Monte Carlo simulation of grain growth of single-phase systems with anisotropic boundary energies

The grain growth in single-phase systems with various anisotropic boundary energies is simulated using a modified two-dimensional (2D) Monte Carlo algorithm. Structural self-similarity both in the grain shape distributions and the grain boundary configurations is found regardless of the degree and type of anisotropy. Parabolic evolution kinetics is observed in most cases. The growth rate represented by the time rate of average grain area change is found to be a function of the grain boundary properties. In some cases, the normalized grain size distributions are not time-invariant, and therefore, current grain growth theories cannot explain conclusively the occurrence of the parabolic kinetics in these cases. The effect of anisotropy on the grain growth kinetics is discussed.     

Anelastic properties of aluminium thin films on silicon cantilevers

Thin films (thickness 40 to 250 nm) of Al on microstructurized Si substrates have been investigated by the vibrating-reed technique (typical frequencies 100 Hz to 10 kHz) with strain amplitudes in the range of 10⁻⁷ to 10⁻⁴ and for temperatures up to 850 K. The combined evaluation of flexural and torsional vibrations permits to separate the complex shear modulus and biaxial modulus of the thin layer, which helps to identify the damping mechanisms. For Al thin films with thickness <200 nm, in addition to the well-known damping peak due to grain boundary sliding (peak temperature about 370 K), a further maximum of damping has been observed around 600 K, the nature of which is discussed.     

Articulatory complexity at item boundaries in serial recall: The case of Welsh and English digit span.

The proposition that the difference in memory span between Welsh digits and English digits is accounted for by the longer articulatory duration of Welsh digits is critically reexamined. Two methods of measuring digit duration are contrasted. One is derived from digits spoken in isolation, the other is based on digits spoken in list format. Duration of Welsh digits was greater only when spoken in lists; with isolated production Welsh digits were significantly shorter than English digits. Also, span was shorter for Welsh digits. The results are interpreted in the light of the different articulatory demands made at the junctures between words in the English and Welsh lists. A supplementary experiment, using English words, illustrated that articulatory complexity at item boundaries increased serial recall error. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of Zirconia on Microstructure and Dielectric Properties of Barium Titanate Ceramics

Dielectric properties and structural characteristics of BaTiO₃ ceramics are significantly influenced by small addition (2 wt%) of ZrO₂. SEM and TEM observations revealed enhanced microstructural uniformity and retarded grain growth depending on sintering temperature. Above 1320°C, Zr diffusion into the BaTiO₃ lattice resulted in a chemical modification of the tetragonal structure and the development of core–shell grains. Below 1320°C, TEM analysis showed ZrO₂ at the grain boundaries as discrete particles (∼0.03μm). X-ray diffraction analysis revealed a decrease in the axial (c/a) ratio with decreasing grain size. A corresponding decrease in the spontaneous polarization, and twinned domain structures, were also observed in the fine-grained ceramics. These samples also showed a flattened permittivity response with temperature and significantly lower losses.     

TEM analysis of near-coincidence grain boundaries in silicon

High-precision characterization of grain boundaries with a deviation from the ideal coincidence is presented. The analysis is based on the shift of Kikuchi lines at grain boundaries. The accuracy was controlled using Frank's relationship applied to intrinsic secondary dislocations which accommodate the orientation deviation. An application is presented to coincidences with Σ = 25 and 3 observed in polycrystalline silicon.     

Me, myself, and us: Salient self-threats and relational connections.

Guided by their own amoebic self theory (C. T. Burris & J. K. Rempel, 2004), in 6 studies the authors explore the impact that involvement in an intimate relationship has on how a person appraises and responds to threat. They first show that people in relationship feel less constrained by their physical bodies compared with single people. In 3 subsequent studies involving physical size, blood/body donation, sexual activities, and responses to evil, they show that generalized sensitivity to bodily threat predicts self-protective reactions to specific physical threats among singles, but not among people in relationship, suggesting that intimate relationship involvement decreases the salience of the physical body. In the final pair of studies, they show that the salience of the physical body rebounds when people in relationship are primed, either subliminally or supraliminally, to think of themselves as distinct and separate from their partners. Thus, the present research shows how conceptualizing the self as "us" rather than "me" can transform an individual's response to the outside world, and highlights how physical cues in particular are affected by this process. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of a liquid Phase on Superplasticity of 2-moI%-Y203-StabiIlzed Tetragonal Zirconla Polycrystals

A small addition of CuO to 2-mol%-Y₂O₃-stabilized tetragonal zirconia polycrystals significantly enhances superplasticity by forming an amorhous grain-boundary phase containing primarily Cu⁺, Y³⁺, Zr⁴⁺, and O²⁻. This phase apparently melts at around 1130°C, but it already provides a fast diffusion path even below the melting temperature. There are abrupt changes in stress exponent, activation energy, and grain size exponent across the melting temperature. Superplasticity is diffusion-controlled below the melting temperature and is interfaced-controlled above that.     

Discontinuous Coarsening of Tetragonal Precipitates in Partially Stabilized Zirconia Induced by Diffusional Coherency Strain under Applied Stress

When partially stabilized zirconia with 6 mol% MgO and 4 mol% CaO is aged at 1450°C, intragranular precipitation occurs and concurrently the boundaries between the grains migrate, forming a Ca-enriched precipitate-free cubic phase and large tetragonal precipitates behind them. At these compositions and temperature the boundary migration is rapid and shows the characteristics of a discontinuous coarsening. A uniaxial compressive stress applied to this specimen during the aging treatment increases or decreases the migration rate of the boundaries parallel or perpendicular to the stress axis, respectively, in agreement with the prediction that a compressive coherency strain due to the diffusion of Ca atoms is produced at the surface of the retreating grains and drives the migration. The diffusional coherency strain energy is thus expected to be the dominant driving force for the discontinuous coarsening in this solid.     

Micro-scale fracture toughness of textured alumina ceramics

Enhanced fracture resistance of textured alumina is ascribed to crack deflection along grain boundaries. In this work, we quantify and compare the micro-scale fracture toughness of textured alumina grains and grain boundaries by micro-bending tests. Notched micro-cantilevers were milled from single alumina textured grains (perpendicular to the [0001] direction) and across several textured grains (along the [0001] direction), using a focused ion beam technique. Bending tests were performed with a nanoindenter. A shape function for notched pentagonal-shaped cantilevers was developed using finite element analysis. The critical stress intensity factor at the notch tip was determined based on the measured fracture loads. The micro-scale fracture toughness of the textured alumina grain boundaries (2.3 ± 0.2 MPa m^1/2) was about 30% lower than that of the grains (3.3 ± 0.2 MPa m^1/2). These findings at the micro-scale are paramount for understanding the macroscopic fracture behaviour of textured alumina ceramics.     

Reliability of atom column positions in a ternary system determined by quantitative high-resolution transmission electron microscopy

Employing an iterative structure refinement procedure, we have determined the atomistic structure of the Σ3 (111) grain boundary in strontium titanate (SrTiO₃) from high-resolution transmission electron microscopy (HRTEM) images. This grain boundary serves as a model system to study the effect of column occupancies on the reliability of the column positions. In this paper we introduce a method to derive confidence regions for the positions of individual atom columns at crystal defects. Based on a statistical approach we first determine the reliabilities of different types of atom columns in regions of unfaulted crystal. Next we extrapolate these reliabilities to obtain the reliabilities of individual atom columns at the grain boundary. The method accounts correctly for random errors and promises to be generally applicable provided that repetitive units of unfaulted crystal structure are contained in the HRTEM image. Under the conditions of the present study, the reliability of a column position correlates with the projected electrostatic potential of the column. Accordingly, the reliabilities of the column positions at the boundary vary with the column type: 0.008 nm for Sr–O columns, 0.014 nm for Ti columns, and 0.018 nm for O–O columns.