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Tilt Grain Boundaries (tilt + grain_boundary)
Selected AbstractsAb Initio Calculations of Pristine and Doped Zirconia ,5 (310)/[001] Tilt Grain BoundariesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2002Zugang Mao The structure of the cubic-ZrO2 symmetrical tilt ,5 (310)/[001] grain boundary is examined using density functional theory within the local density and pseudopotential approximations. Several pristine stoichiometric grain-boundary structures are investigated and compared with Z-contrast scanning transmission electron microscopy and electron energy loss spectroscopy results. The lowest-energy grain-boundary structure is found to agree well with the experimental data. When Y3+ is substituted for Zr4+ at various sites in the lowest-energy grain-boundary structure, the calculations indicate that Y3+ segregation to the grain boundary is energetically preferred to bulk doping, in agreement with experimental results. [source] Unraveling Deterministic Mesoscopic Polarization Switching Mechanisms: Spatially Resolved Studies of a Tilt Grain Boundary in Bismuth FerriteADVANCED FUNCTIONAL MATERIALS, Issue 13 2009Brian J. Rodriguez Abstract The deterministic mesoscopic mechanism of ferroelectric domain nucleation is probed at a single atomically-defined model defect: an artificially fabricated bicrystal grain boundary (GB) in an epitaxial bismuth ferrite film. Switching spectroscopy piezoresponse force microscopy (SS-PFM) is used to map the variation of local hysteresis loops at the GB and in its immediate vicinity. It is found that the the influence of the GB on nucleation results in a slight shift of the negative nucleation bias to larger voltages. The mesoscopic mechanisms of domain nucleation in the bulk and at the GB are studied in detail using phase-field modeling, elucidating the complex mechanisms governed by the interplay between ferroelectric and ferroelastic wall energies, depolarization fields, and interface charge. The combination of phase-field modeling and SS-PFM allows quantitative analysis of the mesoscopic mechanisms for polarization switching, and hence suggests a route for unraveling the mechanisms of polarization switching at a single defect level and ultimately optimizing materials properties through microstructure engineering. [source] Unusual current-voltage characteristics of single crystalline and bicrystalline La0.7Ca0.3MnO3 filmsANNALEN DER PHYSIK, Issue 10 2004A. Sawa Abstract The current-voltage characteristics of single crystalline and bicrystalline La0.7Ca0.3MnO3 films were measured and analyzed. Several epitaxial films, as well as 45° [001]-tilt grain boundaries, display current-voltage characteristics which are asymmetric with respect to polarity reversal of the bias current. One epitaxial film has a polarity dependent resistance of ,340k, and of ,670k, in forward and in reverse direction, respectively. [source] Molecular dynamics simulation of crack tip blunting in opposing directions along a symmetrical tilt grain boundary of copper bicrystalFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 11 2007A. LUQUE ABSTRACT Mode I crack growth along some grain boundaries of copper embrittled by solute segregation shows strong anisotropy. For instance, growth along the direction on the symmetrical tilt boundary has been reported to occur by intergranular brittle fracture, whereas growth along the opposite sense occurs in a ductile manner. In this paper, we simulate such crack configurations using molecular dynamics (embedded atom method [EAM]) in 3-dimensional perfect bicrystalline samples of pure copper of the aforementioned orientation at room temperature. In both cases the response is ductile, crack opening taking place by dislocation emission from the crack tip. The critical stress intensity factors (SIFs) for dislocation emission have been calculated by matching the displacement fields of the atoms in the tip neighbourhood with the continuum elastic fields. They are of the same order of magnitude for both growth senses despite the different morphology of their respective blunted crack tips and of the patterns of dislocations constituting their plastic zones. Thus, it seems that, in agreement with published results of continuum crystalline plasticity for the same problem, the plastic anisotropy associated with the different orientation of the slip systems with respect to the crack cannot in this case explain the experimental behaviour observed with solute embrittled bicrystals. [source] | ||||||||||