Synthesis of Potassium Jarosite Solid Solutions: Characterization and Evaluation of Their Potential Electrical Properties.

The structural behavior of ceramic solid solutions (1\ensuremath{-}$x$)Na${}_{1/2}$Bi${}_{1/2}$TiO${}_{3}$--$x$K${}_{1/2}$Bi${}_{1/2}$TiO${}_{3}$ (NBT-KBT) was studied using high-resolution powder diffraction and transmission electron microscopy. A temperature-independent morphotropic phase boundary (MPB) separating NBT-like pseudorhombohedral (R) and KBT-like pseudotetragonal (T) phases was observed at $x$ \ensuremath{\approx} 0.2. For $x<0.2$, both local and average room-temperature structures are similar to those in NBT. Simultaneous long-range antiphase and short-range in-phase octahedral rotations average, resulting in effective antiphase ${a}^{\ensuremath{-}}{a}^{\ensuremath{-}}{c}^{\ensuremath{-}}$ tilting, which yields monoclinic symmetry when probed by x-ray diffraction (XRD). For these compositions, polar ordering is coupled to antiphase octahedral rotations so that tilting and ferroelectric (FE) domains coincide. Compositions with $x>0.2$ exhibit a tetragonal-like distortion; however, complex splitting of reflections in XRD patterns suggests that the actual symmetry is lower than tetragonal. For $0.2\ensuremath{\le}x\ensuremath{\le}0.5$, in-phase octahedral tilting ${a}^{0}{b}^{+}{a}^{0}$ (or ${a}^{+}{b}^{0}{b}^{0}$) is present but confined to the nanoscale, while for $x>0.5$ the structure becomes untilted. In-phase tilting evolves above the ferroelectric transition and occurs around a nonpolar ($a$ or $b$) axis of the average T structure. The onset of polar order has no significant effect on the coherence length of in-phase tilting, which suggests only weak coupling between the two phenomena. The average symmetry of the T phase is determined by the effective symmetry (Imm2) of assemblages of coherent in-phase tilted nanodomains. Near the MPB, the coexistence of extended R- and T-like regions is observed, but lattice distortions within each phase are small, yielding narrow peaks with a pseudocubic appearance in XRD. The temperature of the FE phase transition exhibits a minimum at the MPB. The structured diffuse scattering observed in electron diffraction patterns for all the compositions suggests that polar order in NBT-KBT solid solutions is modulated away from the average displacements refined using powder diffraction data.

Solid solution treatment on Cu-1.0Cr-0.1Zr alloy was performed at different temperatures and holding times to study the impact on solid solution behavior. At low temperatures, the results show that solid solutions do not form in the Cr-rich phase, but they start to form when temperatures rise above 900 °C. The dissolution rate first increases and then decreases, as temperatures approach higher values. At 950 °C, substantial solid solution forms, and as the holding time extends, the dissolution rate gradually decreases until the formation of solid solution completed. The pinning of dislocations by the Cr-rich phase leads to fine grain generation in the structure to further enhance the strength and lower the conductivity. Formation of solid solution completes when held at 950 °C for 120 min. The strength is 63.7 HB and conductivity is 34.5% IACS. Solid solution increases strength and resistivity by 43.91% and 63.59%, respectively.

Temperature dependence of the mechanical properties of equiatomic solid solution alloys with face-centered cubic crystal structures

Beitrag zur kenntnis des ausscheidungsverhaltens einiger magnesium-mischkristalle

The classification of equilibrium between ionic solid solutions and aqueous solutions by Roozeboom is interpreted as being a result of the ideal or regular behaviour of the ionic solid solutions. Due to the fact that the solubility products of isomorphous compounds which form ionic solid solutions differs in general by several orders of magnitude, it is very unlikely that precipitates differ much from the stoichiometry of one of these compounds. This principle is applied to the problem of biominerals, especially bone mineral. As a result it appears that the first mineral deposited in bone is octocalcium phosphate. Under in vivo conditions this phase is transformed into a mixture of three other calcium phosphates having a much lower solubility. The solubility controlling phase in living bone appears to be octocalcium phosphate which is continuously formed during the turn‐over of bone. This model for bone mineral has lead to the explanation of the formation of renal stones, pathological calcifications and osteoporosis as a consequence of slight chronic magnesium deficiency. The action of magnesium is mediated by the osteocytes.

It is shown that the distribution of ions over the solid phase and an aqueous solution can be interpreted in terms of Roozeboom's classification in the case of ideal ionic solid solutions and regular ionic solid solutions with and without ordering or substitutional disorder. A general relation is derived between the distribution coefficient D of the system and the solubility products of the components of the solid phase. In this way D can be determined experimentally in an independent way. It appears that in practice type II and type III systems are indistinguishable from type I systems, when the distribution coefficient D differs about one order of magnitude or more from unity even in the case of good recryatallization. In those cases distribution diagrams are not suitable to derive the nature of the series of solid solutions involved.

Calcium monoaluminate is the main phase in calcium aluminate cements and participates in the hydration, forming calcium aluminate hydrates. The amount of incorporation of foreign ions influences the hydration behaviour. Strontium aluminate is an important phase in producing phosphorescent materials when doped with rare-earth elements (REE) such as Eu, Dy, and La. These monoaluminates occur in different forms. Monocalcium aluminate forms a monoclinic and an orthorhombic modification, whereas monostrontium aluminate forms a monoclinic low-temperature and a hexagonal high-temperature form. Monoclinic calcium monoaluminate and monoclinic strontium aluminate form a partial solid-solution series. The hydration behaviour of different solid solutions was also investigated using calorimetry. The newly formed strontium aluminate hydrates could be identified while similar strontium aluminate hydrates are formed. Solid solutions of strontium- and calcium-aluminate hydrates will be investigated.

The data of Rau (1967) on the H 2 S/H 2 ratios of gas in equilibrium with high digenite solid solutions permit the calculation of the activity of Cu 2 S as a function of temperature and composition. The activity of Cu 2 S falls to 0.5 when the mole fraction (in the system Cu 2 S-S) drops only to 0.87. These calculations also permit the estimation of the activity of S 2 -temperature curve for the hexagonal chalcocite-high digenite reaction and a revised standard free energy for covellite.New data on the variation of the activity of S 2 in equilibrium with various metal/sulfur ratios for Cu = Fe in the intermediate solid solution permit the calculation of the activity of CuFeS 2 and show that it may drop as low as 0.2 at a mole fraction of 0.90 (system CuFeS 2 -Cu 2 Fe 2 S 2 ). The behavior of the copper-bearing solid solutions closely parallels that of pyrrhotite (Toulmin and Barton, 1964) in which the activity of FeS falls to 0.4 at a mole fraction of 0.9. A phase diagram is given for the CuFe-S join between 400 degrees and 700 degrees C.

* The analysis of metal distribution in Imperata cylindrica, a perennial grass isolated from the banks of Tinto River (Iberian Pyritic Belt), an extreme acidic environment with high content in metals, has shown a remarkable accumulation of iron. This property has been used to study iron speciation and its distribution among different tissues and structures of the plant. * Mossbauer (MS) and X-ray diffraction (XRD) were used to determine the iron species, scanning electron microscopy (SEM) to locate iron biominerals among plant tissue structures, and energy-dispersive X-ray microanalysis (EDAX), X-ray fluorescence (TXRF) and inductively coupled plasma emission spectroscopy (ICP-MS) to confirm their elemental composition. * The MS spectral analysis indicated that iron accumulated in this plant mainly as jarosite and ferritin. The presence of jarosite was confirmed by XRD and the distribution of both minerals in structures of different tissues was ascertained by SEM-EDAX analysis. * The convergent results obtained by complementary techniques suggest a complex iron management system in I. cylindrica, probably as a consequence of the environmental conditions of its habitat.

A citric acid ligand assisted self-assembly method is used for the synthesis of ternary mesoporous cerium lanthanum solid solution doped with metal elements (Co, Zr, Mg). Their textural property was characterized by X-ray diffraction, transmission electron microscopy, N2 adsorption-desorption, X-ray photoelectron spectroscopy and TPD techniques, and so on. The results of catalytic testing for synthesis of dimethyl carbonate (DMC) from CH3OH and CO2 indicated that the DMC yield reached 316 mmol/g on Ce-La-Co solid solution when the reaction temperature was 413 K and the reaction pressure was 8.0 MPa. It was found that Co had synergistic effect with La and Ce, doping of Co on the mesoporous Ce-La solid solution was helpful to increase the surface area of the catalyst, promote CO2 adsorption and activation, and improve the redox performance of solid solution catalyst. The conversion of Co2+ to Co3+ resulted in the continuous redox cycle between Ce4+ and Ce3+, and the oxygen vacancy content of the catalyst was increased. Studies have shown that the catalytic performance of Ce-La-Co solid solution is positively correlated with oxygen vacancy content. On this basis, the reaction mechanism of DMC synthesis from CO2 and CH3OH on the catalyst was speculated.

Structural characterization and crystal growth of the 2-amino-5-nitropyridinium dihydrogenphosphate/arsenate hybrid solid solution

Performance characteristics of lithium vanadium phosphate as a cathode material for lithium-ion batteries

To describe effectively the creep behavior of concentrated solid solutions in the diffusion-controlled power law regime in terms of dislocation climb and viscous glide mechanisms, values of key structural and physical properties are needed. The constitutive relations for these mechanisms reveal important contributions from elastic moduli and the appropriate diffusivities to the steady-state creep rate. Empirical modifications of these formulations further suggest the need for structural parameter values, such as the stacking fault energies, short range order coefficients, and atomic size differences, of the alloy systems of interest. The objective of this research is to characterize the Ni-Mo and Ni-W terminal solid solutions in terms of the above parameters and to define and interpret the calculated steady-state creep rates for both climb and viscous glide as a function of solute content. The calculated creep rates for the Ni-W system are lower than those for the Ni-Mo system for both mechanisms due to the higher moduli and atomic size factor, and lower diffusivities of the former. The short range order contribution to the viscous glide parameters of the Ni-Mo system is the largest observed in such analyses to date (up to 12 pct). Reasons for the marked slope differences between the Ni-Mo climb and glide solute dependencies are presented.

The low-temperature magnetic properties and Néel temperature, TN, behavior of four silicate substitutional solid solutions containing paramagnetic ions are analyzed. The four systems are: fayaliteforsterite olivine [Fe22+SiO4-Mg2SiO4], and the garnet series, grossular-andradite [Ca3(Alx,Fe1−x3+)2Si3O12], grossular-spessartine [(Cax,Mn1−x2+)3Al2Si3O12], and almandine-spessartine [(Fex2+,Mn1−x2+)3Al2Si3O12]. Local magnetic behavior of the transition-metal-bearing end-members is taken from published neutron diffraction results and computational studies. TN values are from calorimetric heat capacity, CP, and magnetic susceptibility measurements. These end-members, along with more transition-metal-rich solid solutions, show a paramagnetic to antiferromagnetic phase transition. It is marked by a CP λ-anomaly that decreases in temperature and magnitude with increasing substitution of the diamagnetic component. For olivines, TN varies between 65 and 18 K and TN for the various garnets is less than 12 K. Local magnetic behavior can involve one or more superexchange interactions mediated through oxygen atoms. TN behavior shows a quasi-plateau-like effect for the systems fayalite-forsterite, grossular-andradite, and grossular-spessartine. More transition-metal-rich crystals show a stronger TN dependence compared to transition-metal-poor ones. The latter may possibly show superparamagnetic behavior. (Fex2+,Mn1−x2+)3Al2Si3O12 garnets show fundamentally different magnetic behavior. End-member almandine and spessartine have different and complex interacting local superexchange mechanisms and intermediate compositions show a double-exchange magnetic mechanism. For the latter, TN values show negative deviations from linear interpolated TN values between the end-members. Double exchange seldom occurs in oxides, and this may be the first documentation of this magnetic mechanism in a silicate. TN behavior may possibly be used to better understand the nature of macroscopic thermodynamic functions, CP and S°, of both end-member and substitutional solid-solution phases.

Considerable experimental and theoretical work concerning crystallisation in gels can be found in the scientific literature. After the pioneer book by Henish [1], crystal growth in gels has shown to be a simple and suitable method for making single crystals of sparingly soluble salts, small-molecule compounds, and macromolecules, e.g.: [2,3]. The gel medium suppresses convection and advection only allowing diffusion of the aqueous species, which eventually can react to form solids. From experimental data it is abundantly clear that gels reduce the nucleation chance and, in that sense, offer certain research opportunities that crystallization from ’’free’’ aqueous solutions cannot provide. So, in the context of purposeful crystal growth, the suppression of nucleation is the principal function of the gel because a lower nucleation density favours the development of larger crystals. However, a more fundamental interest of gels arises from their possibilities to explore crystallisation behaviour in a variety of environments, including microgravity, and to simulate a diversity of unusual crystallization phenomena, e.g.: [4-10]. Here, we present a brief review of previous work carried out with this kind of systems, which includes a miscellany of topics, such as 1) nucleation behaviour of stoichiometric compounds and solid solutions in porous media, 2) reaction paths and generation of patterns during the growth process, 3) metastable crystallization and subsequent solvent-mediated phase transformations, 4) simulation of biomineralization processes and generation of biomimetic crystalline aggregates, 5) sorption of pollutants by surface precipitation of pollutantbearing phases on minerals embedded in gel media, and 6) simulation of mineral replacement and other mineral-fluid interaction phenomena.