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Misoriented grain boundaries vicinal to the (1 1 1) <1 1¯0> twin in nickel Part I: Thermodynamics & temperature-dependent structure

Philosophical Magazine (2003, Print)

Brien, Michael J.'.; Medlin, Douglas L.; Foiles, Stephen M.

Here, grain boundary-engineered materials are of immense interest for their corrosion resistance, fracture resistance and microstructural stability. This work contributes to a larger goal of understanding both the structure and thermodynamic properties of grain boundaries vicinal (within ±30°) to the Σ3(1 1 1) <1 1¯0> (coherent twin) boundary which is found in grain boundary-engineered materials. The misoriented boundaries vicinal to the twin show structural changes at elevated temperatures. In the case of nickel, this transition temperature is substantially below the melting point and at temperatures commonly reached during processing, making the existence of such boundaries very likely in applications. Thus, the thermodynamic stability of such features is thoroughly investigated in order to predict and fully understand the structure of boundaries vicinal to twins. Low misorientation angle grain boundaries (|θ| ≲ 16°) show distinct ±1/3(1 1 1) disconnections which accommodate misorientation in opposite senses. The two types of disconnection have differing low-temperature structures which show different temperature-dependent behaviours with one type undergoing a structural transition at approximately 600 K. At misorientation angles greater than approximately ±16°, the discrete disconnection nature is lost as the disconnections merge into one another. Free energy calculations demonstrate that these high-angle boundaries, which exhibit a transition from a planar to a faceted structure, are thermodynamically more stable in the faceted configuration.

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TYPE Journal Article YEAR 2016
DOIOSTI

Controlling compositional homogeneity and crystalline orientation in Bi0.8Sb0.2 thermoelectric thin films

APL Materials

Friedman, Caitlin A.R.; Medlin, Douglas L.; Erickson, K.J.; Siegal, Michael P.

Compositional-homogeneity and crystalline-orientation are necessary attributes to achieve high thermoelectric performance in Bi1-xSbx thin films. Following deposition in vacuum, and upon air exposure, we find that 50%-95% of the Sb in 100-nm thick films segregates to form a nanocrystalline Sb2O3 surface layer, leaving the film bulk as Bi-metal. However, we demonstrate that a thin SiN capping layer deposited prior to air exposure prevents Sb-segregation, preserving a uniform film composition. Furthermore, the capping layer enables annealing in forming gas to improve crystalline orientations along the preferred trigonal axis, beneficially reducing electrical resistivity.

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TYPE Journal Article YEAR 2015
DOIOSTIScopus
Results 101–125 of 218
Results 101–125 of 218