Search Results (21)

Calcite habit engineering offers a route to transform CO₂ mineralization from bulk sequestration into value-added nanomaterial production. Here, we demonstrate that additive chemistry and seeding strategy can serve as separable, recipe-level levers for directing calcite habit formation within a unified CaO/Ca(OH)₂ gas–liquid carbonation platform. This strategy highlights how solution-mediated habit control can bridge fundamental calcite crystallization mechanisms with scalable CO₂ utilization and value-added carbonate nanomaterial production. Sodium glutamate yielded ~100 nm rhombohedral nanoparticles, staged MgSO₄/ZnSO₄ dosing produced whisker-like crystalline nanorods with aspect ratios of 4–7, and two-step seeded carbonation with NH₄Cl generated fusiform spindle subunits that assembled into hierarchical rosette architectures. X-ray diffraction confirmed calcite as the only crystalline calcium carbonate phase detected under the present measurement conditions, with no detectable aragonite or vaterite reflections. SEM/TEM revealed distinct primary-subunit architectures, including internal striations in spindle particles indicative of oriented attachment. Thermogravimetry, N₂ physisorption, and EDS further distinguished the products and showed that Mg/Zn/S modifiers in the whisker route are retained predominantly at crystal surfaces rather than incorporated into the calcite lattice. These results define calcite habit control through two independent levers: additive-driven facet selectivity and kinetic decoupling of nucleation from growth/assembly. The platform links scalable synthesis, CO₂ utilization, and functional carbonate design. Full article

Crystallization and blockage in tunnel drainage systems represent a major challenge in the operation and maintenance of tunnels in karst regions. This study focuses on a tunnel in Guilin, Guangxi, employing a combined approach of field investigation, laboratory characterization, and molecular dynamics (MD) simulations to explore the atomic-scale mechanism of CaCO₃ crystallization within the drainage system. Field investigations reveal that the groundwater is dominated by Ca²⁺ and HCO₃⁻ ions, and the crystalline products consist primarily of high-crystallinity single-phase calcite, characterized by typical rhombohedral geometric structures and heterogeneous stacking. Molecular dynamics simulations indicate that the CaCO₃ nucleation process is accompanied by the desolvation of Ca²⁺, while background electrolyte ions exert distinct regulatory effects on the nucleation kinetics. SO₄²⁻ participates in cluster construction through strong coordination, inducing the formation of loose, chain-like aggregates; conversely, Cl⁻ delays cluster coalescence primarily through charge shielding and steric hindrance effects. Additionally, Na⁺ influences the overall solution dynamics and the stability of pre-nucleation clusters by constructing stable hydration shells and providing charge neutralization. This research reveals the formation mechanism of tunnel crystallization from a microscopic perspective, providing theoretical support for the prevention and control of crystallization in tunnel drainage systems. Full article

Magnesium whitlockite (Mg-WH) has emerged as a promising biomaterial for bone regeneration due to its compositional similarity to natural bone minerals. This study aimed to systematically modify a dissolution–precipitation synthesis method to produce Mg-WH granules with tailored morphologies and controlled phase compositions for possible use in bone regeneration applications. Three distinct precursor granules were prepared by mixing varying amounts of ammonium dihydrogen phosphate and magnesium hydrogen phosphate with calcium sulfate. The precursors were then transformed into biphasic and single-phase Mg-WH granules by means of immersion in magnesium- and phosphate-containing solutions under controlled conditions. The X-ray diffraction results demonstrated that biphasic materials containing Mg-WH and either calcium-deficient hydroxyapatite (CDHA) or dicalcium phosphate anhydrous (DCPA) formed after 24 h of synthesis, depending on the synthesis conditions. Prolonging the reaction time to 48 h resulted in complete transformation into single-phase Mg-WH granules. Fourier-transform infrared spectroscopy confirmed the presence of functional groups characteristic of Mg-WH, CDHA, and DCPA in the intermediate products. The spectra also indicated the absence of precursor phases and the progressive elimination of secondary phases as the reaction time increased. Scanning electron microscopy analyses revealed notable morphological transformations from the raw granules to the product granules, with the latter exhibiting interlocked spherical and rod-like particles composed of fine Mg-WH rhombohedral crystals. N₂ adsorption–desorption analyses exposed significant differences in the surface properties of the synthesized granules. By varying precursor, reaction solution compositions, and reaction times, the study elucidated the phase evolution mechanisms and demonstrated their impact on the structural, morphological, and surface properties of Mg-WH granules. Full article

BiFeO₃/LaFeO₃ (BFO/LFO) epitaxial superlattices (SLs) with different bilayer thicknesses were grown via pulsed laser deposition on a (001)-SrTiO₃ substrate buffered with a SrRuO₃ bottom electrode. Room-temperature X-ray diffraction demonstrated strong structural changes in tuning the bilayer thickness while keeping the total thickness constant. Superlattices with thin periods were characterized by an antiferroelectric Pnma-like phase, while thick bilayers of the SLs were more likely to be described by a mixed state, including a rhombohedral ferroelectric bulk-like phase. Raman scattering analysis further confirmed the structural behaviour deduced by X-ray diffraction. Strain relaxation and symmetry changes were moreover accompanied by modifications in the dielectric properties correlated with the deduced (anti)ferroic structural phases. Full article

Binary As_xSe_100−x alloys from the border of a glass-forming region (65 < x < 70) subjected to nanomilling in dry and dry–wet modes are characterized by the XRPD, micro-Raman scattering (micro-RS) and revised positron annihilation lifetime (PAL) methods complemented by a disproportionality analysis using the quantum–chemical cluster modeling approach. These alloys are examined with respect to tetra-arsenic biselenide As₄Se₂ stoichiometry, realized in glassy g-As₆₅Se₃₅, glassy–crystalline g/c-As₆₇Se₃₃ and glassy–crystalline g/c-As₇₀Se₃₀. From the XRPD results, the number of rhombohedral As and cubic arsenolite As₂O₃ phases in As-Se alloys increases after nanomilling, especially in the wet mode realized in a PVP water solution. Nanomilling-driven amorphization and reamorphization transformations in these alloys are identified by an analysis of diffuse peak halos in their XRPD patterning, showing the interplay between the levels of a medium-range structure (disruption of the intermediate-range ordering at the cost of an extended-range one). From the micro-RS spectroscopy results, these alloys are stabilized by molecular thioarsenides As₄Se_n (n = 3, 4), regardless of their phase composition, remnants of thioarsenide molecules destructed under nanomilling being reincorporated into a glass network undergoing a polyamorphic transition. From the PAL spectroscopy results, volumetric changes in the wet-milled alloys with respect to the dry-milled ones are identified as resulting from a direct conversion of the bound positron–electron (Ps, positronium) states in the positron traps. Ps-hosting holes in the PVP medium appear instead of positron traps, with ~0.36–0.38 ns lifetimes ascribed to multivacancies in the As-Se matrix. The superposition of PAL spectrum peaks and tails for pelletized PVP, unmilled, dry-milled, and dry–wet-milled As-Se samples shows a spectacular smoothly decaying trend. The microstructure scenarios of the spontaneous (under quenching) and activated (under nanomilling) decomposition of principal network clusters in As₄Se₂-bearing arsenoselenides are recognized. Over-constrained As_6·(2/3) ring-like network clusters acting as pre-cursors of the rhombohedral As phase are the main products of this decomposition. Two spontaneous processes for creating thioarsenides with crystalline counterparts explain the location of the glass-forming border in an As-Se system near the As₄Se₂ composition, while an activated decomposition process for creating layered As₂Se₃ structures is responsible for the nanomilling-driven molecular-to-network transition. Full article

(1-x)(Ba_0.75Sr_0.1Bi_0.1)(Ti_0.9Zr_0.1)O₃-x(Sb_0.5Li_0.5)TiO₃ (abbreviated as BSBiTZ-xSLT, x = 0.025, 0.05, 0.075, 0.1) ceramics were prepared via a conventional solid-state sintering method under different sintering temperatures. All BSBiTZ-xSLT ceramics have predominantly perovskite phase structures with the coexistence of tetragonal, rhombohedral and orthogonal phases, and present mainly spherical-like shaped grains relating to a liquid-phase sintering mechanism due to adding SLT and Bi₂O₃. By adjusting the sintering temperature, all compositions obtain the highest relative density and present densified micro-morphology, and doping SLT tends to promote the growth of grain size and the grain size distribution becomes nonuniform gradually. Due to the addition of heterovalent ions and SLT, typical relaxor ferroelectric characteristic is realized, dielectric performance stability is broadened to ~120 °C with variation less than 10%, and very long and slim hysteresis loops are obtained, which is especially beneficial for energy storage application. All samples show extremely fast discharge performance where the discharge time t_0.9 (time for 90% discharge energy density) is less than 160 ns and the largest discharge current occurs at around 30 ns. The 1155 °C sintered BSBiTZ-0.025SLT ceramics exhibit rather large energy storage density, very high energy storage efficiency and excellent pulse charge–discharge performance, providing the possibility to develop novel BT-based dielectric ceramics for pulse energy storage applications. Full article

In this work, the local conductance of the tetragonal-like (T-like) and rhombohedral-like (R-like) phases of epitaxial BiFeO₃ film is systematically studied via conductive atomic force microscopy. At higher tip voltage, there is a mutual transition between the T-like and R-like phases, which could be attributed to the strain relaxation in the T-like phase induced by electric poling, as well as local polarization switching. The T-like phase exhibits a higher conductance, which is related to the lower interface potential barrier between the tip and film surface. Reversible low- and high-current states in the T-like phase can be tuned by polarization switching. These results will be helpful for designing novel nanoelectronic devices, such as voltage and strain sensors. Full article

Nanoparticles of iron carbides and nitrides enclosed in graphite shells were obtained at 2 ÷ 8 GPa pressures and temperatures of around 800 °C from ferrocene and ferrocene–melamine mixture. The average core–shell particle size was below 60 nm. The graphite-like shells over the iron nitride cores were built of concentric graphene layers packed in a rhombohedral shape. It was found that at a pressure of 4 GPa and temperature of 800 °C, the stability of the nanoscale phases increases in a Fe₇C₃ -> Fe₃C -> Fe₃N_1+x sequence and at 8 GPa in a Fe₃C -> Fe₇C₃ -> Fe₃N_1+x sequence. At pressures of 2 ÷ 8 GPa and temperatures up to 1600 °C, iron nitride Fe₃N_1+x is more stable than iron carbides. At 8 GPa and 1600 °C, the average particle size of iron nitride increased to 0.5 ÷ 1 μm, while simultaneously formed free carbon particles had the shape of graphite discs with a size of 1 ÷ 2 μm. Structural refinement of the iron nitride using the Rietveld method gave the best result for the space group P6₃22. The refined composition of the samples obtained from a mixture of ferrocene and melamine at 8 GPa/800 °C corresponded to Fe₃N_1.208, and at 8 GPa/1650 °C to Fe₃N_1.259. The iron nitride core–shell nanoparticles exhibited magnetic behavior. Specific magnetization at 7.5 kOe of pure Fe₃N_1.208 was estimated to be 70 emu/g. Compared to other methods, the high-pressure method allows easy synthesis of the iron nitride cores inside pure carbon shells and control of the particle size. And in general, pressure is a good tool for modifying the phase and chemical composition of the iron-containing cores. Full article

The non-natural mineralization of CaCO₃ with special structures or morphologies is generated during the migration of crude oil and is the main form of scale in alkaline/surfactant/polymer (ASP) flooding in oilfields, adversely affecting oil recovery and causing environmental pollution. To date, the mineralization of aragonite superstructures and the role of heavy alkyl-benzene sulfonate (HABS) in mineralization are still unclear. In this work, aragonite-based superstructures of CaCO₃ crystals were obtained in an O/W emulsion with HABS to help deepen the understanding of the diversified growth of CaCO₃ scaling in oilfields. As a result, rosette-like, bouquet-like, and dumbbell-shaped CaCO₃ crystals with vaterite–aragonite, aragonite, and calcite–aragonite phases were formed with 200 mg/L HABS concentration at 45 °C for 60 min and spherical vaterite phase stabilized at a high HABS concentration (800 mg/L and 1000 mg/L). Rhombohedral calcite content experienced a fluctuation of about 40% as the HABS concentration varied. Needle-like and bundle-like aragonite precipitates were generated with increasing temperatures from 65 °C to 85 °C. Thus, HABS affects the nucleation and growth of the precipitated CaCO₃ solid, leading to modifications in the structure and morphology of the crystals. The synergistic effect between HABS and temperature can regulate ion pairs with the calcium ions and block sites that are essential to the incorporation of new solutes into the crystal lattice, which leads to the heterogeneous nucleation of vaterite and aragonite on calcite, forming aragonite-based superstructures in kerosene emulsion. This work may enrich the understanding of CaCO₃ mineralization in oilfields, and also provide a novel strategy for manufacturing organic–inorganic composites. Full article

The symmetric nano morphologies, asymmetric electronic structures, and as well as the heterojunctions of the developed photocatalytic systems perform a vital role in promoting light absorption, separation of electron and hole pairs and charge carrier transport to the surface when exposed to near-infrared (NIR) light. In this present work, we synthesized hematite (α-Fe₂O₃) nanoparticles (NPs) by a facile hydrothermal method and studied their structural, optical, and photocatalytic properties. Powder X-ray diffraction (XRD) confirmed the rhombohedral phase of the α-Fe₂O₃ NPs, and Fourier transform infrared spectroscopy (FT-IR) was used to investigate symmetric and asymmetric stretching vibrations of the functional groups on the surface of the catalysts. The optical bandgap energy was estimated to be 2.25 eV using UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS) and scanning electron microscopy (SEM) images indicated sphere like morphology. The oxidation and reduction properties of α-Fe₂O₃ NPs were analyzed by cyclic voltammetry (CV). The α-Fe₂O₃ NPs were utilized for the degradation of methylene blue (MB) dye under natural sunlight. The experimental results demonstrate that the degradation efficiency was achieved at 33% in 2 h, and the pseudo-first-order rate constant was calculated to be 0.0033 min⁻¹. Full article

Bismuth telluride thin films were grown by pulsed laser deposition by implementing a novel method that combines both Te and Bi plasmas resulting from the laser ablation of individual Bi and Te targets. Furthermore, the mean kinetic ion energy and density of the plasmas, as estimated by TOF curves obtained from Langmuir probe measurements, were used as control parameters for the deposition process. The obtained thin films exhibit a metallic mirror-like appearance and present good adhesion to the substrate. Morphology of the thin films was observed by SEM, yielding smooth surfaces where particulates were also observed (splashing). Chemical composition analysis obtained by EDS showed that apparently the films have a Te-rich composition (ratio of Te/Bi of 3); however, Te excess arises from the splashing as revealed by the structural characterization (XRD and Raman spectroscopy). The XRD pattern indicated that depositions have the rhombohedral (${\mathrm{D}}_{3d}^5$ ($\mathrm{R}\overline{3}\mathrm{m})$) structure of Bi₂Te₃. Likewise, Raman spectra exhibited the presence of signals that correspond to ${\mathrm{E}}_{\mathrm{g}}^2$, ${\mathrm{A}}_{1\mathrm{u}}^2$ and ${\mathrm{A}}_{1\mathrm{g}}^2$(LO) vibrational modes of the same rhombohedral phase of Bi₂Te₃. Additionally, oxidation states, analyzed by XPS, resulted in signals associated to Bi³⁺ and Te^2- that correspond to the Bi₂Te₃ compound. Finally, surface topology and thickness profiles were obtained from AFM measurements, confirming a combination of a smooth surface with particulates on top of it and a film thickness of 400 nm. Full article

Different nanostructured semiconducting ZnO photoanodes were prepared by Hydrothermal (HT), Co-precipitation (CoP) and Chemical Bath Deposition (CBD) methods for their use in the Dye Sensitized Solar Cells (DSSCs) in the present study. Additionally, different ZnO nanocomposites were synthesized by mixing the Carbon Nanotubes (CNTs), Graphene Oxide (GO) and their combination with the ZnO nanostructures. Scanning electron microscopy (SEM) revealed various morphologies of ZnO nanostructures and nanocomposites such as nanoflowers, nanorods, rhombohedral, cubic, and cauliflower-like nanorods, and nanorods with hexagonal symmetry. Energy Dispersive X-ray (EDX) spectra confirmed the purity of the synthesized samples. X-ray Diffraction (XRD) demonstrated the hexagonal wurtzite phase of ZnO and a minor presence of CNTs and graphene. The UV-Visible, transmittance and diffuse reflectance spectra demonstrated that the ZnO synthesized through the CBD method exhibits the highest transmittance as 70–71% in the UV-Vis range and reduced % R. Optical band gaps of the samples were determined with the help of Tauc plots. Comparison of J-V characteristics showed that the ZnO synthesized via the HT method exhibits the highest conversion efficiency of 1.45%. Comparison among pristine ZnO synthesized via CBD and ZnO nanocomposites revealed that ZnO/CNTs possesses the highest energy conversion efficiency of 1.23% with enhanced J_SC of 4.49 mA/cm². Full article

Outstanding ferroelectric and piezoelectric properties of PbZr_xTi_1-xO₃ (PZT) make nano and sub-micrometer particles of this material interesting for future nanotechnological applications as well as for fundamental studies of ferroelectricity at the nanoscale. In the present work, the prospects of a new hydrothermal approach were explored to control the particle size, aggregation stage, and composition of the PZT with the target composition of Zr/Ti = 60/40 (x = 0.6). Starting with water-soluble Zr-, Ti-, and Pb-precursors, the PZT formation was examined in the broad base (KOH) concentration range. The PZT particle size and composition were governed by the ratio of KOH with respect to Pb and not by the absolute KOH concentration (c_KOH). The incorporation of Zr into the PZT perovskite phase began to decline at KOH:Pb ≤ 1.7 and at KOH:Pb > 20. In the concentration range of 20 ≥ KOH:Pb > 1.5, the PZT particles adopted a cube-like shape, the size of which decreased with a decrease in the KOH:Pb ratio. The smallest (<200 nm) and well-separated PZT particles were obtained at KOH:Pb = 1.7. The prevailing PZT crystal structure at a Zr/Ti composition of around 60/40 was rhombohedral; the tetragonal phase also began to appear in Ti-richer PZT compositions (Zr/Ti ≤ 50/50). The developed understanding established the basis for further tailoring of PZT particle morphologies for application-oriented or fundamental research. Full article

Cocrystals of Active Pharmaceutical Ingredients (APIs) are an attractive therapeutic alternative to salt formations. However, due to the molecular scale processes involved, the earliest stages of cocrystal formation remain poorly understood. In this paper, some light is shed on the thermodynamics and kinetics of co-crystallization. Importantly, to mimic the molecular scale processes of cocrystal formation, we use 2D Monte Carlo simulations and a computational model with short-range attraction and a mixture of two types of patchy particles (PPs) monomers. Each type possesses four patches, grouped in two by two, and each couple of patches is characterized by its specific placement on the circumference of the monomer and corresponding patch strength (a strong and narrow or weak and wide interaction). The spatial placement of the patches on both PPs monomers (alternating periodically through 60 and 120 degrees and vice versa) selected by us shows the emergence of both rhombohedral (metastable) and trihexagonal (stable) Kagome-like structures. The Kagome-like structures are preceded by formation of two types of trimers involving strong bonds only, or mixed trimers of strong and weak bonds, the later serving as building blocks for the finally generated Kagome patchy cocrystal, after prolonged simulation times. The step-by step process governing the cocrystal formation is discussed in detail, concerning the temperature interval, concentrations of PPs, the specific patch geometry and patch anisotropy as well. It is to be hoped that an understanding of the mechanisms of co-crystallization can help to control practical cocrystal synthesis and the possible phase transformations. Full article

Bi₈Te₃ is a member of the tetradymite homologous series, previously shown to be compositionally and structurally distinct from hedleyite, Bi₇Te₃, yet inadequately characterized structurally. The phase is identified in a sample from the Hedley district, British Columbia, Canada. Compositions are documented by electron probe microanalysis and structures are directly imaged using high-angle annular dark field (HAADF) scanning transmission electron microscopy (STEM). Results confirm that Bi₈Te₃ has an 11-atom layer structure, in which three Bi-Bi pairs are placed adjacent to the five-atom sequence (Te-Bi-Te-Bi-Te). Bi₈Te₃ has trigonal symmetry (space group R$\overline{3}$m) with unit cell dimensions of a = ~4.4 Å and c = ~63 Å calculated from measurements on representative electron diffraction patterns. The model is assessed by STEM simulations and EDS mapping, all displaying good agreement with the HAADF STEM imaging. Lattice-scale intergrowths are documented in phases replacing Bi₈Te₃, accounting for the rarity of this phase in nature. These results support prior predictions of crystal structures in the tetradymite homologous series from theoretical modeling and indicate that other phases are likely to exist for future discovery. Tetradymite homologues are mixed-layer compounds derived as one-dimensional superstructures of a basic rhombohedral sub-cell. Each member of the series has a discrete stoichiometric composition and unique crystal structure. Full article