Dislocations of the (c+a) type are widely recognized as the primary defects limiting the ductility of magnesium. While their glide can be activated in small magnesium crystals under high flow stresses, our in-situ transmission electron microscopy compression tests, conducted over a large strain range, reveal that (c+a) dislocation plasticity becomes inactive following initial activation, leading to dislocation avalanches and subsequent deformation twinning. Initially, pyramidal II slip mediated by (c+a) dislocations accommodates plastic deformation in caxis-oriented magnesium pillars under compression. However, as deformation progresses, interactions among dislocations increasingly impede further glide and prevent surface annihilation. Correlative atomistic simulations indicate that this limited dislocation plasticity arises from the formation of basal I1 and I2 stacking faults, generated by interactions between glissile pyramidal II dislocations. The restricted motion of (c+a) dislocations consequently results in stress accumulation, which triggers dislocation avalanches and deformation twinning. This deformation behavior fundamentally differs from the typical dislocation starvation or exhaustion mechanisms observed in small-scale plasticity, offering novel insights into plasticity and work hardening in bulk magnesium.

A total of five Zintl phase compounds in the solid-solution BaZn2-xCdxSb2 (0.10(2) <= x <= 2) system have been successfully synthesized by the molten Pb-flux method. Both powder X-ray and single-crystal X-ray diffraction analyses proved that the title compounds displayed the phase transition between the BaCu2S2-type phase (space group Pnma, Z = 4) and the CaAl2Si2-type phase (space group P3m1, Z = 1) depending on the Zn/Cd mixed ratio. Furthermore, this kind of structure selectivity was dictated by the radius ratio criterion between the cationic and the anionic elements (r+/r-): three Zn-rich compounds with the r+/r- > 1 (BaZn1.90(1)Cd0.10Sb2, BaZn1.75 (2)Cd0.25Sb2, and BaZn1.62(2)Cd0.38Sb2) preferred to adopt the BaCu2S2-type phase, while two Cd-rich compounds with the r(+)/r(-) <= 1 (BaZn0.16(2)Cd1.84Sb2 and BaCd2Sb2) preferred to crystallize in the trigonal CaAl2Si2-type phase. A series of TB-LMTO calculations using the two hypothetical models: BaZn1.5Cd0.5Sb2 and BaZn0.5Cd1.5Sb2, proved that a resonance peak in the density of states of BaZn1.5Cd0.5Sb2 implied the enhanced Seebeck coefficient of the three Zn-rich compounds, and the reduction of band gap observed in a band structure of BaZn0.5Cd1.5Sb2 influenced the electrical conductivity of the Cd-rich BaZn0.16(2)Cd1.84Sb2. Temperaturedependent thermoelectric property measurements showed the maximum ZT of 0.54 for the quaternary BaZn1.62(2)Cd0.38Sb2, which should mainly be attributed to the reduced kappa tot due to the Zn and Cd disordering in the anionic frameworks.

Three co-substituted quaternary and quinary Zintl phases belonging to the Ba1-xSrxZn2-yCuySb2 (x = 0, 0.09; 0.24 <= y <= 0.42) system were prepared by the molten Pb metal-flux method. Co-substitution using the cationic Sr and anionic Cu for Ba and Zn was initially applied to lower the thermal conductivities and to improve the electric conductivities of these title compounds simultaneously. The homogeneities of single-phase products were verified by powder x-ray diffraction analysis, and the BaCu2S2-type orthorhombic crystal structures with the Ba/Sr and the Zn/Cu mixed-sites were refined by single crystal x-ray diffraction analysis. Structural selectivity for the observed BaCu2S2-type phase was rationalized by the radius ratio of cationic and anionic elements, where r(+)/r(-) > 1. DFT calculations using the three structural models revealed that the Sr and Cu substitutions can increase the structural stability and the hole carrier concentration. A series of temperature-dependent electrical transport property measurements for BaZn1.76Cu0.24Sb2 and Ba0.91Sr0.09Zn1.70Cu0.30Sb2 successfully proved that the co-substitution using Sr and Cu enhanced electrical conductivities, but reduced the Seebeck coefficients resulting in the slight change in power factor.

Abstract ⟨c+a⟩ dislocations are considered as the primary defects limiting the ductility of magnesium. It is argued that in small magnesium crystals the glide of such dislocations can be activated to accommodate plastic strain at high flow stress levels that are rarely achieved in the bulk. Here, we report ⟨c+a⟩ dislocation-mediated small-scale plasticity of c-axis oriented submicrometer-sized magnesium pillars observed by in situ transmission electron microscopy compression tests. After mobile ⟨c+a⟩ dislocations accommodate the initial plasticity of pillars, interactions between dislocations develop local dislocation entanglements, thereby preventing consecutive dislocation glide and surface annihilation. Supported by atomistic simulations, this increased pinning and multiplication is attributed to the formation of basal I1 and I2 stacking faults, induced by interaction of glissile pyramidal II dislocations, which serve as anchor points for dislocation sources. The ensuing plastic strain is accommodated via dislocation avalanches caused by simultaneous activation of multiple dislocation sources at increasing stress levels, forming a dislocation forest of ⟨c+a⟩ dislocations in the confined volume. This observation distinctly differs to common small-scale plasticity associated with a dislocation starved or exhausted state and provides a new concept towards plasticity and work hardening in bulk Mg.

Five novel Zintl phase solid solutions in the Ba1-x Sr x Zn2-y Cd y Sb2 (0 & LE; x & LE; 0.13(1); 0 & LE; y & LE; 0.32(2)) system were successfully synthesized by the moltenPb metal-flux method, and the powder X-ray diffraction and single-crystalX-ray diffraction analyses proved that all five title compounds adoptedthe BaCu2S2-type phase having the orthorhombic Pnma space group (Z = 4, Pearson code oP20) with five crystallographically independent atomicsites. The previously studied BaCu2S2-type antimonidesdemonstrated a limited tolerance for doping in contrast to the CaAl2Si2-type antimonides. To understand the relativelynarrower phase width and limited dopability of the title BaCu2S2-type phase than the CaAl2Si2-type phase in the overall Ba1-x Sr x Zn2-y Cd y Sb2 system, the radiusratio of cations and anionic elements r (+)/r (-) for two structure types werethoroughly investigated. For the first time, the r (+)/r (-) ratio was identifiedas a critical factor for the phase selectivity: (1) r (+)/r (-) > 1 favoredtheBaCu(2)S(2)-type phase, and (2) r (+)/r (-) < 1 favoredthe CaAl2Si2-type phase. We also revealed thestructural transformation mechanism from the more widely observedCaAl(2)Si(2)-type phase to the title BaCu2S2-type phase as the relatively larger cationic elementswere introduced to the system. A series of DFT calculations usingthe three hypothetical models indicated that a resonance peak near E (F) in the density of states curves was descendedfrom the relatively flat band structure at several special symmetrypoints rationalizing the enhanced Seebeck coefficients of Ba0.94(1)Sr0.06Zn1.86(3)Cd0.14Sb2 and Ba0.96(1)Sr0.04Zn1.68(2)Cd0.32Sb2. Electron localization function analysisrationalized the correlation between the polarity change of anionicZn/Cd-Sb bonds and the charge carrier mobility on the anionicframeworks. Temperature-dependent thermoelectric properties were studiedfor the four title compounds, and the results proved that the Sr andCd doping in the title Ba1-x Sr x Zn2-y Cd y Sb2 system successfully enhancedthe ZT values through the increased Seebeck coefficientsand the reduced total thermal conductivities.

Materials displaying negative Poisson’s ratio, referred to as auxeticity, have been found in nature and created in engineering through various structural mechanisms. However, uniting auxeticity with high strength and high stiffness has been challenging. Here, combining in situ nanomechanical testing with microstructure-based modeling, we show that the leading part of limpet teeth successfully achieves this combination of properties through a unique microstructure consisting of an amorphous hydrated silica matrix embedded with bundles of single-crystal iron oxide hydroxide nanorods arranged in a pseudo-cholesteric pattern. During deformation, this microstructure allows local coordinated displacement and rotation of the nanorods, enabling auxetic behavior while maintaining one of the highest strengths among natural materials. These findings lay a foundation for designing biomimetic auxetic materials with extreme strength and high stiffness.

Most current generation thin-film circuits feature copper-based material systems as their metallization components due to their superior electrical properties. Enhanced electrical and mechanical properties are desired to meet the demands of the harsh environments and high power densities and subsequently to prevent stress induced failures in these components. The development of high strength copper alloys is therefore of particular interest, which requires mechanical characterization of these systems on a micrometer length scale especially in conditions mimicking their operational temperatures. Combinatorial material synthesis of thin-film material libraries was used to produce Cu-Ag alloys to enhance the mechanical properties while preserving the electrical properties. The mechanical properties on substrate-attached films were investigated using nanoindentation and on free-standing tensile-test samples, fabricated using photolithography and sputtering, using tensile testing in an electron microscope. This approach enables high-throughput mechanical characterization of Cu-Ag system with a compositional range of 1-8 at. % Ag in Cu. The alloys were tested both in the as-deposited and annealed states. In addition, mechanical properties were investigated at elevated temperatures (400°C) by tensile testing with a micro deformation stage. The investigations show a substantial improvement in the mechanical strength of these thin films at room temperature along the compositional gradient and a mild influence on the thin film conductivity. Beside the testing protocol and results, we also discuss the mechanism-based origin of this behavior with respect to the thin film microstructure.

Fe72.4Co13.9Cr10.4Mn2.7B0.34 high entropy steel was prepared by magnetron sputtering. The alloy exhibits a high yield strength of 2.92 ± 0.36 GPa while achieving appreciable plasticity of 13.7 ± 1.9% at the ultimate compressive strength (3.37 ± 0.36 GPa). The distribution of iron and chromium shows an unusual, characteristic spinodal-like pattern at the nanometer scale, where compositions of Fe and Cr show strong anticorrelation and vary by as much as 20 at.%. The high strength is largely attributable to the compositional modulations, combined with fine grains with body-centered cubic (BCC) crystal structure, as well as grain boundary segregation of interstitial boron. The impressive plasticity is accommodated by the formation and operation of multiplanar, multicharacter dislocation slips, mediated by coherent interfaces, and controlled by shear bandings. The excellent strength–ductility combination is thus enabled by a range of distinctive strengthening mechanisms, rendering the new alloy a potential candidate for safety-critical, load-bearing structural applications.

Fuel cells recombine water from H2 and O2 thereby can power, for example, cars or houses with no direct carbon emission. In anion-exchange membrane fuel cells (AEMFCs), to reach high power densities, operating at high pH is an alternative to using large volumes of noble metals catalysts at the cathode, where the oxygen-reduction reaction occurs. However, the sluggish kinetics of the hydrogen-oxidation reaction (HOR) hinders upscaling despite promising catalysts. Here, the authors observe an unexpected ingress of B into Pd nanocatalysts synthesized by wet-chemistry, gaining control over this B-doping, and report on its influence on the HOR activity in alkaline conditions. They rationalize their findings using ab initio calculations of both H- and OH-adsorption on B-doped Pd. Using this "impurity engineering" approach, they thus design Pt-free catalysts as required in electrochemical energy conversion devices, for example, next generations of AEMFCs, that satisfy the economic and environmental constraints, that is, reasonable operating costs and long-term stability, to enable the "hydrogen economy."

Three Li- and Mg-cosubstituted compounds in the Gd5-x(Li/Mg)xGe4 (x = 1.04(2), 1.17(2), 1.53(2)) system have been successfully prepared by conventional high-temperature reactions. According to powder and single-crystal X-ray diffraction analyses, all three compounds adopt a Gd5Si4-type phase with the orthorhombic Pnma space group (Pearson code oP16, Z = 4) and six crystallographically independent atomic sites. The crystal structure can be described as a combination of two-dimensional Mo2FeB2-type ∞2[Gd2(Li/Mg)Ge2] layers and [Ge2] dimers. Interestingly, as 64% of Li and 26% of Gd at the RE3 and RE2 sites, respectively, were exclusively substituted by Mg in Gd3.47(1)Li0.36(2)Mg1.17(3)Ge4, the lattice parameter b was selectively shortened as a result of the RE3-Ge1 bond shrinkage in comparison to that in Gd4LiGe4, while lattice parameters a and c remained nearly intact. A series of theoretical calculations using the tight-binding linear muffin-tin orbital (TB-LMTO) method indicated that the reduction of the particular RE3-Ge1 bond distance in the title compounds could also be explained by an optimization of bonding based on the corresponding RE3-Ge1 crystal orbital Hamilton population (COHP) curve. Moreover, the specific site preference of Mg for the RE3 site was supported by both size-factor as well as electronic-factor criteria on the basis of the smallest atomic size and the highest electronegativity of Mg among the three cations. Therefore, the overall electronic structure was further interrogated by a density of states (DOS) analysis. The influence of nonmagnetic Li/Mg cosubstitution for the magnetic Gd atoms in the title Gd5-x(Li/Mg)xGe4 system on the magnetic characteristics was also thoroughly studied by isofield magnetization at 100 Oe and 10 kOe and isothermal magnetization measurements at 4 K using two of the title compounds: Gd3.83(1)Li0.48Mg0.69(3)Ge4 and Gd3.47(1)Li0.36(2)Mg1.17(3)Ge4.

Three Zintl phase solid solutions in the Yb5 - xRExAl2Sb6 (RE = Pr, Nd, Sm) system have successfully been synthesized by arc melting followed by annealing. The isotypic crystal structure of these compounds was characterized by PXRD and SXRD analyses, and their Ca5Al2Bi6-type structure (space group Pbam, Z = 2) was described as a combination of (1) the 3-dimensional anionic [Al-2(Sb4Sb4/2)] frameworks and (2) the space-filling cations Yb2+ and RE3+ located in between the anionic frameworks. In particular, the anionic frameworks were originally built from the two neighboring tetrahedral [AlSb4] moieties via the Sb1-Sb1 bridges. The site-preference of RE3+ for the Yb3/RE-site with the mixed occupation ratio between ca. 9% and 16% of RE3+ was elucidated by the size-factor criterion based on the size match between the cationic size and the site volume. The band structures, density of states, and crystal orbital Hamilton population curve analyses were conducted by the tight-binding linear muffin-tin orbital method, and the results proved that the RE3+-doping increased the band degeneracies and the number of resonance peaks near the Fermi level resulting in the improved Seebeck coefficients. The electrical transport property measurements proved that despite the successful addition of n-type RE3+ dopants in the title Yb5 - xRExAl2Sb6 system, the electrical conductivity decreased due to the canceling off of the newly added n-type carriers by the already existing p-type carriers resulting in still the p-type character. However, the enhanced Seebeck coefficients predicted by the increased effective mass from the DFT calculations eventually improved the overall power factor of the RE3+-doped title compounds.

This work presents the new template matching capabilities implemented in Pyxem, an open source Python library for analyzing four-dimensional scanning transmission electron microscopy (4D-STEM) data. Template matching is a brute force approach for deriving local crystal orientations. It works by comparing a library of simulated diffraction patterns to experimental patterns collected with nano-beam and precession electron diffraction (NBED and PED). This is a computationally demanding task, therefore the implementation combines efficiency and scalability by utilizing multiple CPU cores or a graphical processing unit (GPU). The code is built on top of the scientific Python ecosystem, and is designed to support custom and reproducible workflows that combine the image processing, template library generation, indexation and visualization all in one environment. The tools are agnostic to file size and format, which is significant in light of the increased adoption of pixelated detectors from different manufacturers. This paper details the implementation and validation of the method. The method is illustrated by calculating orientation maps of nanocrystalline materials and precipitates embedded in a crystalline matrix. The combination of speed and flexibility opens the door for automated parameter studies and real-time on-line orientation mapping inside the TEM.

Metal nanogels combine a large surface area, a high structural stability, and a high catalytic activity toward a variety of chemical reactions. Their performance is underpinned by the atomic-level distribution of their constituents, yet analyzing their subnanoscale structure and composition to guide property optimization remains extremely challenging. Here, we synthesized Pd nanogels using a conventional wet chemistry route, and a near-atomic-scale analysis reveals that impurities from the reactants (Na and K) are integrated into the grain boundaries of the poly crystalline gel, typically loci of high catalytic activity. We demonstrate that the level of impurities is controlled by the reaction condition. Based on ab initio calculations, we provide a detailed mechanism to explain how surface-bound impurities become trapped at grain boundaries that form as the particles coalesce during synthesis, possibly facilitating their decohesion. If controlled, impurity integration into grain boundaries may offer opportunities for designing new nanogels.

Two advanced, automated crystal orientation mapping techniques suited for nanocrystalline materials—precession electron diffraction (PED) in transmission electron microscopy (TEM) and on-axis transmission Kikuchi diffraction (TKD) in scanning electron microscopy (SEM)—are evaluated by comparing the orientation maps obtained from the identical location on a 30 nm-thick nanocrystalline tungsten (W) thin film. A side-by-side comparison of the orientation maps directly showed that the large-scale orientation features are almost identical. However, there are differences in the fine details, which arise from the fundamentally different nature of the spot pattern and Kikuchi line pattern in terms of the excitation volume and the angular resolution. While TEM-PED is more reliable to characterize grains oriented along low-index zone axes, the high angular resolution of SEM-TKD allows the detection of small misorientation between grains and thus yields better quantification and statistical analysis of grain orientation. Given that both TEM-PED and SEM-TKD orientation mapping techniques are complementary tools for nanocrystalline materials, one can be favorably selected depending on the requirements of the analysis, as they have competitive performance in terms of angular resolution and texture quantification.

The recent development of electron sensitive and pixelated detectors has attracted the use of four-dimensional scanning transmission electron microscopy (4D-STEM). Here, we present a precession electron diffraction assisted 4D-STEM technique for automated orientation mapping using diffraction spot patterns directly captured by an in-column scintillator based complementary metal-oxide-semiconductor (CMOS) detector. We compare the results to a conventional approach, which utilizes a phosphor screen filmed by an external CCD camera. The high dynamic range and signal to noise characteristics of the detector largely improve the image quality of the diffraction patterns, especially the visibility of diffraction spots at high scattering angles. Moreover, the afterimage formation during probe scanning, which obscures orientation indexing in the conventional approach, is suppressed by the fast read-out rate of the detector. The scintillator was found to be robust during the acquisition of nanobeam diffraction pattern including the unblocked transmitted beam in a TEM operated at 200 kV. In the orientation maps reconstructed via the template matching process, the CMOS data yields a significant reduction of false indexing and a higher reliability compared to the conventional approach. This is because the orientation sensitive, weak and small diffraction spots at high scattering angle are more significant. The angular resolution could also be improved in both accuracy and precision by masking reflections close to the direct beam. The results show that fine details such as nano grains, nano twins and sub-grain boundaries can be resolved with sub-degree angular resolution which is comparable Kikuchi-diffraction based orientation mapping.

Multiple interstitial elements (B, C and O), were incorporated into a body-centred cubic (BCC) FeMnCoCr-based interstitial high entropy alloy (iHEA). While achieving an impressive yield strength of 2.55 GPa, the new alloy also possesses appreciable ductility under mechanical loading. The unusual combination of hardening effects brought about by interstitial atoms, compositional fluctuations, and fine grain size greatly strengthened the alloy by inhibiting dislocation motion. Moreover, interstitial elements helped reinforce the grain boundaries through segregation and also assisted in tuning the phase stability. The new alloy transformed from the BCC to hexagonal closed-packed (HCP) phase initially. With increasing load the HCP phase was gradually converted into face-centred cubic (FCC); the resultant HCP/FCC nanolaminates enhanced plasticity via strain partitioning. Under higher loads, the FCC phase became dominant, giving rise to deformation twinning. Taken together, the newly developed BCC structured iHEA affords not only high strength, but also confers remarkable ductility through multiple deformation pathways.

The recent development of electron-sensitive and pixelated detectors has attracted the use of four-dimensional scanning transmission electron microscopy (4D-STEM). Here, we present a precession electron diffraction-assisted 4D-STEM technique for automated orientation mapping using diffraction spot patterns directly captured by an in-column scintillator-based complementary metal-oxide-semiconductor (CMOS) detector. We compare the results to a conventional approach, which utilizes a fluorescent screen filmed by an external charge charge-coupled device camera. The high-dynamic range and signal-to-noise characteristics of the detector greatly improve the image quality of the diffraction patterns, especially the visibility of diffraction spots at high scattering angles. In the orientation maps reconstructed via the template matching process, the CMOS data yield a significant reduction of false indexing and higher reliability compared to the conventional approach. The angular resolution of misorientation measurement could also be improved by masking reflections close to the direct beam. This is because the orientation sensitive, weak, and small diffraction spots at high scattering angles are more significant. The results show that fine details, such as nanograins, nanotwins, and sub-grain boundaries, can be resolved with a sub-degree angular resolution which is comparable to orientation mapping using Kikuchi diffraction patterns.

Scanning nano-beam electron diffraction with a pixelated detector was employed to investigate the orientation relationship of nanometer sized, irradiation induced G-phase (M_6Ni_16Si_7) precipitates in an austenite matrix. Using this detector, the faint diffraction spots originating from the small G-phase particles could be resolved simultaneously as the intense matrix reflections. The diffraction patterns were analyzed using a two-stage template matching scheme, whereby the matrix is indexed first and the precipitates are indexed second after subtraction of the matrix contribution to the diffraction patterns. The results show that G-phase forms with orientation relationships relative to austenite that are characteristic of face-centered cubic (FCC) to body-centered cubic (BCC) transformations. This work demonstrates that nano-beam electron diffraction with a pixelated detector is a promising technique to investigate orientation relationships of nano-sized precipitates with complex crystal structures in other material systems with relative ease.

The advent of miniaturised testing techniques led to excessive studies on size effects in materials. Concomitantly, these techniques also offer the capability to thoroughly examine deformation mechanisms operative in small volumes, in particular when performed in-situ in electron microscopes. This opens the feasibility of a comprehensive assessment of plasticity by spatially arranging samples specifically with respect to the crystal unit cell of interest. In the present manuscript, we will showcase this less commonly utilised aspect of small-scale testing on the case of the hexagonal metal Mg, where, besides dislocation slip on different slip planes, twinning also exists as a possible deformation mechanism. While it is close to impossible to examine individual deformation mechanisms in macroscale tests, where local multiaxial stress states in polycrystalline structures will always favour multiple mechanisms of plasticity, we demonstrate that miniaturised uniaxial experiments conducted in-situ in the scanning electron microscope are ideally suited for a detailed assessment of specific processes.