Composition Phase Diagram Research Articles

Displacive Phase Transitions in and Strain Analysis of Fe-Doped CaTiO 3 Perovskites at High Temperatures by Neutron Diffraction

The influence of small amounts of Fe 3+ on the phase transitions of CaTiO 3 perovskite has been studied by means of in situ high-temperature neutron diffraction. The same sequence of phase transitions as observed in CaTiO 3 is shown by both CaTi 0.9Fe 0.1O 2.95 and CaTi 0.8Fe 0.2O 2.90 perovskites: from orthorhombic Pnma symmetry at room temperature (RT) to cubic Pm3 m at high temperature, with an intermediate I4/ mcm tetragonal phase which exists over a temperature range of about 100°C. The two phase boundaries in the temperature vs composition phase diagram of the system CaFe x Ti 1− x O 3− x/2 (0≤ x≤0.4) decrease in a quasi-linear manner with increasing Fe content up to x=0.2 and then they both drop abruptly to RT. The existence of a second orthorhombic phase ( Cmcm), which has been postulated for CaTiO 3, is ruled out in the Fe-doped CaTiO 3 perovskites in view of the behavior of specific diffraction peaks. Strain analysis shows first-order thermodynamic character for the Pnma→ I4/ mcm transition, while the character of the Pm3 m→ I4/ mcm transition could be second order or tricritical. Shear strains behave more or less classically, as described by order parameter coupling and shear strain/order parameter coupling models. The volume strain has an anomalous coupling with the order parameter components, which appears to be temperature-dependent.

Right and wrong near critical endpoints

The implications of convexity (or thermodynamic stability) for isothermal density (or composition) phase diagrams near critical endpoints are investigated. In particular, Schreinemakers’ rules for the geometry of three coexisting phases in a space of densities are refined and extended physically to apply at and in the vicinity of a critical endpoint. Seemingly plausible phase diagrams are presented which violate the extended rules (and, in most cases, the Second Law of Thermodynamics). The requirements of convexity, supplemented for Ising-related systems by the Griffiths–Kelly–Sherman inequalities, also restrict the signs of important expansion coefficients of thermodynamic scaling functions for criticality and provide bounds on universal critical amplitude ratios.

An index of lipid phase diagrams

There is a growing awareness of the utility of lipid phase behavior data in studies of membrane-related phenomena. Such miscibility information is commonly reported in the form of temperature–composition ( T– C) phase diagrams. The current index is a conduit to the relevant literature. It lists lipid phase diagrams, their components and conditions of measurement, and complete bibliographic information. The main focus of the index is on lipids of membrane origin where water is the dispersing medium. However, it also includes records on acylglycerols, fatty acids, cationic lipids, and detergent-containing systems. The miscibility of synthetic and natural lipids with other lipids, with water, and with biomolecules (proteins, nucleic acids, carbohydrates, etc.) and non-biological materials (drugs, anesthetics, organic solvents, etc.) is within the purview of the index. There are 2188 phase diagram records in the index, the bulk (81%) of which refers to binary (two-component) T– C phase diagrams. The remainder is made up of more complex (ternary, quaternary) systems, pressure– T phase diagrams, and other more exotic miscibility studies. The index covers the period from 1965 through to July, 2001.

Temperature–composition phase diagrams of binary blends of block copolymer and homopolymer

The temperature–composition phase diagrams for six pairs of diblock copolymer and homopolymer are presented, putting emphasis on the effects of block copolymer composition and the molecular weight of added homopolymers. For the study, two polystyrene- block-polyisoprene (SI diblock) copolymers having lamellar or spherical microdomains, a polystyrene- block-polybutadiene (SB diblock) copolymer having lamellar microdomains, and a series of polystyrene (PS), polyisoprene (PI), and polybutadiene (PB) were used to prepare SI/PS, SI/PI, SB/PS, and SB/PB binary blends, via solvent casting, over a wide range of compositions. The shape of temperature–composition phase diagram of block copolymer/homopolymer blend is greatly affected by a small change in the ratio of the molecular weight of added homopolymer to the molecular weight of corresponding block ( M H,A/ M C,A or M H,B/ M C,B) when the block copolymer is highly asymmetric in composition but only moderately even for a large change in M H,A/ M C,A ratio when the block copolymer is symmetric or nearly symmetric in composition. The boundary between the mesophase (M 1) of block copolymer and the homogeneous phase (H) of block copolymer/homopolymer blend was determined using oscillatory shear rheometry, and the boundary between the homogeneous phase (H) and two-phase liquid mixture (L 1+L 2) with L 1 being disordered block copolymer and L 2 being macrophase-separated homopolymer was determined using cloud point measurement. It is found that the addition of PI to a lamella-forming SI diblock copolymer or the addition of PB to a lamella-forming SB diblock copolymer gives rise to disordered micelles (DM) having no long-range order, while the addition of PS to a lamella-forming SB diblock copolymer retains lamellar microdomain structure until microdomains disappear completely. Thus, the phase diagram of SI/PI or SB/PB blends looks more complicated than that of SI/PS or SB/PS blends.

Mapping of physical properties–composition phase diagrams of complex material systems using continuous composition material chips

Efforts to speed up experimental exploration of complex material systems in the pursuit to uncover the myth of fascinating phenomena of condensed matter physics are described. We focus our discussion to the experimental techniques of epitaxial growth of thin film “continuous phase diagrams” (CPDs) and mapping their physical properties. As an example, we discuss the results of mapping optical, electrical and magnetic properties of manganese oxides as functions of doping concentration, ionic radius, etc. We discuss the surprising evidences that suggest various electronic phase transitions such as spin-orbital orderings and electronic smectic phase formation in this highly correlated electronic system.

Diagramme d'équilibre liquide vapeur du système binaire NH3-CH3NH2

A static equilibrium apparatus is described which permits vapour - liquid equilibrium measurements in the range of 293 to 473K and pressure up to 100 bar. Both phases are analysed in a gas chromatography. Measurements are reported on ammonia - monomethylarnine. The temperature - composition phase diagram of the biiary system between 6 to 18bar is given.

Phase diagram of dilute lattice surfactant solution

We have studied the temperature–composition phase diagram for a dilute surfactant model solution on the square lattice through Monte Carlo simulations. A micellar region and a solubility line were identified from the measurement of different properties, among which the volume fraction of aggregate, specific heat, and convergence of relaxation from different initial conditions. We have compared properties of the above system with those of a symmetric lattice solution in the dilute regime. Comparison of data allow an interpretation of the micellar phase as a transition region between a microscopically homogeneous phase and a solid phase.

Pseudo-retrograde hydrate phenomena at low pressures

A Gibbs free energy minimization technique has been applied to calculating phase equilibria of solid hydrates. The van der Waals and Platteeuw theory was used to predict the fugacity of water in each of the hydrate phases. Model parameters for ethane and propane were optimized to pure and binary incipient hydrate equilibrium data as well as to structural transition points for the ethane+propane+water system. It is usually assumed that hydrates never dissociate with an increase in pressure. Predictions show, however, that for a wide water-free composition range, slight increases in pressure will result in the dissociation of sII hydrates (pseudo-retrograde dissociation). Pressure versus temperature and pressure versus composition phase diagrams for the ethane+propane+water system showed that pseudo-retrograde phenomena exist at low pressures (approximately 10–15 atm) near a temperature of 278 K. Pseudo-retrograde hydrate behavior was predicted in the ethane+ i-butane+water and ethane+propane+decane+water systems as well. Two different experimental methods were used to verify the model predictions for the ethane+propane+water system.

Preparation and characterization of two-phase melt systems of lidocaine

The melting point of lidocaine was significantly lowered when mixed with thymol and/or aqueous ethanol. Mixtures of lidocaine and thymol at ratios within the range of 30:70–70:30 (w:w) became homogeneous oils at 25°C. In a pH 9.2 carbonate buffer containing 25% ethanol, lidocaine (5%, w:w) also liquefied at 25°C. The studies led to the development of novel two-phase melt systems of lidocaine (TMS) which consisted of a highly concentrated oil phase of lidocaine and an alcoholic aqueous phase. A compositional phase diagram showed that in aqueous dispersions of lidocaine, concurrent use of thymol and ethanol depressed the melting point of lidocaine more effectively than when they were used individually. Both thymol and aqueous ethanol were necessary as melting point depressing agents to achieve the highest possible lidocaine concentration of 87% (w:w) in the oil phase of a TMS at 25°C. Containing an internal oil phase and an external aqueous phase at ambient temperature, such a TMS can be readily formulated into topical O/W cream after addition of proper surfactants and thickening agents. In an anesthetic activity test using mouse tail-flick model, a 5% lidocaine cream prepared was highly effective as shown by the prolonged latency time of the mice to a heat stimulus as compared with a placebo ( P<0.05).

Magnetic phase transitions for body-centered tetragonal FeRh 1− xPt x system

The magnetic phase transitions near the triple point of FeRh 1− x Pt x system with body-centered tetragonal structure were studied by means of magnetization measurement and Mössbauer spectroscopy. The composition ( x) vs. temperature ( T) phase diagram is determined. The triple point exists at x=0.715 and T=388 K. It is noted that the spin fluctuation plays an important role in the magnetic phase transition around the triple point.

Single-crystal growth of Bi 2Sr 2Ca 2Cu 3O 10+ δ (Bi-2223) by TSFZ method

The traveling solvent floating-zone (TSFZ) method has the potential advantage over the usual flux method that crystal growth can be performed at one point on the temperature–composition phase diagram, and provides an opportunity to grow large single crystals even if their crystallization field is very narrow. Here, we report the first successful preparation of the triple-layered system Bi 2Sr 2Ca 2Cu 3O 10+ δ (Bi-2223) single crystals by improving the TSFZ method condition by applying slow growth velocity and higher temperature gradient. The obtained crystals are as large as 4×2×0.1 mm 3. X-ray diffraction pattern shows only sharp Bi-2223 peaks, confirming its good crystallinity. DC susceptibility of the as-grown samples exhibits a sharp superconducting transition with T c =105 K . After annealing the sample under O 2 flow at 600°C, T c increased to the maximum value (=110 K). High-resolution transmission electron microscope images were taken to investigate the phase purity. It confirms that the crystals cleaved from the last part of grown boule are almost single-phase Bi-2223.

X-ray diffraction and spectroscopic studies of oleic acid–sodium oleate

The sodium oleate–oleic acid (1:1) complex (NaHOl 2) is characterized using X-ray diffraction, FT-IR photoacoustic spectroscopy, FT–Raman spectroscopy, and DSC. The special arrangement of hydrogen-bonded pairs of carboxylic acid and carboxylate groups into unique ‘head-group’ is supported by frequency shifts and partial or total disappearance of characteristic vibrations of carboxylic acid dimer and of carboxylate groups. The well-ordered state of hydrocarbon chains is demonstrated by the existence of sharp Raman bands in the CC stretching region (1000–1150 cm −1) and other conformationally sensitive modes. The FT–Raman results suggest that the transition at about 32°C involves the cooperative melting of methyl- and carboxyl/carboxylate-sided hydrocarbon chains. From the X-ray diffraction data it is clear that this transition is associated with the disintegration of the hydrogen-bonded carboxylate–carboxylic acid complex, followed by the separate formation of oleic acid and sodium oleate. The packing of hydrocarbon chain in the acid–soap complex is different from the parent oleic acid or sodium oleate. The hydrocarbon chains in the NaHOl 2 form more stable packing (O ‖ subcell) in comparison to that of oleic acid. A temperature composition phase diagram is presented.

Comparative study of microstructural and tribological properties of sintered, bulk icosahedral samples

We have investigated a number of quasicrystalline and related samples prepared by sintering under either hot isostatic pressure (HIP) or low uniaxial pressure (LUP). Attention was focused to the influence of the preparation process parameters onto the resulting crystallographic structure and morphology of the phases. Altogether, we found some differences between the two kinds of samples as far as hardness and friction coefficient were concerned. For instance, HIPed specimens containing boron exhibited small rod-shaped precipitates whereas LUPed samples did not. The LUPed specimens revealed better wear resistance and lower friction towards steel and tungsten carbide riders than the HIPed materials. The present study clearly points out that pressure–temperature–composition phase diagrams and preparation processes of quasicrystals, as well as for most other materials, have a significant influence on the final properties which may be eventually used in view of technological applications.

Crystal growth of Cd 1− x−yMn xHg yTe 1− zSe z by a zone-melt method using a pressurized cast ingot

II–VI diluted magnetic semiconductor of Cd 1− x−y Mn x Hg y Te 1− z Se z crystal ( 0.1<x , y <0.3, 0⩽z⩽0.02 ) has a high Hg vapor pressure at a temperature of crystal growth from a melt and also has temperature–composition phase diagrams with a wide solid solution. A quenched polycrystal ingot starting from a stoichiometric Cd 1− x−y Mn x Hg y Te 1− z Se z melt was scaled up to a large size (20 mm diameter by 30 mm length) using a high-pressure synthesizing furnace, where a sealed quartz ampoule is subject to a high external pressure of argon gas (e.g. 14.0 MPa at 1060°C). Using this quenched polycrystal ingot, a large oriented single crystal has been grown by the zone melt method (ZM) for the first time. It has a large size (20 mm diameter by 25 mm length), low insertion loss (0.2 dB at 0.98 μm) and compositional uniformity both in the axial and radial directions.

Three decades of prospecting for novel electronic states and phenomena in f-electron materials

During the past three decades, f-electron materials have proven to be a rich reservoir of novel electronic states and extraordinary superconducting and magnetic phenomena, many of which are surveyed in this paper. The electronic states described include the non-magnetic Kondo many-body singlet, valence fluctuation, heavy fermion, and non-Fermi liquid states. The superconducting and magnetic phenomena recounted include reentrant superconductivity due to the Kondo effect or the onset of ferromagnetic order, the sinusoidally modulated magnetic state that coexists with superconductivity in ferromagnetic superconductors, coexistence of superconductivity and antiferromagnetic order, pressure-induced demagnetization of rare earth ions in dilute and concentrated rare earth systems, and anisotropic superconductivity in which the energy gap vanishes at points or on lines on the Fermi surface, possibly mediated by spin fluctuations, in heavy fermion f-electron and high- T c cuprate superconductors. The temperature vs. pressure or composition phase diagrams of f-electron compounds and high- T c cuprate superconductors in the vicinity of their antiferromagnetic quantum critical points are briefly compared.

The temperature, concentration phase diagram for Tb1−xDyxZn: Failure of crystal field theory

We have calculated the free energy of a crystal field model designed to reproduce the magnetic temperature, composition phase diagram for Tb1−xDyxZn alloys. Using fourth- and sixth-order coefficients consistent with single-ion theory, it was found to be impossible to reproduce the experimental phase boundaries. A reasonable fit to the entire diagram was obtained when the coefficients were chosen to be of the same sign for Dy and Tb, rather than of opposite sign, as required by single-ion theory. To explain this discrepancy, a model is introduced which includes a contribution to the crystal field coming from quadrupole–quadrupole interactions. It is argued that the reason for the success of the calculation using coefficients of the same sign is directly related to the dependence of the strength of the quadrupole coupling on the square of the second-order Stevens factor.

Non-Fermi liquid regimes in the low-temperature phase diagrams of the systems U 1− xM xPd 2Al 3 (M=Y,Th)

Temperature–composition ( T– x) phase diagrams and non-Fermi liquid (NFL) characteristics in the electrical resistivity, specific heat, and magnetic susceptibility at low temperatures for the U 1− x M x Pd 2Al 3 (M=Y,Th) systems are described. The T– x phase diagrams, the NFL characteristics, and the underlying mechanisms for the NFL behavior exhibit distinct differences for M=Y 3+ and Th 4+, apparently reflecting the difference in valence of the M atom substituents, and suggesting that U is tetravalent in these two systems.

On the occurrence of ternary complexes in agarose gels as studied by the contrast variation method

The contrast variation method by isotopic labelling as used in small-angle neutron scattering experiments is applied to the case of agarose systems (sol and gels) in order to cast some light on the occurrence of complexes (crystallosolvates). This approach proves to be helpful for giving further support to the existence of ternary complexes in agarose/water/DMSO gels and in agarose/DMSO sols. The results are discussed in the light of temperature–composition phase diagrams established previously.

Temperature−Composition Phase Diagrams for Binary Blends Consisting of Chemically Dissimilar Diblock Copolymers

Temperature−composition phase diagrams for binary blends of chemically dissimilar diblock copolymers, (A-block-B) and (A-block-C) copolymers, were constructed experimentally. For the study, two polystyrene-block-polyisoprene (SI diblock) copolymers (SI-7/8 and SI-10/53) and three polystyrene-block-polybutadiene (SB diblock) copolymers (SB-9/8, SB-5/36, and SB-10/10) were used. Three binary blend systems were prepared: (i) (SI-7/8)/(SB-9/8) blends consisting of two nearly symmetric lamella-forming diblock copolymers having different chemical structures, (ii) (SI-10/53)/(SB-5/36) blends consisting of two highly asymmetric sphere-forming diblock copolymers having different chemical structures, and (iii) (SB-10/10)/(SB-9/8) blends consisting of two nearly symmetric lamella-forming diblock copolymers having different microstructures in the polybutene block. It has been found, via transmission electron microscopy (TEM), that no macrophase separation took place in each binary blend system over the entire range of blend compositions investigated. The order−disorder transition temperature of each binary blend was determined using oscillatory shear rheometry, enabling us to construct a temperature−composition phase diagram for each blend system. It has been found that the temperature−composition phase diagrams for the (SB-9/8)/(SI-7/8) and (SB-10/10)/(SB-9/8) blend systems follow nearly a linear relationship, whereas the temperature−composition phase diagrams for the (SI-10/53)/(SB-5/36) blend system show positive deviation from linearity. The experimentally determined temperature−composition phase diagrams are found to be consistent with the predictions from random phase approximation calculations. It has been found that the microdomain structure, as determined by TEM, of each binary blend was the same as that of the constituent block copolymers.

Phase transitions in Ca1 − xSrxTiO3 perovskites: effects of composition and temperature

The crystal structures of Ca0.6Sr0.4TiO3 and Ca0.8Sr0.2TiO3 perovskites have been studied at high temperatures by X-ray powder diffraction. The most likely sequence of phase transitions with increasing temperature in Ca0.6Sr0.4TiO3 is the same as that shown by the system CaTiO3–SrTiO3 with increasing Sr content at room temperature. This sequence is: orthorhombic Pbnm, orthorhombic Bmmb, tetragonal I4/mcm and cubic Pmm. The second orthorhombic phase could not be determined in Ca0.8Sr0.2TiO3, either due to the poorer resolution of the diffractometer employed or because the Bmmb phase might not have a stability field at this composition. The transition temperatures decrease on going from Ca0.8Sr0.2TiO3 to Ca0.6Sr0.4TiO3. Calorimetric measurements on 12 samples spanning the system CaTiO3–SrTiO3 then allow one to draw, in combination with the RT XRD data, the temperature vs. composition phase diagram. Phase boundaries show a linear shift toward lower Sr content with the increase of temperature, implying a negligible plateau effect near the CaTiO3 composition, but quantum saturation occurs at low temperatures near the SrTiO3 composition.