Precursor Phase Research Articles

Implication of polymeric template agent on the formation process of hybrid halide perovskite films

The use of polymeric additives supporting the growth of hybrid halide perovskites has proven to be a successful approach aiming at high quality active layers targeting optoelectronic exploitation. A detailed description of the complex process involving the self-assembly of the precursors into the perovskite crystallites in presence of the polymer is, however, still missing. Here we take starch:CH3NH3PbI3 (MAPbI3) as example of highly performing composite, both in solar cells and light emitting diodes, and study the film formation process through differential scanning calorimetry and in situ time-resolved grazing incidence wide-angle x-ray scattering, performed during spin coating. These measurements reveal that starch beneficially influences the nucleation and growth of the perovskite precursor phase, leading to improved structural properties of the resulting film which turns into higher stability towards environmental conditions.

High efficient co-doping in plasma electrolytic oxidation to obtain long-term self-lubrication on Ti6Al4V

Titanium alloys are important aerospace metals but suffer the poor mechanical property in high-loading area. Plasma electrolytic oxidation can improve their hardness and reduce friction but the precursor competition of functional phases in PEO electrolyte is inevitable. This work provides a new strategy to avoid ions competition and precipitation by choosing anionic salt (K2ZrF6) and cationic salt (Ce(Ac)3) as the precursors of the hard phase (ZrO2) and lubrication phase (monoclinic CePO4), respectively. As a result, the ions competition is avoided to achieve simultaneous high-content doping of functional phases. The optimized coating shows a maximum hardness of 626 HV, small friction coefficient of 0.12 and a lower wear rate of only 3.1 × 10−5 ± 0.15 mm3 N−1 m−1, indicating excellent long-term self-lubrication property and wear resistance.

How to build a bone? - Hydroxyapatite or Posner’s clusters as bone minerals

For decades, hydroxyapatite has been considered the main mineral phase of mammalian tooth enamel and bone that crystallizes from a precursor phase, amorphous calcium phosphate. Amorphous calcium phosphate, in turn, is proposed to be made from small clusters of ions known as Posner’s clusters, with a size of 0.95 ​nm and chemical formula of Ca9(PO4)6. In isolation, Posner’s clusters are extremely unstable and spontaneously aggregate and nucleate to the thermodynamically stable phase of hydroxyapatite within a few seconds. In this critical review, we will discuss the progress made in identifying the role of Posner’s clusters in the bone mineralization process, visualization of the clusters and associated challenges, and potential pathways to utilize them in bone tissue engineering strategies. We hypothesize, based on collective data in the literature and our recent experimental data, that Posner’s cluster agglomerates and amorphous calcium phosphate particles are in fact the main mineral component of bone, and hydroxyapatite crystals are, in part, artefacts of sample processing.

Tailoring precursor and medium of ball milling to optimize magnetic properties in Mn-Al bonded permanent magnets

Ball milled Mn-Al powders are ideal raw materials for fabricating bonded Mn-Al permanent magnets, and selecting proper precursor phase and milling medium for ball milling are of great importance to realize optimal magnetic properties in the final magnets. In this work, we studied the effect of different precursors and mediums of ball milling on the magnetic properties in the bonded magnets and the corresponding microstructural origins. ε-phase as the precursor leads to a serious decomposition behavior during the subsequent annealing after ball milling, resulting in a strong reduction in magnetization in the powders but just slightly better coercivity, so τ-phase is a superior choice as the precursor. In the case that τ-phase is adopted as the precursor, the milling medium of ethanol (wet-milling) or argon (dry-milling) has a remarkable influence on the morphologies of the milled powders. The former condition can fabricate thin polycrystalline flakes, and form stronger texture inside simultaneously, while the latter condition produces isotropic polycrystalline particles. The bonded magnets prepared using wet-milled powders thoroughly show superior magnetic properties including magnetization, remanence and coercivity than the magnets based on dry-milled particles. This work may promote the understanding of the nanostructures of Mn-Al ball milled powders, and provide the reference for the fabrication of Mn-Al rare-earth-free bonded magnets.Prime Novelty Statement.Ball milled Mn-Al powders are ideal raw materials for fabricating bonded Mn-Al permanent magnets, and selecting appropriate precursors and milling mediums for ball milling are important to obtain optimal magnetic properties in bonded magnets. In this work, ball milling with two precursors, ε phase (high temperature phase) and τ phase (metastable ferromagnetic phase), are performed. Powders from τ-precursor after annealing treatment showing good properties (M1200kA/m of 73 Am2/kg and Hc of 250 kA/m). While for ε-precursor, during the subsequent annealing treatment for the transformation from ε to τ, obvious decomposition occurs, inducing the distinct magnetization deterioration (36 Am2/kg) as well as slightly higher coercivity (331 kA/m). In comparison, the τ-precursor is superior to ε-precursor. In case that τ-phase is adopted as the precursor, the milling medium of ethanol (wet-milling) and argon (dry-milling) has a remarkable influence on the morphologies of the milled powders. Wet-milling condition can fabricate polycrystalline thin flakes with stronger texture, while the dry-milling condition produces isotropic particles. The bonded magnets prepared using wet-milled powders thoroughly show superior magnetic properties including magnetization, remanence and coercivity than the magnets based on dry-milled particles. This work may promote the understanding of the nanostructures of Mn-Al ball milled powders, and provide the reference for the fabrication of Mn-Al rare-earth-free bonded magnets.

Experimental investigation of a partial collapse during the sawtooth instability in EAST

ABSTRACT In this article, partial and full collapses of sawtooth activity are investigated with the high-resolution two-dimensional electron cyclotron emission (ECE) Imaging diagnostic in EAST. The partial collapse in normal sawtooth behavior is detected during the precursor phase of an L-mode plasma heated by ICRF. The electron heat diffusivity is determined with the time-to-peak analysis. The experimental results revealed that heat diffusivity suppresses at the time of the partial collapse. As a result, the partial collapse process interrupts and the small amount of heat releases outward. The hot core survives and is enclosed by the cold magnetic island. The inversion radii are estimated with the help of sawtooth and the only single inversion radius is found during the entire collapse process.

Linear MHD analyses of locked-mode-like instabilities in LHD

To investigate the driving mechanism of the locked-mode-like instability observed in the large helical device, we reconstruct the magnetohydrodynamic (MHD) equilibria consistent with the measurement and identify a dominant MHD instability in the precursor phase based on linear MHD analyses. From the dependence of the linear growth rate on the magnetic Reynolds number, the radial mode structure of the electrostatic potential fluctuation and other indices, the ideal interchange mode is found to be dominant. Moreover, it is found that the Mercier parameter, D I, becomes much larger than 0.3 during the phase, while the precursor has constant frequency and fluctuation amplitude. Therefore, D I ≫ 0.3 is a good index of the on-set condition of the minor collapse itself. It is also found that the achievement of D I ≫ 0.3 is due to the movement of the resonant surface to the inner plasma region, which corresponds to the larger pressure gradient region.

Synthesis, characterization and kinetic study of the Sr2FeMoO6-δ double perovskite: New findings on the calcination of one of its precursors

Sr2FeMoO6-δ double perovskites are widely-recognized due to several important factors: high electronic conductivity and electrocatalytic activity, structural stability under reducing atmospheres, high transition temperature, enormous magnetoresistance, reasonable tolerance to carbon formation, and their desirable capacity to avoid sulfur poisoning. One of the methods most commonly-used to synthetize these perovskites is solid-state reaction. The precursor phases usually associated with this method are the oxides SrMoO4 and SrFeO3-δ when Fe2O3, SrCO3, and MoO3 are the initial reagents used. Morphological, XRD (Rietveld), and thermogravimetry (calcination and reduction) analyses are steps or routes towards achieving the final result. While recent studies suggest that the temperature of calcination is always 900 °C and that reduction occurs at 1200 °C, they fail to explain why this occurs. This article demonstrates, according to the results of thermogravimetric analysis (TGA), that as calcination advances weight loss increases until a temperature of 850 °C is reached. In addition, it stresses the importance of the ball milling technique at ambient temperature to prevent sublimation of the MoO3 compound at 700 °C in the later steps of synthesis, such as calcination and reduction. According to the kinetic study, the values of activation energy (Ea) and reaction order (n) were 130.47 kJ/mol and 1 respectively.

Synthesis and Hydrolysis of Brushite (DCPD): The Role of Ionic Substitution

Brushite (dicalcium phosphate dihydrate, DCPD) is considered one of the possible precursors of the apatitic phase that constitutes the mineral component of bones, and it is often utilized in the pr...

Self-similar mesocrystals form via interface-driven nucleation and assembly.

Crystallization by particle attachment (CPA) is a frequently occurring mechanism of colloidal crystallization that results in hierarchical morphologies1-4. CPA has been exploited to create nanomaterials with unusual properties4-6 and is implicated in the development of complex mineral textures1,7. Oriented attachment7,8-a form of CPA in which particles align along specific crystallographic directions-produces mesocrystals that diffract as single crystals do, although the constituent particles are still discernible2,9. The conventional view of CPA is that nucleation provides a supply of particles that aggregate via Brownian motion biased by attractive interparticle potentials1,9-12. However, mesocrystals often exhibit regular morphologies and uniform sizes. Although many crystal systems form mesocrystals1-9 and individual attachment events have been directly visualized10, how random attachment events lead to well defined, self-similar morphologies remains unknown, as does the role of surface-bound ligands, which are ubiquitous in nanoparticle systems3,9,11. Attempts to understand mesocrystal formation are further complicated in many systems by the presence of precursor nanoparticles with a phase distinct from that of the bulk1,13,14. Some studies propose that such particles convert before attachment15, whereas others attribute conversion to the attachment process itself16 and yet others conclude that transformation occurs after the mesocrystals exceed a characteristic size14,17. Here we investigate mesocrystal formation by iron oxides, which are important colloidal phases in natural environments18,19 and classic examples of systems forming ubiquitous precursor phases and undergoing CPA accompanied by phase transformations15,19-21. Combining in situ transmission electron microscopy (TEM) at 80degrees Celsius with 'freeze-and-look' TEM, we tracked the formation of haematite (Hm) mesocrystals in the presence of oxalate (Ox), which is abundant in soils, where iron oxides are common. We find that isolated Hm particles rarely appear, but once formed, interfacial gradients at the Ox-covered surfaces drive Hm particles to nucleate repeatedly about two nanometres from the surfaces, to which they then attach, thereby generating mesocrystals. Comparison to natural and synthetic systems suggests that interface-driven pathways are widespread.

Recombinant major ampullate spidroin-particles as biotemplates for manganese carbonate mineralization

Mineral deposition in biological systems is often templated by organic matrices including proteins directing the nucleation and growth of bioceramics by interacting with early stage species of the mineralization process or coordinating specific facets of the forming crystal. Structurally, charged surface patches are a characteristic motif of biomineralization-associated proteins, which are able to accumulate and bind ions from the surrounding media and, therefore, initiate, promote or inhibit mineralization. Controlled protein engineering enables the manipulation and control of bioinspired in vitro precipitation systems, and thus not only opens prospects for the design of environmentally benign synthetic strategies towards hierarchically structured functional materials, but also enhances the understanding of fundamental interaction mechanisms in biomineralization processes. Here, two recombinant variants of the spider silk protein ADF4 were engineered with oppositely charged peptide tags. Both were processed into micrometer-sized particles and investigated for their influence on manganese carbonate mineralization. Micro- and nano-structured manganese carbonate represents an attractive material for diverse applications including catalysis and wastewater treatment. While both types of spider silk particles were incorporated into the mineral structure, the positively tagged proteins appeared to interact more strongly with the formed manganese carbonate crystals than their negatively charged counterparts. Combination of the spider silk particles and poly(acrylic acid) (PAA), a water-soluble structure-directing agent associated with the stabilization of amorphous precursor phases in carbonates, resulted in the formation of film-like non-equilibrium structures of MnCO3 entrapping the spider silk particles. With the aim to gain mechanistic insights and to elucidate the interaction between the different components involved in the mineralization process, we studied the interplay between PAA, positively or negatively tagged spider silk particles, and Mn(II) ions by time-resolved dynamic light scattering. The here used set-up affords the possibility to identify control strategies for the template-mediated mineralization of manganese carbonate.

Evolution of helimagnetic correlations when approaching the quantum critical point of Mn1−xFexSi

We present a comprehensive investigation of the evolution of helimagnetic correlations in Mn$_{1-x}$Fe$_x$Si with increasing doping. By combining polarised neutron scattering and high resolution Neutron Spin Echo spectroscopy we investigate three samples with $x$=0.09, 0.11 and 0.14, i.e. with compositions on both sides of the concentration $x^* \sim 0.11$ where the helimagnetic Bragg peaks disappear and between $x^*$ and the quantum critical concentration $x_C \sim 0.17$, where $T_C$ vanishes. We find that the abrupt disappearance of the long range helical periodicity at $x^*$, does not affect the precursor fluctuating correlations. These build up with decreasing temperature in a similar way as for the parent compound MnSi. Also the dynamics bears strong similarities to MnSi. The analysis of our results indicates that frustration, possibly due to achiral RKKY interactions, increases with increasing Fe doping. We argue that this effect explains both the expansion of the precursor phase with increasing $x$ and the abrupt disappearance of long range helimagnetic periodicity at $x^*$.

Edge modes of gravity. Part III. Corner simplicity constraints

In the tetrad formulation of gravity, the so-called simplicity constraints play a central role. They appear in the Hamiltonian analysis of the theory, and in the Lagrangian path integral when constructing the gravity partition function from topological BF theory. We develop here a systematic analysis of the corner symplectic structure encoding the symmetry algebra of gravity, and perform a thorough analysis of the simplicity constraints. Starting from a precursor phase space with Poincaré and Heisenberg symmetry, we obtain the corner phase space of BF theory by imposing kinematical constraints. This amounts to fixing the Heisenberg frame with a choice of position and spin operators. The simplicity constraints then further reduce the Poincaré symmetry of the BF phase space to a Lorentz subalgebra. This picture provides a particle-like description of (quantum) geometry: the internal normal plays the role of the four-momentum, the Barbero-Immirzi parameter that of the mass, the flux that of a relativistic position, and the frame that of a spin harmonic oscillator. Moreover, we show that the corner area element corresponds to the Poincaré spin Casimir. We achieve this central result by properly splitting, in the continuum, the corner simplicity constraints into first and second class parts. We construct the complete set of Dirac observables, which includes the generators of the local mathfrak{sl}left(2,mathrm{mathbb{C}}right) subalgebra of Poincaré, and the components of the tangential corner metric satisfying an mathfrak{sl}left(2,mathrm{mathbb{R}}right) algebra. We then present a preliminary analysis of the covariant and continuous irreducible representations of the infinite-dimensional corner algebra. Moreover, as an alternative path to quantization, we also introduce a regularization of the corner algebra and interpret this discrete setting in terms of an extended notion of twisted geometries.

Lamellar carbon-aluminosilicate nanocomposites with macroscopic orientation.

Novel preparative approaches towards lamellar nanocomposites of carbon and inorganic materials are relevant for a broad range of technological applications. Here, we describe how to utilize the co-assembly of a liquid-crystalline hexaphenylene amphiphile and an aluminosilicate precursor to prepare carbon-aluminosilicate nanocomposites with controlled lamellar orientation and macroscopic order. To this end, the shear-induced alignment of a precursor phase of the two components resulted in thin films comprising lamellae with periodicities on the order of the molecular length scale, an "edge-on" orientation relative to the substrate and parallel to the shearing direction with order on the centimeter length scale. The lamellar structure, orientation, and macroscopic alignment were preserved in the subsequent pyrolysis that yielded the corresponding carbon-aluminosilicate nanocomposites.

Pro-angiogenic and osteogenic composite scaffolds of fibrin, alginate and calcium phosphate for bone tissue engineering

Due to the limitations of bone autografts, we aimed to develop new composite biomaterials with pro-angiogenic and osteogenic properties to be used as scaffolds in bone tissue engineering applications. We used a porous, cross-linked and slowly biodegradable fibrin/alginate scaffold originally developed in our laboratory for wound healing, throughout which deposits of calcium phosphate (CaP) were evenly incorporated using an established biomimetic method. Material characterisation revealed the porous nature and confirmed the deposition of CaP precursor phases throughout the scaffolds. MC3T3-E1 cells adhered to the scaffolds, proliferated, migrated and differentiated down the osteogenic pathway during the culture period. Chick chorioallantoic membrane (CAM) assay results showed that the scaffolds were pro-angiogenic and biocompatible. The work presented here gave useful insights into the potential of these pro-angiogenic and osteogenic scaffolds for bone tissue engineering and merits further research in a pre-clinical model prior to its clinical translation.

Structure of the amorphous titania precursor phase of N-doped photocatalysts.

Amorphous titania samples prepared by ammonia solution neutralization of titanyl sulphate have been characterized by chemical and thermal analyses, and with reciprocal-space and real-space fitting of wide-angle synchrotron X-ray scattering data. A model that fits both the chemical and structural data comprises small segments of lepidocrocite-type layer that are offset by corner-sharing as in the monoclinic titanic acids H2TinO2n+1·mH2O. The amorphous phase composition that best fits the combined chemical and scattering data is [(NH4)3H21Ti20O52]·14H2O, where the formula within the brackets is the cluster composition and the H2O outside the brackets is physically adsorbed. The NH4+ cations are an integral part of the clusters and are bonded to layer anions at the corners of the offset layers, as occurs in the alkali metal stepped-layer titanates. The stepped-layer model is shown to give a consistent mechanism for the reaction of aqueous ammonia with solid hydrated titanyl sulphate, in which the amorphous product retains the exact size and shape of the reacting titanyl sulphate crystals.

Designing Evolutionary-based Interception Strategies to Block the Transition from Precursor Phases to Multiple Myeloma.

The development of next-generation sequencing technology has dramatically improved our understanding of the genetic landscape of multiple myeloma. Several new drivers and recurrent events have been reported and linked to a potential driver role. This complex landscape is enhanced by intraclonal mutational heterogeneity and variability introduced through the dimensions of time and space. The evolutionary history of multiple myeloma is driven by both the accumulation of different genomic drivers and by the activity of different mutational processes active overtime. In this review, we describe how these new findings and sequencing technologies have been progressively allowed to understand and reshape our knowledge of the complexity of multiple myeloma at each of its developmental stages: premalignant, at diagnosis, and in relapsed/refractory states. We discuss how these evolutionary concepts can be utilized in the clinic to alter evolutionary trajectories providing a framework for therapeutic intervention at early-disease stages.

Generality of liquid precursor phases in gas diffusion-based calcium carbonate synthesis

We confirm the presence of liquid calcium carbonate precursor species in absence of additives in gas diffusion systems.

Rapid collagen-directed mineralization of calcium fluoride nanocrystals with periodically patterned nanostructures.

Collagen fibrils present periodic structures, which provide space for intrafibrillar growth of oriented hydroxyapatite nanocrystals in bone and contribute to the good mechanical properties of bone. However, there are not many reports focused on bioprocess-inspired synthesis of non-native inorganic materials inside collagen fibrils and detailed forming processes of crystals inside collagen fibrils remain poorly understood. Herein, the rapid intrafibrillar mineralization of calcium fluoride nanocrystals with a periodically patterned nanostructure is demonstrated. The negatively charged calcium fluoride precursor phase infiltrates collagen fibrils through the gap zones creating an intricate periodic mineralization pattern. Later, the nanocrystals initially filling the gap zones only expand gradually into the remaining space within the collagen fibrils. Mineralized tendons with organized calcium fluoride nanocrystals acquire mechanical properties (indentation elastic modulus ∼25.1 GPa and hardness ∼1.5 GPa) comparable or even superior to those of native human dentin and lamellar bone. Understanding the mineral growth processes in collagen may facilitate the development of tissue engineering and repairing.

A Comparative Study of Pathological Nanomineral Aggregates with Distinct Morphology in Human Aortic Atherosclerotic Plaques.

Calcification exists in atherosclerotic plaques in the form of nanomineral aggregates and is closely related to the development of atherosclerosis. Spheroidal and massive calcification are two major types of calcification found in atherosclerotic tissue. However, the exact difference between these two types of calcification is still not clear. Samples composed entirely of spheroidal calcifications and massive calcifications were isolated from aortic atherosclerotic plaques and tested using both bulk and microscopic analysis techniques. Scanning electron microscopy and transmission electron microscopy showed that spheroidal calcifications had a core-shell structure. Massive calcifications were composed of randomly arranged nanocrystals. Synchrotron radiation X-ray diffraction, Raman spectroscopy and selected area electron diffraction showed amorphous calcium phosphate, whitlockite and carbonate hydroxyapatite all existing in spheroidal calcification, while massive calcification only consisted of carbonate hydroxyapatite. We conclude that amorphous calcium phosphate may act as a precursor phase of spheroidal calcifications that eventually transforms into a crystalline phase, while whitlockite in lesions could aggravate the progression of atherosclerosis.

Dual function of poly(acrylic acid) on controlling amorphous mediated hydroxyapatite crystallization

Hydroxyapatite (HAP, Ca5(PO4)3OH), as the main inorganic component of bone, is regulated by noncollagenous proteins (NCPs) that are rich in acidic amino acid. Poly(acrylic acid) (pAA) is widely used as an NCPs mimic because of its rich in carboxyl acid groups. Here we show that pAA plays a dual role in amorphous calcium phosphate (ACP, Ca3(PO4)2) mediated HAP crystallization, in which ACP is usually considered as the precursor phase of HAP crystallization in vitro and in vivo. The appropriate concentration of pAA can promote HAP crystallization due to it is mainly incorporated into ACP and more likely leads to form smaller ACP nanoparticles, thus provide a large specific surface area to HAP nucleation. While excessive pAA (incorporated into and adsorbed on the ACP) impairs the crystallization of HAP, in that surface associated pAA prevent the nucleation of HAP on ACP. Interestingly, pAA adsorbed on the ACP surface inhibits HAP nucleation significantly and changes the aggregation events of ACP. This finding points out that appropriate regulation of pAA concentration is vital for amorphous mediated biomineralization. Moreover, this study is of considerable importance for the future regulation and design of bone substitutes associated with NCPs.