Phase Formation Process Research Articles

Origin of Ferroelectric Phase in Undoped HfO2 Films Deposited by Sputtering

AbstractThin film metal–insulator–metal capacitors with undoped HfO2 as the insulator are fabricated by sputtering from ceramic targets and subsequently annealed. The influence of film thickness and annealing temperature is characterized by electrical and structural methods. After annealing, the films show distinct ferroelectric properties. Grazing incidence X‐ray diffraction measurements reveal a dominant ferroelectric orthorhombic phase for thicknesses in the 10–50 nm range and a negligible non‐ferroelectric monoclinic phase fraction. Sputtering HfO2 with additional oxygen during the deposition decreases the remanent polarization. Overall, the impact of oxygen vacancies and interstitials in the HfO2 film during deposition and annealing is correlated to the phase formation process.

Recovery of flavonoids using novel biodegradable choline amino acids ionic liquids based ATPS

In this work, different ionic liquids composed by choline as cation and amino acid as anion (CAAILs) have been synthetized and applied to establish aqueous two-phase systems (ATPS) with two phosphate salts. In order to understand the phase formation process of the ATPS, binodal curves, tie-lines and their respective tie-line lengths were determined at T = 298.15 K and atmospheric pressure. Besides, the tie-lines were fitted using Othmer-Tobias and Bancroft equations. Furthermore, with the aim to analyse the application of the studied ATPS in the recovery of flavonoids, partition coefficients of rutin and quercetin were calculated at T = 298.15 K and atmospheric pressure. Finally, the obtained results were compared with those found in literature.

Изучение фазового состава продуктов электрохимического окисления сульфидных гранул системы Cu1.96S–Ni3S2–Cu–Ni

The crystallization rate of copper and nickel sulfides influences on the phase formation processes. The high crystallization rate (about 103 degrees/s), achieved through granulation of the sulfide copper-nickel melt, leads to the stabilization of non-stoichiometric phases, the formation of ultrafine structures, which are grains and partial dissolution of the metal component in the sulfide. The structure of the granules is formed by nickel sulfide (Cu1.96S) phases in the form of dendritic inclusions of 2-20 µm in size in the nickel sulfide phase (Ni3S2). According to the phase diagram of the state of Cu – Ni – S, a solid solution of Cu – Ni may be present in the composition of eutectic compounds with copper and nickel sulphides. The electrochemical oxidation of copper and nickel sulfides in a solution of sulfuric acid occurs through a series of successive phase transformations described in the work, during which the conversion of sulfides occurs in intermediate oxidation states oxidizing to the elemental state: Cu1.96S → Cu1.8S → Cu1.75S → CuS → S; Ni3S2 → NiS → S. The non-stoichiometric composition of compounds suggests the presence of excessive or deficient sulfur and metal contents in the crystal lattice, which can affect the mechanism and sequence of phase transformations during the electrochemical oxidation of sulfide granules. Dissolution occurs not only on the surface of the granules, but also along the grain boundaries. The leached areas form capillaries inside the granules, through which electrolyte enters the electrochemical reactions. Porous sulfur sulfide sludge forms on the surface of the granules. The phase composition of the sludge was studied. The main phase components of poorly soluble products are nickel granules Ni3+хS2–Cu2-хS.

Synthesis, formation process, and luminescence properties of well-defined NaGd(MoO4)2 hollow spheres

Well-defined NaGd(MoO4)2 hollow spheres have been synthesized by a template-directed route with 3-aminophenol-formaldehyde (APF) resin as template. During the synthesis process, the core-shell structured precursor was fabricated via a homogeneous precipitation and subsequent solvothermal method. Finally, the crystalline NaGd(MoO4)2 hollow spheres were obtained after an annealing process. The phase structure, morphology, formation process, and luminescence properties of the NaGd(MoO4)2 hollow spheres were systematically investigated. The excellent down- and up-conversion multicolor emissions can be realized by doping appropriate lanthanide ions (Ln3+) into the NaGd(MoO4)2 host matrix. Furthermore, this synthesis strategy may pave a critical way for the design and preparation of other hollow spherical molybdates functional materials.

Operando soft X‐ray microscope study of rechargeable Zn–air battery anodes in deep eutectic solvent electrolyte

Zn–air batteries are very promising devices for energy storage at high energy density due to their intrinsic safety, environmental friendliness, and low cost, but still, there are key issues to be solved to get to the industrial scale. One of the unsolved problems is the poor cyclability of batteries based on aqueous solvents that urges to consider nonaqueous solvents. Among different possible options are deep eutectic solvents, which are cost‐effective and technologically relatively easy to implement. The present investigation reports for the first time an operando scanning soft X‐ray microscope analysis of the Zn behaviour in a choline–chloride/urea deep eutectic solvents electrolyte during the cathodic and anodic phase formation processes taking place in battery charge and discharge, providing a platform for in‐depth space–time dependent investigations of the chemistry of crystallites evolving during potential cycling. These operando measurements have been enabled by the construction of a novel wet cell, improving the design and filling protocol of earlier generation cells developed by authors.High‐resolution soft X‐ray microscope images were acquired in two modes: (a) dynamic mode at a fixed beam energy, allowing to follow morphology evolution under electrochemical control and (b) static mode for selected morphologies representative of characteristic Zn growth and dissolution steps.

Toward an Atomic-Scale Understanding of Electrochemical Interface Structure and Dynamics.

For the knowledged-based development of electrochemical processes, a better fundamental understanding of the interfaces between electrodes and electrolytes is necessary. This requires insight into the interface structure and dynamics on the atomic-scale, including that of the liquid electrolyte in the near-surface region, i.e., in the inner and outer part of the electrochemical double layer. This perspective describes current studies of simple and well-defined electrochemical interfaces by first-principles electronic structure calculations and in situ structure-sensitive methods. It is shown that these experimental and theoretical studies are now approaching a level, where they can operate on the same footing, making direct comparison of the obtained results feasible. Using selected examples, progress in clarifying the structure and dynamics of the double layer, of adsorbed species on electrode surfaces, and of initial steps in electrochemical phase formation processes is discussed.

Peculiarities of Phase Formation Processes in Activated Ti + Al Powder Mixture during Transition from Combustion Synthesis to High-temperature Annealing

ABSTRACTIn the present work, the experimental study of the features of phase formation processes in preliminary mechanically activated powder mixture Ti+Al was conducted. The synthesis was realized in the thermal explosion mode with the use of microwave heating. It was established that in the case of a continuous transition from the fast heating mode (thermal explosion) to the high-temperature annealing regime the structural relaxation processes occurs. These processes lead to equalization of the phase composition in the volume of the mixture and formation of the almost single phase compound TiAl. At later stages of annealing, the transition to thermodynamic equilibrium state takes place. This process is accompanied by formation of compounds which are in equilibrium with each other at a given temperature.

Strain‐Induced Dissolution and Precipitation of Secondary Phases and Synergetic Stengthening Mechanisms of Al–Zn–Mg–Cu Alloy during ECAP

The evolution of secondary phase of 7A60 aluminum alloy before and after equal channel angular pressing (ECAP) deformation and the resultant variation of mechanical properties are studied by means of X‐ray diffractometer (XRD), transmission electron microscopy (TEM), optical microscope (OM), and Instron testing machine. The results show that grains are refined to submicron level after ECAP (from 9.86 µm to about 1 µm). As the strain increases, the main secondary phase (MgZn2) dissolves into the aluminum matrix to form a supersaturated solid solution. Part of the solute atoms diffuses along the vacancies and dislocations under the combined effect of interface energy, strain energy, and grain boundary energy. In addition, grain boundary segregation occurs and further leads to relatively coarse secondary phase. With the increase of temperature, discontinuous precipitation (DP), which occurs from the grain boundary to the grain internal, dominates the formation process of secondary phases. The phase transformation brings about significant precipitation strengthening, resultantly, enhances strength, and ductility are achieved for 7A60 aluminum alloy via ECAP. Moreover, the precipitation strengthening effect, which is closely related with the dissolution and DP, first enhances and then attenuates with the increase of ECAP passes. Dislocation strengthening and Hall‐Petch strengthening aggravate monotonically with the ECAP passes but play less important roles in the overall stress responses.

Interfacial phenomena associated with Li electrodeposition on liquid Ga substrates in propylene carbonate

Li electrodeposition on liquid Ga substrates was carried out in PC-LiClO4 at 40 °C. It was found that interfacial flow phenomena were induced by differences in interfacial tension between the liquid Ga and the liquid Ga-Li alloy formed on the substrate under potentiostatic electrolysis at −1.0 V (vs. Li+/Li), which caused the interfacial shape change of the liquid Ga electrode. We carried out in-situ observations in order to understand why such interfacial phenomena occur between the liquid electrolyte and the liquid metal cathode. Moreover, a significant difference in electrochemical response between liquid and solid Ga substrates was also noticed employing the current-time transient technique. These experimental results suggest that the process of liquid Ga-Li phase formation by the dissolution of electrodeposited Li atoms into the liquid Ga substrate dominated during the initial stage of Li electrodeposition. In contrast, the typical peaks induced by growth of solid Ga-Li alloy phase and Li metal phase were observed on solid Ga substrates. These results provide new insight into the design of electrochemical processing involving liquid electrolyte/liquid metal interface.

Growth mechanism of black phosphorus synthesized by different ball milling techniques

Black Phosphorus (BP), a layered structure material with good electrical conductance, has been applied in many occasions and it can be synthesized by many methods including ball milling. However, there lacks a clear understanding about the growth mechanisms. In this paper, we adopt three different ball milling techniques (planetary milling, shake milling and plasma-assisted ball milling) to synthesize BP samples and investigate the mechanism of the formation processes. It is found that BP can be successfully synthesized by all these three ball milling techniques and the (020) orientation is preferential during the milling formation processes. And mechanical energy plays an important role in the conversion process of RP to BP by ball milling. The higher mechanical energy could reduce the milling time and improve crystallinity of the synthesized BP. Furthermore, the huge mechanical energy produced in a short time can form a local high energy intensity area, which is beneficial to the phase transition and formation process. The pressure on the sample powders, formed by the impact between balls and between the balls and the vessel wall, is the main influencing factor affecting the transformation process of RP to BP compared with temperature (additional temperature, not the local temperature generated during the milling process). The synthesized BP based composite presents excellent electrochemical performance as lithium ion battery anode material. This work opens new gateway on facile synthesis of BP for various energy applications.

Mechanisms of the formation of phases in mechanosynthesis of Fe–C alloys

Based on the analysis of the literature data, the phase formation processes in alloys of the Fe-C system are compared in mechanical alloying and quenching of melts. It is shown that there are common features between these processes. In addition, the types of phases formed coincide. From this it is concluded that, as in the quenching of melts, thermally activated processes of nucleation and growth play an important role in the formation of phases during mechanical alloying. The heat required for these processes is stored by the alloy during deformation.

Effect of Ultrasonic Treatment on Phase Formation Processes in Amorphous Alloy Fe76Ni4Si14B6

Effect of Ultrasonic Treatment on Phase Formation Processes in Amorphous Alloy Fe76Ni4Si14B6

Superior Stability and Dynamic Performance of Single Crystal LiNi1/3Co1/3Mn1/3O2 Nanorods from β-MnO2 Template for Lithium-Ion Batteries

Single crystal LiNi1/3Co1/3Mn1/3O2 nanorods cathode material with diameter of about 250 nm have been successfully synthesized via a facile template method followed with heat-treatment, using single crystal β-MnO2 nanorods as self-template and Mn source. The structural changes of LiNi1/3Co1/3Mn1/3O2 nanorods during phase formation and first charge-discharge process are further explored by ex-situ XRD characterization, demonstrating the excellent structural reversibility for long cycling. The electrochemical measurements reveal that LiNi1/3Co1/3Mn1/3O2 nanorods exhibit excellent rate performance with a high discharge capacity of 100.5 mAh g−1 at 5 C. Particularly, the materials can deliver an excellent discharge capacity of 170.5 mAh g−1 with a capacity retention of 90.2% at 0.5 C after 200 cycles. The improved electrochemical properties are ascribed to the short Li-ion transport pathways along diameter direction, large surface-to-volume ratio and excellent strain relaxation of LiNi1/3Co1/3Mn1/3O2 nanorods, which could facilitate the diffusion of Li-ion and structural stability.

Фазообразование, структура и ионная проводимость антимонат-молибдатов серебра

Silver antimonate-based compounds, formed at partial substitution of ions of quinquevalent antimony with ions of hexavalent molybdenum, have been synthesized using the method of solid-phase reaction. Specificities of phase formation processes of mixtures with various mole ratios of the initial components of a system containing silver nitrate and oxides of trivalent antimony and hexavalent molybdenum have been studied in a wide temperature range from 300 to 1023 K. Using the thermogravimetric analysis data, optimal temperatures for synthesis of powders have been determined. Using the method of qualitative X-ray phase analysis together with the method of high-temperature X-ray diffraction, compositions of reaction products of solid-phase interaction at open air heating have been determined. For the temperature of 1023 K, a homogenous area of formation of a solid solution of silver antimonat-molibdates with the structure of a defective pyrochlore-type within 0,0 ≤ x ≤ 2,0 concentration interval has been determined. In the frameworks of Fd-3m spatial group, a full-profile analysis (the Rietveld method) has been carried out to specify the crystal structure (coordinates of population of ions by crystallographic positions, elementary cell parameters), and interrelation in compositions of the obtained pyrochlore phases with their structural disorder and ion-conducting properties has been determined. Ceramic properties (relative density and average size of particles) of the samples sintered at the temperature of 1373 K have been studied.

Template-directed synthesis, properties, and dual-modal bioapplications of multifunctional GdPO4 hierarchical hollow spheres

Well-defined GdPO4 hierarchical hollow spheres have been synthesized via a novel template-directed synthesis approach with 3-aminophenol-formaldehyde resin spheres as template. The core-shell structured precursor was firstly prepared by a homogeneous precipitation and subsequent hydrothermal route. Finally, the GdPO4 hollow spheres were obtained after an annealing process in air. The phase structure, morphology, and formation process were also investigated in detail. Moreover, the as-synthesized GdPO4 hollow spheres show good biocompatibility and excellent drug loading and sustained drug release ability. Interestingly, the lanthanide activator ions doped GdPO4 hollow spheres exhibit multimodal imaging functionality for combined optical and magnetic resonance imaging (MRI). Due to the well-defined hollow structure, good biocompatibility, luminescence properties, positive magnetic signal-enhancement ability, and drug loading/release patterns, the as-obtained GdPO4 samples may be potentially applied in fields of bioimaging, drug delivery, and disease diagnosis. Furthermore, this novel synthetic strategy may pave a critical way for the preparation of other similar lanthanide orthophosphate functional materials with perfect hollow spherical structure, tunable particle sizes, and good physicochemical properties.

Studying the physicochemical regularities in the color- and phase formation processes of clinker ceramic materials

The paper reports results of a comprehensive study, aimed at developing formulation-technological parameters for obtaining volumetrically dyed clinker ceramic materials with a wide range of colors. A possibility has been proven to obtain a ceramic clinker when using the polymineral clay raw materials at a temperature of 1,100 °C. The expediency has been shown to replace expensive ceramic pigments in the composition of masses with anthropogenic materials containing the oxides of metals with variable valency: wastes from alkaline earth syenite extraction, pegmatite enrichment, and production of ferrotitanium alloys. This shows possibilities for reducing the production cost of clinker ceramic articles. The influence of the formulation of raw materials compositions on the processes of color- and phase-formation of ceramic clinker has been investigated, depending on the character of furnace atmosphere. It was established that the brown coloration of clinker ceramics under conditions of oxidative annealing is predetermined by the presence of phases of hematite α-Fe 2 O 3 and Mn 2 O 3 . At annealing in a reducing medium, products acquire color in the range from dark brown to black at the expense of formation of magnetite Fe 3 O 4 and gaussmanite Mn 3 O 4 . The products' terracotta color is due to the presence of phases of hematite and hedenbergitis CaFeSi 2 O 6 . The condition for obtaining clinker ceramics of yellow color is to limit the formulation's content of Fe 2 O 3 to 3 % by weight, as well as the presence of the SiO 2 rutile phase. The paper illustrates the effect of the overall content of oxides of metals with a variable valence S(Fe 2 O 3 +FeO+MnO+Mn 3 O 4 ) on the coloration characteristics of clinker ceramics. The ratios have been derived between the phase-forming oxides Fe 2 O 3 /(Al 2 O 3 +CaO), (Fe 2 O 3 +Mn 2 O 3 )/(FeO+Mn 3 O 4 ) and TiO 2 /(Al 2 O 3 +CaO), as well as the limits in their variation, providing for the formation of color-carrying phases responsible for obtaining products of the desired color under conditions of oxidative and reductive annealing

Granularity impact on hotspot formation and local chemistry in shocked nanostructured RDX

The nanostructuration of energetic materials results in interesting properties. In particular, the detonation of carbon-rich explosives leads to the formation of nanodiamonds, the size of which is linked to the initial size of the explosive nanograins. This correlation could come from the role played by the granularity in the shock properties, especially the local temperature, which could be enhanced when the shock front crosses the various interfaces and nanoporosities of the material. More generally, the granularity-dependent reactivity also concerns some aspects of the sensitivity of energetic materials and subsequent inhibition or safety issues. In order to investigate this hypothesis, we perform classical and reactive molecular dynamics shock-simulations on cyclotrimethylene trinitramine (RDX), a common high-explosive. We design various nanogranular structures using the body-centered-cubic stacking of nanoparticles shaped as Kelvin cells (truncated octahedra) with slightly-bumped faces. The nanograin size and the bump radius allow to independently control the porosity value and its nanostructure. We show that the global shock properties, especially the temperature, are sensitive to the porosity value but not to the nanograin size. The porosity nanostructure has a local impact, enhancing the temperature heterogeneities between the inter- and intra-grain regions by a few hundred degrees and slowing down the thermal homogenization. For a given porosity, the larger the nanograins, the larger and the hotter the hotspots. In such hotspots, the local chemistry is significantly modified, resulting in a larger reactivity with a quicker formation of some final products. We suggest that the quicker consumption of heteroatoms (namely, H, O, and N) along with higher local temperatures is likely to impact the formation process of solid carbonaceous phases.

Time-dependent carbide phase formation in palladium nanoparticles

Palladium-based catalysts are widely applied for the selective hydrogenation of acetylene in acetylene/ethylene mixtures. Under reaction conditions, palladium hydride or carbide phases can be formed, which change the catalytic properties of material. In the current work, we focus on the process of carbide phase formation in supported palladium nanoparticles (NPs) exposed to acetylene and ethylene at 100 °С. The evolution of carbide phase was monitored in situ by X-ray absorption near edge structure (XANES) spectroscopy, extended X-ray absorption fine structure (EXAFS) spectroscopy and X-ray powder diffraction (XRPD). The degree of the lattice expansion determined by XRPD and EXAFS was extrapolated to obtain the saturated values, which were found to be similar for ethylene- and acetylene-exposed samples, while the rate of carbide formation was higher in the case of acetylene.

Effect of calcium and lithium on alkali-silica reaction kinetics and phase development

This study aims to investigate the influence of lithium and calcium content on the alkali-silica reaction kinetics and phase formation processes at atomic scales. The atomic structure of the reacted ASR gels was analyzed with the Pair Distribution Function (PDF) measurement. The analysis results can explain the expansion potential difference of gels with different chemical composition. The in situ PDF characterizations of the samples containing lithium compounds identified the formation of the LiSi phase, and thus both the alkali-silica reaction and the reaction between dissolved silica and Ca(OH)2 were suppressed. The alkali-silica reaction kinetics was further indicated with the changes of SiO peak intensity. The amorphous structure of the generated LiSi phase was confirmed with in situ XRD tests. The results strongly support the formed amorphous LiSi phase can act as a surface barrier for silica dissolution, and thus prohibit both the alkali-silica reaction and pozzolanic reaction in hardened concrete.

Structurization, Phase Rule Diagram, Relaxation Processes and Radio-Absorbing Properties of Solid Solutions Based on a Binary System BaNb2O6-SrNb2O6

The investigation results of the processes of phase formation in barium niobate, strontium, and their solid solutions in the conditions of the variability of the thermodynamic background are presented. The formation of a grain landscape and dielectric properties (including relaxation phenomena) in the solid solutions of strontium niobate and their solid solutions and the establishment of regularities in the formation of radio-absorbing properties in them are studied.