Interfacial defects in YBa2Cu3O7-δ/SrTiO3(0 0 1) heterostructures studied by aberration-corrected ultrahigh-resolution electron microscopy

The microstructure of interfacial defects in YBa₂Cu₃O_7-δ/SrTiO₃(0?0?1) heterostructures has been investigated by aberration-corrected ultrahigh-resolution electron microscopy. We determine that c-axis-oriented YBa₂Cu₃O_7-δ thin films epitaxially grow on SrTiO₃(0?0?1) with two types of interface structure. The coalescence of nucleation sites with different types of interface structure leads to the formation of antiphase domain boundaries in YBa₂Cu₃O_7-δ thin films, which terminate at planar faults with different configurations near the interface. Stand-off misfit dislocations are observed and the dislocation core structure is explored. Based on the interface structure and interfacial defects, the initial growth mode of YBa₂Cu₃O_7-δ thin films on SrTiO₃(0?0?1) is discussed.     

The deformation-induced zone below large and shallow nanoindentations: A comparative study using EBSD and TEM

A comparison is made between the deformation-induced zone beneath nanoindentations obtained by Electron Backscatter Diffraction (EBSD) and Transmission Electron Microscopy (TEM). Since there are resolutional limitations associated with EBSD, especially at very small scan sizes, it is not known how accurately the deformed volume beneath the imprints can be characterized. To aid in answering this question, cross-sectional EBSD and TEM samples of nanoindentations were fabricated by means of a Focused Ion Beam (FIB) workstation, analyzed, and subsequently compared with each other. For large indentations as well as for shallow ones, agreement of the determined zones was found. The results of the EBSD and TEM experiments were also used to characterize the deformed volumes. In the EBSD maps of large indentations, strongly confined deformation patterns were found, while for the shallow indentations the observed patterns are more diffuse. The TEM micrographs and the Selected-Area Electron Diffraction (SAED) support these facts and give insight into the dislocation structure of the deformation zone.     

Role of surface roughness in hysteresis during adhesive elastic contact

In experiments that involve contact with adhesion between two surfaces, as found in atomic force microscopy or nanoindentation, two distinct contact force (P) versus indentation-depth (h) curves are often measured depending on whether the indenter moves towards or away from the sample. The origin of this hysteresis is not well understood and is often attributed to moisture, plasticity or viscoelasticity. Here we report experiments which show that hysteresis can exist in the absence of these effects, and that its magnitude depends on surface roughness. We develop a theoretical model in which the hysteresis appears as the result of a series of surface instabilities, in which the contact area grows or recedes by a finite amount. The model can be used to estimate material properties from contact experiments even when the measured P–h curves are not unique.     

Enhanced grain growth in yttria-doped zirconia thin film structures synthesized under photon irradiation

Enhanced grain growth in ultra-thin yttria-doped zirconia (YDZ) films synthesized under ultraviolet (UV) irradiation is reported. The mean grain size in UV-synthesized 7.5 mol% YDZ films nearly 56 nm thick increased to 85 nm upon annealing in an oxygen-rich ambient at 900°C for 1 h, while in thermally grown YDZ they grew only to ～15 nm under identical annealing conditions. In situ electron microscopy kinetic studies reveal an enhanced kinetic constant and self-limiting grain growth behaviour in the UV-synthesized oxide films. The difference between UV and thermally grown films was not significant in undoped films when compared to the case of 7.5 mol% YDZ.     

Voids formed from solidifying tin particles in solid aluminium

In this study, voids commonly associated with tin particles in two aluminium alloys containing microalloying additions (0.01 at.%) of tin have been observed by transmission electron microscopy. The voids were generated by quenching the alloys at moderate rates (10²–10³ K s^?1) from a temperature (718 K) in excess of the melting temperature (501 K) of elemental tin in tin–microalloyed aluminium. Estimates of the void volume as a function of the volume of the associated tin particle reveal a linear relationship consistent with the excess volume resulting from the solidification of the tin particle. The formation and stabilisation of shrinkage voids in metallic alloys are suggested to arise from a combination of high vacancy supersaturation, the large volumetric misfit strain of the solidifying tin particle and a reduction in void surface energy associated with segregation of alloying elements.     

Formation of omega and Ti2Ni phases in a residual Ti–Ni–Ti multilayer between stainless steel and zirconia after bonding at 1173 K

Stainless steel (316L) and 8 mol pct Y₂O₃-stabilized zirconia (8Y-ZrO₂) were bonded using a Ti–Ni–Ti multilayer at 1173 K (900 °C) for 1 h. Cross-sectional transmission electron microscopy specimens were prepared by an innovative focused ion beam plus lift-out technique. In addition to acicular α-Ti, the dissolution of Fe, Cr, and Ni diffusing outwards from 316L into β-Ti led to the precipitation of the omega (ω) phase with different variants in the residual Ti foil between 316L and Ni. The ω-phase was not found in the residual Ti foil between Ni and 8Y-ZrO₂, while Ti₂Ni precipitates were precipitated in some α-Ti grains owing to the exclusion of Ni from the β-Ti.     

Effect of electron concentration on the Laves phase stability of NbCr2–Ni produced by powder metallurgy

The powder metallurgy technology of mechanical alloying followed by hot-pressing consolidation has been used to obtain NbCr₂–Ni Laves phases. High-purity Nb, Cr, and Ni crystalline powders were milled for periods up to 35 h. These powders were vacuum sintered at 1250°C for 0.5 h under 45 MPa. The phase transformations of NbCr₂–Ni Laves phases have been investigated by X-ray diffraction. The grain size decreases and the microstrain increases with increased Ni content. Different phase transformations were observed from NbCr₂–Ni intermetallics. It is found that the electron concentration and phase stability correlation is obeyed in the Nb–Cr–Ni systems. However, the electron concentration corresponding to the C15/C14 phase transition is found to move to a higher value (i.e. 6.103) than the predicted one (i.e. 5.88) in the literature.     

Type II twinning in devitrite,Na2Ca3Si6O16

Nanometre-scale twins found in the triclinic crystalline phase devitrite, Na₂Ca₃Si₆O₁₆, are shown to exhibit the relatively rare form of twinning, Type II twinning, in which the crystal structure of one of the parts is related to the crystal structure of the other by a rotation of 180° about η ₁?=?[1?0?0]. Although formally, the twin plane K ₁ is irrational, it is in essence (0?1?0).     

The inherent tensile strength of iron

The cohesive energy of Fe as a function of structure, strain and magnetic state has been computed using the full potential linearized augmented-plane-wave method within the framework of density functional theory and the generalized gradient approximation. Calculations corresponding to uniaxial stress in the <100> direction reveal that the ideal tensile strength of bcc Fe is about 14.2GPa and is determined by instability with respect to transformation into an unstable ferromagnetic fcc structure. The low-energy fcc phase is a modulatedantiferromagnetic fcc structure that is connected to the bcc phase via a first-order magnetic transformation and does not compromise its ideal strength.     

Clinical Commentary

Abstract

This paper is the narrative of a first-time father with a son born seven weeks early by Caesarean section. Against the anxiety and trauma of his infant's birth and his wife's illness, another inner darker drama is being relived. Michael shows all the wounds of a battered child. He asks two awesome questions - Will I be to my son as my father was to me? Will my son be to me as I was to my father? Fearful and at first unvoiced questions, the developing interviews gave them a voice. We respected Michael's sharing of the early and fearful days and nights when his infant first came home. We sometimes found it hard to empathize with his running away to hide in work, until we understood what he was hiding from. Most poignant was his struggle with his anger and hurt with his father and his desire to understand, ‘Why?’, so that he would not be like this to his son. We saw a sensitive revelation of life being born inside him anew, as he made contact with his real infant and his psychic infant within. Of particular interest was the therapeutic use of the research interview space and the interviewer.