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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. Molybdenum-titanium phase diagram evaluated from ab initio calculations

    NASA Astrophysics Data System (ADS)

    Barzilai, Shmuel; Toher, Cormac; Curtarolo, Stefano; Levy, Ohad

    2017-07-01

    The design of next generation β -type titanium implants requires detailed knowledge of the relevant stable and metastable phases at temperatures where metallurgical heat treatments can be performed. Recently, a standard specification for surgical implant applications was established for Mo-Ti alloys. However, the thermodynamic properties of this binary system are not well known and two conflicting descriptions of the β -phase stability have been presented in the literature. In this study, we use ab initio calculations to investigate the Mo-Ti phase diagram. These calculations predict that the β phase is stable over a wide concentration range, in qualitative agreement with one of the reported phase diagrams. In addition, they predict stoichiometric compounds, stable at temperatures below 300 ∘C , which have not yet been detected by experiments. The resulting solvus, which defines the transition to the β -phase solid solution, therefore occurs at lower temperatures and is more complex than previously anticipated.

  3. Si-Ge-metal ternary phase diagram calculations

    NASA Technical Reports Server (NTRS)

    Fleurial, J. P.; Borshchevsky, A.

    1990-01-01

    Solution crystal growth and doping conditions of Si-Ge alloys used for high-temperature thermoelectric generation are determined here. Liquid-phase epitaxy (LPE) has been successfully employed recently to obtain single-crystalline homogeneous layers of Si-Ge solid solutions from a liquid metal solvent. Knowledge of Si-Ge-metallic solvent ternary phase diagrams is essential for further single-crystal growth development. Consequently, a thermodynamic equilibrium model was used to calculate the phase diagrams of the Si-Ge-M systems, including solid solubilities, where M is Al, Ga, In, Sn, Pb, Sb, or Bi. Good agreement between calculated liquidus and solidus data and experimental DTA and microprobe results was obtained. The results are used to compare the suitability of the different systems for crystal growth (by LPE-type process).

  4. 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.

  5. 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.

  6. The Molybdenum titanium Phase Diagram Evaluated from Ab initio Calculations

    DTIC Science & Technology

    2016-10-07

    between Titanium- Tantalum Alloy and Pure Titanium for Biomedical Applications, Mater. Trans. 48-3 (2007) 380-384. 8 E. B. Taddei, V. A. R. Henriques, C...surgical implant applications", Nov 2013 (originally approved in 2011). 13 L. Kaufman, Coupled thermochemical and phase diagram data for tantalum based...S. Barzilai, C. Toher, S. Curtarolo, O. Levy, Evaluation of the tantalum -titanium phase diagram from

  7. DNA unzipping phase diagram calculated via replica theory

    NASA Astrophysics Data System (ADS)

    Roland, C. Brian; Hatch, Kristi Adamson; Prentiss, Mara; Shakhnovich, Eugene I.

    2009-05-01

    We show how single-molecule unzipping experiments can provide strong evidence that the zero-force melting transition of long molecules of natural dsDNA should be classified as a phase transition of the higher-order type (continuous). Toward this end, we study a statistical-mechanics model for the fluctuating structure of a long molecule of dsDNA, and compute the equilibrium phase diagram for the experiment in which the molecule is unzipped under applied force. We consider a perfect-matching dsDNA model, in which the loops are volume-excluding chains with arbitrary loop exponent c . We include stacking interactions, hydrogen bonds, and main-chain entropy. We include sequence heterogeneity at the level of random sequences; in particular, there is no correlation in the base-pairing (bp) energy from one sequence position to the next. We present heuristic arguments to demonstrate that the low-temperature macrostate does not exhibit degenerate ergodicity breaking. We use this claim to understand the results of our replica-theoretic calculation of the equilibrium properties of the system. As a function of temperature, we obtain the minimal force at which the molecule separates completely. This critical-force curve is a line in the temperature-force phase diagram that marks the regions where the molecule exists primarily as a double helix versus the region where the molecule exists as two separate strands. We compare our random-sequence model to magnetic tweezer experiments performed on the 48502 bp genome of bacteriophage λ . We find good agreement with the experimental data, which is restricted to temperatures between 24 and 50°C . At higher temperatures, the critical-force curve of our random-sequence model is very different for that of the homogeneous-sequence version of our model. For both sequence models, the critical force falls to zero at the melting temperature Tc like |T-Tc|α . For the homogeneous-sequence model, α=1/2 almost exactly, while for the random

  8. 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.

  9. Phase diagram and thermodynamic calculations of alkali and alkaline earth metal zirconates

    NASA Astrophysics Data System (ADS)

    Dash, Smruti; Sood, D. D.; Prasad, R.

    1996-02-01

    The ternary phase diagrams and partial pressures of various gaseous species over the equilibrium phase fields have been calculated for the MZrO (M = Li, Na, K, Rb, Cs, Sr and Ba) systems by using the SOLGASMIX-PV program, which computes equilibrium composition by direct minimization of the Gibbs energy of a system. The available experimental Gibbs energy data reported in the literature for binary and ternary compounds were used for these calculations. Where no data exist, values were estimated. These ternary phase diagrams are being reported for the first time, except for the lithium system.

  10. Phase Diagram

    NASA Astrophysics Data System (ADS)

    Walker, Matthew S.; Fruehan, Richard J.

    2014-08-01

    The thermodynamics of several aspects of the carbothermic reduction of alumina have been examined. In Part I, the results of measuring the evolved CO from the reaction between Al2O3 and C mixtures were used to determine the temperature and carbon contents for carbide formation at alumina saturation and at carbide saturation in the Al2O3-Al4C3 system. In this part of the paper, results are presented for a thermogravimetric study of the reactions of Al2O3 with carbon, as well as those for the determination of the Al2O3 liquidus line and the Al2O3-Al4O4C eutectic in the Al2O3-Al4C3 phase diagram. The critical temperature for Al2O3 and C to react, producing gas at 1 atm., was in agreement with that predicted from thermodynamics and measured in Part I of this paper. However, the Al2O3 liquidus appeared to be steeper and the eutectic temperature lower than the predicted phase diagram.

  11. The CSA calculation of the bcc Zr-Be phase diagram

    NASA Astrophysics Data System (ADS)

    Zereg, M.; Bourki, S.

    2009-12-01

    In the recent years it has been shown that the fcc-based phase diagram can be calculated from the cluster site approximation (CSA) with remarkable accuracy and great computational simplicity over the cluster variation method (CVM). The basis of this method is briefly recalled in this paper. The CSA approximation is applied to estimate the bcc based order disorder phase diagrams of the Be-Zr system. The input parameters are the cluster interactions which are obtained from first principles calculations published recently. We discuss in detail the relationships between the adjustable parameter in this method and the order disorder transition temperature. Calculations of the formation Gibbs energies are carried out for the ordered and disordered phases and are compared with the ones obtained by the CVM method.

  12. J.L. Meijering's contribution to the calculation of phase diagrams — A personal perspective

    NASA Astrophysics Data System (ADS)

    Kaufman, Larry

    1981-01-01

    During the 1950s the present author had the benefit of studying with Wagner, Chipman, and Cohen, reading the work of Zener, Kubaschewski, Darken and Meijering, and having student colleagues such as Hillert, Hilliard and Cahn wiht whom one could argue and disagree. Notwithstanding the fact that all of these individuals contributed substantially to the author's appreciation of the interaction between thermochemistry and phase diagrams, none had a greater impact than J.L. Meijering. Although I did not meet him in person until 1967, I found that his 1950-1963 papers (listed below) and the extensive correspondence we conducted on lattice stability had the most profound influence on my own perception of the importance of phase diagram calculations. In this brief paper I hope to review Meijering's contribution to the development of our understanding of binary phase diagram characteristics, synthesis of ternary phase diagrams from the components binary diagrams, miscibility gap phenomena, magnetic contributions, and lattice stability. I will try to convince you of my own opinion that Meijering has been the most successful disciple of Van Laar in our time in enhancing the tradition of the Dutch school of thermodynamicists.

  13. 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).

  14. Thermodynamic Calculations of Ternary Polyalcohol and Amine Phase Diagrams for Thermal Energy Storage Materials

    NASA Astrophysics Data System (ADS)

    Shi, Renhai

    Organic polyalcohol and amine globular molecular crystal materials as phase change materials (PCMs) such as Pentaglycerine (PG-(CH3)C(CH 2OH)3), Tris(hydroxymethyl)aminomethane (TRIS-(NH2)C(CH 2OH)3), 2-amino-2methyl-1,3-propanediol (AMPL-(NH2)(CH3)C(CH2OH)2), and neopentylglycol (NPG-(CH3)2C(CH2OH) 2) can be considered to be potential candidates for thermal energy storage (TES) applications such as waste heat recovery, solar energy utilization, energy saving in buildings, and electronic device management during heating or cooling process in which the latent heat and sensible heat can be reversibly stored or released through solid state phase transitions over a range of temperatures. In order to understand the polymorphism of phase transition of these organic materials and provide more choice of materials design for TES, binary systems have been studied to lower the temperature of solid-state phase transition for the specific application. To our best knowledge, the study of ternary systems in these organic materials is limited. Based on this motivation, four ternary systems of PG-TRIS-AMPL, PG-TRIS-NPG, PG-AMPL-NPG, and TRIS-AMPL-NPG are proposed in this dissertation. Firstly, thermodynamic assessment with CALPHAD method is used to construct the Gibbs energy functions into thermodynamic database for these four materials based on available experimental results from X-Ray Diffraction (XRD) and Differential Scanning Calorimetry (DSC). The phase stability and thermodynamic characteristics of these four materials calculated from present thermodynamic database with CALPHAD method can match well the present experimental results from XRD and DSC. Secondly, related six binary phase diagrams of PG-TRIS, PG-AMPL, PG-NPG, TRIS-AMPL, TRIS-NPG, and AMPL-NPG are optimized with CALPHAD method in Thermo-Calc software based on available experimental results, in which the substitutional model is used and excess Gibbs energy is expressed with Redlich-Kister formalism. The

  15. A temperature-concentration (T-X) phase diagram calculated using the mean field theory for liquid crystals.

    PubMed

    Yurtseven, Hamit; Salihoglu, Selami; Karacali, Huseyin

    2013-06-01

    Phase-line equations for smectic-hexatic phase transitions in liquid crystals were derived using the Landau phenomenological theory. In particular, second-order transitions for the smectic-A-smectic-C (SmA-SmC) and hexatic-B-hexatic-F (or HexI) transitions were studied and the tricritical points for these transitions were located. The calculated phase-line equations were fitted (using experimental data for various liquid crystals) to construct a generalized T-X phase diagram. It was shown that the T-X phase diagram calculated from the free energy adequately describes the observed behavior of liquid crystals during smectic-hexatic transitions.

  16. 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.

  17. First principles calculation of phase diagrams of V-Nb, V-Ta and Nb-Ta alloys

    SciTech Connect

    Ravi, C.; Panigrahi, B. K.; Valsakumar, M. C.; Walle, A. Van de

    2012-06-05

    We report the solid state phase diagram of V-Nb, V-Ta and Nb-Ta alloys computed by combining the density functional theory total energies with the cluster expansion and Monte Carlo techniques. From the computed phase diagrams, we find that V-Nb and Nb-Ta alloys form continuous series of solid solutions and the solid solution phase is stable down to ambient temperatures, consistent with experiments. The calculated bcc V-Ta phase diagram exhibits complete miscibility. Since the current cluster expansion ignore V{sub 2}Ta phase, the chemical interaction due to relatively large electronegativity difference, which cause the ordering of V{sub 2}Ta phase from the bcc solid solution, appears to manifest by making the solid solution phase remain stable for the complete concentration range, down to ambient temperatures, perhaps with some short-range-order. This work further demonstrates the dominant role of constituent strains in the accurate calculation of phase diagram of alloys of constituents with significant size mismatches.

  18. Interpretation of high-temperature tensile properties by thermodynamically calculated equilibrium phase diagrams of heat-resistant austenitic cast steels

    NASA Astrophysics Data System (ADS)

    Jung, Seungmun; Sohn, Seok Su; Choi, Won-Mi; Lee, Byeong-Joo; Oh, Yong-Jun; Jang, Seongsik; Lee, Sunghak

    2017-01-01

    High-temperature tensile properties of three heat-resistant austenitic cast steels fabricated by varying W, Mo, and Al contents were interpreted by thermodynamically calculated equilibrium phase diagrams of austenite, ferrite, and carbides as well as microstructural analyses. A two-step calculation method was adopted to cast steel microstructures below the liquid dissolution temperature because the casting route was not an equilibrium state. Thermodynamically calculated fractions of equilibrium phases were well matched with experimentally measured fractions. Ferrites existed at room and high temperatures in both equilibrium phase diagrams and actual microstructures, which has not been reported in previous researches on austenitic cast steels. In the W2Mo1Al1 steel, 38% and 12% of ferrite existed in the equilibrium phase diagram and actual microstructure, respectively, and led to the void initiation and coalescence at ferrites and consequently to the serious deterioration of high-temperature strengths. The present equilibrium phase diagrams, besides detailed microstructural analyses, effectively evaluated the high-temperature performance by estimating high-temperature equilibrium phases, and provided an important idea on whether ferrite were formed or not in the heat-resistant austenitic cast steels.

  19. PHASE EQUILIBRIA INVESTIGATION OF BINARY, TERNARY, AND HIGHER ORDER SYSTEMS. PART 9. CALCULATION OF THERMODYNAMIC QUANTITIES FROM PHASE DIAGRAMS

    DTIC Science & Technology

    The thermodynamic fundamentals relating phase equilibria in binary and ternary systems to the thermodynamic properties of the phases are reviewed and...system demonstrate the application of the equations for extracting thermodynamic data from phase diagrams and also for the prediction of phase equilibria .

  20. Molecular Simulation of the Phase Diagram of Methane Hydrate: Free Energy Calculations, Direct Coexistence Method, and Hyper Parallel Tempering.

    PubMed

    Jin, Dongliang; Coasne, Benoit

    2017-08-09

    Different molecular simulation strategies are used to assess the stability of methane hydrate under various temperature and pressure conditions. First, using two water molecular models, free energy calculations consisting of the Einstein molecule approach in combination with semi-grand Monte Carlo simulations are used to determine the pressure--temperature phase diagram of methane hydrate. With these calculations, we also estimate the chemical potentials of water and methane and methane occupancy at coexistence. Second, we also consider two other advanced molecular simulation techniques that allow probing the phase diagram of methane hydrate: the direct coexistence method in the Grand Canonical ensemble and the hyper parallel tempering Monte Carlo method. These two direct techniques are found to provide stability conditions that are consistent with the pressure--temperature phase diagram obtained using rigorous free energy calculations. The phase diagram obtained in this work, which is found to be consistent with previous simulation studies, is close to its experimental counterpart provided the TIP4P/Ice model is used to describe the water molecule.

  1. Insights into the phase diagram of bismuth ferrite from quasiharmonic free-energy calculations

    NASA Astrophysics Data System (ADS)

    Cazorla, Claudio; Iñiguez, Jorge

    2013-12-01

    We have used first-principles methods to investigate the phase diagram of multiferroic bismuth ferrite (BiFeO3 or BFO), revealing the energetic and vibrational features that control the occurrence of various relevant structures. More precisely, we have studied the relative stability of four low-energy BFO polymorphs by computing their free energies within the quasiharmonic approximation, introducing a practical scheme that allows us to account for the main effects of spin disorder. As expected, we find that the ferroelectric ground state of the material (with R3c space group) transforms into an orthorhombic paraelectric phase (Pnma) upon heating. We show that this transition is not significantly affected by magnetic disorder, and that the occurrence of the Pnma structure relies on its being vibrationally (although not elastically) softer than the R3c phase. We also investigate a representative member of the family of nanotwinned polymorphs recently predicted for BFO [S. Prosandeev et al., Adv. Funct. Mater. 23, 234 (2013), 10.1002/adfm.201201467] and discuss their possible stabilization at the boundaries separating the R3c and Pnma regions in the corresponding pressure-temperature phase diagram. Finally, we elucidate the intriguing case of the so-called supertetragonal phases of BFO: Our results explain why such structures have never been observed in the bulk material, despite their being stable polymorphs of very low energy. Quantitative comparison with experiment is provided whenever possible, and the relative importance of various physical effects (zero-point motion, spin fluctuations, thermal expansion) and technical features (employed exchange-correlation energy density functional) is discussed. Our work attests the validity and usefulness of the quasiharmonic scheme to investigate the phase diagram of this complex oxide, and prospective applications are discussed.

  2. 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.

  3. Oxidation Phase Diagram of Small Aluminum Clusters Based on First-Principles Calculations

    NASA Astrophysics Data System (ADS)

    Wang, Ligen; Kuklja, Maija M.

    2009-12-01

    We present a density functional theory study of the structure and properties of Al13 and Al12Ni clusters, oxygen adsorptions on the cluster surfaces, and the completely oxidized clusters. The relative stability of various phases at various oxygen pressures and temperatures is investigated based on the "atomistic thermodynamics" which was previously employed for studying metal surfaces. We construct the two-dimensional (P, T) oxidation phase diagrams for these systems. We find that alloying the Al cluster with Ni does not improve its resistance to oxidation. The present study provides valuable insight into basic behaviors of small Al clusters in the presence of oxygen and a theoretical basis for exploring practical applications of these clusters.

  4. Application of Computer Methods for Calculation of Multicomponent Phase Diagrams of High Temperature Structural Ceramics.

    DTIC Science & Technology

    1986-02-28

    Ceramic Systems" CALPHAD XIV, M.I.T. Cambridge, MA June 1985. 2. "Calculation of Ternary Isothermal Sections in the Ni- Cr -Al and Ni- Cr -SI Systems...Massachusetts 02139 4.- C= rE C. F F TTCIENTFIC .ESZ ARCH (AFSC)i ".?T[?E, F IANS:{ T O DTIC hi:; te 8h;’icl report h been reviewd and is -r.T -’Vvd f or public...Methods for Annual Report Calculation of Multicomponent Phase Diagr Ot 8 o 8Fe.8 of Structural Ceramics 16 aroMN Dc.REOTalmr 6. AuuRAT R RAT ire)~s Larry

  5. Density of configurational states from first-principles calculations: the phase diagram of Al-Na surface alloys.

    PubMed

    Borg, Mikael; Stampfl, Catherine; Mikkelsen, Anders; Gustafson, Johan; Lundgren, Edvin; Scheffler, Matthias; Andersen, Jesper N

    2005-09-05

    The structural phases of Al(x)Na(1-x) surface alloys have been investigated theoretically and experimentally. We describe the system using a lattice-gas Hamiltonian, determined from density functional theory, together with Monte Carlo (MC) calculations. The obtained phase diagram reproduces the experiment on a quantitative level. From calculation of the (configurational) density of states by the recently introduced Wang-Landau MC algorithm, we derive thermodynamic quantities, such as the free energy and entropy, which are not directly accessible from conventional MC simulations. We accurately reproduce the stoichiometry, as well as the temperature at which an order-disorder phase transition occurs, and demonstrate the crucial role, and magnitude, of the configurational entropy.

  6. Ab initio calculations of the thermodynamics and phase diagram of zirconium

    NASA Astrophysics Data System (ADS)

    Hao, Yan-Jun; Zhang, Lin; Chen, Xiang-Rong; Cai, Ling-Cang; Wu, Qiang; Alfè, Dario

    2008-10-01

    The finite-temperature density-functional theory and quasiharmonic lattice dynamics are used to calculate the Gibbs free energy and quasiharmonic phonons of the hexagonal-close-packed (hcp) and omega (ω) crystal structures for Zr. The hcp phonon dispersions agree with experiment; the ω phonon dispersions have not been measured yet. From the free energy, the volume thermal expansion coefficients of α-Zr are predicted. The calculated volume thermal expansion coefficients for α-Zr are in good agreement with the experiment data at T>100K . Our calculated results found that at zero-temperature the lowest-energy phase is not the ω but the hcp phase. This conclusion is in accordance with the result of Schnell and Albers, but in disagreement with those of Ahuja and Jona and Marcus. The predicted phase boundary of α→ω is in good agreement with the available experiment; however, other theoretical results are far from the experiment at high temperatures.

  7. Phase diagrams of polyelectrolyte solutions

    NASA Astrophysics Data System (ADS)

    Mahdi, Khaled A.

    We study the phase diagram of polyelectrolyte solutions in salt and salt-free environments. We examine the phase behavior of polyelectrolyte solutions, in the semidilute regime, using different physical models, namely the Random Phase Approximation (RPA) and the cross-linked model. In the RPA, we calculate the electrostatic free energy by summing all the fluctuations of the chains and all present ionic species. Within this approximation, the phase diagrams of salt-free polyelectrolyte solutions show phase separation even without including short-range attractions or ion condensation. We find that the phase behavior of large chains resembles the phase diagram of polymer network solutions. That is, the equilibrium is established between a network phase and a chain-free phase. Upon the addition of salt, the dissociated ions increase the entropy of the system and overcome the energy from the electrostatic fluctuations. When the short-range attraction between monomers is included in the model, the free energy predicts phase segregation for all salt valences at high salt concentrations (1 mol/l and higher). The phenomenon is called salting-out and occurs simply because the addition of salt reduces the quality of the solvent and induces precipitation. However, phase segregation in the presence of multivalent ions in polyelectrolyte solutions occurs at low salt concentrations (less than 1 mol/l). We propose that this phase separation is due to polyions cross-linked by multivalent ions. We constructed a phenomenological two-state model to examine this phenomenon. The two phases coexisting in the solution are a network-like phase and a polymer-free phase. The polymer-free phase is modeled using Debye-Huckel theory. In the cross-linked phase, each condensed multivalent ion attracts an equal number of monomers creating a neutral cluster. The energy of the cluster is evaluated by a simple Coulombic energy. The bare monomer charges between the linkages are treated as line of

  8. 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.

  9. 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.

  10. Application of Computer Methods for Calculation of Multi Component Phase Diagrams of High Temperature Structural Ceramics.

    DTIC Science & Technology

    1987-07-31

    o ! tt’.it base cover combilnatlons of Cr 201 , Y~.’r0 A)2 03 0 sio?2) CaO, Si 3 N40 A) ?." be, o ’ T" o and 0e...technology as well as descriptions of the CrO 2-Si0 2 and NiO-SiO 2 system was provided. Calculations of the Fe-Ni- O , Fe- Cr -0, TI-C-4 and Al2 O 3-Y2 0...system was provided. Calculations of the Fe-NI- O , Fe- Cr - O , TI-C-N and Al 0 -Y 0 -ZrO 4 systems were performed on the new "Thermoca’c" system H

  11. Application of Computer Methods for Calculation of Multicomponent Phase Diagrams of High Temperature Structural Ceramics.

    DTIC Science & Technology

    1987-02-27

    been largely completed. The system is available at NBS and at MIT in Cambridge, Massachusetts. Modeling of the Fe-Ni- O , Fe- Cr - O , Ti-C-N, ZrO2 -Y 2 0 3... O ~d 009T Figure 43. Calculated isothermai Sections in the HO(1/3HfO 2) DO(1/2CaO) -ZO(1/3Zro 2 ) system 7 0 i-l 0 ’I a Ne C"rj + L Cr c C ’i4-i cLI...IT. DST 014410rI@.. A SALINT faI She abathago afte.erd aoe 91J.h s. of 01laweent #rein. epej of RLY WORDS (feaev en "Ve ,. Ojos o at ereslae. done

  12. 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.

  13. t-Jz ladder: Density-matrix renormalization group and series expansion calculations of the phase diagram

    NASA Astrophysics Data System (ADS)

    Weisse, A.; Bursill, R. J.; Hamer, C. J.; Weihong, Zheng

    2006-04-01

    The phase diagram of the two-leg t-Jz ladder is explored, using the density-matrix renormalization group method. Results are obtained for energy gaps, electron density profiles, and correlation functions for the half filled and quarter filled cases. The effective Lagrangian velocity parameter vρ is shown to vanish at half filling. The behavior of the one-hole gap in the Nagaoka limit is investigated, and found to disagree with theoretical predictions. A tentative phase diagram is presented, which is quite similar to the full t-J ladder, but scaled up by a factor of about 2 in coupling. Near half filling a Luther-Emery phase is found, which may be expected to show superconducting correlations, while near quarter filling the system appears to be in a Tomonaga-Luttinger phase.

  14. TERNARY PHASE EQUILIBRIA IN TRANSITION METAL-BORON-CARBON-SILICON SYSTEMS. PART 4. THERMOCHEMICAL CALCULATIONS, VOLUME 3. COMPUTATIONAL APPROACH TO THE CALCULATION OF TERNARY PHASE DIAGRAMS

    DTIC Science & Technology

    The general conditional equations which govern the phase equilibria in three-component systems are presented. Using the general conditional equations...a general method has been developed to precalculate the phase equilibria in three-component systems from first principle using computer technique...The method developed has been applied to several model examples and the system Ta-Hf-C. The phase equilibria in three-component systems calculated

  15. 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.

  16. Ion mixing and phase diagrams

    NASA Astrophysics Data System (ADS)

    Lau, S. S.; Liu, B. X.; Nicolet, M.-A.

    1983-05-01

    Interactions induced by ion irradiation are generally considered to be non-equilibrium processes, whereas phase diagrams are determined by phase equilibria. These two entities are seemingly unrelated. However, if one assumes that quasi-equilibrium conditions prevail after the prompt events, subsequent reactions are driven toward equilibrium by thermodynamical forces. Under this assumption, ion-induced reactions are related to equilibrium and therefore to phase diagrams. This relationship can be seen in the similarity that exists in thin films between reactions induced by ion irradiation and reactions induced by thermal annealing. In the latter case, phase diagrams have been used to predict the phase sequence of stable compound formation, notably so in cases of silicide formation. Ion-induced mixing not only can lead to stable compound formation, but also to metastable alloy formation. In some metal-metal systems, terminal solubilities can be greatly extended by ion mixing. In other cases, where the two constituents of the system have different crystal structures, extension of terminal solubility from both sides of the phase diagram eventually becomes structurally incompatible and a glassy (amorphous) mixture can form. The composition range where this bifurcation is likely to occur is in the two-phase regions of the phase diagram. These concepts are potentially useful guides in selecting metal pairs that from metallic glasses by ion mixing. In this report, phenomenological correlation between stable (and metastable) phase formation and phase diagram is discussed in terms of recent experimental data.

  17. Total Energy Calculations using DFT+DMFT: Application to the Pressure-composition Phase Diagram of Rare-earth Element Nickelates

    NASA Astrophysics Data System (ADS)

    Park, Hyowon

    2014-03-01

    Ab-initio total energy calculations have been implemented within the fully self-consistent density functional theory plus dynamical mean field theory (DFT+DMFT) method, using a Wannier orbital basis. The method is used to calculate the structural and metal-insulator transition phase diagrams of the rare-earth element nickelate RNiO3 perovskites as a function of rare-earth ion, pressure and temperature. This phase diagram is of interest because the insulating phase arises from a remarkable site-selective Mott state, in which unusual electronic physics is strongly coupled to a breathing-mode Ni-O bond disproportionation. Conventional DFT fails to stabilize the breathing distortion and thus does not reproduce the insulating phase. DFT+U overpredicts order, in particular finding that La NiO3 is disproportionated, in disagreement with experiment. In contrast to these theories, the DFT+DMFT method can quantitatively reproduce the metal-insulator and structural phase diagram of all RNiO3 perovskites in the plane of pressure and rare-earth elements. The calculated temperature dependence of the energetics of the phase transformation indicates that the thermal transition is driven by phonon entropy effects. This present method can be generally applied to nano-structured or artificially structured strongly correlated materials including heterostructures and thin films, whose electronic phases are strongly coupled to their lattice degrees of freedom. The authors acknowledge funding from the U. S. Army Research Office via grant No. W911NF0910345 56032PH, US Department of Energy under grant DOE-ER-046169, and in part by FAME, a Semiconductor Research Corporation program sponsored by MARCO and DARPA.

  18. 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.

  19. Quantum Dimer Model: Phase Diagrams

    NASA Astrophysics Data System (ADS)

    Goldstein, Garry; Chamon, Claudio; Castelnovo, Claudio

    We present new theoretical analysis of the Quantum Dimer Model. We study dimer models on square, cubic and triangular lattices and we reproduce their phase diagrams (which were previously known only numerically). We show that there are several types of dimer liquids and solids. We present preliminary analysis of several other models including doped dimers and planar spin ice, and some results on the Kagome and hexagonal lattices.

  20. Phase diagram of crushed powders

    NASA Astrophysics Data System (ADS)

    Bodard, Sébastien; Jalbaud, Olivier; Saurel, Richard; Burtschell, Yves; Lapebie, Emmanuel

    2016-12-01

    Compression of monodisperse powder samples in quasistatic conditions is addressed in a pressure range such that particles fragmentation occurs while the solid remains incompressible (typical pressure range of 1-300 MPa for glass powders). For a granular bed made of particles of given size, the existence of three stages is observed during compression and crush up. First, classical compression occurs and the pressure of the granular bed increases along a characteristic curve as the volume decreases. Then, a critical pressure is reached for which fragmentation begins. During the fragmentation process, the granular pressure stays constant in a given volume range. At the end of this second stage, 20%-50% of initial grains are reduced to finer particles, depending on the initial size. Then the compression undergoes the third stage and the pressure increases along another characteristic curve, in the absence of extra fragmentation. The present paper analyses the analogies between the phase transition in liquid-vapour systems and powder compression with crush-up. Fragmentation diagram for a soda lime glass is determined by experimental means. The analogues of the saturation pressure and latent heat of phase change are determined. Two thermodynamic models are then examined to represent the crush-up diagram. The first one uses piecewise functions while the second one is of van der Waals type. Both equations of state relate granular pressure, solid volume fraction, and initial particle diameter. The piecewise functions approach provides reasonable representations of the phase diagram while the van der Waals one fails.

  1. 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.

  2. Phase Diagrams, Criticality, and Local Properties of Spin Glasses and Random-Field Ising Models from Renormalization - Calculations.

    NASA Astrophysics Data System (ADS)

    Hartford, Edward John

    This position-space renormalization-group study focuses on two systems with quenched disorder: the Ising spin glass and the asymmetric random-field Ising model. We have employed the Migdal-Kadanoff approach to determine local recursion relations and have retained the full correlated probability distribution of interactions and fields at each iteration in a series of histograms. We find an equilibrium spin-glass phase in three dimensions, but not in two. The spin glass is characterized by a distribution of effective interactions that broadens under iteration, signaling both the long-range order of the phase and the importance of competing interactions on all length scales. We have introduced a method to calculate the distribution of local properties by differentiating the free energy with respect to a particular magnetic field or interaction. Within the spin-glass phase, the nearest neighbor correlation < S_ {i}S_{j}> ranges from negative one to one, showing the strong correlations and the local variation within the phase. The spin-glass-to-paramagnet phase transition is second order, with a smooth specific heat indicated by a negative critical exponent alpha. The multicritical point separating the spin-glass, paramagnetic, and ferromagnetic phases lies along the Nishimori line and also has a nondivergent specific heat. When the system undergoes quenched dilution, the resulting critical and multicritical behaviors are identical to those of the undiluted system. Even the addition of an infinitesimal magnetic field destroys the long-range spin-glass order; however, the characteristic broadening of the distribution continues for several iterations for small fields and low temperatures, suggesting the persistence of sizable spin-glass domains. Our study of the asymmetric random-field Ising model is motivated by recent experiments on phase transitions in porous media and mean-field treatments, which suggest that new critical behavior could occur when the distribution of

  3. Phase diagrams for sonoluminescing bubbles

    NASA Astrophysics Data System (ADS)

    Hilgenfeldt, Sascha; Lohse, Detlef; Brenner, Michael P.

    1996-11-01

    Sound driven gas bubbles in water can emit light pulses. This phenomenon is called sonoluminescence (SL). Two different phases of single bubble SL have been proposed: diffusively stable and diffusively unstable SL. We present phase diagrams in the gas concentration versus forcing pressure state space and also in the ambient radius versus gas concentration and versus forcing pressure state spaces. These phase diagrams are based on the thresholds for energy focusing in the bubble and two kinds of instabilities, namely (i) shape instabilities and (ii) diffusive instabilities. Stable SL only occurs in a tiny parameter window of large forcing pressure amplitude Pa˜1.2-1.5 atm and low gas concentration of less than 0.4% of the saturation. The upper concentration threshold becomes smaller with increased forcing. Our results quantitatively agree with experimental results of Putterman's UCLA group on argon, but not on air. However, air bubbles and other gas mixtures can also successfully be treated in this approach if in addition (iii) chemical instabilities are considered. All statements are based on the Rayleigh-Plesset ODE approximation of the bubble dynamics, extended in an adiabatic approximation to include mass diffusion effects. This approximation is the only way to explore considerable portions of parameter space, as solving the full PDEs is numerically too expensive. Therefore, we checked the adiabatic approximation by comparison with the full numerical solution of the advection diffusion PDE and find good agreement.

  4. 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.

  5. Phase diagram of ammonium nitrate

    NASA Astrophysics Data System (ADS)

    Dunuwille, Mihindra; Yoo, Choong-Shik

    2013-12-01

    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 N2, N2O, and H2O 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' transition above 17 GPa and provide new constraints for the melting and phase diagram of AN to 40 GPa and 400°C.

  6. Origin and use of crystallization phase diagrams

    PubMed Central

    Rupp, Bernhard

    2015-01-01

    Crystallization phase diagrams are frequently used to conceptualize the phase relations and also the processes taking place during the crystallization of macromolecules. While a great deal of freedom is given in crystallization phase diagrams owing to a lack of specific knowledge about the actual phase boundaries and phase equilibria, crucial fundamental features of phase diagrams can be derived from thermodynamic first principles. Consequently, there are limits to what can be reasonably displayed in a phase diagram, and imagination may start to conflict with thermodynamic realities. Here, the commonly used ‘crystallization phase diagrams’ are derived from thermodynamic excess properties and their limitations and appropriate use is discussed. PMID:25760697

  7. Phase diagram of Hertzian spheres

    NASA Astrophysics Data System (ADS)

    Pàmies, Josep C.; Cacciuto, Angelo; Frenkel, Daan

    2009-07-01

    We report the phase diagram of interpenetrating Hertzian spheres. The Hertz potential is purely repulsive, bounded at zero separation, and decreases monotonically as a power law with exponent 5/2, vanishing at the overlapping threshold. This simple functional describes the elastic interaction of weakly deformable bodies and, therefore, it is a reliable physical model of soft macromolecules, like star polymers and globular micelles. Using thermodynamic integration and extensive Monte Carlo simulations, we computed accurate free energies of the fluid phase and a large number of crystal structures. For this, we defined a general primitive unit cell that allows for the simulation of any lattice. We found multiple re-entrant melting and first-order transitions between crystals with cubic, trigonal, tetragonal, and hexagonal symmetries.

  8. Phase Equilibria, Phase Diagrams and Phase Transformations - 2nd Edition

    NASA Astrophysics Data System (ADS)

    Hillert, Mats

    2006-03-01

    Computational tools allow material scientists to model and analyze increasingly complicated systems to appreciate material behavior. Accurate use and interpretation however, requires a strong understanding of the thermodynamic principles that underpin phase equilibrium, transformation and state. This fully revised and updated edition covers the fundamentals of thermodynamics, with a view to modern computer applications. The theoretical basis of chemical equilibria and chemical changes is covered with an emphasis on the properties of phase diagrams. Starting with the basic principles, discussion moves to systems involving multiple phases. New chapters cover irreversible thermodynamics, extremum principles, and the thermodynamics of surfaces and interfaces. Theoretical descriptions of equilibrium conditions, the state of systems at equilibrium and the changes as equilibrium is reached, are all demonstrated graphically. With illustrative examples - many computer calculated - and worked examples, this textbook is an valuable resource for advanced undergraduates and graduate students in materials science and engineering. Fully revised and updated edition covering the fundamentals of thermodynamics with a view to modern computer applications such as Thermo-Calc Emphasis is placed on phase diagrams, the key application of thermodynamics Contains numerous illustrative examples, many computer-calculated and some for real systems, and worked examples to help demonstrate the principles

  9. 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.

  10. 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.

  11. 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.

  12. Phase diagram of elastic spheres.

    PubMed

    Athanasopoulou, L; Ziherl, P

    2017-02-15

    Experiments show that polymeric nanoparticles often self-assemble into several non-close-packed lattices in addition to the face-centered cubic lattice. Here, we explore theoretically the possibility that the observed phase sequences may be associated with the softness of the particles, which are modeled as elastic spheres interacting upon contact. The spheres are described by two finite-deformation theories of elasticity, the modified Saint-Venant-Kirchhoff model and the neo-Hookean model. We determine the range of indentations where the repulsion between the spheres is pairwise additive and agrees with the Hertz theory. By computing the elastic energies of nine trial crystal lattices at densities far beyond the Hertzian range, we construct the phase diagram and find the face- and body-centered cubic lattices as well as the A15 lattice and the simple hexagonal lattice, with the last two being stable at large densities where the spheres are completely faceted. These results are qualitatively consistent with observations, suggesting that deformability may indeed be viewed as a generic property that determines the phase behavior in nanocolloidal suspensions.

  13. Phase diagram of the Shastry-Sutherland Kondo lattice model with classical localized spins: a variational calculation study

    NASA Astrophysics Data System (ADS)

    Shahzad, Munir; Sengupta, Pinaki

    2017-08-01

    We study the Shastry-Sutherland Kondo lattice model with additional Dzyaloshinskii-Moriya (DM) interactions, exploring the possible magnetic phases in its multi-dimensional parameter space. Treating the local moments as classical spins and using a variational ansatz, we identify the parameter ranges over which various common magnetic orderings are potentially stabilized. Our results reveal that the competing interactions result in a heightened susceptibility towards a wide range of spin configurations including longitudinal ferromagnetic and antiferromagnetic order, coplanar flux configurations and most interestingly, multiple non-coplanar configurations including a novel canted-flux state as the different Hamiltonian parameters like electron density, interaction strengths and degree of frustration are varied. The non-coplanar and non-collinear magnetic ordering of localized spins behave like emergent electromagnetic fields and drive unusual transport and electronic phenomena.

  14. Phase diagrams for high Tc superconductors

    SciTech Connect

    Whitler, J.D.; Roth, R.S. NIST, Gaithersburg, MD )

    1991-01-01

    The phase diagrams of ternary and quaternary systems containing superconducting phases are presented, as are the phase diagrams of the associated binary systems. The diagrams are divided into two large groups: (1) alkaline earth-rare earth-copper-oxygen diagrams, and (2) alkaline earth-bismuth/lead-copper-oxygen diagrams. The first group includes BaO-REO-CuO systems followed by SrO-REO-CuO or Nd2O3-CeO-CuO systems. The second group includes systems related to the AE-Bi2O3-CuO and AE-PbO-CuO systems. The phase diagrams are accompanied by notes relating procedures used in the studies, results obtained, and comparisons with the results in the literature for the same system.

  15. Ab initio phase diagram of iridium

    NASA Astrophysics Data System (ADS)

    Burakovsky, L.; Burakovsky, N.; Cawkwell, M. J.; Preston, D. L.; Errandonea, D.; Simak, S. I.

    2016-09-01

    The phase diagram of iridium is investigated using the Z methodology. The Z methodology is a technique for phase diagram studies that combines the direct Z method for the computation of melting curves and the inverse Z method for the calculation of solid-solid phase boundaries. In the direct Z method, the solid phases along the melting curve are determined by comparing the solid-liquid equilibrium boundaries of candidate crystal structures. The inverse Z method involves quenching the liquid into the most stable solid phase at various temperatures and pressures to locate a solid-solid boundary. Although excellent agreement with the available experimental data (to ≲65 GPa) is found for the equation of state (EOS) of Ir, it is the third-order Birch-Murnaghan EOS with B0'=5 rather than the more widely accepted B0'=4 that describes our ab initio data to higher pressure (P ) . Our results suggest the existence of a random-stacking hexagonal close-packed structure of iridium at high P . We offer an explanation for the 14-layer hexagonal structure observed in experiments by Cerenius and Dubrovinsky.

  16. Vesicle deformation by microtubules: A phase diagram

    NASA Astrophysics Data System (ADS)

    Emsellem, Virginie; Cardoso, Olivier; Tabeling, Patrick

    1998-10-01

    The experimental investigation of vesicles deformed by the growth of encapsulated microtubules shows that the axisymmetric morphologies can be classified into ovals, lemons, φ, cherries, dumbbells, and pearls. A geometrical phase diagram is established. Numerical minimization of the elastic energy of the membrane reproduces satisfactorily well the observed morphologies and the corresponding phase diagram.

  17. 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

  18. Calculation of Ceramic Phase Diagrams

    DTIC Science & Technology

    1979-11-30

    Quasiternary Electroptical semiconductors Ceramic Systems Superalloys HEM silicon solar cells Sialons Molten Salts metatectic reactions in hafnium alloys...in hafnium alloys and the growth of HEM silicon solar cell materials. The initial results obtained by applying these techniques to CVD synthesis of...battery electrodes, hardenability, synthesis of hydrogen storage compounds, grain refinement in aluminum alloys, metatectic reactions in hafnium alloys

  19. 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.

  20. 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.

  1. 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.).

  2. Pressure-temperature phase diagrams of biomolecules.

    PubMed

    Smeller, László

    2002-03-25

    The pressure-temperature phase diagram of various biomolecules is reviewed. Special attention is focused on the elliptic phase diagram of proteins. The phenomenological thermodynamic theory describing this diagram explains the heat, cold and pressure denaturations in a unified picture. The limitations and possible developments of this theory are discussed as well. It is pointed out that a more complex diagram can be obtained when the intermolecular interactions are also taken into account. In this case metastable states appear on the pressure-temperature (p-T) diagram due to intermolecular interactions. Pressure-temperature phase diagrams of other biopolymers are also discussed. While the p-T diagrams of helix-coil transition of nucleic acids and of gel-liquid crystal transition of lipid bilayers are non-elliptical, those of gelatinization of starch and of phase separation of some synthetic polymers show an elliptic profile, similar to that of proteins. Finally, the p-T diagram of bacterial inactivation is shown to be elliptic. From the point of view of basic science, this fact shows that the key factor of inactivation should be the protein type, and from the viewpoint of practical applications, it serves as the theoretical basis of pressure treatment of biosystems.

  3. Phase diagrams of self-organizing maps

    NASA Astrophysics Data System (ADS)

    Bauer, H.-U.; Riesenhuber, M.; Geisel, T.

    1996-09-01

    We present a method which allows the analytic determination of phase diagrams in the self-organizing map, a model for the formation of topographic projection patterns in the brain and in signal processing applications. The method only requires an ansatz for the tesselation of the data space induced by the map, not for the explicit state of the map. We analytically obtain phase diagrams for various examples, including models for the development of orientation and ocular-dominance maps. The latter phase diagram exhibits transitions to broadening ocular-dominance patterns as observed in a recent experiment.

  4. Analysis of "solution effects" injury. Equations for calculating phase diagram information for the ternary systems NaCl-dimethylsulfoxide-water and NaCl-glycerol-water.

    PubMed Central

    Fahy, G M

    1980-01-01

    Slowly frozen cells are said to be subject to solution effects injury. An understanding of the mechanism of solution effects injury depends upon an understanding of the compositional changes brought about in the extracellular solution during the freezing process. To facilitate analysis of the mechanisms of freezing injury during slow cooling, empirical equations have been developed which permit a description of these changes in composition for the NaCl-dimethylsulfoxide-water ternary system and for the NaCl-glycerol-water ternary system. The equations describe the region of the phase diagram in which compositional changes are brought about only as a result of the precipitation of ice. The present phase diagram equations may be rearranged to give expression for composition variables such as water content, salt concentration, unfrozen fraction of the solution, etc., which may be employed in the analysis of the relationship between solution composition and solution effects injury. PMID:7260303

  5. Phase Diagram Calculation of Gas Mixtures for Refrigeration; Reflection & Transmission Coefficients and the Effective Mass: Superconducting Proximity I-V Measurements.

    NASA Astrophysics Data System (ADS)

    Friedmann, Gideon

    The efficiency of Joule-Thomson refrigerators greatly improves with the addition of hydrocarbons to nitrogen as coolant, and is highly dependent on the mixture composition. To optimize it, we calculated the mixture phase diagram using the Peng-Robinson equation of state. A program was developed to solve numerically a set of coupled non-linear equations for the equilibrium of the vapor and liquid phases of each mixture component. The program is highly efficient, quite stable, and reliable. Gases can be easily added to the program's database. We found that the cooling efficiency of the mixtures has a sharp ridge in composition space, and explain this. To better understand tunneling spectra of the high T_{rm c} cuprate superconductors, we analyzed the one-dimensional behavior of the wavefunction of a free particle striking a crystal interface. We describe the free particle using a wavepacket of plane waves, and the crystal using the Kronig-Penney model. We find that when the wavepacket is spread over many unit cells, it behaves like a free particle wavepacket striking a small potential step. The reflection and transmission coefficients are derived and one finds that they do not contain the particle's effective mass. We determine that the boundary conditions used in a standard effective mass approach must be modified to make it work. We conclude that one should not use the effective mass approximation in treating high T_{rm c} superconductor interfaces. We measured the dynamic resistance of a superconducting -normal metal-normal metal (SNN') geometry and observed that N', a superconductor at low enough temperatures, displays superconducting properties above its critical temperature. They disappear well below the critical temperature of S. We present a simple model of the proximity effect, which is self-consistent at any temperature and good for arbitrary thicknesses of N. The model shows how the superconducting gap decays with the distance from S. We observe that the

  6. Pressure-Temperature Phase Diagram of Vanadium Dioxide.

    PubMed

    Chen, Yabin; Zhang, Shuai; Ke, Feng; Ko, Changhyun; Lee, Sangwook; Liu, Kai; Chen, Bin; Ager, Joel W; Jeanloz, Raymond; Eyert, Volker; Wu, Junqiao

    2017-03-08

    The complexity of strongly correlated electron physics in vanadium dioxide is exemplified as its rich phase diagrams of all kinds, which in turn shed light on the mechanisms behind its various phase transitions. In this work, we map out the hydrostatic pressure-temperature phase diagram of vanadium dioxide nanobeams by independently varying pressure and temperature with a diamond anvil cell. In addition to the well-known insulating M1 (monoclinic) and metallic R (tetragonal) phases, the diagram identifies the existence at high pressures of the insulating M1' (monoclinic, more conductive than M1) phase and two metallic phases of X (monoclinic) and O (orthorhombic, at high temperature only). Systematic optical and electrical measurements combined with density functional calculations allow us to delineate their phase boundaries as well as reveal some basic features of the transitions.

  7. Theoretical phase diagrams for solid H{sub 2}

    SciTech Connect

    Surh, M.P.; Runge, K.J.

    1993-07-01

    Possible phase diagrams for solid molecular para-hydrogen in the 0-200 GPa pressure regime are constructed on the basis of ab initio calculations. Structures for the broken symmetry phase (BSP) and H-A phase have recently been proposed under the assumption that the molecules are centered on sites of a hexagonal close-packed lattice with the ideal c/a ratio, i.e., only molecular orientational and electronic changes are allowed. Symmetry considerations then dictate the simplest phase diagrams consistent with experimental observations, although the possibility of additional transitions cannot be ruled out. A simple model is introduced to describe the BSP and H-A transitions.

  8. 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.

  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. Phase diagram of silica from computer simulation

    NASA Astrophysics Data System (ADS)

    Saika-Voivod, Ivan; Sciortino, Francesco; Grande, Tor; Poole, Peter H.

    2004-12-01

    We evaluate the phase diagram of the “BKS” potential [van Beest, Kramer, and van Santen, Phys. Rev. Lett. 64, 1955 (1990)], a model of silica widely used in molecular dynamics (MD) simulations. We conduct MD simulations of the liquid, and three crystals ( β -quartz, coesite, and stishovite) over wide ranges of temperature and density, and evaluate the total Gibbs free energy of each phase. The phase boundaries are determined by the intersection of these free energy surfaces. Not unexpectedly for a classical pair potential, our results reveal quantitative discrepancies between the locations of the BKS and real silica phase boundaries. At the same time, we find that the topology of the real phase diagram is reproduced, confirming that the BKS model provides a satisfactory qualitative description of a silicalike material. We also compare the phase boundaries with the locations of liquid-state thermodynamic anomalies identified in previous studies of the BKS model.

  11. Complete Phase Diagram for the 3-d Hubbard Model

    NASA Astrophysics Data System (ADS)

    Berker, A. Nihat

    2000-03-01

    The Hubbard and tJ models are the basic microscopic models for electronic conductivity. Surprisingly, their phase diagrams, in temperature versus electron density, had not been known away from zero temperature, away from half-filling electron density, and in three dimensions (d=3). We have calculated these phase diagrams, in d=2 and 3, at all finite temperatures and for the full range of electron densities, for the tJ[1,2] and Hubbard[3] models. We use an approximate renormalization-group theory with respectively four- and ten-dimensional flows. In the d=3 Hubbard model, an antiferromagnetic phase occurs near half-filling, but is unstable to at most 10% electron or hole doping. Between 30-40% electron or hole doping, a new phase (which we called the tau phase) occurs, in which the electron hopping strength t renormalizes to infinity; in all other phases, t renormalizes to zero. Most recent renormalization-group work[4] shows that the tau phase supports current in the absence of applied voltage. At temperatures above the tau phase, an incommensurate spin modulation phase is indicated. Near the tau phase, a first-order transition occurs with a remarkably narrow phase separation, namely a jump in electron density less than 2%. Clearly this phase diagram shows similarity to the experimental phase diagrams of high-Tc superconductors. The tJ model in d=3 exhibits a similar phase diagram. In d=2, the Hubbard model exhibits no phase transition at finite temperatures, whereas the tJ model exhibits phase separation for t/J<0.25. [1] A. Falicov and A.N. Berker, Phys. Rev. B 51, 12458 (1995). [2] A. Falicov and A.N. Berker, Turk. J. Phys. 19, 127 (1995). [3] G. Migliorini and A.N. Berker, MIT-ITU-Gursey preprint (1998). [4] A. Kabakcioglu and A.N. Berker, to be published.

  12. 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…

  13. 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…

  14. 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…

  15. Fluctuations and the QCD Phase Diagram

    SciTech Connect

    Koch, Volker; Bzdak, Adam

    2016-07-01

    Here, we will discuss how the study of various fluctuation observables may be used to explore the phase diagram of the strong interaction. Furthermore, we will briefly summarize the present study of experimental and theoretical research in this area. We will then discuss various corrections and issues which need to be understood and applied for a meaningful comparison of experimental measurements with theoretical predictions.

  16. 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…

  17. 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.

  18. 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

  19. 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.

  20. Phase diagram of UCoGe

    NASA Astrophysics Data System (ADS)

    Mineev, V. P.

    2017-03-01

    The temperature-pressure phase diagram of ferromagnetic superconductor UCoGe includes four phase transitions. They are between the paramagnetic and the ferromagnetic states with the subsequent transition in the superconducting ferromagnetic state and between the normal and the superconducting states after which the transition to the superconducting ferromagnetic state has to occur. Here we have developed the Landau theory description of the phase diagram and established the specific ordering arising at each type of transition. The phase transitions to the ferromagnetic superconducting state are inevitably accompanied by the emergence of screening currents. The corresponding magnetostatics considerations allow for establishing the significant difference between the transition from the ferromagnetic to the ferromagnetic superconducting state and the transition from the superconducting to the ferromagnetic superconducting state.

  1. Phase diagram of a traffic roundabout

    NASA Astrophysics Data System (ADS)

    Huang, Ding-wei

    2007-09-01

    We propose a simple cellular automaton model to study the traffic dynamics in a roundabout. Both numerical and analytical results are presented. We are able to obtain exact solutions in the full parameter space. Exact phase diagrams are derived. When the traffic from two directions mixed, there are only five distinct phases. Some of the combinations from naive intuition are strictly forbidden. We also compare the results to a signaled intersection.

  2. 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.

  3. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-10-01

    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.

  5. 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.

  6. 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.

  7. Energetic Studies and Phase Diagram of Thioxanthene

    NASA Astrophysics Data System (ADS)

    Freitas, Vera L. S.; Monte, Manuel J. S.; Santos, Luís M. N. B. F.; Gomes, José R. B.; Ribeiro da Silva, Maria D. M. C.

    2009-10-01

    The molecular stability of thioxanthene, a key species from which very important compounds with industrial relevance are derived, has been studied by a combination of several experimental techniques and computational approaches. The standard (p° = 0.1 MPa) molar enthalpy of formation of crystalline thioxanthene (117.4 ± 4.1 kJ·mol-1) was determined from the experimental standard molar energy of combustion, in oxygen, measured by rotating-bomb combustion calorimetry at T = 298.15 K. The enthalpy of sublimation was determined by a direct method, using the vacuum drop microcalorimetric technique, and also by an indirect method, using a static apparatus, where the vapor pressures at different temperatures were measured. The latter technique was used for both crystalline and undercooled liquid samples, and the phase diagram of thioxanthene near the triple point was obtained (triple point coordinates T = 402.71 K and p = 144.7 Pa). From the two methods, a mean value for the standard (p° = 0.1 MPa) molar enthalpy of sublimation, at T = 298.15 K (101.3 ± 0.8 kJ·mol-1), was derived. From the latter value and from the enthalpy of formation of the solid, the standard (p° = 0.1 MPa) enthalpy of formation of gaseous thioxanthene was calculated as 218.7 ± 4.2 kJ·mol-1. Standard ab initio molecular orbital calculations were performed using the G3(MP2)//B3LYP composite procedure and several homodesmotic reactions in order to derive the standard molar enthalpy of formation of thioxanthene. The ab initio results are in excellent agreement with the experimental data.

  8. Antiferromagnetic phase diagram of the cuprate superconductors

    NASA Astrophysics Data System (ADS)

    Nunes, L. H. C. M.; Teixeira, A. W.; Marino, E. C.

    2017-02-01

    Taking the spin-fermion model as the starting point for describing the cuprate superconductors, we obtain an effective nonlinear sigma-field hamiltonian, which takes into account the effect of doping in the system. We obtain an expression for the spin-wave velocity as a function of the chemical potential. For appropriate values of the parameters we determine the antiferromagnetic phase diagram for the YBa2Cu3O6+x compound as a function of the dopant concentration in good agreement with the experimental data. Furthermore, our approach provides a unified description for the phase diagrams of the hole-doped and the electron doped compounds, which is consistent with the remarkable similarity between the phase diagrams of these compounds, since we have obtained the suppression of the antiferromagnetic phase as the modulus of the chemical potential increases. The aforementioned result then follows by considering positive values of the chemical potential related to the addition of holes to the system, while negative values correspond to the addition of electrons.

  9. Hydrodynamics of bacterial colonies: Phase diagrams

    NASA Astrophysics Data System (ADS)

    Lega, J.; Passot, T.

    2004-09-01

    We present numerical simulations of a recent hydrodynamic model describing the growth of bacterial colonies on agar plates. We show that this model is able to qualitatively reproduce experimentally observed phase diagrams, which relate a colony shape to the initial quantity of nutrients on the plate and the initial wetness of the agar. We also discuss the principal features resulting from the interplay between hydrodynamic motions and colony growth, as described by our model.

  10. The phase diagram of water at negative pressures: virtual ices.

    PubMed

    Conde, M M; Vega, C; Tribello, G A; Slater, B

    2009-07-21

    The phase diagram of water at negative pressures as obtained from computer simulations for two models of water, TIP4P/2005 and TIP5P is presented. Several solid structures with lower densities than ice Ih, so-called virtual ices, were considered as possible candidates to occupy the negative pressure region of the phase diagram of water. In particular the empty hydrate structures sI, sII, and sH and another, recently proposed, low-density ice structure. The relative stabilities of these structures at 0 K was determined using empirical water potentials and density functional theory calculations. By performing free energy calculations and Gibbs-Duhem integration the phase diagram of TIP4P/2005 was determined at negative pressures. The empty hydrates sII and sH appear to be the stable solid phases of water at negative pressures. The phase boundary between ice Ih and sII clathrate occurs at moderate negative pressures, while at large negative pressures sH becomes the most stable phase. This behavior is in reasonable agreement with what is observed in density functional theory calculations.

  11. Combinatorial entropy and phase diagram of partially ordered ice phases.

    PubMed

    Macdowell, Luis G; Sanz, Eduardo; Vega, Carlos; Abascal, José Luis F

    2004-11-22

    A close analytical estimate for the combinatorial entropy of partially ordered ice phases is presented. The expression obtained is very general, as it can be used for any ice phase obeying the Bernal-Fowler rules. The only input required is a number of crystallographic parameters, and the experimentally observed proton site occupancies. For fully disordered phases such as hexagonal ice, it recovers the result deduced by Pauling, while for fully ordered ice it is found to vanish. Although the space groups determined for ice I, VI, and VII require random proton site occupancies, it is found that such random allocation of protons does not necessarily imply random orientational disorder. The theoretical estimate for the combinatorial entropy is employed together with free energy calculations in order to obtain the phase diagram of ice from 0 to 10 GPa. Overall qualitative agreement with experiment is found for the TIP4P model of water. An accurate estimate of the combinatorial entropy is found to play an important role in determining the stability of partially ordered ice phases, such as ice III and ice V.

  12. 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.

  13. On the iron-carbon phase diagram

    NASA Astrophysics Data System (ADS)

    Ustinovshikov, Yu. I.

    2009-10-01

    Experimental results that are obtained by electron microscopy, X-ray diffraction, and carbide analysis and indicate the precipitation of carbon atoms clusters in a hypereutectoid steel during its annealing above the eutectoid temperature are presented. These results are compared to the reported data in order to construct a new Fe-C phase diagram, where cementite forms below the eutectoid temperature due to the tendency of the Fe-C system toward ordering and carbon unbound to iron precipitates above this temperature in the form of clusters or graphite particles due to the tendency of this system toward phase separation.

  14. 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.

  15. 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.

  16. Phase diagram of chirally imbalanced QCD matter

    SciTech Connect

    Chernodub, M. N.; Nedelin, A. S.

    2011-05-15

    We compute the QCD phase diagram in the plane of the chiral chemical potential and temperature using the linear sigma model coupled to quarks and to the Polyakov loop. The chiral chemical potential accounts for effects of imbalanced chirality due to QCD sphaleron transitions which may emerge in heavy-ion collisions. We found three effects caused by the chiral chemical potential: the imbalanced chirality (i) tightens the link between deconfinement and chiral phase transitions; (ii) lowers the common critical temperature; (iii) strengthens the order of the phase transition by converting the crossover into the strong first order phase transition passing via the second order end point. Since the fermionic determinant with the chiral chemical potential has no sign problem, the chirally imbalanced QCD matter can be studied in numerical lattice simulations.

  17. Phase diagram of hydrogen adsorbed on Ni(111)

    NASA Astrophysics Data System (ADS)

    Nagai, Kiyoshi; Ohno, Yuichi; Nakamura, Takashi

    1984-08-01

    The phase diagram for the H/Ni(111) system is calculated by treating a lattice gas on a honeycomb lattice through the position-space renormalization-group theory with prefacing transformation. The following interparticle interactions are considered: (A) nearest-neighbor exclusion, second-neighbor repulsion, and third-neighbor attraction, which was previously proposed by Domany et al.; (B) nearest-neighbor exclusion, second- and third-neighbor repulsions, and further-neighbor interactions up to the sixth-neighbor one. When the interaction parameters involved are suitably adjusted, both the interactions (A) and (B) lead to the phase diagrams in good agreement with the experimental one by Christmann et al. The change of the isosteric heat of hydrogen adsorption with the adsorbed amount is also calculated. The result obtained from interaction (B) is consistent with experiment, whereas that from interaction (A) is not.

  18. 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.

  19. Revisiting the phase diagram of hard ellipsoids.

    PubMed

    Odriozola, Gerardo

    2012-04-07

    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.

  20. Reentrant phase diagram of network fluids.

    PubMed

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

    2011-02-25

    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)]. 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.

  1. Phase Diagram of the Frustrated Hubbard Model

    NASA Astrophysics Data System (ADS)

    Zitzler, R.; Tong, N.-H.; Pruschke, Th.; Bulla, R.

    2004-07-01

    The Mott-Hubbard metal-insulator transition in the paramagnetic phase of the one-band Hubbard model has long been used to describe similar features in real materials like V2O3. In this Letter we investigate the antiferromagnetic phase of this model with frustration. At T=0 we find a first-order transition from a paramagnetic metal to an antiferromagnetic insulator. We show that even in the presence of strong magnetic frustration, the paramagnetic metal-insulator transition is hidden inside an extended antiferromagnetic region. This raises the question of whether the one-band Hubbard model with frustration is sufficient to describe the phase diagram of V2O3 or similar transition metal oxides even qualitatively.

  2. 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.

  3. Understanding starch gelatinization: The phase diagram approach.

    PubMed

    Carlstedt, Jonas; Wojtasz, Joanna; Fyhr, Peter; Kocherbitov, Vitaly

    2015-09-20

    By constructing a detailed phase diagram for the potato starch-water system based on data from optical microscopy, synchrotron X-ray scattering and differential scanning calorimetry, we show that gelatinization can be interpreted in analogy with a eutectic transition. The phase rule explains why the temperature of the gelatinization transition (G) is independent on water content. Furthermore, the melting (M1) endotherm observed in DSC represents a liquidus line; the temperature for this event increases with increasing starch concentration. Both the lamellar spacing and the inter-helix distance were observed to decrease with increasing starch content for starch concentrations between approximately 65 wt% and 75 wt%, while the inter-helix distance continued decreasing upon further dehydration. Understanding starch gelatinization has been a longstanding challenge. The novel approach presented here shows interpretation of this phenomenon from a phase equilibria perspective.

  4. First-principles calculations of the structural, electronic, elastic, phase diagram and thermal properties of Zn1-xBexTe ternary alloy

    NASA Astrophysics Data System (ADS)

    Boumaza, A.; Ghemid, S.; Chouahda, Z.; Meradji, H.; El Haj Hassan, F.

    2012-09-01

    The structural, electronic, elastic, thermal and thermodynamic properties of Zn1-xBexTe semiconductor alloys have been investigated using the full-potential linearized augmented plane wave method within density functional theory. We use both the Wu-Cohen and the Engel-Vosko generalized gradient approximations of the exchange-correlation energy that are based on the optimization of the total energy and the corresponding potential, respectively. The ground state properties such as lattice constants, bulk modulus and elastic constants are in good agreement with numerous experimental and theoretical data. The calculated band structures show that the band gap undergoes a direct to indirect transition at a given concentration. A regular-solution model is used to investigate the thermodynamic stability of the alloy that mainly indicates a phase miscibility gap. In addition, the quasi-harmonic Debye model is applied to determine the thermal properties of the alloy.

  5. QCD phase diagram with a chiral chemical potential

    NASA Astrophysics Data System (ADS)

    Lu, Ya; Cui, Zhu-Fang; Pan, Zan; Chang, Chao-Hsi; Zong, Hong-Shi

    2016-04-01

    The effect of chirality imbalance on the QCD phase diagram is studied within the two flavors Nambu-Jona-Lasinio model. We focus especially on the issues related to how the chiral chemical potential (μ5 ) affects the phase diagram, and find the "chiral catalysis" as well as "inverse chiral catalysis" effects, which are analogous to the magnetic catalysis and inverse magnetic catalysis effects. Furthermore, our results are different from the existing chiral model calculations, namely, there is no CEP5 on the T -μ5 plane, since the whole phase transition is a crossover. In addition, with the introduction of the chiral chemical potential, various QCD susceptibilities and the corresponding critical exponents are also studied.

  6. Phase Diagram of the Two-Chain Hubbard Model

    NASA Technical Reports Server (NTRS)

    Park, Youngho; Liang, Shoudan; Lee, T. K.

    1999-01-01

    We have calculated the charge gap and spin gap for the two-chain Hubbard model as a function of the on-site Coulomb interaction and the interchain hopping amplitude. We used the density matrix renormalization group method and developed a method to calculate separately the gaps numerically for the symmetric and antisymmetric modes with respect to the exchange of the chain indices. We have found very different behaviors for the weak and strong interaction cases. Our calculated phase diagram is compared to the one obtained by Balents and Fisher using the weak coupling renormalization group technique.

  7. Dynamical phase diagram of Gaussian wave packets in optical lattices.

    PubMed

    Hennig, H; Neff, T; Fleischmann, R

    2016-03-01

    We study the dynamics of self-trapping in Bose-Einstein condensates (BECs) loaded in deep optical lattices with Gaussian initial conditions, when the dynamics is well described by the discrete nonlinear Schrödinger equation (DNLSE). In the literature an approximate dynamical phase diagram based on a variational approach was introduced to distinguish different dynamical regimes: diffusion, self-trapping, and moving breathers. However, we find that the actual DNLSE dynamics shows a completely different diagram than the variational prediction. We calculate numerically a detailed dynamical phase diagram accurately describing the different dynamical regimes. It exhibits a complex structure that can readily be tested in current experiments in BECs in optical lattices and in optical waveguide arrays. Moreover, we derive an explicit theoretical estimate for the transition to self-trapping in excellent agreement with our numerical findings, which may be a valuable guide as well for future studies on a quantum dynamical phase diagram based on the Bose-Hubbard Hamiltonian.

  8. Electrochemical Phase Diagrams for Aqueous Redox Systems

    DTIC Science & Technology

    1989-12-22

    theoretical analysis permits a classification of potential-pH diagrams into two basic types: 1) Pourbaix diagrams , in which 1 the stability field of solid...property" diagrams will contain conventional Pourbaix and Ellingham diagrams as subsets. 3. Improve the data-base supporting the computations by...research grant DAAL03-86-K-0062 and the preceding grant DAAG29-84-K-0074. 1. John C. Angus and Charles T. Angus, "Computation of Pourbaix Diagrams Using

  9. Thermodynamic forward models to calculate P-T phase diagrams that reflect fractional equilibrium crystallisation of garnet in path-dependent reacting bulk rock chemistries

    NASA Astrophysics Data System (ADS)

    Klitscher, N.; Konrad-Schmolke, M.; Schildhauer, H.

    2012-04-01

    Predictions on phase assemblages and phase compositions in metamorphic rock based on thermodynamic equilibrium calculations, such as pseudosections, are prone to misinterpretations due to sluggish reaction kinetics. It is evident that commonly applied thermodynamic calculations require equilibrated chemical potentials within all minerals and throughout the entire considered rock volume. Compositionally zoned metamorphic minerals, often present in metamorphic rocks, indicate element fractionation into the early crystallised cores due to fractional crystallisation and thus reflect small scale chemical disequilibrium domains during the metamorphic evolution of the rock. Garnet, one of the most important minerals in metamorphic petrology, is a classic example of a mineral that often preserves such compositional growth zonations. These compositional variations are blossom and curse, as on the one hand they complicate the extraction of thermodynamic parameters due to their disequilibrium characteristics, on the one hand they record geodynamic processes that can be interpreted if disequilibrium effects are considered in thermodynamic models. Several works have shown that garnet growth is discontinuous along certain prograde pressure-temperature paths and that bulk rock depletion due to element fractionation can lead to garnet growth interruptions during prograde metamorphism, which in turn leads to characteristic, often step-like compositional zoning and typical concentric inclusion patterns. Understanding of these characteristic patterns will enable more precise quantification of geodynamically relevant factors, such as garnet growth rates and detailed reaction paths. Here we present thermodynamic forward models that concentrate on the metamorphic evolution of garnet in commonly observed metamorphic settings under the consideration of element fractionation from the effective, i.e. reacting bulk rock composition (EBC) due to fractional garnet crystallisation. We model

  10. Phase diagram of water in carbon nanotubes.

    PubMed

    Takaiwa, Daisuke; Hatano, Itaru; Koga, Kenichiro; Tanaka, Hideki

    2008-01-08

    A phase diagram of water in single-walled carbon nanotubes at atmospheric pressure is proposed, which summarizes ice structures and their melting points as a function of the tube diameter up to 1.7 nm. The investigation is based on extensive molecular dynamics simulations over numerous thermodynamic states on the temperature-diameter plane. Spontaneous freezing of water in the simulations and the analysis of ice structures at 0 K suggest that there exist at least nine ice phases in the cylindrical space, including those reported by x-ray diffraction studies and those unreported by simulation or experiment. Each ice has a structure that maximizes the number of hydrogen bonds under the cylindrical confinement. The results show that the melting curve has many local maxima, each corresponding to the highest melting point for each ice form. The global maximum in the melting curve is located at approximately 11 A, where water freezes in a square ice nanotube.

  11. Phase diagram of hard snowman-shaped particles.

    PubMed

    Dennison, Matthew; Milinković, Kristina; Dijkstra, Marjolein

    2012-07-28

    We present the phase diagram of hard snowman-shaped particles calculated using Monte Carlo simulations and free energy calculations. The snowman particles consist of two hard spheres rigidly attached at their surfaces. We find a rich phase behavior with isotropic, plastic crystal, and aperiodic crystal phases. The crystalline phases found to be stable for a given sphere diameter ratio correspond mostly to the close packed structures predicted for equimolar binary hard-sphere mixtures of the same diameter ratio. However, our results also show several crystal-crystal phase transitions, with structures with a higher degree of degeneracy found to be stable at lower densities, while those with the best packing are found to be stable at higher densities.

  12. Phase diagram of hard snowman-shaped particles

    NASA Astrophysics Data System (ADS)

    Dennison, Matthew; Milinković, Kristina; Dijkstra, Marjolein

    2012-07-01

    We present the phase diagram of hard snowman-shaped particles calculated using Monte Carlo simulations and free energy calculations. The snowman particles consist of two hard spheres rigidly attached at their surfaces. We find a rich phase behavior with isotropic, plastic crystal, and aperiodic crystal phases. The crystalline phases found to be stable for a given sphere diameter ratio correspond mostly to the close packed structures predicted for equimolar binary hard-sphere mixtures of the same diameter ratio. However, our results also show several crystal-crystal phase transitions, with structures with a higher degree of degeneracy found to be stable at lower densities, while those with the best packing are found to be stable at higher densities.

  13. 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.

  14. Microfluidic Evaporation for Phase Diagram Screening

    NASA Astrophysics Data System (ADS)

    Moreau, Patrick; Salmon, Jean-Baptiste; Leng, Jacques

    2007-11-01

    We use a pervaporation-based microfluidic device to concentrate solutions in a controlled way. This allows us to develop chips for phase diagram screening,and to study both fundamental and technological issues, such as the impact of kinetic pathway of concentration on a variety of aqueous solutions (colloids, surfactants, polymers and mixtures of thereof). The first part of the presentation will deals with the characterization of the concentration process (including analytical results, numerical simulations, and experimental observations). It will be shown that our device is well suited for a wide range of particle sizes in the colloidal range. In the second part, we will present results obtained on several systems during (along) the concentration process (surfactants and polymers). On-chip FRAP (fluorescence recovery after photobleaching) and microrheology measurements will be presented in addition to optical and fluorescence microscopy.

  15. Phase diagram study of Fulleride family

    NASA Astrophysics Data System (ADS)

    Meddeb, D.; Charfi-Kaddour, S.; Héritier, M.; Bennaceur, R.

    2004-08-01

    The phase diagram of the Fulleride compounds is studied as a function of n, i.e. the band filling of the LUMO or HOMO energy band, depending on the nature of the electron or hole doping, performed either chemically or by an electric field effect. We discuss the role of strong electron-electron correlation, related to electron-vibron interaction and Jahn-Teller distorsion. Superconducting coupling is expected for odd values of n and is expected to be strongest for n=3 in electron doped systems. We take into account the correlated nature of the electron Fermi liquid, which should exhibit a pseudogap phenomenon. Superconductivity is discussed within a strong coupling approach. We show that Tc( n) decrease away from n=3 on both sides of this maximum. Moreover, for even values of n, we obtain that the system is the neighbourhood of metal-insulator transition. The case of hole doping, although chemically unaccessible is also discussed.

  16. Phase diagram of tobacco mosaic virus solutions

    NASA Astrophysics Data System (ADS)

    Graf, Hartmut; Löwen, Hartmut

    1999-02-01

    The phase behavior of an aqueous suspension of rodlike tobacco mosaic viruses is investigated theoretically as a function of the virus density and the concentration of added salt. The total free energy involves ``volume terms'' from the microscopic counter- and co-ions and an effective pair interaction between the colloidal rods described by a Yukawa-segment model according to linear screening theory. Within a thermodynamic perturbation approach, the short-range repulsion between the rods is mapped onto a reference system of effective hard spherocylinders. The free energy of the spherocylinder system is gained from combining a cell model with scaled particle theory, which yields a reasonable phase diagram. The remaining long-range interaction is treated within a mean-field approximation. As a result we find stable fluid, nematic, and smectic phases as well as AAA- and ABC-stacked crystals. For increasing salt concentration at fixed rod concentration, there is a nematic reentrant transition. We finally discuss our results in view of experimental data.

  17. Workshop on Applications of Phase Diagrams in Metallurgy and Ceramics

    NASA Technical Reports Server (NTRS)

    Bennett, L. H.; Carter, G. C.

    1977-01-01

    A workshop was held to assess the current national and international status of phase diagram determinations and evaluations for alloys, ceramics, and semiconductors; to determine the needs and priorities, especially technological, for phase diagram determinations and evaluations; and to estimate the resources being used and potentially available for phase diagram evaluation. Highlights of the workshop, description of a new poster board design used in the poster sessions, lists of attendees and demonstrations, the program, and descriptions of the presentations are included.

  18. Phase diagrams of hard spheres with algebraic attractive interactions.

    PubMed

    Camp, Philip J

    2003-01-01

    The phase diagrams of systems made up of hard spheres interacting with attractive potentials of the form -1/r(3+sigma) are calculated using Monte Carlo simulations, second-order thermodynamic perturbation theory, and an augmented van der Waals theory. In simulations of the systems with sigma=0.1, 1, and 3, fluid-solid coexistence results are obtained using the Gibbs-Duhem integration technique; simulation data for the vapor-liquid coexistence envelopes and critical points are taken from previously published work [P. J. Camp and G. N. Patey, J. Chem. Phys. 114, 399 (2001)]. It is shown that the agreement between the theoretical and simulated phase diagrams improves as the range of the potential is increased, reflecting the decreasing role of short-range correlations in determining the bulk thermodynamics. In the extreme case of sigma=0.1 both theories are in excellent agreement with simulations. Phase diagrams for systems with sigma=4, 5, and 6 are computed using second-order thermodynamic perturbation theory. The results indicate that the vapor-liquid transition becomes metastable with respect to freezing when sigma > or approximately equal to 5, in broad agreement with results for the hard-sphere attractive Yukawa system which is commonly used to model colloidal particles, globular proteins, and nanoparticles.

  19. 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.

  20. 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.

  1. 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 .

  2. Enantiomeric 3-chloromandelic acid system: binary melting point phase diagram, ternary solubility phase diagrams and polymorphism.

    PubMed

    Le Minh, Tam; von Langermann, Jan; Lorenz, Heike; Seidel-Morgenstern, Andreas

    2010-09-01

    A systematic study of binary melting point and ternary solubility phase diagrams of the enantiomeric 3-chloromandelic acid (3-ClMA) system was performed under consideration of polymorphism. The melting point phase diagram was measured by means of thermal analysis, that is, using heat-flux differential scanning calorimetry (DSC). The results reveal that 3-ClMA belongs to the racemic compound-forming systems. Polymorphism was found for both the enantiomer and the racemate as confirmed by X-ray powder diffraction analysis. The ternary solubility phase diagram of 3-ClMA in water was determined between 5 and 50 degrees C by the classical isothermal technique. The solubilities of the pure enantiomers are extremely temperature-dependent. The solid-liquid equilibria of racemic 3-ClMA are not trivial due to the existence of polymorphism. The eutectic composition in the chiral system changes as a function of temperature. Further, solubility data in the alternative solvent toluene are also presented.

  3. 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.

  4. Application of quaternary phase diagrams to compound semiconductor processing

    SciTech Connect

    Sinclair, R.

    1994-10-01

    Isobaric, isothermal phase diagrams are a molar representation of condensed phases in equilibrium with each other at a fixed temperature, pressure, and composition. Since three or four elements are usually involved at a fabricated interface in a semiconductor device, knowledge of the appropriate ternary or quaternary phase diagram is important for optimizing the processing parameters and designing long term stability of devices. While the use of phase diagrams is well-established in the fields of metallurgy, ceramics and mineralogy, only recently have phase diagrams been employed to provide a framework for understanding thin film reactions on a substrate, encountered in semiconductor processing. Even though there are many examples of applications of ternary phase diagrams in the semiconductor literature (for instance, metallization of GaAs, the use of refractory metal silicides for metallization layers in VLSI devices and oxidation of III-V compounds), the same is not true for quaternary phase diagrams. To date, the only application is oxidation of mercury cadmium telluride. This lack of examples is not warranted, as four elements are often involved at a critical interface in compound semiconductor processing and devices. This paper reports on the progress made to remedy this situation by considering the application of quaternary phase diagrams to understanding and predicting the behavior of II-VI thin film interfaces in photovoltaic devices under annealing conditions. Moreover, for the first time, solid solubility is taken into account for quaternary phase diagrams of semiconductor systems.

  5. Simple thermodynamic model for the hydrogen phase diagram

    NASA Astrophysics Data System (ADS)

    Magdǎu, Ioan B.; Marqués, Miriam; Borgulya, Balint; Ackland, Graeme J.

    2017-03-01

    We describe a classical thermodynamic model that reproduces the main features of the solid hydrogen phase diagram. In particular, we show how the general structure types, which are found by electronic structure calculations and the quantum nature of the protons, can also be understood from a classical viewpoint. The model provides a picture not only of crystal structure, but also for the anomalous melting curve and insights into isotope effects, liquid metallisation, and infrared activity. The existence of a classical picture for this most quantum of condensed matter systems provides a surprising extension of the correspondence principle of quantum mechanics, in particular the equivalent effects of classical and quantum uncertainty.

  6. 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…

  7. First-Principles Phase Diagram for Ce-Th System

    SciTech Connect

    Landa, A; Soderlind, P; Ruban, A; Vitos, L; Pourovskii, L

    2004-05-11

    Ab initio total energy calculations based on the exact muffin-tin orbitals (EMTO) theory are used to determine the high pressure and low temperature phase diagram of Ce and Th metals as well as the Ce{sub 43}Th{sub 57} disordered alloy. The compositional disorder for the alloy is treated in the framework of the coherent potential approximation (CPA). Equation of state for Ce, Th and Ce{sub 43}Th{sub 57} has been calculated up to 1 Mbar in good comparison with experimental data: upon compression the Ce-Th system undergoes crystallographic phase transformation from an fcc to a bct structure and the transition pressure increases with Th content in the alloy.

  8. A Three-dimensional Topological Model of Ternary Phase Diagram

    NASA Astrophysics Data System (ADS)

    Mu, Yingxue; Bao, Hong

    2017-01-01

    In order to obtain a visualization of the complex internal structure of ternary phase diagram, the paper realized a three-dimensional topology model of ternary phase diagram with the designed data structure and improved algorithm, under the guidance of relevant theories of computer graphics. The purpose of the model is mainly to analyze the relationship between each phase region of a ternary phase diagram. The model not only obtain isothermal section graph at any temperature, but also extract a particular phase region in which users are interested.

  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

    2015-06-07

    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.

  10. Modelling the phase diagram of magnetic shape memory Heusler alloys

    NASA Astrophysics Data System (ADS)

    Entel, P.; Buchelnikov, V. D.; Khovailo, V. V.; Zayak, A. T.; Adeagbo, W. A.; Gruner, M. E.; Herper, H. C.; Wassermann, E. F.

    2006-03-01

    We have modelled the phase diagram of magnetic shape memory alloys of the Heusler type by using the phenomenological Ginzburg-Landau theory. When fixing the parameters by realistic values taken from experiment we are able to reproduce most details of, for example, the phase diagram of Ni2+xMn1-xGa in the (T, x) plane. We present the results of ab initio calculations of the electronic and phonon properties of several ferromagnetic Heusler alloys, which allow one to characterize the structural changes associated with the martensitic instability leading to the modulated and tetragonal phases. From the ab initio investigations emerges a complex pattern of the interplay of magic valence electron per atom numbers (Hume-Rothery rules for magnetic ternary alloys), Fermi surface nesting and phonon instability. As the main result, we find that the driving force for structural transformations is considerably enhanced by the extremely low lying optical modes of Ni in the Ni-based Heusler alloys, which interfere with the acoustical modes enhancing phonon softening of the TA2 mode. In contrast, the ferromagnetic Co-based Heusler alloys show no tendency for phonon softening.

  11. Phase diagram of the modified Lennard-Jones system.

    PubMed

    Asano, Yuta; Fuchizaki, Kazuhiro

    2012-11-07

    An investigation of the precise determination of melting temperature in the modified Lennard-Jones system under pressure-free conditions [Y. Asano and K. Fuchizaki, J. Phys. Soc. Jpn. 78, 055002 (2009)] was extended under finite-pressure conditions to obtain the phase diagram. The temperature and pressure of the triple point were estimated to be 0.61 ε∕k(B) and 0.0018(5) ε∕σ(3), and those of the critical point were 1.0709(19) ε∕k(B) and 0.1228(20) ε∕σ(3), where ε and σ are the Lennard-Jones parameters for energy and length scales, respectively, and k(B) is the Boltzmann constant. The potential used here has a finite attractive tail and does not suffer from cutoff problems. The potential can thus be a useful standard in examining statistical-mechanical problems in which different treatments for the tail would lead to different conclusions. The present phase diagram will then be a useful guide not only for equilibrium calculations but also for nonequilibrium problems such as discussions of the limits of phase (in)stability.

  12. Quantum phase diagrams and phase transitions in frustrated two-dimensional Heisenberg models

    NASA Astrophysics Data System (ADS)

    Sheng, Donna

    2014-03-01

    The quantum spin liquid is an emergent state of matter, which has attracted a lot of recent attention. I will review recent numerical progress based on the density matrix renormalization calculations in identifying gapped spin liquid in two-dimensional frustrated spin systems. I will first focus on extended model with Heisenberg exchange couplings on kagome lattice and demonstrate a topological state with fractionalized spinon and emergent gauge field clearly shown in numerical simulations. I will present concrete results on the quantum phase diagram of the extended kagome Heisenberg model, and compare that with the phase diagrams of the square and honeycomb lattice models with the dominant plaquette valence bond phase in nonmagnetic region. I will discuss numerical effort and theoretical challenge in fully pinning down the nature of the gapped topological phase, and also the nature of the quantum phase transitions in these Heisenberg systems. The research was supported by the National Science Foundation grant DMR-0906816.

  13. 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.

  14. Dimensionality-strain phase diagram of strontium iridates

    NASA Astrophysics Data System (ADS)

    Kim, Bongjae; Liu, Peitao; Franchini, Cesare

    2017-03-01

    The competition between spin-orbit coupling, bandwidth (W ), and electron-electron interaction (U ) makes iridates highly susceptible to small external perturbations, which can trigger the onset of novel types of electronic and magnetic states. Here we employ first principles calculations based on density functional theory and on the constrained random phase approximation to study how dimensionality and strain affect the strength of U and W in (SrIrO3)m/(SrTiO3) superlattices. The result is a phase diagram explaining two different types of controllable magnetic and electronic transitions, spin-flop and insulator-to-metal, connected with the disruption of the Jeff=1 /2 state which cannot be understood within a simplified local picture.

  15. Electronic phase diagram of single-element silicon "strain" superlattices.

    PubMed

    Liu, Zheng; Wu, Jian; Duan, Wenhui; Lagally, Max G; Liu, Feng

    2010-07-02

    The evidence that the band gap of Si changes significantly with strain suggests that by alternating regions of strained and unstrained Si one creates a single-element electronic heterojunction superlattice (SL), with the carrier confinement defined by strain rather than by the chemical differences in conventional compositional SLs. Using first-principles calculations, we map out the electronic phase diagram of a one-dimensional pure-silicon SL. It exhibits a high level of phase tunability, e.g., tuning from type I to type II. Our theory rationalizes a recent observation of a strain SL in a Si nanowire and provides general guidance for the fabrication of single-element strain SLs.

  16. 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)

  17. 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)

  18. 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.

  19. Phase diagram of a three-sublattice mixed ferro-ferrimagnetic Heisenberg system

    NASA Astrophysics Data System (ADS)

    Mert, H. Şevki; Mert, Gülistan

    2013-10-01

    We present a numerical study of a three-sublattice mixed ferro-ferrimagnetic Heisenberg system. Green's function technique is used to calculate the magnetization as a function of temperature. The technique involves the random phase approximation and Anderson-Callen's decoupling. We obtain phase diagram and the first-order phase transition.

  20. 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…

  1. 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…

  2. Phase diagram of hydrogen adsorbed on Ni(111)

    NASA Astrophysics Data System (ADS)

    Nagai, K.

    An explanation for the phase diagram of the H/Ni(111) system is proposed, where the existence of the p(2×2) phase is assumed in addition to the (2×2) phase. Using the position-space renormalization-group theory with prefacing transformation, a lattice gas on a honeycom lattice, including up to 6th nearest neighbor interactions, is treated. Another explanation previously put forward by Domany et al. is also examined, where the occurrence of the (2×2) ordered phase and the gas+p(2×2) coexistence phase is assumed. The phase diagrams thus obtained for these two cases are exhibited and discussed.

  3. Phase diagram of hydrogen adsorbed on Ni(111)

    NASA Astrophysics Data System (ADS)

    Nagai, K.

    1984-01-01

    An explanation for the phase diagram of the H/Ni(111) system is proposed, where the existence of the p(2 × 2) phase is assumed in addition to the (2 × 2) phase. Using the position-space renormalization-group theory with prefacing transformation, a lattice gas on a honeycomb lattice, including up to 6th nearest neighbor interactions, is treated. Another explanation previously put forward by Domany et al. is also examined, where the occurrence of the (2 × 2) ordered phase and the gas + p(2 × 2) coexistence phase is assumed. The phase diagrams thus obtained for these two cases are exhibited and discussed.

  4. 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.

  5. Phase diagram for assembly of biologically-active peptide amphiphiles.

    PubMed

    Tsonchev, Stefan; Niece, Krista L; Schatz, George C; Ratner, Mark A; Stupp, Samuel I

    2008-01-17

    We construct a phase diagram for self-assembling biologically active peptide amphiphiles. The structure and stability of the assemblies are studied as a function of pH and salinity of the solution. The general features of the phase diagram are predicted based on theoretical modeling of the self-assembly process, as well as experimental data, and further experiments are performed to verify and ascertain the boundary locations of the diagram. Depending on solution conditions, the amphiphiles can form cylindrical or spherical micelles, intermediate structures between these, or may not assemble at all. We also demonstrate that changing conditions may result in phase transitions among these structures. This type of phase diagram could be useful in the design of certain supramolecular nanostructures by providing information on the necessary conditions to form them.

  6. Concentration fields of the ternary systems and trajectory of phases in T-x-y Diagrams

    NASA Astrophysics Data System (ADS)

    Lutsyk, V.; Zelenaya, A.

    2017-01-01

    The possibility of computer models of T-x-y diagrams for analysis two-, one- and zero-dimensional concentration fields are demonstrated using T-x-y diagram of systems CaO-SiO2-Al2O3 and MgO-SiO2-Al2O3. The characteristics of processes proceeding in the concentration fields can be analyzed with the help of diagrams of vertical mass balances, which show the increase or decrease of phases portions for each phase region. Calculation of crystallization paths was made.

  7. Solid dispersion of pharmaceutical ternary systems I: Phase diagram of aspirin-acetaminophen-urea system.

    PubMed

    el-Banna, H M

    1978-08-01

    The phase diagram of an aspirin-acetaminophen-urea system was constructed. The data obtained by the thermomicroscopic method showed that the binary systems of aspirin-acetaminophen, aspirin-urea, and acetaminophen-urea are simple eutectic mixtures with negligible formation of solid solutions or molecular compounds. The equilateral triangular phase diagram of the ternary system revealed that it forms, upon solidification, solid dispersions of the mechanical mixture type. The ternary eutectic corresponded to a composition of 60% aspirin, 20% acetaminophen, and 20% urea at 72 degrees. The method of calculating the composition finally solidified melts, lying within any area of the phase diagram, is presented. Use of the phase diagram in selecting the optimum ratio of components to enhance dissolution rates of these drugs may be possible.

  8. 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.

  9. Phase Diagram Studies of ZnS Systems

    DTIC Science & Technology

    1988-09-01

    mechanical, processing of ZnS-base ’alloys’. Knowledge of the phase equilibria of various ZnS-rich systems is essential to achieve our objectives...initial studies of the solid-state phase equilibria in the ZnS-CdS and ZnS-Ga2s3 phase diagrams.

  10. Phase Diagram and Electronic Structure of Praseodymium and Plutonium

    DOE PAGES

    Lanatà, Nicola; Yao, Yongxin; Wang, Cai-Zhuang; ...

    2015-01-29

    We develop a new implementation of the Gutzwiller approximation in combination with the local density approximation, which enables us to study complex 4f and 5f systems beyond the reach of previous approaches. We calculate from first principles the zero-temperature phase diagram and electronic structure of Pr and Pu, finding good agreement with the experiments. Our study of Pr indicates that its pressure-induced volume-collapse transition would not occur without change of lattice structure—contrarily to Ce. Our study of Pu shows that the most important effect originating the differentiation between the equilibrium densities of its allotropes is the competition between the Peierlsmore » effect and the Madelung interaction and not the dependence of the electron correlations on the lattice structure.« less

  11. Interacting Weyl fermions: Phases, phase transitions, and global phase diagram

    NASA Astrophysics Data System (ADS)

    Roy, Bitan; Goswami, Pallab; Juričić, Vladimir

    2017-05-01

    We study the effects of short-range interactions on a generalized three-dimensional Weyl semimetal, where the band touching points act as the (anti)monopoles of Abelian Berry curvature of strength n . We show that any local interaction has a negative scaling dimension -2 /n . Consequently, all Weyl semimetals are stable against weak short-range interactions. For sufficiently strong interactions, we demonstrate that the Weyl semimetal either undergoes a first-order transition into a band insulator or a continuous transition into a symmetry breaking phase. A translational symmetry breaking axion insulator and a rotational symmetry breaking semimetal are two prominent candidates for the broken symmetry phase. At the one-loop order, the correlation length exponent for continuous transitions is ν =n /2 , indicating their non-Gaussian nature for any n >1 . We also discuss the scaling of the thermodynamic and transport quantities in general Weyl semimetals as well as inside broken symmetry phases.

  12. 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.

  13. Localization phase diagram of two-dimensional quantum percolation

    NASA Astrophysics Data System (ADS)

    Dillon, Brianna S.; Nakanishi, Hisao

    2014-12-01

    We examine quantum percolation on a square lattice with random dilution up to q = 38% and energy 0.001 ≤ E ≤ 1.6 (measured in units of the hopping matrix element), using numerical calculations of the transmission coefficient at a much larger scale than previously. Our results confirm the previous finding that the two dimensional quantum percolation model exhibits localization-delocalization transitions, where the localized region splits into an exponentially localized region and a power-law localization region. We determine a fuller phase diagram confirming all three regions for energies as low as E = 0.1, and the delocalized and exponentially localized regions for energies down to E = 0.001. We also examine the scaling behavior of the residual transmission coefficient in the delocalized region, the power law exponent in the power-law localized region, and the localization length in the exponentially localized region. Our results suggest that the residual transmission at the delocalized to power-law localized phase boundary may be discontinuous, and that the localization length is likely not to diverge with a power-law at the exponentially localized to power-law localized phase boundary. However, further work is needed to definitively assess the characters of the two phase transitions as well as the nature of the intermediate power-law regime.

  14. Phase diagram of the lattice G2 Higgs model

    NASA Astrophysics Data System (ADS)

    Wellegehausen, Björn H.; Wipf, Andreas; Wozar, Christian

    2011-06-01

    We study the phases and phase transition lines of the finite temperature G2 Higgs model. Our work is based on an efficient local hybrid Monte-Carlo algorithm which allows for accurate measurements of expectation values, histograms, and susceptibilities. On smaller lattices we calculate the phase diagram in terms of the inverse gauge coupling β and the hopping parameter κ. For κ→0 the model reduces to G2 gluodynamics and for κ→∞ to SU(3) gluodynamics. In both limits the system shows a first order confinement-deconfinement transition. We show that the first order transitions at asymptotic values of the hopping parameter are almost joined by a line of first order transitions. A careful analysis reveals that there exists a small gap in the line where the first order transitions turn into continuous transitions or a crossover region. For β→∞ the gauge degrees of freedom are frozen and one finds a nonlinear O(7) sigma model which exhibits a second order transition from a massive O(7) symmetric to a massless O(6) symmetric phase. The corresponding second order line for large β remains second order for intermediate β until it comes close to the gap between the two first order lines. Besides this second order line and the first order confinement-deconfinement transitions we find a line of monopole-driven bulk transitions which do not interfere with the confinement-deconfinment transitions.

  15. New View of the QCD Phase Diagram

    SciTech Connect

    McLerran,L.

    2009-07-09

    Quarkyonic matter is confining but can have densities much larger than 3QCD. Its existence isargued in the large Nc limit of QCD and implies that there are at least three phases of QCD with greatly different bulk properties. These are a Confined Phase of hadrons, a Deconfined Phase ofquarks and gluons, and the Quarkyonic Phase. In the Quarkyonic Phase, the baryon density isaccounted for by a quasi-free gas of quarks, and the the antiquarks and gluons are confined intomesons, glueballs. Quarks near the Fermi surface also are treated as baryons. (In addition tothese phases, there is a color superconducting phase that has vastly different transport properties than the above, but with bulk properties, such as pressure and energy density, that are not greatlydifferent than that of Quarkyonic Matter.)

  16. Summaries of recent computer-assisted Feynam diagram calculations

    SciTech Connect

    Mark Fischler

    2001-08-16

    The AIHENP Workshop series has traditionally included cutting edge work on automated computation of Feynman diagrams. The conveners of the Symbolic Problem Solving topic in this ACAT conference felt it would be useful to solicit presentations of brief summaries of the interesting recent calculations. Since this conference was the first in the series to be held in the Western Hemisphere, it was decided that the summaries would be solicited both from attendees and from researchers who could not attend the conference. This would represent a sampling of many of the key calculations being performed. The results were presented at the Poster session; contributions from ten researchers were displayed and posted on the web. Although the poster presentation, which can be viewed at conferences.fnal.gov/acat2000/ placed equal emphasis on results presented at the conference and other contributions, here we primarily discuss the latter, which do not appear in full form in these proceedings. This brief paper can't do full justice to each contribution; interested readers can find details of the work not presented at this conference in references (1), (2), (3), (4), (5), (6), (7).

  17. Microcanonical phase diagrams of short-range ferromagnets.

    PubMed

    Kastner, Michael; Pleimling, Michel

    2009-06-19

    A phase diagram is a graph in parameter space showing the phase boundaries of a many-particle system. Commonly, the control parameters are chosen to be those of the (generalized) canonical ensemble, such as temperature and magnetic field. However, depending on the physical situation of interest, the (generalized) microcanonical ensemble may be more appropriate, with the corresponding control parameters being energy and magnetization. We show that the phase diagram on this parameter space looks remarkably different from the canonical one. The general features of such a microcanonical phase diagram are investigated by studying two models of ferromagnets with short-range interactions. The physical consequences of the findings are discussed, including possible applications to nuclear fragmentation, adatoms on surfaces, and cold atoms in optical lattices.

  18. 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.

  19. Electrical phase diagram of bulk BiFeO3

    NASA Astrophysics Data System (ADS)

    Stengel, Massimiliano; Íñiguez, Jorge

    2015-12-01

    We study the electrical behavior of multiferroic BiFeO3 by means of first-principles calculations. We do so by constraining a specific component of the electric displacement field along a variety of structural paths, and by monitoring the evolution of the relevant physical properties of the crystal along the way. We find a complex interplay of ferroelectric, antiferroelectric, and antiferrodistortive degrees of freedom that leads to an unusually rich electrical phase diagram, which strongly departs from the paradigmatic double-well model of simpler ferroelectric materials. In particular, we show that many of the structural phases that were recently reported in the literature, e.g., those characterized by a giant aspect ratio, can be in principle accessed via application of an external electric field starting from the R 3 c ground state. Our results also reveal ways in which nonpolar distortions (e.g., the antiferrodistortive ones associated with rotations of the oxygen octahedra in the perovskite lattice) can be controlled by means of applied electric fields, as well as the basic features characterizing the switching between the ferroelectric and antiferroelectric phases of BiFeO3. We discuss the multimode couplings behind this wealth of effects, while highlighting the implications of our work as regards both theoretical and experimental literature on BiFeO3.

  20. Phase diagrams of low-density polyethylene-alkylbenzene systems

    NASA Astrophysics Data System (ADS)

    Ilyasova, A. N.; Kudryavtsev, Y. V.; Lebedeva, T. N.; Levashova, I. V.; Flyagina, Yu. A.; Pochivalov, K. V.

    2017-03-01

    Complete phase diagrams for mixtures of low-density polyethylene with p- and m-xylene are plotted by optical means in developing the concept of which partially crystalline polymers are microstructured liquids. It is shown that in contrast to the ones presented in the literature, both diagrams contain the solubility boundary curve of the low-molecular weight component in the polymer, above which the polyethylene has the structure of a single-phase gel (crosslinks formed by crystallites and amorphous regions saturated with xylene). At the figurative point on the diagrams, a situation is observed in which the dissolution of all the liquid contained in the initial two-phase system in the polymer is accompanied by its simultaneous complete amorphization. The parameters of the figurative point allow us to estimate the thermodynamic affinity of different alkylbenzenes toward polyethylene.

  1. Monte Carlo study of Dirac semimetals phase diagram

    NASA Astrophysics Data System (ADS)

    Braguta, V. V.; Katsnelson, M. I.; Kotov, A. Yu.; Nikolaev, A. A.

    2016-11-01

    In this paper the phase diagram of Dirac semimetals is studied within a lattice Monte Carlo simulation. In particular, we concentrate on the dynamical chiral symmetry breaking which results in a semimetal-insulator transition. Using numerical simulation, we determine the values of the critical coupling constant of the semimetal-insulator transition for different values of the anisotropy of the Fermi velocity. This measurement allows us to draw a tentative phase diagram for Dirac semimetals. It turns out that within the Dirac model with Coulomb interaction both Na3Bi and Cd3As2 , known experimentally to be Dirac semimetals, would lie deep in the insulating region of the phase diagram. This result probably shows a decisive role of screening of the interelectron interaction in real materials, similar to the situation in graphene.

  2. 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.

  3. The NaNO3-KNO3 phase diagram

    NASA Astrophysics Data System (ADS)

    Benages-Vilau, R.; Calvet, T.; Cuevas-Diarte, M. A.; Oonk, H. A. J.

    2016-01-01

    Many papers have been published in relation to the NaNO3-KNO3 phase diagram determination in the last 160 years. These papers fall in two categories: (1) the solid-liquid equilibrium is assumed to be of the eutectic type, and (2) the solid-liquid equilibrium is considered as a loop with a minimum. The discordance between the two views is related to the slow transition kinetics that complicate the assessment of thermal 'fluctuations', and also to the appearance of a metastable form of potassium nitrate. The main result of this paper is the experimental phase diagram constructed with new experimental data so that we can assure that the second option is correct. This phase diagram is defined by a eutectoid invariant, an asymmetric immiscibility gap and a continuous solid solution with a minimum of melting point. Additionally, the ABθ model simulates correctly the experimental piece of evidence.

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

    PubMed

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

    2005-10-08

    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.

  5. Melting point and phase diagram of methanol as obtained from computer simulations of the OPLS model.

    PubMed

    Gonzalez Salgado, D; Vega, C

    2010-03-07

    In this work, the melting point and the phase diagram of methanol is determined via computer simulations using the OPLS model. The three different solid structures that are found experimentally were considered. By computing the free energies of both the fluid phase and the three different solid structures (alpha, beta, gamma), the initial solid-solid and fluid-solid coexistence points were determined. By performing Gibbs-Duhem integration, the complete coexistence lines were evaluated. In this way, it was possible to compute, for the first time, the complete phase diagram for a potential model of methanol. It is found that the optimized potential model for liquid simulations (OPLS) provides reasonable predictions for the densities of the three solid polymorphs, although they tend to be somewhat low when compared with the experiment. Overall the model provides a qualitatively correct description of the phase diagram of methanol. The beta solid, which is thermodynamically stable in the experimental phase diagram of methanol, is found to be metastable in the phase diagram of the model. The alpha phase is stable at low pressures and the gamma phase is stable at high pressures, in agreement with experiment. Thus, the model is able to predict the existence of the gamma solid at high pressure. From free energy calculations we found that the melting point of the model at room pressure is 215 K. That was further confirmed by direct coexistence simulations. Thus, the model presents a melting point about 40 K above the experimental value of 175 K. Thus the OPLS model provides a reasonable description of the phase diagram of methanol, but it could probably be modified to improve the phase diagram predictions.

  6. Melting point and phase diagram of methanol as obtained from computer simulations of the OPLS model

    NASA Astrophysics Data System (ADS)

    Gonzalez Salgado, D.; Vega, C.

    2010-03-01

    In this work, the melting point and the phase diagram of methanol is determined via computer simulations using the OPLS model. The three different solid structures that are found experimentally were considered. By computing the free energies of both the fluid phase and the three different solid structures (α,β,γ), the initial solid-solid and fluid-solid coexistence points were determined. By performing Gibbs-Duhem integration, the complete coexistence lines were evaluated. In this way, it was possible to compute, for the first time, the complete phase diagram for a potential model of methanol. It is found that the optimized potential model for liquid simulations (OPLS) provides reasonable predictions for the densities of the three solid polymorphs, although they tend to be somewhat low when compared with the experiment. Overall the model provides a qualitatively correct description of the phase diagram of methanol. The β solid, which is thermodynamically stable in the experimental phase diagram of methanol, is found to be metastable in the phase diagram of the model. The α phase is stable at low pressures and the γ phase is stable at high pressures, in agreement with experiment. Thus, the model is able to predict the existence of the γ solid at high pressure. From free energy calculations we found that the melting point of the model at room pressure is 215 K. That was further confirmed by direct coexistence simulations. Thus, the model presents a melting point about 40 K above the experimental value of 175 K. Thus the OPLS model provides a reasonable description of the phase diagram of methanol, but it could probably be modified to improve the phase diagram predictions.

  7. Phase diagram of one-patch colloids forming tubes and lamellae.

    PubMed

    Preisler, Zdenek; Vissers, Teun; Smallenburg, Frank; Munaò, Gianmarco; Sciortino, Francesco

    2013-08-15

    We numerically calculate the equilibrium phase diagram of one-patch particles with 30% patch coverage. It has been previously shown that in the fluid phase these particles organize into extremely long tubelike aggregates (G. Munaò et al. Soft Matter 2013, 9, 2652). Here, we demonstrate by means of free-energy calculations that such a disordered tube phase, despite forming spontaneously from the fluid phase below a density-dependent temperature, is always metastable against a lamellar crystal. We also show that a crystal of infinitely long packed tubes is thermodynamically stable, but only at high pressure. The full phase diagram of the model, beside the fluid phase, displays four different stable crystals. A gas-liquid critical point, and hence a liquid phase, is not detected.

  8. Effects of interactions between depletants in phase diagrams of binary hard-sphere systems

    NASA Astrophysics Data System (ADS)

    Suematsu, A.; Yoshimori, A.; Akiyama, R.

    2016-11-01

    Fluid-solid phase diagrams for binary hard-sphere systems were calculated to study the effects of interactions between depletants. Two effective potentials between large hard spheres were examined. One was the Asakura-Oosawa (AO) potential, and the other was an effective potential obtained by using an integral equation theory (IE potential). The IE potential has oscillations caused by the interactions between depletants, whereas in the AO potential, the inter-depletant correlation is ignored. The phase diagrams were obtained by using the thermodynamic perturbation theory with the density functional theory. The phase diagrams for the IE potential systems differed from those for the AO potential systems because of the inter-depletant correlation. The differences in the present calculation were caused by the first minimum of the effective potential.

  9. Microevaporators for Kinetic Exploration of Phase Diagrams

    NASA Astrophysics Data System (ADS)

    Leng, Jacques; Lonetti, Barbara; Tabeling, Patrick; Joanicot, Mathieu; Ajdari, Armand

    2006-03-01

    We use pervaporation-based microfluidic devices to concentrate species in aqueous solutions with spatial and temporal control of the process. Using experiments and modeling, we quantitatively describe the advection-diffusion behavior of the concentration field of various solutions (electrolytes, colloids, etc.) and demonstrate the potential of these devices as universal tools for the kinetic exploration of the phases and textures that form upon concentration.

  10. 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.

  11. Phase diagrams and ionic defects in the 2212 and 2201 phases of the bismuth system

    NASA Astrophysics Data System (ADS)

    Idemoto, Yasushi; Kobayashi, Shinichi; Fueki, Kazuo

    1994-08-01

    The compositional diagrams representing the stability regions of the 2212 and 2201 phases of the bismuth system were constructed for several temperatures above 820°C. The actual densities of both phases were determined by pycnometry and compared with the theoretical densities. It was found that the maximum ion deficiency is about 2% for the 2212 phase and nearly zero for the 2201 phase. The valences of Bi and Cu were determined by chemical analysis and the excess oxygen was calculated. The maximum excess oxygen was found to be 2.5% and 3% for the 2212 and 2201 phases, respectively. From the ion deficiency and the excess oxygen, it was concluded that the excess oxygen occupies not the vacancy but the interstitial site.

  12. 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.

  13. 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.

  14. Phase diagram of a model of the protein amelogenin

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

    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.

  15. Phase diagram for the Eigen quasispecies theory with a truncated fitness landscape

    NASA Astrophysics Data System (ADS)

    Saakian, David B.; Biebricher, Christof K.; Hu, Chin-Kun

    2009-04-01

    Using methods of statistical physics, we present rigorous theoretical calculations of Eigen’s quasispecies theory with the truncated fitness landscape which dramatically limits the available sequence space of information carriers. As the mutation rate is increased from small values to large values, one can observe three phases: the first (I) selective (also known as ferromagnetic) phase, the second (II) intermediate phase with some residual order, and the third (III) completely randomized (also known as paramagnetic) phase. We calculate the phase diagram for these phases and the concentration of information carriers in the master sequence (also known as peak configuration) x0 and other classes of information carriers. As the phase point moves across the boundary between phase I and phase II, x0 changes continuously; as the phase point moves across the boundary between phase II and phase III, x0 has a large change. Our results are applicable for the general case of a fitness landscape.

  16. 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

  17. 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

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

    2010-08-01

    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.

  18. Phase diagram of matrix compressed sensing.

    PubMed

    Schülke, Christophe; Schniter, Philip; Zdeborová, Lenka

    2016-12-01

    In the problem of matrix compressed sensing, we aim to recover a low-rank matrix from a few noisy linear measurements. In this contribution, we analyze the asymptotic performance of a Bayes-optimal inference procedure for a model where the matrix to be recovered is a product of random matrices. The results that we obtain using the replica method describe the state evolution of the Parametric Bilinear Generalized Approximate Message Passing (P-BiG-AMP) algorithm, recently introduced in J. T. Parker and P. Schniter [IEEE J. Select. Top. Signal Process. 10, 795 (2016)1932-455310.1109/JSTSP.2016.2539123]. We show the existence of two different types of phase transition and their implications for the solvability of the problem, and we compare the results of our theoretical analysis to the numerical performance reached by P-BiG-AMP. Remarkably, the asymptotic replica equations for matrix compressed sensing are the same as those for a related but formally different problem of matrix factorization.

  19. Phase diagram of matrix compressed sensing

    NASA Astrophysics Data System (ADS)

    Schülke, Christophe; Schniter, Philip; Zdeborová, Lenka

    2016-12-01

    In the problem of matrix compressed sensing, we aim to recover a low-rank matrix from a few noisy linear measurements. In this contribution, we analyze the asymptotic performance of a Bayes-optimal inference procedure for a model where the matrix to be recovered is a product of random matrices. The results that we obtain using the replica method describe the state evolution of the Parametric Bilinear Generalized Approximate Message Passing (P-BiG-AMP) algorithm, recently introduced in J. T. Parker and P. Schniter [IEEE J. Select. Top. Signal Process. 10, 795 (2016), 10.1109/JSTSP.2016.2539123]. We show the existence of two different types of phase transition and their implications for the solvability of the problem, and we compare the results of our theoretical analysis to the numerical performance reached by P-BiG-AMP. Remarkably, the asymptotic replica equations for matrix compressed sensing are the same as those for a related but formally different problem of matrix factorization.

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

    SciTech Connect

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

    2016-05-20

    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.

  1. 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…

  2. 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…

  3. 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…

  4. 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.

  5. 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…

  6. Investigating the QCD phase diagram with hadron multiplicities at NICA

    NASA Astrophysics Data System (ADS)

    Becattini, F.; Stock, R.

    2016-08-01

    We discuss the potential of the experimental programme at NICA to investigate the QCD phase diagram and particularly the position of the critical line at large baryon-chemical potential with accurate measurements of particle multiplicities. We briefly review the present status and we outline the tasks to be accomplished both theoretically and the experimentally to make hadronic abundances a sensitive probe.

  7. 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.

  8. Magnetic phase diagrams of classical triangular and kagome antiferromagnets.

    PubMed

    Gvozdikova, M V; Melchy, P-E; Zhitomirsky, M E

    2011-04-27

    We investigate the effect of geometrical frustration on the H-T phase diagrams of the classical Heisenberg antiferromagnets on triangular and kagome lattices. The phase diagrams for the two models are obtained from large-scale Monte Carlo simulations. For the kagome antiferromagnet, thermal fluctuations are unable to lift degeneracy completely and stabilize translationally disordered multipolar phases. We find a substantial difference in the temperature scales of the order by disorder effect related to different degeneracy of the low- and the high-field classical ground states in the kagome antiferromagnet. In the low-field regime, the Kosterlitz-Thouless transition into a spin-nematic phase is produced by unbinding of half-quantum vortices.

  9. Zero-temperature phase diagram of D₂ physisorbed on graphane.

    PubMed

    Carbonell-Coronado, C; De Soto, F; Cazorla, C; Boronat, J; Gordillo, M C

    2013-11-06

    We determined the zero-temperature phase diagram of D₂ physisorbed on graphane using the diffusion Monte Carlo method. The substrate used was C-graphane, an allotropic form of the compound that has been experimentally obtained through hydrogenation of graphene. We found that the ground state is the δ phase, a commensurate structure observed experimentally when D₂ is adsorbed on graphite, and not the registered √3 x √3 structure characteristic of H₂ on the same substrate.

  10. Phase diagram investigations of K-Sr-U-O system

    NASA Astrophysics Data System (ADS)

    Keskar, Meera; Agarwal, R.

    2011-06-01

    In continuation of our previous work on phase diagram investigations of alkali metal-alkaline earth metal-uranium oxides, the sub-solidus phase relations in K-Sr-U-O quaternary system were determined at 850 °C in air. A pseudo-ternary phase diagram of UO 3-SrO-K 2O was drawn using reported ternary compounds in K 2O-UO 3 and SrO-UO 3 systems, a single quaternary compound, K 8Sr 2U 6O 24 and various phase mixtures. These compounds and mixtures were synthesized by solid route, by heating K 2CO 3, SrCO 3 and UO 3 in different molar proportions at 850 °C. The phase fields of K 2O-SrO-UO 3 pseudo-ternary phase diagram were established by X-ray powder diffraction analysis. Gibbs energies of formation of binary and ternary uranates were estimated. The Gibbs energies of formations of A8Sr 2U 6O 24 ( A = Na/K/Rb/Cs) type compounds for different alkali metals were compared to find a reason for the stability of the compound for sodium, potassium and rubidium and its instability for cesium.

  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. 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.

  13. 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.

  14. Spin Density Wave Phase Diagram in Thin Cr(110) Films

    NASA Astrophysics Data System (ADS)

    Rotenberg, Eli; Freelon, B. K.; Koh, H.; Rossnagel, K.; Kevan, S. D.

    2004-03-01

    Using angle-resolved photoemission, we have mapped the antiferromagnetic phase diagram of Cr(110) thin films grown on Mo(110) and W(110) substrates systematically as a function of both film thickness and temperature. We find commensurate and incommensurate spin density wave and paramagnetic phases that are separated by nearly continuous transitions. We determine how the spin density wave band gap evolves near the Fermi level through these phases. Our results suggest a simple model to explain the delicate interplay between commensurate and incommensurate phases that involves a balance between spin density wave stabilization energy and surface and interface magnetic anisotropies.

  15. Tensor renormalization group: local magnetizations, correlation functions, and phase diagrams of systems with quenched randomness.

    PubMed

    Güven, Can; Hinczewski, Michael; Berker, A Nihat

    2010-11-01

    The tensor renormalization-group method, developed by Levin and Nave, brings systematic improvability to the position-space renormalization-group method and yields essentially exact results for phase diagrams and entire thermodynamic functions. The method, previously used on systems with no quenched randomness, is extended in this study to systems with quenched randomness. Local magnetizations and correlation functions as a function of spin separation are calculated as tensor products subject to renormalization-group transformation. Phase diagrams are extracted from the long-distance behavior of the correlation functions. The approach is illustrated with the quenched bond-diluted Ising model on the triangular lattice. An accurate phase diagram is obtained in temperature and bond-dilution probability for the entire temperature range down to the percolation threshold at zero temperature.

  16. Tensor renormalization group: Local magnetizations, correlation functions, and phase diagrams of systems with quenched randomness

    NASA Astrophysics Data System (ADS)

    Güven, Can; Hinczewski, Michael; Berker, A. Nihat

    2011-03-01

    The tensor renormalization-group method, developed by Levin and Nave, brings systematic improvability to the position-space renormalization-group method and yields essentially exact results for phase diagrams and entire thermodynamic functions. The method, previously used on systems with no quenched randomness, is extended in this study to systems with quenched randomness. Local magnetizations and correlation functions as a function of spin separation are calculated as tensor products subject to renormalization-group transformation. Phase diagrams are extracted from the long-distance behavior of the correlation functions. The approach is illustrated with the quenched bond-diluted Ising model on the triangular lattice. An accurate phase diagram is obtained in temperature and bond-dilution probability for the entire temperature range down to the percolation threshold at zero temperature. This research was supported by the Alexander von Humboldt Foundation, the Scientific and Technological Research Council of Turkey (TÜBITAK), and the Academy of Sciences of Turkey.

  17. Tensor renormalization group: Local magnetizations, correlation functions, and phase diagrams of systems with quenched randomness

    NASA Astrophysics Data System (ADS)

    Güven, Can; Hinczewski, Michael; Berker, A. Nihat

    2010-11-01

    The tensor renormalization-group method, developed by Levin and Nave, brings systematic improvability to the position-space renormalization-group method and yields essentially exact results for phase diagrams and entire thermodynamic functions. The method, previously used on systems with no quenched randomness, is extended in this study to systems with quenched randomness. Local magnetizations and correlation functions as a function of spin separation are calculated as tensor products subject to renormalization-group transformation. Phase diagrams are extracted from the long-distance behavior of the correlation functions. The approach is illustrated with the quenched bond-diluted Ising model on the triangular lattice. An accurate phase diagram is obtained in temperature and bond-dilution probability for the entire temperature range down to the percolation threshold at zero temperature.

  18. 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.

  19. Mapping Isobaric Aging onto the Equilibrium Phase Diagram

    NASA Astrophysics Data System (ADS)

    Niss, Kristine

    2017-09-01

    The linear volume relaxation and the nonlinear volume aging of a glass-forming liquid are measured, directly compared, and used to extract the out-of-equilibrium relaxation time. This opens a window to investigate how the relaxation time depends on temperature, structure, and volume in parts of phase space that are not accessed by the equilibrium liquid. It is found that the temperature dependence of relaxation time is non-Arrhenius even in the isostructural case—challenging the Adam-Gibbs entropy model. Based on the presented data and the idea that aging happens through quasiequilibrium states, we suggest a mapping of the out-of-equilibrium states during isobaric aging to the equilibrium phase diagram. This mapping implies the existence of isostructural lines in the equilibrium phase diagram. The relaxation time is found to depend on the bath temperature, density, and a just single structural parameter, referred to as an effective temperature.

  20. 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.

  1. Thermal fluctuations and phase diagrams of the phase-field crystal model with pinning.

    PubMed

    Ramos, J A P; Granato, E; Achim, C V; Ying, S C; Elder, K R; Ala-Nissila, T

    2008-09-01

    We study the influence of thermal fluctuations in the phase diagram of a recently introduced two-dimensional phase field crystal model with an external pinning potential. The model provides a continuum description of pinned lattice systems allowing for both elastic deformations and topological defects. We introduce a nonconserved version of the model and determine the ground-state phase diagram as a function of lattice mismatch and strength of the pinning potential. Monte Carlo simulations are used to determine the phase diagram as a function of temperature near commensurate phases. The results show a rich phase diagram with commensurate, incommensurate, and liquidlike phases with a topology strongly dependent on the type of ordered structure. A finite-size scaling analysis of the melting transition for the c(2x2) commensurate phase shows that the thermal correlation length exponent nu and specific heat behavior are consistent with the Ising universality class as expected from analytical arguments.

  2. Experimental and computed phase diagrams of the Fe-Re system

    NASA Astrophysics Data System (ADS)

    Breidi, A.; Andasmas, M.; Crivello, J.-C.; Dupin, N.; Joubert, J.-M.

    2014-12-01

    In order to clarify controversial reports on the Fe-Re phase diagram, a new experimental investigation has been carried out. Three intermetallic phases have been evidenced, including the new report of the P phase found for the first time in a binary system. The phase relations involving the σ phase were established. In parallel, a first-principles study has been performed which provided the heat of formation of every ordered configuration for four intermetallic phases (D8b, A12, A13 and P). The mixing energy of solid solutions (fcc, bcc, hcp) was calculated using the special quasi-random structure method. Calculations were performed with the help of the density functional theory, with and without spin polarization. From these results, in the frame of the Compound Energy Formalism using the Bragg-Williams approximation, the Fe-Re phase diagram has been computed without the use of adjustable parameters. Different thermodynamic parameters obtained experimentally and theoretically, as the site occupancies, are compared. The computed phase diagram presents several differences with the experimental one. To understand these differences, the influence of several parameters on the phase stability, such as the magnetic contribution has been evaluated.

  3. Phase diagram of highly asymmetric binary hard-sphere mixtures.

    PubMed

    Dijkstra, M; van Roij, R; Evans, R

    1999-05-01

    We study the phase behavior and structure of highly asymmetric binary hard-sphere mixtures. By first integrating out the degrees of freedom of the small spheres in the partition function we derive a formal expression for the effective Hamiltonian of the large spheres. Then using an explicit pairwise (depletion) potential approximation to this effective Hamiltonian in computer simulations, we determine fluid-solid coexistence for size ratios q=0.033, 0.05, 0.1, 0.2, and 1.0. The resulting two-phase region becomes very broad in packing fractions of the large spheres as q becomes very small. We find a stable, isostructural solid-solid transition for q< or =0.05 and a fluid-fluid transition for q< or =0.10. However, the latter remains metastable with respect to the fluid-solid transition for all size ratios we investigate. In the limit q-->0 the phase diagram mimics that of the sticky-sphere system. As expected, the radial distribution function g(r) and the structure factor S(k) of the effective one-component system show no sharp signature of the onset of the freezing transition and we find that at most points on the fluid-solid boundary the value of S(k) at its first peak is much lower than the value given by the Hansen-Verlet freezing criterion. Direct simulations of the true binary mixture of hard spheres were performed for q > or =0.05 in order to test the predictions from the effective Hamiltonian. For those packing fractions of the small spheres where direct simulations are possible, we find remarkably good agreement between the phase boundaries calculated from the two approaches-even up to the symmetric limit q=1 and for very high packings of the large spheres, where the solid-solid transition occurs. In both limits one might expect that an approximation which neglects higher-body terms should fail, but our results support the notion that the main features of the phase equilibria of asymmetric binary hard-sphere mixtures are accounted for by the effective

  4. Global phase diagram of disordered type-II Weyl semimetals

    NASA Astrophysics Data System (ADS)

    Wu, Yijia; Liu, Haiwen; Jiang, Hua; Xie, X. C.

    2017-07-01

    With electron and hole pockets touching at the Weyl node, type-II Weyl semimetal is a newly proposed topological state distinct from its type-I cousin. We numerically study the localization effect for tilted type-I as well as type-II Weyl semimetals and give the global phase diagram. For disordered type-I Weyl semimetal, an intermediate three-dimensional quantum anomalous Hall phase is confirmed between Weyl semimetal phase and diffusive metal phase. However, this intermediate phase is absent for disordered type-II Weyl semimetal. Besides, along the direction of tilt, comparing to its type-I cousin, type-II Weyl semimetal typically possesses longer normalized localization length and therefore it is more robust against disorder. Near the phase boundary between the type-I and the type-II Weyl semimetals, infinitesimal disorder will induce an insulating phase so that, in this region, the concept of Weyl semimetal is meaningless for real materials.

  5. 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.

  6. Phase diagram of a reentrant gel of patchy particles.

    PubMed

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

    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.

  7. 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.

  8. Phase Diagrams for the PEO-LiX Electrolyte System.

    DTIC Science & Technology

    1987-01-01

    rather flat, in sharp contrast to previous results. 3.2c PEO- LiBF4 System Pure PEO forms complexes with LiBF , and the subsequent phase diagram for...study; 0 ----NMR(15); 0 -DSC or DTA(7, 10,12); A ---a.c.conductivity(6,10,12); 4- optical microscopy(6). is 350 - (PEO) n- LiBF4 300 (PEO) n-LiCF 3SO 3...the PEO- LiBF4 system IS" , " ATOM RATIO O/Li 50 25 8 4 2 1 250 200 150 1 00 -50I 0 0 0.1 0.2 0.3 0.4 0.5 XLiPF6 -’+’ Figure 6. Phase diagram of the

  9. Phase Diagram of Fatty Acid Langmuir Monolayers from Rheological Measurements.

    PubMed

    Tajuelo, J; Guzmán, E; Ortega, F; Rubio, R G; Rubio, M A

    2017-05-02

    Langmuir monolayers of fatty acids and alcohols are two-dimensional systems with a rich equilibrium phase diagram. We have explored the temperature and surface-pressure-dependent shear response of monolayers formed by fatty acids of different chain lengths and a fatty alcohol. This has been accomplished with an interfacial shear rheometer utilizing magnetic tweezers and equipped with a refined temperature control and acquisition system. Our rheological results have allowed us to draw a phase diagram from the viscoelastic properties of these 2-D systems and show new phenomena that strongly depend on temperature: the existence of a maximum in viscosity at the L2' phase, the behavior of the elastic modulus to the storage modulus ratio at the L2 phase, and the increase or decrease in viscosity at the L2-LS phase transition. In addition, we unambiguously show that the LS phase displays a counterintuitive behavior in which the loss modulus increases with temperature. We demonstrate, through isothermal surface pressure sweeps and isobaric temperature sweeps, that the exponential dependence of the loss modulus on temperature at the LS phase appears for all hydrophobic tail lengths studied and for both acid and alcohol head groups.

  10. Duality and phase diagram of one-dimensional transport

    NASA Astrophysics Data System (ADS)

    Bhattacharjee, Somendra M.

    2007-02-01

    The idea of duality in one-dimensional nonequilibrium transport is introduced by generalizing the observations by Mukherji and Mishra. A general approach is developed for the classification and characterization of the steady state phase diagrams which are shown to be determined by the nature of the zeros of a set of coarse-grained functions that encode the microscopic dynamics. A new class of nonequilibrium multicritical points has been identified.

  11. Behavior of universal critical parameters in the QCD phase diagram

    NASA Astrophysics Data System (ADS)

    Bluhm, Marcus; Nahrgang, Marlene; Bass, Steffen A.; Schäfer, Thomas

    2017-01-01

    We determine the dependence of important parameters for critical fluctuations on temperature and baryon chemical potential in the QCD phase diagram. The analysis is based on an identification of the fluctuations of the order parameter obtained from the Ising model equation of state and the Ginzburg-Landau effective potential approach. The impact of the mapping from Ising model variables to QCD thermodynamics is discussed.

  12. Free energy and phase diagram of chromium alloys

    SciTech Connect

    Fishman, R.S. ); Liu, S.H. )

    1993-08-01

    The phase diagram of chromium alloys is remarkably rich. At the Neel temperature of 310 K, pure chromium undergoes a weakly first-order phase transition into an incommensurate spin-density wave (SDW) state. When doped with more than 0.2% manganese, this transition becomes second order and the SDW becomes commensurate. Over 25 years ago, Koehler [ital et] [ital al]. and Komura, Hamaguchi, and Kunitomi observed a first-order commensurate-to-incommensurate (CI) transition in CrMn alloys. The temperature of this CI transition decreased to zero as the manganese concentration increases from about 0.2% to about 1.5%. Using mean-field theory, we have constructed the free energy and phase diagram of chromium alloys in the presence of electron scattering. In the absence of scattering, the phase diagram allows a first-order phase transition from the incommensurate to the commensurate states with decreasing temperature. But if the damping is sufficiently large, the phase-separation curve flips from the right side of the tricritical point to the left. So within a small window of manganese concentrations, the commensurate state undergoes a first-order transition into the incommensurate state with decreasing temperature, in agreement with the experiments of Koehler [ital et] [ital al]. At zero temperature, we find a first-order phase transition from the incommensurate to the commensurate state with manganese doping, in agreement with the work of Komura, Hamaguchi, and Kunitomi. In the absence of damping, the zero-temperature energy gap [Delta](0) in the commensurate regime is independent of manganese concentration. But in the presence of damping [Delta](0) becomes an increasing function of the manganese concentration.

  13. Free energy and phase diagram of chromium alloys

    NASA Astrophysics Data System (ADS)

    Fishman, R. S.; Liu, S. H.

    1993-08-01

    The phase diagram of chromium alloys is remarkably rich. At the Néel temperature of 310 K, pure chromium undergoes a weakly first-order phase transition into an incommensurate spin-density wave (SDW) state. When doped with more than 0.2% manganese, this transition becomes second order and the SDW becomes commensurate. Over 25 years ago, Koehler et al. and Komura, Hamaguchi, and Kunitomi observed a first-order commensurate-to-incommensurate (CI) transition in CrMn alloys. The temperature of this CI transition decreased to zero as the manganese concentration increases from about 0.2% to about 1.5%. Using mean-field theory, we have constructed the free energy and phase diagram of chromium alloys in the presence of electron scattering. In the absence of scattering, the phase diagram allows a first-order phase transition from the incommensurate to the commensurate states with decreasing temperature. But if the damping is sufficiently large, the phase-separation curve flips from the right side of the tricritical point to the left. So within a small window of manganese concentrations, the commensurate state undergoes a first-order transition into the incommensurate state with decreasing temperature, in agreement with the experiments of Koehler et al. At zero temperature, we find a first-order phase transition from the incommensurate to the commensurate state with manganese doping, in agreement with the work of Komura, Hamaguchi, and Kunitomi. In the absence of damping, the zero-temperature energy gap Δ(0) in the commensurate regime is independent of manganese concentration. But in the presence of damping Δ(0) becomes an increasing function of the manganese concentration.

  14. 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.

  15. Phase diagrams of colloidal spheres with a constant zeta-potential.

    PubMed

    Smallenburg, Frank; Boon, Niels; Kater, Maarten; Dijkstra, Marjolein; van Roij, René

    2011-02-21

    We study suspensions of colloidal spheres with a constant zeta-potential within Poisson-Boltzmann theory, quantifying the discharging of the spheres with increasing colloid density and decreasing salt concentration. We use the calculated renormalized charge of the colloids to determine their pairwise effective screened-Coulomb repulsions. Bulk phase diagrams in the colloid concentration-salt concentration representation follow, for various zeta-potentials, by a mapping onto published fits of phase boundaries of point-Yukawa systems. Although the resulting phase diagrams do feature face-centered cubic and body-centered cubic phases, they are dominated by the (re-entrant) fluid phase due to the colloidal discharging with increasing colloid concentration and decreasing salt concentration.

  16. Yoshimori-Kasai Model Phase Diagram and Naniwa Series for Quantum Dynamics

    NASA Astrophysics Data System (ADS)

    Arguelles, Elvis; Shimizu, Koji; Nakanishi, Hiroshi; Kasai, Hideaki

    We present the phase diagram of heavy fermions system (HFS) and muon adsorption calculations on Pd (111) surface. HFS undergoes phase transitions from Fermi liquid (FL) to non-Fermi liquid (NFL). Furthermore, antiferromagnetic (AF), spin-density wave (SDW)and superconductivity can be realized by changing electron densities and temperature. It is shown that at upper Hubbard band filling, HFS changes phase from antiferromagnetic to superconducting at low temperatures. Furthermore, in an attempt to elucidate muon dynamics on surfaces and subsurfaces, we show thatmuon exhibits tunneling effects independent of surface vibrations from quantum dynamical calculations. The results shown herein may have important implications on future ultra-slow muon experiments.

  17. Exploring the Nuclear Phase Diagram with Beam Energy Scans

    NASA Astrophysics Data System (ADS)

    Horvat, Stephen

    2017-04-01

    The nuclear phase diagram is mapped using beam energy scans of relativistic heavy-ion collisions. This mapping is possible because different collision energies develop along different trajectories through the phase diagram. High energy collisions will evolve though a crossover phase transition according to lattice QCD, but lower collision energies may traverse a first order phase transition. There are hints for this first order phase transition and its critical endpoint, but further measurements and theoretical guidance is needed. In addition to mapping the phase transition, beam energy scans allow us to see if we can turn off the signatures of deconfinement. If an observable is a real signature for the formation of the deconfined state called quark-gluon plasma, then it should turn off at sufficiently low collision energies. In this summary talk I will show the current state of the field using beam energy scan results from RHIC and SPS, I will show where precise theoretical guidance is needed for understanding recent measurements, and I will motivate the need for more data and new measurements from FAIR, NICA, RHIC, and the SPS.

  18. 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.

  19. First-principles phase diagram calculations for the rocksalt-structure quasibinary systems TiN-ZrN, TiN-HfN and ZrN-HfN.

    PubMed

    Liu, Z T Y; Burton, B P; Khare, S V; Gall, D

    2017-01-25

    We have studied the phase equilibria of three ceramic quasibinary systems Ti1-x Zr x N, Ti1-x Hf x N and Zr1-x Hf x N (0  ⩽  x  ⩽  1) with density functional theory, cluster expansion and Monte Carlo simulations. We predict consolute temperatures (T C), at which miscibility gaps close, for Ti1-x Zr x N to be 1400 K, for Ti1-x Hf x N to be 700 K, and below 200 K for Zr1-x Hf x N. The asymmetry of the formation energy ΔE f(x) is greater for Ti1-x Hf x N than Ti1-x Zr x N, with less solubility on the smaller cation TiN-side, and similar asymmetries were predicted for the corresponding phase diagrams. We also analyzed different energetic contributions: ΔE f of the random solid solutions were decomposed into a volume change term, [Formula: see text], and a chemical exchange and relaxation term, [Formula: see text]. These two energies partially cancel one another. We conclude that [Formula: see text] influences the magnitude of T C and [Formula: see text] influences the asymmetry of ΔE f(x) and phase boundaries. We also conclude that the absence of experimentally observed phase separation in Ti1-x Zr x N and Ti1-x Hf x N is due to slow kinetics at low temperatures. In addition, elastic constants and mechanical properties of the random solid solutions were studied with the special quasirandom solution approach. Monotonic trends, in the composition dependence, of shear-related mechanical properties, such as Vickers hardness between 18 to 23 GPa, were predicted. Trends for Ti1-x Zr x N and Ti1-x Hf x N exhibit down-bowing (convexity). It shows that mixing nitrides of same group transition metals does not lead to hardness increase from an electronic origin, but through solution hardening mechanism. The mixed thin films show consistency and stability with little phase separation, making them desirable coating choices.

  20. First-principles phase diagram calculations for the rocksalt-structure quasibinary systems TiN-ZrN, TiN-HfN and ZrN-HfN

    NASA Astrophysics Data System (ADS)

    Liu, Z. T. Y.; Burton, B. P.; Khare, S. V.; Gall, D.

    2017-01-01

    We have studied the phase equilibria of three ceramic quasibinary systems Ti1-x Zr x N, Ti1-x Hf x N and Zr1-x Hf x N (0  ⩽  x  ⩽  1) with density functional theory, cluster expansion and Monte Carlo simulations. We predict consolute temperatures (T C), at which miscibility gaps close, for Ti1-x Zr x N to be 1400 K, for Ti1-x Hf x N to be 700 K, and below 200 K for Zr1-x Hf x N. The asymmetry of the formation energy ΔE f(x) is greater for Ti1-x Hf x N than Ti1-x Zr x N, with less solubility on the smaller cation TiN-side, and similar asymmetries were predicted for the corresponding phase diagrams. We also analyzed different energetic contributions: ΔE f of the random solid solutions were decomposed into a volume change term, Δ {{E}\\text{vc}} , and a chemical exchange and relaxation term, Δ {{E}\\text{xc\\text{-rlx}}} . These two energies partially cancel one another. We conclude that Δ {{E}\\text{vc}} influences the magnitude of T C and Δ {{E}\\text{xc\\text{-rlx}}} influences the asymmetry of ΔE f(x) and phase boundaries. We also conclude that the absence of experimentally observed phase separation in Ti1-x Zr x N and Ti1-x Hf x N is due to slow kinetics at low temperatures. In addition, elastic constants and mechanical properties of the random solid solutions were studied with the special quasirandom solution approach. Monotonic trends, in the composition dependence, of shear-related mechanical properties, such as Vickers hardness between 18 to 23 GPa, were predicted. Trends for Ti1-x Zr x N and Ti1-x Hf x N exhibit down-bowing (convexity). It shows that mixing nitrides of same group transition metals does not lead to hardness increase from an electronic origin, but through solution hardening mechanism. The mixed thin films show consistency and stability with little phase separation, making them desirable coating choices.

  1. Ground-State Phase Diagram of S = 1 Diamond Chains

    NASA Astrophysics Data System (ADS)

    Hida, Kazuo; Takano, Ken'ichi

    2017-03-01

    We investigate the ground-state phase diagram of a spin-1 diamond chain. Owing to a series of conservation laws, any eigenstate of this system can be expressed using the eigenstates of finite odd-length chains or infinite chains with spins 1 and 2. The ground state undergoes quantum phase transitions with varying λ, a parameter that controls frustration. Exact upper and lower bounds for the phase boundaries between these phases are obtained. The phase boundaries are determined numerically in the region not explored in a previous work [Takano et al., J. Phys.: Condens. Matter 8, 6405 (1996)].

  2. Modeling of metastable phase formation diagrams for sputtered thin films

    PubMed Central

    Chang, Keke; Music, Denis; to Baben, Moritz; Lange, Dennis; Bolvardi, Hamid; Schneider, Jochen M.

    2016-01-01

    Abstract A method to model the metastable phase formation in the Cu–W system based on the critical surface diffusion distance has been developed. The driver for the formation of a second phase is the critical diffusion distance which is dependent on the solubility of W in Cu and on the solubility of Cu in W. Based on comparative theoretical and experimental data, we can describe the relationship between the solubilities and the critical diffusion distances in order to model the metastable phase formation. Metastable phase formation diagrams for Cu–W and Cu–V thin films are predicted and validated by combinatorial magnetron sputtering experiments. The correlative experimental and theoretical research strategy adopted here enables us to efficiently describe the relationship between the solubilities and the critical diffusion distances in order to model the metastable phase formation during magnetron sputtering. PMID:27877871

  3. Thermodynamic and topological phase diagrams of correlated topological insulators

    NASA Astrophysics Data System (ADS)

    Zdulski, Damian; Byczuk, Krzysztof

    2015-09-01

    A definition of topological phases of density matrices is presented. The topological invariants in case of both noninteracting and interacting systems are extended to nonzero temperatures. The influence of electron interactions on topological insulators at finite temperatures is investigated. A correlated topological insulator is described by the Kane-Mele model, which is extended by the interaction term of the Falicov-Kimball type. Within the Hartree-Fock and the Hubbard I approximations, thermodynamic and topological phase diagrams are determined where the long-range order is included. The results show that correlation effects lead to a strong suppression of the existence of the nontrivial topological phase. In the homogeneous phase, we find a purely correlation driven phase transition into the topologically trivial Mott insulator.

  4. Modeling of metastable phase formation diagrams for sputtered thin films.

    PubMed

    Chang, Keke; Music, Denis; To Baben, Moritz; Lange, Dennis; Bolvardi, Hamid; Schneider, Jochen M

    2016-01-01

    A method to model the metastable phase formation in the Cu-W system based on the critical surface diffusion distance has been developed. The driver for the formation of a second phase is the critical diffusion distance which is dependent on the solubility of W in Cu and on the solubility of Cu in W. Based on comparative theoretical and experimental data, we can describe the relationship between the solubilities and the critical diffusion distances in order to model the metastable phase formation. Metastable phase formation diagrams for Cu-W and Cu-V thin films are predicted and validated by combinatorial magnetron sputtering experiments. The correlative experimental and theoretical research strategy adopted here enables us to efficiently describe the relationship between the solubilities and the critical diffusion distances in order to model the metastable phase formation during magnetron sputtering.

  5. Phase diagram and critical end point for strongly interacting quarks.

    PubMed

    Qin, Si-xue; Chang, Lei; Chen, Huan; Liu, Yu-xin; Roberts, Craig D

    2011-04-29

    We introduce a method based on chiral susceptibility, which enables one to draw a phase diagram in the chemical-potential-temperature plane for strongly interacting quarks whose interactions are described by any reasonable gap equation, even if the diagrammatic content of the quark-gluon vertex is unknown. We locate a critical end point at (μ(E),T(E))∼(1.0,0.9)T(c), where T(c) is the critical temperature for chiral-symmetry restoration at μ=0, and find that a domain of phase coexistence opens at the critical end point whose area increases as a confinement length scale grows.

  6. A Ternary Phase Diagram for a Less Hazardous System

    NASA Astrophysics Data System (ADS)

    Udale, Barbara A.; Wells, John D.

    1995-12-01

    The ternary phase diagram for the partially miscible liquid system n-propanol-n-heptane-water can be determined readily in an undergraduate laboratory experiment. The coexistence curve is obtained from titration results. Tie lines are then estimated from the compositions of pairs of phases in equilibrium, the propanol concentrations being determined by gas chromatography. The reagents are less hazardous than those of the classic acetic acid-chloroform-water system, and the gas chromatographic analysis has more interest for students than the acid-base titrations of the older experiment.

  7. Pseudo-ternary phase diagrams in the system water/sodium chloride/heptane/1-butanol/sodium dodecyl sulphate

    SciTech Connect

    Gilje, E.; Maledal, T. )

    1992-01-01

    An entirely empirical model for estimating the pseudo-components in quarternary microemulsion systems has been adopted. Data for the system water/NaCl/ heptane/1-butanol/sodium dodecyl sulphate (SDS) are used in the empirical model. In this paper calculated phase volumes and interfacial tensions are compared with experimental data. Further, a calculated pseudo-ternary phase diagram is compared with the data obtained from an experimental phase diagram where the pseudo-components are determined from the model. The results show a good agreement between calculated and experimental data.

  8. Pitfalls and feedback when constructing topological pressure-temperature phase diagrams

    NASA Astrophysics Data System (ADS)

    Ceolin, R.; Toscani, S.; Rietveld, Ivo B.; Barrio, M.; Tamarit, J. Ll.

    2017-04-01

    The stability hierarchy between different phases of a chemical compound can be accurately reproduced in a topological phase diagram. This type of phase diagrams may appear to be the result of simple extrapolations, however, experimental complications quickly increase in the case of crystalline trimorphism (and higher order polymorphism). To ensure the accurate positioning of stable phase domains, a topological phase diagram needs to be consistent. This paper gives an example of how thermodynamic feedback can be used in the topological construction of phase diagrams to ensure overall consistency in a phase diagram based on the case of piracetam crystalline trimorphism.

  9. Pitfalls and feedback when constructing topological pressure-temperature phase diagrams

    NASA Astrophysics Data System (ADS)

    Ceolin, R.; Toscani, S.; Rietveld, Ivo B.; Barrio, M.; Tamarit, J. Ll.

    2016-09-01

    The stability hierarchy between different phases of a chemical compound can be accurately reproduced in a topological phase diagram. This type of phase diagrams may appear to be the result of simple extrapolations, however, experimental complications quickly increase in the case of crystalline trimorphism (and higher order polymorphism). To ensure the accurate positioning of stable phase domains, a topological phase diagram needs to be consistent. This paper gives an example of how thermodynamic feedback can be used in the topological construction of phase diagrams to ensure overall consistency in a phase diagram based on the case of piracetam crystalline trimorphism.

  10. Phase diagram of the triangular-lattice Potts antiferromagnet

    NASA Astrophysics Data System (ADS)

    Lykke Jacobsen, Jesper; Salas, Jesús; Scullard, Christian R.

    2017-08-01

    We study the phase diagram of the triangular-lattice Q-state Potts model in the real (Q, v) -plane, where v=e^J-1 is the temperature variable. Our first goal is to provide an obviously missing feature of this diagram: the position of the antiferromagnetic critical curve. This curve turns out to possess a bifurcation point with two branches emerging from it, entailing important consequences for the global phase diagram. We have obtained accurate numerical estimates for the position of this curve by combining the transfer-matrix approach for strip graphs with toroidal boundary conditions and the recent method of critical polynomials. The second goal of this work is to study the corresponding Ap-1 RSOS model on the torus, for integer p=4, 5, \\ldots, 8 . We clarify its relation to the corresponding Potts model, in particular concerning the role of boundary conditions. For certain values of p, we identify several new critical points and regimes for the RSOS model and we initiate the study of the flows between the corresponding field theories.

  11. 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.

  12. 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.

  13. 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.

  14. Influence of finite volume and magnetic field effects on the QCD phase diagram

    NASA Astrophysics Data System (ADS)

    Magdy, Niseem; Csanád, M.; Lacey, Roy A.

    2017-02-01

    The 2 + 1 SU(3) Polyakov linear sigma model is used to investigate the respective influence of a finite volume and a magnetic field on the quark-hadron phase boundary in the plane of baryon chemical potential ({μ }B) versus temperature (T) of the quantum chromodynamics (QCD) phase diagram. The calculated results indicate sizable shifts of the quark-hadron phase boundary to lower values of ({μ }B {and} T) for increasing magnetic field strength, and an opposite shift to higher values of ({μ }B {and} T) for decreasing system volume. Such shifts could have important implications for the extraction of the thermodynamic properties of the QCD phase diagram from heavy ion data.

  15. 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

    2015-07-28

    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.

  16. 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.

  17. Phase diagram of incoherently driven strongly correlated photonic lattices

    NASA Astrophysics Data System (ADS)

    Biella, Alberto; Storme, Florent; Lebreuilly, José; Rossini, Davide; Fazio, Rosario; Carusotto, Iacopo; Ciuti, Cristiano

    2017-08-01

    We explore theoretically the nonequilibrium photonic phases of an array of coupled cavities in presence of incoherent driving and dissipation. In particular, we consider a Hubbard model system where each site is a Kerr nonlinear resonator coupled to a two-level emitter, which is pumped incoherently. Within a Gutzwiller mean-field approach, we determine the steady-state phase diagram of such a system. We find that, at a critical value of the intercavity photon hopping rate, a second-order nonequilibrium phase transition associated with the spontaneous breaking of the U(1 ) symmetry occurs. The transition from an incompressible Mott-like photon fluid to a coherent delocalized phase is driven by commensurability effects and not by the competition between photon hopping and optical nonlinearity. The essence of the mean-field predictions is corroborated by finite-size simulations obtained with matrix product operators and corner-space renormalization methods.

  18. 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.

  19. 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.

  20. 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.

  1. 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

  2. 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

  3. Equation of state and phase diagram of dense hydrogen

    NASA Technical Reports Server (NTRS)

    Kerley, G. I.

    1972-01-01

    The equation of state of hydrogen was calculated for specific volumes ranging from 0.01 to 0.0001 cm3/mole and for temperatures ranging from 200 to 1 million K. Three phases are considered: the molecular solid, the metallic solid and the fluid. Chemical equilibrium between molecules, atoms, ions and electrons is considered in calculating the properties of the fluid phase. Transitions between the three phases will be discussed. The triple point, where the three phases coexist, is calculated to occur at 2.3 Mbar and 1679 K. At higher temperatures and pressures, the molecular solid is unstable.

  4. Thermodynamic functions, freezing transition, and phase diagram of dense carbon-oxygen mixtures in white dwarfs

    SciTech Connect

    Iyetomi, H.; Ogata, S.; Ichimaru, S.

    1989-07-01

    Equations of state for dense carbon-oxygen (C-O) binary-ionic mixtures (BIM's) appropriate to the interiors of white dwarfs are investigated through Monte Carlo simulations, by solution of relevant integral equations andvariational calculations in the density-functional formalism. It is thereby shown that the internal energies of the C-O BIM solids and fluids both obey precisely the linear mixing formulas. We then present an accurate calculation of the phase diagram associated with freezing transitions in such BIM materials, resulting in a novel prediction of an azeotropic diagram. Discontinuities of the mass density across the azeotropic phase boundaries areevaluated numerically for application to a study of white-dwarf evolution.

  5. Low Temperature Phase Diagram in γ-p-NPNN

    NASA Astrophysics Data System (ADS)

    Kajiyoshi, Koichi

    2005-03-01

    We performed the magnetic torque measurements of γ-phase of para-Nitrophenyl Nitronyl Nitroxide (being p-NPNN), which is considered to be as a quasi-one-dimensional ferromagnet, in the vicinity of TN (=0.65K) using a piezo-resistive micro-cantilever. Typical sample dimension is about 0.25x0.10x0.10mm^3. At 0.4K, a spin-flop transition (HSF) and an antiferromagnetic-paramagnetic transition (HC) are clearly observed in the magnetic field of about 470 Gauss and 2100 Gauss, respectively. The spin-easy axis is almost parallel to the direction to phenyl ring from the ONCNO fragments. H-T phase diagram is determined properly. These results are consistent with our recent low frequency (˜ 300 MHz) and low-temperature (0.4 K) ESR. We will discuss the H-T phase diagram of γ-p-NPNN in comparison with the one- dimensional Heisenberg ferromagnetic model.

  6. Phase diagram of a lattice of pancake vortex molecules

    NASA Astrophysics Data System (ADS)

    Tanaka, Y.; Crisan, A.; Shivagan, D. D.; Iyo, A.; Shirage, P. M.; Tokiwa, K.; Watanabe, T.; Terada, N.

    2009-10-01

    On a superconducting bi-layer with thickness much smaller than the penetration depth, λ, a vortex molecule might form. A vortex molecule is composed of two fractional vortices and a soliton wall. The soliton wall can be regarded as a Josephson vortex missing magnetic flux (degenerate Josephson vortex) due to an incomplete shielding. The magnetic energy carried by fractional vortices is less than in the conventional vortex. This energy gain can pay a cost to form a degenerate Josephson vortex. The phase diagram of the vortex molecule is rich because of its rotational freedom.

  7. Exact phase diagram for an asymmetric avalanche process.

    PubMed

    Priezzhev, V B; Ivashkevich, E V; Povolotsky, A M; Hu, C K

    2001-08-20

    The Bethe ansatz method and an iterative procedure based on detailed balance are used to obtain exact results for an asymmetric avalanche process on a ring. The average velocity of particle flow, v, is derived as a function of the toppling probabilities and the density of particles, rho. As rho increases, the system shows a transition from intermittent to continuous flow, and v diverges at a critical point rho(c) with exponent alpha. The exact phase diagram of the transition is obtained and alpha is found to depend on the toppling rules.

  8. Mapping the topological phase diagram of multiband semiconductors with supercurrents

    NASA Astrophysics Data System (ADS)

    Prada, Elsa; San-Jose, Pablo; Aguado, Ramon

    2014-03-01

    We show that Josephson junctions made of multiband semiconductors with strong spin-orbit coupling carry a critical supercurrent Ic that contains information about the non-trivial topology of the system. In particular, we find that the emergence and annihilation of Majorana bound states in the junction is reflected in strong even-odd effects in Ic under specific conditions. This effect allows for a mapping between Ic and the topological phase diagram of the junction, thus providing a dc measurement of its topology. European Research Council, Spanish Ministry of Economy and Innovation and the Ramón y Cajal Program.

  9. Disordering transitions in vortex matter: Peak effect and phase diagram

    SciTech Connect

    Olson, C.J.; Reichhardt, C.; Zimanyi, G.T.; Gronbech-Jensen, Niels

    2000-08-01

    Using numerical simulations of magnetically interacting vortices in disordered layered superconductors we obtain the static vortex phase diagram as a function of magnetic field and temperature. For increasing field or temperature, we find a transition from ordered straight vortices to disordered decoupled vortices. This transition is associated with a peak effect in the critical current as well as plastic flow of the vortices. For samples with increasing disorder strength the field at which the decoupling occurs decreases. Long range interactions in the c-axis are required to observe the effect.

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

    DOE PAGES

    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

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

    SciTech Connect

    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, 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.

  12. Phase diagram of the two-dimensional negative-U Hubbard model

    NASA Technical Reports Server (NTRS)

    Scalettar, R. T.; Loh, E. Y.; Gubernatis, J. E.; Moreo, A.; White, S. R.

    1989-01-01

    Theoretical arguments and numerical calculations are used to discuss the phase diagram of the two-dimensional negative-U Hubbard model. The results are consistent with (1) a vanishing transition temperature at half-filling but with a ground state having both superconducting and charge-density-wave long-range order, and (2) a Kosterlitz-Thouless transition at a finite temperature into a superconducting state with power-law decay of the pairing correlations away from half-filling.

  13. 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.

  14. Calculation of Energy Diagram of Asymmetric Graded-Band-Gap Semiconductor Superlattices.

    PubMed

    Monastyrskii, Liubomyr S; Sokolovskii, Bogdan S; Alekseichyk, Mariya P

    2017-12-01

    The paper theoretically investigates the peculiarities of energy diagram of asymmetric graded-band-gap superlattices with linear coordinate dependences of band gap and electron affinity. For calculating the energy diagram of asymmetric graded-band-gap superlattices, linearized Poisson's equation has been solved for the two layers forming a period of the superlattice. The obtained coordinate dependences of edges of the conduction and valence bands demonstrate substantial transformation of the shape of the energy diagram at changing the period of the lattice and the ratio of width of the adjacent layers. The most marked changes in the energy diagram take place when the period of lattice is comparable with the Debye screening length. In the case when the lattice period is much smaller that the Debye screening length, the energy diagram has the shape of a sawtooth-like pattern.

  15. Calculation of Energy Diagram of Asymmetric Graded-Band-Gap Semiconductor Superlattices

    NASA Astrophysics Data System (ADS)

    Monastyrskii, Liubomyr S.; Sokolovskii, Bogdan S.; Alekseichyk, Mariya P.

    2017-03-01

    The paper theoretically investigates the peculiarities of energy diagram of asymmetric graded-band-gap superlattices with linear coordinate dependences of band gap and electron affinity. For calculating the energy diagram of asymmetric graded-band-gap superlattices, linearized Poisson's equation has been solved for the two layers forming a period of the superlattice. The obtained coordinate dependences of edges of the conduction and valence bands demonstrate substantial transformation of the shape of the energy diagram at changing the period of the lattice and the ratio of width of the adjacent layers. The most marked changes in the energy diagram take place when the period of lattice is comparable with the Debye screening length. In the case when the lattice period is much smaller that the Debye screening length, the energy diagram has the shape of a sawtooth-like pattern.

  16. 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)

  17. 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)

  18. 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)

  19. Universality and phase diagram in the quantum Hall effect

    NASA Astrophysics Data System (ADS)

    Wong, Lauren Wai-Wing

    We have designed and conducted detailed experiments to explore the following critical, unsolved issues in regarding to the global behavior of the two-dimensional electron gas (2DEG) in the presence of disorder and many-body interaction in the quantum Hall effect (QHE) regime: (1) nature of the quantum Hall liquid-Hall insulator (QHL-HI) phase transition induced by disorder, (2) topological phase diagram and possible existence of a thermodynamically stable "metallic phase" around filling factor nu =1/2, and (3) whether the termination of spin-resolved Landau levels in general a phase transition. First, I present our studies of the disorder-tuned QHL-HI phase transition in both the integer and fractional QHE regimes. We found that the longitudinal resistivity near the critical points shows reflection symmetry and good scaling behavior over a wide range of densities and temperature with the same critical exponent. This supports the notion that quantum phase transitions in the QHE belong to same universality class. Furthermore, the critical conductivities are universal at the transitions. Our approach to investigate the second issue is to map out the phase boundaries corresponding to different QHLs around nu =1/2. We identified a line on which the value of the Hall conductivity equals to 1/2(esp2/h) in the phase diagram; and an another line on which the value of the Hall resistivity equals to 2(h/esp2). We interpreted the later is a result predicted by the composite-fermion theory. The phase boundaries between the HI and the principal QHLs at nu =1 and 1/3 show levitation of the delocalized states of the first Landau levels for electrons and Composite fermions. Our data suggest that there is no true metallic state around nu =1/2. Finally, I present our magnetotransport studies of the spin-resolved integer QHE by changing disorder. For a given Landau level, the difference in filling factors of a pair of spin-split resistivity peaks changes rapidly from one to zero near

  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. Phase Diagram of a 4-Component Lipid Mixture: DSPC/DOPC/POPC/chol

    PubMed Central

    Konyakhina, Tatyana M.; Wu, Jing; Mastroianni, James D.; Heberle, Frederick A.; Feigenson, Gerald W.

    2013-01-01

    We report the first 4-component phase diagram for the lipid bilayer mixture, DSPC/DOPC/POPC/chol (distearoylphosphatidylcholine/dioleoylphosphatidylcholine/1-palmitoyl, 2-oleoylphosphatidylcholine/cholesterol). This phase diagram, which has macroscopic Ld + Lo phase domains, clearly shows that all phase boundaries determined for the 3-component mixture containing DOPC transition smoothly into the boundaries for the 3-component mixture containing POPC, which has nanoscopic phase domains of Ld + Lo. Our studies start from two published ternary phase diagrams, and show how these can be combined into a quaternary phase diagram by study of a few hundred samples of intermediate compositions. PMID:23747294

  2. 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.

  3. 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

  4. The phase diagram and hardness of carbon nitrides

    DOE PAGES

    Dong, Huafeng; Oganov, Artem R.; Zhu, Qiang; ...

    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

  5. Phase diagram of the 1-in-3 satisfiability problem

    NASA Astrophysics Data System (ADS)

    Raymond, Jack; Sportiello, Andrea; Zdeborová, Lenka

    2007-07-01

    We study typical case properties of the 1-in-3 satisfiability problem, the Boolean satisfaction problem, where a clause is satisfied by exactly one literal, in an enlarged random ensemble parametrized by average connectivity and probability of negation of a variable in a clause. Random 1-in-3 satisfiability and exact 3-cover are special cases of this ensemble. We interpolate between these cases from a region where satisfiability can be typically decided for all connectivities in polynomial time to a region where deciding satisfiability is hard, in some interval of connectivities. We derive several rigorous results in the first region and develop a one-step replica-symmetry-breaking cavity analysis in the second one. We discuss the prediction for the transition between the almost surely satisfiable and the almost surely unsatisfiable phase, and other structural properties of the phase diagram, in light of cavity method results.

  6. The phase diagram and hardness of carbon nitrides.

    PubMed

    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 () is dynamically unstable, and we find the lowest-energy structure based on s-triazine unit and s-heptazine unit.

  7. Magnetic phase diagrams of α-MnMoO 4

    NASA Astrophysics Data System (ADS)

    Ehrenberg, H.; Schwarz, B.; Weitzel, H.

    2006-10-01

    Field-induced spin-flop transitions in α-MnMoO 4 are summarized in magnetic H-T phase diagrams for different directions of the applied magnetic field up to 12 T. The antiferromagnetic arrangement in the spin-flop phase is preserved at least up to this field for a field parallel to the easy direction. This high transition field is in contrast to the low one of α-NiMoO 4 and favours a model, based on dominant antiferromagnetic supersuperexchange couplings in α-MnMoO 4 over a ferromagnetic Mn 4 "cluster" model. The Néel temperature of 9.8(1) K was determined from the corresponding specific-heat anomaly, measured on a single crystal of α-MnMoO 4.

  8. Sandwichlike strain glass phase diagram of Ti49Ni51 -xPdx

    NASA Astrophysics Data System (ADS)

    Ren, Shuai; Zhou, Chao; Xue, Dezhen; Wang, Dong; Zhang, Jian; Ding, Xiangdong; Otsuka, Kazuhiro; Ren, Xiaobing

    2016-12-01

    Two kinds of phase diagrams can be observed in doped ferroic materials. A glass phase diagram is formed by doping a nontransforming end into a ferroic matrix, while doping a transforming end forms phase diagrams with a phase boundary separating two different ferroic phases. Here we report a phase diagram in which a strain glass state is sandwiched between two distinct ferroelastic phases. This type of phase diagram in doped ferroelastic materials bridges the one with a glass state and the one with a phase boundary. We thus establish a 3D phase diagram of Ti50 -yNi50 +y -xPdx ternary alloys, in which the evolution of these different kinds of phase diagrams can be observed. An understanding from the Landau free energy landscape suggests that the transforming doping end plays three roles in influencing the ferroic matrix: (1) to destabilize the ferroic matrix phase, (2) to stabilize another ferroic phase different from the matrix one, and (3) to create random local fields. The competition between these effects determines various phase diagrams in doped ferroic materials. Thus our work may provide an experimental foundation for a unified mechanism to all three kinds of phase diagrams.

  9. Pseudo-critical point in anomalous phase diagrams of simple plasma models

    NASA Astrophysics Data System (ADS)

    Chigvintsev, A. Yu; Iosilevskiy, I. L.; Noginova, L. Yu

    2016-11-01

    Anomalous phase diagrams in subclass of simplified (“non-associative”) Coulomb models is under discussion. The common feature of this subclass is absence on definition of individual correlations for charges of opposite sign. It is e.g. modified OCP of ions on uniformly compressible background of ideal Fermi-gas of electrons OCP(∼), or a superposition of two non-ideal OCP(∼) models of ions and electrons etc. In contrast to the ordinary OCP model on non-compressible (“rigid”) background OCP(#) two new phase transitions with upper critical point, boiling and sublimation, appear in OCP(∼) phase diagram in addition to the well-known Wigner crystallization. The point is that the topology of phase diagram in OCP(∼) becomes anomalous at high enough value of ionic charge number Z. Namely, the only one unified crystal- fluid phase transition without critical point exists as continuous superposition of melting and sublimation in OCP(∼) at the interval (Z 1 < Z < Z 2). The most remarkable is appearance of pseudo-critical points at both boundary values Z = Z 1 ≈ 35.5 and Z = Z 2 ≈ 40.0. It should be stressed that critical isotherm is exactly cubic in both these pseudo-critical points. In this study we have improved our previous calculations and utilized more complicated model components equation of state provided by Chabrier and Potekhin (1998 Phys. Rev. E 58 4941).

  10. The phase diagram of the square lattice bilayer Hubbard model: a variational Monte Carlo study

    NASA Astrophysics Data System (ADS)

    Rüger, Robert; Tocchio, Luca F.; Valentí, Roser; Gros, Claudius

    2014-03-01

    We investigate the phase diagram of the square lattice bilayer Hubbard model at half-filling with the variational Monte Carlo method for both the magnetic and the paramagnetic case as a function of the interlayer hopping {{t}_{\\bot }} and on-site Coulomb repulsion U. With this study we resolve some discrepancies in previous calculations based on the dynamical mean-field theory, and we are able to determine the nature of the phase transitions between metal, Mott insulator and band insulator. In the magnetic case we find only two phases: an antiferromagnetic Mott insulator at small {{t}_{\\bot }} for any value of U and a band insulator at large {{t}_{\\bot }}. At large U values we approach the Heisenberg limit. The paramagnetic phase diagram shows at small {{t}_{\\bot }} a metal to Mott insulator transition at moderate U values and a Mott to band insulator transition at larger U values. We also observe a re-entrant Mott insulator to metal transition and metal to band insulator transition for increasing {{t}_{\\bot }} in the range of 5.5t. Finally, we discuss the phase diagrams obtained in relation to findings from previous studies based on different many-body approaches.

  11. 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.

  12. Ab Initio Construction of Magnetic Phase Diagrams in Alloys: The Case of Fe1 -xMnx Pt

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

    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 Fe1 -xMnx 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.

  13. 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.

  14. 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

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

    DOE PAGES

    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

  16. 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.

  17. Au-Ge MEAM potential fitted to the binary phase diagram

    NASA Astrophysics Data System (ADS)

    Wang, Yanming; Santana, Adriano; Cai, Wei

    2017-02-01

    We have developed a modified embedded atom method potential for the gold-germanium (Au-Ge) binary system that is fitted to the experimental binary phase diagram. The phase diagram is obtained from the common tangent construction of the free energy curves calculated by the adiabatic switching method. While maintaining the accuracy of the melting points of pure Au and Ge, this potential reproduces the eutectic temperature, eutectic composition and the solubility of Ge in solid Au, all in good agreement with the experimental values. To demonstrate the self-consistency of the potential, we performed benchmark molecular dynamics simulations of Ge crystal growth and etching in contact with a Au-Ge liquid alloy.

  18. Analytical phase diagrams for colloids and non-adsorbing polymer.

    PubMed

    Fleer, Gerard J; Tuinier, Remco

    2008-11-04

    We review the free-volume theory (FVT) of Lekkerkerker et al. [Europhys. Lett. 20 (1992) 559] for the phase behavior of colloids in the presence of non-adsorbing polymer and we extend this theory in several aspects: (i) We take the solvent into account as a separate component and show that the natural thermodynamic parameter for the polymer properties is the insertion work Pi(v), where Pi is the osmotic pressure of the (external) polymer solution and v the volume of a colloid particle. (ii) Curvature effects are included along the lines of Aarts et al. [J. Phys.: Condens. Matt. 14 (2002) 7551] but we find accurate simple power laws which simplify the mathematical procedure considerably. (iii) We find analytical forms for the first, second, and third derivatives of the grand potential, needed for the calculation of the colloid chemical potential, the pressure, gas-liquid critical points and the critical endpoint (cep), where the (stable) critical line ends and then coincides with the triple point. This cep determines the boundary condition for a stable liquid. We first apply these modifications to the so-called colloid limit, where the size ratio q(R)=R/a between the radius of gyration R of the polymer and the particle radius a is small. In this limit the binodal polymer concentrations are below overlap: the depletion thickness delta is nearly equal to R, and Pi can be approximated by the ideal (van't Hoff) law Pi=Pi(0)=phi/N, where phi is the polymer volume fraction and N the number of segments per chain. The results are close to those of the original Lekkerkerker theory. However, our analysis enables very simple analytical expressions for the polymer and colloid concentrations in the critical and triple points and along the binodals as a function of q(R). Also the position of the cep is found analytically. In order to make the model applicable to higher size ratio's q(R) (including the so-called protein limit where q(R)>1) further extensions are needed. We

  19. 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.

  20. Zero Temperature Phase Diagram of an Asymmetric Spin Ladder

    NASA Astrophysics Data System (ADS)

    Capriotti, Luca; Becca, Federico; Parola, Alberto; Sorella, Sandro

    2003-03-01

    Asymmetric spin-half ladders (ASL) have recently attracted much theoretical interest due to possible experimental realizations in delafossite cuprates such as YCuO_2.5 [1] and the unusual physical effects that the asymmetry in the leg exchanges could introduce both in the ground-state correlations and in the properties of the excitation spectrum. Using conformal field theory and Lanczos exact diagonalizations, we demonstrate that for small frustration these systems are in a Luttinger spin-fluid phase, with gapless excitations, and a finite spin-wave velocity. In the regime of strong frustration, instead, the ground state is spontaneously dimerized and the bond alternation reduces the triplet gap, leading to a slight enhancement of the critical point separating the Luttinger phase from the gapped one. An accurate determination of the phase boundary, is obtained numerically from the study of the excitation spectrum. Our study completely clarifies the much debated zero-temperature phase diagram of the ASL model. [2] [1] G. Van Tendeloo, O. Garlea, C. Darie, C. Bougerol-Chaillout, and P. Bordet, J. Solid State Chem. 156, 428 (2001). [2] L. Capriotti, F. Becca, S. Sorella, and A. Parola, Phys. Rev. Lett. 89, 149701 (2002); to be published.

  1. Phase diagram of the interacting Majorana chain model

    NASA Astrophysics Data System (ADS)

    Rahmani, Armin; Zhu, Xiaoyu; Franz, Marcel; Affleck, Ian

    2015-12-01

    The Hubbard and spinless fermion chains are paradigms of strongly correlated systems, very well understood using the Bethe ansatz, density matrix renormalization group (DMRG), and field theory/renormalization group (RG) methods. They have been applied to one-dimensional materials and have provided important insights for understanding higher-dimensional cases. Recently, an interacting fermion model has been introduced, with possible applications to topological materials. It has a single Majorana fermion operator on each lattice site and interactions with the shortest possible range that involve four sites. We present a thorough analysis of the phase diagram of this model in one dimension using field-theory/RG and DMRG methods. It includes a gapped supersymmetric region and a gapless phase with coexisting Luttinger liquid and Ising degrees of freedom. In addition to a first-order transition, three critical points occur: tricritical Ising, Lifshitz, and a generalization of the commensurate-incommensurate transition. We also survey various gapped phases of the system that arise when the translation symmetry is broken by dimerization and find both trivial and topological phases with 0, 1, and 2 Majorana zero modes bound to the edges of the chain with open boundary conditions.

  2. Phase diagram of microcavity exciton-polariton condensates

    NASA Astrophysics Data System (ADS)

    Bui, Dinh-Hoi; Phan, Van-Nham

    2016-12-01

    In this work, we study the exciton-polariton condensate phase transition in a microcavity matter-light system in which electron-hole Coulomb interaction and matter-light coupling effects are treated on an equal footing. In the framework of the unrestricted Hartree-Fock approximation applying the two-dimensional exciton-polariton model, we derive the self-consistent equations determining simultaneously the excitonic and the photonic condenstate order parameters. In the thermal-equilibrium limit, we find a condensed state of the exciton-polariton systems and phase diagrams are then constructed. At a given low temperature, the condensate by its nature shows a crossover from an excitonic to a polaritonic and finally photonic condensed state as the excitation density increases at large detuning. Without the detuning, the excitonic condensed state disappears whereas the polaritonic or photonic phases dominate. The crossover is also found by lowering the Coulomb interaction at a finite matter-light coupling. Lowering the Coulomb interaction or increasing the temperature, the excitonic Mott transition occurs, at which the exciton-polariton condensates dissociate to free electron-hole/photon. Depending on temperature and excitation density, the phase transition of the exciton-polariton condensates is also addressed in signatures of photoluminescence mapping to the photonic momentum distribution.

  3. 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.

  4. Mean-field phase diagram of disordered bosons in a lattice at nonzero temperature

    NASA Astrophysics Data System (ADS)

    Krutitsky, K. V.; Pelster, A.; Graham, R.

    2006-09-01

    Bosons in a periodic lattice with on-site disorder at low but nonzero temperatures are considered within a mean-field theory. The criteria used for the definition of the superfluid, Mott insulator and Bose glass are analysed. Since the compressibility never vanishes at nonzero temperatures, it cannot be used as a general criterion. We show that the phases are unambiguously distinguished by the superfluid density and the density of states of the low-energy excitations. The phase diagram of the system is calculated. It is shown that even a tiny temperature leads to a significant shift of the boundary between the Bose glass and superfluid.

  5. 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.

  6. Phase diagram and superconductivity of compressed zirconium hydrides.

    PubMed

    Li, Xiao-Feng; Hu, Zi-Yu; Huang, Bing

    2017-02-01

    It is known that pressure can be applied to fundamentally alter the bonding patterns between the chemical elements. By employing an unbiased structure search method based on a particle swarm optimization (PSO) methodology, the phase diagram and crystal structures of Zr-H compounds are systematically investigated at a high pressure up to 150 GPa. Interestingly, some unexpectedly stable compounds with unusual chemical and physical properties are predicted to be formed, for example, four stable and metallic species with stoichiometries of ZrH, ZrH2, ZrH3, and ZrH6 are identified for the first time. It is interesting to note that Cmc21-ZrH6 adopts intriguing structures with H2 units. Surprisingly, it is found that Cmcm-ZrH is superconducting with Tc as high as 10.6 K. Our study opens a novel avenue for designing superconducting Zr-H compounds by applying pressure.

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

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

    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.

  8. 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.

  9. LETTER: Phase diagrams for DNA denaturation under stretching forces

    NASA Astrophysics Data System (ADS)

    Marenduzzo, D.; Maritan, A.; Orlandini, E.; Seno, F.; Trovato, A.

    2009-04-01

    Double-stranded DNA denaturation induced by an external force is modeled as a pair of complementary self-avoiding polymers with inter-strand binding potential. The resulting force-temperature phase diagram is determined using heuristic arguments, exactly solvable models and 3D Monte Carlo simulations. The results are qualitatively different for the cases where the force is applied to only one strand or to both strands. Crucial ingredients for getting a qualitative agreement with experimental results are the persistence lengths and the monomer sizes of single-stranded and double-stranded DNA. The subtle dependence of the small force behavior on the latter parameters, on the stretching mode and on the presence of denaturation bubbles is analyzed in detail.

  10. Universal phase diagrams with superconducting domes for electronic flat bands

    NASA Astrophysics Data System (ADS)

    Löthman, Tomas; Black-Schaffer, Annica M.

    2017-08-01

    Condensed matter systems with flat bands close to the Fermi level generally exhibit, due to their very large density of states, extraordinarily high critical ordering temperatures of symmetry-breaking orders, such as superconductivity and magnetism. Here we show that the critical temperatures follow one of two universal curves with doping away from a flat band depending on the ordering channel, which completely dictates both the general order competition and the phase diagram. Notably, we find that orders in the particle-particle channel (superconducting orders) survive decisively farther than orders in the particle-hole channel (magnetic or charge orders) because the channels have fundamentally different polarizabilities. Thus, even if a magnetic or charge order initially dominates, superconducting domes are still likely to exist on the flanks of flat bands. We apply these general results to both the topological surface flat bands of rhombohedral ABC-stacked graphite and to the Van Hove singularity of graphene.

  11. Cumulants and correlation functions versus the QCD phase diagram

    DOE PAGES

    Bzdak, Adam; Koch, Volker; Strodthoff, Nils

    2017-05-12

    Here, we discuss the relation of particle number cumulants and correlation functions. It is argued that measuring couplings of the genuine multiparticle correlation functions could provide cleaner information on possible nontrivial dynamics in heavy-ion collisions. We also extract integrated multiproton correlation functions from the presently available experimental data on proton cumulants. We find that the STAR data contain significant four-proton correlations, at least at the lower energies, with indication of changing dynamics in central collisions. We also find that these correlations are rather long ranged in rapidity. Finally, using the Ising model, we demonstrate how the signs of the multiprotonmore » correlation functions may be used to exclude certain regions of the phase diagram close to the critical point.« less

  12. A phase diagram for microfabrication of geometrically controlled hydrogel scaffolds.

    PubMed

    Tirella, A; Orsini, A; Vozzi, G; Ahluwalia, A

    2009-12-01

    Hydrogels are considered as excellent candidates for tissue substitutes by virtue of their high water content and biphasic nature. However, the fact that they are soft, wet and floppy renders them difficult to process and use as custom-designed scaffolds. To address this problem alginate hydrogels were modeled and characterized by measuring stress-strain and creep behavior as well as viscosity as a function of sodium alginate concentration, cross-linking time and calcium ion concentration. The gels were then microfabricated into scaffolds using the pressure-assisted microsyringe. The mechanical and viscous characteristics were used to generate a processing window in the form of a phase diagram which describes the fidelity of the scaffolds as a function of the material and machine parameters. The approach can be applied to a variety of microfabrication methods and biomaterials in order to design well-controlled custom scaffolds.

  13. Fabrication of Colloidal Laves Phases via Hard Tetramers and Hard Spheres: Bulk Phase Diagram and Sedimentation Behavior.

    PubMed

    Avvisati, Guido; Dasgupta, Tonnishtha; Dijkstra, Marjolein

    2017-08-22

    Colloidal photonic crystals display peculiar optical properties that make them particularly suitable for application in different fields. However, the low packing fraction of the targeted structures usually poses a real challenge in the fabrication stage. Here, we propose a route to colloidal photonic crystals via a binary mixture of hard tetramers and hard spheres. By combining theory and computer simulations, we calculate the phase diagram as well as the stacking diagram of the mixture and show that a colloidal analogue of the MgCu2 Laves phase-which can serve as a precursor of a photonic band-gap structure-is a thermodynamically stable phase in a large region of the phase diagram. Our findings show a relatively large coexistence region between the fluid and the Laves phase, which is potentially accessible by experiments. Furthermore, we determine the sedimentation behavior of the suggested mixture, by identifying several stacking sequences in the sediment. Our work uncovers a self-assembly path toward a photonic structure with a band gap in the visible region.

  14. Thermochemistry and phase diagram studies in the copper(indium,gallium)selenium system

    NASA Astrophysics Data System (ADS)

    Ider, Muhsin

    Polycrystalline Cu(In,Ga)Se2 and related semiconductors show great potential as alternative materials in production of high efficiency solar cells. This dissertation reports the experimental determination of Gibbs energy changes and phase diagram calculations for selected sections of the Cu-Ga-In-Se system. The Gibbs energy changes were measured with solid-state electrochemical cells and this data along with selected literature data were assessed and model parameters suggested. The homogeneity range of beta-Cu2-xSe was measured by coulometric titration and the thermodynamic properties for defect species estimated. The composition difference between the Se-rich and the Cu-rich boundaries was measured at 900K. A defect model was developed based on vacancy formation on the Cu sublattice. The gas phase equilibrium data for Cu-Se system and the results of a recent assessment of selenium unary system were used to predict defect concentrations. A thermodynamic description of the Cu2Se-In2Se 3 was obtained by optimization of the available phase equilibrium and thermodynamic information along with the direct results of EMF experiments. The Gibbs energy of formation of alpha-CuInSe2 was directly measured by a solid oxide galvanic cell experiment. The transformation enthalpy and Gibbs energy data for CuIn3Se5 and CuIn5Se 8 were estimated. The Redlich-Kister model with a 3-coefficient expression was employed to define the Gibbs energy of the liquid phase. The intermediate beta-CuIn 3Se5 and gamma-CuIn5Se8 phases were modeled with a 2-coefficient expansion of the Redlich-Kister model. The alpha and delta modifications of CuInSe2 phases were modeled with a specific sublattice model. A reasonable agreement between the model calculated values and the thermodynamic phase equilibrium data was achieved. The thermochemistry and phase diagram of GaSe system was critically studied. The activity of Ga was measured along the liquidus between 800--1000K. Selected invariant phase transition

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

    DOE PAGES

    Pujari, B. S.; Larson, P.; Antropov, V. P.; ...

    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

  16. 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.

  17. Magnetic field-temperature phase diagram of multiferroic [(CH3)2NH2] Mn (HCOO) 3

    NASA Astrophysics Data System (ADS)

    Clune, A. J.; Hughey, K. D.; Lee, C.; Abhyankar, N.; Ding, X.; Dalal, N. S.; Whangbo, M.-H.; Singleton, J.; Musfeldt, J. L.

    2017-09-01

    We combined pulsed field magnetization and first-principles spin-density calculations to reveal the magnetic field-temperature phase diagram and spin state character in multiferroic [(CH3)2NH2] Mn (HCOO) 3 . Despite similarities with the rare earth manganites, the phase diagram is analogous to other Mn-based quantum magnets with a 0.31 T spin flop, a 15.3 T transition to the fully polarized state, and short-range correlations that persist above the ordering temperature. The experimentally accessible saturation field opens the door to exploration of the high-field phase.

  18. Dynamical charge density waves rule the phase diagram of cuprates

    NASA Astrophysics Data System (ADS)

    Caprara, S.; Di Castro, C.; Seibold, G.; Grilli, M.

    2017-06-01

    In the last few years, charge density waves (CDWs) have been ubiquitously observed in high-temperature superconducting cuprates and are now the most investigated among the competing orders in the still hot debate on these systems. A wealth of new experimental data raises several fundamental issues that challenge the various theoretical proposals. We here relate our mean-field instability line TCDW0 of a strongly correlated Fermi liquid to the pseudogap T*(p ) line, marking in this way the onset of CDW-fluctuations. These fluctuations reduce strongly the mean-field critical line. Controlling this reduction via an infrared frequency cutoff related to the characteristic time of the probes, we account for the complex experimental temperature versus doping phase diagram. We provide a coherent scenario explaining why different CDW onset curves are observed by different experimental probes and seem to extrapolate at zero temperature into seemingly different quantum critical points (QCPs) in the intermediate and overdoped region. The nearly singular anisotropic scattering mediated by these fluctuations also accounts for the rapid changes of the Hall number seen in experiments and provides the first necessary step for a possible Fermi surface reconstruction fully establishing at lower doping. Finally, we show that phase fluctuations of the CDWs, which are enhanced in the presence of strong correlations near the Mott insulating phase, naturally account for the disappearance of the CDWs at low doping with yet another QCP as seen by the experiments.

  19. Determination of Phase Diagrams for Soluble and Membrane Protein Systems

    SciTech Connect

    Talreja, S.; Perry, S; Guha, S; Zukoski, C; Kenis, P

    2010-01-01

    Methods to efficiently determine the phase behavior of novel proteins have the potential to significantly benefit structural biology efforts. Here, we present protocols to determine both the solubility boundary and the supersolubility boundary for protein/precipitant systems using an evaporation-based crystallization platform. This strategy takes advantage of the well-defined rates of evaporation that occur in this platform to determine the state of the droplet at any point in time without relying on an equilibrium-based end point. The dynamic nature of this method efficiently traverses phase space along a known path, such that a solubility diagram can be mapped out for both soluble and membrane proteins while using a smaller amount of protein than what is typically used in optimization screens. Furthermore, a variation on this method can be used to decouple crystal nucleation and growth events, so fewer and larger crystals can be obtained within a given droplet. The latter protocol can be used to rescue a crystallization trial where showers of tiny crystals were observed. We validated both of the protocols to determine the phase behavior and the protocol to optimize crystal quality using the soluble proteins lysozyme and ribonuclease A as well as the membrane protein bacteriorhodopsin.

  20. 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 .

  1. 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.

  2. Determination of the Phase Diagram for Soluble and Membrane Proteins

    PubMed Central

    2010-01-01

    Methods to efficiently determine the phase behavior of novel proteins have the potential to significantly benefit structural biology efforts. Here, we present protocols to determine both the solubility boundary and the supersolubility boundary for protein/precipitant systems using an evaporation-based crystallization platform. This strategy takes advantage of the well-defined rates of evaporation that occur in this platform to determine the state of the droplet at any point in time without relying on an equilibrium-based end point. The dynamic nature of this method efficiently traverses phase space along a known path, such that a solubility diagram can be mapped out for both soluble and membrane proteins while using a smaller amount of protein than what is typically used in optimization screens. Furthermore, a variation on this method can be used to decouple crystal nucleation and growth events, so fewer and larger crystals can be obtained within a given droplet. The latter protocol can be used to rescue a crystallization trial where showers of tiny crystals were observed. We validated both of the protocols to determine the phase behavior and the protocol to optimize crystal quality using the soluble proteins lysozyme and ribonuclease A as well as the membrane protein bacteriorhodopsin. PMID:20235520

  3. 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.

  4. Sedimentation stacking diagram of binary colloidal mixtures and bulk phases in the plane of chemical potentials.

    PubMed

    de las Heras, Daniel; Schmidt, Matthias

    2015-05-20

    We give a full account of a recently proposed theory that explicitly relates the bulk phase diagram of a binary colloidal mixture to its phase stacking phenomenology under gravity (de las Heras and Schmidt 2013 Soft Matter 9 8636). As we demonstrate, the full set of possible phase stacking sequences in sedimentation-diffusion equilibrium originates from straight lines (sedimentation paths) in the chemical potential representation of the bulk phase diagram. From the analysis of various standard topologies of bulk phase diagrams, we conclude that the corresponding sedimentation stacking diagrams can be very rich, even more so when finite sample height is taken into account. We apply the theory to obtain the stacking diagram of a mixture of nonadsorbing polymers and colloids. We also present a catalog of generic phase diagrams in the plane of chemical potentials in order to facilitate the practical application of our concept, which also generalizes to multi-component mixtures.

  5. 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

  6. 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.

  7. a Thermodynamic Solution to the Iron-Phase Diagram

    NASA Astrophysics Data System (ADS)

    Saxena, S.; Belonoshko, A.; Eriksson, G.; Fries, S. G.

    2008-05-01

    Iron, being one of the most abundant elements in Earth with a suitable density, is recognized as the principal component of the core. There is intensified interest in study of iron at physical conditions of the core because of new developments in high pressure-temperature theoretical techniques. Iron occurs in four distinct polymorphs. Three (BCC body centered cubic, delta-BCC and FCC) are stable at one atmosphere and the fourth (HCP) phase at high pressures. We have combined all the available experimental and theoretical data to obtain a phase diagram of iron at core conditions. The thermodynamic data on all the solid phases and melt are assessed following Baysian optimization procedure. The goal was to account for the latest theoretical computations by one of us [1], according to which there should be a stability field of iron in the BCC structure at core conditions. Dubrovinsky et al [2] determined the BCC structure to be stable at 225 GPa and 3400 K for an Fe-Ni alloy. Our results show that a thermodynamic data description can be provided for such a BCC structure. For want of a distinct connection between the delta-BCC and this phase, we call it Theta-iron. The presence of theta-phase was postulated by Anderson to explain the large disparity between the temperatures of melting between shock wave data and the extrapolation from static pressure data. A formal thermodynamic treatment appears to suggest that a theta phase, with equilibrium boundaries against HCP phase melts at significantly higher temperatures than the HCP phase and can explain all the discrepancies encountered previously between the static pressure and some of the shock-wave data. The Theta-iron melts at ~6900 K at 360 GPa, providing a constraint on the inner core temperature. [1].Anatoly B. Belonoshko, Rajeev Ahuja and Borje Johansson, Stability of the body-centred-cubic phase of iron in the Earth's inner core, Nature, 424, 1032 (2003). [2]. L. Durovinsky et. al., Body-Cenetered Cubic Iron

  8. Thermodynamics at the nanoscale: phase diagrams of nickel-carbon nanoclusters and equilibrium constants for phase transitions.

    PubMed

    Engelmann, Yannick; Bogaerts, Annemie; Neyts, Erik C

    2014-10-21

    Using reactive molecular dynamics simulations, the melting behavior of nickel-carbon nanoclusters is examined. The phase diagrams of icosahedral and Wulff polyhedron clusters are determined using both the Lindemann index and the potential energy. Formulae are derived for calculating the equilibrium constants and the solid and liquid fractions during a phase transition, allowing more rational determination of the melting temperature with respect to the arbitrary Lindemann value. These results give more insight into the properties of nickel-carbon nanoclusters in general and can specifically be very useful for a better understanding of the synthesis of carbon nanotubes using the catalytic chemical vapor deposition method.

  9. Fabrication of Colloidal Laves Phases via Hard Tetramers and Hard Spheres: Bulk Phase Diagram and Sedimentation Behavior

    PubMed Central

    2017-01-01

    Colloidal photonic crystals display peculiar optical properties that make them particularly suitable for application in different fields. However, the low packing fraction of the targeted structures usually poses a real challenge in the fabrication stage. Here, we propose a route to colloidal photonic crystals via a binary mixture of hard tetramers and hard spheres. By combining theory and computer simulations, we calculate the phase diagram as well as the stacking diagram of the mixture and show that a colloidal analogue of the MgCu2 Laves phase—which can serve as a precursor of a photonic band-gap structure—is a thermodynamically stable phase in a large region of the phase diagram. Our findings show a relatively large coexistence region between the fluid and the Laves phase, which is potentially accessible by experiments. Furthermore, we determine the sedimentation behavior of the suggested mixture, by identifying several stacking sequences in the sediment. Our work uncovers a self-assembly path toward a photonic structure with a band gap in the visible region. PMID:28787126

  10. A Closer Look at Phase Diagrams for the General Chemistry Course.

    ERIC Educational Resources Information Center

    Gramsch, Stephen A.

    2000-01-01

    Information concerning structural chemistry and phase equilibria contained in the full phase diagrams of common substances is a great deal richer than the general chemistry students are given to believe. Discusses ways of enriching the traditional presentation of phase diagrams in general chemistry courses. (Contains over 20 references.) (WRM)

  11. 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

  12. 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.

  13. 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.

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

    PubMed

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

    2015-09-04

    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.

  15. Schaeffler-Type Phase Diagram of Ti-Based Alloys

    NASA Astrophysics Data System (ADS)

    Ishida, K.

    2017-07-01

    The α(hcp)/β(bcc) phase equilibria of Ti-based multi-component alloys can be described by a Schaeffler-type diagram, where Al and Mo equivalents (Aleq and Moeq) are used. Aleq is thermodynamically defined by the ratio of partial molar free energy changes transfer of one mole of each α forming element and Al from a dilute solution of α to β phases, while Moeq is also deduced by similar thermodynamic quantities of β forming element and Mo. Aleq and Moeq for 40 alloying elements are estimated from the thermodynamic parameters assessed by Kaufman and Murray. It is shown that three types of Ti alloys, i.e., α and near α, α+β, and β alloys, can be exactly classified using Aleq and Moeq. The Ms and β transus temperatures can also be predicted by Aleq and Moeq. The proposed Aleq and Moeq are very useful for alloy design, heat treatment, and microstructural evolution of Ti-based alloys.

  16. 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

  17. Schaeffler-Type Phase Diagram of Ti-Based Alloys

    NASA Astrophysics Data System (ADS)

    Ishida, K.

    2017-10-01

    The α(hcp)/β(bcc) phase equilibria of Ti-based multi-component alloys can be described by a Schaeffler-type diagram, where Al and Mo equivalents (Aleq and Moeq) are used. Aleq is thermodynamically defined by the ratio of partial molar free energy changes transfer of one mole of each α forming element and Al from a dilute solution of α to β phases, while Moeq is also deduced by similar thermodynamic quantities of β forming element and Mo. Aleq and Moeq for 40 alloying elements are estimated from the thermodynamic parameters assessed by Kaufman and Murray. It is shown that three types of Ti alloys, i.e., α and near α, α+β, and β alloys, can be exactly classified using Aleq and Moeq. The Ms and β transus temperatures can also be predicted by Aleq and Moeq. The proposed Aleq and Moeq are very useful for alloy design, heat treatment, and microstructural evolution of Ti-based alloys.

  18. Phase diagram of split 2D dipolar spin ice

    NASA Astrophysics Data System (ADS)

    Roscilde, Tommaso; Henry, Louis-Paul

    2013-03-01

    Long-ranged dipolar interactions, which are very natural in artificial square-lattice spin ice, can mask some of the most relevant aspects of spin-ice physics, as they remove the extensive degeneracy of the ground state manifold to give a unique ground state, and they bind monopole pairs into localized spin flips. Following an earlier idea of G. Möller and R. Moessner [Phys. Rev. Lett. 96, 237202 (2006)] we investigate how adding a third direction to square ice allows to recover fundamental traits of spin-ice physics even in the presence of dipolar interactions. Using Monte Carlo simulations based on a generalized loop algorithm, we explore the phase diagram of square dipolar spin ice in which horizontal and vertical dipoles are spatially separated in a third direction (split 2D spin ice). As a function of the splitting we recover a two-fold degenerate staggered state for coplanar dipoles, and a four-fold degenerate ``Manhattan'' state for strongly split dipoles, separated by a first order transition. The competition between the two states at intermediate splitting leads to a strong suppression of the ordering transition temperatures, and makes space for the observation of a hallmark of spin-ice physics in the paramagnetic phase: pinch points in the static structure factor.

  19. Reinvestigation of the Cd-Gd phase diagram.

    PubMed

    Reichmann, Thomas L; Ipser, Herbert

    2014-12-25

    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.

  20. Direct use of the chemical potential function in thermodynamic modeling of alloy phase diagrams

    NASA Astrophysics Data System (ADS)

    Kundrat, D. M.

    1986-08-01

    A modeling procedure for obtaining thermodynamic parameters from a limited knowledge of the phase diagram and a thermodynamic description of the participating phases is described. The procedure is to calculate compositions and parameters from specified compositions and parameters in a thermodynamic model employing the chemical potential function directly. Several calculations in the Fe-C and Fe-Cr-C systems are made for illustration. These results demonstrate for the two-phase equilibrium that only one phase boundary, or the partition ratio of each solute, and the thermodynamic parameter(s) for one of the phases need to be specified to calculate the other phase boundary and the thermodynamic parameter(s) for the other phase. The results for the Fe-C and Fe-Cr-C systems, for which the specified quantities were either the composition of the liquidus, or the partition ratios of the solute elements and temperature, and the parameter(s) for the liquid phase for the regular and quasi-regular solution models, are in good agreement with the results obtained by an error-minimization method.

  1. Inhomogeneous hard-core bosonic mixture with checkerboard supersolid phase: Quantum and thermal phase diagram

    NASA Astrophysics Data System (ADS)

    Heydarinasab, F.; Abouie, J.

    2017-09-01

    We introduce an inhomogeneous bosonic mixture composed of two kinds of hard-core and semi-hard-core bosons with different nilpotency conditions and demonstrate that in contrast with the standard hard-core Bose-Hubbard model, our bosonic mixture with nearest- and next-nearest-neighbor interactions on a square lattice develops the checkerboard supersolid phase characterized by the simultaneous superfluid and checkerboard solid orders. Our bosonic mixture is created from a two-orbital Bose-Hubbard model including two kinds of bosons: a single-orbital boson and a two-orbital boson. By mapping the bosonic mixture to an anisotropic inhomogeneous spin model in the presence of a magnetic field, we study the ground-state phase diagram of the model by means of cluster mean field theory and linear spin-wave theory and show that various phases such as solid, superfluid, supersolid, and Mott insulator appear in the phase diagram of the mixture. Competition between the interactions and magnetic field causes the mixture to undergo different kinds of first- and second-order phase transitions. By studying the behavior of the spin-wave excitations, we find the reasons of all first- and second-order phase transitions. We also obtain the temperature phase diagram of the system using cluster mean field theory. We show that the checkerboard supersolid phase persists at finite temperature comparable with the interaction energies of bosons.

  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. 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.

  4. 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…

  5. 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.

  6. Employing Fluid Inclusions as an Application of Phase Diagrams and an Introduction to Geothermobarometry

    NASA Astrophysics Data System (ADS)

    Farver, J. R.; Onasch, C. M.

    2003-12-01

    One of the ongoing challenges in petrology course development is designing meaningful student learning activities that promote understanding of phase diagrams and their application to relevant geologic processes. In addition, an important component of a modern petrology course is to provide a foundation in the methods employed to establish temperature and pressure conditions during geologic events. We have developed a laboratory exercise wherein students analyze fluid inclusions (water + NaCl) in natural samples of quartz or fluorite. Using a USGS-type fluid inclusion stage, the students observe the heating and cooling behavior of the fluid inclusions and measure the temperatures of homogenization, last ice melting, and the eutectic. In this fashion, students can attach a physical meaning to the phase diagram of water + NaCl that they determined in a previous laboratory exercise (after Brady, 1992, JGE, v.40, p.116-118). Each student collects a set of data that they then combine with the data of their colleagues to produce histograms that they must interpret. The second component of the exercise is to fix the trapping temperature and pressure of the fluid inclusions. Using the data they collect, students calculate the isochore and plot it on a P-T diagram. They also plot the lithostatic and hydrostatic pressure gradients for a given geothermal gradient on the P-T diagram. At this point, additional information on the geologic/tectonic setting of the sample can be provided so that students can consider the overall P-T history of the sample/region. We typically use samples containing both primary and secondary inclusions to illustrate the utility of fluid inclusions to fix P-T conditions during mineral growth as well as later tectonic events. This leads to a general discussion of geothermometric/barometric systems and the requisite assumptions and limitations of the different techniques currently employed. In addition to providing students with a hands-on opportunity

  7. The Earth's Core and the Phase Diagram of Iron

    NASA Astrophysics Data System (ADS)

    Anderson, O. L.

    1982-08-01

    The phase diagram of iron is presented for P <= 330 GPa. The melting curve is derived from Stevenson's generalized form of Lindemann's law, successfully connecting the low-pressure (5-20 GPa) measurements to the new shock-wave measurements of 250 GPa. The isothermal equation of state of ɛ -iron (h.c.p.) and γ -iron (f.c.c.), indicate that the inner core density is that of pure solid iron. The present experiments cannot distinguish between the ɛ or γ phase for the inner core, but preference is given to γ -iron. From these constructions, it is concluded that the melting temperature of iron at the inner core - outer core boundary pressure, Tmi (i.c.b.), is 5200-6600 K. A likely model of the outer core temperature is presented by taking 5800 K as the probable value of Tmi (i.c.b.), and assuming a temperature drop of 1000 K due to chemically induced melting point depression. This yields 3620 K for the T of the core side of the core-mantle boundary (c.m.b.). This model results in a large Δ T (D' '), (700 K), at the c.m.b., but the shock-wave data also allow other models where Δ T (D' ') is less. A numerical experiment reveals that the value for Δ T (D' ') of 700 K does not lead to distortion of the density profile. The (γ -ɛ -liquid) triple point is beyond the i.c.b. Thus, diluted γ -iron in the liquid phase constitutes the outer core. The experiments support a thermally driven model of the geomagnetic dynamo, and further support a model of a slowly freezing inner core for the energy source.

  8. High-field phase-diagram of Fe arsenide superconductors

    NASA Astrophysics Data System (ADS)

    Jo, Y. J.; Jaroszynski, J.; Yamamoto, A.; Gurevich, A.; Riggs, S. C.; Boebinger, G. S.; Larbalestier, D.; Wen, H. H.; Zhigadlo, N. D.; Katrych, S.; Bukowski, Z.; Karpinski, J.; Liu, R. H.; Chen, H.; Chen, X. H.; Balicas, L.

    2009-05-01

    Here, we report an overview of the phase-diagram of single-layered and double-layered Fe arsenide superconductors at high magnetic fields. Our systematic magneto-transport measurements of polycrystalline SmFeAsO 1- xF x at different doping levels confirm the upward curvature of the upper critical magnetic field Hc2 ( T) as a function of temperature T defining the phase boundary between the superconducting and metallic states for crystallites with the ab planes oriented nearly perpendicular to the magnetic field. We further show from measurements on single-crystals that this feature, which was interpreted in terms of the existence of two superconducting gaps, is ubiquitous among both series of single- and double-layered compounds. In all compounds explored by us the zero temperature upper critical field Hc2 (0), estimated either through the Ginzburg-Landau or the Werthamer-Helfand-Hohenberg single gap theories, strongly surpasses the weak-coupling Pauli paramagnetic limiting field. This clearly indicates the strong-coupling nature of the superconducting state and the importance of magnetic correlations for these materials. Our measurements indicate that the superconducting anisotropy, as estimated through the ratio of the effective masses γ = ( mc/ mab) 1/2 for carriers moving along the c-axis and the ab-planes, respectively, is relatively modest as compared to the high- Tc cuprates, but it is temperature, field and even doping dependent. Finally, our preliminary estimations of the irreversibility field Hm( T), separating the vortex-solid from the vortex-liquid phase in the single-layered compounds, indicates that it is well described by the melting of a vortex lattice in a moderately anisotropic uniaxial superconductor.

  9. Pourbaix diagrams of alkaline earth metal elements by combination of first principles calculations and thermochemical data

    NASA Astrophysics Data System (ADS)

    Suzuki, T.; Mori, M.; Matsunaga, K.; Tanaka, I.

    2010-09-01

    Based on first principles calculations for crystals and experimental thermochemical data for aqueous solutions and molecules, Pourbaix diagrams of alkaline earth metal systems at 298.15 K are constructed. Phonon frequencies are computed for all crystals of interests by the first principles method. Then individual contributions of zero-point energies and vibrational free energies are examined. The contribution of the zero-point energy is found to be 7-8% of the total formation free energy at 298.15 K in hydroxides, which can be ascribed to the presence of high frequency OH stretching modes. The agreements between computed and experimental Pourbaix diagrams are quite satisfactory.

  10. Pourbaix diagrams of alkaline earth metal elements by combination of first principles calculations and thermochemical data.

    PubMed

    Suzuki, T; Mori, M; Matsunaga, K; Tanaka, I

    2010-09-29

    Based on first principles calculations for crystals and experimental thermochemical data for aqueous solutions and molecules, Pourbaix diagrams of alkaline earth metal systems at 298.15 K are constructed. Phonon frequencies are computed for all crystals of interests by the first principles method. Then individual contributions of zero-point energies and vibrational free energies are examined. The contribution of the zero-point energy is found to be 7-8% of the total formation free energy at 298.15 K in hydroxides, which can be ascribed to the presence of high frequency OH stretching modes. The agreements between computed and experimental Pourbaix diagrams are quite satisfactory.

  11. Finite-Temperature Phase Diagram of the d=3 tJ Model with Quenched Disorder

    NASA Astrophysics Data System (ADS)

    Berker, A. Nihat; Hinczewski, Michael

    2008-03-01

    We study a quenched disordered d=3 tJ Hamiltonian with static vacancies as a model of nonmagnetic impurities in high-Tc materials.[1,2] Using a position-space renormalization-group approach, we calculate the evolution of the finite-temperature phase diagram with impurity concentration p, and find several features with close experimental parallels: away from half-filling we see the rapid destruction of a spin-singlet liquid phase (analogous to the superconducting phase in cuprates) which is eliminated for p >=0.05; in the same region for these dilute impurity concentrations we observe an enhancement of antiferromagnetism. The antiferromagnetic phase near half-filling is robust against impurity addition, and disappears only for p >=0.40. [1] M. Hinczewski and A.N. Berker, Eur. Phys. J. B 51, 461 (2006). [2] M. Hinczewski and A.N. Berker, arXiv:cond-mat/0607171v1 [cond-mat.str-el].

  12. 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.

  13. 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.

  14. Theoretical Prediction of Melting Relations in the Deep Mantle: the Phase Diagram Approach

    NASA Astrophysics Data System (ADS)

    Belmonte, D.; Ottonello, G. A.; Vetuschi Zuccolini, M.; Attene, M.

    2016-12-01

    Despite the outstanding progress in computer technology and experimental facilities, understanding melting phase relations in the deep mantle is still an open challenge. In this work a novel computational scheme to predict melting relations at HP-HT by a combination of first principles DFT calculations, polymer chemistry and equilibrium thermodynamics is presented and discussed. The adopted theoretical framework is physically-consistent and allows to compute multi-component phase diagrams relevant to Earth's deep interior in a broad range of P-T conditions by a convex-hull algorithm for Gibbs free energy minimisation purposely developed for high-rank simplexes. The calculated phase diagrams are in turn used as a source of information to gain new insights on the P-T-X evolution of magmas in the deep mantle, providing some thermodynamic constraints to both present-day and early Earth melting processes. High-pressure melting curves of mantle silicates are also obtained as by-product of phase diagram calculation. Application of the above method to the MgO-Al2O3-SiO2 (MAS) ternary system highlights as pressure effects are not only able to change the nature of melting of some minerals (like olivine and pyroxene) from eutectic to peritectic (and vice versa), but also simplify melting relations by drastically reducing the number of phases with a primary phase field at HP-HT conditions. It turns out that mineral phases like Majorite-Pyrope garnet and Anhydrous Phase B (Mg14Si5O24), which are often disregarded in modelling melting processes of mantle assemblages, are stable phases at solidus or liquidus conditions in a P-T range compatible with the mantle transition zone (i.e. P = 16 - 23 GPa and T = 2200 - 2700 °C) when their thermodynamic and thermophysical properties are properly assessed. Financial support to the Senior Author (D.B.) during his stay as Invited Scientist at the Institut de Physique du Globe de Paris (IPGP, Paris) is warmly acknowledged.

  15. Predicting solubilisation features of ternary phase diagrams of fully dilutable lecithin linker microemulsions.

    PubMed

    Nouraei, Mehdi; Acosta, Edgar J

    2017-06-01

    Fully dilutable microemulsions (μEs), used to design self-microemulsifying delivery system (SMEDS), are formulated as concentrate solutions containing oil and surfactants, without water. As water is added to dilute these systems, various μEs are produced (water-swollen reverse micelles, bicontinuous systems, and oil-swollen micelles), without the onset of phase separation. Currently, the formulation dilutable μEs follows a trial and error approach that has had a limited success. The objective of this work is to introduce the use of the hydrophilic-lipophilic-difference (HLD) and net-average-curvature (NAC) frameworks to predict the solubilisation features of ternary phase diagrams of lecithin-linker μEs and the use of these predictions to guide the formulation of dilutable μEs. To this end, the characteristic curvatures (Cc) of soybean lecithin (surfactant), glycerol monooleate (lipophilic linker) and polyglycerol caprylate (hydrophilic linker) and the equivalent alkane carbon number (EACN) of ethyl caprate (oil) were obtained via phase scans with reference surfactant-oil systems. These parameters were then used to calculate the HLD of lecithin-linkers-ethyl caprate microemulsions. The calculated HLDs were able to predict the phase transitions observed in the phase scans. The NAC was then used to fit and predict phase volumes obtained from salinity phase scans, and to predict the solubilisation features of ternary phase diagrams of the lecithin-linker formulations. The HLD-NAC predictions were reasonably accurate, and indicated that the largest region for dilutable μEs was obtained with slightly negative HLD values. The NAC framework also predicted, and explained, the changes in microemulsion properties along dilution lines. Copyright © 2017 Elsevier Inc. All rights reserved.

  16. Phase diagrams and dynamics of a computationally efficient map-based neuron model

    PubMed Central

    Gonsalves, Jheniffer J.; Tragtenberg, Marcelo H. R.

    2017-01-01

    We introduce a new map-based neuron model derived from the dynamical perceptron family that has the best compromise between computational efficiency, analytical tractability, reduced parameter space and many dynamical behaviors. We calculate bifurcation and phase diagrams analytically and computationally that underpins a rich repertoire of autonomous and excitable dynamical behaviors. We report the existence of a new regime of cardiac spikes corresponding to nonchaotic aperiodic behavior. We compare the features of our model to standard neuron models currently available in the literature. PMID:28358843

  17. Phase diagram of the system with the repulsive shoulder potential in two dimensions: Density functional approach

    NASA Astrophysics Data System (ADS)

    Chumakov, E. S.; Fomin, Y. D.; Shangina, E. L.; Tareyeva, E. E.; Tsiok, E. N.; Ryzhov, V. N.

    2015-08-01

    In the framework of the density functional theory of freezing proposed in our previous works, we calculate the phase diagram of two-dimensional system of particles interacting through the repulsive shoulder potential. This potential consists of the hard core and repulsive shoulder of the larger radius. It is shown that at low densities the system melts through the continuous transition in accordance with the Kosterlitz-Thouless-Halperin-Nelson-Young (KTHNY) scenario, while at high densities the conventional first order transition takes place.

  18. Nanoalloy composition-temperature phase diagram for catalyst design: Case study of Ag-Au

    SciTech Connect

    Wang, Lin-Lin; Tan, Teck L.; Johnson, Duane D.

    2012-07-23

    By coupling a cluster expansion with density functional theory (DFT) calculations, we determine the configurational thermodynamics (site preferences and occupations) for alloyed nanoparticles (NPs) as functions of composition (c) and temperature (T), exemplified using a 55-atom Ag-Au truncated cuboctahedron NP. The c-T phase diagram for site occupations gives detailed design information for alloyed NP, especially the thermodynamically stable active sites for catalysis and how they change with stoichiometry and processing temperature. Generally, Ag prefers core and Au prefers shell, agreeing with our universal core-shell preference assessed from DFT impurity segregation energies but with interesting multishell configurations having specific active sites.

  19. Phase diagrams of the quantum XY spin glass model in a transverse field

    NASA Astrophysics Data System (ADS)

    Büttner, G.; Kopeć, T. K.; Usadel, K. D.

    1990-10-01

    The infinite range XY spin glass model in a transverse field Γ is investigated by means of the static approximation within the Trotter-Suzuki approach and thermo-field dynamics. The corresponding phase diagrams are obtained showing that a spin glass transition takes place for non-zero values of the transverse field up to a critical value. However, it is found that the results from both methods disagree considerably from recent calculations by De Cesare et al. on this model, performed by using the two-spin cluster approximation.

  20. Structural Phase Diagrams for Dendrimer:DNA Complexes

    NASA Astrophysics Data System (ADS)

    Evans, Heather M.; Ahmad, A.; Pfohl, T.; Martin, A.; Safinya, C. R.

    2002-03-01

    Polypropylene imine (PPI) dendrimers become positively charged in aqueous solution and are consequently a useful tool for packaging DNA in gene delivery applications. Studies of PPI and DNA help to improve the efficiency of DNA delivery as well as model more complex biological systems such as histones. PPI is synthesized in a stepwise manner, and at each step the product is referred to as a generation (G1 through G5). We show structural phase diagrams based on synchrotron x-ray diffraction as a function of PPI/DNA charge ratio (P/D). At lower generations PPI bundling with DNA is similar to DNA condensation caused by small multivalent salts such as spermidine. Remarkably, for G4 and G5 distinct structural transitions are seen with increasing P/D. In particular, G4:DNA complexes show a salt-like bundling at low P/D, followed by both square and hexagonal lattices with addition of PPI. Optical microscopy and supporting size and charge measurements will also be shown. Funding provided by NIH GM59288 and NSF DMR-9972246.

  1. 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.

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

    PubMed

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

    2014-06-03

    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.

  3. Coformer screening using thermal analysis based on binary phase diagrams.

    PubMed

    Yamashita, Hiroyuki; Hirakura, Yutaka; Yuda, Masamichi; Terada, Katsuhide

    2014-08-01

    The advent of cocrystals has demonstrated a growing need for efficient and comprehensive coformer screening in search of better development forms, including salt forms. Here, we investigated a coformer screening system for salts and cocrystals based on binary phase diagrams using thermal analysis and examined the effectiveness of the method. Indomethacin and tenoxicam were used as models of active pharmaceutical ingredients (APIs). Physical mixtures of an API and 42 kinds of coformers were analyzed using Differential Scanning Calorimetry (DSC) and X-ray DSC. We also conducted coformer screening using a conventional slurry method and compared these results with those from the thermal analysis method and previous studies. Compared with the slurry method, the thermal analysis method was a high-performance screening system, particularly for APIs with low solubility and/or propensity to form solvates. However, this method faced hurdles for screening coformers combined with an API in the presence of kinetic hindrance for salt or cocrystal formation during heating or if there is degradation near the metastable eutectic temperature. The thermal analysis and slurry methods are considered complementary to each other for coformer screening. Feasibility of the thermal analysis method in drug discovery practice is ensured given its small scale and high throughput.

  4. 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.

  5. A thermal analysis method to predict the complete phase diagram of drug-polymer solid dispersions.

    PubMed

    Lin, Dexi; Huang, Yanbin

    2010-10-31

    The aim of this work was to develop a method which uses experimentally obtainable data to predict the complete phase diagram of drug-polymer solid dispersion systems, for the first time in literature. Felodipine-poly(acrylic acid) (PAA) solid dispersion was used as an example to illustrate the application of this method. Samples were prepared with different drug loading and analyzed using differential scanning calorimetry (DSC). Values of the drug-polymer interaction parameter χ(T(m)) were calculated from the drug crystal melting point depression data. Since χ is a function of temperature (χ∼1/T) according to the Flory-Huggins theory, the obtained χ-T relationship thus enabled calculation of the complete temperature-composition phase diagram of a drug-polymer solid dispersion system. In experiments, felodipine was shown to be immiscible with PAA in almost the whole range of drug content at room temperature. Two glass transition temperatures were observed, corresponding to almost pure felodipine and pure PAA, respectively, in consistent with the predicted phase behavior. Copyright © 2010 Elsevier B.V. All rights reserved.

  6. 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…

  7. 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…

  8. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

    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.

  10. 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.

  11. Anderson Localization and the Quantum Phase Diagram of Three Dimensional Disordered Dirac Semimetals

    NASA Astrophysics Data System (ADS)

    Pixley, J. H.; Goswami, Pallab; Das Sarma, S.

    2015-08-01

    We study the quantum phase diagram of a three dimensional noninteracting Dirac semimetal in the presence of either quenched axial or scalar potential disorder, by calculating the average and the typical density of states as well as the inverse participation ratio using numerically exact methods. We show that as a function of the disorder strength a half-filled (i.e., undoped) Dirac semimetal displays three distinct ground states, namely an incompressible semimetal, a compressible diffusive metal, and a localized Anderson insulator, in stark contrast to a conventional dirty metal that only supports the latter two phases. We establish the existence of two distinct quantum critical points, which respectively govern the semimetal-metal and the metal-insulator quantum phase transitions and also reveal their underlying multifractal nature. Away from half-filling the (doped) system behaves as a diffusive metal that can undergo Anderson localization only, which is shown by determining the mobility edge and the phase diagram in terms of energy and disorder.

  12. The Pressure-Temperature Phase Diagram of Metacetamol and Its Comparison to the Phase Diagram of Paracetamol.

    PubMed

    Barrio, Maria; Huguet, Judit; Rietveld, Ivo B; Robert, Benoît; Céolin, René; Tamarit, Josep-Lluis

    2017-06-01

    Understanding the polymorphic behavior of active pharmaceutical ingredients is important for formulation purposes and regulatory reasons. Metacetamol is an isomer of paracetamol and it similarly exhibits polymorphism. In the present article, it has been found that one of the polymorphs of metacetamol is only stable under increased pressure, which has led to the conclusion that metacetamol like paracetamol is a monotropic system under ordinary (= laboratory) conditions and that it becomes enantiotropic under pressure with the I-II-L triple point coordinates for metacetamol TI-II-L = 535 ± 10 K and PI-II-L = 692 ± 70 MPa. However, whereas for paracetamol the enantiotropy under pressure can be foreseen, because the metastable polymorph is denser, in the case of metacetamol this is not possible, as the metastable polymorph is less dense than the stable one. The existence of the stability domain for the less dense polymorph of metacetamol can only be demonstrated by the construction of the topological phase diagram as presented in this article. It is a delicate interplay between the specific volume differences and the enthalpy differences causing the stability domain of the less dense polymorph to be sandwiched between the denser polymorph and the liquid. Metacetamol shares this behavior with bicalutamide and fluoxetine nitrate. Copyright © 2017 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.

  13. The phase diagram of molybdenum at extreme conditions and the role of local liquid structures

    SciTech Connect

    Ross, M

    2008-08-15

    Recent DAC measurements made of the Mo melting curve by the x-ray diffraction studies confirms that, up to at least 110 GPa (3300K) melting is directly from bcc to liquid, evidence that there is no basis for a speculated bcc-hcp or fcc transition. An examination of the Poisson Ratio, obtained from shock sound speed measurements, provides evidence that the 210 GPa (4100K) transition detected from shock experiments is a continuation of the bcc-liquid melting, but is from a bcc-to a solid-like mixed phase rather than to liquid. Calculations, modeled to include the free energy of liquid local structures, predict that the transition from the liquid to the mixed phase is near 150 GPa(3500K). The presence of local structures provides the simplest and most direct explanation for the Mo phase diagram, and the low melting slopes.

  14. Phase diagram with a region of liquid carbon-diamond metastable states

    NASA Astrophysics Data System (ADS)

    Basharin, A. Yu.; Dozhdikov, V. S.; Kirillin, A. V.; Turchaninov, M. A.; Fokin, L. R.

    2010-06-01

    Metastable cubic diamond has been found in the structure of solid carbon obtained by quenching of a liquid phase at a pressure (0.012 GPa) much lower than that corresponding to the existence of stable diamond. It is suggested that this metastable diamond is formed as a result of the recalescence of supercooled liquid carbon to the melting point ( T dm) of metastable diamond due to a lower energy barrier for the formation of diamond as compared to that of graphite. A comparison between the calculated Gibbs energies of metastable phases provided an estimate of T dm = 4160 ± 50 K. For the first time, metastable continuations of the curve of diamond melting at pressures of up to 0.012 GPa are constructed on the phase diagrams of carbon (according to various published data) using analytical curves described by a two-parametric Simon equation.

  15. 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

  16. 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.

  17. Phase diagram and surface tension of the hard-core attractive Yukawa model of variable range: Monte Carlo simulations.

    PubMed

    Duda, Yurko; Romero-Martínez, Ascención; Orea, Pedro

    2007-06-14

    The liquid-vapor phase diagram and surface tension for hard-core Yukawa potential with 4calculated by applying canonical Monte Carlo simulation. The authors' new simulation results are more precise than those reported before, which allows them to affirm the accuracy of the previously reported self-consistent Ornstein-Zernike approximation calculations for kappa=5 and 7.

  18. Force-Field Based Quasi-Chemical Method for Rapid Evaluation of Binary Phase Diagrams.

    PubMed

    Sweere, Augustinus J M; Fraaije, Johannes G E M

    2015-11-05

    We present the Pair Configurations to Molecular Activity Coefficients (PAC-MAC) method. The method is based on the pair sampling technique of Blanco (Fan, C. F.; Olafson, B. D.; Blanco, M.; Hsu, S. L. Application of Molecular Simulation to Derive Phase Diagrams of Binary Mixtures. Macromolecules 1992, 25, 3667-3676) with an extension that takes the packing of the molecules into account by a free energy model. The intermolecular energy is calculated using classical force fields. PAC-MAC is able to predict activity coefficients and corresponding vapor-liquid equilibrium diagrams at least 4 orders of magnitude faster than molecular simulations. The accuracy of the PAC-MAC method is tested by comparing the results with experimental data and with the results of the COSMO-SAC model (Lin, S.-T.; Sandler, S. I. A Priori Phase Equilibrium Prediction from a Segment Contribution Solvation Model. Ind. Eng. Chem. Res. 2002, 41, 899-913). PAC-MAC (using the OPLS-aa force field) is shown to be comparable in accuracy to COSMO-SAC, at the considerable advantage that PAC-MAC in principle does not require quantum calculation, provided proper force fields to be available.

  19. Closed-loop phase diagrams, vaporization, and multicriticality in binary liquid mixtures

    NASA Astrophysics Data System (ADS)

    Caflisch, Robert G.; Walker, James S.

    1983-09-01

    The coupled Potts-Ising models of Walker and Vause, which successfully describe closed-loop phase diagrams in hydrogen-bonding mixtures, are generalized to encompass the vapor phase, and are studied using position-space renormalization-group techniques. Global phase diagrams are generated, exhibiting such features as miscibility-immiscibility criticality, liquid-vapor critical points, critical end points, and bicritical and tricritical points. In addition, new types of phase diagrams are found, involving upper and lower azeotropes, for example, which are expected to be physically realizable in experimental systems.

  20. Phase Diagram of Iron, Revised-Core Temperatures

    SciTech Connect

    Ahrens, T.J.; Chen, G.Q.; Holland, K.G.

    1999-01-27

    Shock-wave experiments on iron preheated to 1,573 K conducted from 14 to 73 GPa, yield new data for sound velocities of the {gamma}- and liquid-phases. Melting was observed in the highest pressure ({approximately} 71 {+-} 2 GPa) experiments at calculated shock temperatures of 2,775 {+-} 160 K. This single crossing of the {gamma}-liquid boundary measured here agrees closely with the {gamma}-iron melting line determined by Boehler [1993], Saxena et al. [1993], and Jephcoat and Besedin [1997]. This {gamma}-iron melting curve is {approximately} 300 C lower than that of Shen et al. [1998b] at 80 GPa.

  1. 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.

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

    PubMed

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

    2016-08-07

    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.

  3. Thermodynamic studies and the phase diagram of the Li-Mg system

    SciTech Connect

    Gasior, W.; Moser, Z.; Zakulski, W.; Schwitzgebel, G.

    1996-09-01

    By means of the electromotive force (emf) method of concentration cells of the following scheme: Li (1)/LiCl-LiF (eut) or LiCi-KCl (eut)/Li-Mg (1) or Li (1)/LiCl-LiF (eut)/Li-Mg (s). Li activities for liquid and solid alloys at the (Mg), (Li), and (Mg) + (Li) two-phase region of the Li-Mg system were determined. Liquid alloys were examined at temperatures from 638 to 889 K at various Li concentrations. The (Mg) solid solutions were investigated in two series: at constant temperatures between 773 and 876 K, with varying Li content, and at fixed Li concentrations, equal to 0.125 and 0.160 molar fractions, at different temperatures between 772 and 849 K. At the two-phase region, (Mg) + (Li), emf measurements were performed in the temperature range 773 to 838 K, with fixed Li concentrations equal to 0.20, 0.25, and 0.275 molar fractions. For (Li) solid alloys, experiments were done at temperatures 773 to 849 K for several constant Li concentrations, between 0.30 and 0.45 molar fractions, respectively. Studies on solid alloys enabled the authors also to determine the boundaries (Li)/[(Mg) + (Li)] and (Mg)/[(Mg) + (Li)] at temperatures 773 to 831 K. The resulting thermodynamic and phase boundary data of this study were used with other selected references for a critical assessment of the Li-Mg system. The Lukas BINGSS optimization program and BINFKT for the calculation of the thermodynamic functions and of the phase diagram were used. The calculated equilibrium phase diagram at temperatures below 750 K indicates a slightly lower solid solubility of Mg in (Li) in comparison with results from thermal analysis and the recently published Saunders evaluation.

  4. Thermodynamic studies and the phase diagram of the Li-Mg system

    NASA Astrophysics Data System (ADS)

    Gasior, W.; Moser, Z.; Zakulski, W.; Schwitzgebel, G.

    1996-09-01

    By means of the electromotive force (emf) method of concentration cells of the following scheme: Li (1) / LiCl-LiF (eut) or LiCi-KCl (eut) / Li-Mg (1) or Li (1) / LiCl-LiF (eut) / Li-Mg (s) Li activities for liquid and solid alloys at the (Mg), (Li), and (Mg) + (Li) two-phase region of the Li-Mg system were determined. Liquid alloys were examined at temperatures from 638 to 889 K at various Li concentrations. The (Mg) solid solutions were investigated in two series: at constant temperatures between 773 and 876 K, with varying Li content, and at fixed Li concentrations, equal to 0.125 and 0.160 molar fractions, at different temperatures between 772 and 849 K. At the two-phase region, (Mg) + (Li), emf measurements were performed in the temperature range 773 to 838 K, with fixed Li concentrations equal to 0.20, 0.25, and 0.275 molar fractions. For (Li) solid alloys, experiments were done at temperatures 773 to 849 K for several constant Li concentrations, between 0.30 to 0.45 molar fractions, respectively. Studies on solid alloys enabled us also to determine the boundaries (Li)/[(Mg) + (Li)] and (Mg)/[(Mg) + (Li)] at temperatures 773 to 831 K. The resulting thermodynamic and phase boundary data of this study were used with other selected references for a critical assessment of the Li-Mg system. The Lukas BINGSS optimization program and BINFKT for the calculation of the thermodynamic functions and of the phase diagram were used. The calculated equilibrium phase diagram at temperatures below 750 K indicates a slightly lower solid solubility of Mg in (Li) in comparison with results from thermal analysis and the recently published Saunders evaluation.

  5. Global phase diagram and quantum spin liquids in a spin-1/2 triangular antiferromagnet

    NASA Astrophysics Data System (ADS)

    Gong, Shou-Shu; Zhu, W.; Zhu, J.-X.; Sheng, D. N.; Yang, Kun

    2017-08-01

    We study the spin-1 /2 Heisenberg model on the triangular lattice with the nearest-neighbor J1>0 , the next-nearest-neighobr J2>0 Heisenberg interactions, and the additional scalar chiral interaction Jχ(S⃗i×S⃗j) .S⃗k for the three spins in all the triangles using large-scale density matrix renormalization group calculation on cylinder geometry. With increasing J2 (J2/J1≤0.3 ) and Jχ (Jχ/J1≤1.0 ) interactions, we establish a quantum phase diagram with the magnetically ordered 120∘, stripe, and noncoplanar tetrahedral phase. In between these magnetic order phases, we find a chiral spin liquid (CSL) phase, which is identified as a ν =1 /2 bosonic fractional quantum Hall state with possible spontaneous rotational symmetry breaking. By switching on the chiral interaction, we find that the previously identified spin liquid in the J1-J2 triangular model (0.08 ≲J2/J1≲0.15 ) shows a phase transition to the CSL phase at very small Jχ. We also compute the spin triplet gap in both spin liquid phases, and our finite-size results suggest a large gap in the odd topological sector but a small or vanishing gap in the even sector. We discuss the implications of our results on the nature of the spin liquid phases.

  6. A general formalism for phase space calculations

    NASA Technical Reports Server (NTRS)

    Norbury, John W.; Deutchman, Philip A.; Townsend, Lawrence W.; Cucinotta, Francis A.

    1988-01-01

    General formulas for calculating the interactions of galactic cosmic rays with target nuclei are presented. Methods for calculating the appropriate normalization volume elements and phase space factors are presented. Particular emphasis is placed on obtaining correct phase space factors for 2-, and 3-body final states. Calculations for both Lorentz-invariant and noninvariant phase space are presented.

  7. Phase diagram of harmonically confined one-dimensional fermions with attractive and repulsive interactions

    SciTech Connect

    Campo, V. L. Jr.; Capelle, K.

    2005-12-15

    We construct the complete U-{mu} phase diagram for harmonically confined ultracold fermionic atoms with repulsive and attractive interactions({mu} is the chemical potential and U the interaction strength). Our approach is based on density-functional theory, and employs analytical expressions for the kinetic and correlation energy functionals, permitting us to obtain closed expressions for all phase boundaries and characteristic lines of the phase diagram, both for repulsive and attractive interactions.

  8. Magnetic phase diagram of superantiferromagnetic TbCu2 nanoparticles

    NASA Astrophysics Data System (ADS)

    Echevarria-Bonet, C.; Rojas, D. P.; Espeso, J. I.; Rodríguez Fernández, J.; de la Fuente Rodríguez, M.; Fernández Barquín, L.; Rodríguez Fernández, L.; Gorria, P.; Blanco, J. A.; Fdez-Gubieda, M. L.; Bauer, E.; Damay, F.

    2015-12-01

    The structural state and static and dynamic magnetic properties of TbCu2 nanoparticles are reported to be produced by mechanical milling under inert atmosphere. The randomly dispersed nanoparticles as detected by TEM retain the bulk symmetry with an orthorhombic Imma lattice and Tb and Cu in the 4e and 8h positions, respectively. Rietveld refinements confirm that the milling produces a controlled reduction of particle sizes reaching ≃6 nm and an increase of the microstrain up to ≃0.6%. The electrical resistivity indicates a metallic behavior and the presence of a magnetic contribution to the electronic scattering which decreases with milling times. The dc-susceptibility shows a reduction of the Néel transition (from 49 K to 43 K) and a progressive increase of a peak (from 9 K to 15 K) in the zero-field-cooled magnetization with size reduction. The exchange anisotropy is very weak (a bias field of ≃30 Oe) and is due to the presence of a disordered (thin) shell coupled to the antiferromagnetic core. The dynamic susceptibility evidences a critical slowing down in the spin-disordered state for the lowest temperature peak associated with a spin glass-like freezing with a tendency of zv and β exponents to increase when the size becomes 6 nm (zv≃ 6.6 and β ≃ 0.85 ). A Rietveld analysis of the neutron diffraction patterns 1.8≤slant T≤slant 60 K, including the magnetic structure determination, reveals that there is a reduction of the expected moment (≃80%), which must be connected to the presence of the disordered particle shell. The core magnetic structure retains the bulk antiferromagnetic arrangement. The overall interpretation is based on a superantiferromagnetic behavior which at low temperatures coexists with a canting of surface moments and a mismatch of the antiferromagnetic sublattices of the nanoparticles. We propose a novel magnetic phase diagram where changes are provoked by a combination of the decrease of size and the increase of

  9. Phase diagram of the transverse Ising model in a random field

    NASA Astrophysics Data System (ADS)

    Milman, F. S.; Hauser, P. R.; Figueiredo, W.

    1991-06-01

    We determine the phase diagram of the transverse Ising model with a trimodal distribution (sum of three δ functions) for a longitudinal random field at T=0, using a mean-field approximation. The phase diagram includes tricritical points, ordered critical points, a fourth-order point, critical end points, and a double critical end point. Our T=0 phase diagram is completely equivalent to the one obtained by Kaufman, Klunzinger, and Khurana for the random-field Ising model. We show that the temperature and the magnitude of the transverse field play a similar role.

  10. Phase diagrams of block copolymer melts by dissipative particle dynamics simulations.

    PubMed

    Gavrilov, Alexey A; Kudryavtsev, Yaroslav V; Chertovich, Alexander V

    2013-12-14

    Phase diagrams for monodisperse and polydisperse diblock copolymer melts and a random multiblock copolymer melt are constructed using dissipative particle dynamics simulations. A thorough visual analysis and calculation of the static structure factor in several hundreds of points at each of the diagrams prove the ability of mesoscopic molecular dynamics to predict the phase behavior of polymer systems as effectively as the self-consistent field-theory and Monte Carlo simulations do. It is demonstrated that the order-disorder transition (ODT) curve for monodisperse diblocks can be precisely located by a spike in the dependence of the mean square pressure fluctuation on χN, where χ is the Flory-Huggins parameter and N is the chain length. For two other copolymer types, the continuous ODTs are observed. Large polydispersity of both blocks obeying the Flory distribution in length does not shift the ODT curve but considerably narrows the domains of the cylindrical and lamellar phases partially replacing them with the wormlike micelle and perforated lamellar phases, respectively. Instead of the pure 3d-bicontinuous phase in monodisperse diblocks, which could be identified as the gyroid, a coexistence of the 3d phase and cylindrical micelles is detected in polydisperse diblocks. The lamellar domain spacing D in monodisperse diblocks follows the strong-segregation theory prediction, D∕N(1∕2) ~ (χN)(1∕6), whereas in polydisperse diblocks it is almost independent of χN at χN < 100. Completely random multiblock copolymers cannot form ordered microstructures other than lamellas at any composition.

  11. Novel phase diagram behavior and materials design in heterostructural semiconductor alloys.

    PubMed

    Holder, Aaron M; Siol, Sebastian; Ndione, Paul F; Peng, Haowei; Deml, Ann M; Matthews, Bethany E; Schelhas, Laura T; Toney, Michael F; Gordon, Roy G; Tumas, William; Perkins, John D; Ginley, David S; Gorman, Brian P; Tate, Janet; Zakutayev, Andriy; Lany, Stephan

    2017-06-01

    Structure and composition control the behavior of materials. Isostructural alloying is historically an extremely successful approach for tuning materials properties, but it is often limited by binodal and spinodal decomposition, which correspond to the thermodynamic solubility limit and the stability against composition fluctuations, respectively. We show that heterostructural alloys can exhibit a markedly increased range of metastable alloy compositions between the binodal and spinodal lines, thereby opening up a vast phase space for novel homogeneous single-phase alloys. We distinguish two types of heterostructural alloys, that is, those between commensurate and incommensurate phases. Because of the structural transition around the critical composition, the properties change in a highly nonlinear or even discontinuous fashion, providing a mechanism for materials design that does not exist in conventional isostructural alloys. The novel phase diagram behavior follows from standard alloy models using mixing enthalpies from first-principles calculations. Thin-film deposition demonstrates the viability of the synthesis of these metastable single-phase domains and validates the computationally predicted phase separation mechanism above the upper temperature bound of the nonequilibrium single-phase region.

  12. Novel phase diagram behavior and materials design in heterostructural semiconductor alloys

    DOE PAGES

    Holder, Aaron M.; Siol, Sebastian; Ndione, Paul F.; ...

    2017-06-07

    Structure and composition control the behavior of materials. Isostructural alloying is historically an extremely successful approach for tuning materials properties, but it is often limited by binodal and spinodal decomposition, which correspond to the thermodynamic solubility limit and the stability against composition fluctuations, respectively. We show that heterostructural alloys can exhibit a markedly increased range of metastable alloy compositions between the binodal and spinodal lines, thereby opening up a vast phase space for novel homogeneous single-phase alloys. We distinguish two types of heterostructural alloys, that is, those between commensurate and incommensurate phases. Because of the structural transition around the criticalmore » composition, the properties change in a highly nonlinear or even discontinuous fashion, providing a mechanism for materials design that does not exist in conventional isostructural alloys. The novel phase diagram behavior follows from standard alloy models using mixing enthalpies from first-principles calculations. Furthermore, thin-film deposition demonstrates the viability of the synthesis of these metastable single-phase domains and validates the computationally predicted phase separation mechanism above the upper temperature bound of the nonequilibrium single-phase region.« less

  13. Novel phase diagram behavior and materials design in heterostructural semiconductor alloys

    PubMed Central

    Holder, Aaron M.; Siol, Sebastian; Ndione, Paul F.; Peng, Haowei; Deml, Ann M.; Matthews, Bethany E.; Schelhas, Laura T.; Toney, Michael F.; Gordon, Roy G.; Tumas, William; Perkins, John D.; Ginley, David S.; Gorman, Brian P.; Tate, Janet; Zakutayev, Andriy; Lany, Stephan

    2017-01-01

    Structure and composition control the behavior of materials. Isostructural alloying is historically an extremely successful approach for tuning materials properties, but it is often limited by binodal and spinodal decomposition, which correspond to the thermodynamic solubility limit and the stability against composition fluctuations, respectively. We show that heterostructural alloys can exhibit a markedly increased range of metastable alloy compositions between the binodal and spinodal lines, thereby opening up a vast phase space for novel homogeneous single-phase alloys. We distinguish two types of heterostructural alloys, that is, those between commensurate and incommensurate phases. Because of the structural transition around the critical composition, the properties change in a highly nonlinear or even discontinuous fashion, providing a mechanism for materials design that does not exist in conventional isostructural alloys. The novel phase diagram behavior follows from standard alloy models using mixing enthalpies from first-principles calculations. Thin-film deposition demonstrates the viability of the synthesis of these metastable single-phase domains and validates the computationally predicted phase separation mechanism above the upper temperature bound of the nonequilibrium single-phase region. PMID:28630928

  14. Phase diagram of PbBi alloys: structure-property relations and the superconducting coupling

    NASA Astrophysics Data System (ADS)

    Gandhi, Ashish C.; Chan, Ting Shan; Wu, Sheng Yun

    2017-10-01

    We report on the crystal structure transformation and superconducting phase diagrams for a Pb m Bi100‑m (0 < m < 100 in %) alloy. The superconducting coupling strength is resolved by analyzing the dependency of T C on the applied magnetic field. The phase diagram shows evidence for strong-coupling s-wave superconductivity for all alloys of Pb m Bi100‑m and the dependency of the superconducting parameters on the weight percent of each constituent phase is discussed in the phase diagram. Very strong coupling of 2Δo/k B T C ∼ 5.174 is observed in the present Pb m Bi100‑m phase diagram.

  15. Interface-roughening phase diagram of the three-dimensional Ising model for all interaction anisotropies from hard-spin mean-field theory.

    PubMed

    Cağlar, Tolga; Berker, A Nihat

    2011-11-01

    The roughening phase diagram of the d=3 Ising model with uniaxially anisotropic interactions is calculated for the entire range of anisotropy, from decoupled planes to the isotropic model to the solid-on-solid model, using hard-spin mean-field theory. The phase diagram contains the line of ordering phase transitions and, at lower temperatures, the line of roughening phase transitions, where the interface between ordered domains roughens. Upon increasing the anisotropy, roughening transition temperatures settle after the isotropic case, whereas the ordering transition temperature increases to infinity. The calculation is repeated for the d=2 Ising model for the full range of anisotropy, yielding no roughening transition.

  16. A new phase diagram for layered antiferromagnetic films.

    PubMed

    Hellwig, Olav; Kirk, Taryl L; Kortright, Jeffrey B; Berger, Andreas; Fullerton, Eric E

    2003-02-01

    Magnetic multilayer films provide convenient model systems for studying the physics of antiferromagnetic films and surfaces. Here we report on the magnetic reversal and domain structure in antiferromagnetically coupled Co/Pt multilayers that are isomorphic to layered antiferromagnetic films with perpendicular magnetic anisotropy. We observe two distinct remanent states and reversal modes of the system. In mode 1 the magnetization in each layer reverses independently, producing an antiferromagnetic remanent state that shows full lateral correlation and vertical anticorrelation across the interlayers. In mode 2 the reversal in adjacent layers is locally synchronized with a remanent state that is vertically correlated but laterally anticorrelated in ferromagnetic stripe domains. Theoretical energy calculations of the two ground states identify a new phase boundary that is in good agreement with our experimental results.

  17. A composite phase diagram of structure H hydrates using Schreinemakers' geometric approach

    USGS Publications Warehouse

    Mehta, A.P.; Makogon, T.Y.; Burruss, R.C.; Wendlandt, R.F.; Sloan, E.D.

    1996-01-01

    A composite phase diagram is presented for Structure H (sH) clathrate hydrates. In this work, we derived the reactions occurring among the various phases along each four-phase (Ice/Liquid water, liquid hydrocarbon, vapor, and hydrate) equilibrium line. A powerful method (though seldom used in chemical engineering) for multicomponent equilibria developed by Schreinemakers is applied to determine the relative location of all quadruple (four-phase) lines emanating from three quintuple (five-phase) points. Experimental evidence validating the approximate phase diagram is also provided. The use of Schreinemakers' rules for the development of the phase diagram is novel for hydrates, but these rules may be extended to resolve the phase space of other more complex systems commonly encountered in chemical engineering.

  18. The non-equilibrium phase diagrams of flow-induced crystallization and melting of polyethylene

    NASA Astrophysics Data System (ADS)

    Wang, Zhen; Ju, Jianzhu; Yang, Junsheng; Ma, Zhe; Liu, Dong; Cui, Kunpeng; Yang, Haoran; Chang, Jiarui; Huang, Ningdong; Li, Liangbin

    2016-09-01

    Combining extensional rheology with in-situ synchrotron ultrafast x-ray scattering, we studied flow-induced phase behaviors of polyethylene (PE) in a wide temperature range up to 240 °C. Non-equilibrium phase diagrams of crystallization and melting under flow conditions are constructed in stress-temperature space, composing of melt, non-crystalline δ, hexagonal and orthorhombic phases. The non-crystalline δ phase is demonstrated to be either a metastable transient pre-order for crystallization or a thermodynamically stable phase. Based on the non-equilibrium phase diagrams, nearly all observations in flow-induced crystallization (FIC) of PE can be well understood. The interplay of thermodynamic stabilities and kinetic competitions of the four phases creates rich kinetic pathways for FIC and diverse final structures. The non-equilibrium flow phase diagrams provide a detailed roadmap for precisely processing of PE with designed structures and properties.

  19. The non-equilibrium phase diagrams of flow-induced crystallization and melting of polyethylene

    PubMed Central

    Wang, Zhen; Ju, Jianzhu; Yang, Junsheng; Ma, Zhe; Liu, Dong; Cui, Kunpeng; Yang, Haoran; Chang, Jiarui; Huang, Ningdong; Li, Liangbin

    2016-01-01

    Combining extensional rheology with in-situ synchrotron ultrafast x-ray scattering, we studied flow-induced phase behaviors of polyethylene (PE) in a wide temperature range up to 240 °C. Non-equilibrium phase diagrams of crystallization and melting under flow conditions are constructed in stress-temperature space, composing of melt, non-crystalline δ, hexagonal and orthorhombic phases. The non-crystalline δ phase is demonstrated to be either a metastable transient pre-order for crystallization or a thermodynamically stable phase. Based on the non-equilibrium phase diagrams, nearly all observations in flow-induced crystallization (FIC) of PE can be well understood. The interplay of thermodynamic stabilities and kinetic competitions of the four phases creates rich kinetic pathways for FIC and diverse final structures. The non-equilibrium flow phase diagrams provide a detailed roadmap for precisely processing of PE with designed structures and properties. PMID:27609305

  20. Phase diagram, solubility limit and hydrodynamic properties of cellulose in binary solvents with ionic liquid.

    PubMed

    Le, Kim Anh; Rudaz, Cyrielle; Budtova, Tatiana

    2014-05-25

    Cellulose solubility phase diagrams in two binary solvents based on 1-ethyl-3-methylimidazolium acetate (EmimAc) mixed with water and with dimethylsulfoxide (DMSO) were built. The minimal amount of EmimAc molecules needed to dissolve cellulose is 2.5-3moles per anhydroglucose unit. This proportion allows calculation of the maximal cellulose concentration soluble in EmimAc-DMSO at any composition; in EmimAc it is around 25-27wt%. Water forms hydrogen bonds with EmimAc and thus competes with cellulose for ionic liquid; the solubility of cellulose in EmimAc-water is much lower than that in EmimAc-DMSO. Hydrodynamic properties of cellulose in two solvent systems were compared. In EmimAc-DMSO cellulose intrinsic viscosity practically does not depend on DMSO content as predicted by the phase diagram. The intrinsic viscosity in EmimAc-water first increases with water content due to cellulose self-aggregation and then abruptly decreases due to coagulation.

  1. Structural Phase Diagram for Multi-lamellar Tubular Deformations of Lipid Mesophases

    NASA Astrophysics Data System (ADS)

    Tayebi, Lobat; Parikh, Atul

    2011-03-01

    Stable multi-lamellar cylindrical tubules protrude readily from concentrated mass of amphiphilic molecules in response to a variety of external stresses. Using energetic considerations, we have developed an phase diagram, predicting various types of morphologies of equilibrium multilamellar tubular deformations that stabilize for a broad range of their bending rigidity and surface tension values. Tubular morphologies are described in terms of core radius(rc) and number of lamellae(N). Results of the calculations reveal that emergent tubular morphologies can be classified into three major classes: (1) thin tethers (small rc and low N); (2) solid tubes (high N); and (3) hollow tubes (large rc and and low N). Experimental validation of these predictions is obtained in experiments involving hydration of dry stack lipids Here, tubular deformations, referred to as myelin figures, of all predicted morphologies form in separate populations. Furthermore, the phase diagram also sheds light on a long-standing question of the determinants of the thickness of such myelin figures.

  2. Binary Solid-Liquid Phase Diagram of Phenol and t-Butanol: An Undergraduate Physical Chemistry Experiment

    ERIC Educational Resources Information Center

    Xu, Xinhua; Wang, Xiaogang; Wu, Meifen

    2014-01-01

    The determination of the solid-liquid phase diagram of a binary system is always used as an experiment in the undergraduate physical chemistry laboratory courses. However, most phase diagrams investigated in the lab are simple eutectic ones, despite the fact that complex binary solid-liquid phase diagrams are more common. In this article, the…

  3. Binary Solid-Liquid Phase Diagram of Phenol and t-Butanol: An Undergraduate Physical Chemistry Experiment

    ERIC Educational Resources Information Center

    Xu, Xinhua; Wang, Xiaogang; Wu, Meifen

    2014-01-01

    The determination of the solid-liquid phase diagram of a binary system is always used as an experiment in the undergraduate physical chemistry laboratory courses. However, most phase diagrams investigated in the lab are simple eutectic ones, despite the fact that complex binary solid-liquid phase diagrams are more common. In this article, the…

  4. Phase diagram of a lattice U(1) gauge theory with gauge fixing

    SciTech Connect

    Bock, W.; Golterman, M.F.; Shamir, Y.

    1998-09-01

    As a first step towards a nonperturbative investigation of the gauge-fixing (Rome) approach to lattice chiral gauge theories we study a U(1) model with an action that includes a local gauge-fixing term and a mass counterterm for the gauge fields. The model is studied on the trivial orbit so that only the dynamics of the longitudinal gauge degrees of freedom is taken into account. Mean-field and numerical calculations reveal that the phase diagram of this {open_quotes}reduced{close_quotes} model contains, in addition to ferromagnetic (FM), antiferromagnetic (AM) and paramagnetic (PM) phases, also a novel so-called helicoidal ferromagnetic (FMD) phase with broken U(1) symmetry and a nonvanishing condensate of the vector field. The continuum limit is defined by approaching the FM-FMD phase transition from within the FM phase. We show that the global U(1) symmetry is restored in this continuum limit, both numerically and in perturbation theory. The numerical results for the magnetization in the FM and FMD phases are in good agreement with perturbation theory. {copyright} {ital 1998} {ital The American Physical Society}

  5. Emergence of bistable states and phase diagrams of traffic flow at an unsignalized intersection

    NASA Astrophysics Data System (ADS)

    Li, Qi-Lang; Jiang, Rui; Wang, Bing-Hong

    2015-02-01

    This paper studies phase diagrams of traffic states induced by the bottleneck of an unsignalized intersection which consists of two perpendicular one-lane roads. Parallel updates rules are employed for both roads. At the crossing point, in order to avoid colliding, the consideration of yield dynamics may be suitable herein. Different from previous studies, the deterministic Nagel and Schreckenberg model is adopted in this work. Based on theoretical analysis and computer simulations, the phase diagrams of traffic flow have been presented and the flow formulas in all regions have been derived in the phase diagram. The results of theoretical analysis are in good agreement with computer simulation ones. One finds an interesting phenomenon: there exist bistable states in some regions of the phase diagrams.

  6. Phase diagram of the layered oxide SnO: GW and electron-phonon studies

    PubMed Central

    Chen, Peng-Jen; Jeng, Horng-Tay

    2015-01-01

    First-principles calculations are performed to study the electronic properties and the electron-phonon interactions of the layered oxide semiconductor SnO. In addition to the high hole mobility that makes SnO a promising material in electronics, it has recently been reported that the semimetallic phase under pressure is superconducting. The superconducting Tc curve exhibits a dome-like feature under pressure and reaches the maximum of 1.4 K at p = 9.2 GPa. Both its crystal structure and the dome-like Tc curve are reminiscent of the Fe-based superconductor FeSe. Motivated by this observation, we investigate the electronic, phonon, and their interactions in SnO using first-principles schemes. GW approximation is adopted to correct the underestimated band gaps, including real and continuous band gaps in the semiconducting and semimetallic phases. The phase diagram showing the semiconductor-to-semimetal transition and the Tc curve has been successfully reproduced. Detailed analysis of the electron-phonon interactions demonstrate the importance of the out-of-plane motions of O atoms and the Sn-s lone pairs for the superconductivity to occur. Our method combining GW and e-ph calculations can be further extended to the study of other materials that undergo insulator-to-superconductor phase transition. PMID:26553414

  7. Phase diagram of the layered oxide SnO: GW and electron-phonon studies.

    PubMed

    Chen, Peng-Jen; Jeng, Horng-Tay

    2015-11-10

    First-principles calculations are performed to study the electronic properties and the electron-phonon interactions of the layered oxide semiconductor SnO. In addition to the high hole mobility that makes SnO a promising material in electronics, it has recently been reported that the semimetallic phase under pressure is superconducting. The superconducting Tc curve exhibits a dome-like feature under pressure and reaches the maximum of 1.4 K at p = 9.2 GPa. Both its crystal structure and the dome-like Tc curve are reminiscent of the Fe-based superconductor FeSe. Motivated by this observation, we investigate the electronic, phonon, and their interactions in SnO using first-principles schemes. GW approximation is adopted to correct the underestimated band gaps, including real and continuous band gaps in the semiconducting and semimetallic phases. The phase diagram showing the semiconductor-to-semimetal transition and the Tc curve has been successfully reproduced. Detailed analysis of the electron-phonon interactions demonstrate the importance of the out-of-plane motions of O atoms and the Sn-s lone pairs for the superconductivity to occur. Our method combining GW and e-ph calculations can be further extended to the study of other materials that undergo insulator-to-superconductor phase transition.

  8. Rich magnetoelectric phase diagrams of multiferroic single-crystal α -NaFeO2

    NASA Astrophysics Data System (ADS)

    Terada, Noriki; Ikedo, Yuta; Sato, Hirohiko; Khalyavin, Dmitry D.; Manuel, Pascal; Miyake, Atsushi; Matsuo, Akira; Tokunaga, Masashi; Kindo, Koichi

    2017-07-01

    The magnetic and dielectric properties of the multiferroic triangular lattice magnet compound α -NaFeO2 were studied by magnetization, specific heat, dielectric permittivity, and pyroelectric current measurements and by neutron diffraction experiments using single crystals grown by a hydrothermal synthesis method. This work produced magnetic field (in the monoclinic a b -plane, Ba b, and along the c*-axis, Bc) versus temperature magnetic phase diagrams, including five and six magnetically ordered phases in Ba b and along Bc, respectively. In zero magnetic field, two spin-density-wave orderings with different k vectors—(0 ,q ,1/2 ) in phase I and (qa,qb,qc ) in phase II—appeared at T =9.5 and 8.25 K, respectively. Below T =5 K, a commensurate order with k =(0.5 ,0 ,0.5 ) was stabilized as the ground state in phase III. Both Ba b≥3 T and Bc≥5 T were found to induce ferroelectric phases at the lowest temperature (2 K), with an electric polarization that was not confined to any highly symmetric directions in phases IVa b (3.3 ≤Ba b≤8.5 T), Va b (8.5 ≤Ba b≤13.6 T), IVc (5.0 ≤Bc≤8.5 T), and Vc (8.5 ≤Bc≤13.5 T). In phase VIc, within a narrow temperature region in Bc, the polarization was confined to the a b plane. For each of the ferroelectric phases, the k vector was (qa,qb,qc ), and noncollinear structures were identified, including a general spiral in IVa b an a b cycloid in IVc and Vc, and a proper screw in VIc, along with a triclinic 11' magnetic point group allowing polarization in the general direction. Comparing the polarization direction to the magnetic structures in the ferroelectric phases, we conclude that the extended inverse Dzyaloshinskii-Moriya mechanism expressed by the orthogonal components p1∝ri j×(Si×Sj) and p2∝Si×Sj can explain the polarization directions. Based on calculations incorporating exchange interactions up to fourth-nearest-neighbor (NN) couplings, we infer that competition among antiferromagnetic second NN

  9. The topological phase diagram of cimetidine: A case of overall monotropy.

    PubMed

    Céolin, R; Rietveld, I B

    2017-03-01

    Cimetidine is a histamine H2-receptor antagonist used against peptic ulcers. It is known to exhibit crystalline polymorphism. Forms A and D melt within 0.35 degrees from each other and the enthalpies of fusion are similar as well. The present paper demonstrates how to construct a pressure-temperature phase diagram with only calorimetric and volumetric data available. The phase diagram provides the stability domains and the phase equilibria for the phases A, D, the liquid and the vapor. Cimetidine is overall monotropic with form D the only stable solid phase. Copyright © 2016 Académie Nationale de Pharmacie. Published by Elsevier Masson SAS. All rights reserved.

  10. Phase diagrams and magnetic properties of tri-layer superlattices: Mean field study

    NASA Astrophysics Data System (ADS)

    Naji, S.; Belhaj, A.; Labrim, H.; Bahmad, L.; Benyoussef, A.; El Kenz, A.

    2014-04-01

    Motivated by spintronic device applications, we engineer a superlattice model based on periodic tri-layers consisting of spins σ={1}/{2}, S=1 and q={3}/{2} residing on the sites of a square lattice, interacting with an external magnetic field. We study its phase diagrams and magnetic properties. We determine the corresponding ground state phase diagrams. Then, we show that this Ising lattice model exhibits a ferromagnetic phase F1, two ferrimagnetic phases F2, F3 and an antiferromagnetic phase F4. It is found that the magnetic behaviors depend on the moduli space controlled by the exchange interaction couplings. More precisely, the hysteresis loops have been established.

  11. Phase diagrams and microscopic structures of (Hg,Cd)Te, (Hg,Zn)Te, and (Cd,Zn)Te alloys

    NASA Technical Reports Server (NTRS)

    Patrick, R. S.; Chen, A.-B.; Sher, A.; Berding, M. A.

    1988-01-01

    A cluster theory based on the quasi-chemical approximation has been applied to study the local correlation bond-length distribution, and phase diagrams of the II-VI pseudobinary alloys Hg(1 - x)Cd(x)Te, Hg(1 - x)Zn(x)Te, and Cd(1 - x)Zn(x)Te. The cluster energy is calculated by letting it relax in some effective alloy medium and then considering the contributions from the strain and chemical energies. Two different models are presented to simulate the alloy medium. While both models show that all three alloys have nearly random distributions, the signs of the local correlation prove to be sensitive to the alloy medium chosen for the energy calculation. Good agreement is found between experiment and the bond lengths and phase diagrams in both models.

  12. Phase diagram of mixtures of hard colloidal spheres and discs: a free-volume scaled-particle approach.

    PubMed

    Oversteegen, S M; Lekkerkerker, H N W

    2004-02-01

    Phase diagrams of mixtures of colloidal hard spheres with hard discs are calculated by means of the free-volume theory. The free-volume fraction available to the discs is determined from scaled-particle theory. The calculations show that depletion induced phase separation should occur at low disc concentrations in systems now experimentally available. The gas-liquid equilibrium of the spheres becomes stable at comparable size ratios as with bimodal mixtures of spheres or mixtures of rods and spheres. Introducing finite thickness of the platelets gives rise to a significant lowering of the fluid branch of the binodal. Copyright 2004 American Institute of Physics

  13. Comparison of actual vs. synthesized ternary phase diagrams for solutes of cryobiological interest.

    PubMed

    Kleinhans, F W; Mazur, Peter

    2007-04-01

    Phase diagrams are of great utility in cryobiology, especially, those consisting of a cryoprotective agent (CPA) dissolved in a physiological salt solution. These ternary phase diagrams consist of plots of the freezing points of increasing concentrations of solutions of cryoprotective agents (CPA) plus NaCl. Because they are time-consuming to generate, ternary diagrams are only available for a small number of CPAs. We wanted to determine whether accurate ternary phase diagrams could be synthesized by adding together the freezing point depressions of binary solutions of CPA/water and NaCl/water which match the corresponding solute molality concentrations in the ternary solution. We begin with a low concentration of a solution of CPA+salt of given R (CPA/salt) weight ratio. Ice formation in that solution is mimicked by withdrawing water from it which increases the concentrations of both the CPA and the NaCl. We compute the individual solute concentrations, determine their freezing points from published binary phase diagrams, and sum the freezing points. These yield the synthesized ternary phase diagram for a solution of given R. They were compared with published experimental ternary phase diagrams for glycerol, dimethyl sulfoxide (DMSO), sucrose, and ethylene glycol (EG) plus NaCl in water. For the first three, the synthesized and experimental phase diagrams agreed closely, with some divergence occurring as wt% concentrations exceeded 30% for DMSO and 55% for glycerol, and sucrose. However, in the case of EG there were substantial differences over nearly the entire range of concentrations which we attribute to systematic errors in the experimental EG data. New experimental EG work will be required to resolve this issue.

  14. Comparison of actual vs synthesized ternary phase diagrams for solutes of cryobiological interest☆

    PubMed Central

    Kleinhans, F.W.; Mazur, Peter

    2009-01-01

    Phase diagrams are of great utility in cryobiology, especially those consisting of a cryoprotective agent (CPA) dissolved in a physiological salt solution. These ternary phase diagrams consist of plots of the freezing points of increasing concentrations of solutions of cryoprotective agents (CPA) plus NaCl. Because they are time-consuming to generate, ternary diagrams are only available for a small number of CPA's. We wanted to determine whether accurate ternary phase diagrams could be synthesized by adding together the freezing point depressions of binary solutions of CPA/water and NaCl/water which match the corresponding solute molality concentrations in the ternary solution. We begin with a low concentration of a solution of CPA + salt of given R (CPA/salt) weight ratio. Ice formation in that solution is mimicked by withdrawing water from it which increases the concentrations of both the CPA and the NaCl. We compute the individual solute concentrations, determine their freezing points from published binary phase diagrams, and sum the freezing points. These yield the synthesized ternary phase diagram for a solution of given R. They were compared with published experimental ternary phase diagrams for glycerol, dimethyl sulfoxide (DMSO), sucrose, and ethylene glycol (EG) plus NaCl in water. For the first three, the synthesized and experimental phase diagrams agreed closely, with some divergence occurring as wt % concentrations exceeded 30% for DMSO and 55% for glycerol and sucrose. However, in the case of EG there were substantial differences over nearly the entire range of concentrations which we attribute to systematic errors in the experimental EG data. New experimental EG work will be required to resolve this issue. PMID:17350609

  15. Phase diagrams for clathrate hydrates of methane, ethane, and propane from first-principles thermodynamics.

    PubMed

    Cao, Xiaoxiao; Huang, Yingying; Li, Wenbo; Zheng, Zhaoyang; Jiang, Xue; Su, Yan; Zhao, Jijun; Liu, Changling

    2016-01-28

    Natural gas hydrates are inclusion compounds composed of major light hydrocarbon gaseous molecules (CH4, C2H6, and C3H8) and a water clathrate framework. Understanding the phase stability and formation conditions of natural gas hydrates is crucial for their future exploitation and applications and requires an accurate description of intermolecular interactions. Previous ab initio calculations on gas hydrates were mainly limited by the cluster models, whereas the phase diagram and equilibrium conditions of hydrate formation were usually investigated using the thermodynamic models or empirical molecular simulations. For the first time, we construct the chemical potential phase diagrams of type II clathrate hydrates encapsulated with methane/ethane/propane guest molecules using first-principles thermodynamics. We find that the partially occupied structures (136H2O·1CH4, 136H2O·16CH4, 136H2O·20CH4, 136H2O·1C2H6, and 136H2O·1C3H8) and fully occupied structures (136H2O·24CH4, 136H2O·8C2H6, and 136H2O·8C3H8) are thermodynamically favorable under given pressure-temperature (p-T) conditions. The theoretically predicted equilibrium pressures for pure CH4, C2H6 and C3H8 hydrates at the phase transition point are consistent with the experimental data. These results provide valuable guidance for establishing the relationship between the accurate description of intermolecular noncovalent interactions and the p-T equilibrium conditions of clathrate hydrates and other molecular crystals.

  16. Thermochemical measurements and assessment of the phase diagrams in the system Y-Ba-Cu-O

    SciTech Connect

    Boudene, A.; Mohammad, A.; Hack, K.

    1996-04-01

    The aim of this project was to provide a self-consistent set of Gibbs energy data for all phases in the system Y-Ba-Cu-O. Experimental thermochemical investigations by differential thermal analysis (DTA), thermogravimetry (TG), electromotive force measurements (EMF), oxygen coulometric titration (OCT), drop and solution calorimetry, and conventional phase analysis (annealing, quenching, and X-ray diffraction [XRD]) as well as ab initio calculations of interaction energies for the 123 phase have been carried out. The experimental information (phase equilibria, heat capacity, enthalpies of formation, oxygen partial pressures, and so forth) has been used in computer-based assessments of the Gibbs energies. These data have been employed to generate phase diagrams by way of equilibrium computations. All binary and ternary subsystems have been fully assessed. For the quaternary system a dataset covering the subsolidus range has been derived. Applications of the data to practical questions, such as the production of 123 superconductors by an MOCVD process, the producibility of metallic precursors, and the oxidation of a copper-enriched stoichiometric oxide precursor, are demonstrated.

  17. Morphology and phase diagram of complex block copolymers: ABC linear triblock copolymers.

    PubMed

    Tang, Ping; Qiu, Feng; Zhang, Hongdong; Yang, Yuliang

    2004-03-01

    Using a real space implementation of the self-consistent field theory for the polymeric system, we explore microphases of ABC linear triblock copolymers. For the sake of numerical tractability, the calculation is carried out in a two-dimensional (2D) space. Seven microphases are found to be stable for the ABC triblock copolymer in 2D, which include lamellae, hexagonal lattice, core-shell hexagonal lattice, tetragonal lattice, lamellae with beads inside, lamellae with beads at the interface, and hexagonal phase with beads at the interface. By systematically varying the composition, triangle phase diagrams are constructed for four classes of typical triblock polymers in terms of the relative strengths of the interaction energies between different species. In general, when both volume fractions and interaction energies of the three species are comparable, lamellar phases are found to be the most stable. While one of the volume fractions is large, core-shell hexagonal or tetragonal phases can be formed, depending on which of the blocks dominates. Furthermore, more complex morphologies, such as lamellae with beads inside, lamellae with beads at the interface, and hexagonal phases with beads at the interface compete for stability with lamellae structures, as the interaction energies between distinct blocks become asymmetric. Our study provides guidance for the design of microstructures in complex block copolymers.

  18. Phase diagram of nuclear 'pasta' and its uncertainties in supernova cores

    SciTech Connect

    Sonoda, Hidetaka; Watanabe, Gentaro; Sato, Katsuhiko; Yasuoka, Kenji; Ebisuzaki, Toshikazu

    2008-03-15

    We examine the model dependence of the phase diagram of inhomogeneous nulcear matter in supernova cores using the quantum molecular dynamics (QMD). Inhomogeneous matter includes crystallized matter with nonspherical nuclei--''pasta'' phases--and the liquid-gas phase-separating nuclear matter. Major differences between the phase diagrams of the QMD models can be explained by the energy of pure neutron matter at low densities and the saturation density of asymmetric nuclear matter. We show the density dependence of the symmetry energy is also useful to understand uncertainties of the phase diagram. We point out that, for typical nuclear models, the mass fraction of the pasta phases in the later stage of the collapsing cores is higher than 10-20%.

  19. Program calculates two-phase pressure drop

    SciTech Connect

    Blackwell, W.W.

    1980-11-24

    Analysts have developed a program for determining the two-phase pressure drop in piping. Written for the TI-59 programmable calculator used with a PC-100C printer, the program incorporates several unique features: it calculates single-phase as well as two-phase pressure drops, has a 10-20 s execution time, permits the operating data to be changed easily, and includes an option for calculating the estimated surface tension of paraffinic hydrocarbon liquids.

  20. Nanostructures and phase diagrams of ABC star triblock copolymers in pore geometries.

    PubMed

    Li, Shiben; Qiu, Wenjuan; Zhang, Linxi; Liang, Haojun

    2012-03-28

    The nanostructures and phase diagrams of ABC star triblock copolymers in pore geometries are investigated using the real-space self-consistent field theory in two-dimensional space. Two types of pores with neutral surfaces, namely, pores with small and large diameters, are considered. A rich variety of nanostructures are exhibited by the ABC star triblock copolymers in these two types of pores, which differ from those observed in bulk and in other confinements. These structures include perpendicular undulating lamellae, concentric core-shell cylinders, polygonal tiling with cylindrical arrangements, and other complex structures. Triangular phase diagrams for the ABC star triblock copolymers are constructed. The small pores clearly affect the corner and central space of the phase diagrams by distorting the bulk structures into concentric arrangements. Meanwhile, the large pores induce the transformation of bulk structures into concentric structures in most of the phase space, but slightly affect the structures at the center of the phase diagrams. Furthermore, the order-order and order-disorder phase transitions, as well as the stable and metastable phases, in the triangular phase diagrams are examined by analyzing their free energies. These observations on the ABC star triblock copolymers in the pore geometries provide a deeper insight into the behavior of macromolecules in a confined system.

  1. Two-dimensional Ising model with competing interactions: Phase diagram and low-temperature remanent disorder

    NASA Astrophysics Data System (ADS)

    O'Hare, A.; Kusmartsev, F. V.; Kugel, K. I.

    2009-01-01

    The two-dimensional Ising model with competing nearest-neighbor and diagonal interactions on the square lattice is studied by the transfer-matrix technique and by the Monte Carlo simulations. The phase diagram of this model is constructed with a special emphasis to the analysis of a glassy state arising as an order to disorder transition at low temperatures. Evidence of the glassy state (based, in particular, on the calculation of the average length of domain walls and on the Edwards-Anderson order parameter) and its characteristics are presented. It was shown that, in the frustrated Ising model, the domain-wall length correlates to the onset of the glassy state, that is, it may play the role of the order parameter for the Ising glass or for glasslike states in other frustrated magnetic systems.

  2. Density functional theory study of sulfur tolerance of copper: New copper-sulfur phase diagram

    NASA Astrophysics Data System (ADS)

    Malyi, Oleksandr I.; Bai, Kewu; Kulish, Vadym V.; Wu, Ping; Chen, Zhong

    2012-04-01

    We study two possible mechanisms of sulfur (S) poisoning of copper (Cu) surfaces: S adsorption and formation of Cu-S compounds. Based on the performed calculations, we predict new Cu-S phase diagram that not only describes the formation of Cu-S compounds but also predicts a dependence of the transition temperature between clean and contaminated Cu surfaces on partial pressure ratio of H2 and H2S (PH2/PH2S). Since conditions under which sulfur sorbs and desorbs at Cu surfaces cannot be predicted directly from the classical thermodynamic database, our study enhances current understanding of Cu-S interaction and mechanisms of S poisoning of Cu-based catalysts.

  3. Melt-gas phase equilibria and state diagrams of the selenium-tellurium system

    NASA Astrophysics Data System (ADS)

    Volodin, V. N.; Trebukhov, S. A.; Burabaeva, N. M.; Nitsenko, A. V.

    2017-05-01

    The partial pressures of saturated vapor of the components in the Se-Te system are determined and presented in the form of temperature-concentration dependences from which the boundaries of the melt-gas phase transition are calculated at atmospheric pressure and vacuums of 2000 and 100 Pa. The existence of azeotropic mixtures is revealed. It is found that the points of inseparably boiling melts correspond to 7.5 at % of Se and 995°C at 101325 Pa, 10.9 at % at 673°C and 19.5 at % at 522°C in vacuums of 2000 and 100 Pa, respectively. A complete state diagram is constructed, including the fields of gas-liquid equilibria at atmospheric and low pressures, the boundaries of which allow us to assess the behavior of selenium and tellurium upon distillation fractionation.

  4. Nonlinear Magnetic Dynamics and The Switching Phase Diagrams in Spintronic Devices

    NASA Astrophysics Data System (ADS)

    Yan, Shu

    Spin-transfer torque induced magnetic switching, by which the spin-polarized current transfers its magnetic moment to the ferromagnetic layer and changes its magnetization, holds great promise towards faster and smaller magnetic bits in data-storage applications due to the lower power consumption and better scalability. We propose an analytic approach which can be used to calculate the switching phase diagram of a nanomagnetic system in the presence of both magnetic field and spin-transfer torque in an exact fashion. This method is applied to the study of switching conditions for the uniaxial, single domain magnetic layers in different spin-transfer devices. In a spin valve with spin polarization collinear with the easy axis, we get a modified Stoner-Wohlfarth astroid which represents many of the features that have been found in experiment. It also shows a self-crossing boundary and demonstrates a region with three stable equilibria. We demonstrate that the region of stable equilibria with energy near the maximum can be reached only through a narrow bottleneck in the field space, which sets a stringent requirement for magnetic field alignment in the experiments. Switching diagrams are then calculated for the setups with magnetic field not perfectly aligned with the easy axis. In a ferromagnet-heavy-metal bilayer device with strong spin Hall effect, the in plane current becomes spin-polarized and transfers its magnetic moment to the ferromagnetic layer by diffusion. The three-dimensional asymmetric phase diagram is calculated. In the case that the external field is confined in the vertical plane defined by the direction of the current and the easy axis, the spin-transfer torque shifts the conventional in-plane (IP) equilibria within the same plane, and also creates two out-of-plane (OOP) equilibria, one of which can be stable. The threshold switching currents for IP switching and OOP switching are discussed. We also address the magnetic switching processes. Damping

  5. Phase diagram of the Kondo necklace model with planar and local anisotropies

    NASA Astrophysics Data System (ADS)

    Mendoza-Arenas, J. J.; Franco, R.; Silva-Valencia, J.

    2010-12-01

    We use the density matrix renormalization group to study the quantum critical behavior of a one-dimensional Kondo necklace model with two anisotropies: η in the XY interaction of conduction spins and Δ in the local exchange between localized and conduction spins (characterized by J). To do so, we calculate the gap between the ground and the first excited state for different values of η and Δ as a function of J, and fit it to a Kosterlitz-Thouless tendency; the point in which the gap vanishes is the quantum critical point Jc. To support our results, we calculate correlation functions and structure factors near the obtained critical points. The use of entanglement measures, specifically the von Neumann block entropy, to identify the quantum phase transition is also presented. Then we build the phase diagram of the model: for every Δ considered, any value of η > 0 generates a quantum phase transition from a Kondo singlet to an antiferromagnetic state at a finite value of J, and as η diminishes, so does Jc; when Δ diminishes for a fixed η, Jc increases, favoring the antiferromagnetic state.

  6. Large vibrational effects upon calculated phase boundaries in Al-Sc.

    PubMed

    Ozoliņs, V; Asta, M

    2001-01-15

    The fcc portion of the Al-Sc phase diagram is calculated from first principles including contributions to alloy free energies associated with ionic vibrations. It is found that vibrational entropy accounts for a 27-fold increase in the calculated solubility limits for Sc in fcc Al at high temperatures, bringing calculated and measured values into very good agreement. The present work gives a clear example demonstrating a large effect of vibrational entropy upon calculated phase boundaries in substitutional alloys.

  7. Ferromagnetic quantum criticality: New aspects from the phase diagram of LaCrGe3

    DOE PAGES

    Taufour, Valentin; Kaluarachchi, Udhara S.; Bud'ko, Sergey L.; ...

    2017-08-25

    Some Recent theoretical and experimental studies have shown that ferromagnetic quantum criticality is always avoided in clean systems. Two possibilities have been identified. In the first scenario, the ferromagnetic transition becomes of the first order at a tricritical point before being suppressed. A wing structure phase diagram is observed indicating the possibility of a new type of quantum critical point under magnetic field. In a second scenario, a transition to a modulated magnetic phase occurs. Our earlier studies on the compound LaCrGe3 illustrate a third scenario where not only a new magnetic phase occurs, but also a change of ordermore » of the transition at a tricritical point leading to a wing-structure phase diagram. Careful experimental study of the phase diagram near the tricritical point also illustrates new rules near this type of point.« less

  8. Phase diagram of the Bose-Hubbard model with T{sub 3} symmetry

    SciTech Connect

    Rizzi, Matteo; Fazio, Rosario; Cataudella, Vittorio

    2006-04-01

    We study the quantum phase transition between the insulating and the globally coherent superfluid phases in the Bose-Hubbard model with T{sub 3} structure, the 'dice lattice'. Even in the absence of any frustration the superfluid phase is characterized by modulation of the order parameter on the different sublattices of the T{sub 3} structure. The zero-temperature critical point as a function of magnetic field shows the characteristic 'butterfly' form. At full frustration the superfluid region is strongly suppressed. In addition, due to the existence of the Aharonov-Bohm cages at f=1/2, we find some evidence for the existence of an intermediate insulating phase characterized by a zero superfluid stiffness but finite compressibility. In this intermediate phase bosons are localized due to the external frustration and the topology of the T{sub 3} lattice. We name this new phase the Aharonov-Bohm insulator. In the presence of charge frustration the phase diagram acquires the typical lobe structure. The form and hierarchy of the Mott insulating states with fractional fillings are dictated by the particular topology of the T{sub 3} lattice. The results presented were obtained by a variety of analytical methods: mean-field and variational techniques to approach the phase boundary from the superconducting side and a strongly coupled expansion appropriate for the Mott insulating region. In addition we performed quantum Monte Carlo simulations of the corresponding (2+1)-dimensional XY model to corroborate the analytical calculations with a more accurate quantitative analysis. We finally discuss experimental realization of the T{sub 3} lattice both with optical lattices and with Josephson junction arrays.

  9. High pressure–low temperature phase diagram of barium: Simplicity versus complexity

    SciTech Connect

    Desgreniers, Serge; Tse, John S.; Matsuoka, Takahiro; Ohishi, Yasuo

    2015-11-30

    Barium holds a distinctive position among all elements studied upon densification. Indeed, it was the first example shown to violate the long-standing notion that high compression of simple metals should preserve or yield close-packed structures. From modest pressure conditions at room temperature, barium transforms at higher pressures from its simple structures to the extraordinarily complex atomic arrangements of the incommensurate and self-hosting Ba-IV phases. By a detailed mapping of the pressure/temperature structures of barium, we demonstrate the existence of another crystalline arrangement of barium, Ba-VI, at low temperature and high pressure. The simple structure of Ba-VI is unlike that of complex Ba-IV, the phase encountered in a similar pressure range at room temperature. First-principles calculations predict Ba-VI to be stable at high pressure and superconductive. The results illustrate the complexity of the low temperature-high pressure phase diagram of barium and the significant effect of temperature on structural phase transformations.

  10. Effect of disorder in the frustrated Ising FCC antiferromagnet: phase diagram and stretched exponential relaxation

    NASA Astrophysics Data System (ADS)

    Ngo, V. Thanh; Hoang, D. Tien; Diep, H. T.; Campbell, I. A.

    2014-04-01

    In this paper, we study the phase transition in a face-centered-cubic antiferromagnet with Ising spins as a function of the concentration p of ferromagnetic bonds randomly introduced into the system. Such a model describes the spin-glass phase at strong bond disorder. Using the standard Monte Carlo simulation and the powerful Wang-Landau flat-histogram method, we carry out in this work intensive simulations over the whole range of p. We show that the first-order transition disappears with a tiny amount of ferromagnetic bonds, namely p 0.01, in agreement with theories and simulations on other 3D models. The antiferromagnetic long-range order is also destroyed with a very small p (≃5%). With increasing p, the system changes into a spin glass and then to a ferromagnetic phase when p > 0.65. The phase diagram in the space (Tc, p) shows an asymmetry, unlike the case of the ±J Ising spin glass on the simple cubic lattice. We calculate the relaxation time around the spin-glass transition temperature and we show that the spin autocorrelation follows a stretched exponential relaxation law where the factor b is equal to ≃1/3 at the transition as suggested by the percolation-based theory. This value is in agreement with experiments performed on various spin glasses and with Monte Carlo simulations on different SG models.

  11. The phase diagram of high-pressure superionic ice

    NASA Astrophysics Data System (ADS)

    Sun, Jiming; Clark, Bryan K.; Torquato, Salvatore; Car, Roberto

    2015-08-01

    Superionic ice is a special group of ice phases at high temperature and pressure, which may exist in ice-rich planets and exoplanets. In superionic ice liquid hydrogen coexists with a crystalline oxygen sublattice. At high pressures, the properties of superionic ice are largely unknown. Here we report evidence that from 280 GPa to 1.3 TPa, there are several competing phases within the close-packed oxygen sublattice. At even higher pressure, the close-packed structure of the oxygen sublattice becomes unstable to a new unusual superionic phase in which the oxygen sublattice takes the P21/c symmetry. We also discover that higher pressure phases have lower transition temperatures. The diffusive hydrogen in the P21/c superionic phase shows strong anisotropic behaviour and forms a quasi-two-dimensional liquid. The ionic conductivity changes abruptly in the solid to close-packed superionic phase transition, but continuously in the solid to P21/c superionic phase transition.

  12. Cold hydrogen EOS/phase diagram from DAC experiments to 300 GPa

    NASA Astrophysics Data System (ADS)

    Eremets, Mikhail

    2013-06-01

    Two new phases of hydrogen have been discovered at room temperature: phase IV above 220 GPa and phase V above 280 GPa. In the present work we studied these phases in a wide temperature range with the aid of Raman, infrared absorption, and electrical measurements at pressures up to 340 GPa. Also, we revised the I-III phase boundary and thus have built a new phase diagram of hydrogen. In particular, we established a new triple point at the phase diagram at 208 GPa and T = 308 K. Our new data further support the previous work that hydrogen is semiconductor in phase IV and most likely semimetal in phase V. M. I. Eremets, I. A. Troyan, A. Drozdov, Ph. Lerch, P. Naumov, Paul Scherrer, Institute, CH 5232 VILLIGEN-PSI, Switzerland.

  13. The phase diagram of water at high pressures as obtained by computer simulations of the TIP4P/2005 model: the appearance of a plastic crystal phase.

    PubMed

    Aragones, J L; Conde, M M; Noya, E G; Vega, C

    2009-01-21

    In this work the high pressure region of the phase diagram of water has been studied by computer simulation by using the TIP4P/2005 model of water. Free energy calculations were performed for ices VII and VIII and for the fluid phase to determine the melting curve of these ices. In addition, molecular dynamics simulations were performed at high temperatures (440 K) observing the spontaneous freezing of the liquid into a solid phase at pressures of about 80,000 bar. The analysis of the structure obtained lead to the conclusion that a plastic crystal phase was formed. In the plastic crystal phase the oxygen atoms were arranged forming a body center cubic structure, as in ice VII, but the water molecules were able to rotate almost freely. Free energy calculations were performed for this new phase, and it was found that for TIP4P/2005 this plastic crystal phase is thermodynamically stable with respect to ices VII and VIII for temperatures higher than about 400 K, although the precise value depends on the pressure. By using Gibbs-Duhem simulations, all coexistence lines were determined, and the phase diagram of the TIP4P/2005 model was obtained, including ices VIII and VII and the new plastic crystal phase. The TIP4P/2005 model is able to describe qualitatively the phase diagram of water. It would be of interest to study if such a plastic crystal phase does indeed exist for real water. The nearly spherical shape of water makes possible the formation of a plastic crystal phase at high temperatures. The formation of a plastic crystal phase at high temperatures (with a bcc arrangements of oxygen atoms) is fast from a kinetic point of view occurring in about 2 ns. This is in contrast to the nucleation of ice Ih which requires simulations of the order of hundreds of ns.

  14. Quantum phases of the Shastry-Sutherland Kondo lattice: implications for the global phase diagram of heavy-fermion metals.

    PubMed

    Pixley, J H; Yu, Rong; Si, Qimiao

    2014-10-24

    Considerable recent theoretical and experimental effort has been devoted to the study of quantum criticality and novel phases of antiferromagnetic heavy-fermion metals. In particular, quantum phase transitions have been discovered in heavy-fermion compounds with geometrical frustration. These developments have motivated us to study the competition between the Ruderman-Kittel-Kasuya-Yosida and Kondo interactions on the Shastry-Sutherland lattice. We determine the zero-temperature phase diagram as a function of magnetic frustration and Kondo coupling within a slave-fermion approach. Pertinent phases include the valence bond solid and heavy Fermi liquid. In the presence of antiferromagnetic order, our zero-temperature phase diagram is remarkably similar to the global phase diagram proposed earlier based on general grounds. We discuss the implications of our results for the experiments on Yb2Pt2Pb and related compounds.

  15. Exploring the Conformational Space of Chromatin Fibers and Their Stability by Numerical Dynamic Phase Diagrams

    PubMed Central

    Stehr, René; Schöpflin, Robert; Ettig, Ramona; Kepper, Nick; Rippe, Karsten; Wedemann, Gero

    2010-01-01

    The three-dimensional structure of chromatin affects DNA accessibility and is therefore a key regulator of gene expression. However, the path of the DNA between consecutive nucleosomes, and the resulting chromatin fiber organization remain controversial. The conformational space available for the folding of the nucleosome chain has been analytically described by phase diagrams with a two-angle model, which describes the chain trajectory by a DNA entry-exit angle at the nucleosome and a torsion angle between consecutive nucleosomes. Here, a novel type of numerical phase diagrams is introduced that relates the geometric phase space to the energy associated with a given chromatin conformation. The resulting phase diagrams revealed differences in the energy landscape that reflect the probability of a given conformation to form in thermal equilibrium. Furthermore, we investigated the effects of entropy and additional degrees of freedom in the dynamic phase diagrams by performing Monte Carlo simulations of the initial chain trajectories. Using our approach, we were able to demonstrate that conformations that initially were geometrically impossible could evolve into energetically favorable states in thermal equilibrium due to DNA bending and torsion. In addition, dynamic phase diagrams were applied to identify chromatin fibers that reflect certain experimentally determined features. PMID:20303860

  16. Miscibility Phase Diagrams of Giant Vesicles Containing Sphingomyelin

    NASA Astrophysics Data System (ADS)

    Veatch, Sarah L.; Keller, Sarah L.

    2005-04-01

    Saturated sphingomyelin (SM) lipids are implicated in lipid rafts in cell plasma membranes. Here we use fluorescence microscopy to observe coexisting liquid domains in vesicles containing SM, an unsaturated phosphatidylcholine lipid (either DOPC or POPC), and cholesterol. We note similar phase behavior in a model membrane mixture without SM (DOPC/DPPC/Chol), but find no micron-scale liquid domains in membranes of POPC/PSM/Chol. We delineate the onset of solid phases below the miscibility transition temperature, and detail indirect evidence for a three-phase coexistence of one solid and two liquid phases.

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

    SciTech Connect

    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 phase diagram is demonstrated.

  18. Phase diagram of speed gradient model with an on-ramp

    NASA Astrophysics Data System (ADS)

    Tang, Chang-Fu; Jiang, Rui; Wu, Qing-Song

    2007-04-01

    In this paper, phase transitions are investigated in speed gradient model with an on-ramp. Phase diagrams of traffic flow composed of manually driven vehicles and adaptive cruise control (ACC) vehicles are studied, respectively. The traffic flow composed of ACC vehicles is modeled by enhancing propagation speed of small disturbance. The phase diagram of traffic flow composed of manually driven vehicles is similar to that in previous works, in which such states as pinned localized cluster (PLC), moving localized cluster (MLC), triggered stop-and-go traffic (TSG), oscillatory congested traffic (OCT), and homogeneous congested traffic (HCT) are reproduced. In the phase diagram of traffic flow composed of ACC vehicles, traffic stability is enhanced and such states as PLC, MLC, and TSG disappear. Furthermore, some interesting phenomena, such as stationary OCT upstream of on-ramp and appearance of second OCT in HCT, are identified.

  19. Phase diagram of a rotating Bose-Einstein condensate with anharmonic confinement

    SciTech Connect

    Jackson, A.D.; Kavoulakis, G.M.; Lundh, E.

    2004-05-01

    We examine the phase diagram of an effectively repulsive Bose-Einstein condensate of atoms that rotates in a quadratic-plus-quartic potential. With use of a variational method we identify the three possible phases of the system as a function of the rotational frequency of the trap and of the coupling constant. The derived phase diagram is shown to be universal and partly exact in the limit of weak interactions and small anharmonicity. The variational results are found to be consistent with numerical solutions of the Gross-Pitaevskii equation.

  20. The topological pressure-temperature phase diagram of fluoxetine nitrate: monotropy unexpectedly turning into enantiotropy

    NASA Astrophysics Data System (ADS)

    Céolin, René; Rietveld, Ivo B.

    2016-09-01

    The phase behavior of pharmaceuticals is important for regulatory requirements and dosage form development. Racemic fluoxetine nitrate possesses two crystalline forms for which initial measurements indicated that they have a monotropic relationship with form I the only stable form. By constructing the topological pressure-temperature phase diagram, it has been shown that unexpectedly form II has a stable domain in the phase diagram and can be easily obtained by heating and grinding. The pressure necessary to obtain form II is only 11 MPa, which is much lower than most pressure used for tableting in the pharmaceutical industry.

  1. The topological pressure-temperature phase diagram of fluoxetine nitrate: monotropy unexpectedly turning into enantiotropy

    NASA Astrophysics Data System (ADS)

    Céolin, René; Rietveld, Ivo B.

    2017-04-01

    The phase behavior of pharmaceuticals is important for regulatory requirements and dosage form development. Racemic fluoxetine nitrate possesses two crystalline forms for which initial measurements indicated that they have a monotropic relationship with form I the only stable form. By constructing the topological pressure-temperature phase diagram, it has been shown that unexpectedly form II has a stable domain in the phase diagram and can be easily obtained by heating and grinding. The pressure necessary to obtain form II is only 11 MPa, which is much lower than most pressure used for tableting in the pharmaceutical industry.

  2. Phase Diagrams of Quasispecies Theory with Recombination and Horizontal Gene Transfer

    NASA Astrophysics Data System (ADS)

    Park, J.-M.; Deem, M. W.

    2007-02-01

    We consider how transfer of genetic information between individuals influences the phase diagram and mean fitness of both the Eigen and the parallel, or Crow-Kimura, models of evolution. In the absence of genetic transfer, these physical models of evolution consider the replication and point mutation of the genomes of independent individuals in a large population. A phase transition occurs, such that below a critical mutation rate an identifiable quasispecies forms. We show how transfer of genetic information changes the phase diagram and mean fitness and introduces metastability in quasispecies theory, via an analytic field theoretic mapping.

  3. Phase diagram of nanoscale alloy particles used for vapor-liquid-solid growth of semiconductor nanowires.

    PubMed

    Sutter, Eli; Sutter, Peter

    2008-02-01

    We use transmission electron microscopy observations to establish the parts of the phase diagram of nanometer sized Au-Ge alloy drops at the tips of Ge nanowires (NWs) that determine their temperature-dependent equilibrium composition and, hence, their exchange of semiconductor material with the NWs. We find that the phase diagram of the nanoscale drop deviates significantly from that of the bulk alloy, which explains discrepancies between actual growth results and predictions on the basis of the bulk-phase equilibria. Our findings provide the basis for tailoring vapor-liquid-solid growth to achieve complex one-dimensional materials geometries.

  4. First-principles atomistic thermodynamics for oxidation catalysis: surface phase diagrams and catalytically interesting regions.

    PubMed

    Reuter, Karsten; Scheffler, Matthias

    2003-01-31

    Present knowledge of the function of materials is largely based on studies (experimental and theoretical) that are performed at low temperatures and ultralow pressures. However, the majority of everyday applications, like, e.g., catalysis, operate at atmospheric pressures and temperatures at or higher than 300 K. Here we employ ab initio, atomistic thermodynamics to construct a phase diagram of surface structures in the (T,p) space from ultrahigh vacuum to technically relevant pressures and temperatures. We emphasize the value of such phase diagrams as well as the importance of the reaction kinetics that may be crucial, e.g., close to phase boundaries.

  5. Ratioed scatter diagrams - An erotetic method for phase identification on complex surfaces using scanning Auger microscopy

    NASA Technical Reports Server (NTRS)

    Browning, R.

    1984-01-01

    By ratioing multiple Auger intensities and plotting a two-dimensional occupational scatter diagram while digitally scanning across an area, the number and elemental association of surface phases can be determined. This can prove a useful tool in scanning Auger microscopic analysis of complex materials. The technique is illustrated by results from an anomalous region on the reaction zone of a SiC/Ti-6Al-4V metal matrix composite material. The anomalous region is shown to be a single phase associated with sulphur and phosphorus impurities. Imaging of a selected phase from the ratioed scatter diagram is possible and may be a useful technique for presenting multiple scanning Auger images.

  6. Phase diagram of a polydisperse soft-spheres model for liquids and colloids.

    PubMed

    Fernández, L A; Martín-Mayor, V; Verrocchio, P

    2007-02-23

    The phase diagram of soft spheres with size dispersion is studied by means of an optimized Monte Carlo algorithm which allows us to equilibrate below the kinetic glass transition for all size distributions. The system ubiquitously undergoes a first-order freezing transition. While for a small size dispersion the frozen phase has a crystalline structure, large density inhomogeneities appear in the highly disperse systems. Studying the interplay between the equilibrium phase diagram and the kinetic glass transition, we argue that the experimentally found terminal polydispersity of colloids is a purely kinetic phenomenon.

  7. Phase diagrams of vortex matter with multi-scale inter-vortex interactions in layered superconductors.

    PubMed

    Meng, Qingyou; Varney, Christopher N; Fangohr, Hans; Babaev, Egor

    2017-01-25

    It was recently proposed to use the stray magnetic fields of superconducting vortex lattices to trap ultracold atoms for building quantum emulators. This calls for new methods for engineering and manipulating of the vortex states. One of the possible routes utilizes type-1.5 superconducting layered systems with multi-scale inter-vortex interactions. In order to explore the possible vortex states that can be engineered, we present two phase diagrams of phenomenological vortex matter models with multi-scale inter-vortex interactions featuring several attractive and repulsive length scales. The phase diagrams exhibit a plethora of phases, including conventional 2D lattice phases, five stripe phases, dimer, trimer, and tetramer phases, void phases, and stable low-temperature disordered phases. The transitions between these states can be controlled by the value of an applied external field.

  8. Phase diagrams of vortex matter with multi-scale inter-vortex interactions in layered superconductors

    NASA Astrophysics Data System (ADS)

    Meng, Qingyou; Varney, Christopher N.; Fangohr, Hans; Babaev, Egor

    2017-01-01

    It was recently proposed to use the stray magnetic fields of superconducting vortex lattices to trap ultracold atoms for building quantum emulators. This calls for new methods for engineering and manipulating of the vortex states. One of the possible routes utilizes type-1.5 superconducting layered systems with multi-scale inter-vortex interactions. In order to explore the possible vortex states that can be engineered, we present two phase diagrams of phenomenological vortex matter models with multi-scale inter-vortex interactions featuring several attractive and repulsive length scales. The phase diagrams exhibit a plethora of phases, including conventional 2D lattice phases, five stripe phases, dimer, trimer, and tetramer phases, void phases, and stable low-temperature disordered phases. The transitions between these states can be controlled by the value of an applied external field.

  9. Dirac-semimetal phase diagram of two-dimensional black phosphorus

    NASA Astrophysics Data System (ADS)

    Doh, Hyeonjin; Choi, Hyoung Joon

    2017-06-01

    Black phosphorus (BP), a layered van der Waals material, reportedly has a band gap sensitive to external perturbations and manifests a Dirac-semimetal phase when its band gap is closed. Previous studies were focused on effects of each perturbation, lacking a unified picture for the band-gap closing and the Dirac-semimetal phase. Here, using pseudospins from the glide-reflection symmetry, we study the electronic structures of mono- and bilayer BP and construct the phase diagram of the Dirac-semimetal phase in the parameter space related to pressure, strain, and electric field. We find that the Dirac-semimetal phase in BP layers is singly connected in the phase diagram, indicating the phase is topologically identical regardless of the gap-closing mechanism. Our findings can be generalized to the Dirac semimetal phase in anisotropic layered materials and can play a guiding role in search for a new class of topological materials and devices.

  10. Phase diagram of cuprate high-temperature superconductors described by a field theory based on anharmonic oxygen degrees of freedom.

    PubMed

    Hsiao, Jenhao; Martyna, Glenn J; Newns, Dennis M

    2015-03-13

    In high temperature superconductors, although some phenomena such as the Mott transition (MT) at low doping are clearly driven by electron correlations, recent experimental data imply that anharmonic oxygen degrees of freedom-characteristic of perovskite materials-are playing a significant role. A key test of the role of anharmonic oxygen is to reproduce the complex cuprate phase diagram from a simple model. Here, we show that a field theory based on nonlinear coupling to anharmonic oxygens, parametrized from ab initio calculations, quantitatively reproduces the cuprate phase diagram for dopings above the MT. Pairing is mediated by renormalized oxygen vibrations transmuted into excitations of the pseudogap. The observed strong dependence of gap to transition temperature ratio on Tc also emerges from this field theory. This work suggests that including vibrational degrees of freedom is key to developing a complete understanding of the cuprates.

  11. Phase diagram of the Kondo lattice model with a superlattice potential

    NASA Astrophysics Data System (ADS)

    Silva-Valencia, J.; Franco, R.; Figueira, M. S.

    2016-02-01

    We study the ground state of a Kondo lattice model where the free carries undergo a superlattice potential. Using the density matrix renormalization group method, we establish that the model exhibits a ferromagnetic phase and spiral phase whose boundaries in the phase diagram depend on the depth of the potential. Also, we observed that the spiral to ferromagnetic quantum phase transition can be tuned by changing the local coupling or the superlattice strength.

  12. Morphology and phase diagram of comb block copolymer Am+1(BC)m.

    PubMed

    Jiang, Zhibin; Wang, Rong; Xue, Gi

    2009-05-28

    The morphologies and the phase diagram of comb copolymer Am+1(BC)m are investigated by the self-consistent field theory. By changing the volume fractions of the blocks, the interaction parameters between the different blocks, and the side chain number, nine phases are found, including the two-colored lamellar phase, three-colored lamellar phase, hexagonal lattice phase, core shell hexagonal lattice phase, two interpenetrating tetragonal lattice, core shell tetragonal lattice, lamellar phase with beads inside, lamellar phase with alternating beads, and disordered phase. The phase diagrams are constructed for Am+1(BC)m with different side chain numbers of m=1, 2, 3, and 5. Due to the asymmetric topology of comb copolymer Am+1(BC)m, the phases and the diagrams are very different from linear ABC triblock copolymer or star ABC triblock copolymer. When the volume fraction of one of the blocks is the domination, the (core shell) hexagonal phase or two interpenetrating tetragonal lattice can form, depending on which block dominates and the interaction between the blocks. The (core shell) hexagonal phase easily forms at the corner of the block A (fA>or=0.5). The side chain number m affects the phase diagram largely due to the fact that the architecture of a comb copolymer is not invariant under the interchange between the three different monomers. Due to the connectivity of the blocks B and the inner blocks A, Am+1(BC)m comb copolymers with the longer main chain A or longer side chain with short block C, i.e., longer block B, are difficult to phase separate. The results are helpful to design nano- or biomaterials with complex architecture or tailor the phase behavior of comb copolymers.

  13. The phase diagram of the monoolein/water system: metastability and equilibrium aspects.

    PubMed

    Qiu, H; Caffrey, M

    2000-02-01

    Interest in the liquid crystal structure, transport and membrane protein crystallizing properties of the monoolein/water system has grown in the recent past. Monoolein is also an important homolog in a series of monoacylglycerols used to decipher how lipid molecular structure relates to liquid crystal phase behavior--information needed for rational design applications and for understanding the origin of membrane lipid diversity. To make intelligent use of the monoolein/water system, a reliable and detailed temperature-composition phase diagram is needed. The phase diagram of Briggs et al. (J Phys II France 1996;6:723-51) was constructed for this purpose. However, we have established that the liquid crystal phases in the latter below ca. 20 degrees C are metastable. By implementing a sub-zero degree (degrees C) sample incubation prior to data collection in the heating direction, we can reset the system into the lamellar crystal phase which we assume represents equilibrium behavior. We have re-examined the low-temperature part of the phase diagram and characterized structurally the new 'equilibrium' phases by static and time-resolved low- and wide-angle X-ray diffraction and by differential scanning calorimetry. A more complete phase diagram that incorporates the new equilibrium behavior at low temperatures is reported.

  14. A Simple Experiment for Demonstration of Phase Diagram of Carbon Dioxide.

    ERIC Educational Resources Information Center

    Lieu, Van T.

    1996-01-01

    Explains an experiment that can be used to help students visualize the phase changes of carbon dioxide. The equipment consists of tweezers and a small plastic syringe. Dry ice is also required. Results are discussed and the phase diagram for carbon dioxide is provided. (DDR)

  15. The phase diagram of high-pressure superionic ice

    PubMed Central

    Sun, Jiming; Clark, Bryan K.; Torquato, Salvatore; Car, Roberto

    2015-01-01

    Superionic ice is a special group of ice phases at high temperature and pressure, which may exist in ice-rich planets and exoplanets. In superionic ice liquid hydrogen coexists with a crystalline oxygen sublattice. At high pressures, the properties of superionic ice are largely unknown. Here we report evidence that from 280 GPa to 1.3 TPa, there are several competing phases within the close-packed oxygen sublattice. At even higher pressure, the close-packed structure of the oxygen sublattice becomes unstable to a new unusual superionic phase in which the oxygen sublattice takes the P21/c symmetry. We also discover that higher pressure phases have lower transition temperatures. The diffusive hydrogen in the P21/c superionic phase shows strong anisotropic behaviour and forms a quasi-two-dimensional liquid. The ionic conductivity changes abruptly in the solid to close-packed superionic phase transition, but continuously in the solid to P21/c superionic phase transition. PMID:26315260

  16. The phase diagram of high-pressure superionic ice.

    PubMed

    Sun, Jiming; Clark, Bryan K; Torquato, Salvatore; Car, Roberto

    2015-08-28

    Superionic ice is a special group of ice phases at high temperature and pressure, which may exist in ice-rich planets and exoplanets. In superionic ice liquid hydrogen coexists with a crystalline oxygen sublattice. At high pressures, the properties of superionic ice are largely unknown. Here we report evidence that from 280 GPa to 1.3 TPa, there are several competing phases within the close-packed oxygen sublattice. At even higher pressure, the close-packed structure of the oxygen sublattice becomes unstable to a new unusual superionic phase in which the oxygen sublattice takes the P2(1)/c symmetry. We also discover that higher pressure phases have lower transition temperatures. The diffusive hydrogen in the P2(1)/c superionic phase shows strong anisotropic behaviour and forms a quasi-two-dimensional liquid. The ionic conductivity changes abruptly in the solid to close-packed superionic phase transition, but continuously in the solid to P2(1)/c superionic phase transition.

  17. Complete Phase Diagram of a Single Polymer Chain

    NASA Astrophysics Data System (ADS)

    Taylor, Mark; Paul, Wolfgang; Binder, Kurt

    2011-10-01

    The phase behavior of a single homopolymer chain is analogous to that of simple liquid, exhibiting an expanded coil (gas-like) phase, a collapsed globule (liquid-like) phase, and a compact solid phase. Using Wang-Landau sampling with bond-rebridging Monte Carlo moves we have studied the complete phase behavior of a flexible interaction-site polymer chain comprised of up to 256 square-well-spheres [1]. Here we present a finite-size scaling analysis for the phase behavior of a SW chain in the long chain limit. For a sufficiently short interaction range, the chain undergoes a direct freezing transition from the expanded coil without an intervening collapse transition. These results confirm the recent lattice model prediction that a collapsed-globule state is unstable with respect to a solid phase for polymers with sufficiently short-range monomer-monomer interactions [2]. [4pt] [1] M.P. Taylor, W. Paul, and K. Binder, J. Chem. Phys. 131, 114907 (2009).[0pt] [2] W. Paul, T. Strauch, F. Rampf, and K. Binder, Phys. Rev. E 75, 060801(R) (2007).

  18. Solubility limits and phase diagrams for fatty alcohols in anionic (SLES) and zwitterionic (CAPB) micellar surfactant solutions.

    PubMed

    Tzocheva, Sylvia S; Danov, Krassimir D; Kralchevsky, Peter A; Georgieva, Gergana S; Post, Albert J; Ananthapadmanabhan, Kavssery P

    2015-07-01

    By analysis of experimental data, a quantitative theoretical interpretation of the solubility limit of medium- and long-chain fatty alcohols in micellar solutions of water-soluble surfactants is presented. A general picture of the phase behavior of the investigated systems is given in the form of phase diagrams. The limited solubility of the fatty alcohols in the micelles of conventional surfactants is explained with the precipitation of their monomers in the bulk, rather than with micelle phase separation. The long chain fatty alcohols (with n=14, 16 and 18 carbon atoms) exhibit an ideal mixing in the micelles of the anionic surfactant sodium laurylethersulfate (SLES) and the zwitterionic surfactant cocamidopropyl betaine (CAPB) at temperatures of 25, 30, 35 and 40 °C. Deviations from ideality are observed for the alcohols of shorter chain (n=10 and 12), which can be explained by a mismatch with the longer chains of the surfactant molecules. Using the determined thermodynamic parameters of the systems, their phase diagrams are constructed. Such a diagram consists of four domains, viz. mixed micelles; coexistent micelles and precipitate (dispersed crystallites or droplets); precipitate without micelles, and molecular solution. The four boundary lines intersect in a quadruple point, Q. For ionic surfactants (like SLES), a detailed theory for calculating the boundary lines of the phase diagrams is developed and verified against data for the positions of the kinks in surface tension isotherms. The theory takes into account the electrostatic interactions in the micellar solutions and the effect of counterion binding. The results can be useful for a quantitative interpretation and prediction of the phase behavior of mixed solutions of two (or more) surfactants, one of them being water soluble and forming micelles, whereas the other one has a limited water solubility, but readily forms mixed micelles with the former surfactant. Copyright © 2014 Elsevier Inc. All rights

  19. Solid-state phase diagram of the zinc sulfide-cadmium sulfide system

    SciTech Connect

    Fedorov, V.A.; Ganshin, V.A.; Korkishko, Y.N. )

    1993-01-01

    The II-VI wide-band compounds zinc sulfide, cadmium sulfide and Cd[sub x]ZN[sub 1[minus]x]S ternary alloys has been of considerable technological interest due to their semiconducting, optical and mechanical properties and are of considerable importance as photoconductors, phosphors, infrared and solar-cell window materials and materials for short-wavelength optoelectronic applications. Structures and phase relation in the ZnS-CdS system were investigated in the temperature range 150-700 C and the boundaries describing the equilibria between the zinc-blend and wurtzite Cd[sub x]An[sub 1[minus]x]S solid solutions were determined by examining the ion exchange processes Cd[sup 2+] [r arrow] Zn[sup 2+] in the ZnS powder. The complete thermodynamical description of the ZnS-CdS system is proposed. It was found, that Cd[sub x]Z[sub n[minus]1]S solid solutions of both modifications obey a regular solution model. Enthalpies of the zinc-blend-to-wurtzite structural phase transition in CdS (550[plus minus]50 J/mol) and in ZnS (1700[plus minus]100 J/mol) were defined. The solid state phase diagram calculated from defined thermodynamical parameters agrees well with the experimental data.

  20. Phase diagram of a semimetal in the magnetic ultra-quantum limit

    NASA Astrophysics Data System (ADS)

    Isidori, Aldo; Arnold, Frank; Kampert, Erik; Yager, Ben; Eschrig, Matthias; Saunders, John

    2015-03-01

    Semimetals like graphite have recently received compelling interest as they not only are able to host topologically non-trivial phases but also can be driven into the ultra-quantum limit by magnetic fields now achievable in modern-day laboratories. Thus, they provide insight into quantum-Hall physics and the physics of massless Dirac fermions in three dimensions. They also represent ideal model systems for studying magnetic-field driven density wave instabilities, as the onset field for such collective excitations is suppressed in semimetals. Using pulsed high-magnetic fields up to 60 T applied to a single crystal of natural Tanzanian graphite, we find a series of field-induced phase transitions into collinear charge-density wave states resulting from enhanced interactions between the lowest four Landau levels. By analysing magneto-transport data and calculating the renormalized Landau level structure at high fields, we establish the phase diagram of graphite in its ultra-quantum limit. Our results imply the existence of a topologically-protected chiral edge state at high fields supporting both charge and spin currents. We acknowledge the support of the HLD-HZDR, member of the European Magnetic Field Laboratory (EMFL), the Hubbard Theory Consortium, and the Engineering and Physical Science Research Council (EPSRC Grant Nos. EP/H048375/1 and EP/J010618/1)

  1. Towards the QCD phase diagram from analytical continuation

    NASA Astrophysics Data System (ADS)

    Bellwied, R.; Borsányi, S.; Fodor, Z.; Günther, J.; Katz, S. D.; Pásztor, A.; Ratti, C.; Szabó, K. K.

    2016-12-01

    We calculate the QCD cross-over temperature, the equation of state and fluctuations of conserved charges at finite density by analytical continuation from imaginary to real chemical potentials. Our calculations are based on new continuum extrapolated lattice simulations using the 4stout staggered actions with a lattice resolution up to Nt = 16. The simulation parameters are tuned such that the strangeness neutrality is maintained, as it is in heavy ion collisions.

  2. Extremely asymmetric phase diagram of homopolymer-monotethered nanoparticles: Competition between chain conformational entropy and particle steric interaction

    NASA Astrophysics Data System (ADS)

    Zhang, Tiancai; Fu, Chao; Yang, Yingzi; Qiu, Feng

    2017-02-01

    The phase behaviors of homopolymer-monotethered nanoparticles (HMNs) in melt are investigated via a theoretical method combining self-consistent field theory for polymers and density functional theory for hard spheres. An extremely asymmetric phase diagram is observed: (i) microphases are only possible for the volume fraction of the tethered polymer fA > 0.35; (ii) in addition to lamellar phase, the system can only self-assemble into various morphologies with a polymer-rich matrix, including gyroid phase, cylindrical phase, and spherical phase. In the frame of this theory, the critical point for HMNs' microphase separation is significantly lower than that of linear diblock copolymers. Furthermore, the characteristic length of microphase-separated structures of HMNs is much smaller than that of linear diblock copolymers with the same molecular weight. Our calculation results on morphologies and characteristic length agree well with recent simulations and experimental observations.

  3. Experimental phase diagram of lithium-intercalated graphite

    SciTech Connect

    Woo, K.C.; Mertwoy, H.; Fischer, J.E.; Kamitakahara, W.A.; Robinson, D.S.

    1983-06-15

    First-order transitions to dilute stage 1 from stages 2--4 and from mixed stages are observed in Li-graphite compounds in the range 430--1020 K. The resulting (T,x) phase boundary agrees generally with predictions by Safran and others except for a sharp peak of very stable stage-2 compositions around xapprox.0.4. The commensurability energy does not contribute to this peak since both low-T and high-T phases are disordered.

  4. Quarkyonic Matter and the Phase Diagram of QCD

    SciTech Connect

    McLerran,L.

    2008-05-15

    Quarkyonic matter is a new phase of QCD at finite temperature and density which is distinct from the confined and de-confined phases. Its existence is unambiguously argued in the large numbers of colors limit, N{sub c} {yields} {infinity}, of QCD. Hints of its existence for QCD, N{sub c} = 3, are shown in lattice Monte-Carlo data and in heavy ion experiments.

  5. Phase diagram of quantum critical system via local convertibility of ground state

    PubMed Central

    Liu, Si-Yuan; Quan, Quan; Chen, Jin-Jun; Zhang, Yu-Ran; Yang, Wen-Li; Fan, Heng

    2016-01-01

    We investigate the relationship between two kinds of ground-state local convertibility and quantum phase transitions in XY model. The local operations and classical communications (LOCC) convertibility is examined by the majorization relations and the entanglement-assisted local operations and classical communications (ELOCC) via Rényi entropy interception. In the phase diagram of XY model, LOCC convertibility and ELOCC convertibility of ground-states are presented and compared. It is shown that different phases in the phase diagram of XY model can have different LOCC or ELOCC convertibility, which can be used to detect the quantum phase transition. This study will enlighten extensive studies of quantum phase transitions from the perspective of local convertibility, e.g., finite-temperature phase transitions and other quantum many-body models. PMID:27381284

  6. Reentrant and forward phase diagrams of the anisotropic three-dimensional Ising spin glass.

    PubMed

    Güven, Can; Berker, A Nihat; Hinczewski, Michael; Nishimori, Hidetoshi

    2008-06-01

    The spatially uniaxially anisotropic d=3 Ising spin glass is solved exactly on a hierarchical lattice. Five different ordered phases, namely, ferromagnetic, columnar, layered, antiferromagnetic, and spin-glass phases, are found in the global phase diagram. The spin-glass phase is more extensive when randomness is introduced within the planes than when it is introduced in lines along one direction. Phase diagram cross sections, with no Nishimori symmetry, with Nishimori symmetry lines, or entirely imbedded into Nishimori symmetry, are studied. The boundary between the ferromagnetic and spin-glass phases can be either reentrant or forward, that is either receding from or penetrating into the spin-glass phase, as temperature is lowered. However, this boundary is always reentrant when the multicritical point terminating it is on the Nishimori symmetry line.

  7. Phase diagram of power law and Lennard-Jones systems: Crystal phases

    SciTech Connect

    Travesset, Alex

    2014-10-28

    An extensive characterization of the low temperature phase diagram of particles interacting with power law or Lennard-Jones potentials is provided from Lattice Dynamical Theory. For power law systems, only two lattice structures are stable for certain values of the exponent (or softness) (A15, body centered cube (bcc)) and two more (face centered cubic (fcc), hexagonal close packed (hcp)) are always stable. Among them, only the fcc and bcc are equilibrium states. For Lennard-Jones systems, the equilibrium states are either hcp or fcc, with a coexistence curve in pressure and temperature that shows reentrant behavior. The hcp solid never coexists with the liquid. In all cases analyzed, for both power law and Lennard-Jones potentials, the fcc crystal has higher entropy than the hcp. The role of anharmonic terms is thoroughly analyzed and a general thermodynamic integration to account for them is proposed.

  8. Phase diagram of power law and Lennard-Jones systems: Crystal phases

    SciTech Connect

    Travesset, Alex

    2014-10-28

    An extensive characterization of the low temperature phase diagram of particles interacting with power law or Lennard-Jones potentials is provided from Lattice Dynamical Theory. For power law systems, only two lattice structures are stable for certain values of the exponent (or softness) (A15, body centered cube (bcc)) and two more (face centered cubic (fcc), hexagonal close packed (hcp)) are always stable. Among them, only the fcc and bcc are equilibrium states. For Lennard-Jones systems, the equilibrium states are either hcp or fcc, with a coexistence curve in pressure and temperature that shows reentrant behavior. The hcp solid never coexists with the liquid. In all cases analyzed, for both power law and Lennard-Jones potentials, the fcc crystal has higher entropy than the hcp. The role of anharmonic terms is thoroughly analyzed and a general thermodynamic integration to account for them is proposed.

  9. Phase diagram of power law and Lennard-Jones systems: Crystal phases

    NASA Astrophysics Data System (ADS)

    Travesset, Alex

    2014-10-01

    An extensive characterization of the low temperature phase diagram of particles interacting with power law or Lennard-Jones potentials is provided from Lattice Dynamical Theory. For power law systems, only two lattice structures are stable for certain values of the exponent (or softness) (A15, body centered cube (bcc)) and two more (face centered cubic (fcc), hexagonal close packed (hcp)) are always stable. Among them, only the fcc and bcc are equilibrium states. For Lennard-Jones systems, the equilibrium states are either hcp or fcc, with a coexistence curve in pressure and temperature that shows reentrant behavior. The hcp solid never coexists with the liquid. In all cases analyzed, for both power law and Lennard-Jones potentials, the fcc crystal has higher entropy than the hcp. The role of anharmonic terms is thoroughly analyzed and a general thermodynamic integration to account for them is proposed.

  10. Phase diagram of power law and Lennard-Jones systems: crystal phases.

    PubMed

    Travesset, Alex

    2014-10-28

    An extensive characterization of the low temperature phase diagram of particles interacting with power law or Lennard-Jones potentials is provided from Lattice Dynamical Theory. For power law systems, only two lattice structures are stable for certain values of the exponent (or softness) (A15, body centered cube (bcc)) and two more (face centered cubic (fcc), hexagonal close packed (hcp)) are always stable. Among them, only the fcc and bcc are equilibrium states. For Lennard-Jones systems, the equilibrium states are either hcp or fcc, with a coexistence curve in pressure and temperature that shows reentrant behavior. The hcp solid never coexists with the liquid. In all cases analyzed, for both power law and Lennard-Jones potentials, the fcc crystal has higher entropy than the hcp. The role of anharmonic terms is thoroughly analyzed and a general thermodynamic integration to account for them is proposed.

  11. Superconducting phase diagrams of cuprates and pnictides as a key to understanding the HTSC mechanism

    NASA Astrophysics Data System (ADS)

    Mitsen, K. V.; Ivanenko, O. M.

    2017-04-01

    This paper reviews experimental phase diagrams of cuprates and pnictides to demonstrate that specific features of the superconducting phase diagrams in both HTSC families can be understood within the framework of the proposed approach, which assumes the formation, under heterovalent doping, of localized trion complexes consisting of a doped carrier and charge transfer (CT) excitons. The geometry of such cells containing CT excitons (CT plaquettes) in the basal plane of the crystal is determined by its crystal structure and the type of dopant, so that the dopant concentration range corresponding to the existence of a percolation cluster of CT plaquettes can be readily determined for each particular compound. These dopant concentration ranges coincide with good accuracy with the experimental ranges of superconducting domes in the phase diagrams of the HTSC compounds considered. The generation of free carriers and the mechanism of superconducting pairing in this pattern is related to biexciton complexes (Heitler-London centers) emerging in neighboring CT plaquettes.

  12. The phase diagram of a directed polymer in random media with p-spin ferromagnetic interactions

    NASA Astrophysics Data System (ADS)

    Wedagedera, J. R.

    2011-01-01

    We consider a directed polymer model with an additive p-spin (p>2) ferromagnetic term in the Hamiltonian. We give a rigorous proof for the specific free energy and derive the phase diagram. This model was proposed previously, and a detailed proof was given in the case p = 2, while the main result was only stated for p > 2. We give a detailed proof of the main result and show the behavior of the model as p → ∞ by constructing the phase diagram also in this case. These results are important in many applications, for instance, in telecommunication and immunology. Our major finding is that in the phase diagram for p > 2, a new transition curve (absent for p = 2) emerges between the paramagnetic region and the so-called mixed region and that the ferromagnetic region diminishes as p → ∞.

  13. Phase diagrams of anisotropic ferrimagnet HoCo{sub 3}Ni{sub 2} with T{sub comp} = T{sub SR1}

    SciTech Connect

    Zawadzki, J.; Szymczak, R.; Zvezdin, A.K.; Krynetski, I.

    1994-03-01

    The magnetic phase diagrams of the hexagonal intermetallic ferrimagnet HoCo{sub 3}Ni{sub 2} showing the spin reorientation transition are presented. The diagrams have been calculated from the thermodynamic potential including the exchange energy as well as the anisotropy energy, taking into consideration the second and fourth-order anisotropy terms. The obtained phase diagrams differ substantially from those of the isotropic or uniaxial ferrimagnets. In fields parallel to the basal plane, the new cone-canting phase with constant susceptibility has been found In the spin reorientation range. In fields parallel to the hexagonal axis there exists a narrow link between low and high-field canted phases. The existence of the new cone-canting phase has been confirmed by magnetization measurements on a single crystal using both ballistic and SQUID magnetometers.

  14. QCD Phase Diagram at Finite Baryon and Isospin Chemical Potentials

    SciTech Connect

    Sasaki, T.; Sakai, Y.; Yahiro, M.; Kouno, H.

    2011-10-21

    The phase structure of two-flavor QCD is explored for finite temperature T and finite baryon- and isospin-chemical potentials, {mu}{sub B} and {mu}{sub I}, by using the Polyakov-loop extended Nambu-Jona-Lasinio (PNJL) model. The PNJL model with the scalar-type eight-quark interaction can reproduce lattice QCD data in the {mu}{sub I}-T plane at {mu}{sub B} = 0. In the {mu}{sub I}-{mu}{sub B}-T space, the critical endpoint of the chiral phase transition in the {mu}{sub B}-T plane at {mu}{sub I} = 0 moves to the tricritical point of the pion-superfluidity phase transition in the {mu}{sub I}-T plane at {mu}{sub B} = 0 as {mu}{sub I} increases.

  15. Phase diagram of superconductors from nonperturbative flow equations

    SciTech Connect

    Bergerhoff, B.; Freire, F.; Litim, D.F.; Lola, S.; Wetterich, C.

    1996-03-01

    The universal behavior of superconductors near the phase transition is described by the three-dimensional field theory of scalar quantum electrodynamics. We approximately solve the model with the help of nonperturbative flow equations. A first- or second-order phase transition is found depending on the relative strength of the scalar versus the gauge coupling. The region of a second-order phase transition is governed by a fixed point of the flow equations with associated critical exponents. We also give an approximate description of the tricritical behavior and briefly discuss the crossover relevant for the onset of scaling near the critical temperature. Final confirmation of a second-order transition for strong type-II superconductors requires further analysis with extended truncations of the flow equations. {copyright} {ital 1996 The American Physical Society.}

  16. Automated Discovery and Construction of Surface Phase Diagrams Using Machine Learning.

    PubMed

    Ulissi, Zachary W; Singh, Aayush R; Tsai, Charlie; Nørskov, Jens K

    2016-10-06

    Surface phase diagrams are necessary for understanding surface chemistry in electrochemical catalysis, where a range of adsorbates and coverages exist at varying applied potentials. These diagrams are typically constructed using intuition, which risks missing complex coverages and configurations at potentials of interest. More accurate cluster expansion methods are often difficult to implement quickly for new surfaces. We adopt a machine learning approach to rectify both issues. Using a Gaussian process regression model, the free energy of all possible adsorbate coverages for surfaces is predicted for a finite number of adsorption sites. Our result demonstrates a rational, simple, and systematic approach for generating accurate free-energy diagrams with reduced computational resources. The Pourbaix diagram for the IrO2(110) surface (with nine coverages from fully hydrogenated to fully oxygenated surfaces) is reconstructed using just 20 electronic structure relaxations, compared to approximately 90 using typical search methods. Similar efficiency is demonstrated for the MoS2 surface.

  17. Solidification of ternary systems with a nonlinear phase diagram

    NASA Astrophysics Data System (ADS)

    Alexandrov, D. V.; Dubovoi, G. Yu.; Malygin, A. P.; Nizovtseva, I. G.; Toropova, L. V.

    2017-02-01

    The directional solidification of a ternary system with an extended phase transition region is theoretically studied. A mathematical model is developed to describe quasi-stationary solidification, and its analytical solution is constructed with allowance for a nonlinear liquidus line equation. A deviation of the liquidus equation from a linear function is shown to result in a substantial change in the solidification parameters.

  18. Quarkyonic Matter and the Revised Phase Diagram of QCD

    SciTech Connect

    McLerran,L.

    2009-03-30

    At high baryon number density, it has been proposed that a new phase of QCD matter controlsthe physics. This matter is confining but can have densities much larger than 3QCD. Its existenceis argued from large Nc approximations, and model computations. It is approximately chirallysymmetric.

  19. T-p phase diagrams and the barocaloric effect in materials with successive phase transitions

    NASA Astrophysics Data System (ADS)

    Gorev, M. V.; Bogdanov, E. V.; Flerov, I. N.

    2017-09-01

    An analysis of the extensive and intensive barocaloric effect (BCE) at successive structural phase transitions in some complex fluorides and oxyfluorides was performed. The high sensitivity of these compounds to a change in the chemical pressure allows one to vary the succession and parameters of the transformations (temperature, entropy, baric coefficient) over a wide range and obtain optimal values of the BCE. A comparison of different types of schematic T-p phase diagrams with the complicated T( p) dependences observed experimentally shows that in some ranges of temperature and pressure the BCE in compounds undergoing successive transformations can be increased due to a summation of caloric effects associated with distinct phase transitions. The maximum values of the extensive and intensive BCE in complex fluorides and oxyfluorides can be realized at rather low pressure (0.1-0.3 GPa). In a narrow temperature range around the triple points conversion from conventional BCE to inverse BCE is observed, which is followed by a gigantic change of both \\vertΔ S_BCE\\vert and \\vertΔ T_AD\\vert .

  20. Analysis of the phase solubility diagram of a phenacetin/competitor/beta-cyclodextrin ternary system, involving competitive inclusion complexation.

    PubMed

    Ono, N; Hirayama, F; Arima, H; Uekama, K

    2001-01-01

    The competitive inclusion complexations in the ternary phenacetin/competitors/beta-cyclodextrin (beta-CyD) systems were investigated by the solubility method, where m-bromobenzoic acid (m-BBA) and o-toluic acid (o-TA) were used as competitors. The solubility changes of the drug and competitors as a function of beta-CyD concentration in the ternary systems were formulated using their stability constants and intrinsic solubilities. The decrease in solubility of phenacetin by the addition of competitors could be quantitatively simulated by the formulation, when both drug and competitor give A(L) type solubility diagrams. On the other hand, when one of the guests gives a B(S) type solubility diagram, its solubility change was clearly reflected in that of the another guest, i.e., phenacetin gave an A(L) type solubility diagram in the binary phenacetin/beta-CyD system and o-TA gave a B(S) type diagram in the binary o-TA/beta-CyD system, but in the ternary phenacetin/o-TA/beta-CyD system, a new plateau region appeared in the original A(L) type diagram of phenacetin. This was explained by the solubilization theory of Higuchi and Connors. The solubility analysis of the ternary drug/competitor/CyD systems may be particularly useful for determination of the stability constant of a drug whose physicochemical and spectroscopic analyses are difficult, because they can be calculated by monitoring the solubility change of a competitor, without monitoring that of a drug. Furthermore, the present results suggest that attention should be paid to the type of the phase solubility diagram, as well as the magnitude of the stability constant and the solubility of the complex, for a rational formulation design of CyD complexes.

  1. The solid-liquid phase diagrams of binary mixtures of consecutive, even saturated fatty acids.

    PubMed

    Costa, Mariana C; Sardo, Mariana; Rolemberg, Marlus P; Coutinho, João A P; Meirelles, Antonio J A; Ribeiro-Claro, Paulo; Krähenbühl, M A

    2009-08-01

    For the first time, the solid-liquid phase diagrams of five binary mixtures of saturated fatty acids are here presented. These mixtures are formed of caprylic acid (C(8:0))+capric acid (C(10:0)), capric acid (C(10:0))+lauric acid (C(12:0)), lauric acid (C(12:0))+myristic acid (C(14:0)), myristic acid (C(14:0))+palmitic acid (C(16:0)) and palmitic acid (C(16:0))+stearic acid (C(18:0)). The information used in these phase diagrams was obtained by differential scanning calorimetry (DSC), X-ray diffraction (XRD), FT-Raman spectrometry and polarized light microscopy, aiming at a complete understanding of the phase diagrams of the fatty acid mixtures. All of the phase diagrams reported here presented the same global behavior and it was shown that this was far more complex than previously imagined. They presented not only peritectic and eutectic reactions, but also metatectic reactions, due to solid-solid phase transitions common in fatty acids and regions of solid solution not previously reported. This work contributes to the elucidation of the phase behavior of these important biochemical molecules, with implications in various industrial applications.

  2. Phase diagrams of the Katz-Lebowitz-Spohn process on lattices with a junction

    NASA Astrophysics Data System (ADS)

    Tian, Bo; Jiang, Rui; Ding, Zhong-Jun; Hu, Mao-Bin; Wu, Qing-Song

    2013-06-01

    This paper studies the Katz-Lebowitz-Spohn (KLS) process on lattices with a junction, where particles move on parallel lattice branches that combine into a single lattice at the junction. It is shown that 11 kinds of phase diagrams could be observed, depending on the two parameters ɛ and δ in the KLS process. We have investigated the phase diagrams as well as bulk density analytically based on flow rate conservation and the extremal current principle. Extensive Monte Carlo computer simulations are performed, and it is found that they are in excellent agreement with theoretical prediction.

  3. The binary phase diagram of propranolol hydrochloride and crystallization-based enantioseparation.

    PubMed

    Polenske, Daniel; Lorenz, Heike; Seidel-Morgenstern, Andreas

    2010-04-01

    Inconsistent results were reported for the solid-state nature of the racemic species of the pharmaceutical relevant compound propranolol hydrochloride. In this work the binary phase diagram of the propranolol hydrochloride enantiomers is studied. Differential scanning calorimetry (DSC), X-ray powder diffraction (XRPD), and high performance liquid chromatography (HPLC) were used as analytical methods. The type of the racemic species, the presence and extent of partial solid solutions and the stability regions of polymorphic forms in the system were investigated. The identified binary phase diagram is sketched. Finally, the feasibility of crystallization-based resolution is discussed. 2009 Wiley-Liss, Inc. and the American Pharmacists Association

  4. Lattice QCD phase diagram in and away from the strong coupling limit.

    PubMed

    de Forcrand, Ph; Langelage, J; Philipsen, O; Unger, W

    2014-10-10

    We study lattice QCD with four flavors of staggered quarks. In the limit of infinite gauge coupling, "dual" variables can be introduced, which render the finite-density sign problem mild and allow a full determination of the μ-T phase diagram by Monte Carlo simulations, also in the chiral limit. However, the continuum limit coincides with the weak coupling limit. We propose a strong-coupling expansion approach towards the continuum limit. We show first results, including the phase diagram and its chiral critical point, from this expansion truncated at next-to-leading order.

  5. Phase diagram of the Fe-Sn-Zr system at 800 °C

    NASA Astrophysics Data System (ADS)

    Nieva, N.; Corvalán, C.; Jiménez, M. J.; Gómez, A.; Arreguez, C.; Joubert, J.-M.; Arias, D.

    2017-04-01

    New experimental results on the Fe-Sn-Zr phase diagram at 800 °C are presented, particularly in the central, Fe rich and Sn rich regions of the Gibbs triangle. Seven ternary alloys were designed, produced and examined by different techniques: optical and scanning electron microscopy, semi-quantitative microanalysis, quantitative microanalysis and X-ray diffraction. The results of this work and previous experimental data were used to determine the phase diagram section at 800 °C which contains at least five ternary compounds: Fe6Sn6Zr, Y, X‧, θ and C36.

  6. Phase diagrams and magnetic properties of a superlattice with alternate layers

    NASA Astrophysics Data System (ADS)

    Feraoun, A.; Zaim, A.; Kerouad, M.

    2015-03-01

    The phase diagrams and magnetic properties of an Ising superlattice are investigated by means of Monte Carlo simulation based on Metropolis algorithm. The system is formed by alternate layers of spins S = 1 and σ = 3 / 2. The effects of the exchange coupling interactions and the crystal field on the phase diagrams and magnetic properties of the system are examined. A number of characteristic behaviors have been found. In particular, tricritical point, critical end point, and isolated critical point may occur in the present system.

  7. Phase diagram of dipolar hard-core bosons on a honeycomb lattice

    NASA Astrophysics Data System (ADS)

    Nakafuji, Takashi; Ito, Takeshi; Nagamori, Yuya; Ichinose, Ikuo

    2016-08-01

    In this paper, we study phase diagrams of dipolar hard-core boson gases on a honeycomb lattice. The system is described by the Haldane-Bose-Hubbard model with complex hopping amplitudes and nearest-neighbor repulsion. By using the slave-particle representation of the hard-core bosons and also the path-integral quantum Monte Carlo simulations, we investigate the system and show that the systems have a rich phase diagram. There are Mott, superfluid, chiral superfluid, and sublattice chiral superfluid phases as well as the density-wave phase. We also found a coexisting phase of superfluid and chiral superfluid. Critical behaviors of the phase transitions are also clarified.

  8. Novel phase diagram of antiferromagnetism and superconductivity in CeRhIn5

    NASA Astrophysics Data System (ADS)

    Yashima, M.; Kawasaki, S.; Mukuda, H.; Kitaoka, Y.; Shishido, H.; Settai, R.; Ōnuki, Y.

    2007-03-01

    We report on the pressure (P)-induced phase diagram of antiferromagnetism (AFM) and superconductivity (SC) which emerges at their border at zero magnetic field. The nuclear-quadrupole-resonance (NQR) measurements have revealed that AFM can take place in the superconducting state with Tc˜2.1 K at P=2.05 GPa. The present experiments have, for the first time, demonstrated that AFM phase, AFM+SC uniformly coexisting phase, SC phase and paramagnetic phase all contact with each other at Ttetra˜2.1 K and Ptetra˜2 GPa which evidence the existence of the tetracritical point in the P- T phase diagram of AFM and SC in CeRnIn5.

  9. New approaches to the simulation of heat-capacity curves and phase diagrams of pseudobinary phospholipid mixtures.

    PubMed Central

    Johann, C; Garidel, P; Mennicke, L; Blume, A

    1996-01-01

    A simulation program using least-squares minimization was developed to calculate and fit heat capacity (cp) curves to experimental thermograms of dilute aqueous dispersions of phospholipid mixtures determined by high-sensitivity differential scanning calorimetry. We analyzed cp curves and phase diagrams of the pseudobinary aqueous lipid systems 1,2-dimyristoyl-sn-glycero-3-phosphatidylglycerol/ 1,2-dipalmitoyl-sn-glycero-3phosphatidylcholine (DMPG/DPPC) and 1,2-dimyristoyl-sn-glycero-3-phosphatidic acid/1, 2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DMPA/DPPC) at pH 7. The simulation of the cp curves is based on regular solution theory using two nonideality parameters rho g and rho l for symmetric nonideal mixing in the gel and the liquid-crystalline phases. The broadening of the cp curves owing to limited cooperativity is incorporated into the simulation by convolution of the cp curves calculated for infinite cooperativity with a broadening function derived from a simple two-state transition model with the cooperative unit size n = delta HVH/delta Hcal as an adjustable parameter. The nonideality parameters and the cooperative unit size turn out to be functions of composition. In a second step, phase diagrams were calculated and fitted to the experimental data by use of regular solution theory with four different model assumptions. The best fits were obtained with a four-parameter model based on nonsymmetric, nonideal mixing in both phases. The simulations of the phase diagrams show that the absolute values of the nonideality parameters can be changed in a certain range without large effects on the shape of the phase diagram as long as the difference of the nonideality parameters for rho g for the gel and rho l for the liquid-crystalline phase remains constant. The miscibility in DMPG/DPPC and DMPA/DPPC mixtures differs remarkably because, for DMPG/DPPC, delta rho = rho l -rho g is negative, whereas for DMPA/DPPC this difference is positive. For DMPA/DPPC, this

  10. Magnetic phase diagram of magnetoelectric LiMnPO4

    SciTech Connect

    Toft-Petersen, Rasmus; Andersen, Niels H.; Li, Haifeng; Li, Jiying; Tian, Wei; Budko, Serguei L.; Jensen, Thomas B.S.; Niedermayer, Christof; Laver, Mark; Zaharko, Oksana; Lynn, Jeffrey W.; Vaknin, David

    2012-06-14

    The nature of the spin-flop (SF) transition in the magnetoelectric quasi-2D Heisenberg system LiMnPO4 is studied in fields applied along the a axis. A refinement of the magnetic structure using neutron diffraction data in the SF phase reveals that the spins reorient from being parallel to the a axis to be nearly along the c axis at magnetic fields between 4 and 4.7 T, depending on temperature. The low-field antiferromagnetic phase boundary is shown to join the spin-flop line tangentially at the so-called bicritical point, where there is a suppression of the ordering temperature. At the bicritical field, we observe an increased intensity of the Lorentz broadened elastic scattering at magnetic Bragg peaks above TN as compared to zero field and 10 T, without an increase in peak width. This suggests an increased density of fluctuations at the bicritical field as compared to zero field.

  11. Phase diagram of interacting spinless fermions on the honeycomb lattice.

    PubMed

    Capponi, Sylvain

    2017-02-01

    Fermions hopping on a hexagonal lattice represent one of the most active research fields in condensed matter since the discovery of graphene in 2004 and its numerous applications. Another exciting aspect of the interplay between geometry and quantum mechanical effects is given by the Haldane model (Haldane 1988 Phys. Rev. Lett. 61 2015), where spinless fermions experiencing a certain flux pattern on the honeycomb lattice leads to the stabilization of a topological phase of matter, distinct from a Mott insulator and nowadays dubbed Chern insulator. In this context, it is crucial to understand the role of interactions and this review will describe recent results that have been obtained for a minimal model, namely spinless fermions with nearest and next-nearest neighbour density-density interactions on the honeycomb lattice at half-filling. Topics addressed include an introduction of the minimal model and a discussion of the possible instabilities of the Dirac semimetal, a presentation of various theoretical and numerical approaches, and a summary of the results with a particular emphasis on the stability or not of some exotic quantum phases such as charge ordered ones (similar to Wigner crystals) and spontaneous Chern insulator phases.

  12. Phase diagram of interacting spinless fermions on the honeycomb lattice

    NASA Astrophysics Data System (ADS)

    Capponi, Sylvain

    2017-02-01

    Fermions hopping on a hexagonal lattice represent one of the most active research fields in condensed matter since the discovery of graphene in 2004 and its numerous applications. Another exciting aspect of the interplay between geometry and quantum mechanical effects is given by the Haldane model (Haldane 1988 Phys. Rev. Lett. 61 2015), where spinless fermions experiencing a certain flux pattern on the honeycomb lattice leads to the stabilization of a topological phase of matter, distinct from a Mott insulator and nowadays dubbed Chern insulator. In this context, it is crucial to understand the role of interactions and this review will describe recent results that have been obtained for a minimal model, namely spinless fermions with nearest and next-nearest neighbour density-density interactions on the honeycomb lattice at half-filling. Topics addressed include an introduction of the minimal model and a discussion of the possible instabilities of the Dirac semimetal, a presentation of various theoretical and numerical approaches, and a summary of the results with a particular emphasis on the stability or not of some exotic quantum phases such as charge ordered ones (similar to Wigner crystals) and spontaneous Chern insulator phases.

  13. Partial Redetermination of the Fe-W Phase Diagram

    NASA Astrophysics Data System (ADS)

    Antoni-Zdziobek, Annie; Commeau, Thierry; Joubert, Jean-Marc

    2013-07-01

    The objective of the current study is to perform a careful investigation of the (Fe) and (W) solvus and of the intermetallic compounds in the Fe-W system as it could have a significant impact on higher-order systems based on this binary system. Two key alloys, Fe-14 at. pct W and Fe-50 at. pct W, and a diffusion couple were synthesized based on the literature. They were studied by long time annealing experiments with a selected heat treatment route, X-Ray diffraction analysis, and electron microprobe analysis with a careful control of impurity levels of C, Si, and O. The two intermetallic phases μ-Fe7W6 and λ-Fe2W are characterized and the composition range of the μ-Fe7W6 phase is specified. The phase previously reported as FeW is most probably a ternary carbide with low carbon content. An accurate determination of the solubility of W in αFe and of Fe in αW is presented.

  14. QCD phase diagram at finite baryon and isospin chemical potentials

    SciTech Connect

    Sasaki, Takahiro; Sakai, Yuji; Yahiro, Masanobu; Kouno, Hiroaki

    2010-12-01

    The phase structure of two-flavor QCD is explored for thermal systems with finite baryon- and isospin-chemical potentials, {mu}{sub B} and {mu}{sub iso}, by using the Polyakov-loop extended Nambu-Jona-Lasinio (PNJL) model. The PNJL model with the scalar-type eight-quark interaction can reproduce lattice QCD data at not only {mu}{sub iso}={mu}{sub B}=0, but also {mu}{sub iso}>0 and {mu}{sub B}=0. In the {mu}{sub iso}-{mu}{sub B}-T space, where T is temperature, the critical endpoint of the chiral phase transition in the {mu}{sub B}-T plane at {mu}{sub iso}=0 moves to the tricritical point of the pion-superfluidity phase transition in the {mu}{sub iso}-T plane at {mu}{sub B}=0 as {mu}{sub iso} increases. The thermodynamics at small T is controlled by {radical}({sigma}{sup 2}+{pi}{sup 2}) defined by the chiral and pion condensates, {sigma} and {pi}.

  15. Computational phase diagrams of noble gas hydrates under pressure

    NASA Astrophysics Data System (ADS)

    Teeratchanan, Pattanasak; Hermann, Andreas

    2015-10-01

    We present results from a first-principles study on the stability of noble gas-water compounds in the pressure range 0-100 kbar. Filled-ice structures based on the host water networks ice-Ih, ice-Ic, ice-II, and C0 interacting with guest species He, Ne, and Ar are investigated, using density functional theory (DFT) with four different exchange-correlation functionals that include dispersion effects to various degrees: the non-local density-based optPBE-van der Waals (vdW) and rPW86-vdW2 functionals, the semi-empirical D2 atom pair correction, and the semi-local PBE functional. In the He-water system, the sequence of stable phases closely matches that seen in the hydrogen hydrates, a guest species of comparable size. In the Ne-water system, we predict a novel hydrate structure based on the C0 water network to be stable or at least competitive at relatively low pressure. In the Ar-water system, as expected, no filled-ice phases are stable; however, a partially occupied Ar-C0 hydrate structure is metastable with respect to the constituents. The ability of the different DFT functionals to describe the weak host-guest interactions is analysed and compared to coupled cluster results on gas phase systems.

  16. Computational phase diagrams of noble gas hydrates under pressure

    SciTech Connect

    Teeratchanan, Pattanasak Hermann, Andreas

    2015-10-21

    We present results from a first-principles study on the stability of noble gas-water compounds in the pressure range 0-100 kbar. Filled-ice structures based on the host water networks ice-I{sub h}, ice-I{sub c}, ice-II, and C{sub 0} interacting with guest species He, Ne, and Ar are investigated, using density functional theory (DFT) with four different exchange-correlation functionals that include dispersion effects to various degrees: the non-local density-based optPBE-van der Waals (vdW) and rPW86-vdW2 functionals, the semi-empirical D2 atom pair correction, and the semi-local PBE functional. In the He-water system, the sequence of stable phases closely matches that seen in the hydrogen hydrates, a guest species of comparable size. In the Ne-water system, we predict a novel hydrate structure based on the C{sub 0} water network to be stable or at least competitive at relatively low pressure. In the Ar-water system, as expected, no filled-ice phases are stable; however, a partially occupied Ar-C{sub 0} hydrate structure is metastable with respect to the constituents. The ability of the different DFT functionals to describe the weak host-guest interactions is analysed and compared to coupled cluster results on gas phase systems.

  17. Spinodal decomposition in amorphous metal-silicate thin films: Phase diagram analysis and interface effects on kinetics

    NASA Astrophysics Data System (ADS)

    Kim, H.; McIntyre, P. C.

    2002-11-01

    Among several metal silicate candidates for high permittivity gate dielectric applications, the mixing thermodynamics of the ZrO2-SiO2 system were analyzed, based on previously published experimental phase diagrams. The driving force for spinodal decomposition was investigated in an amorphous silicate that was treated as a supercooled liquid solution. A subregular model was used for the excess free energy of mixing of the liquid, and measured invariant points were adopted for the calculations. The resulting simulated ZrO2-SiO2 phase diagram matched the experimental results reasonably well and indicated that a driving force exists for amorphous Zr-silicate compositions between approx40 mol % and approx90 mol % SiO2 to decompose into a ZrO2-rich phase (approx20 mol % SiO2) and SiO2-rich phase (>98 mol % SiO2) through diffusional phase separation at a temperature of 900 degC. These predictions are consistent with recent experimental reports of phase separation in amorphous Zr-silicate thin films. Other metal-silicate systems were also investigated and composition ranges for phase separation in amorphous Hf, La, and Y silicates were identified from the published bulk phase diagrams. The kinetics of one-dimensional spinodal decomposition normal to the plane of the film were simulated for an initially homogeneous Zr-silicate dielectric layer. We examined the effects that local stresses and the capillary driving force for component segregation to the interface have on the rate of spinodal decomposition in amorphous metal-silicate thin films.

  18. Determination of the Fe-rich portion of the Fe-Ni-C phase diagram

    NASA Technical Reports Server (NTRS)

    Romig, A. D., Jr.; Goldstein, J. I.

    1978-01-01

    The iron-enriched section of the phase diagram for the ternary alloy Fe-Ni-C of various compositions is determined at 773, 873, 923, and 1003 C. The two-phase tie lines and three-phase tie triangles are measured by electron microprobe analyses. Tie lines in samples without bulk equilibrium are obtained by extrapolated interface compositions under the assumption of local equilibrium at the interface. It is shown that Ni addition somewhat reduces carbon solubility in austenite while decreasing the stability of the carbide phase. In particular, the carbide is always poor in Ni relative to the coexisting metal phase(s).

  19. Bistable optical response of a nanoparticle heterodimer: Mechanism, phase diagram, and switching time

    NASA Astrophysics Data System (ADS)

    Nugroho, Bintoro S.; Iskandar, Alexander A.; Malyshev, Victor A.; Knoester, Jasper

    2013-07-01

    We conduct a theoretical study of the bistable optical response of a nanoparticle heterodimer comprised of a closely spaced semiconductor quantum dot and a metal nanoparticle. The bistable nature of the response results from the interplay between the quantum dot's optical nonlinearity and its self-action (feedback) originating from the presence of the metal nanoparticle. The feedback is governed by a complex valued coupling parameter G = GR + iGI. We calculate the bistability phase diagram within the system's parameter space: spanned by GR, GI, and Δ, the latter being the detuning between the driving frequency and the transition frequency of the quantum dot. Additionally, switching times from the lower stable branch to the upper one (and vice versa) are calculated as a function of the intensity of the driving field. The conditions for bistability to occur can be realized, for example, for a heterodimer comprised of a closely spaced CdSe (or CdSe/ZnSe) quantum dot and a gold nanosphere.

  20. Investigation of phase diagrams and physical stability of drug-polymer solid dispersions.

    PubMed

    Lu, Jiannan; Shah, Sejal; Jo, Seongbong; Majumdar, Soumyajit; Gryczke, Andreas; Kolter, Karl; Langley, Nigel; Repka, Michael A

    2015-01-01

    Solid dispersion technology has been widely explored to improve the solubility and bioavailability of poorly water-soluble compounds. One of the critical drawbacks associated with this technology is the lack of physical stability, i.e. the solid dispersion would undergo recrystallization or phase separation thus limiting a product's shelf life. In the current study, the melting point depression method was utilized to construct a complete phase diagram for felodipine (FEL)-Soluplus® (SOL) and ketoconazole (KTZ)-Soluplus® (SOL) binary systems, respectively, based on the Flory-Huggins theory. The miscibility or solubility of the two compounds in SOL was also determined. The Flory-Huggins interaction parameter χ values of both systems were calculated as positive at room temperature (25 °C), indicating either compound was miscible with SOL. In addition, the glass transition temperatures of both solid dispersion systems were theoretically predicted using three empirical equations and compared with the practical values. Furthermore, the FEL-SOL solid dispersions were subjected to accelerated stability studies for up to 3 months.

  1. Magnetic and superconducting phase diagram of the half-Heusler topological semimetal HoPdBi.

    PubMed

    Nikitin, A M; Pan, Y; Mao, X; Jehee, R; Araizi, G K; Huang, Y K; Paulsen, C; Wu, S C; Yan, B H; de Visser, A

    2015-07-15

    We report a study of the magnetic and electronic properties of the non-centrosymmetric half-Heusler antiferromagnet HoPdBi (TN = 2.0 K). Magnetotransport measurements show HoPdBi has a semimetallic behavior with a carrier concentration n = 3.7 × 10(18) cm(-3) extracted from the Shubnikov-de Haas effect. The magnetic phase diagram in the field-temperature plane has been determined by transport, magnetization, and thermal expansion measurements: magnetic order is suppressed at BM ~ 3.6 T for T --> 0. Superconductivity with Tc ~ 1.9 K is found in the antiferromagnetic phase. Ac-susceptibility measurements provide solid evidence for bulk superconductivity below Tc = 0.75 K with a screening signal close to a volume fraction of 100%. The upper critical field shows an unusual linear temperature variation with Bc2(T --> 0) = 1.1 T. We also report electronic structure calculations that classify HoPdBi as a new topological semimetal, with a non-trivial band inversion of 0.25 eV.

  2. Temperature-composition phase diagrams of Gd-doped EuO and EuS

    NASA Astrophysics Data System (ADS)

    An, Joonhee; Barabash, S.; Belashchenko, K.

    2009-03-01

    We have computed the temperature-phase diagram of Eu1-xGdxO alloys by combining density functional theory in the generalized-gradient approximation with Hubbard U correction on f-orbitals with the regular cluster expansion and Monte-Carlo approach. The cluster expansion fit has been performed with varying numbers of distinct cluster types until the formal cross-validation score is minimized. Our results indicate that (i) pair interactions are relatively stronger than other cluster types, (ii) the pair terms decay rapidly with distance up to 10 å, (iii) the pair terms are attractive for direct interactions between cations and repulsive for indirect interactions through anions, and (iv) the calculated convex hull is asymmetric about x=0.5, displaying more deep ground states in Eu-rich regions than in Gd-rich regions. The asymmetry of the convex hull may imply relative instability of Gd-rich compounds, as was shown by previously-reported experimental difficulties to make Gd-rich compounds. A comparison with a similar binary system - sulfur replacing oxygen - is made, showing that both oxides and sulphides are dominated by deformation interaction. The sulphides have a marginal tendency to phase-separate into pure compounds at low temperatures, whereas the oxides tend to order.

  3. The Cu-Li-Sn Phase Diagram: Isopleths, Liquidus Projection and Reaction Scheme.

    PubMed

    Fürtauer, Siegfried; Flandorfer, Hans

    2016-01-01

    The Cu-Li-Sn phase diagram was constructed based on XRD and DTA data of 60 different alloy compositions. Eight ternary phases and 14 binary solid phases form 44 invariant ternary reactions, which are illustrated by a Scheil-Schulz reaction scheme and a liquidus projection. Phase equilibria as a function of concentration and temperature are shown along nine isopleths. This report together with an earlier publication of our group provides for the first time comprehensive investigations of phase equilibria and respective phase diagrams. Most of the phase equilibria could be established based on our experimental results. Only in the Li-rich part where many binary and ternary compounds are present estimations had to be done which are all indicated by dashed lines. A stable ternary miscibility gap could be found which was predicted by modelling the liquid ternary phase in a recent work. The phase diagrams are a crucial input for material databases and thermodynamic optimizations regarding new anode materials for high-power Li-ion batteries.

  4. The Cu-Li-Sn Phase Diagram: Isopleths, Liquidus Projection and Reaction Scheme

    PubMed Central

    Flandorfer, Hans

    2016-01-01

    The Cu-Li-Sn phase diagram was constructed based on XRD and DTA data of 60 different alloy compositions. Eight ternary phases and 14 binary solid phases form 44 invariant ternary reactions, which are illustrated by a Scheil-Schulz reaction scheme and a liquidus projection. Phase equilibria as a function of concentration and temperature are shown along nine isopleths. This report together with an earlier publication of our group provides for the first time comprehensive investigations of phase equilibria and respective phase diagrams. Most of the phase equilibria could be established based on our experimental results. Only in the Li-rich part where many binary and ternary compounds are present estimations had to be done which are all indicated by dashed lines. A stable ternary miscibility gap could be found which was predicted by modelling the liquid ternary phase in a recent work. The phase diagrams are a crucial input for material databases and thermodynamic optimizations regarding new anode materials for high-power Li-ion batteries. PMID:27788175

  5. Binary Phase Diagrams and Thermodynamic Properties of Silicon and Essential Doping Elements (Al, As, B, Bi, Ga, In, N, P, Sb and Tl).

    PubMed

    Mostafa, Ahmad; Medraj, Mamoun

    2017-06-20

    Fabrication of solar and electronic silicon wafers involves direct contact between solid, liquid and gas phases at near equilibrium conditions. Understanding of the phase diagrams and thermochemical properties of the Si-dopant binary systems is essential for providing processing conditions and for understanding the phase formation and transformation. In this work, ten Si-based binary phase diagrams, including Si with group IIIA elements (Al, B, Ga, In and Tl) and with group VA elements (As, Bi, N, P and Sb), have been reviewed. Each of these systems has been critically discussed on both aspects of phase diagram and thermodynamic properties. The available experimental data and thermodynamic parameters in the literature have been summarized and assessed thoroughly to provide consistent understanding of each system. Some systems were re-calculated to obtain a combination of the best evaluated phase diagram and a set of optimized thermodynamic parameters. As doping levels of solar and electronic silicon are of high technological importance, diffusion data has been presented to serve as a useful reference on the properties, behavior and quantities of metal impurities in silicon. This paper is meant to bridge the theoretical understanding of phase diagrams with the research and development of solar-grade silicon production, relying on the available information in the literature and our own analysis.

  6. Binary Phase Diagrams and Thermodynamic Properties of Silicon and Essential Doping Elements (Al, As, B, Bi, Ga, In, N, P, Sb and Tl)

    PubMed Central

    Mostafa, Ahmad; Medraj, Mamoun

    2017-01-01

    Fabrication of solar and electronic silicon wafers involves direct contact between solid, liquid and gas phases at near equilibrium conditions. Understanding of the phase diagrams and thermochemical properties of the Si-dopant binary systems is essential for providing processing conditions and for understanding the phase formation and transformation. In this work, ten Si-based binary phase diagrams, including Si with group IIIA elements (Al, B, Ga, In and Tl) and with group VA elements (As, Bi, N, P and Sb), have been reviewed. Each of these systems has been critically discussed on both aspects of phase diagram and thermodynamic properties. The available experimental data and thermodynamic parameters in the literature have been summarized and assessed thoroughly to provide consistent understanding of each system. Some systems were re-calculated to obtain a combination of the best evaluated phase diagram and a set of optimized thermodynamic parameters. As doping levels of solar and electronic silicon are of high technological importance, diffusion data has been presented to serve as a useful reference on the properties, behavior and quantities of metal impurities in silicon. This paper is meant to bridge the theoretical understanding of phase diagrams with the research and development of solar-grade silicon production, relying on the available information in the literature and our own analysis. PMID:28773034

  7. Phase diagram for the trapping kinetics of partially coherent excitons

    NASA Astrophysics Data System (ADS)

    Pearlstein, Robert M.

    1998-06-01

    The kinetics of exciton trapping within molecular assemblies similar to those of recently reported structural models of photosynthetic light-harvesting antennas have been described theoretically for any degree of exciton coherence. It is shown here that in the space of two of the kinetic parameters - the local exciton scattering rate constant and the nearest-neighbor separation distance of the exciton-generating transition dipoles - the trapping kinetics segregate into coherent and incoherent phases delineated by universal curves. Consequences of these findings are discussed, particularly as they may apply to purple photosynthetic bacteria.

  8. Phase Diagram of the ABC Model on an Interval

    NASA Astrophysics Data System (ADS)

    Ayyer, A.; Carlen, E. A.; Lebowitz, J. L.; Mohanty, P. K.; Mukamel, D.; Speer, E. R.

    2009-12-01

    The three species asymmetric ABC model was initially defined on a ring by Evans, Kafri, Koduvely, and Mukamel, and the weakly asymmetric version was later studied by Clincy, Derrida, and Evans. Here the latter model is studied on a one-dimensional lattice of N sites with closed (zero flux) boundaries. In this geometry the local particle conserving dynamics satisfies detailed balance with respect to a canonical Gibbs measure with long range asymmetric pair interactions. This generalizes results for the ring case, where detailed balance holds, and in fact the steady state measure is known, only for the case of equal densities of the different species: in the latter case the stationary states of the system on a ring and on an interval are the same. We prove that in the limit N→∞ the scaled density profiles are given by (pieces of) the periodic trajectory of a particle moving in a quartic confining potential. We further prove uniqueness of the profiles, i.e., the existence of a single phase, in all regions of the parameter space (of average densities and temperature) except at low temperature with all densities equal; in this case a continuum of phases, differing by translation, coexist. The results for the equal density case apply also to the system on the ring, and there extend results of Clincy et al.

  9. Phase diagram of boron carbide with variable carbon composition

    NASA Astrophysics Data System (ADS)

    Yao, Sanxi; Gao, Qin; Widom, Michael

    2017-02-01

    Boron carbide exhibits intrinsic substitutional disorder over a broad composition range. The structure consists of 12-atom icosahedra placed at the vertices of a rhombohedral lattice, together with a 3-atom chain along the threefold axis. In the high-carbon limit, one or two carbon atoms can replace boron atoms on the icosahedra while the chains are primarily of type C-B-C. We fit an interatomic pair interaction model to density-functional-theory total energies to investigate the substitutional carbon disorder. Monte Carlo simulations with sampling improved by replica exchange and augmented by two-dimensional multiple histogram analysis predict three phases. The low-temperature, high-carbon-composition monoclinic C m structure disorders through a pair of phase transitions, first via an Ising-like transition to a monoclinic centrosymmetric state with space group C 2 /m , then via a first-order three-state Potts-like transition to the experimentally observed rhombohedral R 3 ¯m symmetry.

  10. Phase diagram of Fe-based superconductor Sr2 FeAs(Mg,Ti)O3

    NASA Astrophysics Data System (ADS)

    Ogino, Hiraku; Singh, Shiv Jee; Yamamoto, Akiyasu; Kishio, Kohji; Shimoyama, Jun-Ichi

    2014-03-01

    In iron-based superconductors, many compounds having perovskite-type blocking layers such as Sr2FeAs(Mg,Ti)O3 and Ca4Fe2As2(Mg,Ti)3O8 were discovered. There compounds have chemical and structural varieties, and have much thicker blocking layers compared to other phases. Generally superconducting transitions appear without intentional carrier doping, and Tc reaches as high as 47 K. On the other hand, electronic state and electronic phase diagram of these compounds are much less studied compared to other phases, and there are no clear observation of antiferromagnetic ordering in these compounds. In this study, we have systematically investigated phase diagram of Sr2FeAs(Mg,Ti)O3 phase by controlling carriers through oxygen composition and post-annealing. Relationship between crystal structure, chemical compositions and physical properties will be discussed.

  11. Solid/Liquid phase diagram of the ammonium sulfate/maleic acid/water system.

    PubMed

    Beyer, Keith D; Schroeder, Jason R; Pearson, Christian S

    2011-12-01

    We have studied the low temperature phase diagram and water activities of the ammonium sulfate/maleic acid/water system using differential scanning calorimetry and infrared spectroscopy of thin films. Using the results from our experiments, we have mapped the solid/liquid ternary phase diagram, determined the water activities based on the freezing point depression, and determined the ice/maleic acid phase boundary as well as the ternary eutectic composition and temperature. We also compare our results to the predictions of the extended AIM aerosol thermodynamics model and find good agreement for the ice melting points in the ice primary phase field of this system; however significant differences were found with respect to phase boundaries, maleic acid dissolution, and ammonium sulfate dissolution.

  12. Effect of polydispersity on the phase diagrams of linear ABC triblock copolymers in two dimensions.

    PubMed

    Jiang, Ying; Yan, Xiaoyan; Liang, Haojun; Shi, An-Chang

    2005-11-10

    By using a two-dimensional (2D) real-space self-consistent field theory, we present the phase diagrams of monodisperse ABC triblock copolymers in a three-component triangle style with the interaction energies given between the distinct blocks; this system displays richer phase behavior when compared with the corresponding diblock copolymers. Polydispersity of the end or middle blocks in the ABC linear block copolymer chains results in a completely different phase diagram. The presence of a polydisperse end block may cause strong segregation to occur among the three distinct components and larger domain sizes of the dispersed phases; a polydisperse middle block may allow a connection to form between the two phases of the two end blocks.

  13. Phase diagram of ammonium perchlorate: Raman spectroscopic constrains at high pressures and temperatures

    NASA Astrophysics Data System (ADS)

    Dunuwille, Mihindra; Yoo, Choong-Shik

    2016-06-01

    We present the pressure-temperature (PT) induced physical and chemical transformations in ammonium perchlorates (APs) up to 50 GPa and 450 °C, using diamond anvil cells and confocal micro-Raman spectroscopy, which provide new constraints for the phase diagram of AP. The results show spectral evidences for three new polymorphs (III, IV, and VI) of AP, in addition to two previously known phases (I and II), at various PT conditions with varying degrees of hydrogen bonding and lack of strong spectral evidence for previously known high-temperature cubic phase (phase V). Upon further heating, AP chemically decomposes to N2, N2O, and H2O. The present phase diagram is, therefore, in sharp contrast to the previous one, underscoring a rich polymorphism, a large stability field for solids, and a replacement of the melt with a decomposition line.

  14. Block voter model: Phase diagram and critical behavior

    NASA Astrophysics Data System (ADS)

    Sampaio-Filho, C. I. N.; Moreira, F. G. B.

    2011-11-01

    We introduce and study the block voter model with noise on two-dimensional square lattices using Monte Carlo simulations and finite-size scaling techniques. The model is defined by an outflow dynamics where a central set of NPCS spins, here denoted by persuasive cluster spins (PCS), tries to influence the opinion of their neighboring counterparts. We consider the collective behavior of the entire system with varying PCS size. When NPCS>2, the system exhibits an order-disorder phase transition at a critical noise parameter qc which is a monotonically increasing function of the size of the persuasive cluster. We conclude that a larger PCS has more power of persuasion, when compared to a smaller one. It also seems that the resulting critical behavior is Ising-like independent of the range of interaction.

  15. The Cu-Sn phase diagram, Part I: New experimental results.

    PubMed

    Fürtauer, S; Li, D; Cupid, D; Flandorfer, H

    2013-03-01

    Phase diagram investigation of the Cu-Sn system was carried out on twenty Cu-rich samples by thermal analysis (DTA), metallographic methods (EPMA/SEM-EDX) and crystallographic analysis (powder XRD, high temperature powder XRD). One main issue in this work was to investigate the high temperature phases beta (W-type) and gamma (BiF3-type) and to check the phase relations between them. In the high temperature powder XRD experiments the presence of the two-phase-field between the beta- and the gamma-phase could not be confirmed. Detailed study of primary literature together with our experimental results leads to a new phase diagram version with a higher order transformation between these two high temperature phases. The present work is designated as part I of our joint publication. The new findings described here have been included into a completely new thermodynamic assessment of the Cu-Sn phase diagram which is presented in part II.

  16. Direct determination of metastable phase diagram by synchrotron radiation experiments on undercooled metallic melts.

    PubMed

    Notthoff, C; Feuerbacher, B; Franz, H; Herlach, D M; Holland-Moritz, D

    2001-02-05

    The phase selection process during the crystallization of undercooled metallic melts is studied in situ by combining the electromagnetic levitation technique with energy dispersive x-ray diffraction of synchrotron radiation. The crystallization of metastable bcc phase in binary Ni-V alloys was identified. A metastable phase diagram of Ni-V alloy is constructed, which shows the primarily solidifying phase as a function of composition and undercooling. The analysis within nucleation theory emphasizes the important role of metal oxide as a heterogeneous nucleation site controlling the phase selection.

  17. Phase diagram and criticality of the two-dimensional prisoner's dilemma model

    NASA Astrophysics Data System (ADS)

    Santos, M.; Ferreira, A. L.; Figueiredo, W.

    2017-07-01

    The stationary states of the prisoner's dilemma model are studied on a square lattice taking into account the role of a noise parameter in the decision-making process. Only first neighboring players—defectors and cooperators—are considered in each step of the game. Through Monte Carlo simulations we determined the phase diagrams of the model in the plane noise versus the temptation to defect for a large range of values of the noise parameter. We observed three phases: cooperators and defectors absorbing phases, and a coexistence phase between them. The phase transitions as well as the critical exponents associated with them were determined using both static and dynamical scaling laws.

  18. Phase diagram of a model of nanoparticles in electrolyte solutions.

    PubMed

    Li, Xiaofei; Lettieri, S; Wentzel, N; Gunton, J D

    2008-10-28

    We obtain accurate fluid-fluid coexistence curves for a recent simple model of interacting nanoparticles that includes the effects of ion-dispersion forces. It has been proposed that these ion-dispersion forces provide at least a partial explanation for the Hofmeister effect [M. Bostrom et al. Phys. Rev. Lett. 87, 168103 (2001)]. We study a model of aluminum oxide nanoparticle [Deniz et al., Colloids Surf. A 319, 98 (2008)] for three different electrolyte solutions with added salt type being sodium chloride, sodium iodide, and a nonpolarizable salt. We observe that the fluid-fluid coexistence curves depend substantially on the identity of added salt; this provides an efficient way of tuning the phase behavior of nanoparticles. The methods we employ include finite-size scaling (FSS), multicanonical histogram reweighting, and Gibbs ensemble methods. We show that, as expected, all three cases belong to the Ising universality class. The scaling fields and critical point parameters are obtained in the thermodynamic limit of infinite system size by extrapolation of our FSS results.

  19. Phase diagram of the ZnSiAs2-MnAs system

    NASA Astrophysics Data System (ADS)

    Fedorchenko, I. V.; Ril, A. I.; Marenkin, S. F.; Rabinovich, O. I.; Legotin, S. A.; Didenko, S. I.; Skupiñski, P.; Kilanski, L.; Dobrowolski, W.

    2017-06-01

    Phase diagram in the ZnSiAs2-MnAs nanocomposite system was studied by Х-ray, DTA and SEM. The system has an eutectic character. The coordinates of eutectic are 87±1 mol% MnAs and 847±10 °C. The eutectic consists of the manganese arsenide lattice with ZnSiAs2 inclusions.

  20. Phase diagram and segregation of Ag-Co nanoalloys: insights from theory and simulation.

    PubMed

    Zhao, Zheng; Fisher, Adrian; Cheng, Daojian

    2016-03-18

    Understanding the phase diagram is the first step to identifying the structure-performance relationship of a material at the nanoscale. In this work, a modified nanothermodynamical model has been developed to predict the phase diagrams of Ag-Co nanoalloys with the size of 1 ∼ 100 nm, which also overcomes the difference in the predicted results between theory and simulation for the first time. Based on this modified model, the phase diagrams of Ag-Co nanoalloys with various polyhedral morphologies (tetrahedron, cube, octahedron, decahedron, dodecahedron, rhombic dodecahedron, truncated octahedron, cuboctahedron, and icosahedron) have been predicted, showing good agreement with molecular dynamics simulations at the nanoscale of 1 ∼ 4 nm. In addition, the surface segregation of Ag-Co nanoalloys has been predicted with a Co-rich core/Ag-rich surface, which is also consistent with the simulation results. Our results highlight a useful roadmap for bridging the difference between theory and simulation in the prediction of the phase diagram at the nanoscale, which will help both theorists and experimentalists.