Formation Of Intermediate Phase Research Articles

Methylammonium Chloride Additive in Lead Iodide Optimizing the Crystallization Process for Efficient Perovskite Solar Cells

Perovskite solar cells (PSCs) were fabricated using a two-step spin-coating method with MACl added to the inorganic layer. The properties of the perovskite films were characterized by SEM, XRD, PL, UV-vis spectra, etc. The morphology of the PbI2 film was significantly changed, and the formation of MACl-related intermediate phase was observed at the grain boundaries. The grain size and crystallinity of the perovskite film increased, and the morphology at grain boundaries was optimized, while the composition of perovskite remained unchanged. The introduction of MACl improved the open circuit voltage (VOC) and fill factor (FF) of PSCs, and the optimal device efficiency reached 21.59%. This paper presents a new approach using additives in inorganic layers to optimize the crystallization process for efficient PSCs.

Tuning the strength and ductility of near β titanium alloy Ti-5321 by ω and O′ intermediate phases via low-temperature aging

The formation of intermediate phases ω and O′ during low-temperature aging at 200 °C and its effect on plastic deformation in a new-developed near β-Ti alloy Ti–5Al–3Mo–3V–2Cr–2Zr–1Nb–1Fe (wt %) have been studied in this work. The results showed that the ω and O′ phases were continuously transformed upon aging, and larger amount of O′ precipitates was developed in air-cooled sample than water-quenched one. Upon early aging the yield strength and ductility of alloy were simultaneously improved until 60 min. The trade-off relationship of strength and ductility was overcome by the simultaneous precipitation of ω and O′ phases. It was suggested that the ω and O′ precipitation changed the deformation mechanisms, leading to this alloy exhibited different deformation behaviors and mechanical properties. With the quantities of ω and O′ increasing, the strain-induced α′′ martensite transformation was gradually suppressed, and the primary deformation mechanism changed into a mixture of strain-induced ω transformation, mechanical twining and dislocation slipping. These findings would provide an insight to achieve better combinations of strength and ductility in near β-Ti alloys through tailoring the ω and O′ phase transformations.

Adhesion strength of electrodeposited Ni, Zn, and Fe coatings with copper substrates

ABSTRACT This paper presents the adhesive strength values of electrodeposited nickel, zinc, and iron coatings on copper substrates at various deposition parameters, including laser-assisted stimulation of the deposition process. One of the factors determined to be responsible for the adhesive strength of metal films with a metal substrate is the formation of a diffusion zone at the ‘coating-substrate’ interface. It is shown that an increase in adhesive strength is achieved due to the expansion of the diffusion zone and the formation of solid solutions. The decrease in adhesive strength at high overpotentials is associated with the release of hydrogen and the formation of intermediate phases.

Amorphization-induced energy loss of amorphous Si anodes for Li-ion batteries

The thermodynamic stability and energy loss (kinetic overpotential) of amorphous Si (a-Si) anodes during electrochemical cycling are investigated by intensive free energy analysis based on molecular dynamics simulations. We first demonstrate the trade-off between energy loss and specific capacity that the enhancement of maximum Li concentration (specific capacity) is compensated with the increase of kinetic overpotential. The effects of external pressure and reaction rate on the formation enthalpy and kinetic overpotential of a-Si anodes are also explored. We find that both effects destabilize amorphous Li-Si (a-LixSi) phases with raised formation enthalpies, and result in the increased kinetic overpotential of a-Si anodes during electrochemical cycling. Our thermodynamic analysis predicts the constant value of overpotential, due to the neglect of ohmic contribution and possible formation of intermediate crystalline LixSi phases. These computational results provide a better understanding of the amorphization effect on the energy loss of alloying-type anodes.

Bulk diffusion regulated nanopore formation during vapor phase dealloying of a Zn-Cu alloy

Dealloying is a robust method for fabricating 3D bicontinuous porous materials with open porosity and large specific surface areas. The formation of nanopores usually results from two kinetically competing processes at dealloying fronts: desertion of sacrificed elements and self-assembly of lingered elements by diffusion. Since surface and interface diffusivities are usually much higher than bulk, dealloying is typically fulfilled by the fast processes while the slow bulk alloy diffusion in precursor alloys is not commonly involved into the formation of open porosity during a dealloying process. Here we report that open pore formation in a Cu12Zn88 alloy is regulated by the bulk alloy diffusion during high-temperature vapor phase dealloying. The growth of dealloyed porous microstructure is facilitated by the formation of an up-front γ-Cu34Zn66 intermediate phase and, thereby, the dealloying kinetics is mediated by the evolution of the solid intermediate phase through bulk diffusion. The two-step dealloying process may pave a new way to tailor porous microstructure by designing and controlling intermediate phase formation.

Sensitive temperature-dependent phase resolution of polyethylene-clay nanocomposites

With the help of spectroscopic and differential scanning calorimetry (DSC) techniques, we have studied conformational and phase reorganizations as function of temperature in intercalated polymer-clay nanocomposites based on low-, middle-, and high-density polyethylene (PE) matrices. We show that Raman spectroscopy is sensitive to structural changes appearing during heating at much lower temperatures (about 47 °C) in comparison to DSC measurements. In fact, in the melting region where DSC traces show endotherms, Raman spectra reveal dramatic changes in the phase and conformational compositions of PE and PE-matrices within PE-clay nanocomposites. Noteworthy, the structural reorganization pathway, through which the semicrystalline nanocomposites transform into a melt state, depends primarily on the PE density and weakly on the filler (nanoclay). Moreover, the temperature-dependent crystallinity degree and the total amount of trans-conformers of the PE system are determined, and the evidence for the formation of intermediate crystal-like phase during heating is shown.

Kinetics of antigorite dehydroxylation for CO2 sequestration

Heat-treatment of serpentine minerals generates structural amorphicity and increases reactivity during subsequent mineral carbonation, a strategy for large-scale sequestration of CO2. This study employs thermal analyses (TGA-DSC) in conjunction with in-situ synchrotron powder X-ray diffraction (PXRD) to record concurrent mass loss, heat flow, and mineralogical changes during thermal treatment of antigorite. Isoconversional kinetic modelling demonstrates that thermal decomposition of antigorite is a complex multi-step reaction, with activation energies (Eα) varying between 290 and 515 kJ mol−1. We identify three intermediate phases forming during antigorite dehydroxylation, a semi-crystalline chlorite-like phase (γ-metaserpentine) showing an additional reaction pathway for the decomposition of Al2O3-rich antigorite into pyrope, and two distinct amorphous components (α and β-metaserpentine) which convert into forsterite and enstatite at higher temperature, respectively. The combination of isoconversional kinetics with in-situ synchrotron PXRD illustrates, for the first time, that local crystal structure changes, related to intermediate phase and forsterite formation, are responsible for the steep increase in activation energy above 650 °C and only 49% dehydroxylation can be achieved prior to this increase. This suggests that the high thermal stability of Al2O3-rich antigorite would severely limit Mg extraction during application of mineral carbonation under flue gas conditions.

Modulating crystal growth of formamidinium–caesium perovskites for over 200 cm2 photovoltaic sub-modules

Upscalable fabrication of efficient and stable perovskite solar modules is urgently needed for commercialization. Here we introduce methylammonium chloride additives in the co-solvent system of N-methyl-2-pyrrolidone/N,N-dimethylformamide to control the formation of intermediate phases during the growth of formamidinium–caesium lead triiodide perovskite films. We achieve high-quality films upon drying without the use of anti-solvent. By implementing bulk and surface passivation, champion efficiencies of 24.02% for a small-sized solar cell and 20.5% for a 5 cm × 5 cm solar mini-module on an aperture area of 22.4 cm2 (geometric fill factor ∼ 96%) are achieved by spin-coating. The fully blade-coated perovskite solar sub-module demonstrates a champion efficiency of 15.3% on an aperture area of 205 cm2. The solar mini-module exhibits impressive operational stability with a T80 lifetime of over 1,000 h at maximum power point tracking under continuous light illumination. Upscaling perovskite solar cells requires control of the crystallization of perovskite films over large areas. Here, the authors tailor the composition of the precursor ink and achieve 15.3% efficient solar cells over a 205 cm2 area without the use of anti-solvent.

The coprecipitation formation study of iron oxide nanoparticles with the assist of a gas/liquid mixed phase fluidic reactor

Coprecipitation is the most commonly used method to synthesize iron oxide nanoparticles (IONPs) due to its low cost and environmentally friendly synthesis process. Recently, several studies have proposed that the coprecipitation formation of IONPs is through the aggregation of initially formed primary particles. However, there are still lack of systematic researches about the room temperature coprecipitation formation process of IONPs under quick mixing mode. Here, a gas/liquid mixed phase fluidic reactor was specially designed, and the influences of reaction time, reaction pH and valence of iron ions on the coprecipitation formation of IONPs in quick mixing mode were studied. The NH3 gas was used as the alkaline reactant. At pH above 10.0, the iron ions promptly hydrolyzed and precipitated to form primary nanoparticles, and then the primary nanoparticles accreted to form Fe3O4 nanoparticles in 2 min 30 s. As the reaction pH increased from 2.5 to 9.5, extremely small particles gradually aggregated to form Fe3O4 nanoparticles. Large Fe3O4 nanoparticles with a mean diameter of ~ 8.1 nm were completely formed at pH 9.5. And a small amount of poorly crystalline intermediate phases including akageneite, ferrihydrite and goethite were observed during this process. When Fe2+ ions were absent during the reaction process, the final products had poor crystallinity and weak magnetic properties. While if only Fe2+ ions were used in the precursor, the sheet-like green rusts generated firstly, and Fe3O4 nanoparticles would gradually form on the surface of green rusts with the partial oxidation of Fe2+ ions. The results of regulating the reaction conditions especially reaction pH indicate that this reaction design can effectively reduce the formation of intermediate crystal phases.

Influence of pressure on the kinetics of ferroelectric phase transition in BaTiO3

The ferroelectric phase transition in barium titanate under pressure was studied within the framework of Landau – Ginzburg theory using differential scanning calorimetry. An innovative method for high-sensitive thermal measurements under pressure was demonstrated. It was shown that the relaxation process proceeds nonmonotonically with the formation of intermediate short-lived phases. It was established that polydomain ordering is preferred but the monodomenization of the sample is possible under certain conditions. A narrowing of the temperature hysteresis with increasing pressure was revealed. A new tricritical point in barium titanate crystals characterizing the changing of the phase transition has been experimentally determined and theoretically confirmed.

Magnesiothermic Reduction of Natural Quartz

In the current work, the metallothermic reduction of natural quartz by magnesium has been studied at 1373 K under different reaction conditions, i.e. quartz type, quartz particle size, Mg:SiO2 mole ratio and reaction time. The microstructure of reaction products was studied to illustrate the reaction progression through scanning and transmission electron microscopy techniques. X-ray diffraction analysis with Rietveld phase quantification was used to calculate the change in the amount of phases at different reaction conditions. The results showed that the Mg:SiO2 mole ratio strongly affects reaction mechanism and product characteristics such as phase content and microstructure. At lower Mg:SiO2 mole ratios, the reaction rate is fast at the beginning and the formation of a product layer consisting of different phases such as MgO, Si, Mg2Si, Mg2SiO4 and MgSiO3 around quartz particles limits the Mg diffusion. This phenomenon is more noticeable for larger quartz particle sizes where Mg should diffuse longer distance towards the quartz core to react with it. At higher Mg:SiO2 mole ratios, a significant amount of Si–Mg liquid alloy is formed during reaction where the high mobility of Mg in this liquid phase and cracking of quartz particles result in significantly higher reaction rate. Here the formation of intermediate phases is not significant and the products would be the mixture of MgO, Mg2Si, and either Si or Mg phases.

Elimination of Composition Segregation in 33Al-45Cu-22Fe (at.%) Powder by Two-Stage High-Energy Mechanical Alloying.

In the present work, complex powder alloys containing spinel as a minor phase were produced by mechanical alloying in a high-energy planetary ball mill from a 33Al–45Cu–22Fe (at.%) powder blend. These alloys show characteristics suitable for the synthesis of promising catalysts. The alloying was conducted in two stages: at the first stage, a Cu+Fe powder mixture was ball-milled for 90 min; at the second stage, Al was added, and the milling process was continued for another 24 min. The main products of mechanical alloying formed at each stage were studied using X-ray diffraction phase analysis, Mössbauer spectroscopy, transmission electron microscopy, and energy-dispersive spectroscopy. At the end of the first stage, crystalline iron was not found. The main product of the first stage was a metastable Cu(Fe) solid solution with a face-centered cubic structure. At the second stage, the Cu(Fe) solid solution transformed to Cu(Al), several Fe-containing amorphous phases, and a spinel phase. The products of the two-stage process were different from those of the single-stage mechanical alloying of the ternary elemental powder mixture; the formation of undesirable intermediate phases was avoided, which ensured excellent composition uniformity. A sequence of solid-state reactions occurring during mechanical alloying was proposed. Mesopores and a spinel phase were the features of the two-stage milled material (both are desirable for the target catalyst).

Utilization of Na2CO3 for intermediate phase formation in vanadium-zircon pigment synthesis

Zircon-based pigments have extensive usage in the ceramic industries because of their good thermal and chemical stability. Zircon pigments are conventionally produced by heating zirconia, silica, a mineralizer, and a coloring agent that is known as the solid-state route. Many innovative procedures have been developed to reduce production costs. One of them is called the intermediate production route that utilizes zircon as raw material instead of costly zirconia. Therefore zircon ones decompose to their ingredients and again form zircon but with coloring dopants. In this research, sodium carbonate was introduced for the intermediate production synthesis and all steps were studied exactly. The intermediate product is an alkaline silico-zirconate that was formed at a broad range of temperatures and its decomposition with HCl acid was studied. In this research, no washing was employed and there was no material loss. Be best quality pigment was obtained by the intermediate production synthesis at 850 °C and the pigment synthesis with 0.2 M ratio of V2O5/ZrO2 at 800 °C. This specimen has better quality than a commercial specimen.

Effect of milling duration on structural properties of polycrystalline bulk barium hexaferrite

Polycrystalline bulk Barium hexaferrite, BaFe12O19 were synthesised by ball milling for different milling duration followed by sintering at high temperature. Effect of milling duration on structural, morphological and dc electrical properties were studied for 4, 8, 12 and 16 h of milling using planetary ball mill. X-ray diffraction measurement data shows the formation of single phase barium hexaferrite which belongs to P63/mmc group for 8, 12 and 16 h milled samples. There is formation of intermediate phase along with M−phase of barium hexaferrite in 4 h milled sample. Inverse relation of the crystallite size and lattice strain was observed. The saturation value of crystallite size and maximum lattice strain were observed for 12 h milled sample. Morphological studies for 8 and 16 h milled samples reveals the formation of hexagonal plate like grains for the former and agglomerates with different grain size for the latter. High porosity for 8 h milled sample was observed by density measurements. Resistivity of the samples measured from I-V characteristics using 2 probe method exhibits maximum resistivity for 8 h milled sample and minimum resistivity for 12 h milled samples. Linear relationship was observed between electrical resistivity and porosity.

Cation inter-diffusion and formation of intermediate phases in CoO and La2NiO4+δ diffusion couples

Cation interdiffusion between La2NiO4+δ (LN) and CoO diffusion couples was investigated by thermal annealing in ambient air at 1200 °C for 48 and 168 h, and analysis of the cross sections by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Co diffusion into the LN layer was significant, while Ni diffusion into the CoO layer was minor. Formation of LaCoO3, LaCo0.5Ni0.5O3, and La3(Ni0.8Co0.2)2O7 were observed in the LN layer at increasing distance from the boundary.

Electronic structure and plasmonic activity in co-evaporated Ag-In bimetallic alloys

Thin Ag-In films, covering the whole range of compositions from 0 to 100 at% In, were deposited by thermal co-evaporation. Alloying and formation of solid solutions and intermediate phases were realized without further processing of the films. The phase composition was analyzed by X-ray diffraction. The spectra of the complex permittivity, ε were determined by spectroscopic ellipsometry and their compositional dependencies were traced out in terms of their electronic structure, calculated using the Density-functional theory (DFT). The analysis of the Lorentz component of the spectra of the complex permittivity showed that the increase of the indium content in the thin layers leads to a decrease in the number of electrons participating in the interband transitions with energies of 4–6 eV, which causes improvement of their plasmon activity in the ultraviolet spectral range. It was found out that the thin films containing intermediate Ag-In compounds in their structure are the most perspective for excitation of plasmon resonance in this spectral region of interest.

Изучение фазообразования при гетерогенном синтезе гидроксокарбоната алюминия-аммония

Synthesis of ammonium aluminium carbonate hydroxide NH4AlCO3(OH)2 from hydrated alumina received by ammonization of ammonia alums NH4Al(SO4)2·12H2O was studied. It was found the synthesis of NH4AlCO3(OH)2 occurs without the formation of intermediate phases.

Temperature-Dependent Crystallization Mechanisms of Methylammonium Lead Iodide Perovskite From Different Solvents

Hybrid perovskites are a novel type of semiconductors that show great potential for solution-processed optoelectronic devices. For all applications, the device performance is determined by the quality of the solution-processed perovskite thin films. During solution processing, the interaction of solvent with precursor molecules often leads to the formation of solvate intermediate phases that may diverge the crystallization pathway from simple solvent evaporation to a multi-step formation process. We here investigate the crystallization of methylammonium lead iodide (MAPbI3) from a range of commonly utilized solvents, namely dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), and gamma-butyrolactone (GBL) at different temperatures ranging from 40°C to >100°C by in-situ grazing-incidence wide-angle X-ray scattering (GIWAXS) measurements. For all solvents but GBL, we clearly observe the formation of solvate-intermediate phases at moderate processing temperatures. With increasing temperatures, an increasing fraction of the MAPbI3 perovskite phase is observed to form directly. From the temperature-dependence of the phase-formation and phase-decomposition rates, the activation energy to form the MAPbI3 perovskite phase from the solvate-phases are determined as a quantitative metric for the binding strength of the solvent within the solvate-intermediate phases and we observe a trend of DMSO > DMF > NMP > GBL. These results enable prediction of processing temperatures at which solvent molecules can be effectively removed.

Room Temperature Synthesis of [Pd(cyclam)]5{H3Nb6O19}2 ⋅ 26H2O: a Suitable Precursor for the in‐situ Generation of a Highly Active Catalyst for Light‐Driven Hydrogen Evolution

AbstractThe first Pd2+ containing polyoxoniobate [Pd(cyclam)]5{H3Nb6O19}2 ⋅ 26H2O (I) was prepared at room temperature. In the structure, two hexaniobate clusters are surrounded by a bi‐capped cube formed by Pd2+ centered complexes. This motif is arranged in a layer‐like fashion with crystal water molecules located between cations and anions. Temperature resolved in‐situ X‐ray diffraction experiments demonstrate that successive removal of the crystal water molecules leads to formation of several crystalline intermediate phases. Water sorption investigations show that thermally removed H2O can be successfully reintegrated proceeding via two distinct steps. The catalytic performance for the light‐driven hydrogen evolution reaction (HER) was investigated in a sacrificial system and fluorescein Na+ salt as sensitizer yielding a high value of 90 μmol/h H2. Surprisingly, a composite Pd@Na7[HNb6O19] ⋅ 15H2O is in‐situ formed during the catalytic reaction by cation exchange with simultaneous reduction of Pd2+ nanoparticles decorating the hexaniobate support. The recovered catalyst was even more active producing 157 μmol/h H2 with an apparent quantum efficiency of 1.85 %. Photocatalytic experiments performed with ex‐situ generated Pd nanoparticles deposited on Na7[HNb6O19] ⋅ 15H2O show much lower activities indicating a synergistic effect of the in‐situ generated Pd@Na7[HNb6O19] ⋅ 15H2O catalyst.

CuO/ZrO2 modified by WO3 oxygen carriers for chemical looping with oxygen uncoupling

The use of mixed metal oxides as oxygen carriers for chemical looping with oxygen uncoupling (CLOU) applications has shown great potential compared to single metal oxide-based oxygen carriers. In this work, the effects of adding WO3 to CuO/ZrO2 oxygen carriers on the oxygen capacity and rate indices for CLOU applications are investigated using nitrogen gas environment. Two synthesis methods were used to prepare the CuO-WO3/ZrO2 oxygen carriers, namely the coimpregnation and sequential impregnation, to evaluate the role of the oxygen carriers’ preparation method. The resulting oxygen carriers were thoroughly characterized using XRD, ICP-OES, SEM-EDS and H2-TPR characterization techniques to evaluate the physicochemical properties of the mixed oxide oxygen carriers. The oxygen transport capacity was found to significantly increase for the WO3-modified oxygen carriers compared with the single metal oxide CuO/ZrO2 which was due to the formation of a Cu-W intermediate phases that was found to enhance the redox characteristics of the oxygen carriers. Moreover, the sample synthesized via coimpregnation method displayed higher oxygen release capacity than the sequentially impregnated sample. This was ascribed to the formation a Cu-rich intermediate phase (Cu3WO6) possessing higher Cu/W ratio on the coimpregnated sample compared with a CuWO4-x phase with lower Cu/W ratio and larger crystallite structure formed on the sequentially impregnated oxygen carrier. The mixed metal oxide oxygen carriers also showed a stable redox performance which highlights the potential of WO3 as a modifier to Cu-based oxygen carriers to enhance the oxygen capacity and subsequently decrease the solids inventory. The proposed WO3-based promotors offer significant trait to synthesize Cu-based oxygen carriers with excellent properties for CLOU applications.