that the results obtained within both methods have good qualitative and quantitative consistency in the intermediate-to-strong-coupling regime at zero temperature as well as at finite temperature. On increasing the temperature, the AFM order is lost via a first-order phase transition at a transition temperature TA F(U ,Δ ) [or, equivalently, on decreasing U below UA F(T ,Δ ) ], within both methods, for weak to intermediate values of U /t . In the strongly correlated regime, where the effective low-energy Hamiltonian is the Heisenberg model, IPT is unable to capture the thermal (Neel) transition from the AFM phase to the paramagnetic phase, but the CTQMC does. At a finite temperature T , DMFT +CTQMC shows a second phase transition (not seen within DMFT +IPT ) on increasing U beyond UA F. At UN>UA F , when the Neel temperature TN for the effective Heisenberg model becomes lower than T , the AFM order is lost via a second-order transition. For U ≫Δ , TN˜t2/U (1 -x2) , where x =2 Δ /U and thus TN increases with increase in Δ /U . In the three-dimensional parameter space of (U /t ,T /t ,andΔ /t ) , as T increases, the surface of first

  13. First-principles study of an interfacial phase diagram in the V-doped WC-Co system

    NASA Astrophysics Data System (ADS)

    Johansson, S. A. E.; Wahnström, G.

    2012-07-01

    We present a method of determining an interfacial phase diagram using density functional theory calculations for interface energetics. Cluster expansions based on these calculations are used in Monte Carlo simulations to obtain configurational free energies. The method is applied to study the segregation of V to the WC(0001)/Co interface and to construct the corresponding interface diagram, a “complexion” phase diagram. By CALPHAD-type analysis for the adjoining bulk phases, a connection with real materials is made. We find that, in equilibrium, the interface contains a thin V-rich film for a wide range of temperatures and chemical potentials of V corresponding to V additions below the (V,W)Cx solubility limit. The results are compared with available experimental data, and implications of the strong segregation of V for the sintering process of V-doped WC-Co are discussed.

  14. Phase Diagram of the Frustrated Square-Lattice Hubbard Model: Variational Cluster Approach

    NASA Astrophysics Data System (ADS)

    Misumi, Kazuma; Kaneko, Tatsuya; Ohta, Yukinori

    2016-06-01

    The variational cluster approximation is used to study the frustrated Hubbard model at half filling defined on the two-dimensional square lattice with anisotropic next-nearest-neighbor hopping parameters. We calculate the ground-state phase diagrams of the model in a wide parameter space for a variety of lattice geometries, including square, crossed-square, and triangular lattices. We examine the Mott metal-insulator transition and show that, in the Mott insulating phase, magnetic phases with Néel, collinear, and spiral orders appear in relevant parameter regions, and in an intermediate region between these phases, a nonmagnetic insulating phase caused by the quantum fluctuations in the geometrically frustrated spin degrees of freedom emerges.

  15. Reinvestigation of the Cd–Gd phase diagram

    PubMed Central

    Reichmann, Thomas L.; Ipser, Herbert

    2014-01-01

    The complete Cd–Gd equilibrium phase diagram was investigated by a combination of powder-XRD, SEM and DTA. All previously reported phases, i.e., CdGd, Cd2Gd, Cd3Gd, Cd45Gd11, Cd58Gd13, and Cd6Gd, could be confirmed. In addition, a new intermetallic compound with a stoichiometric composition corresponding to “Cd8Gd” was found to exist. It was obtained that “Cd8Gd” decomposes peritectically at 465 °C. Homogeneity ranges of all intermetallic compounds were determined at distinct temperatures. In addition, the maximum solubilities of Cd in the low- and high-temperature modifications of Gd were determined precisely as 4.6 and 22.6 at.%, respectively. All invariant reaction temperatures (with the exception of the formation of Cd58Gd13) as well as liquidus temperatures were determined, most probably, Cd58Gd13 is formed in a peritectoid reaction from Cd45Gd11 and Cd6Gd at a temperature below 700 °C. PMID:25544803

  16. Tertiary phase diagram of cellulose, ionic liquid and organic solvent

    NASA Astrophysics Data System (ADS)

    Zhang, Xin; Henderson, Doug; Tyagi, Madhusudan; Mao, Yimin; Briber, Robert M.; Wang, Howard

    Cellulose is the most abundant natural polymer on earth, and widely used in products from clothing to paper. Fundamental understanding of molecular solutions of cellulose is the key to realize advanced technologies beyond cellulose fibers. It has been reported that certain ionic liquid/organic solvent mixtures dissolve cellulose. In this study, the tertiary phase diagram of microcrystalline cellulose, 1-Ethyl-3-methylimidazolium acetate (EMIMAc), and dimethylformamide (DMF) mixtures has been determined using optical cloud point method and small angle neutron scattering (SANS). Data indicate that a molar ratio of EMIMAc to cellulose repeating unit equal or greater than 3 is necessary but not sufficient in forming one-phase homogeneous solutions. A miscibility gap exists in the dilute regime, where a minimum of 5 mol% of EMIM Ac in DMF is needed to form homogenous solutions. SANS show that cellulose chains adopt Gaussian-like conformation in homogenous solutions. The solutions exhibit the characteristics of upper critical solution temperature. Clustering of cellulose chains occurs at low EMIMAc/DMF or EMIMAc/cellulose ratio, or at low temperatures. The mechanism of cellulose dissolution in tertiary mixture is discussed.

  17. Determination of QCD phase diagram from the imaginary chemical potential

    NASA Astrophysics Data System (ADS)

    Yuji, Sakai; Kouji, Kashiwa; Hiroaki, Kouno; Masanobu, Yahiro

    2009-10-01

    Lattice QCD has the well-known sign problem at real chemical potential. An approach to circumvent the problem is the analytic continuation to real chemical potential from imaginary one. We propose a new analytic continuation by using the Polyakov-loop extended Nambu--Jona-Lasinio (PNJL) model. This work is published in our papers of Phys. Rev. D77, 051901 (2008), Phys. Rev. D78, 036001 (2008), Phys. Rev. D78 076007 (2008), Phys. Rev. D 79, 076008 (2009), Phys. Rev. D 79, 096001 (2009). This talk presents the latest result of these studies. The partition function of QCD has the Roberge-Weiss (RW) periodicity in the imaginary chemical potential region. We revealed that the PNJL model has the RW periodicity. Strength parameters of the vector-type four-quark and scalar-type eight- quark interactions are determined so as to reproduce lattice data on pseudocritical temperatures of the deconfinement and chiral phase transitions in the imaginary chemical potential region. The QCD phase diagram in the real chemical potential region is predicted by the PNJL model. The critical endpoint survives, even if the vector-type four-quark interaction is taken into account.

  18. Phase Diagram Characterization Using Magnetic Beads as Liquid Carriers.

    PubMed

    Blumenschein, Nicholas; Han, Daewoo; Steckl, Andrew J

    2015-01-01

    Magnetic beads with ~1.9 µm average diameter were used to transport microliter volumes of liquids between contiguous liquid segments with a tube for the purpose of investigating phase change of those liquid segments. The magnetic beads were externally controlled using a magnet, allowing for the beads to bridge the air valve between the adjacent liquid segments. A hydrophobic coating was applied to the inner surface of the tube to enhance the separation between two liquid segments. The applied magnetic field formed an aggregate cluster of magnetic beads, capturing a certain liquid amount within the cluster that is referred to as carry-over volume. A fluorescent dye was added to one liquid segment, followed by a series of liquid transfers, which then changed the fluorescence intensity in the neighboring liquid segment. Based on the numerical analysis of the measured fluorescence intensity change, the carry-over volume per mass of magnetic beads has been found to be ~2 to 3 µl/mg. This small amount of liquid allowed for the use of comparatively small liquid segments of a couple hundred microliters, enhancing the feasibility of the device for a lab-in-tube approach. This technique of applying small compositional variation in a liquid volume was applied to analyzing the binary phase diagram between water and the surfactant C12E5 (pentaethylene glycol monododecyl ether), leading to quicker analysis with smaller sample volumes than conventional methods. PMID:26381055

  19. Temperature-pressure phase diagram of cubic Laves phase Au2Pb

    NASA Astrophysics Data System (ADS)

    Chen, K. W.; Graf, D.; Besara, T.; Gallagher, A.; Kikugawa, N.; Balicas, L.; Siegrist, T.; Shekhter, A.; Baumbach, R. E.

    2016-01-01

    The temperature (T ) as a function of pressure (P ) phase diagram is reported for the cubic Laves phase compound Au2Pb, which was recently proposed to support linearly dispersing topological bands, together with conventional quadratic bands. At ambient pressure, Au2Pb exhibits several structural phase transitions at T1=97 K , T2=51 K , and T3=40 K with superconductivity below Tc=1.2 K . Applied pressure results in a rich phase diagram where T1,T2, and T3 evolve strongly with P and a possible new phase is stabilized for P >0.64 GPa that also supports superconductivity below 1.1 K. These observations suggest that Au2Pb is an ideal system in which to investigate the relationship between structural degrees of freedom, band topology, and resulting anomalous behaviors.

  20. Effect of shape anisotropy on the phase diagram of the Gay-Berne fluid

    NASA Astrophysics Data System (ADS)

    Mishra, Pankaj; Ram, Jokhan

    2005-07-01

    We have used the density functional theory to study the effect of molecular elongation on the isotropic-nematic, isotropic-smectic A and nematic-smectic A phase transitions of a fluid of molecules interacting via the Gay-Berne intermolecular potential. We have considered a range of length-to-width parameter 3.0 ≤ x0 ≤ 4.0 in steps of 0.2 at different densities and temperatures. Pair correlation functions needed as input information in density functional theory are calculated using the Percus-Yevick integral equation theory. Within the small range of elongation, the phase diagram shows significant changes. The fluid at low temperature is found to freeze directly from isotropic to smectic A phase for all the values of x0 considered by us on increasing the density while the nematic phase stabilizes in between isotropic and smectic A phases only at high temperatures and densities. Both isotropic-nematic and nematic-smectic A transition density and pressure are found to decrease as we increase x0. The phase diagram obtained is compared with computer simulation result of the same model potential and is found to be in good qualitative agreement.

  1. Effect of shape anisotropy on the phase diagram of the Gay-Berne fluid.

    PubMed

    Mishra, Pankaj; Ram, Jokhan

    2005-07-01

    We have used the density functional theory to study the effect of molecular elongation on the isotropic-nematic, isotropic-smectic A and nematic-smectic A phase transitions of a fluid of molecules interacting via the Gay-Berne intermolecular potential. We have considered a range of length-to-width parameter 3.0 < or = x(0) < or = 4.0 in steps of 0.2 at different densities and temperatures. Pair correlation functions needed as input information in density functional theory are calculated using the Percus-Yevick integral equation theory. Within the small range of elongation, the phase diagram shows significant changes. The fluid at low temperature is found to freeze directly from isotropic to smectic A phase for all the values of x(0) considered by us on increasing the density while the nematic phase stabilizes in between isotropic and smectic A phases only at high temperatures and densities. Both isotropic-nematic and nematic-smectic A transition density and pressure are found to decrease as we increase x(0). The phase diagram obtained is compared with computer simulation result of the same model potential and is found to be in good qualitative agreement. PMID:16007371

  2. Understanding the Phase Diagram of Self-Assembled Monolayers of Alkanethiolates on Gold

    PubMed Central

    2016-01-01

    Alkanethiolate monolayers on gold are important both for applications in nanoscience as well as fundamental studies of adsorption and self-assembly at metal surfaces. While considerable experimental effort has been put into understanding the phase diagram of these systems, theoretical work based on density functional theory (DFT) has long been hampered by the inability of conventional exchange-correlation functionals to describe dispersive interactions. In this work, we combine dispersion-corrected DFT calculations using the new vdW-DF-CX functional with the ab initio thermodynamics method to study the stability of dense standing-up and low-coverage lying-down phases on Au(111). We demonstrate that the lying-down phase has a thermodynamic region of stability starting from thiolates with alkyl chains consisting of n ≈ 3 methylene units. This phase emerges as a consequence of a competition between dispersive chain–chain and chain–substrate interactions, where the strength of the latter varies more strongly with n. A phase diagram is derived under ultrahigh-vacuum conditions, detailing the phase transition temperatures of the system as a function of the chain length. The present work illustrates that accurate ab initio modeling of dispersive interactions is both feasible and essential for describing self-assembled monolayers. PMID:27313813

  3. Zero-temperature phase diagram of Yukawa bosons

    NASA Astrophysics Data System (ADS)

    Osychenko, O. N.; Astrakharchik, G. E.; Mazzanti, F.; Boronat, J.

    2012-06-01

    We study the zero-temperature phase diagram of bosons interacting via screened Coulomb (Yukawa) potential by means of the diffusion Monte Carlo method. The Yukawa potential is used as a model interaction in the neutron matter, dusty plasmas, and charged colloids. As shown by Petrov [Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.99.130407 99, 130407 (2007)], interactions between weakly bound molecules of heavy and light fermionic atoms are described by an effective Yukawa potential with a strength related to the heavy-light mass ratio M/m, which might lead to crystallization in a two-dimensional geometry if the mass ratio of heavy-light fermions exceeds a certain critical value. In the present work we do a thorough study of the quantum three-dimensional Yukawa system. For strong interactions (equivalently, large mass ratios) the system experiences several phase transitions as the density is increased, passing from gas to solid and to gas phase again. Weakly interacting Yukawa particles do not crystallize at any density. We find the minimal interaction strength at which the crystallization happens. In terms of the two-component fermionic system, this strength corresponds to a heavy-light mass ratio of M/m˜180, so that it is impossible to realize the gas-crystal transition in a conventional bulk system. For the Yukawa model of fermionic mixtures we also analyze the possibility of building molecular systems with very large effective mass ratios by confining the heavy component to a sufficiently deep optical lattice. We show how the effective mass of the heavy component can be made arbitrarily large by increasing the lattice depth, thus leading to a tunable effective mass ratio that can be used to realize a molecular superlattice.

  4. Phase diagram of rod-coil diblock copolymer melts by self-consistent field theory

    NASA Astrophysics Data System (ADS)

    Yan, Dadong; Tang, Jiuzhou; Jiang, Ying; Zhang, Xinghua; Chen, Jeff

    A unified phase diagram is presented for rod-coil diblock copolymer melts in the isotropic phase regime as a function of the asymmetric parameter. The study is based on free-energy calculation, which incorporates three-dimensional spatial variations of the volume fraction with angular dependence. The wormlike-chain model is used in a self-consistent field treatment. Body-centered cubic, A15, hexagonal, gyroid, and lamellar structures where the rod segments are packed inside the convex rod-coil interface are found stable. As the conformational asymmetric parameter increases, the A15 phase region expands and the gyroid phase region reduces. The stability of the structures is analyzed by concepts such as packing frustration, spinodal limit, and interfacial curvature.

  5. Global phase diagram of a doped Kitaev-Heisenberg model

    SciTech Connect

    Okamoto, Satoshi

    2013-01-01

    The global phase diagram of a doped Kitaev-Heisenberg model is studied using an $SU(2)$ slave-boson mean-field method. Near the Kitaev limit, $p$-wave superconducting states which break the time-reversal symmetry are stabilized as reported by You {\\it et al.} [Phys. Rev. B {\\bf 86}, 085145 (2012)] irrespective of the sign of the Kitaev interaction. By further doping, a $d$-wave superconducting state appears when the Kitaev interaction is antiferromagnetic, while another $p$-wave superconducting state appears when the Kitaev interaction is ferromagnetic. This $p$-wave superconducting state does not break the time-reversal symmetry as reported by Hyart {\\it et al.} [Phys. Rev. B {\\bf 85}, 140510 (2012)], and such a superconducting state also appears when the antiferromagnetic Kitaev interaction and the ferromagnetic Heisenberg interaction compete. This work, thus, demonstrates the clear difference between the antiferromagnetic Kitaev model and the ferromagnetic Kitaev model when carriers are doped while these models are equivalent in the undoped limit, and how novel superconducting states emerge when the Kitaev interaction and the Heisenberg interaction compete.

  6. Ground-state phase diagram of the quantum Rabi model

    NASA Astrophysics Data System (ADS)

    Ying, Zu-Jian; Liu, Maoxin; Luo, Hong-Gang; Lin, Hai-Qing; You, J. Q.

    2015-11-01

    The Rabi model plays a fundamental role in understanding light-matter interaction. It reduces to the Jaynes-Cummings model via the rotating-wave approximation, which is applicable only to the cases of near resonance and weak coupling. However, recent experimental breakthroughs in upgrading light-matter coupling order require understanding the physics of the full quantum Rabi model (QRM). Despite the fact that its integrability and energy spectra have been exactly obtained, the challenge to formulate an exact wave function in a general case still hinders physical exploration of the QRM. Here we unveil a ground-state phase diagram of the QRM, consisting of a quadpolaron and a bipolaron as well as their changeover in the weak-, strong-, and intermediate-coupling regimes, respectively. An unexpected overweighted antipolaron is revealed in the quadpolaron state, and a hidden scaling behavior relevant to symmetry breaking is found in the bipolaron state. An experimentally accessible parameter is proposed to test these states, which might provide novel insights into the nature of the light-matter interaction for all regimes of the coupling strengths.

  7. Condensation phase diagrams for lipid-coated perfluorobutane microbubbles.

    PubMed

    Mountford, Paul A; Sirsi, Shashank R; Borden, Mark A

    2014-06-01

    The goal of this study was to explore the thermodynamic conditions necessary to condense aqueous suspensions of lipid-coated gas-filled microbubbles into metastable liquid-filled nanodrops as well as the physicochemical mechanisms involved with this process. Individual perfluorobutane microbubbles and their lipid shells were observed as they were pressurized at 34.5 kPa s(-1) in a microscopic viewing chamber maintained at temperatures ranging from 5 to 75 °C. The microbubbles contracted under pressure, ultimately leading to either full dissolution or microbubble-to-nanodrop condensation. Temperature-pressure phase diagrams conveying condensation and stability transitions were constructed for microbubbles coated with saturated diacylphosphatidylcholine lipids of varying acyl chain length (C16 to C24). The onset of full dissolution was shifted to higher temperatures with the use of longer acyl chain lipids or supersaturated media. Longer chain lipid shells resisted both dissolution of the gas core and mechanical compression through a pronounced wrinkle-to-fold collapse transition. Interestingly, the lipid shell also provided a mechanical resistance to condensation, shifting the vapor-to-liquid transition to higher pressures than for bulk perfluorobutane. This result indicated that the lipid shell can provide a negative apparent surface tension under compression. Overall, the results of this study will aid in the design and formulation of vaporizable fluorocarbon nanodrops for various applications, such as diagnostic ultrasound imaging, targeted drug delivery, and thermal ablation. PMID:24824162

  8. A phase diagram for fluid-driven sediment trasport

    NASA Astrophysics Data System (ADS)

    Clark, Abe

    When a fluid flows laterally over a granular bed, grains may be transported with the flow. This process shapes much of the natural world. The boundary between states with and without grain motion has been studied for decades. However, this boundary is not well understood, since the process whereby grains are transported involves the coupling of several complex phenomena: turbulent fluid flow near a rough boundary, Darcy flow through the pore structure of the granular bed, the yield strength of granular beds comprised of frictional grains with irregular shape, and inertial effects of grains that become entrained in the flow. In order to clarify the essential physics that governs the onset of granular motion, we study this process computationally by including only the minimal features and then adding complexities one by one. We start with a simple numerical model that includes only gravity, grain-grain interactions that are repulsive and frictionless, and a purely horizontal viscous fluid flow. By varying the fluid flow rate and the effective viscosity, we find behavior that is qualitatively consistent with a large collection of experimental data known as the Shields curve. Thus, our results suggest that the main features of this curve result from a competition between grain inertia and viscous damping. We find this phase diagram to be qualitatively insensitive to secondary effects, such as friction, irregular grain shape, and restitution losses. Funded by U.S. Army Research Office under Grant No. W911NF-14-1-0005.

  9. Helicity, anisotropies, and their competition in a multiferroic magnet: Insight from the phase diagram

    NASA Astrophysics Data System (ADS)

    Gvozdikova, M. V.; Ziman, T.; Zhitomirsky, M. E.

    2016-07-01

    Motivated by the complex phase diagram of MnWO4, we investigate the competition between anisotropy, magnetic field, and helicity for the anisotropic next-nearest-neighbor Heisenberg model. Apart from two competing exchanges, which favor a spiral magnetic structure, the model features the biaxial single-ion anisotropy. The model is treated in the real-space mean-field approximation and the phase diagram containing various incommensurate and commensurate states is obtained for different field orientations. We discuss the similarities and differences of the theoretical phase diagram and the experimental diagram of MnWO4.

  10. CALPHAD Modeling of Phase Diagram Boundaries for Binary 2-Amino-2-Methyl-1,3-Propanediol [AMPL] and Tris(hydroxymethyl) Aminomethane [TRIS] system

    NASA Astrophysics Data System (ADS)

    Mekala, Prathyusha

    The phase diagram assessment of binary AMPL-TRIS system was calculated using the CALPHAD approach. Thermo-Calc, TCC software was used to fit the experimental phase diagram data by simultaneous optimization of thermodynamic properties of pure components and phase equilibria data available in the literature, and also calculated in the present work. The measured interaction parameters for low temperature alpha and beta solid solution phases are relatively small and are assumed to be ideal. Preliminary calculation of AMPL-TRIS phase diagram showed complete solid solubility of the high temperature gamma and gamma-prime phases, as reported by Barrio et al. (1994). In the next iteration, we calculated AMPL-TRIS phase diagram using heat capacity data and found that it was in good agreement with the current experimental phase diagram developed by V. Kamisetty (2010). In final calculations, the Parrot module of Thermo-Calc program was used to obtain an optimized phase diagram. The calculated phase corroborates well with V. Kamisetty data. Two eutectoids, one at ~21 mol.% TRIS at 85oC, the other at ~60 mol. % TRIS at 104oC, and one peritectic at 55 mol.% TRIS at 127oC were calculated. The maximum solubility of TRIS in AMPL is 10 mol.%, and that of AMPL in TRIS is 18 mol.% at 85oC. An important feature of this phase diagram is the presence of gamma and gamma-prime phases above 110oC. Details of the methodology and calculations are shown in this thesis.

  11. Percolation phase diagrams for multi-phase models built on the overlapping sphere model

    NASA Astrophysics Data System (ADS)

    Garboczi, E. J.

    2016-01-01

    The overlapping sphere (OS) percolation model gives a two-phase microstructure (matrix plus inclusions) that is useful for testing composite material ideas and other applications, as well as serving as a paradigm of overlapping object percolation and phase transitions. Real materials often have more than two phases, so it is of interest to extend the applicability of the OS model. A flexible variant of the OS model can be constructed by randomly assigning the spheres different phase labels, according to a uniform probability distribution, as they are inserted one by one into the matrix. The resulting three or more phase models can have different amounts of percolating and non-percolating phases, depending on the volume fraction of each phase and the total OS volume fraction. A three-dimensional digital image approach is used to approximately map out the percolation phase diagram of such models, explicitly up to four phases (one matrix plus three spherical inclusion phases) and implicitly for N > 4 phases. For the three phase model, it was found that a single OS sub-phase has a percolation threshold that ranges from about a volume fraction of 0.16, when the matrix volume fraction is about 0.01, to about 0.30, at a matrix volume fraction of about 0.7. The approximate analytical dependence of this sub-phase percolation threshold on the defining model parameters serves to guide the building of the percolation phase diagram for the N-phase model, and is used to determine the maximum value of N(N = 6) at which all N phases can be simultaneously percolated.

  12. One-Component Pressure-Temperature Phase Diagrams in the Presence of Air

    ERIC Educational Resources Information Center

    Andrade-Gamboa, Julio; Martire, Daniel O.; Donati, Edgardo R.

    2010-01-01

    One-component phase diagrams are good approximations to predict pressure-temperature ("P-T") behavior of a substance in the presence of air, provided air pressure is not much higher than the vapor pressure. However, at any air pressure, and from the conceptual point of view, the use of a traditional "P-T" phase diagram is not strictly correct. In…

  13. An Algorithm for the Hierarchical Organization of Path Diagrams and Calculation of Components of Expected Covariance.

    ERIC Educational Resources Information Center

    Boker, Steven M.; McArdle, J. J.; Neale, Michael

    2002-01-01

    Presents an algorithm for the production of a graphical diagram from a matrix formula in such a way that its components are logically and hierarchically arranged. The algorithm, which relies on the matrix equations of J. McArdle and R. McDonald (1984), calculates the individual path components of expected covariance between variables and…

  14. Spent Nuclear Fuel (SNF) Project Multi Canister Overpack (MCO) Process Flow Diagram Mass Balance Calculations

    SciTech Connect

    KLEM, M.J.

    2000-09-08

    The purpose of this calculation document is to develop the bases for the material balances of the Multi-Canister Overpack (MCO) Level 1 Process Flow Diagram (PFD). The attached mass balances support revision two of the PFD for the MCO and provide future reference.

  15. Boron under Pressure: Phase Diagram and Novel High-Pressure Phase

    NASA Astrophysics Data System (ADS)

    Oganov, Artem R.

    Boron has a unique chemistry, responsible for remarkable complexities even in the pure element. I review some of the history of the discovery of this element, and recent surprises found in boron under pressure. I discuss the recent discovery of a new high-pressure phase, ?-B28, consisting of icosahedral B12 clusters and B2 pairs in a NaCl-type arrangement: (B2)δ+(B12)δ-, and displaying a significant charge transfer δ ~ 0.48. Boron is the only light element, for which the phase diagram has become clear only in the last couple of years, and this phase diagram is discussed here among other recent findings.

  16. The Bayesian approach to an internally consistent thermodynamic database: theory, database, and generation of phase diagrams

    NASA Astrophysics Data System (ADS)

    Chatterjee, Niranjan D.; Krüger, Ralf; Haller, Gerd; Olbricht, Walter

    An internally consistent thermodynamic dataset has been derived for 148 endmember phases (145 solids and 3 fluids) comprising the elements Li, Na, K, Be, Mg, Ca, Ti, Cr, Mn, Fe, Zn, Al, Si, C, H, and O. This has been achieved by simultaneous treatment of phase property (like standard enthalpy of formation, standard entropy, molar heat capacity, molar volume, thermal expansivity, bulk modulus etc.) and reaction reversal data by the Bayesian method. The theory underlying the approach, and the computational methods involved, are briefly outlined. (For the benefit of readers unfamiliar with inference statistics, the basic concepts of the Bayes method are also presented in such a way that they can be grasped intuitively.) Although not yet addressed, this method can be extended to refine the thermodynamic mixing properties of crystalline solutions. The sources of the input data, culled from the literature, are summarized in the Appendix. The resulting database is succinctly documented in this paper. It includes the enthalpies of formation and entropies, their uncertainties, and the correlation among them. The database allows calculation of P-T, T-XCO2, P-XCO2, and T-fO2 sections, with error propagation into the computed phase diagrams on a routine basis. A user-friendly computer program has been written to generate such phase diagrams. It is public domain software. The software and the thermodynamic database (which includes a complete documentation of the thermodynamic data above and beyond those listed (Table 2, here) may be downloaded from the web site http://homepage.ruhr-uni-bochum.de/niranjan.chatterjee/Index.htm. Examples of computed phase diagrams are given to illustrate the quality of the data and the capabilities of the software.

  17. Phase equilibrium diagram of the uranium-plutonium-carbon system over the range 1200 to 2430/sup 0/C

    SciTech Connect

    Udovskii, A.L.; Alekseeva, Z.M.

    1982-01-01

    An attempt has been made to construct the phase diagram of the uranium-plutonium-carbide (U-Pc-C) system on the basis of information available in the literature. The isothermal sections for 1200; 1655; 1660; 1730; 1765; 1825; 2025; 2140; 2245; 2380 and 2435/sup 0/C from the UC, UC/sub 1/ /sub 5/, UC/sub 2/ and (U/sub 0/ /sub 5/Pu/sub 0/ /sub 5/)C-(U/sub 0/ /sub 5/Pu/sub 0/ /sub 5/)C/sub 1/ /sub 5/ sections of the phase diagram, and a scheme for the mono- and nonvariant equilibria in the U-P-C system in this temperature range have been constructed for the first time. A knowledge of the phase diagram and the thermodynamic properties of the alloys enables calculations to be made of the jumps in the properties of the alloys at the phase boundaries of the phase diagram, the heat capacity, the compressibility, the thermal expansion coefficient, the mutual diffusion coefficient of the components. The partial enthalpies and entropies of the components accompanying the 2nd-type phase transitions, as well as jumps in the heats for 1st-type phase transformations, i.e., for phase reactions. 3 figures.

  18. Ab initio molecular crystal structures, spectra, and phase diagrams.

    PubMed

    Hirata, So; Gilliard, Kandis; He, Xiao; Li, Jinjin; Sode, Olaseni

    2014-09-16

    Conspectus Molecular crystals are chemists' solids in the sense that their structures and properties can be understood in terms of those of the constituent molecules merely perturbed by a crystalline environment. They form a large and important class of solids including ices of atmospheric species, drugs, explosives, and even some organic optoelectronic materials and supramolecular assemblies. Recently, surprisingly simple yet extremely efficient, versatile, easily implemented, and systematically accurate electronic structure methods for molecular crystals have been developed. The methods, collectively referred to as the embedded-fragment scheme, divide a crystal into monomers and overlapping dimers and apply modern molecular electronic structure methods and software to these fragments of the crystal that are embedded in a self-consistently determined crystalline electrostatic field. They enable facile applications of accurate but otherwise prohibitively expensive ab initio molecular orbital theories such as Møller-Plesset perturbation and coupled-cluster theories to a broad range of properties of solids such as internal energies, enthalpies, structures, equation of state, phonon dispersion curves and density of states, infrared and Raman spectra (including band intensities and sometimes anharmonic effects), inelastic neutron scattering spectra, heat capacities, Gibbs energies, and phase diagrams, while accounting for many-body electrostatic (namely, induction or polarization) effects as well as two-body exchange and dispersion interactions from first principles. They can fundamentally alter the role of computing in the studies of molecular crystals in the same way ab initio molecular orbital theories have transformed research practices in gas-phase physical chemistry and synthetic chemistry in the last half century. In this Account, after a brief summary of formalisms and algorithms, we discuss applications of these methods performed in our group as compelling

  19. Preliminary Phase Diagram for the Richardton H-Chondrite

    NASA Astrophysics Data System (ADS)

    Danielson, L. R.

    2001-12-01

    The earliest history of the accreting Earth involved the removal of metallic liquids to the core and segregation of silicates into a layered Earth. One hypothesis for core formation is that descending metallic liquids equilibrated with silicate liquids in the deep mantle. Of current interest is the possibility that a primordial magma ocean may have acted as a host for both silicate and metallic liquid segregation. The silicate liquid composition may have changed by processes such as crystal settling or flotation during accretion as the planet increased in size. If these were equilibrium processes, a P-T phase diagram of representative accretion material could be used to constrain the chemical evolution of the Earth by identifying silicate minerals and liquidus phases present at elevated pressures and temperatures (Agee, 1990; Agee et al., 1995). Experiments were carried out in a "Walker-type" 6-8 multi-anvil device in a 1100 ton press. Pressures from 5 to 11 GPa, at temperatures from 1050 to 2100 ° C, have been investigated using an 8 mm TEL assembly with a LaCrO3 furnace and either MgO or graphite capsules. Experiment durations were from 4 to 31 minutes. We chose the Richardton H-chondrite as starting material because it is a reasonable representation of the bulk Earth. An ongoing problem with these experiments is containment of the liquids within the MgO capsules. Additionally, the MgO capsule reacts with the silicate liquids, elevating the MgO content of the silicate melt and reducing the FeO content. Experiments conducted in graphite capsules do not have a containment problem. Phases present were tentatively identified using EDS spectroscopy. In the investigated P-T range, run products contain olivine of intermediate composition, low- and high-Ca pyroxene, and small amounts of garnet in subsolidus experiments. Runs conducted at 1700 ° C contain silicate liquid, olivine, and low Ca pyroxene at 6 GPa, but silicate liquid, olivine, low and high Ca pyroxene at 9

  20. Scaling analysis and application: Phase diagram of magnetic nanorings and elliptical nanoparticles

    SciTech Connect

    Zhang Wen; Singh, Rohit; Bray-Ali, Noah; Haas, Stephan

    2008-04-01

    The magnetic properties of single-domain nanoparticles with different geometric shapes, crystalline anisotropies, and lattice structures are investigated. A recently proposed scaling approach is shown to be universal and in agreement with dimensional analysis coupled with the assumption of incomplete self-similarity. It is used to obtain phase diagrams of magnetic nanoparticles featuring three competing configurations: in-plane ferromagnetism, out-of-plane ferromagnetism, and vortex formation. The influence of the vortex core on the scaling behavior and phase diagram is analyzed. Three-dimensional phase diagrams are obtained for cylindrical nanorings depending on their height and outer and inner radii. The triple points in these phase diagrams are shown to be in a linear relationship with the inner radius of the ring. Elliptically shaped magnetic nanoparticles are also studied. A new parametrization for double vortex configurations is proposed, and regions in the phase diagram where the double vortex is a stable ground state are identified.

  1. Constructing multicomponent phase diagrams by overlapping ZPF lines. [Zero Phase Fraction Line for improved mechanical and corrosion properties

    NASA Technical Reports Server (NTRS)

    Gupta, H.; Morral, J. E.; Nowotny, H.

    1986-01-01

    A procedure is introduced which can be used to draw isothermal sections from a multicomponent phase diagram in a matter of minutes, regardless of the diagram complexity. In the proposed method, the zero phase fraction (ZPF) lines are drawn separately for all phases existing in the system; by overlapping these ZPF lines, the desired section is obtained. Two examples - with five components and eight components - are given to illustrate the method. Regarding the second example, it is noted that although the final diagram may be altered to create discontinuities in slope at intersection points, the diagram remains unchanged from a topological standpoint. Thus, the overlapping ZPF lines supply all the information needed to construct complex diagrams. Even if many more phases and components are involved, the final diagram can be drawn with equal facility.

  2. A novel explanation of a low-profile mechanism for unsaturated polyester resins using phase diagrams

    SciTech Connect

    Suspene, L.; Fourquier, D.; Yang, Y.S. )

    1990-04-01

    A novel explanation for the mechanism of low profile additives in unsaturated polyester resins by using a concept of a phase diagram was proposed. According to the ternary phase diagrams for the systems of styrene-unsaturated polyester prepolymer-additives (e.g., polyvinyl acetate, polyurethane), the phenomenon of phase separation was explained. Furthermore, the final morphology of cured resins was correlated to the phase diagram. Microscopic observations showed the morphology was controlled by the phase separation. TEM results also clearly showed that the microvoids were formed in the low profile phase, separated from the resin phase, instead of being in the interfacial region as previously reported. It was concluded that a well controlled phase diagram can lead to a shrinkage-controlled low profile system.

  3. The phase diagram and transport properties of MgO from theory and experiment

    NASA Astrophysics Data System (ADS)

    Shulenburger, Luke

    2013-06-01

    Planetary structure and the formation of terrestrial planets have received tremendous interest due to the discovery of so called super-earth exoplanets. MgO is a major constituent of Earth's mantle, the rocky cores of gas giants and is a likely component of the interiors of many of these exoplanets. The high pressure - high temperature behavior of MgO directly affects equation of state models for planetary structure and formation. In this work, we examine MgO under extreme conditions using experimental and theoretical methods to determine its phase diagram and transport properties. Using plate impact experiments on Sandia's Z facility the solid-solid phase transition from B1 to B2 is clearly determined. The melting transition, on the other hand, is subtle, involving little to no signal in us-up space. Theoretical work utilizing density functional theory (DFT) provides a complementary picture of the phase diagram. The solid-solid phase transition is identified through a series of quasi-harmonic phonon calculations and thermodynamic integration, while the melt boundary is found using phase coexistence calculations. One issue of particular import is the calculation of reflectivity along the Hugoniot and the influence of the ionic structure on the transport properties. Particular care is necessary because of the underestimation of the band gap and attendant overestimation of transport properties due to the use of semi-local density functional theory. We will explore the impact of this theoretical challenge and its potential solutions in this talk. The integrated use of DFT simulations and high-accuracy shock experiments together provide a comprehensive understanding of MgO under extreme conditions. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the U.S. DOE's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  4. Uncertainties on the CP phase α due to Penguin diagrams

    NASA Astrophysics Data System (ADS)

    Aleksan, R.; Buccella, F.; Le Yaouanc, A.; Oliver, L.; Pène, O.; Raynal, J.-C.

    1995-02-01

    A major problem in the determination of the the CP angle α, that should be measured through modes of the type B d, overlineBd → ππ, … , is the uncertainty coming from Penguin diagrams. We consider the different ground state modes ππ, πϱ, ϱϱ, and, assuming the FSI phases to be negligible, we investigate the amount of uncertainty coming from Penguins that can be parametrized by a dilution factor D and an angle shift Δα. The parameter D is either 1 or very close to 1 in all these modes, and it can be measured independently, up to a sign ambiguity, by the t dependence. Assuming factorization, we show that Δα is much smaller for the modes ϱπ and ϱϱ than for ππ, and we plot their allowed region as a function of α itself. Moreover, we show that most of the modes contribute to the asymmetry with the same sign, and define for their sum an effective Deff and an effective Δαeff, an average of Δα for the different modes. It turns out that Deff is of the order of 0.9, Δαeff is between 5% and 10% and, relative to ππ, the statistical gain for the sum is of about a factor 10. Finally, we compute the ratios {Kπ}/{ππ}, … that test the strength of the Penguins and depend on the CP angles, as emphasized by Silva and Wolfenstein and by Deandrea et al.

  5. Vapour-liquid phase diagram for an ionic fluid in a random porous medium.

    PubMed

    Holovko, M F; Patsahan, O; Patsahan, T

    2016-10-19

    We study the vapour-liquid phase behaviour of an ionic fluid confined in a random porous matrix formed by uncharged hard sphere particles. The ionic fluid is modelled as an equimolar binary mixture of oppositely charged equisized hard spheres, the so-called restricted primitive model (RPM). Considering the matrix-fluid system as a partly-quenched model, we develop a theoretical approach which combines the method of collective variables with the extension of the scaled-particle theory (SPT) for a hard-sphere fluid confined in a disordered hard-sphere matrix. The approach allows us to formulate the perturbation theory using the SPT for the description of the thermodynamics of the reference system. The phase diagrams of the RPM in matrices of different porosities and for different size ratios of matrix and fluid particles are calculated in the random-phase approximation and also when the effects of higher-order correlations between ions are taken into account. Both approximations correctly reproduce the basic effects of porous media on the vapour-liquid phase diagram, i.e. with a decrease of porosity the critical point shifts towards lower fluid densities and lower temperatures and the coexistence region gets narrower. For the fixed matrix porosity, both the critical temperature and the critical density increase with an increase of size of matrix particles and tend to the critical values of the bulk RPM. PMID:27548356

  6. Phase diagram of QCD in a magnetic field

    NASA Astrophysics Data System (ADS)

    Andersen, Jens O.; Naylor, William R.; Tranberg, Anders

    2016-04-01

    Recent advances in our understanding of the phase structure and the phase transitions of hadronic matter in strong magnetic fields B and zero quark chemical potentials μf are reviewed in detail. Many aspects of QCD are described using low-energy effective theories and models such as the bag model, the hadron resonance gas model, chiral perturbation theory (χ PT ), the Nambu-Jona-Lasinio (NJL) model, the quark-meson (QM) model, and Polyakov-loop extended versions of the NJL and QM models. Their properties and applications are critically examined. This includes mean-field calculations as well as approaches beyond the mean-field approximation such as the functional renormalization group. Renormalization issues are discussed and the influence of the vacuum fluctuations on the chiral phase transition is pointed out. At T =0 , model calculations and lattice simulations predict magnetic catalysis: The quark condensate increases as a function of the magnetic field. This is covered in detail. Recent lattice results for the thermodynamics of non-Abelian gauge theories with emphasis on S U (2 )c and S U (3 )c are also discussed. In particular, inverse magnetic catalysis around the transition temperature Tc as a competition between contributions from valence quarks and sea quarks resulting in a decrease of Tc as a function of B is focused on. Finally, recent efforts to modify models in order to reproduce the behavior observed on the lattice are discussed.

  7. Phase diagram and collective excitations in an excitonic insulator from an orbital physics viewpoint

    NASA Astrophysics Data System (ADS)

    Nasu, Joji; Watanabe, Tsutomu; Naka, Makoto; Ishihara, Sumio

    2016-05-01

    An excitonic-insulating system is studied from a viewpoint of the orbital physics in strongly correlated electron systems. An effective model Hamiltonian for low-energy electronic states is derived from the two-orbital Hubbard model with a finite-energy difference corresponding to the crystalline-field splitting. The effective model is represented by the spin operators and the pseudospin operators for the spin-state degrees of freedom. The ground-state phase diagram is analyzed by the mean-field approximation. In addition to the low-spin state and high-spin state phases, two kinds of the excitonic-insulating phases emerge as a consequence of the competition between the crystalline-field effect and the Hund coupling. Transitions to the excitonic phases are classified to an Ising-type transition resulted from a spontaneous breaking of the Z2 symmetry. Magnetic structures in the two excitonic-insulating phases are different from each other: an antiferromagnetic order and a spin nematic order. Collective excitations in each phase are examined using the generalized spin-wave approximation. Characteristics in the Goldstone modes in the excitonic-insulating phases are studied through the calculations of the dynamical correlation functions for the spins and pseudospin operators. Both the transverse and longitudinal spin excitation modes are active in the two excitonic-insulating phases in contrast to the low-spin state and high-spin state phases. Relationships of the present results to the perovskite cobalt oxides are discussed.

  8. Phase diagrams properties of the mixed traffic flow on a crossroad

    NASA Astrophysics Data System (ADS)

    Li, Qi-Lang; Wang, Bing-Hong; Liu, Mu-Ren

    2010-11-01

    Based on the Ishibashi and Fukui crossroad traffic flow model [Y. Ishibashi and M. Fukui. J. Phys. Soc. Japan. 70 (2001) 2793], mixed traffic flow (i.e., the fast and slow vehicles with different maximum velocities are mixed) is investigated in this work. According to the numerical simulation results and the principle for constructing the phase diagram, phase diagrams for mixed traffic flow are constructed. It is noted that the topology of these phase diagrams is similar to that of phase diagrams for homogeneous vehicles (which refers to slow vehicles only). From the phase diagrams, it is evident that mixed traffic flow is influenced by the mixing rate f (fraction of slow and fast vehicles) in regions II and V, but not in other regions. Although a mixture of fast and slow vehicles is introduced in the crossroad traffic flow model, the separation between phases in the phase diagrams remains linear. For a given q (the vehicle density on the northbound road), one flow plateau appears in regions IIx or IVy, while two maximum flow plateaus appear in region V in each of the phase diagrams. The maximum flow values in region V reflect the maximum traffic capacity for the traffic system as defined in this work. Since mixed traffic flow is a common phenomenon in real traffic, this work may offer help in real traffic simulations and traffic management.

  9. Stabilizing the hexagonal close packed structure of hard spheres with polymers: Phase diagram, structure, and dynamics

    NASA Astrophysics Data System (ADS)

    Edison, John R.; Dasgupta, Tonnishtha; Dijkstra, Marjolein

    2016-08-01

    We study the phase behaviour of a binary mixture of colloidal hard spheres and freely jointed chains of beads using Monte Carlo simulations. Recently Panagiotopoulos and co-workers predicted [Nat. Commun. 5, 4472 (2014)] that the hexagonal close packed (HCP) structure of hard spheres can be stabilized in such a mixture due to the interplay between polymer and the void structure in the crystal phase. Their predictions were based on estimates of the free-energy penalty for adding a single hard polymer chain in the HCP and the competing face centered cubic (FCC) phase. Here we calculate the phase diagram using free-energy calculations of the full binary mixture and find a broad fluid-solid coexistence region and a metastable gas-liquid coexistence region. For the colloid-monomer size ratio considered in this work, we find that the HCP phase is only stable in a small window at relatively high polymer reservoir packing fractions, where the coexisting HCP phase is nearly close packed. Additionally we investigate the structure and dynamic behaviour of these mixtures.

  10. Stabilizing the hexagonal close packed structure of hard spheres with polymers: Phase diagram, structure, and dynamics.

    PubMed

    Edison, John R; Dasgupta, Tonnishtha; Dijkstra, Marjolein

    2016-08-01

    We study the phase behaviour of a binary mixture of colloidal hard spheres and freely jointed chains of beads using Monte Carlo simulations. Recently Panagiotopoulos and co-workers predicted [Nat. Commun. 5, 4472 (2014)] that the hexagonal close packed (HCP) structure of hard spheres can be stabilized in such a mixture due to the interplay between polymer and the void structure in the crystal phase. Their predictions were based on estimates of the free-energy penalty for adding a single hard polymer chain in the HCP and the competing face centered cubic (FCC) phase. Here we calculate the phase diagram using free-energy calculations of the full binary mixture and find a broad fluid-solid coexistence region and a metastable gas-liquid coexistence region. For the colloid-monomer size ratio considered in this work, we find that the HCP phase is only stable in a small window at relatively high polymer reservoir packing fractions, where the coexisting HCP phase is nearly close packed. Additionally we investigate the structure and dynamic behaviour of these mixtures. PMID:27497577