Solid Transformation Research Articles

Electrical properties of (1−x) BFO – (x) PZT multiferroics synthesized by sol-gel method: Transition from relaxor to non-relaxor

Crystalline solutions of (1−x) BiFeO3 – (x) Pb(Zr0.52Ti0.48)O3 within the composition range 0.50 ≤ x ≤ 1.00 have been made by the sol-gel route. Solid solution formation and structural transformations have been confirmed by diffraction studies. Electrical behaviour of solid solution compositions have been studied at a few selected frequencies in the temperature range 35 °C–600 °C. Overall, three dielectric anomalies have been observed for compositions 0.50 ≤ x ≤ 0.70 whose positions have been found to shift to low temperature side with increasing x and reduced to one broad anomaly at ∼385 °C for x = 1.0. A switching from relaxor behaviour for 0.50 ≤ x ≤ 0.90 to non relaxor behaviour for x = 1.0 has been observed. All the samples have shown low dielectric loss near room temperature. Temperature dependent conductivity variation indicates an Arrhenius type thermally activated process via localized hopping of electrons in the low temperature region. Small polaron and oxygen vacancy motion dominate at intermediate and high temperature range respectively.

Characterization, thermal stability, and solid-state phase transition behaviors of gestodene polymorphs and amorphous phase

In the current work, a systematic investigation on the thermal behavior of gestodene was carried out to understand temperature induced solid-state transitions between its polymorphs and amorphous phase. The focus was on polymorph identification, thermal stability analysis, and the nature of the phase transitions. These characteristics were compared to the complexity of the phase transitions, studied by differential scanning calorimetry (DSC) and variable temperature X-ray powder diffraction (VT-XRD) techniques. DSC studies indicated that the form II was enantiotropically related to form I, which melted at about 470 K. The temperature of polymorphic transition was 309 K, and form II was the more stable form between room temperature and the transition temperature. A schematic Gibbs free energy-temperature diagram was subsequently constructed to describe the thermal stability of the two forms. Amorphous phase converted exothermically to form I at 368 K on heating and was shown by VT-XRD to be accompanied by diffraction pattern changes. In addition, the crystallization kinetics studied by DSC heating technique followed by analysis using the Kissinger–Akahira–Sunose (KAS) method where values of apparent activation energy (E a) were estimated as a function of extent of conversion (α). The variations in E a with α on kinetic analysis from α = 0.10 to 0.88 for the amorphous to form I conversion suggested more complex processes, possibly liquid–solid and solid–solid transformations prior to formation of the form I.

Thermodynamic Model Formulations for Inhomogeneous Solids with Application to Non-isothermal Phase Field Modelling

Abstract The purpose of the current work is the comparison of thermodynamic model formulations for chemically and structurally inhomogeneous solids at finite deformation based on “standard” non-equilibrium thermodynamics [SNET: e. g. S. de Groot and P. Mazur, Non-equilibrium Thermodynamics, North Holland, 1962] and the general equation for non-equilibrium reversible–irreversible coupling (GENERIC) [H. C. Öttinger, Beyond Equilibrium Thermodynamics, Wiley Interscience, 2005]. In the process, non-isothermal generalizations of standard isothermal conservative [e. g. J. W. Cahn and J. E. Hilliard, Free energy of a non-uniform system. I. Interfacial energy. J. Chem. Phys. 28 (1958), 258–267] and non-conservative [e. g. S. M. Allen and J. W. Cahn, A macroscopic theory for antiphase boundary motion and its application to antiphase domain coarsening. Acta Metall. 27 (1979), 1085–1095; A. G. Khachaturyan, Theory of Structural Transformations in Solids, Wiley, New York, 1983] diffuse interface or “phase-field” models [e. g. P. C. Hohenberg and B. I. Halperin, Theory of dynamic critical phenomena, Rev. Modern Phys. 49 (1977), 435–479; N. Provatas and K. Elder, Phase Field Methods in Material Science and Engineering, Wiley-VCH, 2010.] for solids are obtained. The current treatment is consistent with, and includes, previous works [e. g. O. Penrose and P. C. Fife, Thermodynamically consistent models of phase-field type for the kinetics of phase transitions, Phys. D 43 (1990), 44–62; O. Penrose and P. C. Fife, On the relation between the standard phase-field model and a “thermodynamically consistent” phase-field model. Phys. D 69 (1993), 107–113] on non-isothermal systems as a special case. In the context of no-flux boundary conditions, the SNET- and GENERIC-based approaches are shown to be completely consistent with each other and result in equivalent temperature evolution relations.

Wet‐Chemical Processing of Phosphorus Composite Nanosheets for High‐Rate and High‐Capacity Lithium‐Ion Batteries

Phosphorus‐based materials are promising for high‐performance lithium‐ion battery (LIB) applications due to their high theoretical specific capacity. Currently, the existing physical methods render great difficulty toward rational engineering on the nanostructural phosphorus or its composites, thus limiting its high‐rate LIB applications. For the first time, a sublimation‐induced synthesis of phosphorus‐based composite nanosheets by a chemistry‐based solvothermal reaction is reported. Its formation mechanism involves solid–vapor–solid transformation driven by continuous vaporization–condensation process, as well as subsequent bottom‐up assembly growth. The proof‐of‐concept LIBs composed of the phosphorus‐based nanosheets achieve a high capacity of 630 mAh g−1 at an ultrahigh current density of 20 A g−1, which is attributed to efficient lithium‐ion diffusion and electron transfer. Such simple sublimation‐induced transformation opens up new prospects for rational engineering of phosphorus‐based materials for enhancing electrochemical performance.

Determination of the stretch tensor for structural transformations

Structural transformations in crystalline solids are increasingly the basis of the functional behavior of materials. Recently, in diverse alloy systems, both low hysteresis and reversibility of phase transformations have been linked to the satisfaction of the nongeneric conditions of compatibility between phases. According to the Cauchy–Born rule, these conditions are expressed as properties of transformation stretch tensor. The transformation stretch tensor is difficult to measure directly due to the lack of knowledge about the exact transforming pathway during the structural change, and the complicating effects of microstructure. In this paper we give a rigorous algorithmic approach for determining the transformation stretch tensor from X-ray measurements of structure and lattice parameters. For some traditional and emerging phase transformations, the results given by the algorithm suggest unexpected transformation mechanisms.

Rapid solidification and liquid-phase separation of undercooled CoCrCuFexNi high-entropy alloys

Fluxing and cyclic superheating technique was used to investigate the rapid solidification behavior of CoCrCuFexNi (x = 1.0, 1.5, 2.0, molar concentration) high-entropy alloys in this study. The microstructures of CoCrCuFexNi (x = 1.0, 1.5, 2.0) high-entropy alloys solidified at different undercoolings (ΔT) were investigated. Liquid-phase separation leading to Cu-rich and Cu-depleted regions, were obtained in the solidified microstructure from highly undercooled melt. This occurs when the melt undercooling exceeds a critical undercooling (ΔTcrit) of 160 K for CoCrCuFeNi, 190 K for CoCrCuFe1.5Ni and 293 K for CoCrCuFe2Ni alloy. However, typical dendrites and interdendritic regions were observed in rapid-solidified CoCrCuFexNi alloys prepared from melts with a small undercooling (ΔT < ΔTcrit). Conversely, a large amount of Cu-rich spheres and even egg-type structures were observed in alloys solidified from melts with large degree of undercooling, ΔT in excess of the critical value, ΔTcrit. A large amount of Cu-rich nano-phases were found in the matrix, possibly, due to the precipitation of Cu-rich phase from the supersaturated solid solution obtained during solidification. The positive enthalpies of mixing between Cu and the other elements in the multi-component alloys resulted in the occurrence of liquid-phase separation prior to the liquid–solid transformation starts. The sluggish diffusion effect of high-entropy alloys and rapid solidification play an important part in the precipitation of nanophase during the solid-state transformation in the Cu-based matrix. Similar to other immiscible alloys, liquid-phase separation occurred when a critical undercooling was exceeded. Differently, nanophases were found in the microstructures of multi-component CoCrCuFexNi (x = 1.0, 1.5, 2.0) alloys.

Kinetics of the (solid + solid) transformations for the piracetam trimorphic system: Incidence on the construction of the p–T equilibrium phase diagram

The three common polymorphs of piracetam have been characterized by associating thermal analysis, X-ray diffraction and densimetry. DSC experiments showed that the (solid+solid) transition temperature between Forms II and I and between Forms III and I is scan-rate dependent. The transition temperatures decrease when the DSC scan rate decreases and the thermodynamic temperatures were confirmed by isothermal X-ray diffraction.These new results in terms of temperature and enthalpy of transition allow us to propose a new equilibrium phase diagram establishing the relative thermodynamic stability of the three common polymorphs of piracetam as a function of the temperature and the pressure.The diagram suggests that Form II presents a small stability domain located just above the stability domain of Form I. As a consequence, Form I should transform into Form II, which itself can turn into Form III when placed under pressure.

Solid-state electrochemistry on the nanometer and atomic scales: the scanning probe microscopy approach.

Energy technologies of the 21(st) century require an understanding and precise control over ion transport and electrochemistry at all length scales - from single atoms to macroscopic devices. This short review provides a summary of recent studies dedicated to methods of advanced scanning probe microscopy for probing electrochemical transformations in solids at the meso-, nano- and atomic scales. The discussion presents the advantages and limitations of several techniques and a wealth of examples highlighting peculiarities of nanoscale electrochemistry.

In situ monitoring of vapour-induced assembly of pharmaceutical cocrystals using a benchtop powder X-ray diffractometer.

We describe a simple setup for in situ continuous monitoring of vapour-induced transformations of organic solids using a benchtop powder X-ray diffractometer. Proof-of-principle application of this setup to model pharmaceutical cocrystals reveals complex reactivity, transformations of reaction intermediates within minutes, and a simple route to the rarely observed monoclinic form of the pharmaceutical cocrystal of carbamazepine and saccharin.

A phase-field approach to nonequilibrium phase transformations in elastic solids via an intermediate phase (melt) allowing for interface stresses.

A phase-field approach for phase transformations (PTs) between three different phases at nonequilibrium temperatures is developed. It includes advanced mechanics, thermodynamically consistent interfacial stresses, and interface interactions. A thermodynamic Landau-Ginzburg potential developed in terms of polar order parameters satisfies the desired instability and equilibrium conditions for homogeneous phases. The interfacial stresses were introduced with some terms from large-strain formulation even though the small-strain assumption was utilized. The developed model is applied to study the PTs between two solid phases via a highly disordered intermediate phase (IP) or an intermediate melt (IM) hundreds of degrees below the melting temperature. In particular, the β ↔ δ PTs in HMX energetic crystals via IM are analyzed. The effects of various parameters (temperature, ratios of widths and energies of solid-solid (SS) to solid-melt (SM) interfaces, elastic energy, and interfacial stresses) on the formation, stability, and structure of the IM within a propagating SS interface are studied. Interfacial and elastic stresses within a SS interphase and their relaxation and redistribution with the appearance of a partial or complete IM are analyzed. The energy and structure of the critical nucleus (CN) of the IM are studied as well. In particular, the interfacial stresses increase the aspect-ratio of the CN. Although including elastic energy can drastically reduce the energy of the CN of the IM, the activation energy of the CN of the IM within the SS interface increases when interfacial tension is taken into account. The developed thermodynamic potential can also be modified to model other multiphase physical phenomena, such as multi-variant martensitic PTs, grain boundary and surface-induced pre-melting and PTs, as well as developing phase diagrams for IPs.

Insight into a direct solid–solid transformation: a potential approach for the removal of residual solvents

A simple humidity process allows a direct solid–solid transformation from the solvate (methanol trihydrate of cAMPNa) to its hydrate form (pentahydrate).

Fabricating organometallic wheel-and-axle compounds for the creation of dynamically porous crystalline materials

A family of organometallic compounds has been designed based on half-sandwich ruthenium complexes [(arene)Ru(L)X2] (X = Cl, I); this showed dynamic host–guest properties towards volatile molecules, caused by small local reversible structural rearrangements. These features are derived from the supramolecular organization of the compounds in the solid state, based on a so-called wheel-and-axle pattern, which is known to favour guest inclusion. The molecular features of the Ru complexes (arene size and shape, ligand size and chemical properties, and halogen nature) were screened in order to optimize the final performance of the materials. The design strategy has proven to be successful, affording materials capable of allowing dynamic exchange of volatile molecules by gas–solid processes and solid–solid transformations without loss of crystallinity.

Advances of solution chemistry in stabilizing different crystal phases of inorganic nano-compounds

Control of crystal structures is essential to tailor the properties of inorganic polymorphic materials for specific applications. For conventional solid transformations, re-arrangement of structural units is usually done at high temperatures and/or pressures (Dalton Trans., 2012, 41, 11927–11948). Such a case could become relatively mild when using solution chemistries, as there is unique reaction medium that allows for formation or transformation to the desired crystal phase through atomic-level cation–anionic interaction, providing potential opportunities for crystal structure control. In this paper, research progress of solution chemistry is highlighted in crystal phase-controlled synthesis of inorganic nano-compounds such as simple metal oxides, chalcogenides, halides, oxysalts etc. After briefly introducing crystal phase diversity and phase-dependent properties of inorganic nano-compounds, the discussion focuses on the critical driven items in the solution reactions such as precursor, pH value, solvents, ions, and water, as well as kinetic factors. Eventually, based on the current research status of the crystal phase-controlled synthesis of inorganic nano-compounds, some perspectives are provided on the challenges and opportunities in this emerging research field.

Municipal sludge characteristic changes under different aerating condition in a deep-shaft aeration system

A pilot-scale municipal sewage sludge deep-shaft aeration system was implemented in Lanzhou, Gansu Province of China. The reactor depth was 60 m with a diameter of 1.0 m and the sludge to be treated came from a wastewater plant in Lanzhou. In order to obtain the optimum operation conditions, analysis was conducted on the transformations of the volatile suspended solids (VSS), temperature, pH, oxidation-reduction potential (ORP) and pathogens in the deep-shaft reactor under different aeration conditions. Attention was paid to how operating conditions affected the removal efficiency of the VSS and the reaction temperature. As a result, higher volatile solids removal was gained at higher temperature, and the temperature could reach 50.8°C for a complete inactivation of bacteria in the first reaction zone when the deep-shaft aeration system was run for about 18 days. The sludge aeration rate was observed as 1.5 to 1.8 L/(h·L sludge) which enabled the volatile solids removal rate to reach 40.1%. The degradation of VSS occurred under a micro-oxygen environment, and the lowest ORP was found to be -256 mV in the digestive process. Not only aerobic bacteria but also anaerobic and facultative bacteria performed their functions in the reactor.

Controllable synthesis of CdS nanowire by a facile solvothermal method and its temperature dependent photoluminescent property

CdS nanowires with controllable size, orientation, and morphology were synthesized on a large scale by a solvothermal method. The mechanism for the formation of CdS nanowires evolved from CdS spherical particles can be divided into a short-period solid–solid transformation process and a long-period ripening process. Near-band-emission without distinct split phenomenon was observed in the PL spectrum of CdS nanowires at 10 K. The best fit results based on Varshni empirical equation support our assignment of FX. Temperature dependent integrated peak intensity and linewidth of FX were analyzed by means of a two-step quenching process model and well fitted by Toyozawa's theory. All fitted results including thermal activation energy, LO-phonon energy were close to that observed in bulk CdS, indicating high quality of nanomaterial but also revealing its promising applications in photonics.

Cu3TaSe4 and Cu3NbSe4: X-ray diffraction, differential thermal analysis, optical absorption and Raman scattering

Polycrystalline samples of Cu3NbSe4 and Cu3TaSe4 were obtained by the melt and anneal technique. X-ray diffraction patterns show that both materials are single phase and crystallize in the P4¯3m (215) space group. Thermal transitions were obtained by Differential Thermal Analysis (DTA), founding that Cu3TaSe4 and Cu3NbSe4 melts incongruently at 1328 and 1206 K, respectively; several transitions were observed at lower temperatures suggesting successive solid to solid transformations. The optical gap energy of the samples at ambient conditions were measured using the optical absorption technique, the obtained the values were 2.43 eV (indirect gap) for Cu3TaSe4 and 2.14 eV (indirect gap) and 2.45 eV (direct gap) for Cu3NbSe4, respectively. For Cu3TaSe4, the optical band gap was also measured under high pressure in the diamond anvil cell in the pressure range of 0–5.5 GPa, the resulting pressure coefficient is negative with a value of −0.032 eV/GPa. Focalized micro-Raman scattering under high pressure in a diamond anvil cell was performed on Cu3TaSe4 and Cu3NbSe4 polycrystalline samples. The variation of the frequencies as a function of pressure of the respective modes was obtained up to the phase transitions observed in the pressure range 13.7–16.2 GPa for both compounds.

B11-O-11Atomic-scale Tracking Cation Diffusion in Lithium Manganese Oxide

Solid-state phase transition are ubiquitous and of critical importance to numerous technological applications, including energy conversion and storage systems. These transition processes involve local atomic displacements or long-range atom migration without adding/reducing any atoms. For example, in perovskite ferroelectrics the oxygen octahedron shift and/or rotation results in a first order phase transition-polarization switching [ 1 ]. Investigating the dynamic processes of phase transformation in solids is critical to gain insights to understanding the fundamental physical properties of functional materials and benefiting industrial technologies. Here, we track full atoms motion/shift in lithium manganese oxide during a phase transition from spinel to rocksalt by using atomically resolved aberration corrected scanning transmission electron microscopy and spectroscopy. We find that given energy the transition metal cations can readily hop between oxygen tetrahedral and octahedral sites in lithium manganese oxide similar to lithium diffusion behavior, leaving the anion structure framework almost unchanged. During phase transition, the transition metal cation migration path, intermediate state, migration length, and atomic structure of phase boundaries are discovered and the mechanism is discussed. Our observations help us to understand the past experimental phenomena and provide useful information to stabilize the structure of electrode materials and thus improve the life of lithium ion batteries.

High pressure modification of egg components: Exploration of calorimetric, structural and functional characteristics

The effects of high pressure (HP) treatment on the thermal, rheological and functional properties of various egg components (whole liquid egg and liquid egg white) were studied as a function of increasing pressure level and treatment time. Differential scanning calorimetry (DSC) and rheometric analysis were utilized to evaluate the extent of protein denaturation and liquid-gel transformation details (G′, G″). Overall, HP-treated samples exhibited predominantly solid-like (G′ > G″) behavior in the frequency range employed (0.1–10 Hz). Pressure level (350–550 MPa) and treatment time (5–15 min) contributed significantly towards modification of liquid samples to partial gel formation. The highest level of pressure treatment (550 MPa for 15 min) was sufficient to cause complete gelatinization. Egg components exhibited a gradual liquid–solid gel transformation as they coagulated/denatured. Corresponding changes were observed in the flow behavior with increasing consistency behavior (m value) and decreasing flow behavior index (n value) showing pseudoplastic behavior. Functional properties like foaming ability, color and viscosity changed with alteration of rheological/structural properties for liquid egg white; however, whole liquid egg showed fewer significant changes (p < 0.05). Egg is known as a multifunctional food ingredient, and it plays a significant role in improving the functional profile of other finished foods. High-pressure processing can change the flow behaviour and structure by causing denaturation of proteins. These structural changes further induce transformation in the functional behavior of eggs like color, foaming and viscosity that is of prime importance in the food industry. Hence, evaluation of pressure processing conditions for modifying the egg functionality will help in developing egg and egg products with improved functionality.

Influence of thermodynamics within molten pool on migration and distribution state of reinforcement during selective laser melting of AlN/AlSi10Mg composites

A transient three dimensional model for describing the thermo-capillary convection and migration behavior and the resultant distribution state of reinforcing particles during selective laser melting of AlN/AlSi10Mg is proposed. The powder–solid transformation, temperature dependent physical properties and interaction between the reinforcement and the melt are taken into account. The effect of the laser energy per unit length (LEPUL) on the molten pool dynamics, cooling rate and the resultant sizes and distribution state of AlN reinforcement has been investigated. It shows that the thermo-capillary convection pattern changes from inward flow pattern to outward one, due to the appearance of the oxidation in molten pool. Therefore, the morphology of the top surface undergoes a continuous variation from the balling phenomenon, to the discontinuous tracks and finally to the formation of a flat and dense one. Meanwhile, both the clockwise and counterclockwise convection patterns are produced in the molten pool, caused by the interaction of reinforcing particles and the melt. An increase in LEPUL will significantly intensify the thermo-capillary convection whereas result in a decrease in the cooling rate of the molten pool. As LEPUL decreases from 1800J/m to 450J/m, the distribution state of AlN particles changes from the severe aggregation, then to the formation of partial aggregation and finally to the homogeneous distribution in the solidified matrix. The particle sizes of AlN reinforcement are experimentally acquired, which are in a good agreement with the results predicted by simulation.

Crystallization of microporous crystals

Zeolites and related microporous crystalline materials have been widely used as ion-exchangers in detergent industry, catalysts in petrochemical and chemical industry, and adsorbents in air separation by pressure swing adsorption. Its crystallization mechanism has been an important issue in zeolite field. Great efforts have been made to understand the events happened in the crystallization process and how the crystallization started. However, a well-accepted conclusion has far been achieved due to the inherent complexity of the synthesis systems and the low resolution of current characterization techniques. This paper briefly reviewed the studies on the crystallization mechanism and crystallization process of microporous crystals. The main points of view on the nucleation and crystal growth were introduced, including “solution-mediated transport mechanism”, “solid hydrogel transformation mechanism”, “dual-phase transition mechanism”, and “generalized mechanism”. In the study of the crystallization of microporous crystals, the identification of the fragments or small structural units is also very important. The typical characterization techniques that can provide such information are briefly introduced, including high resolution chromatography, in situ and ex situ nuclear magnetic resonance (NMR) with newly developed cross polarization (CP), magic angle spinning (MAS), dipolar diphasing, total side-band suppression, multiple-quantum magic-angle spinning (MQMAS), and rotational-echo double resonance (REDOR) methods, electrospray ionization mass spectrography (ESI-MS), and ultraviolet Raman spectra (UV-Raman). Combination of the experimental data and the corresponding calculation can determine the small structural units that cannot be identified by the experimental data only. In the crystallization of microporous crytals, templates or structure-directing agents played an extremely imporant role. In this paper, the diversity of the templates or structure-directing agents was reviewed and the corresponding classification was applied. Finally, a recently developed “reverse temporal evolution” crystallization process was introduced, which might be used to get the structural information of the species finally included into the structure of the resulting open framework at the very early stage of the formation process as well as the structural information of the starting point of the crystallization that a single crystal grew from.