Temperature-composition Phase Diagram Research Articles

High temperature phase diagram of pseudo binary Ba(Zr0.2Ti0.8)O3-(Ba0.7Ca0.3)TiO3 ceramic system: In situ X-ray diffraction and dielectric studies

ABSTRACTLead free perovskite Ba(Zr0.2Ti0.8)O3-(Ba0.7Ca0.3)TiO3 is considered to be one of the most studied system for piezoelectric and energy harvesting applications. Present work reports the temperature dependent X-ray diffraction and dielectric properties of perovskite (1-x)Ba(Zr0.2Ti0.8)O3–x(Ba0.7Ca0.3)TiO3 ceramic system prepared using a standard high-temperature solid-state reaction method. Dielectric studies showed two dielectric relaxations. The lower phase transition ranged between −10°C (x = 0) to 85°C (x = 1) whiles the high temperature phase transitions, diffusive in character occur from 575°C (x = 0) to 620°C (x = 1), which places the present ceramic system in the list of potential candidate for high temperature applications. The high temperature phase transitions in the system were well supported by in situ X-ray diffraction studies. X-ray diffraction analyses indicated that the present system have a perovskite-type monoclinic (space group: P2/m) at high temperatures. Phase transition behaviour has been illustrated in the form of a temperature-composition phase diagram of BZT-xBCT system.

Thermodynamic, electronic, and optical properties of graphene oxide: A statisticalab initioapproach

We study the incomplete oxidation of graphene or reduction of graphene oxide for hydroxyl and epoxy oxidant groups. While in wet oxidation hydroxyl groups are favorable, in a drier environment an oxygen atom can bridge two neighboring carbon atoms. We model composition variations and structural disorder within a statistical theory, the generalized quasichemical approximation, combined with density functional theory calculations of the local atomic geometries. A generalization of the statistical approach is developed to account for the antiparallel orientation of hydroxyl groups and a fourfold coordination of C atoms. The theoretical framework enables a thermodynamic treatment of graphene oxide as a function of oxygen content, allowing us to derive temperature-composition phase diagrams and investigate possible clustering and segregation. The resulting geometries, local and average electronic structures, and optical absorption spectra are discussed and compared with available experimental data.

Fluid–triangular solid phase transitions in a system of two-dimensional nematic quadrupoles

ABSTRACTDensity functional theory of freezing is used to study the phase transitions in a system of spherical colloidal particles dispersed in nematic host confined to two dimensions. We have considered both the one-component and two-component systems of the colloidal dispersions. Particles are assumed to interact via director distortion-mediated purely repulsive potential which scales as the fifth power of the inverse interparticle separation. The pair correlation functions needed as input information in the density functional theory are calculated by solving Roger–Young integral equation theory. In one-component system, a triangular crystalline phase is found to be stable. On the other hand, considering the freezing of the fluid phase of the binary mixture into a substitutionally disordered triangular solid, the temperature–composition phase diagram is found to have spindle shape for the ratio of quadrupole moment of the particles of the components being 0.9 and 0.8. The phase diagram changes to an azeotrope at a ratio 0.7. The results are verifiable in real-space experiments on nematic quadrupoles confined to a two-dimensional plane.

A thermodynamic potential and the temperature-composition phase diagram for single-crystalline K1-xNaxNbO3 (0 ≤ x ≤ 0.5)

Environment-friendly lead-free piezoelectric materials, such as the niobate perovskite compound (K1-xNaxNbO3), have attracted increasing attention over the last decade. Although extensive efforts have been made to study these materials experimentally, there have been much fewer theoretical studies on the microstructural evolution and property optimization of lead-free systems due to the lack of a comprehensive thermodynamic assessment. In this study, we first established a general procedure for constructing thermodynamic potentials for ferroelectric systems. We then developed an eighth-order Landau thermodynamic potential for K1-xNaxNbO3 (0 ≤ x ≤ 0.5) single crystals, taking into account the low temperature quantum mechanical effects. Based on this potential, we computed the spontaneous polarization and the dielectric constants for each composition as well as an overall temperature-composition phase diagram, all of which agree well with the available experimental data.

Solubilities of Diethyl Phthalate, Dicyclopentadiene, and Styrene in Ionic Liquid 1-Ethyl-3-methylimidazolium Acetate

Solubilities of diethyl phthalate (DEP), dicyclopentadiene (DCPD), and styrene in ionic liquid 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]) were measured in the temperature range T = (283.15–353.15) K and at atmospheric pressure (101.3 kPa) the corresponding temperature–composition phase diagrams were obtained. Solubilities of DEP and DCPD in [Emim][OAc] increase with temperature but the solubility of styrene in [Emim][OAc] decreases with temperature. The ternary liquid–liquid equilibrium data for the system of styrene + glycerol + [Emim][OAc] were also determined at temperatures of 298.15, 308.15, 318.15, and 328.15 K, and the results indicate that the addition of glycerol can significantly reduce the solubility of styrene in [Emim][OAc]. For the ternary system, when the amount of glycerol is enough, the solubility of styrene in [Emim][OAc] increases with temperature. The experimental data were correlated by the nonrandom two-liquid activity coefficient model and the binary interaction parameters we...

Valence fluctuations in Sn(Pb)2P2S6 ferroelectrics

The valence fluctuations which are related to the charge disproportionation of phosphorous ions P4++P4+→P3++P+5 are the origin of ferroelectric and quantum paraelectric states in Sn(Pb)2P2S6 semiconductors. They involve recharging of SnPS3 or PbPS3 structural groups which can be represented as half-filled sites in the crystal lattice. Temperature–pressure phase diagram for Sn2P2S6 compound and temperature-composition phase diagram for (PbySn1–y)2P2S6 mixed crystals, which include tricritical points and where a temperature of phase transitions decrease to 0 K, together with the data about some softening of low energy optic phonons and rise of dielectric susceptibility at cooling in quantum paraelectric state of Pb2P2S6 are analyzed by GGA electron and phonon calculations and compared with electronic correlations models. The anharmonic quantum oscillators model is developed for description of phase diagrams and temperature dependence of dielectric susceptibility.

Creating adjoining polymorphic phase transition (PPT) regions in ferroelectric (Ba,Sr)(Zr,Ti)O3 ceramics

In this work, we report the polymorphic phase transitions(PPT) in ferroelectric Ba0.95Sr0.05ZrxTi(1-x)O3 (BSZT, x=0.01–0.10) ceramics synthesized by using a solid-state reaction method. The doping elements and composition ratios were selected to create adjoining PPT phase boundaries near room temperature, hence to achieve a broadened peak of piezoelectric performance with respect to composition. The temperature-composition phase diagram was constructed and the effects of PPT on the electromechanical and ferroelectric properties of the ceramics were investigated. It was revealed that the two adjacent PPT regions at room temperature showed different characteristics in property enhancement. However, due to the proximity of the phase boundaries, Ba0.95Sr0.05ZrxTi(1-x)O3 ceramics in a fairly broad range of compositions (0.02≤x≤0.07) showed excellent piezoelectric properties, including a large piezoelectric constant (312 pC/N≤d33≤365 pC/N) and a high electromechanical coupling coefficient kp (0.42≤kp≤0.49).

Thermodynamic stability of LuRhO3 in a photoelectrochemical cell

Long term stability of lutetium rhodite (LuRhO3) as an electrode for photoelectrochemical decomposition of water is investigated. The thermodynamic properties of LuRhO3 are determined in the temperature range from 875 to 1300 K using an electrochemical cell incorporating calcia–stabilized zirconia as the solid electrolyte. The standard Gibbs energy of formation of LuRhO3 from its constituent binary oxides Lu2O3 with C-type rare earth oxide crystal structure and Rh2O3 with orthorhombic structure is obtained:ΔGf,oxo(±135)/Jmol−1=−40106+3.282(T/K)The standard entropy of LuRhO3S298.15Ko(LuRhO3)/JK-1mol-1=89.54(±0.35) and standard enthalpy of formation from elements ΔHfo(298.15K)/kJmol−1=−1181.97(±3.86) are derived. The phase relations and stabilities of phases in the LuRhO system are computed from thermodynamic data. An isothermal section of the ternary phase diagram, a 2–D oxygen potential diagram and a 3–D chemical potential diagram at 1200 K are presented along with temperature–composition phase diagrams at various oxygen partial pressures of oxygen. LuRhO3 (p-type) is thermodynamically unstable as a photocathode in contact with hydrogen gas. However, n-type LuRhO3 can be used as a photoanode in the presence of oxygen.

Partially Miscible Water–Triethylamine Solutions and Their Temperature Dependence

A simple and straightforward demonstration of the temperature dependence of partial miscibility is described. The Gibbs phase rule, temperature–composition phase diagrams, and the lever rule serve as the basis for interpretation of the demonstration. The water–triethylamine system is miscible in all mixing ratios at temperatures less than 18 °C, but separates into two immiscible phases for a wide range of bulk compositions as temperature increases through 19–24 °C. A procedure is described in which a range of bulk compositions simultaneously experience an increase in temperature. Students are able to see differences in the temperature of phase separation, plus the evolving compositions and volumes of the separated phases.

Heat Transfer Organic Materials: Robust Polymer Films with the Outstanding Thermal Conductivity Fabricated by the Photopolymerization of Uniaxially Oriented Reactive Discogens.

For the development of advanced heat transfer organic materials (HTOMs) with excellent thermal conductivities, triphenylene-based reactive discogens, 2,3,6,7,10,11-hexakis(but-3-enyloxy)triphenylene (HABET) and 4,4',4″,4‴,4'''',4'''''-(triphenylene-2,3,6,7,10,11-hexaylhexakis(oxy))hexakis(butane-1-thiol) (THBT), were synthesized as discotic liquid crystal (DLC) monomers and cross-linkers, respectively. A temperature-composition phase diagram of HABET-THBT mixtures was first established based on their thermal and microscopic analyses. From the experimental results, it was realized that the thermal conductivity of DLC HTOM was strongly affected by the molecular organizations on a macroscopic length scale. Macroscopic orientation of self-assembled columns in DLC HTOMs was effectively achieved under the rotating magnetic fields and successfully stabilized by the photopolymerization. The DLC HTOM polymer-stabilized at the LC phase exhibited the remarkable thermal conductivity above 1 W/mK. When the DLC HTOM was macroscopically oriented, the thermal conductivity was estimated to be 3 W/mK along the in-plane direction of DLC molecule. The outstanding thermal conductivity of DLC HTOM should be originated not only from the high content of two-dimensional aromatic discogens but also from the macroscopically oriented and self-assembled DLC. The newly developed DLC HTOM with an outstanding thermal conductivity as well as with an excellent mechanical sustainability can be applied as directional heat dissipating materials in electronic and display devices.

Role of cadmium on the phase transitions and electrical properties of BaTiO3 ceramics

The search for high piezoelectric and electromechanical properties near morphotropic phase boundaries (MPB) in lead-free ceramics has attracted considerable interest. The MPB can be obtained in the composition-temperature phase diagram by combining stabilized rhombohedral (R) and tetragonal (T) ends, which possess cubic (C) to R or C to T transitions, respectively. The R-end is usually realized by doping ions Zr4+, Hf4+ or Sn4+ at the Ti4+ site, whereas the T-end can be generated by Ca2+ doped at the Ba2+ site of BaTiO3. Our recent computational work (Phys. Rev. B. 93, 144111, 2016) showed that Cd2+ doped BaTiO3 can be considered as a potential T-end. In the present study, we synthesized (Ba1−xCdx)TiO3 ceramics to investigate the effects of Cd2+ on the phase transition, dielectric, ferroelectric and piezoelectric properties of the ceramics. Although our results show that Cd2+ fails to stabilize the T phase, i.e., the transition temperatures vary little with Cd2+ concentration, the electrical properties are found to be optimized for Cd2+% of 5%. The optimization of the properties is related to the microstructural features including grain size and sample density.

Tunable elastic modulus in Mn-based antiferromagnetic shape memory alloys

Compared with the normal relation between temperature (T) and elastic modulus (E) in most materials, martensitic transformation (MT) and magnetic transition could result in the softening of elastic modulus (dE/dT > 0) within a narrow range of T (<100 °C). It becomes possible in MnFeCu alloys to tune this range and broaden it to about 200 °C through combining MT and paramagnetic-antiferromagnetic (P-A) transition. The alloying elements and their contents play a key role in making MT separate from P-A transition, in which first-order MT made a greater contribution to this maximum value than second-order P-A transition. The intrinsic mechanism is that MT can continue causing the modulus to soften even after the P-A transition ends. This wide range keeps stable under different cooling/heating rates. An expression for dE/dT is deduced based on the proposed free energy model and the corresponding theoretical curve (dE/dT-T) gives a reasonable explanation on the experimental results in MnFeCu alloys. A modulus–temperature–composition phase diagram is obtained to describe such critical behaviors and it is found that there exists a specific triangle zone in which dE/dT > 0. The present results may enrich approaches to designing new functional materials, e.g. the elastic and Elinvar alloys.

Solid state stability and solubility of triethylenetetramine dihydrochloride

The API triethylenetetramine dihydrochloride used as an alternative treatment of Wilson⿿s disease is sensitive to water and it exhibits polymorphism. As this may become an issue for the drug formulation, the physical stability has been studied by differential scanning calorimetry, high-pressure thermal analysis, dynamic vapor sorption, and X-ray diffraction as a function of temperature. In addition, high-pressure liquid chromatography and mass spectrometry have been used to study the purity and chemical stability of the API. A pressure-temperature phase diagram of the pure compound has been constructed and it can be concluded that form II is monotropic in relation to form I, which is the only stable solid. The solubilities of the different solid forms have been determined with the help of a temperature ⿿ composition phase diagram. The API is very soluble, at 20° C about 10% of the saturated solution with respect to the dihydrate consists of API and the solubility of the pure form I is twice as high. Moreover, it has been shown that at 20°C, a relative humidity above 40% induces the formation of the dihydrate and at 70% a saturated solution appears. At higher temperatures, the formation of the dihydrate appears at lower relative humidity values. A clear link has been established between the API⿿s chemical stability, its physical stability and the relative humidity in the air. Humidity levels above 40% are detrimental to the quality of the API.

Resveratrol cocrystals with enhanced solubility and tabletability

Two new 1:1 cocrystals of resveratrol (RES) with 4-aminobenzamide (RES-4ABZ) and isoniazid (RES-ISN) were synthesized by liquid assisted grinding (LAG) and rapid solvent removal (RSR) methods using ethanol as solvent. Their physiochemical properties were characterized using PXRD, DSC, solid state and solution NMR, FT-IR, and HPLC. Pharmaceutically relevant properties, including tabletability, solubility, intrinsic dissolution rate, and hygroscopicity, were evaluated. Temperature-composition phase diagram for RES-ISN cocrystal system was constructed from DSC data. Both cocrystals show higher solubility than resveratrol over a broad range of pH. They are phase stable and non-hygroscopic even under high humidity conditions. Importantly, both cocrystals exhibit improved solubility and tabletability compared with RES, which make them more suitable candidates for tablet formulation development.

Phase behavior of system methane + hydrogen sulfide

An accurate description of the phase behavior of the CH4 + H2S system is given for temperatures from 70 K to the critical temperature of H2S and pressures up to 250 MPa. The study includes the solid phases of CH4 and H2S. A global pressure‐temperature diagram is presented. The types of temperature‐composition and pressure‐composition phase diagrams that can be encountered in the studied temperature and pressure ranges have been described. The temperature and pressure ranges where the phase behavior of the system changes have been identified and a representative phase diagram is presented for each range. Phase diagrams have been obtained through the solid–liquid–vapor equation of state proposed by Yokozeki. The parameters of the equation of state have been regressed on all the available phase equilibrium data for the considered system. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4090–4108, 2016

두 종류의 특정상호작용을 갖는 이성분 용액의 부분 혼합도

In this article, new Gibbs free energy of mixing is derived when there are specific interactions between sol- vent-solute molecules and between solute-solute molecules in binary solutions. It is asssumed that a probability of specific interactions satisfies a binomial distribution. Using this Gibbs free energy of mixing, we investigate possible types of partial miscibilities and show that Ω-shaped temperature-composition phase diagrams can exist. We calculate Ω-shaped temperature- composition phase diagram of water-2-butanol system and compare that with result calculated by the method of Hino 5 et al.

Thermodynamic and analytical studies of drugs binary systems of paracetamol mixed with pseudoephedrine.HCl, dextropropoxyphene.HCl and tramadol.HCl

In this paper, we report a DSC investigation of solid–liquid equilibria in three binary mixtures of paracetamol, namely with pseudoephedrine, dextropropoxyphene and tramadol, resulting in a temperature-composition phase diagrams with eutectic equilibrium. Eutectic mole fractions, temperatures and enthalpies were determined and reported for each system.The study reports also a direct exploitation of the DSC results for the quantification purpose, which were in good agreement with those obtained by a standard analytical method namely high performance thin layer chromatography (HPTLC), used in this work for comparison purpose.

On the early stages of precipitation in dilute Mg–Nd alloys

We report on a first-principles and experimental study of precipitation in supersaturated solid solutions of Mg-rich Mg–Nd alloys. A cluster expansion Hamiltonian combined with Monte Carlo simulations was used to calculate a metastable HCP temperature-composition phase diagram. Aging studies were performed on dilute Mg–Nd alloys that were then characterized with HAADF-STEM. The early stage decomposition of these alloys is dominated by the thermodynamic stability of different Nd orderings on the HCP crystal structure. The observed progression of Guinier-Preston zones can be rationalized by a successive reduction of the Nd chemical potential. HAADF-STEM studies confirm the appearance of β' -like precipitates, however, the observed Nd ordering does not exclusively consist of zig-zag Nd rows but also contains linear strips of Nd-hexagons at non-periodic intervals. First-principles calculations predict that these orderings are stable compounds that belong to a family of hybrid phases formed by combining the β' ordering with the hexagons of β″ (D019) along the [010]β' direction. We label this hierarchy of orderings as β′′′. A high degree of degeneracy among the different β′′′ phases is predicted. This along with a strong composition dependence of the misfit strain is likely responsible for the observed disorder of Nd-hexagon strips. Our experimental and first-principles evidence does not support the formation of Mg3 Nd having D019 ordering. Rather, the features reported as D019 are isolated hexagonal GP rods that show no long-range periodicity. Our study suggests the following precipitation sequence for binary Mg–Nd alloys: SSSS→GP Zones(N,V,hexagons)→β′′′→β1(Mg3Nd)→β(Mg12Nd)→βe(Mg41Nd5).

Stable, low-cost phase change material for building applications: The eutectic mixture of decanoic acid and tetradecanoic acid

We present a thorough characterization of the thermal properties and thermal reliability of the eutectic mixture of decanoic acid with tetradecanoic acid, as a phase change material (PCM) of potential interest for passive temperature control in buildings. From the temperature-composition binary phase diagram we found that the eutectic composition is 0.82±0.02mole fraction (78±2 mass%) decanoic acid. We thoroughly characterized the thermal properties of the eutectic mixture. The eutectic composition has a high latent heat of fusion ΔfusH=153±15Jg−1 and a melting temperature Tonset=20.5±1.5°C. The heat capacity measured as a function of temperature for the solid and liquid phases just below and above the melting point is 1.9 and 2.1±0.2JK−1g−1, respectively. The average value of the thermal conductivity of the solid phase measured between −33 and 9°C is κs=0.20±0.02Wm−1K−1 and for the liquid phase, the thermal conductivity is κl=0.23±0.03Wm−1K−1 for 28 and 38°C. The mixture has a good long-term thermal stability as indicated by negligible changes in ΔfusH and Tonset after 3000 melt–freeze cycles. The parameters determined in this work allow more accurate modeling and optimization of the behavior of the eutectic mixture in preparation for implementation as a thermal energy storage PCM.

Physicochemical properties of a binary mixture of N-methylimidazole and methanol

At atmospheric pressure and over a full molar fraction range, for a binary mixture of x N-methylimidazole + (1-x) methanol, the density, viscosity and refractive index at 308.15K were measured, and the Gibbs energy of activation of viscous flow was calculated. All these properties were, respectively, correlated by a fourth-order polynomial. Based on these properties, the excess molar volume, viscosity deviation and refractive index deviation, and the excess Gibbs energy of activation of viscous flow, were calculated and fitted to a third-order Redlich–Kister polynomial, respectively. The total vapor pressure in the range (303.15–363.15) K was measured and correlated by a cubic equation, as well as the Clausius–Clapeyron equation. The molar enthalpy of vaporization was extrapolated from the Clausius–Clapeyron equation. The compositions of vapor–liquid coexisting phases were measured, and a temperature-composition phase diagram was plotted. A strong attractive molecular interaction between N-methylimidazole and methanol in a liquid mixture is discussed.