Crystalline Solid Solutions Research Articles

Synthesis and Physicochemical Properties of Crystalline and Glassy La14 – x – yGd x Eu y (BO3 )6(GeO4)2O8 Solid Solutions

Using solid-state reactions, La14 – x – yGd x Eu y (BO3)6(GeO4)2O8 solid solutions isostructural with Ln14(BO3)6(GeO4)2O8 (Ln = Pr, Nd, Sm, Eu, Gd) were prepared for the first time, and their melting points and melting behavior were established. Liquid quenching of the solid solutions was found to yield thermally stable glasses containing as much as ≃60 mol % rare-earth oxides. The composition limits of the glass-forming region were determined, and the luminescence spectra of both crystalline and glassy solid solutions were studied.

Heats of solution/substitution of Tl+, Rb+, K+, Br−, I− in crystalline CsCl from heats of solid phase transition by differential scanning calorimetry

Measurements of the change in heat (enthalpy) of transition in crystalline CsCl effected by the presence of guest ions K+, Rb+, Tl+, Br−, I− using differential scanning calorimetry are reported. The nature of each mixed-ion solid, ‘mixed crystal’ or ‘crystalline solid solution’ is discussed. The limits of solubility of each guest ion are found to be consistent with the subsolidus region described in its respective phase diagram. The quantitative heat of transition values are used to calculate some fundamental solution quantities, viz. slope ΔHt/x or ΔH̄solute,χ, ΔHS0, ΔHL0—apparent partial molar heat of solution, partial molar heat of solution at infinite dilution, the heat of solution, recovered lattice energy, respectively.

Heats of solution/substitution in TlNO 3 and CsNO 3 crystals and in RbNO 3 and CsNO 3 crystals from heats of transition: the complete phase diagrams of TlNO 3–CsNO 3 and RbNO 3–CsNO 3 systems

From measurements of the decrease in the heat (enthalpy) of transition in the solid phase using differential scanning calorimetry, the apparent molar heats of solution, slope Δ H t/ x, the partial molar heats of solution at infinite dilution, χ, and the heats of solution, Δ H s °, of Tl + in CsNO 3 crystal and Cs + in TlNO 3 crystal and Rb + in CsNO 3 crystal and Cs + in RbNO 3 crystal along with their recovered lattice energies, Δ H L °, are reported. Δ H s ° of Tl + and Rb + in CsNO 3 crystal are each found to be negligible or zero representing an ideal solid solution, i.e. Δ H mix=0. The complete phase diagrams of the TlNO 3–CsNO 3 and RbNO 3–CsNO 3 systems with details of the sub-solidus regions are included. The properties of Tl (1− x) Cs x NO 3 and Rb (1− x) Cs x NO 3 compositions are discussed in terms of a ‘mixed crystal’ or ‘crystalline solid solution’ in relation to parallel compositions of Tl (1− x) Rb x NO 3.

Lunar Mg suite: Thermobarometry and petrogenesis of parental magmas

Using compilations of internally consistent thermodynamic data on minerals and advances in quantifying the energetics of crystalline solid solutions, we have recalculated the pressures and temperatures of equilibration of troctolite sample 76535 and a number of spinel cataclasites. The five phase assemblage (olivine + orthopyroxene + clinopyroxene + Cr‐spinel + plagioclase), which occurs in symplectite assemblages in 76535, gives equilibration temperatures from 800°–900°C and pressures from 200 to 250 MPa, indicating a deep (40–50 km) crustal source. Spinel cataclasite assemblages give minimum pressures of ∼100 MPa. Mg suite magmas were apparently intruded throughout the lunar crust early in lunar history. The textures and equilibration temperatures in many Mg suite samples are consistent with subsolidus recrystallization and the Mg‐rich minerals of some refractory troctolites and dunites may be residues of a crustal melting process or products of subsolidus elemental redistribution. The Sm‐Nd age of 4.26±0.06 Ga of troctolite 76535 most likely represents the time of subsolidus recrystallization and/or partial melting. In an attempt to identify the primary source material for the Mg suite magmas, a variety of models were tested using the MELTS and MAGFOX codes. A good fit between mineral compositions and crystallization sequences is obtained by ∼20% batch melting at 0.5 GPa of an average whole Moon composition with an Mg # of 0.85. Melts formed by batch melting at higher pressures and melts formed by polybaric partial fusion over the pressure range from 2.0 to 0.3 GPa were either too poor in Mg and/or crystallized clinopyroxene before orthopyroxene. Mixing with 10–20% urKREEP, which is required to satisfy the REE constraints of the Mg suite, reduces the Mg # of the parental magmas and requires a whole Moon Mg # closer to that of the terrestrial mantle.

Critical Solid Solubility of the Ni-Ti System Determined by Molecular Dynamics Simulation and Ion Mixing

From a realistic n-body potential of the Ni–Ti system, the critical concentrations of the Ni- and Ti-rich solid solutions were determined by molecular dynamics (MD) simulation to be 38 at% Ti and 15 at% Ni, respectively, beyond which a disordered atomic configuration was more stable than the respective crystalline solid solutions. It follows that the central composition range bounded by the critical solubilities, i.e. within 38–85 at% of Ti, can be considered as the glass-forming range of the system, which was confirmed by room temperature 200 keV xenon ion mixing of alternately deposited Ni–Ti multilayered films. Moreover, MD simulation of a Ni–Ti bilayer revealed that during the solid-state amorphization reaction, the growth of the amorphous interlayer followed exactly a t1/2 law and grew faster towards the Ti lattice than to the Ni side. The physical origin of such an asymmetric behaviour was found to be due to a difference in critical solid solubilty of the constituent metals.

Effect of the atomic size distribution on glass forming ability of amorphous metallic alloys

A topological approach based on analysis of atomic size distributions has been developed and applied to multicomponent amorphous alloys with different glass-forming ability. The atomic size distributions were obtained by plotting atomic concentrations versus atomic radii of constitutive elements. Ordinary amorphous alloys with high critical cooling rates were found to have single-peak distributions with a concave downward shape. These amorphous systems have at least one alloying element with a smaller radius, and at least one alloying element with a larger radius relative to the base element. The concentration of an alloying element decreases rapidly as the difference in the atomic sizes of the base element and the alloying element increases. Atomic size distributions of Zr, Pd, or Ln-based bulk amorphous alloys, which have a critical cooling rate in the range of 1–100 K/s, have a completely different, concave upward shape with a minimum at an intermediate atomic size. The base alloying element in these alloys has the largest atomic size and the smallest atom often has the next-highest concentration. A model that explains the concave upward shape of atomic size distributions for the bulk amorphous alloys is suggested. This model takes into account that all alloying elements in bulk glass formers are smaller than the matrix element, and some of them are located in interstitial sites while others substitute for matrix atoms in a reference crystalline solid solution. The interstitial and substitutional atoms attract each other and produce short-range ordered atomic configurations that stabilize the amorphous state. According to this model, the critical concentration of an interstitial element required to amorphize the alloy increases with increasing size difference from the matrix atom.

On the stability of the thermally decomposed Co-Al hydrotalcite against retrotopotactic transformation

Retrotopotactic transformation to the original layered double structure of Co-Al hydrotalcite, after thermal treatment at temperatures as low as 473 K, did not occur after 30 days in contact with a wet gas flow (5 vol% H 2O in N 2) or after 12 h in an aqueous solution of 0.5 M Na 2CO 3, which deviates from the typical behavior observed for Mg-based hydrotalcites and other layered compounds. The presence of oxidizable Co 2+ cations in the octahedral sheets of the layered material and their diffusion to the interlayer space in the dehydrated layered structure, and the stability of the homogeneous crystalline solid solution of cobalt spinels, already identified at 423 K, are responsible for this behavior.

Microscopic elasticity theory of ionic crystal and its application to cubic ZrO 2–5.2 mol% Y 2O 3 system

An analytical expression of the strain energy in an ionic crystalline solid solution was obtained by modifying the microscopic theory of elasticity in metal alloys. The Lorentz field originating in the short-range interaction of dipoles, along with a non-Coulomb force field produces specifically the elastic strain. On the other hand, the macroscopic electric field induced by the long-range interaction of dipoles works on each dipole lattice to produce the piezoelectric strain. The theory was applied to a cubic ZrO 2–Y 2O 3 system of ionic crystalline solid solution in order to estimate the microscopic strain energy of the system. The trace of the minimum points in the energy surface indicates possible spinodal decomposition along [1 1 1] direction. It is also revealed that local electrical neutrality can mostly be preserved during the decomposition due to the macroscopic electric field in the ionic crystal.

Interrelation between optical, refractometric, and lattice parameters of Cu6P(S1−x Sex)5I crystals

The influence of the compositional disordering on the energy of the fundamental absorption edge and the refractive index dispersion of the crystalline solid solutions Cu6P(S1−xSex)5I is studied. It is shown that the concentration dependences of the optical pseudogap width, the refractive index, and the lattice parameter in these crystalline solid solutions are interrelated.

The enthalpy state of amorphous alloys in an immiscible system

We performed calorimetric measurements of the enthalpy of formation of amorphous alloys created using vapor quenching in a highly immiscible system, Ag–Ni. The low-enthalpy states observed, as compared with extrapolated liquids and crystalline solid solutions, are in agreement with the findings from molecular dynamics (MD) simulations. The MD results support the proposition that the enthalpy reduction is associated with the ultra-fine-scale phase separation in the liquid/amorphous state.

Homogeneity of lanthanide doped ceria nanocrystal dispersions using high-resolution transmission electron microscopy

Aqueous sols of crystalline solid solutions of the general formula Ce1-xLnxO2-x/2□x/2 [Ln = entire lanthanide range, x = 0–0.50 and square = anion vacancy] were synthesised using inorganic materials. The nanocrystals were dispersed on an amorphous silica support and individual crystals examined for composition and structure by high-resolution transmission electron microscopy (HREM) and energy dispersive analysis of X-rays (EDX). High-resolution pictures showed the nanocrystals to be mainly between 5 and 10 nm in size, rarely elongated and with atomically clean faceted surfaces. Diffractograms were used to measure the lattice parameters of the face-centre-cubic (fcc) fluorite structures giving values, depending on dopant species and concentration of dopant, in the range 5.5–5.8 A. EDX analysis of individual crystals with the same nominal composition compared closely to each other and to that of an average over a large area indicating good homogeneity from the preparation method.

Heats of solution of TlI in TlNO3 and TlBr in TlI crystals. Phase diagrams of TlNO3–TlI and TlBr–TlI systems

From differential scanning calorimetry (DSC) measurements of the decrease in the heat (enthalpy) of transition in the solid phase, the partial molar heats of solution at infinite dilution, χ, and the heats of solution or substitution, ΔHs° of I− in TlNO3 crystal, Br− and NO3− in TlI crystal along with their recovered lattice energies ΔHL° are reported. The phase diagram of the TlNO3–TlI system with details of the subsolidus region along with subsolidus region of the TlBr–TlI diagram are reported. The TlIx(NO3)1−x compositions exhibit properties, viz. structure, transition temperatures and melting temperature characteristic of a “mixed crystal” or “crystalline solid-solution” paralleling Tl(1−x)RbxNO3 behavior.

Dissolution in molten silicates: effects of solid solution

The effects of solid solution and solid state diffusion on crystal dissolution in a multicomponent liquid was examined by studying exact and approximate solutions to equations governing isothermal-isobaric diffusive dissolution of a crystalline solid solution in binary and ternary liquids. The dissolution rate is proportional to the square root of time in diffusive dissolution. The effect of solid state diffusion is to change the dissolved crystal composition from that in the interior of the crystal to that at the crystal-melt interface, which depends on the relative rate of diffusion in the solid to the rate of dissolution. If the dissolution rate is much faster than the diffusive exchange rate in the solid, the dissolved crystal will retain its interior or far-field composition that has not been affected by diffusion (referred to as Regime I dissolution). The dissolution rate is proportional to the diffusion rate in the liquid, independent of the crystallographic orientation of the dissolving crystal. If the dissolution rate is much slower than the rate of diffusion in the solid, the dissolved crystal will have its solidus composition at the crystal-melt interface (termed Regime II dissolution). The dissolution rate is proportional to the diffusion rate in the solid and hence dependent of the crystallographic orientation of the dissolving crystal if the degree of undersaturation is extremely small (i.e., <0.5% difference in concentrations in the liquid). Regime I dissolution is important when the diffusion rate in the liquid is more than four to six orders of magnitude faster than the diffusion rate in the solid. Convection in liquid facilitates crystal dissolution and further diminishes the role of diffusive exchange in crystal. Given the large disparities between diffusion rates in silicate crystals and diffusion rates in silicate melts (typically greater than 10 4), dissolution of practically all silicate xenocrysts and xenoliths in natural molten silicates are characterized by Regime I dissolution. Regime II dissolution is important when the dissolving crystal and melt are in near chemical equilibrium.

Formation of high-conductivity regions in nanostructured SnO2-AOx (A = Ti4+, Zr4+, Sb3+, Sb5+) films exposed to UV radiation or H2

Data are presented on the composition, structure, and electronic properties of SnO2 films doped with Ti, Zr, and Sb oxides. The films were prepared by thermohydrolytic decomposition of SnCl2, TiCl4, ZrCl4, and SbCl3 solutions and were found to contain nanoscale regions of crystalline SnO2-based solid solutions and amorphous SnO2 containing Sn2+ or Sb3+ ions and located on the surface of crystallites or between them. As distinct from SnO2 sensors containing no noble metals, the films exhibit high sensitivity to H2 adsorption and/or UV radiation at 20°C (conductivity increase by 5 orders of magnitude). The results on the nanostructure, electronic spectra, and conductivity indicate that, in the three systems studied, UV irradiation and H2 adsorption give rise to the formation of high-conductivity, metallic regions responsible for the low-temperature H2 sensitivity of the films.

Kinetic, chemical and mechanical factors affecting mechanical alloying of Ni–bcc transition metal mixtures

The influence of enthalpy of mixing and elemental mechanical characteristics on the kinetics of mechanical alloying (MA) of 80 at.% Ni-20 at.% bcc transition metals (Fe, Cr, W, Nb, and Ta) has been studied. The features and structures of milled powders were characterized by X-ray diffraction, optical microscopy, and particle size analysis. Powder caking of the grinding media — in varying amounts depending on the materials alloyed and the alloying time — occurs when these elemental combinations are mechanically alloyed. Differences, if any, between the structures of ‘free’ and ‘caked’ powders were also determined. As expected, for systems with low enthalpies of mixing (Ni/Fe, Ni/Cr, Ni/W) crystalline solid solutions form during MA. Moreover, the compositions of these solid solutions are the same in both free and caked powders. Also as anticipated, for systems with high enthalpies of mixing (Ni/Nb, Ni/Ta), extended MA produces amorphous phases that form from precursor solid solutions. In distinction to systems with low enthalpies of mixing, the structures of the free and caked powders differ for systems with high mixing enthalpies. Caked powders were inhomogeneous, consisting of powder in varying degrees of solid solution and, if the milling time was sufficiently long, also some amorphous powder. However, the free powder was almost entirely noncrystalline. With extended milling, the fraction of free powder increases suggesting that the formation of the amorphous phase takes place on the surface layer of the coated grinding media. Subsequent to its formation, the amorphous phase is abraded from the coated surfaces. The kinetics of solid solution and/or amorphous phase formation is discussed in terms of the differing mechanical characteristics of the bcc transition elements, as well as the system thermodynamics.

Metastable phases in interface controlled materials

Metastable phases may be stabilized at interfaces due to lower surface or interface energies in comparison with the equilibrium phase. An example for this kind of stabilization effect is the phenomenon of surface melting, where a liquid-like film forms at the surface below the actual melting point. The excess energy necessary for the formation of the metastable, undercooled liquid phase is overcompensated by the gain in surface energy. Similar effects have been found in interface controlled materials such as thin films or nanocrystalline materials. In thin films, incoherent interfaces between the film and the underlying substrate contribute significantly to the total energy. The lower interface energy of a metastable film can stabilize the non-equilibrium phase as in the case of surface melting. A study is reviewed of thin Fe(Zr) alloy films which serves as a model system for the investigation of the interface effects. If deposited on suitable substrates, these films grow in the amorphous phase whereas in bulk materials the crystalline solid solution is more stable. Crystallization of the initially amorphous films sets in at a critical thickness where the driving force for crystallization can overcome the stabilizing effect of the interface. Under the experimental conditions, diffusional transport is negligible so that no phase separation can occur. Upon increasing the solute concentration, a polymorphic crystal-to-glass transformation (CGT) is encountered in the volume at a critical solute concentration. At concentrations close to the CGT, the relative stabilities of the competing phases, i.e. the crystalline solid solution and the amorphous alloy, approach each other. Therefore, the chemical composition of the films plays a role equivalent to the temperature in the case of surface melting. In the vicinity of the CGT, the interface energy contributions may dominate phase formation. As a result, a dramatic increase of the critical thickness for crystallization is observed with increasing solute concentration. A thermodynamic model based on the competing energetic contributions can explain the results. A generalized phase diagram is used for the description of interface effects in glass forming systems. Precursor effects like wetting at interfaces close to the conditions for phase transitions in bulk materials are also expected to be significant in systems with a high density of incoherent interfaces. The interfaces may serve as nucleation centres which play an important role for phase transformations in these materials.

Hyperfine Characterization of Pure and Doped Zircons

The aim of this work has been to investigate the influence of two coloring dopant ions on the ZrSiO4 host lattice. Pure, vanadium-doped and praseodymium-doped zircon powders have been synthesized by the ceramic method and analyzed using X-ray diffraction and the perturbed angular correlations (PAC) hyperfine technique, which probes the nearest environments of zirconium ions. XRD results indicated that vanadium and praseodynamium incorporations in the host lattice result in crystalline solid solutions. In turn, PAC information allowed in both cases the determination of two contributions to the hyperfine interaction. In the case of vanadium-doped zircon, V4+ substitutes mainly for Zr4+ and in a minor fraction for Si4+ or else it localizes at a tetrahedral interstitial site. In praseodymium-doped zircon, a low fraction of Pr4+ cations locate at Zr4+ sites. A slight modification of the zircon lattice is probably caused by the incorporation of the remaining cations at tetrahedral interstitial sites of the solid solution.

Connection between Near Millimeter Range Dielectric Loss and High Frequency Acoustic Attenuation

ABSTRACTA series of crystalline isomorphic solid solutions of Yttrium-Lutetium Aluminum Garnets (Y1−cLuc)3Al5O12 (c = 0 – 1) has been studied. The measurements of dielectric loss (DL) tangent tgδ has been performed at electromagnetic wavelengths 1 – 0.6 mm and temperature T = 300 K. The results obtained has been compared with longitudinal acoustic waves (AW) attenuation data for frequencies f = 1 – 9.4 GHz, T = 4.2 – 300 K and with theory. The correlation between the DL and the AW attenuation is observed. The dependencies of DL (at T = 300 K) and AW attenuation (at T &gt; 77 K) on concentration c are qualitatively identical in the whole interval c = 0 – 1. From comparison with theory it follows that the observed DL is due to the two-phonon intrinsic lattice loss. It is caused by the lattice anharmonicity as well as the AW attenuation at not too low temperatures. Also the prediction for concentration dependence of DL at very low temperatures is discussed that follows from comparison with the results of “heat pulse” propagation experiments for the same samples at T = 2 K and theory.

Effect of manganese substitution on the physicochemical properties and catalytic toluene oxidation activities of Mg–Al layered double hydroxides

A series of Mg–Mn–Al ternary hydrotalcite-like layered double hydroxides (LDHs) with (Mg+Mn)/Al atomic ratios of ∼3 and Mg:Mn atomic ratios ranging from 3:0 to 0:3 were synthesized by a co-precipitation method. The incorporation of Mn in the MgAl-LDH was investigated by employing various techniques, such as powder X-ray diffraction, Fourier transform infrared spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, UV–visible diffuse-reflectance spectroscopy (UV–Vis DRS) and thermogravimetry. A single phase corresponding to LDH was obtained up to the composition Mg:Mn:Al=2.2:0.8:1. A further increase in the Mn content resulted in the formation of a mixture of LDH, Mn(OH) 2 and MnCO 3 phases. Partial oxidation of Mn 2+ to Mn 3+ took place during synthesis, as evidenced by UV–Vis DRS. According to the EPR and UV–Vis DRS results, the Mn 2+/Mn 3+ ions were present in a (distorted) octahedral environment. Calcination at 723 K resulted in the formation of a poorly crystalline MgO-like solid solution. Mn retained its +2 oxidation state (EPR active) even upon calcination at very high temperature (1473 K) in air. At a higher Mn content, in addition to the MgO-like phase, spinel phases such as Mn 3O 4 and MnAl 2O 4 were also obtained at 723 K. The catalytic activity of the as-synthesized samples was tested in the liquid-phase oxidation of toluene using tert-butyl hydroperoxide as the oxidant. Benzaldehyde and benzoic acid were the major products with minor amounts of benzyl alcohol. The compound without an LDH phase was found to be less active for the oxidation of toluene under similar reaction conditions. Solvents were found to have a profound influence on the catalytic activity and the product selectivity.

Phase formation and thermal stability of mechanical alloyed iron–tantalum

Iron-rich iron–tantalum solid solutions were prepared by mechanical alloying of elemental powder mixtures. At low Ta concentrations the alloys form a crystalline solid solution with bcc structure. At higher contents additionally an amorphous phase appears. The phase fractions and their compositions were determined by x-ray diffraction and Mössbauer spectroscopy. The thermal stability of the supersaturated solid solutions was investigated by differential scanning calorimetry measurements. Upon annealing, the solid solutions are found to establish a metastable equilibrium by precipitation of the amorphous phase before transformation to the equilibrium phases sets in. The results are discussed on the basis of the phase stabilities of the participating stable and metastable phases. It is concluded that the phase formation in this system during milling can be described by a smeared-out polymorphous transition to the amorphous phase with increasing solute content rather than by a metastable phase equilibrium. The possibility of grain boundary wetting with the amorphous phase is discussed.