Towards a Quantitative Cartography of the Grain Boundary Energy Landscape: Paths and Correlations

We apply a newly developed Voronoi fundamental zone (VFZ) framework to gain insights about grain boundary (GB) structure-property relationships in the five degree-of-freedom (5DOF) space of cubic GBs. We analyze the shape and size of a 5DOF fundamental zone (FZ), molecular statics energy uncertainty, property similarity of GBs that are crystallographically \close" (i.e. correlations), and energy pathways through 5DOF space. Considered together, these insights are important for managing tradeoffs between accuracy, complexity, and design considerations for electron backscatter diffraction/serial sectioning, high-energy diffraction microscopy, molecular statics, and density-functional theory. In terms of the shape and size of a 5DOF FZ, we discover that a FZ is smaller than expected at only ∼65° in the largest principal component. Thus, a 10° difference between two GBs, which may have previously been considered small, is actually quite large. We represent a GB by five transformed Cartesian coordinates equipped with a Euclidean distance metric. Using this representation, we find that the FZ has a low aspect-ratio shape (i.e. width, length, height, etc. are similar) which is important for 5DOF numerical differentiation. Semivariogram and numerical optimization methods reveal that grain boundary energy (GBE) in Ni and Fe are globally correlated within ∼6° to 8° in the grain boundary octonion (GBO) sense (multiply by 2 to convert to misorientation angle). For local correlation lengths of high-symmetry GBs of interest, we notice significant variation relative to global correlation lengths and an inverse relationship with the Brandon criterion. We suggest that property data with no more than ± ∼3 % error and point sets with GBs that are no more than ∼3−4° apart should be used and then paired with high-fidelity interpolation strategies. Finally, in terms of dynamic material behavior, geodesic paths through 5DOF space for Ni suggest that, under appropriate conditions, a certain low-energy Σ7 GB may transform into the frequently observed Σ3 coherent-twin GB which may be interesting to verify by experiment or simulation.

Evaluation of grain boundary energy, structure and stiffness from phase field crystal simulations

A two-mode phase field crystal (PFC) model is employed to investigate the equilibrium configurations of a range of grain boundaries in fcc-structured materials. A total of 80 different symmetrical tilt grain boundaries are evaluated by PFC simulations in 3D and the results are shown to agree well with data taken from the literature, both regarding the variation of grain boundary energy and also in terms of the resulting grain boundary structures. This verification complements existing PFC studies which are almost exclusively focused either on grain boundaries found in 2D systems or in bcc lattices in 3D. The present work facilitates application of PFC in the analysis of grain boundary mechanics in an extended range of materials, in particular such mechanics that take place at extended time scales not tractable for molecular dynamics (MD) simulations. In addition to the verification of predicted grain boundary energies and structures, wavelet transforms of the density field are used in the present work to obtain phase fields from which it is possible to identify grain boundary fluctuations that provide the means to evaluate grain boundary stiffness based on the capillarity fluctuation method. It is discussed how PFC provides benefits compared to alternative methods, such as MD simulations, for this type of investigations.

Study of Mn–Co–Ni–O thin films incorporated with Cu and Cu/Sc elements and properties of the detectors

Thin films [Formula: see text] (MCNO), [Formula: see text] (MCNCuO) and [Formula: see text] (MCNCuScO) are prepared by Chemical Solution Deposition method. The results show that the addition of Cu and Cu/Sc elements can reduce the grain boundary energy and the grain boundary angle to improve the single crystal degree of MCNO thin film. Through the analysis of MCNCuScO thin film, it is found that the stability of spinel structure mainly depends on the octahedron rather than tetrahedron. The bandgap of the samples from small to large is separately MCNCuScO, MCNCuO and MCNO films. The absorptivity within the waveband of [Formula: see text] plays a decisive role in the performance of the detector. At the same frequency, the MCNCuO thin film detector has the highest voltage responsivity, followed by the MCNCuScO thin film detector, while the MCNO film detector has the lowest responsivity.

Sinterability and Luminescence Property of the MgO-YAG:Ce Phosphor Ceramic with Sintering Aids

MgO-YAG:Ce phosphor ceramics with the addition of Y2O3, SiO2, TiO2 and ZrO2 as sintering aids were developed from commercial powders by hot-pressing. In this work, the effects of Y2O3, SiO2, TiO2, ZrO2 on the phase composition, microstructure, sinterability and luminescence intensity of MgO-YAG:Ce phosphor ceramic were investigated. By comparison, the relative density of MgO-YAG:Ce phosphor ceramic with 2 wt.% SiO2 was satisfying, reaching 98.4%, and the luminescence intensity reached the maximum. Because SiO2 and MgO react to form interstitial solid solution Mg2SiO4, which leads to the increase of the grain boundary energy of the MgO matrix, thereby increasing the sintering performance of MgO-YAG:Ce phosphor ceramics. And SiO2 does not react with YAG, maintaining the excellent luminescence properties of YAG itself.