Hexagonal Prismatic Crystals Research Articles

Li+ doped SrAl2O4:Eu2+, Dy3+ long‐persistent luminescence aluminoborosilicate glass‐ceramics: Preparation and properties

AbstractIn the SrO‐Al2O3‐B2O3‐SiO2 glass system, a SrAl2O4:Eu2+, Dy3+ long‐persistent luminescence glass‐ceramic (SAGC) with Li2O was successfully synthesized for the first time using the recrystallization‐melting method. The composition, micromorphology, long‐persistent luminescence (LPL) properties, photoluminescence (PL) properties, and water resistance were measured by X‐ray diffractometer, scanning electron microscope, brightness meter, fluorescence spectrophotometer, and pH meter, respectively. The method involves the formation of grains below the glass transition temperature, followed by the formation of the glass phase at a higher temperature, and finally the formation of products through cooling. The samples exhibited green PL and LPL emissions and demonstrated excellent color purity, homogeneity, and LPL luminescence. After doping Li2O, the purity and crystallinity of the SrAl2O4 were improved, and scalene hexagonal or monoclinic prismatic SrAl2O4 crystals with high regularity were synthesized in the glass matrix. This research indicates that excellent LPL benefits from the complete crystal structure, abundant crystals, and large crystal size. When the Li2O content reached 5 mol%, the crystal size was ∼30 µm, the PL and LPL properties performed best, and greater water resistance was exhibited. The SAGC in this new glass system has potential in optical storage.

Study of Road Performance and Curing Mechanism of Coal Gangue by Curing Agent

Abstract Coal gangue is a type of rock waste product with dark gray color during coal mining and washing. The curing agent stabilizes soils by improving their physico-mechanical properties, allowing the soils to be reused in engineering as the subgrade fill. This study investigates the impact of SAHP curing agent on road performance parameters of coal gangue. The results showed that the road performance parameters of coal gangue increase with the curing agent content. The compressive resilience modulus of 7 days and California bearing ratio of coal gangue with 0.2% curing agent meet the specifications. The scanning electron microscope reveals the presence of agglomerated gels and hexagonal prism crystals between coal gangue particles. The observed crystals are ettringite, and the gels are silicate gel (nSiO2·mH2O) formed by the reaction of Na2O·nSiO2 with CO2 and H2O, as determined by combined X-ray diffraction and energy spectrum analysis. The improved coal gangue by the curing agent can be utilized as subgrade fill, supporting the reuse of coal gangue in highway engineering.

Enhanced downconversion luminescence of NaLuF4:Yb3+,Er3+ micrometer hexagonal prismatic crystals under 980 nm excitation

NaLuF4:Yb3+,Er3+ micrometer prismatic crystals are potential materials for the preparation of optical waveguide devices. However, structural defects and OH– groups are generated inside and on their surfaces during growth processes. The structural defects and OH– groups lead to a large depletion of excitation energy and severely quench the downconversion luminescence of Er3+. In addition, the Yb3+/Er3+ co-doping ratio significantly affects the downconversion luminescence of the microcrystals, which in turn affects the performance of the optical waveguide amplifiers based on the microcrystals. By adjusting the co-doping ratio of Yb3+ and Er3+ in the microcrystals and removing the defects in the crystals, their downconversion luminescence performance was significantly improved. The results showed that the downconversion luminescence under the excitation from a 980 nm laser reached the maximum value when the doping ratio of Yb3+ and Er3+ was 20:1.5. In addition, the OH– groups and structural defects in the micrometer crystals were significantly eliminated by ion-exchange and high-temperature annealing treatments, and the crystalline quality was significantly improved. After ion-exchange and high-temperature annealing treatments, the downconversion luminescence enhancement of NaLuF4:Yb3+,Er3+ microcrystals was 2.5 times that of the untreated samples.

Programming the morphology of DNA origami crystals by magnesium ion strength

Harnessing the programmable nature of DNA origami for controlling structural features in crystalline materials affords opportunities to bring crystal engineering to a remarkable level. However, the challenge of crystallizing a single type of DNA origami unit into varied structural outcomes remains, given the requirement for specific DNA designs for each targeted structure. Here, we show that crystals with distinct equilibrium phases and shapes can be realized using a single DNA origami morphology with an allosteric factor to modulate the binding coordination. As a result, origami crystals undergo phase transitions from a simple cubic lattice to a simple hexagonal (SH) lattice and eventually to a face-centered cubic (FCC) lattice. After selectively removing internal nanoparticles from DNA origami building blocks, the body-centered tetragonal and chalcopyrite lattice are derived from the SH and FCC lattices, respectively, revealing another phase transition involving crystal system conversions. The rich phase space was realized through the de novo synthesis of crystals under varying solution environments, followed by the individual characterizations of the resulting products. Such phase transitions can lead to associated transitions in the shape of the resulting products. Hexagonal prism crystals, crystals characterized by triangular facets, and twinned crystals are observed to form from SH and FCC systems, which have not previously been experimentally realized by DNA origami crystallization. These findings open a promising pathway toward accessing a rich phase space with a single type of building block and wielding other instructions as tools to develop crystalline materials with tunable properties.

Triple-Peak Photoluminescence of DNA-Hybrid Alq3 Crystals Emitting a Depressed Single Peak upon Bio-Recognition.

The green organic semiconductor, tris-(8-hydroxyquinoline)aluminum (Alq3), was hybridized with DNA growing in the shape of hexagonal prismatic crystals. In this study, we applied hydrodynamic flow to the fabrication of Alq3 crystals doped with DNA molecules. The hydrodynamic flow in the Taylor-Couette reactor induced nanoscale pores in the Alq3 crystals, especially at the side part of the particles. The particles exhibited distinctly different photoluminescence emissions divided into three parts compared to common Alq3-DNA hybrid crystals. We named this particle a "three-photonic-unit". After treatment with complementary target DNA, the three-photonic-unit Alq3 particles doped with DNAs were found to emit depressed luminescence from side parts of the particles. This novel phenomenon would expand the technological value of these hybrid crystals with divided photoluminescence emissions toward a wider range of bio-photonic applications.

Betzite, Na6Ca2(Al6Si6O24)Cl4, a New Cancrinite-Group Mineral from the Eifel Paleovolcanic Region, Germany

AbstractBetzite, ideally Na6Ca2(Al6Si6O24)Cl4, a new cancrinite-group mineral, was discovered in a metasomatically altered (pyrometamorphosed) calcic xenolith, hosted by alkaline basalt at the Bellerberg paleovolcano in the Eastern Eifel region, Rhineland-Palatinate, Germany. The associated minerals are anorthite, phlogopite, diopside, grossular, fluorite, calcite, a tobermorite-like mineral, and vanadoallanite-(Ce). Betzite occurs as colorless hexagonal prismatic crystals up to 2 mm long and up to 0.5 mm thick. The new mineral is brittle, with a Mohs' hardness of 5½. Distinct cleavage on {100} and parting on {0001} are observed. The Dmeas = 2.38(2) g/cm3 and Dcalc = 2.363 g/cm3. Betzite is optically uniaxial (+) with ω = 1.528(2) and ε = 1.545(3). The IR spectrum is given. The chemical composition of betzite is (wt.%; electron microprobe, H2O determined by the modified Penfield method): Na2O 11.88, K2O 4.82, CaO 10.74, MgO 0.21, Al2O3 27.32, Fe2O3 0.68, SiO2 32.84, SO3 1.89, Cl 10.48, H2O 1.10, −O≡Cl −2.37, total 99.59. The empirical formula is Na4.22K1.13Ca2.11Mg0.06(Si6.01Al5.90Fe3+0.09O24)Cl3.25(SO4)0.26(H1.34O0.64). The crystal structure was determined using single-crystal X-ray diffraction data. It is hexagonal, space group P63, a = 12.8166(9) Å, c = 5.3562(3) Å, V = 761.95(12) Å3 (at a temperature of 100 K) and Z = 3. Betzite is a dimorph of quadridavyne, with a disordered distribution of extra-framework components occupying channels. The strongest lines of the powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are: 11.14 (31) (100), 4.833 (93) (101), 3.715 (95) (300), 3.313 (100) (211), 2.787 (37) (400), 2.681 (56) (002, 131), 2.474 (35) (112, 401), 2.146 (24) (330). The mineral is named in honor of the German amateur mineralogist Volker Betz (b. 1947).

MIL-96-Al for Li-S Batteries: Shape or Size?

Metal-organic frameworks (MOFs) with controllable shapes and sizes show a great potential in Li-S batteries. However, neither the relationship between shape and specific capacity nor the influence of MOF particle size on cyclic stability have been fully established yet. Herein, MIL-96-Al with various shapes, forming hexagonal platelet crystals (HPC), hexagonal bipyramidal crystals (HBC), and hexagonal prismatic bipyramidal crystals (HPBC) are successfully prepared via cosolvent methods. Density functional theory (DFT) calculations demonstrate that the HBC shape with highly exposed (101) planes can effectively adsorb lithium polysulfides (LPS) during the charge/discharge process. By changing the relative proportion of the cosolvents, HBC samples with different particle sizes are prepared. When these MIL-96-Al crystals are used as sulfur host materials, it is found that those with a smaller size of the HBC shape deliver higher initial capacity. These investigations establish that different crystal planes have different adsorption abilities for LPS, and that the MOF particle size should be considered for a suitable sulfur host. More broadly, this work provides a strategy for designing sulfur hosts in Li-S batteries.

Pliniusite, Ca5(VO4)3F, a new apatite-group mineral and the novel natural ternary solid-solution system pliniusite–svabite–fluorapatite

Abstract The new apatite-group mineral pliniusite, ideally Ca5(VO4)3F, was found in fumarole deposits at the Tolbachik volcano, Kamchatka, Russia, and in a pyrometamorphic rock of the Hatrurim Complex, Israel. Pliniusite, together with fluorapatite and svabite, forms a novel and almost continuous ternary solid-solution system characterized by wide variations of T5+ = P, As, and V. In paleo-fumarolic deposits at Mountain 1004 (Tolbachik), members of this system, including the holotype pliniusite, are associated with hematite, tenorite, diopside, andradite, kainotropite, baryte and supergene volborthite, brochantite, gypsum and opal. In sublimates of the active Arsenatnaya fumarole (Tolbachik), pliniusite–svabite–fluorapatite minerals coexist with anhydrite, diopside, hematite, berzeliite, schäferite, calciojohillerite, forsterite, enstatite, magnesioferrite, ludwigite, rhabdoborite-group fluoroborates, powellite, baryte, udinaite, arsenudinaite, paraberzeliite, and spinel. At Nahal Morag, Negev Desert, Israel, the pliniusite cotype and V-bearing fluorapatite occur in schorlomite-gehlenite paralava with rankinite, walstromite, zadovite-aradite series minerals, magnesioferrite, hematite, khesinite, barioferrite, perovskite, gurimite, baryte, tenorite, delafos-site, wollastonite, and cuspidine. Pliniusite forms hexagonal prismatic crystals up to 0.3 × 0.1 mm and open-work aggregates up to 2 mm across (Mountain 1004) or grains up to 0.02 mm (Nahal Morag and Arsenatnaya fumarole). Pliniusite is transparent to semitransparent, colorless or whitish, with a vitreous luster. The calculated density is 3.402 g/cm−3. Pliniusite is optically uniaxial (–), ω = 1.763(5), ε = 1.738(5). The empirical formulas of pliniusite type specimens calculated based on 13 anions (O+F+Cl) per formula unit are (Ca4.87Na0.06Sr0.03Fe0.02)Σ4.98(V1.69As0.66P0.45S0.12Si0.09)Σ3.01O11.97F1.03 (Mountain 1004) and (Ca4.81Sr0.12Ba0.08Na0.05)Σ5.06(V2.64P0.27S0.07Si0.03)Σ3.01O12.15F0.51Cl0.34 (Nahal Morag). Pliniusite has a hexagonal structure with space group P63/m, a = b = 9.5777(7), c = 6.9659(5) Å, V = 553.39(7) Å3, and Z = 2. The structure was solved using single-crystal (holotype) X-ray diffraction, R = 0.0254. The mineral was named in honor of the famous Roman naturalist Pliny the Elder, born Gaius Plinius Secundus (AD 23–79). It is suggested that the combination of high temperature, low pressure, and high oxygen fugacity favors the incorporation of V5+ into calcium apatite-type compounds, leading to the formation of fluorovanadates.

Chiyokoite, Ca3Si(CO3)[B(OH)4]O(OH)5·12H2O, a new ettringite-group mineral from the Fuka mine, Okayama Prefecture, Japan

ABSTRACT The new ettringite-group mineral chiyokoite, ideally Ca3Si(CO3)[B(OH)4]O(OH)5·12H2O, was found in a hydrothermally altered calc-silicate skarn at the Fuka mine, Okayama Prefecture, Japan. Associated minerals are calcite, henmilite, and tacharanite. Chiyokoite occurs as hexagonal prismatic crystals up to 30 μm long and up to 20 μm thick. The major forms are the hexagonal prism {100} and monohedra {0001} and {000}. The crystals are combined in clusters which form friable nests up to 1 cm across. The mineral is pink to colorless with white streak and vitreous luster. The cleavage is parallel to {100} and {0001}, good. The fracture is stepped. Dmeas is 1.85(1) g/cm3, Dcalc is 1.85 g/cm3. Chiyokoite is optically uniaxial (–), ω = 1.523(2) and ε = 1.492(3) (589 nm). The infrared spectrum is reported. The chemical composition (wt.%) is CaO 27.56, B2O3 3.47, Al2O3 3.05, Fe2O3 0.12, As2O3 4.77, MnO2 0.32, SiO2 6.55, SO3 0.76, H2O 46.3, CO2 7.30, total 100.2. The empirical formula calculated on the basis of 3 Ca apfu is H31.37Ca3(Si0.67Al0.37Mn4+0.02Fe3+0.01)Σ1.07(C1.01B0.61As3+0.29S0.06)Σ1.97O24.19. The simplified general formula is Ca3(Si,Al)(CO3,AsO3)[B(OH)4,AsO3](OH)6·12H2O. Chiyokoite is hexagonal, P63, a = 11.0119(5), c = 10.5252(6) Å, and V = 1105.3(1) Å3. The strongest reflections of the powder X-ray diffraction pattern [d,Å(I)(hkl)] are: 9.53(100)(100), 5.50(24)(110), 4.618(11)(102), 3.812(23)(112), 3.412(15)(211), 2.726(14)(302), 2.521(19)(123), and 2.172(13)(320,402,223). The crystal structure, refined from single-crystal X-ray diffraction data [R1(F) = 0.042], is based on [Ca3(Si,Al)(OH)6(H2O)12] columns parallel to the c axis with B(OH)4– and CO32– and admixed AsO33– anionic groups in channels between the columns. The mineral is named in honor of Professor Chiyoko Henmi (1949–2018).

Siwaqaite, Ca6Al2(CrO4)3(OH)12·26H2O, a new mineral of the ettringite group from the pyrometamorphic Daba-Siwaqa complex, Jordan

Abstract A new mineral, siwaqaite, ideally Ca6Al2(CrO4)3(OH)12·26H2O [P31c, Z = 2, a = 11.3640(2) Å, c = 21.4485(2) Å, V = 2398.78(9) Å3], a member of the ettringite group, was discovered in thin veins and small cavities within the spurrite marble at the North Siwaqa complex, Lisdan-Siwaqa Fault, Hashem region, Jordan. This complex belongs to the widespread pyrometamorphic rock of the Hatrurim Complex. The spurrite marble is mainly composed of calcite, fluorapatite, and brownmillerite. Siwaqaite occurs with calcite and minerals of the baryte-hashemite series. It forms hexagonal prismatic crystals up to 250 μm in size, but most common are grain aggregates. Siwaqaite exhibits a canary yellow color and a yellowish-gray streak. The mineral is transparent and has a vitreous luster. It shows perfect cleavage on (1010). Parting or twinning is not observed. The calculated density of siwaqaite is 1.819 g/cm3. Siwaqaite is optically uniaxial (–) with ω = 1.512(2), ε = 1.502(2) (589 nm), and non-pleochroic. The empirical formula of the holotype siwaqaite calculated on the basis of 8 framework cations and 26 water molecules is Ca6.01(Al1.87Si0.12)Σ1.99[(CrO4)1.71(SO4)1.13(SeO4)0.40]Σ3.24(OH)11.63·26H2O. X-ray diffraction (XRD), Raman, and infrared spectroscopy confirm the presence of OH- groups and H2O molecules and absence of (CO3)2– groups. The crystal structure of this Cr6+-analog of ettringite was solved by direct methods using single-crystal synchrotron XRD data. The structure was refined to an agreement index R1 = 4.54%. The crystal structure of siwaqaite consists of {Ca6[Al(OH)6]2·24H2O}6+ columns with the inter-column space (channels) occupied by (CrO4)2–, (SO4)2–, (SeO4)2–, and (SO3)2– groups and H2O molecules. The tetrahedrally coordinated site occupied by different anion groups is subjected to disordering and rotation of these tetrahedra within the structure. The temperature of siwaqaite formation is not higher than~70–80 °C, as is evident from the mineral association and as inferred from the formation conditions of the natural and synthetic members of the ettringite group minerals, which are stable at conditions of T < 120 °C and pH = 9.5–13. The name siwaqaite is derived from the name of the holotype locality—Siwaqa area, where the mineral was found.

Crystallization process and growth mechanism for hexagonal prism of strontium hydroxyapatite by urea hydrolysis

Strontium hydroxyapatite (SrHAp) is not only used as drug carrier material for bone disease treatment, but also has application prospect in bone tissue engineering. But SrHAp is prepared with by-products strontium hydrogen phosphate (SrHP) and strontium phosphate (TSrP), which requires accurate process optimizations and adjustments to circumvent the undesirable morphology products. The integral hexagonal prism crystals of SrHAp were successfully synthesized by urea hydrolysis at ambient pressure and without any strong acids and bases. Similarly, variable by-products are classified and investigated for their effects on crystallization process of strontium hydroxyapatite via monitoring the urea hydrolysis time-dependent products. The crystallization process of SrHAp can be divided into four stages based on the crystallographic results for the samples acquired by XRD and SEM studies during the entire synthesis processes. In the first stage, SrHP is formed (0–0.17 h); secondly, SrHP is converted into SrHAp (0.17–4 h); TSrP is obtained (4–8 h) at the third stage; and at last, TSrP is transformed into SrHAp (8–24 h), especially the amount of SrHAp obtained at 24 h was the sum of the second and fourth stages. Simultaneously, the growth mechanism of SrHAp crystals was proposed, considered of the formation energy of Gibbs-Thomson crystal plane and Born-Lande lattice energy. By calculating the interfacial energy γ(h k l) of different crystal planes, the γ(1 0 0) of hexagonal prism plane family m{1 0 0} is 1.3 × 10−5U0, the γ(0 0 1) of parallel double-plane family c{0 0 1} is 7.5 × 10−6U0, the normal growth rate of Ic{0 0 1} ≫ Im{1 0 0}. Accordingly, the growth mechanism for the preferential c axis growth maintaining the hexagonal prism shape is derived.

Milarite-group minerals from the NYF pegmatite Velká skála, Písek district, Czech Republic: sole carriers of Be from the magmatic to hydrothermal stage

Four distinct paragenetic, morphological and compositional types of milarite-group minerals were distinguished in the NYF pegmatite Velka skala, Pisek district, Czech Republic (Moldanubian Zone). The simply zoned (Kfs,Plg,Ab,Qz > Bt > Ap > Tur) pegmatite dike, ∼60 cm thick, is enclosed in durbachite (K,Mg-rich melasyenite). The milarite-group minerals include: yellowish, subhedral, prismatic grains of homogeneous milarite I (milarite s.s.); prismatic subparallel aggregates of white to grayish milarite II (zoned milarite s.s. to Sc-rich milarite, up to ∼20 mol% of the oftedalite component) from small pockets; colorless hexagonal prismatic crystals of milarite III (milarite s.s.) lining open fractures and microscopic fillings in recrystallized K-feldspar locally associated with REE-bearing minerals (allanite, aeschynite, titanite); very rare milarite IV (milarite s.s. to agakhanovite) as prismatic crystals and thin overgrowths with complex oscillatory zoning, ≤200 D:\Palash\HWNLM\07_06m in size, on crystals of milarite II and milarite III. Their mineral assemblages, textures and compositions suggest primary (magmatic) for milarite I and hydrothermal origin for milarite II, III, and IV. The simplified compositional evolution in these milarites is: Al + Ca → Be + Sc → Be + Y, HREE →Be+ LREE . Milarite-group minerals are the sole carriers of Be in the pegmatite, no relics or pseudomorphs after other Be-rich minerals were found; thus milarite is now established as an additional primary Be-rich mineral in granitic pegmatites. Mineral assemblages, chemical composition of minerals and close relation to the host durbachite suggest a NYF affinity of the Velka skala pegmatite as well as a close relation to euxenite-type pegmatites of the Třebic Pluton. Milarite-group minerals from Velka Skala exhibit very similar compositional evolution to those found in the Heftetjern pegmatite, Tordal, Norway.

Characteristics of phosphate phase (fluorapatite and monazite) in the South Nam Xe carbonatites, Northwest Vietnam

<p>This paper presents characteristics of appearance and mineral chemistry of phosphate phase, including fluorapatite and monazite in the South Nam Xe carbonatite dykes in Northwest Vietnam. These minerals occur in both calcio- and ferrocarbonatites in various modes. Most of the fluorapatites in the calciocarbonatites are oblong to elongated, and have sharp contacts with calcite, aegirine and phlogopite suggesting their primary origin; whereas those in the ferrocarbonatites are commonly present in forms of stubby to perfect hexagonal prismatic crystals, which partly replaced by the monazite. The monazites in the ferrocarbonatites also occur as hundreds micro isolated crystals, which associated with ankerite, feldspar, magnetite and phlogopite.</p><p>Contents of fluor and rare earth elements (REE) are relatively high (F up to 4.26 wt.%; REE up to 5.19 wt.%) indicating a F- and REE-enriched precipitation for the carbonatites. The enrichment in light REEs in the fluorapatite is paired with an enrichment in Na, varying from 0.25 wt.% to 0.89 wt.%. The replacement of REE and Na for Ca in the fluorapatites, which leads to change in CaO/P<sub>2</sub>O<sub>5</sub> ratios might show an open system where Ca and P are added to areas of the fluorapatite depleted in light REE (LREE). REE contents in the monazite show a very limited variation, and are mainly composed of La, Ce and Nd (La<sub>2</sub>O<sub>3</sub> = 21.09-22.72 wt.%, Ce<sub>2</sub>O<sub>3</sub> = 32.82-33.35 wt.%, Nd<sub>2</sub>O<sub>3</sub> = 6.96-8.20 wt.% in calciocarbonatite; La<sub>2</sub>O<sub>3</sub> = 16.61-17.39 wt.%, Ce<sub>2</sub>O<sub>3</sub> = 32.07-33.52 wt.%, Nd<sub>2</sub>O<sub>3</sub> = 8.92-10.94 wt.% in ferrocarbonatite). </p>

Characteristics of phosphate phase (fluorapatite and monazite) in the South Nam Xe carbonatites, Northwest Vietnam

<p>This paper presents characteristics of appearance and mineral chemistry of phosphate phase, including fluorapatite and monazite in the South Nam Xe carbonatite dykes in Northwest Vietnam. These minerals occur in both calcio- and ferrocarbonatites in various modes. Most of the fluorapatites in the calciocarbonatites are oblong to elongated, and have sharp contacts with calcite, aegirine and phlogopite suggesting their primary origin; whereas those in the ferrocarbonatites are commonly present in forms of stubby to perfect hexagonal prismatic crystals, which partly replaced by the monazite. The monazites in the ferrocarbonatites also occur as hundreds micro isolated crystals, which associated with ankerite, feldspar, magnetite and phlogopite.</p><p>Contents of fluor and rare earth elements (REE) are relatively high (F up to 4.26 wt.%; REE up to 5.19 wt.%) indicating a F- and REE-enriched precipitation for the carbonatites. The enrichment in light REEs in the fluorapatite is paired with an enrichment in Na, varying from 0.25 wt.% to 0.89 wt.%. The replacement of REE and Na for Ca in the fluorapatites, which leads to change in CaO/P<sub>2</sub>O<sub>5</sub> ratios might show an open system where Ca and P are added to areas of the fluorapatite depleted in light REE (LREE). REE contents in the monazite show a very limited variation, and are mainly composed of La, Ce and Nd (La<sub>2</sub>O<sub>3</sub> = 21.09-22.72 wt.%, Ce<sub>2</sub>O<sub>3</sub> = 32.82-33.35 wt.%, Nd<sub>2</sub>O<sub>3</sub> = 6.96-8.20 wt.% in calciocarbonatite; La<sub>2</sub>O<sub>3</sub> = 16.61-17.39 wt.%, Ce<sub>2</sub>O<sub>3</sub> = 32.07-33.52 wt.%, Nd<sub>2</sub>O<sub>3</sub> = 8.92-10.94 wt.% in ferrocarbonatite). </p>

Tubular g‐C3N4 Isotype Heterojunction: Enhanced Visible‐Light Photocatalytic Activity through Cooperative Manipulation of Oriented Electron and Hole Transfer

A tubular g-C3 N4 isotype heterojunction (TCNH) photocatalyst was designed for cooperative manipulation of the oriented transfer of photogenerated electrons and holes to pursue high catalytic performance. The adduct of cyanuric acid and melamine (CA·M) is first hydrothermally treated to assemble into hexagonal prism crystals; then the hybrid precursors of urea and CA·M crystals are calcined to form tubular g-C3 N4 isotype heterojunctions. Upon visible-light irradiation, the photogenerated electrons transfer from g-C3 N4 (CA·M) to g-C3 N4 (urea) driven by the conduction band offset of 0.05 eV, while the photogenerated holes transfer from g-C3 N4 (urea) to g-C3 N4 (CA·M) driven by the valence band offset of 0.18 eV, which renders oriented transfer of the charge carriers across the heterojunction interface. Meanwhile, the tubular structure of TCNH is favorable for oriented electron transfer along the longitudinal dimension, which greatly decreases the chance of charge carrier recombination. Consequently, TCNH exhibits a high hydrogen evolution rate of 63 μmol h(-1) (0.04 g, λ > 420 nm), which is nearly five times of the pristine g-C3 N4 and higher than most of the existing g-C3 N4 photocatalysts. This study demonstrates that isotype heterojunction structure and tubular structure can jointly manipulate the oriented transfer of electrons and holes, thus facilitating the visible-light photocatalysis.

Whitecapsite, a new hydrous iron and trivalent antimony arsenate mineral from the White Caps mine, Nevada, USA

The new mineral species whitecapsite, H 16 Fe 2+ 5 Fe 3+ 14 Sb 3+ 6 (AsO 4 ) 18 O 16 ·120H 2 O, was found in the oxidation zone of the White Caps gold deposit (White Caps mine), Manhattan district, Nye Co., Nevada, USA, and named after the holotype locality. The mineral was found in cavities in a breccia consisting of fragments of jasperoid, silicified marble and mica schist, in association with picropharmacolite, guerinite, pitticite, gypsum, jarosite, goethite, sulfur, metastibnite and earlier quartz, calcite, kaolinite, realgar, stibnite, arsenopyrite, pyrite, sphalerite, orpiment, cinnabar and metacinnabar. Whitecapsite occurs as well-shaped hexagonal prismatic crystals (up to 0.3 × 0.3 × 1.5 mm) terminated with bipyramidal faces (forms: {110} and {111}) and as clusters of crystal up to 1 mm in maximal dimension. It is bright orange to golden-brownish orange, transparent, with a vitreous lustre. Mohs’ hardness is 2–2½. The mineral is brittle, cleavage was not observed, fracture is uneven. D meas = 2.30(3), D calc = 2.297 g cm −3 . Whitecapsite is optically uniaxial (+), ω = 1.590(2) and ɛ = 1.603(3). Chemical composition (wt%, electron probe) is: MnO 0.09, FeO 5.32, Fe 2 O 3 16.82, Sb 2 O 3 13.30, As 2 O 5 30.78, H 2 O calc 34.53, total 100.84. The empirical formula calculated on the basis of 208 O apfu with 256 H apfu is: H 16 Mn 2+ 0.08 Fe 2+ 4.95 Fe 3+ 14.07 Sb 3+ 6.10 As 5+ 17.89 O 88 ·120H 2 O. Both the IR and Raman spectra show high content of H 2 O, the presence of hydrated protons (the complex cations H + · n H 2 O) and an absence of OH groups. Sb L 3 and Fe K XANES spectra show the presence of only Sb 3+ and of both Fe 3+ and Fe 2+ (Fe 3+ > Fe 2+ ). Whitecapsite is hexagonal, P 6 3 / m , a = 16.0916(8), c = 21.7127(9) A, V = 4869.0(4) A 3 and Z = 1. The strongest reflections of the X-ray powder-diffraction pattern [ d ,A ( I ,%) ( hkl )] are: 13.99 (49) (100); 11.73 (100) (101); 5.267 (6) (120); 3.644 (4) (205, 132, 006); 2.999 (8) (411, 126, 225); 2.757 (4) (501, 234); 2.648 (5) (331, 414, 316). The crystal structure was solved by direct methods and refined to R = 0.058. Its major building unit is a heteropolyhedral cluster [(□,Fe 2+ ) 6 Fe 3+ 7 Sb 3 O 8 (AsO 4 ) 9 (H 2 O) 30 ] with the Fe 3+ O 6 trigonal prism as a central polyhedron. These clusters are isolated from each other and linked only via hydrogen bonds to the H 2 O molecules located in the interstitial space.

Adachiite, a Si–poor member of the tourmaline supergroup from the Kiura mine, Oita Prefecture, Japan

Adachiite, CaFe3Al6(Si5AlO18)(BO3)3(OH)3(OH), a Si–poor member of the tourmaline supergroup, is found in the hydrothermal vein cutting emery from Nabagasako of the Kiura mine, Saiki City, Oita Prefecture, Japan. Adachiite occurs as a constituent (several to 300 µm thickness) of hexagonal prismatic crystals, and forms a zoned structure closely associated with schorl. It is transparent with brownish–purple to bluish–purple color, while the massive aggregate shows black in color. Adachiite is trigonal, R3m, a = 15.9290(2), c = 7.1830(1) Å, V = 1578.39(4) Å3, and Z = 3, determined via single crystal XRD refinement (R1 = 0.038). Adachiite is the first member of the tourmaline group formed via Tschermak–like substitution.

Natural age dispersion arising from the analysis of broken crystals. Part I: Theoretical basis and implications for the apatite (U–Th)/He thermochronometer

Over the last decade major progress has been made in developing both the theoretical and practical aspects of apatite (U–Th)/He thermochronometry and it is now standard practice, and generally seen as best practice, to analyse single grain aliquots. These individual prismatic crystals are often broken and are fragments of larger crystals that have broken during mineral separation along the weak basal cleavage in apatite. This is clearly indicated by the common occurrence of only 1 or no clear crystal terminations present on separated apatite grains, and evidence of freshly broken ends when grains are viewed using a scanning electron microscope. This matters because if the 4He distribution within the whole grain is not homogeneous, because of partial loss due to thermal diffusion for example, then the fragments will all yield ages different from each other and from the whole grain age. Here we use a numerical model with a finite cylinder geometry to approximate 4He ingrowth and thermal diffusion within hexagonal prismatic apatite crystals. This is used to quantify the amount and patterns of inherent, natural age dispersion that arises from analysing broken crystals. A series of systematic numerical experiments were conducted to explore and quantify the pattern and behaviour of this source of dispersion using a set of 5 simple thermal histories that represent a range of plausible geological scenarios. In addition some more complex numerical experiments were run to investigate the pattern and behaviour of grain dispersion seen in several real data sets. The results indicate that natural dispersion of a set of single fragment ages (defined as the range divided by the mean) arising from fragmentation alone varies from c. 7% even for rapid (c. 10°C/Ma), monotonic cooling to over 50% for protracted, complex histories that cause significant diffusional loss of 4He. The magnitude of dispersion arising from fragmentation scales with the grain cylindrical radius, and is of a similar magnitude to dispersion expected from differences in absolute grain size alone (spherical equivalent radii of 40–150μm). This source of dispersion is significant compared with typical analytical uncertainties on individual grain analyses (c. 6%) and standard deviations on multiple grain analyses from a single sample (c. 10–20%). Where there is a significant difference in the U and Th concentration of individual grains (eU), the effect of radiation damage accumulation on 4He diffusivity (assessed using the RDAAM model of Flowers et al. (2009)) is the primary cause of dispersion for samples that have experienced a protracted thermal history, and can cause dispersion in excess of 100% for realistic ranges of eU concentration (i.e. 5–100ppm). Expected natural dispersion arising from the combined effects of reasonable variations in grain size (radii 40–125μm), eU concentration (5–150ppm) and fragmentation would typically exceed 100% for complex thermal histories. In addition to adding a significant component of natural dispersion to analyses, the effect of fragmentation also acts to decouple and corrupt expected correlations between grain ages and absolute grain size and to a lesser extent between grain age and effective uranium concentration (eU). Considering fragmentation explicitly as a source of dispersion and analysing how the different sources of natural dispersion all interact with each other provides a quantitative framework for understanding patterns of dispersion that otherwise appear chaotic. An important outcome of these numerical experiments is that they demonstrate that the pattern of age dispersion arising from fragmentation mimics the pattern of 4He distribution within the whole grains, thus providing an important source of information about the thermal history of the sample. We suggest that if the primary focus of a study is to extract the thermal history information from (U–Th)/He analyses then sampling and analytical strategies should aim to maximise the natural dispersion of grain ages, not minimise it, and should aim to analyse circa 20–30 grains from each sample. The key observations and conclusions drawn here are directly applicable to other thermochronometers, such as the apatite, rutile and titanite U–Pb systems, where the diffusion domain is approximated by the physical grain size.

Morphology control of ZnO with citrate: a time and concentration dependent mechanistic insight

The effect of citrate as a crystal habit modifier on the morphology of zinc oxide has been explored in a wide range of citrate/Zn ratio from 0 to 0.67. With an increase in concentration of citrate at the lower range of the ratio, the aspect ratio of the hexagonal prismatic crystals of ZnO decreases, forming flatter disks with a progressive increase of roughness on the hexagonal face. At intermediate ratios, the otherwise smooth rectangular faces also become rough, with progressive formation of porous spherical aggregates. At a high concentration of citrate, solid spherical particles form with very low crystallinity, eventually forming plate-like zinc citrate. Thermal and spectroscopic studies confirm a progressive increase in the adsorbed citrate concentration in the particles. Evidence in support of citrate being adsorbed first on the hexagonal face, followed by the other rectangular faces is presented, and a scheme has been proposed. This adsorbed citrate can be removed by calcination and the morphology remains intact, and so this procedure can be used to make pure ZnO with various morphologies. It was found that the ZnO morphologies synthesized in the presence of citrate show novel photoluminescent and enhanced photocatalytic activities compared with ZnO synthesized in the absence of citrate.

Electrolytic Deposition of Hydroxyapatite Coating on CoNiCrMo Substrates

AbstractHydroxyapatite (HA) coating was fabricated on CoNiCrMo alloy by electrolytic deposition (ELD). Different kinds of uncharged substrates were placed close to the cathode separately during the ELD process. Both CoNiCrMo and uncharged substrates were covered with uniform HA coatings composed of hexagonal prism crystals after 60 min deposition. The pH value of the bulk solution changed hardly while the local pH had a sharp increase after ELD. The results demonstrate the local pH plays a crucial role in the ELD process.