Quadruple Junctions Research Articles

The Interaction of Twin Boundaries with Grain Boundaries in YBa2Cu3O7-δ

AbstractTwins in YBa2Cu3O7-δ may be “correlated” at [001] tilt grain boundaries (i.e. twin boundaries from one grain may meet twin boundaries from the other grain in quadruple junctions) and the twins may also be narrowed or “constricted” at the boundary. These effects are more pronounced in the regime of small angle grain boundaries. Based on TEM observations, a tentative threshold misorientation angle of approximately 15° is identified, below which there is a significant driving force reducing the system energy by correlation. The energies of various grain boundary domain structures associated with the twins were estimated on the basis of the dislocations they contain. Success has been obtained in explaining twin correlation in symmetrical tilt boundaries.

Stability and dissociation of quadruple junctions in polycrystals

Junctions of four grain boundaries (quadruple junctions) may form during grain growth. An analysis of the stability/unstability of quadruple junctions in 2D polycrystals is presented based on simple thermodynamic arguments. Depending on the angles between the four grain boundaries, their junction may dissociate into two triple junctions or be stable. In the first case there are two possible dissociations, but in general one is favored. A stable quadruple junction moves as a whole to a new position before it dissociates. These alternatives in the behavior of a quadruple junction are conveniently displayed in maps which indicate the regions where each alternative occurs.

Fourier packing ordinate: A univariate size-independent measurement of the polygonal packing variation in Paleozoic bryozoans

The Fourier packing ordinate provides a highly sensitive, univariate, and size-independent measurement of the polygonal packing variation in Paleozoic bryozoan colonies. It is potentially useful in quantifying a wide variety of natural packing arrays or polygonal networks, and is preferable to counting the sides of polygons, the frequency of triple or quadruple junctions, the nearest-neighbor statistic, measurements of surface area per unit cell, or individual harmonic amplitudes. Fourier shape analysis provides exact measurements of the levels of two- to six-fold rotational symmetry in all natural packing gradients. In bryozoans these symmetries are intercorrelated because as each order of symmetry is increasing, the previous order is decreasing. Shapes in these packing arrays are normally hybrids of two or more orders of rotational symmetry. The levels of rotational symmetry involved in these packing gradients are significantly correlated with a single principal component, the Fourier packing ordinate, which is independent of both size and cell boundary phenomena. Spatial analysis of the Fourier packing ordinate within an Ordovician bryozoan colony reveals both variation in packing caused by subcolony budding, as well as large scale trends which vary from the colony center to the free-growing margin.

Stability of quadruple junctions

THE analysis of triple junctions (points on the Earth where three lithospheric plates meet) has proved to be a powerful tool in deciphering the plate tectonic evolution of the Earth. In their classic paper on the evolution of triple junctions1, McKenzie and Morgan dismissed the possibility of stable quadruple junctions existing more than instantaneously. We show here that quadruple junctions can be stable according to the vector velocity stability criteria of McKenzie and Morgan.