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The atomic structure of [0001] Σ 7 tilt grain boundaries with { $$12\bar{3}0$$}‖ { $$12\bar{3}0$$}, { $$14\bar{5}0$$}‖ { $$14\bar{5}0$$}, and { $$10\bar{1}0$$}‖ { $$35\bar{8}0$$} boundary planes in ZnO was investigated through high-resolution transmission electron microscopy observation of fiber-textured thin films and atomistic calculations. These boundaries were found to comprise three kinds of common structural units that are characterized by fourfold- to eightfold-coordinated channels along the [0001] direction in contrast to sixfold-coordinated channels in wurtzite structure. The boundary structural units are very similar to the multiple core structures of edge dislocations with Burgers vectors of 1/3 < $$11\bar{2}0$$> . Transformation between two of the three configurations can easily occur through an atom flipping corresponding to dislocation glide. Depending on the orientation of boundary planes with respect to the Burgers vectors, the dislocation-like units exhibit straight or zigzag arrangements with periodicities corresponding to the Σ 7 misorientation. [ABSTRACT FROM AUTHOR]

The atomic and electronic structures of [0001]/( $$\bar{1}\bar{2}30$$) Σ 7 symmetric tilt grain boundary in an undoped ZnO bicrystal were investigated by high-resolution transmission electron microscopy (HRTEM) and first-principles calculations. HRTEM imaging and atomistic calculations revealed that the grain boundary was composed of at least two types of structural units. It was also found that one of the structural units has two threefold-coordinated atoms per a unit and the other has two fivefold-coordinated atoms. First-principles calculations indicated that these atoms with various coordination numbers do not form deep unoccupied electronic states in the band gap of ZnO, which is in consistency with a linear current-voltage characteristic observed for the bicrystal with the Σ 7 boundary. [ABSTRACT FROM AUTHOR]

High temperature plastic flow or grain boundary failure in oxide ceramics such as Al2O3 and tetragonal ZrO2 polycrystal (TZP) is sensitive to small levels of doping by various cations. For example, high temperature creep deformation in fine-grained, polycrystalline Al2O3 is highly suppressed by 0.1 mol% lanthanoid oxide or ZrO2-doping. An elongation to failure in superplastic TZP is improved by 0.2–3 mol% GeO2-doping. A high-resolution transmission electron microscopy (HRTEM) observation and an energy-dispersive X-ray spectroscopy (EDS) analysis revealed that the dopant cations tend to segregate along the grain boundaries in Al2O3 and TZP. The dopant effect is attributed to change in the grain boundary diffusivity due to the grain boundary segregation of the dopant cations. A molecular orbital calculation suggests that ionicity is one of the most important parameters to determine the high temperature flow stress, and probably, the grain boundary diffusivity in the oxide ceramics. [ABSTRACT FROM AUTHOR]

Grain boundary sliding and migration often accompany high temperature deformation in alumina, however the studies of the sliding and migration behavior of individual boundaries in bicrystals during deformation are extremely limited. In this study a single grain boundary in an alumina bicrystal was deformed at high temperature (1450∘C) at a constant strain rate (2× 10−6/s). Evolution of the grain boundary structure during deformation was monitored using optical microscopy. Movement of micron-sized facets inclined to the grain boundary plane led to the facet coarsening and produced macroscopically “curved” regions along the grain boundary. HRTEM studies reveal nanoscale analogues to such “curved” segments, which appear to contain nanoscale facets. Rumpling of the grain boundary during early stages of deformation may assist the nucleation of facets inclined to the original grain boundary plane. Macroscopic facets may develop by either growth and coarsening of atomic-height irregularities initially in the grain boundary or from atomic-height ledges formed during deformation. [ABSTRACT FROM AUTHOR]

Yttrium-doped zirconia bicrystals with [001] symmetric tilt Σ 5 grain boundaries were fabricated by a diffusion bonding technique, and oxygen diffusion behavior across the grain boundary was measured by secondary ion mass spectrometry (SIMS), tracing 18O isotope. It was found that the 18O fraction across the boundary exhibited explicit decrease around the boundary plane, indicating that the oxygen-diffusion is blocked by the presence of the Σ 5 grain boundary. This is the first experimental detection of oxygen diffusion blocking at a single grain boundary in zirconia ceramics. From high-resolution transmission electron microscopy observations and energy dispersive X-ray spectroscopy analysis, neither amorphous layers nor Si impurity segregation were found at the grain boundary. The grain boundary blocking effect of the Σ 5 boundary must be an intrinsic feature arising from its core structure and yttrium solute segregation of the grain boundary. [ABSTRACT FROM AUTHOR]

The electric field effect in ferromagnetic semiconductors enables switching of the magnetization, which is a key technology for spintronic applications. We demonstrated electric field-induced ferromagnetism at room temperature in a magnetic oxide semiconductor, (Ti, Co)O2, by means of electric double-layer gating with high-density electron accumulation (>1014 per square centimeter). By applying a gate voltage of a few volts, a low-carrier paramagnetic state was transformed into a high-carrier ferromagnetic state, thereby revealing the considerable role of electron carriers in high-temperature ferromagnetism and demonstrating a route to room-temperature semiconductor spintronics. [ABSTRACT FROM AUTHOR]