Function Of Misorientation Angle Research Articles

Microstructure and transport behavior of grain boundaries in YBa 2Cu 3O y: A comparison between thin films and bulk bicrystals

The microstructure and transport properties of grain boundaries in thin film and bulk bicrystals of YBa 2Cu 3O 7- δ have been studied in detail. In this paper, we will concentrate on the unique features of grain boundaries in dual-seeded bulk bicrystals, particularly in comparison with grain boundaries in thin film bicrystals. The structures of these two types of grain boundaries can be very different: thin film boundaries typically exhibit meandering and impurity phases that extend through the thickness of the film while the bulk boundaries exhibit long, straight facets that can be relatively free of impurity phases. While the meandering configurations of grain boundaries in thin films has led to inconsistencies in transport results, the planar grain boundaries found in bulk samples provide an excellent opportunity to study the grain boundary transport behavior in a simpler geometry. Furthermore, the fabrication of these bulk bicrystals is flexible and reproducible so that boundaries of virtually any misorientation may be prepared. As an example of this versatility, we have systematically measured the transport critical current density as a function of misorientation angle in bulk bicrystals and compare these results with those measured in thin film bicrystals.

Magnetoresistance of artificial La0.7Sr0.3MnO3 grain boundaries as a function of misorientation angle

The resistance of polycrystalline doped LaMnO3 materials has been shown to be highly sensitive to low magnetic fields. To enable direct study of the properties of isolated grain boundaries we have grown epitaxial La0.7Sr0.3MnO3 films on a series of bicrystal substrates with different misorientation angles and patterned the films into a Wheatstone bridge geometry. We show that the grain boundary resistance and its magnetic field dependence vary strongly with the misorientation angle. The temperature dependence of the grain boundary resistance is also presented. We have obtained resistance changes of over 3% in fields of 2 mT at 300 K.

Vicinal Si(100) surfaces under external strain.

The phase diagram of vicinal Si(100) surfaces is calculated as a function of misorientation angle, temperature, and applied external strain. It is shown that a change of the applied external strain can lead to a phase transition between the single-layer step surface phase and the double-layer step surface phase. The effect of temperature is shown to be negligible up to 300 K. The order parameter of the surface phase transition is also calculated to make contact with experimental measurements. \textcopyright{} 1996 The American Physical Society.

Analysis and prediction of the critical current density across

A qualitative analysis of the expected dilatation strain field in the vicinity of an array of grain-boundary (GB) dislocations is presented. The analysis provides a basis for the prediction of the critical current densities (jc) across low-angle YBa2Cu3O7- (YBCO) GBs as a function of their energy. The introduction of the GB energy allows the extension of the analysis to high-angle GBs using established models which predict the GB energy as a function of misorientation angle. The results are compared to published data for jc across [001]-tilt YBCO GBs for the full range of misorientations, showing a good fit. Since the GB energy is directly related to the GB structure, the analysis may allow a generalization of the scaling behavior of jc with the GB energy. © 1995 The American Physical Society.

Finite-temperature phase diagram of vicinal Si(100) surfaces.

The phase diagram of vicinal Si(100) as a function of misorientation angle and temperature is calculated. Contrary to previous suggestions that only double-layer steps should appear on the equilibrium surface, it is predicted that the single-layer stepped surface is at equilibrium for small misorientation angles. This structure is stabilized by strain relaxation and by the thermal roughening of the steps. For annealed surfaces the critical angle at which the transition between the single- and double-layer stepped surface occurs is calculated to be ${\mathrm{\ensuremath{\theta}}}_{\mathit{c}}$\ensuremath{\approxeq}2\ifmmode^\circ\else\textdegree\fi{}.

DIFFUSION INDUCED GRAIN BOUNDARY MIGRATION IN ASYMMETRICAL TILT GRAIN BOUNDARIES

The phenomenology of diffusion induced grain boundary migration (DIGM) is studied as a function of misorientation angle in a series of asymmetrical tilt grain boundaries with [100] and [110] rotation axes. The diffusion of zinc into copper is investigated under constant conditions for all of the specimens. Interesting comparisons are drawn with previous results on symmetrical boundaries, and with the various theories of DIGM.

Computer simulation on surfaces and [001] symmetric tilt grain boundaries in Ni, Al, and Ni3Al

We have used “local volume” (embedded atom) type potentials to study the surfaces and grain boundaries of Ni, Al, and Ni3Al. The simulations show that with appropriately fit potentials, the surface and grain boundary structure can be realistically calculated. The surface rippling and relaxation show good agreement with experiments. The energies of most surfaces and grain boundaries also agree with existing data. The structural unit model for grain boundaries in Ni3Al shows the same generic units as in pure metals, but with large variations due to distortions and multiplicity. The utility of the structural unit model is thus more limited for alloys. The grain boundary energies were found to be the highest for Al-rich Ni3Al grain boundaries, and depend significantly on the local composition of the grain boundary. The cusps in the grain boundary energy as a function of misorientation angle are different for different grain boundary stoichiometries. The Ni3Al grain boundaries have approximately the same grain boundary energy and cohesive energy as that of Ni.

Orientation dependence of grain-boundary critical currents in YBa2Cu3O7- delta bicrystals.

The critical current densities across grain boundaries have been measured as a function of misorientation angle in the basal plane of bicrystals of $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$. For small misorientation angles, the ratio of the grain-boundary critical current density to the bulk critical current density is roughly proportional to the inverse of the misorientation angle; for large angles, this ratio saturates to a value of about $\frac{1}{50}$. These results imply that achieving a high degree of texture both normal to and within the basal plane is important for the obtaining of very high critical currents in pure polycrystalline samples.

Grain Boundary Fracture in Molybdenum Bicrystals with Various ⟨110⟩ Symmetric Tilt Boundaries

In order to investigate the grain boundary fracture in molybdenum with 〈110〉 symmetric tilt boundaries, the four-point bending test was conducted at 77 K by using bicrystals with various misorientations from 0° to 90°. A stress-strain curve to fracture was measured as a function of misorientation angle φ. Two classes of specimens were used to clarify the impurity effect on the grain boundary fracture: One was as-grown specimens which contained carbide precipitates at grain boundaries and the other was purified specimens in which no precipitates were observed. A marked misorientation dependence of fracture stress and plastic strain to fracture, was observed for the purified specimen; the stress and strain were both much higher for φ=0°–10° (Σ1), around 70° (Σ3, (112) twin boundary) and around 87°(Σ17, (223) twin boundary) than for the other boundaries. The dependence observed for the as-grown specimen was qualitatively similar to, but quantitatively much less than, that for the purified specimen. The misorientation dependence of grain boundary energy (cohesion) and the effect of carbon impurity on this cohesion were discussed.

Segregation of solute atoms at dislocations in low-angle grain boundaries

Bicrystalline thin films of gold, containing 4 and 16° [001] tilt boundaries, have been implanted at room temperature with cobalt, chromium, lead and gold at an energy of 40 keV and integrated fluxes ranging from 1 to 100 × 10 13 ion/cm 2 and subsequently examined by transmission electron microscopy. It is observed that the discrete strain-contrast pattern associated with individual dislocations in low-angle boundaries is obliterated by implantation with cobalt or chromium, but not by implantation with lead or self-implantation with gold at integrated fluxes ranging from 1 to 10 × 10 13 ion/cm 2. It is concluded that cobalt and chromium segregate at grain boundaries, thereby distorting the lattice and obliterating the discrete strain-contrast pattern, whereas lead, being totally immiscible in gold, segregates at free surfaces. This interpretation is consistent with a model wherein the width of dislocation cores is dependent on the gradient of grain boundary energy as a function of misorientation angle. These results suggest that segregation of impurities at low-angle grain boundaries alters grain boundary structure in much the same manner that adsorption of impurities alters surface structure.

⟨110⟩捩り粒界を有するモリブデン双結晶の粒界強度

Grain boundary fracture in molybdenum was investigated by the four-point bending test at 77 K as a function of misorientation angle, by using bicrystals with a 〈110〉 twist boundary. Main results obtained are as follows:(1) Fracture always occurs at the grain boundary. (2) The fracture strength and strain to fracture markedly depend on the misorientation angle, i.e., the bicrystals of misorientation up to 20° and those of around 70° (Σ3) have much higher fracture strength than the others, and some appreciable plastic strain is only observed for these strong bicrystals. (3) Misorientation width of the peak in strength agrees with the predicted value from the Brandon’s equation. (4) There are no peaks in strength around Σ9 and Σ11 coincidence boundaries.

Computer simulation of 〈01l〉 tilt grain boundaries in nickel oxide

Abstract Abstract A series of 〈011〉 symmetric tilt grain boundaries in nickel oxide has been studied using a static-lattice atomistic simulation method. The energy as a function of misorientation angle shows a deep cusp at the (1I1) interface (70·5°) which corresponds to a coherent twin structure. The lower angle orientations (1I1), (12) and (133) have relatively close-packed structures, while the higher-angle (2I1), (3I1) and (4I1) orientations contain arrays of open pipes in the boundary. These are analogous to the structures found for the (001) grain boundaries and may be responsible for the enhanced, anisotropic diffusion properties.