Crystalline Solid Solutions Research Articles

Heats of solution/substitution in TlNO3 and RbNO3 crystals from heats of transition. The complete phase diagram of the TlNO3–RbNO3 system

From measurements of the decrease in the heat (enthalpy) of transition in the solid phase by differential scanning calorimetry, the partial molar heats of solution at infinite dilution, χ, and the heats of solution or substitution, ΔHs°, of Tl+ in RbNO3 crystal and Rb+ in TlNO3 crystal along with their recovered lattice energies, ΔHL°, are reported. The complete phase diagram of the TlNO3–RbNO3 system with details of the sub-solidus regions is reported. The properties of a “mixed crystal’' or “crystalline solid solution’' of Tl(1-x)RbxNO3, viz., structure, transition temperatures, melting temperature, etc., are presented and discussed.

Diffuse scattering measurements of static atomic displacements in crystalline binary solid solutions

Diffuse x-ray scattering from crystalline solid solutions is sensitive to both local chemical order and local bond distances. In short-range ordered alloys, fluctuations of chemistry and bond distances break the long-range symmetry of the crystal within a local region and contribute to the total energy of the alloy. Recent use of tunable synchrotron radiation to change the x-ray scattering contrast between elements has greatly advanced the measurement of bond distances between the three kinds of atom pairs found in crystalline binary alloys. The estimated standard deviation on these recovered static displacements approaches ± 0.001 å (± 0.0001 nm), which is an order of magnitude more precise than obtained with extended x-ray absorption fine structure measurement. In addition, both the radial and tangential displacements can be recovered to five near neighbors and beyond. These static displacement measurements provide new information that challenges the most advanced theoretical models of binary crystalline alloys.

Acousto-optical investigations of crystalline solid solutions

The variation of the acousto-optic figure of merit M in (GaAlN) single crystalline solid solutions with x, temperature and pressure are investigated. It is revealed that an increase of x up to 2.5% leads to an increase of the coefficient M and for higher x we observed a decrease of M. An increase of M with a decrease of temperature below 35 K was also found. The acousto-optical coefficient M reaches its maximal value at 4.2 K. Negligible influence of hydrostatic pressure on the acousto-optical properties of was found. In our opinion this reflects the high stability of the mentioned crystalline solid solutions.

X-ray and neutron diffraction in structural-glass phases of crystalline solid solutions

The x-ray and neutron diffraction in structural-glass phases of crystalline solid solutions is considered in the framework of the quasidomain model of the atomic structure of glass phases. The model presumes that the solid solutions in such phases consist of a number of macroscopic quasidomains with nearly homogeneous random deformations. The general expressions for the intensities and widths of quasi-Bragg scattering for various types of diffraction experiments are obtained for the continuous glass transitions in terms of the matrix of mean-square random deformations ${S}_{\mathrm{mn}}$ and average sizes of quasidomains. The relation of the ${S}_{\mathrm{mn}}$ form to the symmetry of the crystal in the high-temperature phase and the type of glass transition is established. The general results are illustrated on examples of diffraction in glass phases of cubic and hexagonal crystals.

Sample Preparation for MALDI Mass Analysis of Peptides and Proteins

Sample preparation may be the most crucial step in mass spectrometric analysis of peptides and proteins by MALDI. The free dipolar ionic peptides or proteins must be incorporated into a crystalline solid solution that is comprised of excess solvent (the matrix), which modulates desorption/ionization by preferentially absorbing the laser energy at the irradiation wavelength and laser pulse intensity being employed. Usually the cocrystalline sample and matrix are prepared by mixing solutions of each component and permitting the mixture to crystallize through evaporation of the solvents. Two methods employing this approach are presented in this unit: the dried drop method and the rapid evaporation method.

Debye temperature of nanocrystalline Zr - Al solid 1 x x solutions with different grain sizes

Abstract In the Zr1—xAlx system a polymorphous crystal-to-glass transformation (CGT) has been found in earlier work. The CGT is characterized by a softening of the shear elastic constant as observed in both computer simulation and experiments. In this work we report studies of supersaturated Zr1—xAlx crystalline solid solutions with x = 0·1 and x = 0·16 which have been prepared by mechanical alloying or rapid quenching from the melt. From the specific heat measured at low temperatures, the Debye temperatures of the samples are calculated. A large reduction in the Debye temperature with decreasing grain size is found for both concentrations. It is concluded that the effect of grain size plays a major role in the elastic properties of the Zr1—xAlx solid solutions. The possibility of a local stabilization of the amorphous phase at the grain boundaries and the effect on the CGT is discussed.

Debye temperature of nanocrystalline Zr1—xAlxsolid solutions with different grain sizes

Abstract In the Zr1—xAlx system a polymorphous crystal-to-glass transformation (CGT) has been found in earlier work. The CGT is characterized by a softening of the shear elastic constant as observed in both computer simulation and experiments. In this work we report studies of supersaturated Zr1—xAlx crystalline solid solutions with x = 0·1 and x = 0·16 which have been prepared by mechanical alloying or rapid quenching from the melt. From the specific heat measured at low temperatures, the Debye temperatures of the samples are calculated. A large reduction in the Debye temperature with decreasing grain size is found for both concentrations. It is concluded that the effect of grain size plays a major role in the elastic properties of the Zr1—xAlx solid solutions. The possibility of a local stabilization of the amorphous phase at the grain boundaries and the effect on the CGT is discussed.

Dense nanometric ZrO 2Al 2O 3 from spray-pyrolysed powders

Powders of ZrO 2Al 2O 3 synthesized by spray pyrolysis of aqueous solutions of nitrates have been subjected to high-pressure rapid-heating compaction at 700–900 C. The original amorphous phase undergoes decomposition during heat treatment via a series of metastable crystalline solid solutions to the equilibrium phases of monoclinic ZrO 2 and α-alumina. The application of high pressure results in a substantial decrease in the temperature required for each transformation. Maximum densification during pressure-assisted sintering appears to occur at the lowest temperature (700 C), in which the predominant phase is a tetragonal ZrO 2Al 2O 3 solid solution, with a small amount of partitioned γ-alumina. Under these optimum conditions, the crystalline size is 10–20 nm with no evidence of porosity.

Effect of Ge addition to Si 50–55Al 25–20Fe 10Ni 5Cr 5Zr 5 alloys obtained by melt spinning

Microstructure of Si 50-55Al 25-20Fe 10Ni 5Cr 5Zr 5 alloys obtained by rapid solidification changes from homogeneously amorphous to heterogeneous — amorphous+c-Ge (c-Ge: crystalline Ge solid solution) by the addition of Ge. The size, volume fraction and composition of c-Ge particles depend on Ge concentration in the alloy. Fine particles, with a size less than 10 nm, were obtained at 7–10 at.% Ge. Small size and homogeneous distribution of c-Ge particles argue for homogeneous nucleation from the melt during rapid solidification. The Si 5545Al 20Fe 10Ni 5Cr 5Zr 5Geo-10 alloys are characterized by high values of hardness (935–1085 H v) and electrical resistivity(11.0–12.6 μΩm). The exclusion of Ge from the amorphous phase resulted from the complicated interaction between constituent elements when weak bonding nature among Ge, Al and TM (TM-transition metals) atoms is obscured by strong attractive interaction among Si, Al and TM atoms.

Investigation of the ternary phase diagram of mechanically alloyed FeCuAg

The structural and magnetic properties of mechanically alloyed Fe - Cu - Ag at room temperature have been investigated using Mössbauer spectroscopy, x-ray diffraction and differential scanning calorimetry. The elements are naturally immiscible, but through prolonged and energetic ball milling (70 hours at 600 rpm) one can make metastable alloys, the structure of which depends on the elemental composition. In the binary Cu - Ag and Fe - Cu systems, crystalline single-phase solid solutions result, whereas in Fe - Ag the alloying is limited, with the product a mixture of elemental particles. In the ternary system it is possible to produce copper- and silver-rich single-phase fcc alloys, but not the equivalent bcc iron-based structure. As the proportions of the three elements become more equal, the resulting structure becomes highly disordered or amorphous. The composition range of this amorphous phase is different to that observed in sputtered Fe - Cu - Ag systems.

Single-phase and heterophase solid-state chemical kinetics of thermally induced methyl transfer in tetraglycine methyl ester

To better understand the general interrelationships between chemical transformations and physical transformations in solid-state reactions, we have studied the kinetics of methyl transfer in polycrystalline samples of tetraglycine methyl ester [TGME] over the temperature range of 83°C–115°C. Changes in the concentrations of the reactant and various intermediates (sarcosyltriglycine methyl ester METGME, and tetraglycine TG) and products (sarcosyltriglycine METG and N N-dimethyl glycyl triglycine Me2TG) were measured over the entire time course of the reaction using HPLC. Corresponding measurements of physical transformations occurring during the course of the reactions were made using X-ray powder diffractometry and differential scanning calorimetry. Kinetic curves for the loss of TGME in the range of 83°C–115°C have a sigmoldal shape and collapse into one curve when plotted in terms of reduced time. t/t0.5, as do plots of intermediate and product concentration plotted in the same manner. The first 25% of the reaction proceeds homogeneously through what is believed to be the formation of a crystalline solid solution of the intermediates and products in the reactant. The acceleratory character of the kinetic curves in the single-phase portion of the reaction has been described by a kinetic scheme that contains a concentration-dependent rate constant. The apperance of a new crystalline phase beyond 35% of the reaction changes the reaction mechanism from a bulk reaction to an interface-controlled process that causes further acceleration of the methyl transfer. The apparent activation energies for both single-phase and heterophase stages of the reaction are about 100–130 kJ/mole © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 339–348, 1997

Microscopic theory of elasticity of the crystalline solid solution based on pseudopotential method

A theoretical method is developed using the pseudopotential method of electron band theory for calculating the strain energy posed by a crystalline solid solution having solute and solvent atoms that differ in size. In the harmonic approximation, the expression of the strain energy obtained from the pseudopotential method is formally identical to that of the phenomenological theory of elasticity. However, it clarifies the physical significance of the phenomenological parameters (solute, solute-lattice and lattice coupling parameters), so that important characteristics of coupling parameters such as the concentration dependence, the effect of the Fermi surface and the effect of the phonon dispersion curves have been made clear. The analysis reveals the direct effect of the Kohn anomaly on the relaxation of the strain energy of a crystalline solid solution. By applying the result to β-brass, the occurence of spinodal decomposition is consistently explained in the scheme of elastic energy. The pair of concentration (deviation) waves, each of which arises in the α- and β-sublattice, respectively, is theoretically described as an acoustic mode of waves with amplitude ratio β Q( q) Q ( α q ) = 999 .

Interrelationships between phase transformations and organic chemical reactivity in the solid state

A qualitative analysis is presented of the interrelationships between phase transformations and organic chemical reactivity in the solid state, taking into consideration general thermochemical relationships and the thermodynamics of heterophase equilibrium. Two cases, where isomerization reactions depend on the solid-state solubility of the reactant and product, are considered and show that the formation of a new phase can influence both the reaction yield and rate. For example, it is shown that crystallization of a new phase from a crystalline or amorphous solid solution can supply the thermodynamic driving force for chemical transformation. Formation of a new phase may influence solid-state kinetics depending on the solubility of a reactant in the new phase and the relative rates of chemical transformation and formation of the new phase. It is further shown that even for simple monomolecular reactions, kinetic curves for the overall process can consist of up to five parts, depending on the type of phase diagram involved. These principles have been applied to some examples of solid-state isomerization in a way that allows the choice of a proper kinetic scheme and an explanation of the direction and maximum yield observed for a particular reaction.

Formation mechanism of a crystalline Ag50Pd50solid solution by impact ball–materials interaction

The formation of the crystalline Ag50Pd50 solid solution during mechanical alloying under shock interaction of Ag and Pd metallic powders has been studied using electron microscopy and X-ray diffraction. The process involved for impact interaction occurs via the incorporation of the small Pd particles into the Ag matrix in which, under the action of mechanical strain, the mutual diffusion of Ag and Pd leads to the formation of two solid solutions, one rich in Ag and the other rich in Pd. Further grinding allows the homogenization of the two Ag and Pd solid solutions whose composition changes to finally reach the initial Ag50Pd50 composition. The defects as dislocations generated by the impact conditions may be responsible for the reaction mechanism.

Coexistent Phases and their Electrical and Structural Behaviour in the Ternary Re/Mo/O System

AbstractIn order to complete and improve phase diagrams of transition metal oxides the existence and properties of compounds in the Re/Mo/O system have been investigated. Single crystalline solid solutions Re1‐xMoxO2 (0 < x < 0.37) and Mo1‐yReyO2 (0 < y < 0.42) were prepared by Solid State Reactions and Chemical Transport Reactions (CTR) and characterized by means of X‐ray‐diffraction, ICP‐AES, and EPMA. In addition, it was shown that the trioxides Re1‐xMoxO3 or Mo1‐yReyO3 respectively, do not prove a distinct solubility. First results on Re‐doped Magneli phases of Mo are also discussed. There were found two series of solid solutions Mo4‐zRezO11 (0 < z < 0.40) which derive from γ‐Mo4O11 and η‐Mo4O11. The other Magneli phases did not show a significant Re content. Using X‐ray diffraction, AFM and optical microscopy the structure and morphology of single crystals has been studied. It was steated that the dioxide solid solutions were very homogeneous and structural phase transitions depending on x or y did not occur. That is in good agreement with measurements of electrical conductivity σ in the temperature range from 20 K to 300 K in which the samples showed the behaviour of metals with lattice defects. The Magneli phases Mo8O23 and Mo9O26 turned out to be “narrow gap semiconductors” in the low temperature range with activation energies of less than 0.1 eV. The γ‐Mo4 O11‐ and γ‐Mo4O11 crystals, the pure and Re‐doped ones, were found as metallic conductors at higher temperatures and below a transition temperature they show a semiconductive behaviour.

Reversible lithium intercalation in alkali metal vanadium bronzes (M xV 6O 13+δ, where M = K, Rb or Cs)

Thermal treatment of electrochemically prepared crystalline solid solutions of ammonium hexavanadates containing K, Rb or Cs formed adherent electrodes on a conducting substrate without the need for binders. These M x V 6O 13+δ bronzes where M = K, Rb or Cs belong to the ternary system V 2O 4V 2O 5-M 2O. By controlling the electrodeposition/decomposition processes, various alkali metal to vanadium ratios (0.0 to 0.65) and oxygen to vanadium ratios (2.2 to 2.5) were studied. The RbV 6O 13+δ bronzes have not been studied, they are reversible to lithium insertion. For maximum capacity, only small amounts of the alkali metal could be present. Voltage plateaus for small M V ratio bronzes were similar to V 2O 5 for electrodes made by thermal decomposition in air, and to V 6O 13 when heated under a vacuum atmosphere.

Which Systems Can Undergo Inverse Melting?

AbstractIn the process of inverse melting, a crystalline solid solution on cooling becomes less energetically stable than the isocompositional undercooled liquid or amorphous phase. Due to this, the crystal may transform polymorphously to the amorphous or liquid phase. A thermodynamic requirement for this process is the presence of two crossing points of the free energy curves G(T) of the crystalline and liquid or amorphous phases. Fulfillment of the thermodynamic requirement is however not a sufficient criterion for inverse melting to occur. In the present work the question posed in the title is addressed from both a thermodynamic as well as a kinetic standpoint. It is shown that in bcc phases which would otherwise undergo inverse melting, the presence of an energetically favorable B2 phase may prevent inverse melting due to its fast ordering kinetics. This imposes an e/a limit to the occurrence of inverse melting.

An experimental and theoretical study of the glass-forming region of the Mg-Cu-Sn system

The amorphization of Mg-Cu-Sn alloys with various compositions has been studied using the melt-spinning technique, with particular emphasis on the magnesium-rich corner of the ternary phase diagram. The results have been interpreted in terms of Miedema's theory, which highlights competition between the amorphous phase and crystalline solid solutions. Competition by ordered intermetallic compounds has also to be considered in order to explain the restricted amorphization region found in these experiments.

Self- and heterodiffusion in crystalline solid solutions

We present a self-consistent analysis of a complete set of atomic diffusion data in mono-crystalline alkali halide mixed crystals. New measurements of the heterodiffusion coefficients of Na + and Rb + in KCl z Br (1− z) are combined with previous data for the self-diffusion coefficients of the three host ions constitutive of the solid solutions: KCl z Br (1− z) , K z Rb (1− z) Cl and K z Rb (1− z) I. The correlatio have been accounted for by making a systematic use of Manning's equations of the correlation factors for vacancy diffusion in random alloys for unbound free vacancies. The justification and generalization of those equations is discussed in the light of recent simulation and analytical studies. The diffusivity is increased in the mixed crystals. The enhancement effect for both the self- and heterodiffusion coefficients reaches a factor of about 2 around the middle composition ( z $ ̃ 0.5) in the three systems. The major part of the enhancement originates from an increase of the vacancy concentration relative to the pure end members. This effect is qualitatively interpreted in thermodynamic terms. The present conclusions derived in alkali halides may be extended to other similar solids: metallic alloys, solid solutions, etc.

Some recent developments in precursor routes to ceramic nanocomposites

Reactive inorganic polymers and copolymers have recently been used to prepare homogeneously mixed crystalline ceramic solid solutions and composites. The polymers have considerable processing advantages over classical powders, and they may be used to obtain composite fibres, coatings, and dense or porous near net shape forms.