On the structure of the intermediate phases in the praseodymium oxide system

The defect crystal structures for two phases in the praseodymium oxide system (Pr₉O₁₆, ζ phase; and Pr₄₀O₇₂, ε phase) are proposed on the basis of the results of a high-resolution transmission electron microscope (HRTEM) study. Dynamical n-beam electron scattering calculations are used to provide a more accurate and reliable interpretation of the experimental micrographs. In addition, electron diffraction studies reveal the unit-cell dimensions for the n = 11 member in the homologous series of phases in this system. The structural relationships among the related praseodymium oxide phases are discussed.     

Phase equilibria in Cu-Al-Zr system at 1073 K and aluminum concentration of less than 55 at %

X-ray diffraction and electron probe microanalysis were used to investigate phase equilibria in the ternary Cu-Al-Zr system at 1073 K in the Zr-rich region. The fragment of the isothermal section of the system was plotted. The regions of homogeneity of the ternary ZrCu₂Al and ZrCu _x Al_{2 ? x} phases were investigated. The type of phase equilibria between binary and ternary compounds of the Al-Cu-Zr system was established. It was found out that, at a Zr concentration above 55 at %, ternary compounds are not formed, and the Zr₃Al and Zr₂Cu phases were in equilibria with ??-Zr at 1073 K.     

The equilibrium phase diagram of the copper-indium system: a new investigation

The entire phase diagram of the Cu-In system was investigated using differential scanning calorimetry (DSC), powder X-ray diffraction (XRD), metallography and electron probe microanalysis (EPMA) studies. The results indicate the existence of a solubility region of In in Cu with the limit of the solid solution at 5.20 at.% In at 400 °C and of six intermediate phases, the three low-temperature phases δ, η and Cu₁₁In₉, and the three high-temperature phases γ, η′ and β. The boundaries of each phase were defined with respect to temperature and composition.     

Phase equilibria and phase structure in the ternary systems sodium or potassium octanoate-octanoic acid-water

Two isotropic solution regions and several liquid crystalline regions occur in the ternary system sodium octanoate-octanoic acid-water at 20°C The solution regions are an aqueous solution and a solution of sodium octanoate and water in liquid octanoic acid. A region displaying one-dimensional lamellar structure is located in the center of the phase diagram. A region along the soap-water axis has a two-dimensional normal hexagonal structure. Another region at high octanoic acid content has a reversed hexagonal structure. Along the soap-fatty acid axis the acid-soap 2NaC₈:1HC₈ in crystalline state is found.X-ray and density findings for the various phases are presented, and structural parameters for the different liquid crystalline phases are estimated.The phase behavior of the potassium soap system is similar to that of the sodium system.The isothermal ternary phase diagram of a soap, the corresponding fatty acid and water provides information about the ionization state of the system, from the unionized fatty acid to the fully ionized soap.     

Structure and phase behaviour of the ternary system water, n-heptane and the nonionic surfactant Igepal® CA520

The phase behavior of the system water, n-heptane and the nonionic surfactant Igepal^® CA520 has been studied by visual inspection, high-performance liquid chromatography, polarizing microscopy and freeze-fracture electron microscopy. The phase diagram at 25?°C contains two large homogeneous microemulsion phases, an extended region of a lamellar liquid crystalline structure and some two- and three-phase regions. The oil-rich part of the phase diagram has been investigated by static and dynamic light scattering in order to examine the behavior of the collective diffusion coefficient and the scattering intensity in the presence of increasing concentrations of water, starting from the binary system of n-heptane and Igepal^® CA520. The results suggested that at a very low water content the aggregates of the microemulsion are small. With the exception of this region the structure is bicontinuous.     

Solid state phase equilibria in the PtGaAs system

The PtGaAs solid state equilibrium phase diagram was determined at 600 °C with the use of X-ray powder diffraction, electron probe microanalysis (EPMA) and scanning electron microscopy (SEM). No ternary PtGaAs phases were found and limited solid solubility was measured in the constituent binary PtGa and PtAs compounds. GaAs, PtGa and PtAs₂ form a region of three-phase equilibrium which dominates the GaAs side of the phase diagram. The phase diagram is in agreement with previous observations that PtGa and PtAs₂ are the stable phases when platinum thin films are reacted to completion on GaAs.     

Cubic perovskite-related phases in the ternary SrO-CuO-Nb2O5 system

A careful phase analysis study of cubic perovskite-related phases in the ternary SrO-CuO-Nb₂O₅ system has been carried out via the synthesis and compositional analysis of a range of specimens within the ternary SrO-CuO-Nb₂O₅ system. Powder XRD in conjunction with electron probe microanalysis (EPMA) has been used to determine whether the synthesized specimens are single phase or not and to determine the compositions of the various reaction products. Three quite distinct such solid solution phases have been found and their quite distinct electrical and diffraction characteristics investigated.     

On the structures of the intermediate phases in the terbium oxide system

A high-resolution transmission electron microscope investigation of the ordered phases in the terbium oxide system in the range $\text{1.714 <}\text{O}\text{Tb}\text{< 2}$ has been performed. Two ordered phases belonging to the R_nO_2n?2 homologous series of defective fluorite phases have been examined, namely, the n = 11 and n = 12 members. Selected area electron diffraction has revealed two polymorphs of the n = 12 phase in the TbO_x system. In addition, a metastable n = 16 phase was identified by diffraction and imaging techniques. High-resolution (～3 Å) images of thin crystals of these phases are presented. Computer-simulated lattice images based on dynamical scattering theory with the incorporation of the appropriate instrumental parameters at through-focus and through-thicknesses for proposed defect structures of the intermediate terbium oxide phases are presented for comparison. Images calculated at optimum defocus and periodic thicknesses correspond to the projected crystal potential. The remarkably good match between experimental and calculated images at optimum defocus and in a through-focus series supports the choice of the structural models for the real defect structure of the intermediate phases.     

BaO-BiO1.5 phase diagram in the region 80–100 mol % BiO1.5 at p o 2 = 21 kPa

The phase equilibria in the region from 80 to 100 mol % BiO_1.5 are studied in the BaO-BiO_1.5 system in air and under an argon atmosphere using visual polythermal analysis (VPA), X-ray powder diffraction, differential thermal analysis (DTA), electron diffraction (ED), and elemental analysis in a transmission electron microscope (EA/TEM). A series of discrete layered rhombohedral phases (RPs) with the composition Ba₂Bi_8+n O_y, where n = 0, 1, 2, 4, 8, or 10, is discovered. The melting character is determined for these RPs: the 1: 4 phase melts congruently; the 2: 9, 1: 5, 1: 6, and 1: 8 phases melt incongruently. The crystallization fields are 10–30°C. At p _{o 2} = 21 kPa, the 1: 4 phase in the subsolidus region decomposes into a 4: 13 perovskite-like phase and the 2: 9 phase. The other rhombohedral phases decompose into stages to yield Bi₂O₃ and a neighboring RP that is richer in barium. The Ba₂Bi_8+n O_y oxides are stable in argon and experience a first-order phase transformation at about 560°C.     

Modelling the chemically induced liquid crystalline phases in mixtures of disc-shaped mesogens: the phase diagram of quadrupolar Gay-Berne discs revisited

We investigate the phase behaviour of pure systems and mixtures of quadrupolar Gay-Berne discs. The interaction potential mimics that of disc-shaped molecules which exhibit chemically induced phases with a structure based on columns of alternately stacking species. The phase diagram of the pure system is determined over a range of pressures, and the phase sequence is shown to include tilted columnar and nematic phases. The mixtures, in which the species have equal but opposite quadrupole moments, are investigated over a range of pressures using semigrand canonical simulations, such that the composition of the system is allowed to change. The fact that the composition is not fixed is especially important at the phase transitions, where the compositions of the coexisting phases may not necessarily be the same. In this situation, preparation of a system in the ‘biphasic region’ will lead to phase separation into the two distinct phases of differing compositions. The resulting phase diagram obtained using semigrand canonical simulations indicates that the columnar nematic phase observed in previous fixed composition simulations of this model [Liq. Cryst.,24, 229 (1998)] is not stable with respect to phase separation into an isotropic phase rich in a single component and a hexagonal columnar phase composed of roughly equal quantities of the two components. The structure of the columnar phase for the mixture is shown to be based on the alternate stacking of the different species. The relative concentrations of the different species in this phase may deviate up to approximately 60 : 40 mol%, after which any further material added will separate into the pure isotropic state.     

Phase relationships in the Ce-Pd-In system

The interaction of cerium with palladium and indium was studied, and the 773°C isothermal section of the Ce-Pd-In phase diagram was plotted using physicochemical methods: X-ray powder diffraction, single-crystal X-ray diffraction, and electron probe microanalysis. The existence of 12 ternary intermetallic phases in the title system was confirmed, and three new phases were discovered. Crystal structure was determined for seven intermetallic compounds. A single-crystal X-ray diffraction study of CePdIn was carried out for the first time. A high-temperature phase CePdIn₄ was found, and its crystal structure was solved.     

Electron microscopic and light scattering observation on a system with two iridescent phases

Electron microscopic observations and classical light-scattering measurements have been carried out for dodecyldimethylaminoxide/hexanol/water mixtures in the concentration range where iridescent colors occur. This system has two different iridescent phases. The iridescent phase with more hexanol forms quickly, and the phase with less hexanol forms very slowly. Three different isotropic phases which show strong flow birefringence are found near both iridescent phases. The electron microscopic pictures show clearly that only one of these isotropic phases with strong flow birefringence is a bicontinuous sponge phase (L_3h -phase). This is the phase which comes out by adding some alkanol to the upper lamellar phase. The flow birefringent phase below the lower lamellar phase forms unilamellar vesicles. The flow birefringent phase which occurs between both iridescent phases contains multilamellar vesicles and is shown to be a precursor of a lamellar phase.     

Structure formation in doped discotic polymers and low molar mass model systems

Doping of low molar mass materials or polymers, possessing disc-like units, with electron acceptors leads to the stabilization of columnar discotic phases or even to the induction of such phases in compounds which either display a nematic discotic phase or only an amorphous phase in the absence of the electron acceptor. The induced columnar phase corresponds frequently to a hexagonally ordered one. We have observed, however, in addition the induction of new columnar phases such as the rectangularly ordered (D^ro) and the columnar nematic phase (N^c). The enhancement of the tendency towards the formation of columnar phases is a consequence of electron acceptor—electron donor complex formation. Using a model proposed by de Jeu to describe the induction of smectic phases by complex formation we are able to account qualitatively for the experimental findings.     

Investigations into the formation and characterization of microemulsions. I. Phase diagrams of the ternary system water—sodium alkyl benzene sulfonate—hexanol and the quaternary system water—xylene—sodium alkyl benzene sulfonate—hexanol

The phase diagrams of the ternary system water—sodium alkylbenzene sulfonate (NaDBS)-hexanol and the quaternary system water—xylene—NADBS—hexanol have been established at three different temperatures, namely 25, 37, and 50°C. The different phases formed have been qualitatively examined using optical (phase contrast and polarizing) microscopy. The textures of the various liquid crystalline phases in the ternary system have been identified, by comparison with previous studies in the literature. Some of the liquid crystalline phases have been quantitatively assessed using low angle X-ray diffraction. The latter measurements were also used to determine the unit cell dimensions in the various phases studied. With the quaternary system, particular attention was paid to the transparent region which consisted of an L₂ (inverse micellar) phase extending into another transparent region which has a blue “tinge” in some cases, namely the microemulsion (M) region. The amount of water solubilized in the L₂ (reverse micelle) or M + L₂ phase was calculated from the phase diagrams. With the ternary system the results showed a maximum in moles of water solubilized per mole total surfactant (NaDBS + hexanol) at a concentration of 0.3 mole surfactant, at an optimum molar ratio of n-hexanol to NaDBS of 4.5:1. This maximum was about twice with the quaternary system, when compared with that of the ternary system, indicating the importance of the role of xylene in solubilization of water by the surfactants. The present investigation has also shown that the extent of the microemulsion region is significantly reduced by increases of temperature when the NaDBS is lower than 15 wt%.     

Electron-precise/deficient La(5-x)Ca(x)Ge4 (3.4 < or = x < or = 3.8) and Ce(5-x)Ca(x)Ge4 (3.0 < or = x < or = 3.3): probing low-valence electron concentrations in metal-rich Gd5Si4-type germanides

We report for the first time the syntheses of electron-precise/deficient alloys, Ln5-xCaxGe4 (Ln = La, Ce; x = 3.37, 3.66, 3.82 for La; x = 3.00, 3.20, 3.26 for Ce), in the metal-rich R5Tt4 Zintl system (R = rare earth metal; Tt = Si, Ge). The new alloys extend the phase width from electron-rich to open-shell electron-deficient region in the metal-rich Zintl system and demonstrate possible occurrence of varied electron deficiencies in Zintl phases without structural changes, as a result of other existing structure-forming factors.     

Saturated vapor pressure in the thallium-cadmium system

Component vapor pressures in the thallium-cadmium system determined by the method of boiling points (isothermal variant) and the flow method were used to calculate the thermodynamic characteristics of the vapor and condensed phases in the region of the existence of liquid solutions. The temperature-concentration dependences of the thermodynamic values were determined. The phase diagram was augmented by liquid-vapor phase transitions at atmospheric pressure and in a vacuum (100 and 10 Pa) with the determination of the boundaries for the coexistence region of the liquid and vapor phases.     

Novel intermediate phases in an ionic fluorocarbon surfactant/water system

This small angle X-ray scattering study of the lyotropic phases in the binary tetramethylammonium perfluorodecanoate/water system shows that there are no classical lyotropic mesophases present. Much of the liquid crystal region is taken up with a random mesh intermediate phase, Mh₁(0) and a phase with rhombohedral symmetry which is probably a rhombohedral mesh intermediate phase, Mh₁(R3m). This behaviour is unusual since previously these mesh phases have been associated with hydrocarbon surfactants or diblock copolymer melts. All the mesophases found have non-uniform interfacial curvature and a sufficiently strong inter-layer interaction to ensure the long range correlation of structures in some phases.     

P NMR investigation of a ringing gel phase and adjacent phases

The temperature-surfactant concentration phase diagram was examined for the dodecyltrimethylammonium dimethylphosphate/3-methyl-3-methoxybutanol/water ternary system. The phase diagram contained a highly elastic gel phase which is known as a “ringing gel phase”. The ringing gel phase and adjacent phases in the ternary system were investigated by polarized optical microscopy, freeze-fracture transmission electron microscopy, and ³¹P NMR. Globular textures were observed in an optically isotropic gel phase. Since the globules were larger than those found in an isotropic solution, the texture consists of domains of aggregated units in the cubic (I₁) phase. Structure units of domains are equivalent to microemulsions which are constructed by surfactant molecules and swollen by alcohol in the isotropic (L₁) phase. Characteristic polarized microscopic textures were visualized in two phases with higher surfactant concentrations. These phases were identified as being hexagonal (H₁) and lamellar (L) liquid crystals which was confirmed by transmission electron microscopy. The ³¹P NMR signal of the ringing gel showed a sharp singlet the same as that of the L₁ phase, indicating the fully averaged anisotropic interaction of the aggregates. The characteristic NMR signals of the anisotropic hexagonal and lamellar liquid crystal phases displayed chemical shielding with an asymmetric lineshape.     

Notes on phases occurring in the binary tungsten-oxygen system

The phases occurring in the binary tungsten-oxygen system in the composition region WO₃WO₂ have been clarified by electron microscopy and powder X-ray diffraction in the temperature range from 723 to 1373 K. There are five structure types in the binary system, besides WO₃, viz., the {102} CS structures, the {103} CS structures, W₂₄O₆₈, W₁₈O₄₉, and WO₂. The {102} and {103} CS structures, and W₂₄O₆₈ structures, were always disordered and true equilibrium was not achieved even after 5 months of heating at 1373 K. The lowest temperature for the formation of the CS phases was of the order of 873 K, and the disordered W₂₄O₆₈ structure formed at somewhat higher temperatures. The formation of the latter phase was also slower than the formation of the CS phases. The results suggest that elastic strain energy is of importance in controlling the microstructures found in the nonstoichiometric regions.     

Phase equilibria in the Cu-Tl-Ge system

The Cu-Tl-Ge system has been studied by DTA and powder X-ray diffraction. Several polythermal sections, the isothermal section at 400 K, and the liquidus surface projection have been constructed for the phase diagram of this system. Primary phase fields and the types and coordinates of invariant and monovariant equilibria have been determined. An immiscibility region of the Cu-Tl binary subsystem considerably (up to 60 at % Ge) protrudes into the triangular diagram and crosses peritectic and eutectic curves that originate from the Cu-Ge subsystem. This gives rise to a number of four-phase monotectic equilibria in the ternary system. Crystallization ends with peritectic equilibrium and eutectic equilibria, which are all degenerate in the vicinity of thallium. Intermediate ternary phases are not formed in the system. Solubilities in the initial components and in binary phases of the Cu-Ge system do not exceed 0.5 at %.