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This work uses a combination of stress dependent single grain boundary Coble creep and zero-creep experiments to measure interfacial energies, along with grain boundary point defect formation and migration volumes in cubic ZrO2. These data, along with interfacial diffusivities measured in a companion paper are then applied to analyzing two-particle sintering. The analysis presented indicates that the large activation volume, v * = v f + v m primarily derives from a large migration volume and suggests that the grain boundary rate limiting defects are delocalized, possibly due to electrostatic interactions between charge compensating defects. The discrete nature of the sintering and creep process observed in the small-scale experiments supports the hypothesis that grain boundary dislocations serve as sources and sinks for grain boundary point defects and facilitate strain during sintering and Coble creep. Model two-particle sintering experiments demonstrate that initial-stage densification follows interface reaction rate-limited kinetics.

This work demonstrates novel in situ transmission electron microscopy-based microscale single grain boundary Coble creep experiments used to grow nanowires through a solid-state process in cubic ZrO2 between ≈ 1200 °C and ≈ 2100 °C. Experiments indicate Coble creep drives the formation of nanowires from asperity contacts during tensile displacement, which is confirmed by phase field simulations. The experiments also facilitate efficient measurement of grain boundary diffusivity and surface diffusivity. 10 mol% Sc2O3 doped ZrO2 is found to have a cation grain boundary diffusivity of D g b = ( 0.056 ± 0.05 ) exp ( − 380 , 000 ± 41 , 000 R T ) m 2 s − 1 , and surface diffusivity of D s = ( 0.10 ± 0.27 ) exp ( − 380 , 000 ± 28 , 000 R T ) m 2 s − 1 .

This work uses in situ transmission electron microscopy (TEM) based micromechanical testing to isolate and quantify the microstructural toughening mechanisms active in nanostructured Al2O3/GdAlO3 eutectic samples. The effect of fracture direction across orthogonal sections of the rod-like eutectic was used to reveal the influence of different fracture paths and mechanisms on toughening. The average fracture toughnesses of the rod-like structures in the longitudinal cross-section and transverse cross-section are 2.4 MPa·m1/2 and 2.7 MPa·m1/2, respectively. Multiple samples tested in the longitudinal cross-section show significant R-curve toughening response, and obtain values greatly exceeding the initial values upon crack extension. It is concluded that nanoscale crack bridging induces deflection of the crack path, which leads extrinsic energy dissipation as the crack opens. Micropillar compressions are also performed to investigate the composite’s strength. Sample orientation strongly affects the deformation mode and interfacial sliding occurs when the maximal shear stress is parallel to the interface.

Nanocrystalline oxides exhibit exceptional resistance to plastic deformation, manifesting increased strength and hardness with reduced grain size that qualitatively follows the so-called Hall-Petch relationships. However, below a critical grain size, softening has been observed to occur, in the so-called inverse Hall-Petch regime. The mechanisms underlying these phenomena are still not well understood in oxides. Here we observe, using nanopillar compression, that the yield strength initially increases with decreasing grain size for yttria-stabilized zirconia ceramics produced by high-pressure spark plasma sintering. A hardening-to-softening transition occurs at grain sizes below ≈21 nm. The experiments indicate that this transition depends on strain rate, and the onset of the decrease in yield strength occurs before any shear fracture begins. Nanopillar compression combined with in situ electron diffraction demonstrates the onset of softening coincides with an increase in the amount of crystallographic rotation per unit strain, suggesting a change in deformation mechanism.

Polypeptide micelles are widely used as biocompatible nanoplatforms but often suffer from their poor structural stability. Unimolecular polypeptide micelles can effectively address the structure instability issue, but their synthesis with uniform structure and well-controlled and desired sizes remains challenging. Herein we report the convenient preparation of spherical unimolecular micelles through dendritic polyamine-initiated ultrafast ring-opening polymerization of N-carboxyanhydrides (NCAs). Synthetic polypeptides with exceptionally high molecular weights (up to 85 MDa) and low dispersity (Đ < 1.05) can be readily obtained, which are the biggest synthetic polypeptides ever reported. The degree of polymerization was controlled in a vast range (25-3200), giving access to nearly monodisperse unimolecular micelles with predictable sizes. Many NCA monomers can be polymerized using this ultrafast polymerization method, which enables the incorporation of various structural and functional moieties into the unimolecular micelles. Because of the simplicity of the synthesis and superior control over the structure, the unimolecular polypeptide micelles may find applications in nanomedicine, supermolecular chemistry, and bionanotechnology.

Small-scale mechanical testing has been used to isolate the properties of individual grain boundaries and regions of the lattice in undoped UO2 polycrystals. Notched microcantilever specimens were prepared by focused ion beam milling and tested in bending. Fracture toughness values were calculated from finite element analysis of the sample geometry at fracture load using the J-integral method. Lattice and grain boundary fracture toughness values of 1.17 ± 0.16 MPa m1/2 and 1.08 ± 0.08 MPa m1/2, respectively, were obtained. The similarity between the lattice and grain boundary fracture toughness values is consistent with the preference for transgranular room-temperature fracture in UO2. The grain boundary and lattice fracture toughness values also agree well with the toughness of dense polycrystals, which suggests that microstructural-scale toughening mechanisms are limited in such samples.

This work demonstrates a novel approach to ultrahigh-temperature mechanical testing using a combination of in situ nanomechanical testing and localized laser heating. The methodology is applied to characterizing and testing initially nanograined 10 mol % Sc2O3-stabilized ZrO2 up to its melting temperature. The results suggest that the low-temperature strength of nanograined, d < 50 nm, oxides is not influenced by creep. Tensile fracture of ZrO2 bicrystals produce a weak-temperature dependence suggesting that grain boundary energy dominates brittle fracture of grain boundaries even at high homologous temperatures; for example, T = 2050 °C or T ≈ 77% Tmelt. The maximum temperature for mechanical testing in this work is primarily limited by the instability of the sample, due to evaporation or melting, enabling a host of new opportunities for testing materials in the ultrahigh-temperature regime.

Irradiation induced creep (IIC) compliance in NiCoFeCrMn high entropy alloys is measured as a function of grain size (30

A series of nanopillar compression tests were performed on tungsten as a function of temperature using in situ transmission electron microscopy with localized laser heating. Surface oxidation was observed to form on the pillars and grow in thickness with increasing temperature. Deformation between 850 °C and 1120 °C is facilitated by long-range diffusional transport from the tungsten pillar onto adjacent regions of the Y2O3-stabilized ZrO2 indenter. The constraint imposed by the surface oxidation is hypothesized to underly this mechanism for localized plasticity, which is generally the so-called whisker growth mechanism. The results are discussed in context of the tungsten fuzz growth mechanism in He plasma-facing environments. The two processes exhibit similar morphological features and the conditions under which fuzz evolves appear to satisfy the conditions necessary to induce whisker growth.

We demonstrate using theoretical, computational, and experimental studies a morphological instability, in which a polycrystalline nanorod breaks up at grain boundaries (GBs) into an array of isolated domains. Our theoretical model is used to establish a neutral stability surface demarcating stable and unstable perturbations. It is shown that GBs play a destabilizing role in which the critical wavelength for the instability decreases with the increase in the GB energy. We carry out phase field simulations, which reveal accelerated pinch-off kinetics with the increase in the GB energy and predict temporal evolution of interfacial profiles in quantitative agreement with experimental observations.

Fully-dense and single-phase nanostructured scandia-stabilized zirconia specimens were produced by high-pressure spark plasma sintering technique. Nanocrystalline powders were prepared by the coprecipitation method. Green pellets were sintered at temperatures varying from 700 to 900 °C and pressures from 1.4 to 2 GPa, resulting in dense microstructures with single-phase fluorite-type cubic structure within a wide range of Sc2O3 content (6–15 mol%). The average grain size of sintered specimens ranged from 8 to 20 nm. Transmittance spectra confirm translucence in sintered specimens, which is consistent with full density. The results reported here reveal that the polymorphism challenge in the zirconia-scandia system can be successfully suppressed by this consolidation technique, which allows for controlling the grain size of bulk specimens.

This study aims to elucidate the impact of interfacial microstructure and properties on fracture toughness in binary Al2O3/SmAlO3 eutectic and its polycrystalline samples via in-situ microcantilever deflection tests. Al2O3-SmAlO3 eutectic with semi-coherent heterointerfaces exhibits superior interfacial toughness of 2.85 MPa⋅m1/2 relative to randomly oriented interfaces in Al2O3/SmAlO3 polycrystals. SmAlO3 grain boundaries (GBs) have the lowest toughness of 1.97 MPa⋅m1/2 among all the constituents, i.e. bulk and interfaces. The toughness of eutectic Al2O3-SmAlO3 interfaces is intermediate between polycrystalline Al2O3-Al2O3 GBs and SmAlO3-SmAlO3 GBs. Fracture toughness values of both polycrystalline and eutectic Al2O3-SmAlO3 samples obtained by mesoscopic indentation measurements are in the range of 4.2 MPa⋅m1/2to 4.7 MP⋅m1/2, which exceeds all constituent components. Much of the overall fracture toughness of the bulk samples derives from microstructural and geometric energy dissipation mechanisms.

Phase evolution in dilute, strongly immiscible Cu-Mo, Cu-Mo-Ni, and Cu-Mo-Ag alloys during severe plastic deformation at low-temperature has been experimentally investigated. For the Cu95Mo05 alloy, Mo nanoparticles are formed, ∼10 nm in diameter, as part of a steady state microstructure, with less than ∼1 at.% Mo dissolved in the matrix. Addition of 10 or 20 at.% Ni to this binary alloy results in a significant increase in the Mo solubility, whereas comparable additions of Ag has a corresponding little effect. The steady state microstructures of alloys during ball milling of elemental powders are very similar to those during HPT processing of initially homogeneous solutions. The results are discussed in terms of an effective temperature model. Model MD simulations are presented to help relate the predictions of the effective temperature model to atomistic mechanisms.

We report on the chemical lithiation of long microscale helices composed of densely packed amorphous silicon (aSi) nanofibrils, fabricated by glancing angle deposition (GLAD) through e-beam evaporation. In situ electron microscopy and companion finite element modeling demonstrate that the nanofibrillar structure of the aSi helices allows for 2 orders of magnitude faster effective rates for Li diffusion ( D0 = 10-10 cm2/s) compared to solid aSi nanowires, while also averting fragmentation during lithiation. More importantly, it is shown that specific helical geometries can accommodate large, lithium-induced, volumetric expansions without shape distortion. A major advantage of the helical nanostructures is that the compressive force generated due to lithiation-induced expansion is an order of magnitude smaller than in straight nanocolumns that permanently buckle during lithiation. Thus, GLAD-fabricated films composed of dense periodic microscale helices with properly designed coil geometries are highly suitable for robust, high-capacity Li+ anodes.

Polypeptide micelles are widely used as biocompatible nanoplatforms but often suffer from their poor structural stability. Unimolecular polypeptide micelles can effectively address the structure instability issue, but their synthesis with uniform structure and well-controlled and desired sizes remains challenging. Herein we report the convenient preparation of spherical unimolecular micelles through dendritic polyamine-initiated ultrafast ring-opening polymerization of

This work demonstrates a novel approach to ultrahigh-temperature mechanical testing using a combination of in situ nanomechanical testing and localized laser heating. The methodology is applied to characterizing and testing initially nanograined 10 mol % Sc

Determining displacement and/or strain fields at the nanoscale during material deformation can be instrumental in developing a multiscale understanding of material response. Full-field quantitative kinematic measurements based on transmission electron microscopy (TEM) are lagging behind other microscopy techniques. Here, we develop an experimental approach combining digital image correlation (DIC) and particle tracking (PT) for characterizing in situ microscale deformation of amorphous SiO2 in the TEM. Gold nanoparticles deposited on SiO2 provide both the speckle pattern required by DIC when averaged over a subset region and target particles for PT. To demonstrate and validate the feasibility of using DIC and PT in the TEM, micron sized SiO2 beam samples are machined using a focused ion beam (FIB) and loaded in the TEM via indentation. DIC and PT are then applied to measure in situ displacements from a sequence of TEM images taken during loading and creep of the beam. Results of the two measurement methods agree well with each other and with the applied displacement measurements, thus demonstrating their effectiveness in determining local displacements from TEM experiments. Sources of noise resulting from sample drift and image intensity variations are discussed.

In the last decade, reacting Li ion electrodes in situ using vacuum based methods such as transmission electron microscopy (TEM) has become prevalent for assessing their reaction pathways. However, the vast majority of these studies do not perform electrochemical reactions at potentials relevant to batteries and/or characterize electrolytic reactions. Here we demonstrate a simple and flexible approach combining the benefits of solid and liquid electrolytes to enable diverse in situ characterization methods, including optical imaging, electrical measurements, X-ray photoelectron spectroscopy, X-ray diffraction, atomic force microscopy, and transmission electron microscopy. This work demonstrates these methods applied to the novel cell during electrolytic lithiation of the conversion anode ZnO at electrochemically relevant potentials.

Amorphous carbon probably is the most-known and widely used carbon allotrope. However, unlike crystalline carbon such as graphene or carbon nanotubes, amorphous carbon generally is brittle and unable to sustain large mechanical deformation due to the inherent lack of long-rang order. In this work, we demonstrate a significant delay of failure on an amorphous carbon hollow nanosphere due to the buckling and post-buckling deformation of the spherical shell. Both in situ experiments and finite element analyses are conducted to probe deformation mechanism of buckling and post-buckling, suggesting a strong dependence of the shell thickness on the buckling process. A unified deformation energy-based mechanics model is developed to extract the critical buckling and post-buckling force, and shows good agreement with in situ experiments and finite element analyses. Extension of the model to inhomogeneous hollow nanospheres is also discussed and confirmed with finite element analyses.

Improving the mechanical performance of nanocrystalline functional oxides can have major implications for stability and resilience of battery cathodes, development of reliable nuclear oxide fuels, strong and durable catalytic supports. By combining Monte Carlo simulations, experimental thermodynamics, and in-situ transmission electron microscopy, we demonstrate a novel toughening mechanism based on interplay between the thermo-chemistry of the grain boundaries and crack propagation. By using zirconia as a model material, lanthanum segregation to the grain boundaries was used to increase the toughness of individual boundaries and simultaneously promote a smoother energy landscape in which cracks experience multiple deflections through the grain boundary network, ultimately improving fracture toughness.

In situ transmission electron microscopy based nanopillar compression is utilized to investigate the mechanical properties of zinc dialkyldithiophosphate (ZDDP) tribological films. Small scale testing provides localized insights into the properties of ZDDP films that spatially vary in composition at the nanoscale. Large variations in yield strength, between 0.82 and 4.8 GPa, are measured and correlated with local chemistry changes. Lower density regions of the film that tend to be carbon-rich have lower yield stresses, than higher density regions that tend to be zinc-, iron-, and sulfur-rich. It is hypothesized that the strong compositional dependence in mechanical properties at the nanoscale is an important factor contributing to the efficacy of ZDDP as an antiwear tribological film.

This work applies in situ Auger electron spectroscopy and X-ray photoelectron spectroscopy to the study of surface redox on LiNi1/3Mn1/3Co1/3O2 during charging and overcharging. We observe that all three transition metals are surface redox active, and that oxygen oxidation occurs for voltages above ≈4.2 V O2 loss above ≈4.7 V, mediated by carbon redox, leads to partial reduction of the transition metals at the surface during overcharging.

Irradiation induced creep (IIC) rates are measured in compression on Ag nanopillar (square) beams in the sink-limited regime. The IIC rate increases linearly with stress at lower stresses, i.e. below ≈2/3 the high temperature yield stress and parabolically with pillar width, L, for L less than ≈300 nm. The data are obtained by combining in situ transmission electron imaging with simultaneous ion irradiation, laser heating, and nanopillar compression. Results in the larger width regime are consistent with prior literature.

Sn has been proposed for use as a high capacity anode material. Because of its ductile metallic nature, Sn may exhibit unique stress evolution during lithiation. Here, 2D radiography and 3D tomography are employed to visualize the evolution of geometry, internal structure, alloying, and damage during lithiation, delithiation, and rest of Sn wires with micron scale diameters. Lithiation proceeds isotropically, resulting in geometric and dimensional changes after 25% of total lithiation when the tensile stresses are sufficiently high to exceed the flow stress of the unlithiated Sn core and cause elongation and diameter increase. Damage occurs at later stages in the form of cracks terminating at the wire surface and voids forming in the unlithiated core. Notably, significant fragmentation occurs during delithiation which, due to void formation that accommodates the resulting stresses, does not measurably alter the wire cross-section and length. The distinguishing feature of the chemo-mechanics of Sn compared to Si or Ge is the pronounced creep rate at applied strain rates as high as 10−6 s−1, which promotes large strains in the core, eventually leading to void nucleation in the unlithiated core during lithiation, and more importantly, continues driving the deformation of the anode while at rest.

A custom built reusable cell for in situ lithiation and mechanical deformation studies while in an X-ray tomograph was demonstrated, and the strain and volume changes of a composite graphite anode were computed from 3D X-ray microcomputed tomography data via Digital Volume Correlation (DVC). The test anode was a composite electrode comprised of a porous compliant matrix, graphite as the Li+ host material, 5-μm ZrO2 marker particles for use with DVC, and active carbon black to enhance electrical conductivity. The composite electrodes were hot-pressed to control their porosity, and in turn the mechanical integrity of the resulting material. This composite anode was included in a half-cell and lithiated in situ while in a tomograph, and intermittent 3D data were collected at different lithiation levels up to full gravimetric capacity. Strain measurements by DVC demonstrated relatively uniform expansion of the freestanding electrode with average normal strains in the three directions varying by 20%, while the internal shear strains were found to be negligible. The average experimental strains were about 75% of the theoretical value, as estimated by the rule of mixtures, which implies that ~25% of the normal strains in graphite, due to lithiation, are accommodated by the surrounding matrix.

The fracture of micro-cantilever Al 2 O 3 specimens containing single grain boundaries is quantified via in situ bending experiments performed in the transmission electron microscope. The type of grain boundary complexion plays a dominant role in determining the fracture response, while the dopant chemistry has a secondary effect for the same complexion type. More ‘ordered’ complexions, those containing sub-monolayer adsorbates, are tougher than the undoped material. The behaviors of SiO 2 and Y 2 O 3 doped Al 2 O 3 with different complexions are compared and contrasted. In general, grain boundaries exhibiting more ‘disordered’ complexions types, those with multilayer adsorbates, are embrittled relative to undoped Al 2 O 3 .

High pressure torsion (HPT) experiments have been carried out at very low temperatures (−78 °C) on dilute Cu-Nb alloys. The samples were prepared by magnetron sputtering to create solid solutions containing nominally between 1 at.% and 10 at.% Nb. Some samples were pre-annealed to 700 °C to form large Nb precipitates, ∼75 nm in radius, prior to HPT. For the unannealed alloys, HPT at low temperatures led to alloy decomposition for alloys with concentrations greater than ∼2 at.% Nb, with the steady state concentration of Nb increasing from ∼1.5 to ∼3 at.% as the initial concentration of Nb was increased. It was also observed that BCC Nb precipitates formed during low-temperature HPT, with a steady state precipitate size ∼10 nm in radius, which was insensitive to alloy concentration. HPT of pre-annealed Cu-10 at.% alloy led to the same steady state microstructure as the unannealed sample, indicating that the steady state during the low temperature HPT process is independent of the initial state for these Cu-Nb alloys. A model for phase evolution in strongly immiscible alloys during severe, low-temperature deformation is offered and implemented through kinetic Monte Carlo simulations. Good agreement with experiment is obtained.

Irradiation of alloys with energetic particles leads to the forced chemical mixing of atoms and the creation of point defects. At elevated temperatures, the point defects are mobile and enhance diffusion. Since forced mixing occurs in energetic displacement processes, alloy constituents tend to flow down gradients in their concentration, while radiation enhanced diffusion is thermally activated and alloy components respond to gradients in their chemical potential. Phase evolution in irradiated alloys thus depends on the competition between these two dynamics. A similar situation occurs during severe plastic deformation, dislocation glide results in forced chemical mixing, while dislocation reactions lead to the creation of vacancies and enhanced thermally activated diffusion. One possible consequence of these competing dynamics is that alloys self-organize into compositional patterns, i.e., concentration variations adopt a fixed length scale determined by the nature of the driving forces and the internal dynamics of the alloy. The current perspective illustrates how the details of driving forces relate to the length scale of the compositional patterns and their morphology. A surprising finding is that irradiation and severe plastic deformation can both lead to compositional patterning even at low temperatures, i.e., in absence of thermally activated diffusion. While the compositional patterning again derives from competing dynamical processes, the characteristic length scales are determined by quite different aspects of the forced mixing. For irradiation, the ballistic recoil distance limits the maximum length scale for patterning at high temperatures, while it is the extent of the thermal spike at low temperatures. For severe plastic deformation, the glide distance of dislocations controls the largest length scale for patterning at high temperatures, whereas kinetic roughening of precipitates controls the maximum length at low temperatures.

Average lattice diffusivities of Cr3+ in undoped, MgO-doped, and SiO2-doped Al2O3 have been measured between 1100 and 1300 °C using scanning transmission electron microscopy based x-ray energy dispersive spectroscopy. It has been demonstrated that both MgO and SiO2 dopants have negligible effect on lattice Cr3+ chemical diffusion. The experimentally determined Arrhenius equations for undoped, MgO-doped, and SiO2-doped samples are D undoped = 1.9 × 10 − 10 exp ( − 298 k J / mol R T ) m 2 / s , D Mg O = 2.0 × 10 − 13 exp ( − 217 kJ / mol R T ) m 2 / s , and D Si O 2 = 6.2 × 10 − 11 exp ( − 273 kJ / mol R T ) m 2 / s , respectively. The weak dopant effect is discussed in the context of the contributions from both extrinsic point defect concentrations and their cluster binding energies.

This work combines nanoscale tribological wear methods, used to prepare zinc dialkyldithiophosphate (ZDDP) tribofilms under conditions of controlled loading, with site specific nanopillar compression testing to derive a relationship between the ZDDP growth conditions and resultant mechanical properties. The key finding is that ZDDP films grown at higher loads exhibit lower yield strength s , which correlate with differences in tribofilm chemistry. We hypothesize that the load sensitivity of tribofilm properties may underlie the efficacy of ZDDP in suppressing wear by functioning as a hard coating at low loads while exhibiting enhanced lubricity at high loads.

This work investigates the relative contributions to strengthening from twinning, solid-solution, precipitation, and irradiation hardening mechanisms in sputtered Cu–W thin films irradiated to different doses. A nanograin solid solution strengthening mechanism with a linear compositional dependence is observed for the as-grown alloys and for the alloy samples irradiated to 0.5 dpa. Solid solution strengthening is the major strengthening mechanism for Cu99.5W0.5 at all irradiation doses. Irradiation induces precipitation in samples with W concentrations greater than or equal to 1% at doses above ≈0.5 dpa. The growth of 1–4 nm precipitates enhances the hardness of these alloys, and the degree of strengthening is determined by the interparticle spacing. While the alloys exhibit steady-state properties after a relatively low dose (≈1 dpa), the different time scales associated with detwinning and damage accumulation in pure Cu lead transients at higher doses (>5 dpa).

This work reports on irradiation-induced creep (IIC) measured on nanolaminate (Cu-W and Ni-Ag) and nanocrystalline alloys (Cu-W) at room temperature using a combination of heavy ion irradiation and nanopillar compression performed concurrently in situ in a transmission electron microscope. Appreciable IIC is observed in multilayers with 50 nm layer thicknesses at high stress, ≈½ the yield strength, but not in multilayers with only 5 nm layer thicknesses.

This work employs in-situ transmission electron microscopy based nanopillar compression of physical vapor deposited multilayers to measure the interfacial shear strengths of model Ag-Pd, Ag-Au, Ag-Ni, Ag-Cu, and Cu-Ni (111) oriented cube-on-cube interfaces. The experimental trends are primarily rationalized by considering the coherency regimes. Coherent interfaces shear via slip transmission across them. Pillars containing semi-coherent interfaces with 5% shear locally and their interfacial shear strength decreases with increasing misfit.

Knowledge of their bulk physical properties often guides selection of appropriate tribological coating materials. However, these properties as well as the microstructure evolve dramatically under the extreme conditions imposed during mechanical wear. The dynamic response ultimately governs the material’s wear performance; thus, understanding the dynamic evolution of the system is critical. This work characterizes the change in mechanical properties and microstructure as a function of wear cycles in model MoS2 films using a combination of nanowear testing, transmission electron microscopy, and site-specific nanopillar compression. Notably, mechanical wear enhances the mechanical properties of the MoS2 while simultaneously evolving a microstructure that reduces the coefficient of friction and wear rate. We hypothesize that this self-optimizing behavior underpins the exceptional lubricity and antiwear performance of MoS2.

CdSe with high densities of coherent polymorphic zincblende/wurtzite (ZB/WZ) interfaces were deposited on TiO2 nanorod arrays (NRAs) by electrodeposition and an optimized annealing process. In situ TEM annealing experiments observed the formation of the ZB/WZ polymorphic junctions that resulted from the change of atomic stacking sequence by dislocation movement induced by stoichiometry changes occurring during annealing. The process deforms CdSe4-tetrahedrons in ZB driving the ZB to WZ phase transition. The formation of ZB/WZ coherent polymorphic junctions enhanced the separation and transport of photo-generated electron-hole pairs in CdSe. The CdSe/TiO2 photoanode produced H2 at a rate of 260.9 μmol cm−2 h-1 under AM 1.5 global sunlight (AM 1.5 G). This is the highest reported value among CdSe-based photoanodes, which indicates the important role of the coherent polymorphic junctions.

In recent decades researchers have revealed a rich variety of grain boundary segregation phenomena, including interfacial phase, or complexion, transitions. Grain boundary complexion transitions have been shown to induce discontinuous changes in materials properties as a function of temperature and chemical potential, and have been used to explain phenomena that had previously evaded satisfactory explanation. This review article discusses how grain boundary complexions relate to mass transport and mechanical properties, by highlighting both what is understood and emphasizing topics requiring additional study.

Tin (Sn) anode active particles were electrochemically lithiated during simultaneous imaging in a scanning electron microscope. Relationships among the reaction mechanism, active particle local strain rate, particle size, and microcrack formation are elucidated to demonstrate the importance of strain relaxation due to mechano-electrochemical interaction in Sn-based electrodes under electrochemical cycling. At low rates of operation, due to significant creep relaxation, large Sn active particles, of size 1 μm, exhibit no significant surface crack formation. Microcrack formation within Sn active particles occurs due to two different mechanisms: (i) large concentration gradient induced stress at the two-phase interface, and (ii) high volume expansion induced stress at the surface of the active particles. From the present study, it can be concluded that majority of the microcracks evolve at or near the particle surface due to high volume expansion induced tension. Concentration gradient induced damage prevails near the center of the active particle, though significantly smaller in magnitude. Comparison with experimental results indicates that at operating conditions of C/2, even 500 nm sized Sn active particles remain free from surface crack formation, which emphasizes the importance of creep relaxation. A phase map has been developed to demonstrate the preferred mechano-electrochemical window of operation of Sn-based electrodes.