Extensive Solid Solution Research Articles

Investigation of the KNd(SO4)2·H2O–SrSO4·0.5H2O System

The cocrystallization of potassium, neodymium, and strontium sulfates from aqueous solutions has been studied using X-ray powder diffraction, thermogravimetry, energy-dispersive X-ray spectral analysis, and electron microscopy. Extensive solid solutions based on trigonal KNd(SO4)2⋅H2O have been found to exist in the concentration range 100–20 mol % of the KNd(SO4)2⋅H2O–SrSO4⋅0.5H2O system. The unit cell parameters of the solid solutions have been determined. Two phases have been discovered: trigonal KNd(SO4)2⋅H2O (space group P3121) and monoclinic KNd(SO4)2⋅H2O (space group P21/c1). The heterovalent substitution scheme 2Sr2+ → K+ + Nd3+ stabilizes the structure of solid solutions based on the isostructural KNd(SO4)2⋅H2O and SrSO4⋅0.5H2O trigonal phases.

The Tb‒Hf‒Al‒Si system (600 C)

Information about systematic investigations of quaternary intermetallic systems with rare-earth elements is scarce, therefore studies of such systems are relevant. Alloys of the Tb‒Hf‒Al‒Si system are promising for the creation of new functional materials thanks to their mechanical (due to the presence of Al in the samples), heat-resistant (Hf), semiconductor (Si), magnetic, superconducting, catalytic, and sorption (Tb) properties. The aim of this work was to investigate the Tb‒Hf‒Al‒Si system: establish the phase composition of alloys, search for new phases and determine their crystal structures. Samples of the Tb‒Hf‒Al‒Si system were prepared by arc-melting the elements under a purified argon atmosphere. The alloys were annealed at 600 °C for 7 months in evacuated quartz ampoules, and subsequently quenched in cold water. X-ray powder diffraction data were recorded on a DRON 2.0M diffractometer, Fe K α radiation, a Panalytical X’Pert, Cu K α radiation, and a STOE Stadi P diffractometer, Cu K α 1 radiation. Energy-dispersive X-ray analyses were performed on a Tescan Vega 3 LMU scanning electron microscope. During the investigation of the Tb‒Hf‒Al‒Si system the formation of the quaternary phase (Tb 0.74 Hf 0.26 )(Al 0.48 Si 0.52 ) was established based on X-ray diffraction and energy-dispersive X-ray analysis. The crystal structure of this phase belongs to the TlI type (Pearson symbol oS 8, space group Cmcm , unit cell parameters: а = 4.312(1), b = 10.793(3), c = 3.973(1) Å) with a statistical mixture of Tb and Hf atoms on the I site and a statistical mixture of Al and Si atoms on the Tl site. Based on the results obtained here, the existence in the quaternary system Tb‒Hf‒Al‒Si of extended solid solutions based on other binary, Hf 5 Si 3 (structure type Mn 5 Si 3 , Pearson symbol hP 16, space group P 6 3 / mcm , 10 at. % Tb and 7 at. % Al – (Tb 0.1 6 Hf 0.8 4 ) 5 (Al 0.1 9 Si 0.8 1 ) 3 ), TbAl 2 (MgCu 2 , cF 24, Fd -3 m , 7 at. % Si – (Tb 0 . 94 Hf 0 . 06 )(Al 0 . 90 Si 0 . 10 ) 2 ), TbAl (DyAl, oP 16, Pbcm , 8 at. % Hf and 5 at. % Si – (Tb 0 . 85 Hf 0 . 15 )(Al 0 . 89 Si 0 . 11 )), HfSi (FeB, oP 8, Pnma , 9 at. % Tb and 7 at.% Al – (Tb 0 . 17 Hf 0 . 83 )(Al 0 . 15 Si 0 . 85 )), and ternary, Tb 2 Hf 3 Si 4 (Sc 2 Re 3 Si 4 , tP 36, P 4 1 2 1 2, 18 at. % Al – (Tb 2 . 4 Hf 2 . 6 (Al 0 . 42 Si 0 . 58 ) 4 ), compounds was established. Within the homogeneity ranges of the solid solutions, the value of the valence electron concentration does practically not change. Keywords : Tb‒Hf‒Al‒Si system, X-ray diffraction, energy-dispersive X-ray analysis, solid solution, TlI structure type.

High seebeck coefficient and low thermal conductivity in Bi and In co-doped GeTe thermoelectric material

Pure GeTe shows inferior thermoelectric performance due to the large carrier concentration caused by the intrinsic high concentration of Ge vacancies. In this study, we report improved thermoelectric performance of Bi and In co-doped GeTe based thermoelectric material where a figure of merit, ZT ∼ 1.7 at 623 K was realized through synergetic effect of tuning the carrier concentration, resonant states, and suppression of thermal conduction. In doping induces resonant states in the density of states near the Fermi energy level. Bi sharply reduces lattice thermal conductivity by formation of extensive solid solution point defects. Moreover, Bi and In co-doping decreases the phase transformation temperature to widen the better thermoelectric performance of cubic GeTe at low temperatures. In addition, microstructural characterization showed herringbone structures, high-density of domain boundaries, and twinning. These, together with the point defects, lead to a significantly reduced thermal conductivity.

Atypical Mineralization Involving Pd-Pt, Au-Ag, REE, Y, Zr, Th, U, and Cl-F in the Oktyabrsky Deposit, Norilsk Complex, Russia

Highly atypical mineralization involving Pd-Pt, Au-Ag, REE, Y, Zr, U, Th, and Cl-F-enriched minerals is found in zones with base metal sulfides (BMS; ~5 vol.% to 20 vol.%) in the eastern portion of the Oktyabrsky deposit in the Norilsk complex (Russia). The overall variations in Mg# index, 100 Mg/(Mg + Fe2+ + Mn), in host-rock minerals are 79.8 → 74.1 in olivine, 77.7 → 65.3 in orthopyroxene, 79.9 → 9.2 in clinopyroxene, and An79.0 → An3.7. The span of clinopyroxene and plagioclase compositions reflects their protracted crystallization from early magmatic to late interstitial associations. The magnesian chromite (Mg# 43.9) trends towards Cr-bearing magnetite with progressive buildups in oxygen fugacity; ilmenite varies from early Mg-rich to late Mn-rich variants. The main BMS are chalcopyrite, pyrrhotite, troilite, and Co-bearing pentlandite, with less abundant cubanite (or isocubanite), rare bornite, Co-bearing pyrite, Cd-bearing sphalerite (or wurtzite), altaite, members of the galena-clausthalite series and nickeline. A full series of Au-Ag alloy compositions is found with minor hessite, acanthite and argentopentlandite. The uncommon assemblage includes monazite-(Ce), thorite-coffinite, thorianite, uraninite, zirconolite, baddeleyite, zircon, bastnäsite-(La), and an unnamed metamict Y-dominant zirconolite-related mineral. About 20 species of PGM (platinum group minerals) were analyzed, including Pd-Pt tellurides, bismuthotellurides, bismuthides and stannides, Pd antimonides and plumbides, a Pd-Ag telluride, a Pt arsenide, a Pd-Ni arsenide, and unnamed Pd stannide-arsenide, Pd germanide-arsenide and Pt-Cu arseno-oxysulfide. The atypical assemblages are associated with Cl-rich annite with up to 7.54 wt.% Cl, Cl-rich hastingsite with up 4.06 wt.% Cl, ferro-hornblende (2.53 wt.% Cl), chlorapatite (>6 wt.% Cl) and extensive solid solutions of chlorapatite, fluorapatite and hydroxylapatite, Cl-bearing members of the chlorite group (chamosite; up to 0.96 wt.% Cl), and a Cl-bearing serpentine (up to 0.79 wt.% Cl). A decoupling of Cl and F in the geochemically evolved system is evident. The complex assemblages formed late from Cl-enriched fluids under subsolidus conditions of crystallization following extensive magmatic differentiation in the ore-bearing sequences.

Raman Spectroscopy Coupled with Reflectance Spectroscopy as a Tool for the Characterization of Key Hydrothermal Alteration Minerals in Epithermal Au-Ag Systems: Utility and Implications for Mineral Exploration.

Raman spectroscopy of fine-grained hydrothermal alteration minerals, and phyllosilicates in particular, presents certain challenges. However, given the increasingly widespread recognition of field portable visible–near infrared–shortwave infrared (Vis-NIR-SWIR) spectroscopy as a valuable tool in the mineral exploration industry, Raman microspectroscopy has promise as an approach for developing detailed complementary information on hydrothermal alteration phases in ore-forming systems. Here we present exemplar high-quality Raman and Vis-NIR-SWIR spectra of four key hydrothermal alteration minerals (pyrophyllite, white mica, chlorite, and alunite) that are common in precious metal epithermal systems, from deposits on the island of Newfoundland, Canada. The results reported here demonstrate that Raman microspectroscopy can accurately characterize pyrophyllite, white mica, chlorite, and alunite and provide details on their compositional variation at the microscale. In particular, spectral differences in the 1000–1150 cm−1 white mica Raman band allows the distinction between low-Tschermak phases (muscovite, paragonite) and phases with higher degrees of Tschermak substitution (phengitic white mica composition). The peak position of the main chlorite Raman band shifts between 683 cm−1 for Mg-rich chlorite and 665 cm−1 for Fe-rich chlorite and can be therefore used for semiquantitative estimation of the Fe2+ content in chlorite. Furthermore, while Vis-NIR-SWIR macrospectroscopy allows the rapid identification of the overall composition of the most abundant hydrothermal alteration mineral in a given sample, Raman microspectroscopy provides an in-depth spectral and chemical characterization of individual mineral grains, preserving the spatial and paragenetic context of each mineral and allowing for the distinction of chemical variation between (and within) different mineral grains. This is particularly useful in the case of alunite, white mica, and chlorite, minerals with extensive solid solution, where microscale characterization can provide information on the alteration zonation useful for mineral exploration and provide insight into mineral deposit genesis.

Chromitites from the Vavdos ophiolite (Chalkidiki, Greece): Petrogenesis and geotectonic settings; constrains from spinel, olivine composition, PGE mineralogy and geochemistry

Podiform chromitites of the Vavdos ophiolite are associated with dunite bodies hosted within residual mantle harzburgite. The mantle source is highly depleted and apparently developed at fore-arc settings as inferred from the presence of boninitic melts. The ascendance of these melts through dunite pathways and their subsequent interaction with the depleted harzburgite instigated chromitite mineralization within dunite. Spinel occurs in a) massive accumulations (Mg# = 0.56–0.68 and Cr# = 0.69–0.77), b) in non-massive disseminated textures (Mg# = 0.52–0.61 and Cr# = 0.80–0.81) and c) in schlieren chromitite deposits within dunite bodies (Mg# = 0.43–0.48 and Cr# = 0.79–0.82). Olivine is the main silicate inclusion in chromitites, whereas the absence of hydrous mineral phases is linked with crystallization at relatively deeper parts of the mantle.Olivine inclusions in spinel are enriched in Fo, Ni and Ca compared to the interstitial olivine grains. No compositional gaps were noted between the mineral analyses of chromitites and dunites; the calculated parental melts are also homogeneous, reinforcing the view for production of melt batches by similar processes. Platinum-group elements (PGE) concentrations and platinum-group minerals (PGM) demonstrate high (Os + Ir + Ru)/ (Rh + Pt + Pd) ratios, typical of many Tethyan ophiolitic chromitites. The main PGM phase is laurite that forms an extended solid solution series with substitution of Ru for Os + Ir, linked to the cooling of the system. Massive chromitites contain Ru-rich laurite and Os-Ir alloys whereas non-massive ores contain Ru-poor laurite. The PGM were included in fresh magnesiochromite favoring their magmatic origin and initial entrapment at ~ 1200 °C and low sulfur fugacity.

High non-linear electrical properties of Li3xCo7–4xSb2+xO12 a new ceramic varistor

In this work, a new varistor with a high non-linear J-E electrical characteristic (α = 54; EB = 9753 V/cm) is reported, synthesized from the binary system Co7Sb2O12-LiCoSbO4 with general formula Li3xCo7–4xSb2+xO12. This new material is a single-phase iso-structural to Co7Sb2O12 spinel. It was shown that the electrical properties improved with increasing the x value in the solid solution. Li3xCo7–4xSb2+xO12 varistor behaviour is explained by the presence of defects in the crystal structure of Co7Sb2O12 when Li+ and Sb5+ are added, which appears to be responsible for the formation of Schottky type potential barriers at the grain boundaries. Also, it is reported the effect of the sintering temperature on the electrical properties of the varistors. In addition, sub-solidus compatibility relations on the ternary system of Li2O-CoO-Sb2O5, up to>50% Li2O, and the binary phase diagram Co7Sb2O12-LiCoSbO4 have been determined, where an extensive solid solution Li3xCo7–4xSb2+xO12: 0.2 ≤ x ≤ 0.7, was formed. The lattice parameter of Li3xCo7–4xSb2+xO12 solid solution exhibit a discontinuity indicating a change in the substitution mechanism or symmetry of the solid solution. XPS analysis showed how Co2p spectra change as Li+ substitutes Co2+ into the structure and how this affects the linearity of the lattice parameter a.

Superstructure formation in the solid solution Sc3Pt3−xIn3 (x = 0–0.93)

Abstract The equiatomic indide ScPtIn (ZrNiAl type, space group P 6 ‾ $‾{6}$ 2m) shows an extended solid solution Sc3Pt3–xIn3. Several samples of the Sc3Pt3–xIn3 series were synthesized from the elements by arc-melting and subsequent annealing, or directly in a high frequency furnace. The lowest platinum content was observed for Sc3Pt2.072(3)In3. All samples were characterized by powder X-ray diffraction and their lattice parameters and several single crystals were studied on the basis of precise single crystal X-ray diffractometer data. The correct platinum occupancy parameters were refined from the diffraction data. Decreasing platinum content leads to decreasing a and c lattice parameters. Satellite reflections were observed for the Sc3Pt3–xIn3 crystals with x = 0.31–0.83. These satellite reflections could be described with a modulation vector ( 1 3 , 1 3 , γ ) $\left(\frac{1}{3},\frac{1}{3},\gamma \right)$ ( γ = 1 2 $\gamma =\frac{1}{2}$ c* for all crystals) and are compatible with trigonal symmetry. The interplay of platinum filled vs. empty In6 trigonal prisms is discussed for an approximant structure with space group P3m1.

Uptake of iodide by calcium aluminate phases (AFm phases)

Iodine-129 is an important dose-determining radionuclide emanating from low and intermediate level radioactive waste (L/ILW) repositories. A good candidate for the immobilization of the hazardous I− anions are AFm phases due to their interlayer anion exchange capacity. The ability of AFm phases to bind iodine was investigated in a set of co-precipitation experiments, in which the formation of solid solutions between the iodine AFm end member monoiodide (I-AFm) and the common AFm phases hemicarbonate (OH,CO3-AFm), monocarbonate (CO3-AFm) and hydroxy-AFm (OH-AFm), was examined. The samples were characterized by TGA, FTIR, XRPD and liquid phase analyses, and the obtained data were used to construct solid solution models with the help of the thermodynamic modelling program GEMS. The formation of extensive solid solutions was found between the AFm end member pairs monoiodide and hydroxy-AFm, and monoiodide and hemicarbonate. In these two cases, the progressive substitution of the interlayer anion is reflected by a gradual change of the interlayer distance, visible by a continuous peak shift of the basal reflexion from one end member towards the other. No solid solution forms between the end members monoiodide and monocarbonate. In the presence of small amounts of carbonate, a mixed (I,OH,CO3)-AFm phase precipitates, similar to the one found in the monoiodide-hemicarbonate set of experiments, indicated by the similarity in the observed d-values. With increasing carbonate concentration, monocarbonate is stabilized. The experimental data suggests that iodine can be incorporated in the AFm interlayer where anion exchange leads to the formation of solid solutions. The solid solution formation is favoured only between end members with similar crystal symmetry. The presence of carbonate favours the formation of monocarbonate in the long term, reducing the capability of AFm phases to immobilize iodide.

Coupled Experimental Study and Thermodynamic Modeling of the MgO-MnO-Mn2O3-Ti2O3-TiO2 System

A coupled phase diagram experiment and thermodynamic modeling of the MgO-MnO-Mn2O3-Ti2O3-TiO2 system at 1 bar total pressure is presented. High temperature equilibration and quenching experiments followed by the phase analysis using electron probe microanalysis and X-ray diffraction were performed to obtain complex phase equilibria between solid solutions and liquid phase in air. Low temperature phases during quenching was inevitable in some samples which lead to inaccuracy in the experimental data. The molten oxide phase was described by using the Modified Quasichemical Model, which considers short-range ordering in liquid state, and the Gibbs energies of the extensive solid solutions (pseudobrookite, ilmenite and spinel) were described using the Compound Energy Formalism based on their crystal structures. A set of optimized model parameters of all phases was obtained, which reproduces all the reliable experimental data within experimental error limits from 25 °C to above the liquidus temperatures over the entire range of composition at air atmosphere. The model can also predict the phase equilibria in the range of oxygen partial pressures from metallic saturation to air. The complex phase relationships in the system have been elucidated for the first time and the database of the model parameters can be used with FactSage software to calculate any phase diagrams and thermodynamic properties of the MgO-MnO-Mn2O3-Ti2O3-TiO2 system.

Asbestiform Minerals of the Franciscan Assemblage in California with a Focus on the Calaveras Dam Replacement Project

ABSTRACT The San Francisco Bay Area is underlain by bedrock of the Franciscan Assemblage, which outcrops in numerous places. A significant portion of these outcrops consists of rock types that contain both regulated and unregulated asbestiform minerals, including ultra-mafic serpentinites, various greenstones, amphibolites, blueschist, and other schists (talc-tremolite, actinolite, etc.). These rocks are a legacy of tectonic activity that occurred on the west coast margin of the North American plate ∼65–150 MY ago during subduction of the East Pacific and Farallon plates. The Calaveras Dam Replacement Project (CDRP), located in Fremont, California, is an example of an area within the Franciscan Assemblage that is substantially underlain by metamorphosed oceanic sedimentary, mafic, and ultra-mafic rocks in a tectonic subduction zone mélange with highly disrupted relationships between adjoining rock bodies with different pressure/temperature metamorphic histories. In order to protect the health of workers and residents in the surrounding area, an extensive effort was taken to identify, categorize, and monitor the types, locations, and concentrations of naturally occurring asbestos at the site. Using a combination of geologic field observations and transmission electron microscopy, energy dispersive X-ray, and selected area electron diffraction analysis of airborne particulate and rock/soil samples, the CDRP was discovered to contain chrysotile-bearing serpentine. It also had as a range of amphibole-containing rocks, including blueschist, amphibolite schist, and eclogite, with at least 19 different regulated and non-regulated fibrous amphibole minerals identified. The extensive solid solution behavior of the amphiboles makes definitive identification difficult, though a scheme was created that allowed asbestos mineral fingerprinting of various areas of the project site.

Pickeringite from the Stone Town Nature Reserve in Ciężkowice (the Outer Carpathians, Poland)

Pickeringite, ideally MgAl2(SO4)4·22H2O, is a member of the halotrichite group minerals XAl2(SO4)4·22H2O that form extensive solid solutions along the joints of the X = Fe-Mg-Mn-Zn. The few comprehensive reports on natural halotrichites indicate their genesis to be mainly the low-pH oxidation of pyrite or other sulfides in the Al-rich environments of weathering rock-forming aluminosilicates. Pickeringite discussed here occurs within the efflorescences on sandstones from the Stone Town Nature Reserve in Ciężkowice (the Polish Outer Carpathians), being most probably the first find on such rocks in Poland. This paper presents mineralogical and geochemical characteristics of the pickeringite (based on SEM-EDS, XRPD, EPMA and RS methods) and suggests its possible origin. It belongs to the pickeringite–apjohnite (Mg-Mn joints) series and has the calculated formula Mg0.75Mn0.21Zn0.02Cu0.01Al2.02(S0.99 to 1.00O4)4·22H2O (based on 16O and 22H2O). The unit cell parameters refined for the monoclinic system space group P21/c are: a = 6.1981(28) Å, b= 24.2963(117) Å, c = 21.2517(184) Å and β = 100.304(65)°. The Raman spectra (SO4) bands are the intensive 994 cm−1 and a low-intensive 975 cm−1 (ν1), low-intensive 1081, 1123 and 1145 cm−1 (ν3), 524, 467 and 425cm−1 (ν2), 615 cm−1 (ν4), while those at 344 and 310 cm−1 are attributed to νg H2O and at 223 cm−1 to the lattice modes. Crystallization of pickeringite within the particular tor resulted from a certain set of conditions: climatic (e.g., season, temperature, humidity), physicochemical (e.g., pH, concentration), mineral (the presence of pyrite), and site-related (location and efflorescence protection). The sulfate ions could have been derived from oxidation of pyrite in the Ciężkowice sandstones and possibly are related to local mineral waters.

Doping mechanisms and dielectric properties of Ca-doped bismuth magnesium niobate pyrochlores

Here we report the doping mechanisms and dielectric properties of Ca-doped bismuth magnesium niobate (BMCN) pyrochlores synthesised using solid-state reaction at 1025 °C over 24–48 h. The extensive solid solution of (Bi3.36Mg0.64-xCax)(Mg1.28Nb2.72)O13.76 (0 ≤ x ≤ 0.7) pyrochlores formed with a fully indexed cubic structure, space group Fd3m and lattice constants, a = b = c in the range 10.5621 (17)−10.5332 (14) Å. The SEM analysis confirmed that the surface morphologies of BMCN pyrochlores were of irregular polyhedral grains and their crystallite sizes, as calculated by Scherrer and Williamson-Hall methods, were found to be in the range 46–70 nm and 38–75 nm, respectively. These thermally stable BMCN pyrochlores were highly insulating materials that showed a reproducible dielectric behaviour over heat-cool cycles and their activation energies were estimated to be in the range 1.17–1.47 eV. High bulk dielectric constants, ε’, 69–171 and low dielectric losses, tan δ, in the order of ~10−3 were recorded at 30 °C and 1 MHz; negative temperature coefficient of capacitance (TCC) in the range, (−319)−(-933) ppm/°C was measured over ~30–300 °C at 1 MHz.

REE-, Sr-, Ca-aluminum-phosphate-sulfate minerals of the alunite supergroup and their role as hosts for radionuclides

AbstractAluminum-phosphate-sulfate (APS) minerals of the alunite supergroup are minor components of uranium-bearing copper ores from the Olympic Dam deposit, South Australia. They typically represent a family of paragenetically late replacement phases after pre-existing REE-bearing phosphates (fluorapatite, monazite, and xenotime). Characterization with respect to textures and composition allows two groups to be distinguished: Ca-Sr-dominant APS minerals that fall within the woodhouseite and svanbergite compositional fields; and a second REE- and phosphate-dominant group closer to florencite in composition. All phases nevertheless display extensive solid solution among end-members in the broader APS clan and show extensive compositional zoning at the grain-scale. Samples representative of the deposit (flotation concentrate and tailings), as well as those that have been chemically altered during the processing cycle (acid leached concentrate), were studied for comparison. NanoSIMS isotope mapping provides evidence that the APS minerals preferentially scavenge and incorporate daughter radionuclides of the 238U decay chain, notably 226Ra and 210Pb, both over geological time within the deposit and during ore processing. These data highlight the role played by minor phases as hosts for geologically mobile deleterious components in ores as well as during mineral processing. Moreover, Sr-Ca-dominant APS minerals exhibit preferential sorption of Pb from fluid sources, in the form of both common Pb and 210Pb, for the first time revealing potential pathways for 210Pb elimination and reduction from ore processing streams.

Realization of High Thermoelectric Figure of Merit in GeTe by Complementary Co-doping of Bi and In

Summary GeTe and its derivatives have recently attracted wide attention as promising thermoelectric materials. The principle challenge in optimizing the thermoelectric figure of merit, zT, is the low Seebeck coefficient (S) and high thermal conductivity of GeTe. Here, we report a high zT of ∼2.1 at 723 K in In and Bi co-doped GeTe along with an extremely high TE conversion efficiency of ∼12.3% in a single-leg thermoelectric generator for the temperature difference of 445 K. In and Bi play a distinct but complementary role. In doping significantly enhances the S through the formation of resonance level, which is confirmed with first-principles density functional theory calculations and Pisarenko plot considering two valance band model. However, Bi doping markedly reduces the lattice thermal conductivity due to the formation of extensive solid solution point defects and domain variants. Moreover, a high value of Vickers microhardness (∼200 Hv, Hv = kgf/mm2) reveals excellent mechanical stability.

Crystallographic and textural evidence for precipitation of rutile, ilmenite, corundum, and apatite lamellae from garnet

Abstract Garnet is a common metamorphic and igneous mineral with extensive solid solution that can be stable to mantle depths ≥400 km. High-T and/or high-P garnet may contain oriented lamellae of other minerals, most commonly simple oxides (e.g., rutile, ilmenite), apatite, and, in ultrahigh-P cases, silicates including pyroxene and amphibole. Lamellae have classically been considered to be precipitation features preserving a record of former garnet chemistry richer in the lamellae nutrients (e.g., Ti4+). Such microtextural origins in precipitation systems (e.g., alloys) have long been studied via the crystallographic orientation relationships (COR) that form between a host and a separating phase, and by the shape-preferred orientation (SPO) of the lamellae. Recently, however, alternative hypotheses to precipitation have been suggested that require emplacement of lamellae in garnet by fluids, or co-growth, overgrowth, or inheritance mechanisms. These hypotheses posit that lamellae cannot be used to study former garnet chemistry. Moreover, they predict that lamellae phases, SPO, and COR should differ widely between localities, as lamellae formation will be controlled by various local rock-specific factors such as fluid presence, fluid chemistry, or mineral growth sequence. On the other hand, if lamellae characteristics are largely consistent between localities, it likely reflects control by precipitation energetics, rather than external factors. There have been few comparative COR studies in geologic systems, but the integrative assessment of COR, SPO, and lamellae assemblages should fingerprint lamellae growth process. To test the precipitation and alternative hypotheses, we collected large electron backscatter diffraction (EBSD) data sets for rutile, ilmenite, and apatite lamellae in garnet from the Brimfield Schist, Connecticut (≥1000 °C metamorphism; Central Maine Terrane, U.S.A.). We analyzed these data alongside published EBSD data for rutile, ilmenite, and corundum from metapegmatites metamorphosed in the eclogite facies from the Austrian Alps (Griffiths et al. 2016). The apatite data set is the first of its kind, and reveals that apatite preferentially aligns its close-packed direction parallel to that of garnet (c-axisapatite//<111>garnet). We also recognize a rutile-garnet COR related to those in meteorites with Widmanstätten patterns that are unequivocal products of exsolution. This is the first identification of direct similarities between silicate-oxide and metal-metal COR of which we are aware. Significantly, this rutile-garnet COR is found in diverse geologic settings including Connecticut and Idaho (U.S.A.), Austria, Germany, Greece, and China over a broad range of bulk-rock compositions. Results for all lamellae minerals show that COR are largely consistent between localities and, furthermore, are shared between apatite, ilmenite, and corundum. Moreover, between 70% and 95% of lamellae have COR and there is a dominant COR for each lamellae phase. Calculations show that d-spacing ratios of host-lamellae pairs can successfully predict the most commonly observed specific COR (those COR with two or more axial alignments with the host). These results, especially similarity of COR from markedly different geologic settings and a low diversity of lamellae minerals, are fully consistent with lamellae formation by precipitation (likely via exsolution). In contrast, the alternative hypotheses remain unsupported by COR results as well as by mineralogical and petrological evidence. Lamellae with similar traits as those in this work should thus be considered precipitates formed during unmixing of garnet compositions originally stable at elevated or extreme pressures and temperatures.

Biopolymer Sol-Gel Synthesis of Anion/Cation Doped Garnet Electrolyte Materials for Solid-State Batteries

Garnet solid-state electrolytes have attracted great interest due to its high Li ion conductivity and good electrochemical stability with electrode materials [1]. To enable the All-Solid-State Batteries, several issues need to be addressed, such as to increase the Li+ ion ionic conductivity, lower the interfacial resistance between electrolyte and electrode materials and prevent the dendrite growth of Li metal through electrolyte materials. There has been significant work investigating doping strategies to improve the conductivity of Li5La3Nb(Ta)2O12 and Li7La3Zr2O12 systems [2-5], with the key conclusions being that Li ion contents of the order of 6.4-6.7 are optimal. In this work, we show that Ce and Zn can be successfully doped into the structure with extensive solid solutions, leading to improved conductivities and lower activation energies compared to the undoped samples. Unlike cation doping, there has been little research on anion doping strategies. Both experimental and computational work [6] has shown that the incorporation of F to give Li7-xLa3Zr2O12-xFx leads to a change from a tetragonal to a cubic cell, along with an enhancement in Li ion conductivity. Specifically, the synthesis of F-doped Li7La3Zr2O12 has been examined through solid state synthesis route using polymer reagents (PTFE) as the fluorine source, a route that we have previously shown to be a very flexible means of F incorporation in solids [7]. As well as the preparation of the above systems via standard solid state synthesis, we present results on the use of a novel low temperature biopolymer sol-gel route. Both undoped and Al-doped Li7La3Zr2O12 has been made successfully at 700 oC in air, with comparable conductivity to the literature. The detailed characterisation of these systems is reported.

Genesis of the Meishan iron oxide–apatite deposit in the Ningwu Basin, eastern China: Constraints from apatite chemistry

The Meishan iron oxide–apatite deposit is located in the Ningwu volcanic basin in eastern China. The deposit comprises massive and brecciated ores in the main orebody, located at the contact between a gabbro–diorite porphyry and biotite–pyroxene andesites, and sub‐economic stockwork and disseminated ores. Among the four stages of alteration and mineralization, apatite coexists with magnetite, andradite, and quartz in massive magnetite ore and occurs in disseminated magnetite ore, coexisting with magnetite, siderite (after diopside), and quartz for Stage 2 iron mineralization. Apatite is also present in the altered gabbro–diorite porphyry. The apatites from the massive and disseminated magnetite–apatite ores are fluor‐ and hydroxyl‐ variety. Those from the altered gabbro–diorite porphyry show extensive solid solution between the hydroxyl‐apatite, fluor‐apatite, and chlor‐apatite end members. The apatites at Meishan record oxidized states during formation of the mineral deposit. The SO3 contents of apatite in the Meishan deposit mostly vary from 0.4 to 1.2 wt%, with the highest value of 4.97 wt%. MnO contents in apatites from our study are less than 0.17 wt%, and most values are below detection limit, indicating that the apatite formed in a high ƒO2 magmatic–hydrothermal fluid. The strong Eu depletion in apatites at Meishan resulted from the fractionation of plagioclase. The gabbro–diorite porphyry, magnetite, and apatite show similar LREE‐enriched patterns with significant negative Eu anomalies for apatite and magnetite, and no Eu anomaly for the gabbro–diorite porphyry. The gabbro–diorite porphyry and Stage 2 apatite associated with iron mineralization have also similar primitive mantle‐normalized trace element patterns, suggesting that the mineralization was related to gabbro–diorite porphyry. The REE pattern with significant negative Eu anomalies in apatite from the Meishan deposit is comparable with that of other Kiruna‐type deposits elsewhere in the world.

Absence of solid solution between Fe(II) and Mg(II) hydroxides and consequences on formation of fougerite and smectites

As there exists extended solid solutions between ferrous and magnesian silicates, experiments were conducted to check if ferrous and magnesian hydroxides can co-precipitate in a solid solution. Results show that no solid solution forms and instead Fe(II) and Mg(II) hydroxides precipitate separately with the same solubilities as pure components. However, in fougerite, F(III), Fe(II) and Mg(II) coexist in a brucitic type hydroxide, with an extended solid solution. This implies that fougerite formation results from Fe(III) precipitation, Fe(III) being surrounded by divalent Fe(II) and Mg(II) to comply with the exclusion rule: Fe(III) ions cannot be direct neighbours. Consequently, Fe(III) - Fe(II) - Mg(II) smectites cannot form by oxidation of a ferrous magnesian brucitic layer, but by silication of fougerite. The impossibility of formation of a solid solution between Fe(II) hydroxide and Mg(II) hydroxide, while their electric charge and ionic radii are identical can be explained by the differences of electronegativities of the elements. Fe(II) and Mg(II) can dimerize separately in aqueous solution, but an heterodimer cannot form.

Thermodynamic mixing properties of alunite supergroup minerals: Quantum-mechanical modeling and thermodynamic analysis of sulfate, chromate, selenate, phosphate, and arsenate solid solutions, as well as uranyl incorporation

Abstract In various geological settings, alunite supergroup minerals, including the end members alunite [KAl3(SO4)2(OH)6] and jarosite [KFe3(SO4)2(OH)6], occur in extensive solid solution on the cation and anion sites, enabling them to accommodate a variety of elements. Jarosite is known for scavenging heavy metals on the K site (e.g., Pb in solid solution between jarosite and plumbojarosite) in acid mine drainage settings, while both jarosite and alunite can be important in controlling toxic anions such as selenate, chromate, or arsenate. However, there is no thermodynamic information on the solubility of these important cations and anions as a function of temperature, in part because this information is difficult to obtain experimentally. In this study, thermodynamic mixing properties of sulfate-chromate (S-Cr), sulfate-selenate (S-Se), and sulfate-phosphate-arsenate (S-P-As) solid solutions in alunite supergroup minerals are investigated based on quantum-mechanical modeling and statistical thermodynamic analysis. S-Cr and S-Se solid solutions in alunite and jarosite are due to the mixing of anions with equivalent charges on the sulfate site. The enthalpy of mixing ( Δ H mix ) is lowest at 0 K (−273 °C) and increases with increasing temperature; it also depends on the arrangement of atoms on the sulfate site (i.e., atomic ordering). Δ H mix is almost constant at −70 °C and higher temperatures. These findings imply that S-Cr and S-Se solid solutions tend to be complete at room temperature and no ordering is acquired at or above ambient conditions. The Gibbs free energy of mixing ( Δ G mix ) indicates that jarosite is more flexible to accommodate chromate and selenate at the sulfate site than the alunite structure and that complete solid solution can be formed between jarosite and both Se- and Cr-analogues at temperatures above −80 °C. Our modeling results of solid solutions in jarosite and alunite demonstrate the critical role of alunite supergroup minerals in controlling toxic elements for long-term immobilization including the relatively favorable incorporation of uranyl (UO22+) into plumbojarosite. The S-P-As solid solution is also explored between alunite family minerals [DAl3(TO4)2(OH, H2O)6] (D is K+, Na+ or Ca2+; TO4 is SO42−, PO43− or AsO43−). The energetic barrier for mixing (reflected by the peak enthalpy of mixing) between ions with different charges (i.e., S-P and As-S solid solution; ∼2–3 kJ/mol of exchangeable atoms) is higher by a factor of two or three compared to anions with the equal charge (P-As solid solution; 1–1.5 kJ/mol of exchangeable atoms). Below 700 °C, ternary S-P-As mixing over a range of compositions in ternary space having alunite, crandallite [CaAl3(PO4)6(OH)5(H2O)], and arsenocrandallite [CaAl3(AsO4)6(OH)5(H2O)] as end members shows large miscibility gaps at compositions close to the ratio of S:P:As = 4:1:1 and 1:1:1 at the TO4 site. Ternary S-P-As mixing between woodhouseite, arsenowoodhouseite, and either alunite or natroalunite shows that arsenate is more compatible with sulfate in natroalunite than sulfate in alunite, whereas substitution of sulfate with phosphate is energetically more favorable in alunite than natroalunite. Our computed phase diagrams of S-P-As mixing suggest that binary solid solutions between pairs of sulfate, phosphate and arsenate in alunite family minerals scarcely occur below 100 °C, is limited at temperatures from 100 to 300 °C and become extensive or complete above 300 °C.