Solid Solution Behavior Research Articles

Mixing and non-stoichiometry in Fe–Ni–Cr–Zn–O spinel compounds: density functional theory calculations

Density functional theory (DFT) calculations have been performed on A(2+)B2(3+)O4(2-) (where A(2+) = Fe, Ni or Zn, and B(3+) = Fe or Cr) spinel oxides in order to determine some of their thermodynamic properties. Mixing energies were calculated for Fe3O4-NiFe2O4, Fe3O4-ZnFe2O4, Fe3O4-FeCr2O4, NiFe2O4-ZnFe2O4, NiFe2O4-NiCr2O4, FeCr2O4-NiCr2O4, FeCr2O4-ZnCr2O4 and ZnCr2O4-ZnFe2O4 pseudo-binaries based on special quasi random (SQS) structures to account for cationic disorder. The results generally agree with available experimental data and the rule that two normal or two inverse spinel compounds easily form solid solutions, while inverse-normal spinel mixtures exhibit positive deviation from solid solution behavior (i.e. immiscibility). Even though the NiFe2O4-NiCr2O4 and Fe3O4-FeCr2O4 systems obey this rule, they exhibit additional features with implications for the corresponding phase diagrams. In addition to mixing enthalpies, non-stoichiometry was also considered by calculating the energies of the relevant defect reactions resulting in A, B and O excess (or deficiency). The DFT calculations predict close to zero or slightly exothermic reactions for both A and B excess in a number of spinel compounds.

Structural characterization and catalytic evaluation of transition and rare earth metal doped ceria-based solid solutions for elemental mercury oxidation

The catalytic behavior of various CeO2-based solid solutions, namely, Ce1−xTMxO2−δ (TM = Mn, Fe, or Zr) and Ce1−xRExO2−δ (RE = Pr, La, or Sm) was studied for the removal of elemental mercury (Hg0) from coal-derived flue gas by catalytic oxidation (Hg0 → Hg2+). The investigated catalysts were synthesized by a coprecipitation method and characterized by various techniques, namely, X-ray diffraction (XRD), Raman spectroscopy (RS), high-resolution electron microscopy (HREM), Brunauer–Emmett–Teller (BET) surface area, X-ray photoelectron spectroscopy (XPS), temperature programmed reduction (TPR), and diffuse reflectance spectroscopy (UV-DRS). The XRD results confirmed the incorporation of Mn, Fe, Zr, La, Pr, and Sm cations into the CeO2 lattice and the formation of nanocrystalline solid solutions. The TEM measurements established the nanocrystalline nature of the solid solutions. The RS measurements suggested that the substitution process promotes the formation of oxygen vacancies, which hastens the diffusion rate of oxygen and improves the Hg oxidation. UV-vis DRS studies demonstrated the presence of the charge transfer transitions O2− → Ce3+ and O2− → Ce4+. The XPS and H2-TPR results suggested that the reduction of Ce4+ → Ce3+ is the foremost reason for the increase in oxygen vacancies, which are beneficial for Hg0 removal. The order of mercury oxidation activity over various doped catalysts is as follows: CM > CL > CZ > CF > CS > C > CP.

Combustion synthesized nanocrystalline Li3V2(PO4)3/C cathode for lithium-ion batteries

Nanocrystalline Li3V2(PO4)3/C composite synthesized using a novel corn assisted combustion method at 850°C exhibits superior physical and electrochemical properties than the one synthesized at 800°C. Despite the charge disproportionation of V4+ and a possible solid solution behavior of Li3V2(PO4)3 cathode upon insertion and extraction of Li+ ions, the structural stability of the same is appreciable, even with the extraction of third lithium at 4.6V. An appreciable specific capacity of 174mAhg−1 and better capacity retention upon high rate applications have been exhibited by Li3V2(PO4)3/C cathode, thus demonstrating the suitability of the same for lithium-ion battery applications.

Calculations of the thermodynamic and kinetic properties of Li1+xV3O8

The phase behavior and kinetic pathways of Li${}_{1+x}$V${}_{3}$O${}_{8}$ are investigated by means of density-functional theory (DFT) and a cluster expansion method that approximates the system Hamiltonian in order to identify the lowest-energy configurations. Although DFT calculations predict the correct ground state for a given composition, both generalized gradient approximation (GGA) and local-density approximation fail to obtain phase stability consistent with experiment due to strongly localized vanadium 3$d$ electrons. A DFT+$U$ method recovers the correct phase stability for an optimized $U$ value of 3.0 eV. GGA+$U$ calculations with this value of $U$ predict electronic structures that qualitatively agree with experiment. The resulting calculations indicate solid solution behavior from Li${}_{1}$V${}_{3}$O${}_{8}$ to Li${}_{2.5}$V${}_{3}$O${}_{8}$ and two-phase coexistence between Li${}_{2.5}$V${}_{3}$O${}_{8}$ and Li${}_{4}$V${}_{3}$O${}_{8}$. Analysis of the lithiation sequence from Li${}_{1}$V${}_{3}$O${}_{8}$ to Li${}_{2.5}$V${}_{3}$O${}_{8}$ reveals the mechanism by which lithium intercalation proceeds in this material. Calculations of lithium migration energies for different lithium concentrations and configurations provide insight into the relevant diffusion pathways and their relationship to structural properties.

Anion-Induced Solid Solution Electrochemical Behavior in Iron Tavorite Phosphates

A simple hydrothermal method was used to produce a new iron hydroxy-fluoro phosphate tavorite: LiFePO4(OH)0.6F0.4. Electrochemical discharge−charge of this 2.60 V material featured a sloping profile over the entire stoichiometry range, indicative of solid-solution behavior, a result of both anion disorder and high ionic conductivity in the lattice.

Differentiating natural organic matter roles in freshwater floc and bed sediment lead dynamics

Natural organic matter (NOM) is shown to be an important determinant of Pb dynamics across nine highly variable freshwater (wetland, stream, lake) ecosystems of Ontario, Canada. Soluble organic–Pb complexes emerged as the dominant Pb aqueous species (68–99%) in NOM-rich ecosystems; while distinct surficial sediment and suspended floc Pb sequestration and solid-solution partitioning patterns were observed across sites, driven by differential roles of living versus refractory NOM respectively within these two compartments. Field results suggest organo-Pb complexes dominate bed sediment Pb solid-solution partitioning, as sites with the highest pH values showed the greatest Pb mobilization, despite site-specific solid-phase Pb sequestration patterns. Contrasting bed sediment results, amorphous Fe oxyhydroxides (FeOOH) collected by floc microbes and extracellular polymeric substances, were the best predictor of floc Pb solid-solution partitioning, more consistent with cationic Pb behavior, as well as the key floc Pb sequestration phase (43–82%) across systems.Laboratory batch experiments assessed Pb solid-solution dynamics as a function of pH (5, 6, 6.5, 7 and 8) for surficial bed sediments (wetland, stream and lake) and limnetic floc (pH 5 and 8) varying in NOM concentrations. Results confirmed the occurrence of stable organo-Pb complexes in NOM-rich sediments, as mobilization of dissolved organic carbon (DOC) and Pb occurred with increasing pH, while Pb release decreased with increasing pH from NOM-poor sediment. The most organic rich, wetland surficial sediments showed the greatest mobilization rate of organo-Pb complexes, indicating dynamic DOC and Pb export is likely from such NOM-rich ecosystems under changing pH conditions. In contrast, experimental floc pH dependent Pb mobilization showed no correlation to DOC concentrations and was consistent with FeOOH-cationic Pb solid-solution behavior, rather than anionic organo-Pb complexes, as suggested in field observations. Results of this combined field and laboratory study demonstrate that establishing the nature of NOM and differential processes impacting NOM abundance/reactivity in each aquatic compartment across intrinsically connected aquatic ecosystems is fundamental to understanding Pb migration in freshwater catchments from upstream NOM-rich wetlands through to downstream NOM-poor littoral lake environments.

CoFe2O4 on a porous Al2O3 nanostructure for solar thermochemical CO2 splitting

Projected growth in global population and continued industrialization of developing countries will increase total world energy consumption by 50% between 2008 and 2035 (U.S. Energy Information Administration (EIA), International Energy Outlook, DOE/EIA-0484(2011) (Washington, DC, September 2011)). This demand for energy will be largely met by burning more fossil fuels, thereby increasing anthropogenic carbon in the atmosphere and further fuelling geopolitical conflicts over control of dwindling energy resources. Recycling CO2 by splitting it in a solar-based thermochemical process is an attractive solution to both of these 21st century problems. In this communication, we examine a novel chemistry for a two-step, non-volatile metal oxide CO2 splitting cycle that shuttles iron oxidation states (Fe2+/3+) between CoFe2O4 and FeAl2O4 spinel compounds within a nano-engineered material. This chemistry is dramatically different than current metal oxide cycles that exploit oxygen non-stoichiometry in ceria or solid solution behaviour in ferrites. The engineered material was prepared using atomic layer deposition and maintained structural integrity over 6 heating cycles under conditions that mimic a concentrated solar power application, namely an oxidation temperature of 1000 °C, reduction at 1460 °C, and a heating rate of 16 °C s−1 from low to high temperature. Oxygen uptake and release behaviour was similar to that of ceria. Raman spectroscopy was used to verify cycle chemistry.

First-Principles Calculations of Structural Properties of NaNbO3

We present ab-initio total energy calculations for different structures of NaNbO3 at different volumes using two different exchange-correlation functionals: the Perdew and Wang version of the local-density approximation (LDA) and the Wu and Cohen version of the generalized gradient approximation (GGA-WC). We found that LDA not only underestimates the equilibrium volume of the system but also predicts an incorrect ground state for this oxide. The GGA-WC functional, on the other hand, significantly improves the equilibrium volume and provides a relative phase stability in better agreement with experiments. We then use the GGA to investigate the presence of structural instabilities as a function of volume in order to provide insights for the understanding of the structural behavior of K1-xNaxNbO3 solid solutions.

Second-harmonic generating properties of polar noncentrosymmetric aluminoborate solid solutions, Al5−xGaxBO9 (0.0 ≤x≤ 0.5)

A series of solid solutions of polar aluminoborate materials, Al(5-x)Ga(x)BO(9) (0.0 ≤x≤ 0.5) have been synthesized by standard solid-state reactions using Al(2)O(3), Ga(2)O(5), and B(OH)(3) as reagents. The phase purities, crystal structures, and solid solution behavior of the reported materials have been investigated by powder X-ray diffraction. Solid solutions of Al(5-x)Ga(x)BO(9) crystallize in the polar noncentrosymmetric space group, Cmc2(1), with a three-dimensional structure consisting of distorted MO(4), MO(5), MO(6), and BO(3) polyhedra (M = Al or Ga). Powder second-harmonic generating (SHG) measurements on the Al(5)BO(9) using 1064 nm radiation, indicate the material has a SHG efficiency of approximately 2 times that of α-SiO(2) and is not phase-matchable (type 1). Further nonlinear optical (NLO) measurements on the Al(5-x)Ga(x)BO(9) solid solutions indicate a sharp increase in SHG efficiency up to 10 times that of α-SiO(2) for x≥ 0.4. Close structural examination suggests that the alignment of the asymmetric π-delocalization of BO(3) groups is responsible for the abrupt increase of SHG efficiency.

Spectroscopic and Structural Characterization of the CyNHC Adduct of B2pin2 in Solution and in the Solid State

The Lewis base adduct of B(2)pin(2) and the NHC (1,3-bis(cyclohexyl)imidazol-2-ylidene), which was proposed to act as a source of nucleophilic boryl groups in the β-borylation of α,β-unsaturated ketones, has been isolated, and its solid state structure and solution behavior was studied. In solution, the binding is weak, and NMR spectroscopy reveals a rapid exchange of the NHC between the two boron centers. DFT calculations reveal that the exchange involves dissociation and reassociation of NHC rather than an intramolecular process.

155Gd Mössbauer spectroscopic and powder X-ray diffraction study of CeO2–GdO1.5 solid solution

Powder X-ray diffractometry and 155Gd-Mössbauer spectroscopy have been applied to Ce1 − y Gd y O2 − y/2 (0 ≤ y ≤ 1.0) prepared at 1,450°C. The former shows that this system forms a complete solid solution being the disordered defect-fluorite type in the 0 ≤ y ≤ 0.3 range and the ordered C-type in the 0.3 <y ≤ 1.0 range. Its marked positive non-Vegardianity was consistently interpreted as a generalized Vegard-law behaviour of this distortion-dilated solid solution having Gd3 + —oxygen vacancy associative nature. The latter also clarifies that in the ordered C-type phase with decreasing y the 8b-site 155Gd-Mössbauer intensity steadily diminishes and vanishes at y ~ 0.50, indicating that the more distorted minor 8b Gd3 + in C-type GdO1.5 is being preferentially replaced with Ce4 + .

Adsorption of gases on binary and multicomponent semiconductors of the ZnSe-CdTe system

Adsorption of carbon monoxide(II) and oxygen on powders and nanofilms of solid solutions and binary compounds of the ZnSe-CdTe system was studied volumetrically, and by piezoquartz microweighing and IR spectroscopy of multiple disturbed complete internal reflections. The mechanisms and principles of adsorption were established in dependence on the conditions of the habitus of an experimental sample and the composition of the system’s semiconductors, based on an analysis of IR spectra; the thermodynamic and kinetic characteristics of adsorption; experimental dependences αp = f(T), αT = f(P), and αT = f(t); and the acid-base and other physicochemical characteristics of adsorbents and the electron nature of adsorbate molecules. Conclusions drawn earlier as to the retention of local active centers on the surface of a diamond-like semiconductor (which are responsible for adsorption and catalytic processes) upon a change in the habitus of a sample were confirmed. Certain features in the behavior of solid solutions (ZnSe)x(CdTe)1 − x were revealed alongside commonalities with binary compounds (ZnSe, CdTe), testifying to the presence of critical points on “adsorption characteristics-composition” diagrams. The most active adsorbents (with respect to CO and O2) were discovered on the basis of these diagrams, which were used in creating highly sensitive and selective sensors.

Neutron and X-ray Diffraction Study of Pyrophosphate-Based Li2–xMP2O7 (M = Fe, Co) for Lithium Rechargeable Battery Electrodes

Structural characterization of Li2–xMP2O7 (M = Fe, Co) was carried out using neutron diffraction (ND) and X-ray diffraction (XRD) analyses to elucidate structural information and structural changes during an electrochemical reaction. The crystal system and space group were determined to be monoclinic P21/c for both materials with a = 11.0192 (4) A, b = 9.7488 (3) A, c = 9.8057 (4) A, and β = 101.569 (3)° for Li2–xFeP2O7 and a = 10.9574 (3), b = 9.6921 (3), c = 9.7611 (3), and β = 101.776 (2)° for Li2–xCoP2O7. XRD analysis revealed partial occupancy of iron and cobalt in the structures of Li2–xFeP2O7 and Li2–xCoP2O7, respectively. Also, ND identified lithium positions and partial occupancies in five different Li sites of Li2–xMP2O7 (M = Fe, Co). Further ex situ XRD showed that the charging/discharging of Li2–xFeP2O7 occurred primarily via a two-phase reaction with a slight solid solution behavior. We also demonstrated for the first time that Li2–xCoP2O7 electrodes are electrochemically active, with a redox...

Melting behaviour, morphology and conductivity of solid solutions of PEO/PAc blends and LiClO4

The melting behaviours of poly(ethylene oxide)/polyacrylate (PEO/PAc) and PEO/PAc doped with LiClO4 were investigated by differential scanning calorimetry. The equilibrium melting temperature and the crystallinity of PEO show no significant variation with the addition of PAc but are suppressed by the incorporation of LiClO4. The deformed structure of PEO spherulite resulting from disrupted crystallisation is observed in salt doped PEO and its blends. Conductivity as a function of salt concentration is studied using the power law. Lower ion mobility and correlation of ions for PAc corroborate with its lower conductivity as compared to PEO. Despite a reasonable amount of LiClO4 being solvated by PAc, the conductivity of the solid solutions of PEO/PAc blends is primarily governed by PEO.

Topochemical Synthesis of Sodium Metal Phosphate Olivines for Sodium-Ion Batteries

New metastable olivine phases of sodium metal phosphates, Na[Mn1–xMx]PO4 (M = Fe, Ca, Mg), nanorods are synthesized by a simple solid-state reaction at low temperature (≤100 °C) by means of a topotactic molten salt reaction that converts NH4[Mn1–xMx]PO4•H2O (M = Fe, Ca, Mg) to Na[Mn1–xMx]PO4. Their crystal structures are characterized via XRD Rietveld refinement and electron diffraction. A full range of solid solution behavior was observed for olivine Na1–xMn0.5Fe0.5PO4, in contrast to that of LiMPO4 (M = Fe, Mn) olivine materials, and is ascribed to ion size effects. The solid solution behavior of NaMn0.5Fe0.5PO4 was confirmed by electrochemical characterization.

Continuum model of irradiation-induced spinodal decomposition in the presence of dislocations

A model of phase-separation kinetics in systems exposed to energetic particle irradiation has been extended to include the effects of mobile dislocations. It is shown that when dislocations are allowed to participate in the decomposition reaction, phase separation can occur at temperatures above the coherent spinodal, which is in agreement with several experiments on irradiated alloys. A linear stability analysis of the governing kinetic equations is performed and three regimes of microstructural evolution are identified within the parameter space of damage cascade size vs incident flux: complete phase separation, solid-solution behavior, and compositional patterning. In addition, numerical simulations of the evolving dislocation density and composition fields are performed. The numerical results provide the amplitude and wavelength of the stable patterns that can form under irradiation and elucidate the role of misfit dislocations in reducing the coherency strain due to atomic size mismatch.

Np-incorporation into uranyl phases: A quantum–mechanical evaluation

Density functional theory calculations are used to compare mechanisms of charge-balanced Np 5+-incorporation into boltwoodite [K(UO 2)(SiO 3OH)(H 2O) 1.5]. The charge-balancing mechanisms considered include: (i) H + addition (Np 5+ + H + ↔ U 6+), (ii) interlayer substitution (Np 5+ + Ca 2+/Mg 2+ ↔ U 6+ + K +), and (iii) intra-layer substitution (Np 5+ + P 5+ ↔ U 6+ + Si 4+). The choice of the source (of Np 5+, H +, Ca 2+, Mg 2+, P 5+) and sink (of substituted U 6+, K +, Si 4+) phases, the reference phases, for the cations involved in the incorporation reaction greatly affects the final calculated incorporation energy (Δ E rxn) . The incorporation energies using oxide (Δ E rxn = 183.5 kJ/mol) and silicate (Δ E rxn = 67.5 kJ/mol) reference phases are compared for the interlayer substitution mechanism. Since both the source of Np in environmental systems and the cations released are typically aqueous complexes, a newly-developed approach of combining cluster and periodic simulations was employed to model exchange with aqueous complexes. For the H + addition mechanism, incorporation from oxides reference phases (Δ E rxn = 93.6 kJ/mol) is less favorable than from aqueous (Δ E rxn = 12.5 kJ/mol) reference species. Estimates of the solid-solution behavior of Np 5+/P 5+- and U 6+/Si 4+-boltwoodite and Np 5+/Ca 2+- and U 6+/K +-boltwoodite solid solutions are used to predict the limit of Np-incorporation into boltwoodite. For the interlayer and intra-layer substitution mechanisms, the substitution energies are 67.5 and −2.9 kJ/mol, respectively, resulting in a maximum amount of incorporation at 300 °C of 172 ppm and 768 ppm, respectively.

Fabrication of LiVOPO4/carbon composite via glass-ceramic processing

Carbon coating of β-LiVOPO4 produced by glass-ceramic processing was carried out by the pyrolysis of glucose. Li2O-V2O2-P2O5 (LVP) glass-ceramics were produced by heat treatment at 400°C (sample α1), 600°C (sample β1) and 600+720°C (sample β2). Sample β1 was subsequently heat treated in the presence of glucose at 500 and 600°C in a N2 atmosphere to produce samples β2 and β3, respectively. From X-ray diffraction (XRD) and differential thermal analyses, it was found that sample β1 consisted mainly of β-LiVOPO4 crystals and did not contain any other crystalline phases. However, in samples β2 and β3, decomposition of LiVOPO4 took place due to the strongly reducing effect of residual carbon. For sample β3, XRD diffraction peaks associated with Li3V2(PO4)3 were found. From the charge-discharge measurements, the decomposed LVP glass-ceramics were also found to act as active materials. However, samples β2 and β3 exhibited Li3V2(PO4)3-like and solid-solution behaviour, respectively.

Mixed-ligand complexes of zinc(II), cobalt(II) and cadmium(II) with sulfur, nitrogen and oxygen ligands. Analysis of the solid state structure and solution behavior. Implications for metal ion substitution in alcohol dehydrogenase

In this paper we characterize new, mixed ligand complexes of zinc(II), cobalt(II) and cadmium(II) with tri- tert-butoxysilanethiolate and 2-(2′-hydroxyethyl)pyridine ligands. Due to the chelating versus non-chelating behavior of 2-(2′-hydroxyethyl)pyridine ligand we have obtained an interesting structural variety in the studied system. The presented coordination patterns together with the results of NMR studies have been used to illustrate a rapid chemical exchange undergoing in methanolic solutions of zinc(II) and cadmium(II) complexes. UV–Vis spectra of cobalt(II) species have also evidenced an exchange in the case of cobalt(II) complex. The relative strength of hydrogen bond formed by hydroxyl group bonded to Zn(II), Co(II) or Cd(II) was evaluated by analysis of structural parameters and position of the OH stretching vibrations in the FT-IR spectra of the complexes in solid state. The data were compared with the activity of zinc (native) alcohol dehydrogenase and alcohol dehydrogenase substituted with cobalt and cadmium ions. The enthalpies of proton abstraction in zinc and cobalt complexes were calculated and found to be very similar. The attempt to apply zinc tri- tert-butoxysilanethiolate as a catalyst in the biomimetic reaction of reduction of N-benzylnicotinamide chloride by ethanol was unsuccessful.

Surface properties, thermal expansion, and segregation in the U–Zr solid solution

Atomistic simulation results of the (γU, βZr) solid solution behavior are discussed, including the behavior of the lattice parameter and coefficient of thermal expansion as a function of concentration and temperature. Output from these calculations is used to study the surface structure of U–Zr for different crystallographic orientations, determining the respective concentration profiles, surface energy, and segregation behavior. The segregation of Zr to the surface and overall composition of the near-surface region is studied as a function of concentration and temperature.