Water uptake and energetics of the formation of barium zirconate based multicomponent oxides.

A group of multi-component oxides based on BaZrO3 have been prepared using a solid-state reaction method and examined in terms of their water uptake and thermodynamics of formation. Depending on the type and amount of acceptor substitution, the synthesized compounds exhibit various proton defect concentrations, reaching up to 0.2 mol/mol for a compound containing 10 different elements in the B-sublattice, where 50% of them are acceptors. For the most promising materials, van't Hoff plots were created and the enthalpies and entropies of hydration were calculated. At higher temperatures, these parameters do not differ from the values for the reference yttrium doped barium zirconate. However, at lower temperatures they are more negative, indicating a more exothermic process of proton incorporation.

Energetic Stability and Its Role in the Mechanism of Ionic Transport in NASICON-Type Solid-State Electrolyte Li1+xAlxTi2-x(PO4)3.

We apply high-temperature oxide melt solution calorimetry to assess the thermodynamic properties of the material Li1+xAlxTi2-x(PO4)3, which has been broadly recognized as one of the best Li-ion-conducting solid electrolytes of the NASICON family. The experimental results reveal large exothermic enthalpies of formation from binary oxides (ΔHf,ox°) and elements (ΔHf,el°) for all compositions in the range 0 ≤ x ≤ 0.5. This indicates substantial stability of Li1+xAlxTi2-x(PO4)3, driven by thermodynamics and not just kinetics, during long-term battery operation. The stability increases with increasing Al3+ content. Furthermore, the dependence of the formation enthalpy on the Al3+ content shows a change in behavior at x = 0.3, a composition near which the Li+ conductivity reaches the highest values. The strong correlation among thermodynamic stability, ionic transport, and clustering is a general phenomenon in ionic conductors that is independent of the crystal structure as well as the type of charge carrier. Therefore, the thermodynamic results can serve as guidelines for the selection of compositions with potentially the highest Li+ conductivity among different NASICON-type series with variable dopant contents.

Greigite (Fe3S4) is thermodynamically stable: Implications for its terrestrial and planetary occurrence.

Iron sulfide minerals are widespread on Earth and likely in planetary bodies in and beyond our solar system. Using measured enthalpies of formation for three magnetic iron sulfide phases: bulk and nanophase Fe3S4 spinel (greigite), and its high-pressure monoclinic phase, we show that greigite is a stable phase in the Fe-S phase diagram at ambient temperature. The thermodynamic stability and low surface energy of greigite supports the common occurrence of fine-grained Fe3S4 in many anoxic terrestrial settings. The high-pressure monoclinic phase, thermodynamically metastable below about 3 GPa, shows a calculated negative P-T slope for its formation from the spinel. The stability of these three phases suggests their potential existence on Mercury and their magnetism may contribute to its present magnetic field.

Conductivity, structure, and thermodynamics of Y2Ti2O7-Y3NbO7 solid solutions.

The defect fluorite yttrium niobate Y3NbO7 and pyrochlore yttrium titanate Y2Ti2O7 solid solutions have been synthesized via a solid state synthesis route. The resulting stoichiometry of the oxides is Y2+xTi2-2xNbxO7, where x = 0 to x = 1. All of the samples were single-phase; however, for those with a predominant fluorite phase, a small amount of additional pyrochlore phase was detected. The volume of the solid solution unit cells linearly increases with increase in yttrium niobate content. The water uptake increases with (x) and the protonic defect concentration reaches almost 4.5 × 10-3 mol mol-1 at 300 °C. The calculated enthalpy of formation from oxides suggests strong stability for all of the compositions, with the values of enthalpy ranging from -84.6 to -114.3 kJ mol-1. The total conductivity does not have a visible dependence on Y3NbO7 content. For each compound, the total conductivity is higher in wet air. Interestingly, for samples where x < 0.5, the ratio of conductivity in hydrogen to air increases with increasing temperature, while for x > 0.5, the trend is the opposite.

Disorder in Ho2Ti2-x Zr x O7: pyrochlore to defect fluorite solid solution series.

Pyrochlore (A2B2O7) is an important, isometric structure-type because of its large variety of compositions and structural derivatives that are generally related to different disordering mechanisms at various spatial scales. The disordering is key to understanding variations in properties, such as magnetic behavior or ionic conduction. Neutron and X-ray total scattering methods were used to investigate the degree of structural disorder in the Ho2Ti2-x Zr x O7 (x = 0.0-2.0, Δx = 0.25) solid solution series as a function of the Zr-content, x. Ordered pyrochlores (Fd3̄m) disorder to defect fluorite (Fm3̄m) via cation and anion disordering. Total scattering experiments with sensitivity to the cation and anion sublattices provide unique insight into the underlying atomic processes. Using simultaneous Rietveld refinement (long-range structure) and small-box refinement PDF analysis (short-range structure), we show that the series undergoes a rapid transformation from pyrochlore to defect fluorite at x ≈ 1.2, while the short-range structure exhibits a linear increase in a local weberite-type phase, C2221, over the entire composition range. Enthalpies of formation from the oxides determined using high temperature oxide melt solution calorimetry support the structural data and provide insight into the effect of local ordering on the energetics of disorder. The measured enthalpies of mixing are negative and are fit by a regular solution parameter of W = -31.8 ± 3.7 kJ mol-1. However, the extensive short-range ordering determined from the structural analysis strongly suggests that the entropies of mixing must be far less positive than implied by the random mixing of a regular solution. We propose a local disordering scheme involving the pyrochlore 48f to 8a site oxygen Frenkel defect that creates 7-coordinated Zr sites contained within local weberite-type coherent nanodomains. Thus, the solid solution is best described as a mixture of two phases, with the weberite-type nanodomains triggering the long-range structural transformation to defect fluorite after accumulation above a critical concentration (50% Ti replaced by Zr).

Towards a nanoparticle-based prophylactic for maternal autoantibody-related autism.

Recently, the causative agents of Maternal Autoantibody-Related (MAR) autism, pathological autoantibodies and their epitopic targets (e.g. lactate dehydrogenase B [LDH B] peptide), have been identified. Herein, we report on the development of Systems for Nanoparticle-based Autoantibody Reception and Entrapment (SNAREs), which we hypothesized could scavenge disease-propagating MAR autoantibodies from the maternal blood. To demonstrate this functionality, we synthesized 15 nm dextran iron oxide nanoparticles surface-modified with citric acid, methoxy PEG(10 kDa) amine, and LDH B peptide (33.8 µg peptide/cm2). In vitro, we demonstrated significantly lower macrophage uptake for SNAREs compared to control NPs. The hallmark result of this study was the efficacy of the SNAREs to remove 90% of LDH B autoantibody from patient-derived serum. Further, in vitro cytotoxicity testing and a maximal tolerated dose study in mice demonstrated the safety of the SNARE formulation. This work establishes the feasibility of SNAREs as the first-ever prophylactic against MAR autism.

Structure and Thermochemistry of Perrhenate Sodalite and Mixed Guest Perrhenate/Pertechnetate Sodalite.

Treatment and immobilization of technetium-99 (99Tc) contained in reprocessed nuclear waste and present in contaminated subsurface systems represents a major environmental challenge. One potential approach to managing this highly mobile and long-lived radionuclide is immobilization into micro- and meso-porous crystalline solids, specifically sodalite. We synthesized and characterized the structure of perrhenate sodalite, Na8[AlSiO4]6(ReO4)2, and the structure of a mixed guest perrhenate/pertechnetate sodalite, Na8[AlSiO4]6(ReO4)2-x(TcO4)x. Perrhenate was used as a chemical analogue for pertechnetate. Bulk analyses of each solid confirm a cubic sodalite-type structure (P4̅3n, No. 218 space group) with rhenium and technetium in the 7+ oxidation state. High-resolution nanometer scale characterization measurements provide first-of-a-kind evidence that the ReO4- anions are distributed in a periodic array in the sample, nanoscale clustering is not observed, and the ReO4- anion occupies the center of the sodalite ß-cage in Na8[AlSiO4]6(ReO4)2. We also demonstrate, for the first time, that the TcO4- anion can be incorporated into the sodalite structure. Lastly, thermochemistry measurements for the perrhenate sodalite were used to estimate the thermochemistry of pertechnetate sodalite based on a relationship between ionic potential and the enthalpy and Gibbs free energy of formation for previously measured oxyanion-bearing feldspathoid phases. The results collected in this study suggest that micro- and mesoporous crystalline solids maybe viable candidates for the treatment and immobilization of 99Tc present in reprocessed nuclear waste streams and contaminated subsurface environments.

Thermodynamics of Fe3O4-Co3O4 and Fe3O4-Mn3O4 spinel solid solutions at the bulk and nanoscale.

High temperature oxide melt solution calorimetry has been performed to investigate the enthalpies of mixing (ΔmixH) of bulk and nanophase (1 -x)Fe3O4-xM3O4 (M = Co, Mn) spinel solid solutions. The entropies of mixing (ΔmixS) were calculated from the configurational entropies based on cation distributions, and the Gibbs free energies of mixing (ΔmixG) were obtained. The ΔmixH and ΔmixG for the (1 -x)Fe3O4-xCo3O4 system are negative over the complete solid solution range, for both macroscopic and nanoparticulate materials. In (1 -x)Fe3O4-xMn3O4, the formation enthalpies of cubic Fe3O4 (magnetite) and tetragonal Mn3O4 (hausmannite) are negative for Mn3O4 mole fractions less than 0.67 and slightly positive for higher manganese content. Relative to cubic Fe3O4 and cubic Mn3O4 (stable at high temperature), the enthalpies and Gibbs energies of mixing are negative over the entire composition range. A combination of measured mixing enthalpies and reported Gibbs energies in the literature provides experimental entropies of mixing. The experimental entropies of mixing are consistent with those calculated from cation distributions for x > 0.3 but are smaller than those predicted for x < 0.3. This discrepancy may be related to the calculations, having treated Fe(2+) and Fe(3+) as distinguishable species. The measured surface energies of the (1 -x)Fe3O4-xM3O4 solid solutions are in the range of 0.6-0.9 J m(-2), similar to those of many other spinels. Because the surface energies are relatively constant, the thermodynamics of mixing at a given particle size throughout the solid solution can be considered independent of the particular particle size, thus confirming and extending the conclusions of a recent study on iron spinels.

Energetics of spinels in the Fe-Ti-O system at the nanoscale.

The energetics of nanosized Fe/Ti spinel oxides was studied using high-temperature oxide melt solution calorimetry. The mixing properties of the solid solution in the system were obtained, and through comparison to macroscopic materials the effect of particle size on the thermodynamics was assessed. The surface energies of the nanosized materials are similar within the errors regardless of the composition, and are consistent with those determined for other spinels. The enthalpies of oxidation to hematite plus rutile of the iron titanium spinels follow a linear trend with the Fe(2+) content, which allows them to be calculated for any composition or particle size. The heat of formation of the macroscopic and nanosized titanomagnetites was fit as a polynomial function and the numerical coefficients are presented. The enthalpies of mixing in the titanomagnetite and titanomaghemite solid solutions are similar at the macroscopic and nanoscale.

Nanophase transition metal oxides show large thermodynamically driven shifts in oxidation-reduction equilibria.

Knowing the thermodynamic stability of transition metal oxide nanoparticles is important for understanding and controlling their role in a variety of industrial and environmental systems. Using calorimetric data on surface energies for cobalt, iron, manganese, and nickel oxide systems, we show that surface energy strongly influences their redox equilibria and phase stability. Spinels (M(3)O(4)) commonly have lower surface energies than metals (M), rocksalt oxides (MO), and trivalent oxides (M(2)O(3)) of the same metal; thus, the contraction of the stability field of the divalent oxide and expansion of the spinel field appear to be general phenomena. Using tabulated thermodynamic data for bulk phases to calculate redox phase equilibria at the nanoscale can lead to errors of several orders of magnitude in oxygen fugacity and of 100 to 200 kelvin in temperature.