Heterophase Interface Research Articles

Novel Highly Active Anatase/Rutile TiO2 Photocatalyst with Hydrogenated Heterophase Interface Structures for Photoelectrochemical Water Splitting into Hydrogen

In the past few years, anatase/rutile TiO2 heterophase junction structures with highly efficient photocatalytic performance have been explored widely, while their activities are still unsatisfactory in solar-to-hydrogen energy conversion. In this study, a novel anatase/rutile TiO2 photoelectrode with hydrogenated heterophase interface structures (A-H-RTNA) was successfully designed and synthesized for the first time via hydrothermal synthesis–hydrogenation–branching growth. Structure characterization indicated that the hydrogenated interfaces between anatase–branches and rutile–TiO2–nanorod hold appropriate oxygen vacancies and Ti3+ and inferred that new energy levels of oxygen vacancy and Ti–OH lie below the band edge positions of conduction band and valence band of rutile TiO2 nanorod, respectively. The matching energy levels between anatase–branches and hydrogenated rutile–nanorod obviously reduce the recombination of the photogenerated carriers, resulting in a superior photoelectrochemical (PEC) perfo...

Effects of Nb and Ta additions on the strength and coarsening resistance of precipitation-strengthened Al-Zr-Sc-Er-Si alloys

A dilute Al-0.07Zr-0.02Sc-0.005Er-0.06Si (at.%) alloy was microalloyed with 0.08 at.% Nb or Ta. Atom-probe tomography reveals that, upon aging, Nb and Ta partition to the coherent L12-Al3(Zr,Sc,Er) nanoprecipitates (with average concentrations of 0.2 and 0.08 at.%, respectively), with both segregating at the matrix/nanoprecipitate heterophase interface. This is consistent with the Nb- and Ta-modified alloys exhibiting, as compared to the unmodified alloy: (i) higher peak microhardness, from a higher nanoprecipitate volume fraction and/or lattice parameter mismatch; and (ii) improved aging resistance, from slower nanoprecipitate coarsening due to the small diffusivities of niobium and tantalum in aluminum. Analogous results were previously reported for a V-modified alloy.

Atomically resolved calcium phosphate coating on a gold substrate.

Some articles have revealed that the electrodeposition of calcium phosphate (CaP) coatings entails a precursor phase, similarly to biomineralization in vivo. The chemical composition of the initial layer and its thickness are, however, still arguable, to the best of our knowledge. Moreover, while CaP and electrodeposition of metal coatings have been studied utilizing atom-probe tomography (APT), the electrodeposition of CaP ceramics has not been heretofore studied. Herein, we present an investigation of the CaP deposition on a gold substrate. Using APT and transmission electron microscopy (TEM) it is found that a mixture of phases, which could serve as transient precursor phases to hydroxyapatite (HAp), can be detected. The thickness of these phases is tens of nanometers, and they consist of amorphous CaP (ACP), dibasic calcium phosphate dihydrate (DCPD), and octacalcium phosphate (OCP). This demonstrates the value of using atomic-resolved characterization techniques for identifying the precursor phases. It also indicates that the kinetics of their transformation into the more stable HAp is not too fast to enable their observation. The coating gradually displays higher Ca/P atomic ratios, a porous nature, and concomitantly a change in its density.

Elastic Interaction between Dislocation and Interface in Elastically Anisotropic Ceramic Bimaterials Al<sub>2</sub>O<sub>3</sub>-AlN: Image Force Effect

The Al2O3 and AlN materials are often used as electrical insulators (electronic substrates) also the case of pressure sensors where the aluminum nitride (AlN) is selected as the piezoelectric layer and the alumina (Al2O3) as a solid substrate insulating. This study aims to investigate the mobility of dislocations near the heterophase interface of bimaterials based alumina (Al2O3) under the effect of the image force, without the effect of temperature, deformation and external stress These dislocations having a Burgers vector b = 1/3 , they are located in Al2O3. The interface is defined by its plane parallel to the dislocation line and disorientation varies between 0 and 180。 around the axis . Usually, the image force calculated in the context of the anisotropic linear elasticity using Barnett and Lothe theory with Stroh formalism, Fi = ΔE / d, where ΔE is the elastic interaction energy. The results show that dislocation motion under the image force effect depends on the elastic and crystallographic properties of the materials constituting the bicrystals and even disorientation of the interface which has an effect on the intensity of the elastic interaction energy. The dislocations are repelled to the interface if the difference in shear modulus between the two materials is positive (Δμ= μ2 − μ1>0), they are attracted to the interface in the opposite case (Δμ= μ2 − μ1<0).

Interaction between semicoherent interfaces and Volterra-type dislocations in dissimilar anisotropic materials

Abstract

Elucidation of δ-γ Massive like Transformation focusing on hetero-phase interface and competition between nucleation itself and consequent growth

Elucidation of δ-γ Massive like Transformation focusing on hetero-phase interface and competition between nucleation itself and consequent growth

Elastic interactions between interface dislocations and internal stresses in finite-thickness nanolayered materials

Anisotropic elasticity theory is used to analyze elastic strain interactions between heterophase interface dislocations and four types of internal stresses in finite-thickness nanolayered face-centered cubic materials. The first interaction is related to the mechanical forces acting on semicoherent interfaces, which arise from heterogeneous elastic fields between the neighboring materials with free surfaces. The second interaction is associated with the Peach-Koehler force exerted on lattice dislocations in free-standing bi- and tri-nanolayers, and is compared to the limiting case of infinite bicrystals. The third case yields to the interaction energy balance and the corresponding equilibrium distance between two Shockley partial dislocations. The fourth and last case is dedicated to the elastic interaction forces between vacancies and interfaces using the force dipole moment approximation.For such cases, the elastic interaction problems are treated by involving the effects of (i) the dislocation characters, (ii) the anisotropic (versus isotropic) elasticity calculations, and (iii) the additional third coherent MgO layer on bilayered Au/Al systems.

Atomic-Scale Studies of Defect Interactions with Homo- and Heterophase Interfaces

Interfaces are planar metastable defects with singular features capable of controlling diverse material properties, including mechanical response and the microstructure evolution in materials under irradiation. This ability of interfaces to dictate the material response resides inherently in their atomic structure, which controls the interactions of dislocations as well as point and defect clusters with the interface. We recently showed how dislocations nucleated from defect clusters interact with a heterophase interface in Cu–Nb layered composites. We also showed how the ability of the interface to absorb vacancy clusters depends on the atomic structure at the interface. Herein, we elaborate on the effect of the atomic structure on the ability of the interface to absorb dislocations as well as vacancy and self-interstitial defect clusters. We study a physical-vapor-deposited Kurdjumov–Sachs orientation in a Cu–Nb interface and an asymmetric \(\Sigma \)11 grain boundary in pure Cu. On the one hand, the manner in which dislocations react with the interface depends on the misfit dislocation arrangement, which substantially differs between these two cases. On the other hand, vacancy and self-interstitial clusters are absorbed similarly upon interaction with both structures.

Enhanced polarization by the coherent heterophase interface between polar and non-polar phases.

A piezoelectric composite containing the ferroelectric polar (Bi(Na0.8K0.2)0.5TiO3: f-BNKT) and the non-polar (0.94Bi(Na0.75K0.25)0.5TiO3-0.06BiAlO3: BNKT-BA) phases exhibits synergetic properties which combine the beneficial aspects of each phase, i.e., the high saturated polarization (Ps) of the polar phase and the low coercive field (Ec) of the non-polar phase. To understand the origin of such a fruitful outcome from this type of polar/non-polar heterophase structure, comprehensive studies are conducted, including transmission electron microscopy (TEM) and finite element method (FEM) analyses. The TEM results show that the polar/non-polar composite has a core/shell structure in which the polar phase (core) is surrounded by a non-polar phase (shell). In situ electrical biasing TEM experiments visualize that the ferroelectric domains in the polar core are aligned even under an electric field of ∼1 kV mm(-1), which is much lower than its intrinsic coercive field (∼3 kV mm(-1)). From the FEM analyses, we can find that the enhanced polarization of the polar phase is promoted by an additional internal field at the phase boundary which originates from the preferential polarization of the relaxor-like non-polar phase. From the present study, we conclude that the coherent interface between polar and non-polar phases is a key factor for understanding the enhanced piezoelectric properties of the composite.

A chemical-structural model for coherent martensite/parent interface in Mn-based antiferromagnetic shape memory alloys.

The martensite/parent coherent interface of Mn-based shape memory alloys (SMAs) is a significant part in the research of their martensitic transformation, reversible shape memory effect and magnetic shape memory effect. In the present work, a chemical-structural model was proposed to calculate the martensite/parent coherent interfacial energy of Mn-X (X = Cu, Fe) alloys. In this model, the coherent heterophase interfacial energy consists of chemical and structural parts. Resulting from the formation process of the heterophase interface, the chemical interfacial energy is expressed as the incremental value of bond energy, while the structural part is obtained by calculating the interfacial strain energy. The results show that the structural interfacial energy plays the chief role in the total interfacial energy, and the total interfacial energy decreases as the temperature rises when the alloy composition is fixed. In addition, the preferred orientation has noteworthy influence on the total interfacial energy. Using the proposed model, interfacial energy, interfacial entropy, interfacial enthalpy and interfacial heat capacity are found to be correlated with temperature and interface preferred orientation. Furthermore, the influences of alloy composition, modulus softening, and the index of the habit plane on the results were discussed.

Strain rate sensitivity of Cu/Ta multilayered films: Comparison between grain boundary and heterophase interface

Grain boundaries and heterophase interfaces both play important roles in enhancing the strain rate sensitivity (SRS) of engineering materials as they often serve as obstacles for dislocation motion. In this work, however, we carried out nanoindentation tests on Cu/Ta multilayers prepared with a wide range of modulation periods (Λ) and modulation ratios (η) and found negative contribution of incoherent interfaces to SRS. Activation event extension aided by incoherent interface shear was suggested as the dominating mechanism for rate related deformation process in Cu/Ta multilayers. The results provided valuable insights into the fundamental roles of grain boundaries and heterophase interfaces in plastic deformation.

Bridging atomistic simulations and experiments via virtual diffraction: understanding homophase grain boundary and heterophase interface structures

Virtual diffraction is a computational technique that enables a synergistic coupling between experiments and atomistic simulations, which can help to elucidate nanoscale structure–property relationships. The research objective herein is to highlight recent advances in the use of virtual diffraction as a method to study the geometry and structure of homophase grain boundaries and heterophase interfaces with direct experimental validation. Virtual selected area diffraction patterns for two types of boundaries—homophase Al twist grain boundaries and heterophase Al2O3/Al interfaces—are created without a priori assumption of the periodic interface structure by computing diffraction intensities across high-resolution, 3-D reciprocal space meshes. In this work, computed diffraction patterns clearly identify Al grain boundary misorientation angles, reveal subsidiary peaks created by the dislocation arrays within select Al grain boundaries, and allow experimental validation of the minimum energy orientation relationship for the Al2O3/Al interface. Due to its advanced implementation, virtual diffraction characterization used throughout this work can be easily extended providing routes for similar analysis and experimental validation of atomistic simulations.

Mechanical interactions between semicoherent heterophase interfaces and free surfaces in crystalline bilayers

A force formalism is proposed to investigate the interactions between a semicoherent heterophase interface and free surfaces in anisotropic finite-thickness bilayers. The present approach enables the estimation of the mechanical forces acting on interfaces, which arise from inhomogeneous elastic fields between the neighboring materials. These short-range fields are produced by the superposition of coherency strains and the elastic strain fields of dislocation patterns, where the individual Burgers vectors are defined by requiring the global force balance on any internal plane perpendicular to the interfaces. Predictions in heterogeneous free-standing bilayers are compared to results for the homogeneous elasticity problem (i.e., both materials having the same stiffness) and the limiting case of infinite bicrystals. Examples of applications to pure misfit interfaces are given with controlled misfit dislocation spacings by continuously varying the alloy composition. The effect of dislocation density on the stability of semicoherent interfaces interacting with free surfaces is discussed in terms of the change in elastic strain energy of Pt/Pd bilayer systems.

Partitioning of elastic distortions at a semicoherent heterophase interface between anisotropic crystals

Bicrystals containing semicoherent interfaces exhibit distortions produced by the superposition of coherency strains and the elastic strain fields of interface Volterra dislocations. Using an approach that combines the quantized Frank–Bilby equation with anisotropic elasticity theory, this residual elastic state is computed for semicoherent heterophase interfaces formed by face- and body-centered cubic crystals. Elastic distortions are found to be unequally partitioned between the neighboring anisotropic materials. For any given heterophase interface, these distortions determine the coherent reference state within which the Burgers vectors of the interfacial dislocations are defined.

Characterization of a Fe/Y2O3 metal/oxide interface using neutron and x-ray scattering

The structure of metal/oxide interfaces is important to the radiation resistance of oxide dispersion-strengthened steels. We find evidence of gradual variations in stoichiometry and magnetization across a Fe/Y2O3 metal/oxide heterophase interface using neutron and x-ray reflectometry. These findings suggest that the Fe/Y2O3 interface is a transitional zone approximately ∼64 Å-thick containing mixtures or compounds of Fe, Y, and O. Our results illustrate the complex chemical and magnetic nature of Fe/oxide interfaces and demonstrate the utility of combined neutron and x-ray techniques as tools for characterizing them.

Effect of interface dislocation Burgers vectors on elastic fields in anisotropic bicrystals

A recent anisotropic elasticity formalism for quantifying interface dislocation arrays is used to compute the variations in long-range elastic fields and short-range strain energies of misfit dislocations due to changes in the Burgers vectors of the interface dislocations. The importance of selecting proper reference states for tilt and twist grain boundaries as well as a heterophase interface formed by tetragonal crystals is discussed in terms of partitioning of strain and rotation fields. For constrained interfaces consistent with the Frank–Bilby equation, the present work shows that examining the strain energies of different admissible dislocation configurations may be used as a criterion for predicting the most favorable structures.

The Influence of Grain Interactions on the Plastic Stability of Heterophase Interfaces.

Two-phase bimetal composites contain both grain boundaries and bi-phase interfaces between dissimilar crystals. In this work, we use a crystal plasticity finite element framework to explore the effects of grain boundary interactions on the plastic stability of bi-phase interfaces. We show that neighboring grain interactions do not significantly alter interface plastic stability during plane strain compression. The important implications are that stable orientations at bimetal interfaces can be different than those within the bulk layers. This finding provides insight into bi-phase microstructural development and suggests a pathway for tuning interface properties via severe plastic deformation.

Interfacial orientation and misorientation relationships in nanolamellar Cu/Nb composites using transmission-electron-microscope-based orientation and phase mapping

A transmission-electron-microscope-based orientation mapping technique that makes use of beam precession to achieve near-kinematical conditions was used to map the phase and crystal orientations in nanolamellar Cu/Nb composites with average layer thicknesses of 86, 30 and 18nm. Maps of high quality and reliability were obtained by comparing the recorded diffraction patterns with pre-calculated templates. Particular care was taken in optimizing the dewarping parameters and in calibrating the frames of reference. Layers with thicknesses as low as 4nm were successfully mapped. Heterophase interface plane and character distributions (HIPD and HICD, respectively) of Cu and Nb phases from the samples were determined from the orientation maps. In addition, local orientation relation stereograms of the Cu/Nb interfaces were calculated, and these revealed the detailed layer-to-layer texture information. The results are in agreement with previously reported neutron-diffraction-based and precession-electron-diffraction-based measurements on an accumulated roll bonding (ARB)-fabricated Cu/Nb sample with an average layer thickness of 30nm as well as scanning-electron-microscope-based electron backscattered diffraction HIPD/HICD plots of ARB-fabricated Cu/Nb samples with layer thicknesses between 200 and 600nm.

On the Role of Ni in Cu Precipitation in Multicomponent Steels

The nature of Cu precipitation in quench-tempered multicomponent high-strength low-alloy steels is characterized by atom probe tomography. The detected nanometer sized Ni-rich clusters act as preferential nucleation sites for Cu-rich clusters, and Ni segregation at the Cu-rich precipitate/matrix heterophase interface contribute to fast growth of Cu precipitates. Molecular dynamics simulation indicates that local Ni clustering at atomic scale significantly quickens the solute diffusion. The initial Ni composition has a profound effect on the nature of Cu precipitation.

Efficient Atomic-Scale Kinetics through a Complex Heterophase Interface

Atomic-scale imaging and first-principles modeling are applied to the heterophase interface between the Al-Cu solid solution (αCu) and θ' (Al2Cu) phases. Contrary to recent studies, our observations reveal a diffuse interface of complex but well-defined structure that enables the progression from αCu to θ' over a distance of ≈1 nm. We demonstrate that, surprisingly, the observed interfacial structure is not preferred on energetic grounds. Rather, the excess in interfacial energy is compensated by efficient atomic-scale kinetics of the αCu→θ' phase transformation.