Synchrotron XRD Research Articles

(Digital Presentation) Synthesis of Conjugated Polymer Alloy Prepared By Electrochemical Polymerization in Chiral Liquid Crystal

In this research, we synthesized polymer alloy by electrochemical polymerization in chiral liquid crystal. Homopolymers and the copolymer can be synthesized when electrochemical polymerization was conducted in the presence of several types of monomers. The polymer alloy thus prepared contains both blend of homopolymers and copolymers. The polymer alloy shows optical activity. The chirality derived from transcription of liquid crystal during the polymerization reaction results to show optical activity. The polymer alloy can show optical activity with no asymmetric centers. The optical activity is due to existence of charge carriers (polarons) in the main chain as a form of conjugated polymers. This is called chiral charge carrier “chiralions”. This research found that the chiral polymer alloy has chiralions.Polymer alloys have been prepared by blending several kinds of polymers in the reaction. Polymer alloys also can be prepared by melt method. Unsubstituted conjugated polymers have poor solubility and fusibility because of the rigid π-bonds in the skeleton, which is drawback for preparation of π-conjugated polymer-based alloys. We have studied on preparation of chiral conjugated polymer alloys with combination of achiral polymers and chiral polymers.In the present study, conjugated polymer alloys were synthesized with the method described in Figure 1a. Cholesteryl acetate (chiral inducer), 2,7-di(2-thienyl)fluorene (mono1), N-methyl-3,6-di(2-thienyl)carbazole (mono2) and TBAP (supporting salt) were dissolved in 4-cyano-4'-pentylbiphenyl (5CB) as a host liquid crystal to prepare a chiral liquid crystal electrolyte. The electrolyte exhibited a fingerprint structure under observation of polarizing optical microscopy. For the electrochemical polymerization reaction, the electrolyte solution is charged in the cell consisted of two indium-tin-oxide (ITO) glass plates as electrodes and a poly(tetrafluoroethylene) spacer (200 μm thickness). Next, dc voltage of 3.0 V was applied to the ITO glass cell for 30 min for electrochemical polymerization. The polymer was deposited on the anode electrode as a thin film form. After polymerization, the remaining electrolyte solution on the ITO glass electrode was carefully washed with a large amount of hexane, yielding dark blue film. This film is abbreviated as Alloy1. The molecular structure was confirmed by infrared spectroscopy with the KBr method. Alloy1 shows a fingerprint structure under POM observations (Figure 1b). The macroscopic structure of cholesteric liquid crystal was transcribed from the liquid crystal electrolyte solution to Alloy1. Synchrotron XRD measurement was carried out. The peak at 10.3 Å is derived from monomer repeat units. The XRD signal at 5.1 Å and 3.4 Å can be derived from π-stacking of Alloy1. Alloy1 shows UV-vis absorption due to the three signals derived from π-π* transition of the main chain, polarons (radical cations) and bipolarons (radical dications). Electrochemical properties of Alloy1 were evaluated by the cyclic voltammetry (CV). Alloy1 film deposited on the ITO glass was used as a working electrode. An Ag/Ag+ electrode and a platinum wire served as the reference and counter electrodes, respectively. A propylene carbonate solution with 0.1 M of TBAP was employed as an electrolyte solution for the CV measurements. Cyclic voltammograms of Alloy1 shows the oxidation peak and reduction trough (Figure 1c). Plots of the oxidation peak current (I pa) and the reduction peak current (I pc) as a function of the square root of the scan rate show a linear shape of the anodic and cathodic peak current values when scan rates from 10 to 100 mV/s with intervals of 10 mV/s. This result indicated that the redox reaction of Alloy1 was reversible and controlled by electron transfer processes. In-situ circular dichromism (CD) and in-situ optical rotatory dispersion (ORD) spectra of Alloy1 with application of voltages were examined in a propylene carbonate solution with 0.1 M of TBAP. The application voltages were between 0-1.2 V (vs. Ag/Ag+) with intervals of 0.1 V. A negative Cotton effect was observed from the in-situ CD, indicating Alloy1 has left-handed helical structure. The ORD shows negative signals, and changes with applied voltage. The ellipticity signal in the CD and optical rotation in the ORD could control in the electrochemical method, accompanied by electrochemical redox process.We synthesized the polymer alloy by electrochemical polymerization in chiral liquid crystal. The conjugated polymer alloy showed chirality with no chiral centers in the main chain. The CD and ORD bands at NIR range are assigned to doping band as a form of polarons (radical cations). This research evaluated electrochemical control of “chiralions”. Figure 1

Microwave irradiation suppresses the Jahn-Teller distortion in Spinel LiMn2O4 cathode material for lithium-ion batteries

Jahn-Teller (J-T) distortion remains the key challenge to realizing the full electrochemistry potential of the commercialized LiMn2O4 cathode material for lithium-ion batteries. In this work, the application of microwave irradiation to suppress the limiting J-T distortion in pristine LMO (LMO-p) materials and improve the electrochemistry of lithium-ion batteries has been reported. Unlike thermal heating, microwave irradiation inhibits J-T distortion. To establish the underlying science behind the impact of microwave irradiation, both the pristine (LMO-p) and the microwave-treated counterpart (LMO-m) are subjected to several characterization techniques, including synchrotron XRD, XPS, powder neutron diffraction (PND), MAS 7Li NMR, Raman and BET analysis. These techniques prove that LMO-m possesses the needed physico-chemical properties that explain: i) suppressed J-T distortion (such as an increased average Mn oxidation state (i.e., nMn ≥ 3.5+ or Mn4+/Mn3+ > 50%)), decreased lattice parameter, enhanced BET surface area, and enhanced structural crystallinity), and ii) improved electrochemical performance (such as increased specific discharge capacity, electronic and Li-ion transfer kinetics, and Coulombic efficiency). Microwave irradiation improves the specific capacity by about 21% and capacity retention (0.022% capacity loss per cycle for the LMO-m, ∼ 0.036% capacity loss per cycle for LMO-p for 100 cycles). The findings in this work are relevant for the realization of low-cost and environmentally benign scale-up modification processes for LMO spinel and related cathode materials for the development of high-performance lithium-ion batteries.

Formation of lower bainite in a high carbon steel – an in-situ synchrotron XRD study

The microstructural evolution of and simultaneous dimensional changes in high-carbon SAE 52100 bearing steel were monitored continuously during austempering for 120 min at selected temperatures in the range of 210 °C-270 °C, and also during its subsequent tempering to 340 °C for an additional 120 min, via high-energy X-ray diffraction in real time and in-situ dilatometry. The austenite-to-bainitic ferrite transformation induces lattice defects and internal lattice stresses that increase with austempering time and at lower austempering temperatures. These changes are evidenced by the increase in the full-width half-maximum of the relevant reflections in X-ray diffraction. The lattice parameter of bainitic ferrite takes its highest value during the early stages of austempering, and then gradually decreases as the transformation progresses. This observation points to an initial state of carbon supersaturation in the ferritic lattice that is likely reducing due to carbon segregation close to dislocations, fine carbide precipitation within the bainitic ferrite, and carbon partitioning into the surrounding austenite. The carbon partitioning into austenite is evidenced in particular at the higher austempering temperatures of 240 °C and 270 °C, at which there is a noticeable increase in the lattice parameter of the remaining austenite at longer times. The dimensions of the bearing steel specimens are governed by the volume change due to the formation of bainitic ferrite during austempering and by the relaxation of its lattice distortion during tempering at 340 °C in the absence of further phase transformation.

Complementary analysis to de-convolute co-located contaminants in marine archaeological bricks

• Using complimentary analysis to de-convolute complex heritage materials. • Determining the elemental composition of compounds in marine archaeological bricks. • Synchrotron techniques for phase composition of complex archaeological materials. • Understanding the threat posed by compounds present in marine archaeological bricks. Marine archaeological artefacts contain unexpected compounds due to prolonged exposure to the sea. These can remain dormant and embedded within materials until a change in their surrounding environment, such as exposure to oxygen, prompts a transformation. These changes can pose a problem, as acidic compounds are formed which disintegrate the material, or crystals form which physically break the artefact apart. The extent of these transformations is highly heterogeneous due to its dependence on the ability for oxygen to reach and catalyse these reactions. Additionally, these transformations are heavily dependent on the environment the artefact is exposed to, and the pathways available for ingress, either naturally or through previous degradation. This results in materials with a range of different compounds which are often co-located on the macro, micro and nano-scale. Trying to de-convolute these compounds is challenging, and usually requires a suite of complementary techniques to achieve. Here we report on damaging salts found within marine archaeological bricks and show how it is only possible to qualitatively and quantitatively understand what is present by employing a range of analytical techniques, such as XRD, SEM-EDS and SR-XPD. The marine archaeological bricks studied were found to contain a range of different sulfate-based salts, which had grown crystals in preferred orientations. This provides information which will guide further conservation strategies such as how these bricks are stored, conserved and protected in the future. (a) The galley of the Mary Rose (b) salt samples located on and within the bricks (c) SEM analysis of the salts present (d) demonstration of the enhanced data quality of synchrotron XRD compared to laboratory based instruments.

Kinetics and the crystallographic structure of bismuth during liquefaction and solidification on an insulating substrate

Here we study the kinetics of liquefaction and solidification of thin bismuth films grown on an insulating substrate by pulsed laser deposition (PLD) and molecular beam epitaxy (MBE) and investigated by in situ electron and X-ray diffraction. By PLD, we can grow films similar to those obtained using MBE, studied by ex-situ AFM, KPFM, XRR, and XRD. The liquefaction-solidification transition is monitored in real-time by RHEED and synchrotron XRD, observing thereby the dewetting phenomenon and the formation of spherical droplets which size depends on the initial film thickness. Studying this phase transition in more detail, we find abrupt liquefaction and solidification, resulting in formation of the nanodots oriented with the (110) crystallographic plane parallel to the substrate. Furthermore, by analysis of the recorded specular diffraction rods, we propose growth by initial deposition, followed by a transformation into nandots, followed by further deposition. Overall, we demonstrate that controlling the growth scenario for Bi nanostructures, here shown by PLD and MBE, one is able to steer its resulting shape, size and corresponding (materials) properties.

Are photo-induced crystalline sulfur and S-II equivalent under high pressure?

Sulfur is known to be a photo-sensitive material. Photo-induced crystalline sulfur (p-S) was found in high-pressure Raman studies more than two decades ago. However, its structureremains not well understood. In this work, a thin α-S8 crystal was pressurized to 8 GPa in a diamond anvil cell (DAC) and its surface was repeatedly scanned by a 532 nm laser to produce the largest possible amount of p-S. A high-quality XRD pattern of p-S was obtained for the first time. The refinement of experimental data indicated the structural consistency between p-S and high-pressure and high-temperature (HPHT) S-II phases. Moreover, HPHT experiments were conducted to study the effect of temperature on p-S formation. The current work provides a strategy for producing the high-purity photo-induced product. The combination of synchrotron XRD, Raman spectroscopy, and microscopical imaging technology shows an effective way for photochemical research.

Reaction synthesis of SrTiO3 mineral-like ceramics for strontium-90 immobilization via additional in-situ synchrotron studies

The paper presents spark plasma sintering-reaction synthesis (SPS-RS) of SrTiO3-based mineral-like ceramics with a perovskite structure, which is promising for immobilization of Sr-90 radionuclides. Detailed time-resolved study of phase transformations taking place in the reactive mixture (SrCO3 and TiO2) within 20–1000 °C temperature range was conducted using both in situ heating synchrotron XRD and TGA. Structure and composition dependence on consolidation temperature was revealed by the means of SEM and EDX. We determined optimal temperature conditions for rapid formation of SrTiO3 ceramics with density – 4.49 g cm−3, Vickers hardness – up to 6.2 GPa, compressive strength – 279 MPa, and strontium leaching rate of 10−5–10−6 g cm−2·day. These results clearly show strong applied potential of the presented material for radioactive waste management and isotope production fields.

Microstructure and stress analyses in nano-structured alumina layers developed on Fe-Al single crystals

In the present work low index single crystal surfaces of a binary Fe-Al alloy were oxidized in atmospheric air at 700 °C. The oxide layer composition, microstructure and texture were investigated by XPS, TEM and XRD. The oxidation stresses were determined in situ by synchrotron XRD. The results revealed the presence of a dual layered oxide scale, consisting of an inner layer of α-Al2O3 and an external layer of α-Fe2O3 and α-Al2O3. Differences in crystal orientation led to variations in the internal stress distribution in the oxide scales, with compressive stress values α-Al2O3 following (110) > (111) > (100).

4．炭素鋼に生成したさび層における電気化学機構の放射光XRD及びXAFS解析

4．炭素鋼に生成したさび層における電気化学機構の放射光XRD及びXAFS解析

The first lithiation/delithiation mechanism of MFeOPO4 (M: Co, Ni) as revealed by 57Fe Mössbauer spectroscopy

Iron (III) transition metal MFeOPO4@C (M: Co, Ni) oxyphosphates were synthesized using a solid-state reaction. The electrochemical properties of MFeOPO4@C were evaluated versus Li+/Li using two different binders (PVDF and CMC) in the voltage range 0.01–3.0 V. These phosphates show similar electrochemical profiles for both binders. They deliver a high discharge capacity during the first cycle around 755 mA h g−1 and 661 mA h g−1 for CoFeOPO4@C and 735 mA h g−1 and 789 mA h g−1 for NiFeOPO4@C when using PVDF and CMC binders, respectively. In our previous work, the electrochemical mechanism of MFeOPO4@C was investigated using in situ synchrotron XRD and X–ray absorption spectroscopy (XAS) revealing an irreversible amorphization of the crystal structure and the formation of new products at the end of discharge (Fe0, M0, Li2O, and Li3PO4). Moreover, XAS measurements showed that both transition metals M and Fe are active during the discharge/charge process. Our previous hypotheses suggested the oxidation of metallic iron to only divalent iron Fe2+ during charge. However, 57Fe Mössbauer spectroscopy study reported here in this paper demonstrated that Fe3+ is partially reduced to Fe2+ and Fe0 in the first stages of lithiation, and then totally reduced to metallic iron by the end of discharge. Furthermore, when charging MFeOPO4@C against Li+/Li, 57Fe Mössbauer spectroscopy technique surprisingly proved that iron is re-oxidized to + 2 and + 3. Therefore, the new data using 57Fe Mössbauer spectroscopy has revealed insightful findings on the electronic changes of Fe upon the first lithiation/ delithiation.

Transmission electron microscopy image based micromagnetic simulations for optimizing nanostructure of FePt-X heat-assisted magnetic recording media

The areal density of the heat-assisted magnetic recording (HAMR) technology has a potential to reach 4 Tb/in2. However, the bimodal grain size distribution and structural defects that are unavoidable in actual FePt-X nanogranular media must be minimized for further reduction of a jitter noise. Here we report transmission electron microscopy (TEM) image based micromagnetic simulations of the FePt-X nanogranular media in order to elucidate the role of structural defects such as [200] misalignment and {111} twins on the magnetic properties. Micromagnetic approximation of experimental out-of-plane hysteresis loops allows to evaluate micromagnetic parameters and volume fractions of the defects in MgO(6 nm)/FePt-BN(1 nm)/FePt-(BN,C,SiO2)(7 nm) granular thin films. Synchrotron XRD of the films validated that the structural defects can be accurately evaluated by the proposed approach. The developed TEM image based micromagnetic simulations can directly link nanostructure of the FePt-X media with magnetic properties, boosting not only the optimization of the HAMR media but also a design of magnetic nanomaterials in general.

The interaction of evodiamine and rutaecarpine with DPPC liposomes

Evodiamine and rutaecarpine, derived from the traditional chinese medicine Euodia rutaecarpa (Juss.) Benth, have many similar pharmacological effects, but their pharmacological mechanisms are not exactly the same. In this study, liposomes were used as the model of biomembrane. DSC, synchrotron XRD and FTIR techniques have been employed to investigate and compare the interaction of evodiamine and rutaecarpine with DPPC liposomes. The results show that evodiamine and rutaecarpine remarkably affect the DPPC in a concentration-dependent manner. But the concentration dependence of the two drugs is obviously different. The effect of rutaecarpine on liposome membrane was stronger than that of evodiamine, which might be related to the different pharmacological mechanism of evodiamine and rutaecarpine. This study will play an important role in the further investigation of interaction of drugs with biomimetic membranes and further investigation of pharmacological mechanisms of drugs.

Metakaolin-based geopolymers: Efflorescence and its effect on microstructure and mechanical properties

Efflorescence in geopolymers results from mobility of excess alkali and consequent crystallization of alkali carbonates. Efflorescence potential of various geopolymers has been reported previously but the knowledge regarding the effect of efflorescence on the microstructure and mechanical properties of geopolymers remains limited. In this work, metakaolin-based geopolymers were exposed to air, partially immersed in water, and fully immersed, to simulate different processes involved in efflorescence formation. The mechanical properties were assessed by compressive, splitting tensile and flexural strengths, and linear deformation. The microstructural features were investigated by SEM, synchrotron XRD, multinuclear MAS NMR, MIP and synchrotron X-ray microtomography. Extensive efflorescence resulted in a reduction of mechanical strength and changes in the nanostructure and microstructure, which is different from observations for Portland cement-based materials, where efflorescence is usually regarded as a surface or aesthetic problem. The understanding of the relationship between efflorescence formation, the synthesis and exposure conditions provides important insight into the manufacturing and application conditions of geopolymer related materials.

In situ synchrotron Х-ray diffraction study of heat-induced structural changes in TiOy/HAp nanocomposites

In situ synchrotron Х-ray diffraction (XRD) was used to study the interactions between an important biomaterial for tissue engineering and regenerative medicine, hydroxyapatite, and titanium monoxide additives of different stoichiometry, in nanocomposite materials. The study was carried out in the temperature range from ambient to 900 °C in a flow of dry air. During the temperature evolution of the nanocomposites, the mutual influences of the matrix and additives were observed. The dynamics of changes in the phase composition and the effects of TiOy on the thermal stability of the matrix were considered. The addition of 10 wt% TiOy increased the decomposition temperature of HAp by approximately 100 °C. Different additive stoichiometries shifted the temperature ranges of the phase transitions in the nanocomposites. Opposite trends were observed for the dependence of the weight content of the matrix and that of the additive on temperature in the range from 300 to 800 °C. This behaviour was explained by a partial substitution of Ti atoms for Ca atoms. After heat treatment to 900 °C, all nanocomposite phases were biocompatible. The oxyapatite and TiO2 phases retained the nanostates of their initial components, while the α- and β-ТСР phases were microcrystalline. In situ synchrotron XRD method proved to be a highly informative and precise technique for studying new biomaterials.

Influence of proton irradiation on the microstructure and mechanical properties of Nb-1Zr-0.1C alloy

• Effect of proton irradiation on Nb-1Zr-0.1C alloy proposed for CHTR. • XRD line profile analyses of the data collected using synchrotron source. • Prediction of dislocation loop formation with XRDLPA and supported by TEM analysis. • Microstructure-mechanical property correlation by tensile and nanoindentation test. • Comparison of microstructure and mechanical properties with proton irradiated pure Nb . The microstructural evolution and corresponding changes in mechanical properties of proton irradiated Nb-1Zr-0.1C alloy have been studied as a function of irradiation dose. Different XRD line profile analyses (XRDLPA) have been carried out using synchrotron XRD data to evaluate the microstructural parameters. It is observed that coherent domain size decreases with an increasing microstrain within the domain as a function of dose. The dislocation density also increases and shows saturation at the highest dose. The Wilkens arrangement parameter decreases as a function of dose indicating the formation of correlated dislocations in the alloy matrix. Transmission electron microscopy (TEM) analysis confirms the presence of dislocation loops in the highest dose sample supporting the findings of XRDLPA. The strength and ductility of unirradiated and all irradiated samples have been evaluated as a function of dose. It is observed that the ductility reduces continuously along with increasing yield strength (YS) and ultimate tensile strength (UTS) as a function of dose. Nanoindentation was also carried out to measure the change in hardness of the alloy with dose. It is observed that the value of the nanohardness increases continuously from 1.74 GPa for the unirradiated sample to 2.43 GPa in the highest dose irradiated sample. Systematic changes are observed on the morphology of fracture surface as a function of dose. Signature of ductile failure is observed in the unirradiated sample whereas brittle failure is prominent in the irradiated samples with higher dose. The change in microstructure in terms of dislocation density is corroborated with the change in mechanical properties in terms of YS of the irradiated alloy. Contradistinction of the findings of Nb-1Zr-0.1C with those of pure Nb contemplated the role of the alloying additions, especially carbon, in governing the irradiation behaviour of the alloy.

Magnetostructural transition, magnetocaloric effect and critical exponent analysis in Nd(Co0.8Fe0.2)2 alloy

In the present study, the magnetostructural transition, magnetocaloric effect (MCE) and critical behavior of Nd(Co0.8Fe0.2)2 alloy in the vicinity of ferromagnetic transition were studied. The Rietveld refinement analysis of in-situ synchrotron XRD patterns reveals that the present alloy crystallizes in the cubic phase (space group Fd3̅m) at room temperature and undergoes a structural transition to the tetragonal phase (space group I41/amd) below its Curie temperature. Temperature dependent heat capacity measurements under different applied magnetic fields were carried out to investigate the magnetocaloric properties. The maximum magnetic entropy change (ΔSM) of 5.6 J/kgK and relative cooling power (RCP) of 445.7 J/kg are obtained over the wide working temperature range of 82 K under magnetic field change of 5 T. The corresponding adiabatic temperature change (ΔTad) is evaluated to be 2.9 K under the same magnetic field change. The sample shows metallic behavior with its significant magnetoresistance value of −41.2% around phase transition at magnetic field change of 5 T. These results may make Nd(Co0.8Fe0.2)2 alloy as one of the promising material for refrigeration applications. Moreover, the critical parameters (β, γ, and δ) were deduced independently from the magnetization data by using different techniques such as modified Arrott plot, Kouvel–Fisher method and critical magnetization isotherms. The derived β=0.319, γ =1.214, and δ=4.78 values are found to be consistent with the 3D-Ising class signifying the presence of short-range exchange interactions in this alloy. We have further shown that these exponents follow the M(H, ε)=|(T − TC)/TC |βf±H/|(T − TC)/TC|β+γ scaling equation very well for both the above and below Curie temperature demonstrating that the estimated exponents are unambiguous and are intrinsic to this alloy system.

Microstructure evolution during reduction and sintering of 3D-extrusion-printed Bi2O3+TeO2 inks to form Bi2Te3

As an alternative to beam-based additive manufacturing, 3D ink-extrusion additive manufacturing is studied here for thermoelectric Bi2Te3, starting from Bi2O3+TeO2 oxide precursor powders. In situ synchrotron XRD in flowing H2 at elevated temperatures reveals the complex phase evolution upon co-reduction leading to the formation of Bi2Te3, Bi2TeO5 and Bi2TeO2. Sintering trials performed using optimal temperatures identified by in situ XRD show that low heating rates and extensive holding times are required to achieve full co-reduction to pure Bi2Te3. The formation of liquid Bi at the temperatures required for oxide reduction leads to local transient-liquid-phase sintering, creating a coarse-grained porous structure. To limit the amount of free Bi, compositional homogenization prior to reduction is achieved by oxide pre-sintering in air, allowing to access the high temperatures required for interdiffusion. After co-reduction of the complex Bi2Te4O11+Bi2Te2O7+TeO2 pre-sintered ceramic, fine-grained, Te-rich n-type Bi2Te3 is obtained, achieving a zT of ∼0.4 between 373 and 423 K. The present study demonstrates the feasibility of synthesizing thermoelectrics from oxide precursors, with the potential of simplifying the processing chain and reducing cost to obtain 3D-extruded thermoelectric parts with complex shapes and architectures.

Non-Arrhenius Ionic Conductivity Transitions in Sodium Antiperovskite Ionic Conductors

Anti-perovskites materials have recently attracted great interest as a family of solid state electrolytes with high ionic conduction.[1] Typical solid-state ionic conductors have temperature-dependent ionic conductivity following Arrhenius behavior over a substantial range of temperature, corresponding to a constant activation energy Ea. In the Na3OCl antiperovskite (Fig. 1), there are regimes of Arrhenius behavior separated by broad transitions, all while the structure remains cubic, Figure 2. Such non-Arrhenius ionic conductivity of Na3OCl has been observed in previous literature. [2][3] However, there is no clear explanation for this non-Arrhenius transition. Differential scanning calorimetry shows thermal transitions in the vicinity of these conductivity transitions, Figure 3, suggesting order/disorder phase transitions. Reitveld refinement on temperature dependent synchrotron XRD of Na3OCl suggests changes in octahedral tilt systems, which is CmCm in the low temperature region, Pnma in the medium temperature region, and P4/mbm in the high temperature geion, Figure 4. In this work, we use multiple temperature-resolved characterization methods including synchrotron XRD, transport measurements, and calorimetry, and modeling by AIMD and DFT, to understand this behavior and to gain insight into tuning antiperovskites for high ionic conductivity.This work was supported as part of the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences. Figure 1

Structural stability and thermal expansion of TiTaNbMoZr refractory high entropy alloy

A near-equiatomic TiTaNbMoZr refractory high entropy alloy (RHEA) was prepared by vacuum arc melting. It consists of two BCC solid solution phases (predominant and minor phase are named as B-major and B-minor, respectively) at room temperature. Structural stability and thermal expansion were investigated using in-situ synchrotron XRD and dilatometry. B-major phase is observed until 1273 K, whereas B-minor phase is present up to 1173 K. Above 1173 K, the formation of B′ phase is observed. The mean lattice coefficient of thermal expansion (αlm) and the mean dilatometric coefficient of thermal expansion (αdilm) are derived in the range of 323–1173 K and 323–1273 K, respectively. αlm increases linearly in the range of (8.1–8.8)× 10−6 K−1 and the mean αdilm varies from 7.5 × 10−6 K−1 to 10.9 × 10−6 K−1. Dilatometric strain and lattice strain are found to be identical up to 1000 K. However, beyond 1000 K, the dilatometric strain increases considerably in comparison to the lattice strain due to the generation of temperature-induced point defects (vacancies). The present work demonstrates that the TiTaNbMoZr RHEA exhibits structural (phase) stability up to 1173 K and thermal stability up to 1000 K.

Composition-dependent slip planarity in mechanically-stable face centered cubic complex concentrated alloys and its mechanical effects

In metallic materials, enhancing strain hardening capacity positively affects ductility, fracture toughness, ultimate tensile strength, and other properties. Thus, activating mechanically-induced martensitic transformation or twinning mechanisms has been a captivating goal in the design of steels, titanium alloys, cobalt alloys, complex concentrated alloys (CCAs) and others, through modifications to composition or thermo-mechanical processing. Here instead, we focus on the most basic strain hardening effect, arising from dislocation kinematics, and interactions. For this purpose, we designed two model face centered cubic (FCC) CCAs, Ni2CoCrFe and Ni2CoCrFeTi0.2Al0.1. Both alloys develop single, mechanically-stable, FCC phase microstructures upon processing. Mechanical tests of these alloys reveal that the Al and Ti addition enhances the strain hardening capacity, leading to significant increases in strength and ductility. Microstructure analyses based on electron channeling contrast imaging (ECCI), electron-backscatter diffraction (EBSD), and transmission electron microscopy (TEM) confirm the absence of mechanically-induced twinning and martensitic transformation effects, revealing instead a transition from wavy slip to planar slip. In-situ synchrotron XRD tensile tests are used to discuss the origin of the dislocation glide mode transition and the effects on strain hardening. Based on these analyses, the increased degree of short-range ordering (SRO), rather than the changes in stacking fault energy (SFE), is proposed as the main cause for this transition, and the corresponding effects on strain hardenability.