The composition of phosgenite (ideal formula Pb2(CO3)Cl2, sp. gr. P4/mbm with a ≈ 8.15 and c ≈ 8.87 Å) from Monteponi Mine, Iglesias, Sardinia, Italy, its crystal structure and its high-T behaviour up to the onset of decomposition were investigated by a series of chemical analytical and diffraction techniques, including single-crystal X-ray (data collected at 293 K) and neutron diffraction (at 293 and 20 K), in situ high-T powder X-ray diffraction (XRD) and thermogravimetric analysis. Concentrations of >65 elements were measured. The empirical mineralogical formula of phosgenite, obtained by the multi-analytical approach used in this study, is almost identical to the ideal one, with only a few elements measured above the detection limit: Σ(Na2O+K2O+CaO+SiO2) = 0.11 wt.%. The concentration of other industrially relevant elements is insignificant. X-ray and neutron refinements, based on data collected at room T, confirm the previously reported general structural model of phosgenite, while providing a full description of the displacement parameters of all the atomic sites. The building unit of the crystal structure of phosgenite is represented by a Pb-polyhedron, in which Pb is coordinated by 5Cl + 4O (coordination number CN = 9), forming a monocapped square antiprism. The combination of face-sharing Pb-polyhedra generates dense layers parallel to (001), which are connected by (edge-sharing) CO3-groups to form the crystalline edifice. Low-T neutron diffraction data show evidence of a temperature-mediated phase transition towards a lower symmetry (space group P$\bar 4$), with a modest distortion of the building units of the structure. A tentative description of the low-T mechanisms, at the atomic scale, that can lead to the phase transition is provided.

The high-T behaviour of phosgenite proves this mineral is stable at least up to 523 K, at which the first evidence of transformation (with the coexistence of phosgenite + Pb2O2Cl, and probably an amorphous phase) takes place. The XRD pattern at 548 K unveils a more complex scenario, with coexisting: phosgenite (dominant) + Pb2O2Cl (minor) + mendipite [Pb3O2Cl2] (minor) + Pb5O2Cl6 (subordinate) (+ amorphous phase). This phase composition is preserved up to 648 K, after which phosgenite is no longer preserved, and the stable compounds are: mendipite [Pb3O2Cl2] (dominant), Pb2O2Cl (subordinate) + Pb5O2Cl6 (subordinate) + kutnohorite-type [Ca(Mn,Mg,Fe2+)(CO3)2] (likely, very minor) (+ amorphous phase). The same assemblage is observed up to 698 and back to 298 K after a decrease in T, showing an irreversible transformation of the pristine material. Therefore, the irreversible temperature-induced degradation of phosgenite is substantially governed by a decarbonation process.

Young marine green grains, from Fe-rich sediments, were studied by using HRTEM systematically combined with punctual microchemical EDX analyses. Experimental results demonstrated these grains were made of a mixture of very small phases (mainly 1:1 and 2:1 silicates layer phases) with a dominant 7-Å Fe specie. All the main crystallochemically characterized phases appeared intimately related in the same evolutionary process. Each of them experienced different and well described conversion mechanisms. So first, a starting original Fe-rich kaolinite recrystallized via solution into another particular 7-Å Fe-rich phase, the composition of which varies from a di-tri to a pure trioctahedral (Mg + Fe) end member.

This Fe-rich 1:1 mineral is effectively not a classical one. Then crystallization of a 10Å, rather dioctahedral K-rich phase occurs at the expense of it, through 1:½:1 interstratified structures. Such an evolution takes place through a solid state mechanism in which one 10-Å layer replaces one 7-Å layer. Another part of mica-like structures may also directly develop after dissolution of original kaolinites. The development of 10-Å K-rich phases could be significative of the beginning of the glauconitization process in these grains.

X-ray absorption fine structure (XAFS) spectra were collected on a series of ferrihydrite samples prepared over a range of precipitation and drying conditions. Analysis of the XAFS pre-edge structures shows clear evidence of the presence of lower coordination sites in the material. These sites, which are most likely tetrahedral, are believed to be at the surface and become coordination unsaturated (CUS) after dehydroxylation. With chemisorbed water molecules, the CUS sites become the crystal growth sites responsible for the phase transformation of ferrihydrite to hematite at low temperatures. On the other hand, when impurity anions such as SiO4−4 are present in the precipitation solution, the CUS sites may instead absorb the impurity anions, thereby blocking the crystal growth sites and inhibiting the formation of hematite.

Infrared (IR) spectroscopy, in combination with magnetic methods, was used to study the thermally induced transformation of synthetic lepidocrocite (γ-FeOOH) to maghemite (γ-Fe2O3). Magnetic analyses showed that the thermal conversion began at about 175°C with the formation of superparamagnetic maghemite clusters. The overall structural transformation to ferrimagnetic γ-Fe2O3 occurred at 200°C and was complete around 300°C. At higher temperatures, the maghemite converted into hematite (α-Fe2O3). Observation of the transformation from γ-FeOOH to γ-Fe2O3 using variable-temperature IR spectroscopy indicated that dehydroxilation on a molecular level was initiated between 145°C and 155°C. The lag time between the onset of the breaking of OH bonds and the release of H2O from lepidocrocite around 175°C can be explained by diffusive processes. Overall dehydroxilation and the subsequent breakdown of the lepidocrocite structure was complete below 219°C. The comparison of the magnetic and IR data provides evidence that the dehydroxilation may precede the structural conversion to maghemite.

Continuous wave and pulsed electron paramagnetic resonance spectroscopies combined with thermal and chemical methods were used to identify and characterize V(TV), Fe(III), Mn(II) and Cr(III) in a multimineral system that consists of vermiculite and impurities of carbonates. All of these transition metals were structure-bound in mineral phases. The V(IV) was located in octahedral layers of the vermiculite and became oxidized to V(V) during the transformation of the host mineral to enstatite at about 800 °C. The Fe(III) was associated with the vermiculite as well as the carbonate impurities. The Fe(III) identified in the vermiculite was transferred into the enstatite structure during the thermal conversion. An indirect proof of Fe(III) and Cr(III) in the impurities was found in the heated samples in which these cations occurred in Ca and/or Mg oxides that were formed by transformation of the carbonates. The Mn(II) in the untreated samples was associated with the impurities and was also detected in oxides formed from the samples heated at 600 °C.

The transformation process between palygorskite and smectite was studied by examining the morphological and structural relationships between these two minerals in an assemblage from the Meigs Member of the Hawthorne Formation, southern Georgia. Studied samples were related to an alteration horizon with a tan clay unit above and a blue clay unit below. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) were used to study the mechanism of transformation.

From AFM data, both clay units contain euhedral palygorskite fibers. Many fibers are found as parallel intergrowths joined along the [010] direction to form ‘raft-like’ bundles. Degraded fibers, which are common in the tan clay, have a distinctly segmented morphology, suggesting a dissolution texture. Many of the altered palygorskite fibers in the tan clay exhibit an oriented overgrowth of another mineral phase, presumably smectite, displaying a platy morphology. This latter mineral forms along the length of the palygorskite crystals with an interface parallel to {010} of the palygorskite. The resulting grain structures have an elongate ‘wing-like’ morphology.

Imaging by TEM of tan clay material shows smectite lattice-fringe lines intergrown with 2:1 layer ribbon modules (polysomes) of the palygorskite. These features indicate an epitaxial overgrowth of smectite on palygorskite and illustrate the structural relationship between platy overgrowths on fibers observed in AFM data. The epitaxial relationship is described as {010} [001] palygorskite ‖ {010} [001] smectite.

Energy dispersive spectroscopy indicates that the smectite is ferrian montmorillonite. Polysomes of palygorskite fibers involved in these textures commonly vary and polysome widths are consistent with double tetrahedral chains (10.4 Å), triple tetrahedral chains (14.8 Å), quadruple tetrahedral chains (21.7 Å) and quintuple tetrahedral chains (24.5 Å).

The transformation of palygorskite to smectite and the resulting intergrowths will cause variations in bulk physical properties of palygorskite-rich clays. The observation of this transformation in natural samples suggests that this transformation mechanism may be responsible for the lower abundance of palygorskite in Mesozoic and older sediments.

A clear understanding of the solid-state reaction of kaolinite (Kln), quartz (Qtz), and sodium carbonate (Na2CO3) is of great significance for the process optimization of coal gangue calcined with Na2CO3. In this work, a comparative study of the isothermal solid-state reaction systems of Kln–Na2CO3 and Kln–Qtz–Na2CO3 was performed by means of X-ray diffraction (XRD), scanning electron microscope, and energy dispersion spectroscopy (SEM-EDS). The results showed that the calcined products both for these reaction systems mainly contain different kinds of sodium aluminum silicates (e.g., NaAlSiO4, Na1.55Al1.55Si0.45O4, and Na1.95Al1.95Si0.05O4) and various kinds of sodium silicates (e.g., Na2Si3O7, Na2SiO3, and Na6Si2O7). The mass percentage of Na2CO3 played a key role in the phase transformation, determining the Na/Al/Si molar ratio of the formed sodium aluminum silicates. Compared with the reaction system of Kln–Na2CO3, the existence of Qtz inhibited the formation of sodium aluminum silicates in the reaction system of Kln–Qtz–Na2CO3. It should be noted that the formed phases both for these reaction systems were slightly different from that of the thermodynamical calculated results of Na2O–SiO2–Al2O3 using FactSage™ software. According to both the experimental and calculated results, a reasonable batching area for coal gangue activation was proposed that the addition of Na2CO3 should be in the range of 20–50% of the total mass of Kln, Qtz, and Na2CO3.

To produce an optimized matrix for the in situ crystallization of zeolite Y, a commercial kaolin chemically treated with NaOH solution at 97°C for 24 h and thermally transformed from 750 to 1100°C was studied. The kaolin calcined at 750°C has 20% more reactive tetrahedral aluminium species for the synthesis of zeolite Y than kaolin calcined at 865°C. The kaolin calcined at 1000°C has amorphous silica zones that may be extracted using caustic solution; this increases the surface area by a factor of 16 and generates mesopores ~5 nm in diameter. These structural changes in the calcined and treated kaolins were combined to prepare microspheres of the mesoporous matrix, upon which well-dispersed crystals of zeolite Y crystallized.

(AlxGa1−x)2O3 is a novel ultra-wide bandgap semiconductor with the potential to dominate future power electronics industries. High-performance devices demand high Al content in (AlxGa1−x)2O3 but are limited by crystallinity degradation resulting from phase separation. Additionally, the solubility limit of Al is still under debate, and conclusive research is in progress. (AlxGa1−x)2O3 is also limited in high-frequency applications owing to low carrier mobility and requires n-type doping. For commercializing this material, the major obstacle is understanding dopant's behavior in the host (AlxGa1−x)2O3. To investigate these issues, an advanced characterization technique, atom probe tomography (APT), was employed to analyze the structural-chemical evolution of (AlxGa1−x)2O3. In this review, we summarized our recent works on the structure-chemistry investigation of (AlxGa1−x)2O3 with alloy composition and doping interaction. We introduced machine learning algorithms on APT data to reveal unrivaled knowledge, previously not achievable with conventional methodologies. The outstanding capabilities of APT to study (AlxGa1−x)2O3 with Al composition and doping will be considered significant for the wide bandgap semiconductors community.

The development of a consistent framework for Calphad model sensitivity is necessary for the rational reduction of uncertainty via new models and experiments. In the present work, a sensitivity theory for Calphad was developed, and a closed-form expression for the log-likelihood gradient and Hessian of a multi-phase equilibrium measurement was presented. The inherent locality of the defined sensitivity metric was mitigated through the use of Monte Carlo averaging. A case study of the Cr–Ni system was used to demonstrate visualizations and analyses enabled by the developed theory. Criteria based on the classical Cramér–Rao bound were shown to be a useful diagnostic in assessing the accuracy of parameter covariance estimates from Markov Chain Monte Carlo. The developed sensitivity framework was applied to estimate the statistical value of phase equilibria measurements in comparison with thermochemical measurements, with implications for Calphad model uncertainty reduction.

Lead-free ferroelectric electrocaloric ceramics that could convert electrical energy into heat are the promising candidate for environment-friendly cooling devices. For refrigeration devices, a large temperature change (ΔT) and good temperature stability are required, which are highly related to the phase structure and the applied electric field. In this work, a diffused ferroelectric–paraelectric (FP) phase transition is formed in (K, Na)NbO3 (KNN) by using appropriate composition engineering. The relaxor ferroelectrics in this work present both a large ΔT of 1.24 K and a high ΔT/ΔE of 0.19 K mm/kV. In addition, a wide temperature span exceeds 55 °C at the high electrocaloric effect (ECE) criterion (ΔT ≥ 0.5 K) could also be observed. This work not only opens a new strategy for obtaining high-performance ceramics for refrigeration devices but also extends the application area of the KNN-based lead-free ferroelectrics from sensors, actuators and energy harvesting to solid-state cooling applications.

The doped/alloyed HfO2 and ZrO2 thin films revolutionized not only the field of ferroelectric physics but also various ranges of device applications. Especially when the two oxides are combined in an 1:1 ratio, the ferroelectric polarization of the material became the most distinctive. Many researchers have investigated various different process conditions such as controlling Hf0.5Zr0.5O2 (HZO) film thickness and modifying different metal electrodes. Here, we explored the effect of additional Ar plasma treatment to the HZO film. The additional Ar plasma was exposed to the plasma-enhanced atomic layer deposition (PEALD) HZO for this study. Then, the sample was compared with a conventional PEALD and thermal ALD HZO films. By understanding the polarization–electric field (P–E), current–electric field (I–E), and electrical breakdown characteristics of the different samples, it was found that the Ar plasma treatment can control the degree of ferroelectric and antiferroelectric phases of HZO film.

This study presents a dual Eulerian–Lagrangian particle approach for time-accurate computational fluid dynamics (CFD) modeling of volcanic ash in gas turbine engines and initial results. The objective is to enable high-fidelity simulations of calcia–magnesia–alumina-silica (CMAS) particles in gas turbine engines to better predict deposition and particle paths to rapidly test mitigation solutions. The approach uses a primarily first principles framework to account for the various physical phenomena in the system. Particles are modeled using Lagrangian methods which track individual particles and Equilibrium Eulerian methods which track particles in terms of concentration densities. Lagrangian methods become prohibitively expensive for fine particles. Eulerian methods are physically appropriate for fine particles but become inaccurate for large particle sizes. A dual approach using both Eulerian and Lagrangian methods allows for optimal computational cost with maximum accuracy. Simulation results using the proposed approach are compared against experimental data for a representative gas turbine engine blade.

We have synthesized off-stoichiometric Ni40Cu10Mn35Ti15 all-d-metal Heusler alloy with a B2 cubic crystal structure by an arc melting process and investigated its structural, magnetic, electronic, thermal, and mechanical properties under the influence of a single-step thermal annealing. The compound exhibits an antiferromagnetic ordering accompanied by thermal hysteresis indicating a first-order magneto-structural transition. Curie–Weiss molecular field analysis reveals the presence of ferromagnetic interactions competing with long-range antiferromagnetic ordering. Thermal annealing leads to the appearance of a heat capacity sharp peak around antiferromagnetic transition. Electrical resistivity measurements display abrupt changes close to the magneto-structural transition revealing the strong coupling among spin, lattice, and charge degrees of freedom characteristic of a martensitic transition (MT). We have also evaluated its mechanical properties from microhardness measurements, and the results indicate that this alloy exhibits ductile behavior. The occurrence of MT associated with improved ductility is an essential combination for technological application as shape-memory alloys.

The γ″ phase (hexagonal structure with space group ${ P\bar{6}}2{ m}$) plays an important role in the strengthening of Mg–Gd–Y–Ag–Zr alloy. In this study, Cs-corrected high-angle annular dark-field scanning transmission electron microscopy was applied to characterize the Mg–Gd–Y–Ag–Zr alloy in different conditions (as-cast, solution-treated, and isothermally aged at 200 °C). The nucleation, growing process, and transformation behavior of the plate-shaped γ″ phase were systematically investigated on the atomic scale. We found that the nucleation sites of the γ″ phase were separated by close-packed planes of the Mg matrix and the γ″ phase developed in two perpendicular directions of $\langle 10\bar{1}0 \rangle$ and ⟨0001⟩. The growing process of the γ″ phase on the atomic scale was captured. The γ″ phase was thermodynamically stable at room temperature, and no transformation behavior of the γ″ phase was observed up to 200 h during isothermal aging at 200 °C.

This study investigates the effect of C on the deformation mechanisms in Fe–C alloys by molecular dynamics simulations. In uniaxial tensile simulations, the face-centered-cubic (fcc) structures of Fe–C alloys undergo the following deformation processes: (i) fcc→body-centered-cubic (bcc) martensitic transformation, (ii) deformation of bcc phase, and (iii) bcc→hcp martensitic transformation, which are significantly influenced by the C concentration. For the low C concentrations (0–0.8 wt%) fcc phase, the fcc→bcc phase transformation accords a two-stage shear transformation mechanism based on the Bain model, the deformation mechanism of the bcc phase is the first migration of twinning structures and then elastic deformation, and the bcc→hcp phase transformation follows Burgers relations resulting from the shear of the bcc close-packed layers. However, for the fcc phase with high C concentrations (1.0–2.0 wt%), the fcc→bcc phase transformation follows a localized Bain transformation mechanism impeded by the C atoms, the bcc phase only experiences elastic deformation, and the bcc→hcp phase transformation also conforms to Burgers relations but become localized due to the addition of more C atoms. Because of the different phase transformation mechanisms between the high C and low C supercells, the dislocation generation mechanism is also different.

In this study, the effect of the cooling rate on the thermal and thermomechanical behavior of NiTiHf high-temperature shape memory alloy was studied by differential scanning calorimetry and via running isobaric thermal cycling experiments. The cooling rates were set to 5, 10, and 15 °C/min for each cycle in both experiments, while the heating rate was kept as 10 °C/min. It was found that the transformation temperatures and thermal hysteresis values do not depend on the change in the cooling rate. On the other hand, the austenite to martensite transformation enthalpy as measured from DSC analyses increases with the increase in the cooling rate due to the higher measurement sensitivity at higher scanning rates. Recoverable strain values which were determined from isobaric thermal cycling experiments do not differ since the transforming volume does not change with the change of the cooling rate. All these findings are explained based on the fundamental thermodynamical approach.

Localized deformation, including that by the deformation-induced shearing martensitic phase transformation, is responsible for hardening and embrittlement in irradiated face-centered cubic alloys. These localized deformation processes can have profound consequences on the mechanical integrity of common structural metals used in extreme radiation environments such as nuclear reactors. This article aims to review and understand exactly how irradiation affects the martensitic phase transformation in face-centered cubic alloys, with an emphasis on austenitic stainless steel, given its ubiquity in the archival literature. The influence of irradiation on stacking fault energy and subsequent implications on the phase transformation are discussed. Mechanisms by which irradiation-induced microstructures enhance the phase transformation are also described, including the surface energy contribution of irradiation-induced cavities (i.e., voids and bubbles) toward the critical martensite nucleation energy, and partial dislocation–cavity interactions. A deformation mechanism map illustrates how irradiation-induced cavities can modulate the martensitic transformation pathway.

Graphene enticed the scientific community for its interesting properties since its discovery. Among different synthesis routes of graphene, reduction of graphene oxide (GO) is mostly preferred because of scalability and advantage of modulation of properties of the end product. Thermal reduction of GO is considered to be the simplest and economic among different reduction techniques. The current work reports an experimental analysis of the structural evolution of GO to reduced graphene oxide (rGO) during thermal treatment. GO has been thermally annealed at an optimized temperature of 350 °C in ambient. Thermal reduction is observed after 7 min of annealing and confirmed by shifting of the first major peak from 12° to 23° in X-ray diffraction pattern. Significant carbon content enrichment and exfoliation are two aspects of the thermal reduction of GO. Carbon content suddenly enriches from 38 wt% in GO to 77 wt%. Exfoliation is confirmed by morphological alterations and decrease in carbon layers from eleven to three.

With the ever-increasing importance of nanoscale deformation phenomena in contemporary technologies, basic understanding of material behavior at the nanoscale has become of critical importance. Especially, nanomechanical testing that provides the capability to study fundamental nanoscale deformation and phase change phenomena in real time and under controlled loading conditions is essential for nanomaterial research. In this study, acoustic emission (AE) was used in situ to characterize nanoindentation-induced deformation, microfracture, and phase transformation processes intrinsic of bulk single-crystal MgO and polycrystalline Al, thin films of polycrystalline SiC, and thick films of austenitic TiNi shape-memory alloy. Scale-dependent plastic deformation and microfracture affected by the indenter tip radius and the applied normal load are interpreted in terms of the type and intensity of AE events revealed by abrupt displacement excursions in the loading response of the indented materials. The amplitudes of AE waveforms are used to examine characteristic deformation, microfracture, and phase change mechanisms in the time domain. Fast Fourier transformation and short-time Fourier transformation analyses provide further insight into the material behavior and structural changes due to indentation loading in the frequency and time-frequency domain, respectively. The methodology developed in this study represents an effective approach for nanomechanical testing and in situ characterization of nanoscale deformation, microfracture, and phase transformation phenomena.