Homophase boundary

Fig. 14 Grain boundary precipitate growth showing solute transport path during precipitate growth according to the collector-plate mechanism. Solute B is transported to the a-a grain boundary and then along the boundary to form the P precipitate. Diffusion-controlled precipitate growth results in solute depletion from the a phase along the homophase boundary due to fast boundary transport [44].

Grain boundary is the interface between two grains. When these two grains are of the same material, the boundary is called a homophase boundary when they are of different materials, then it is a heterophase boundary. Often, there are other phases that are only a few nanometers thick and can be present between the grains of two different materials in such case, the grain boundary represents three phases. These phases may be crystalline or amorphous. The presence or absence of a third phase has important ramifications on processing, electrical properties, and creep of the material concerned. 

Homophase crystal/crystal interfaces are often called grain boundaries. It is customary to classify such boundaries as either small-angle grain boundaries or large-angle grain boundaries. 

Grain boundaries are the most important type of homophase solid-solid interfaces. An example of crystalline heterophase interfaces with high relevance for technological applications are semiconductor heterostructures. 

The second approach or microheterogeneous model [1, 19-22] is based upon the principle, that the kinetics of the reaction in its initial stage are not that of a homophase polymerisation in a liquid monomer-polymeric solution, but a heterophase one. The reaction proceeding at the boundary liquid monomer - solid polymer microgranules surface under gel conditions. 

Grain boundaries in single-phase materials, defined as homophase interfaces, are regions separating grains of... 

Role of Crain Boundary Structure and Interface Energy at Homophase and Heterophase Interfaces Differences in structure and energy result from the creation of a solid-state interface... 

The primary effect of wetting is related to the existence of a slow mode characterized by a soft dispersion of its relaxation rate, whereas the upper part of the spectrum remains more or less the same as in a homophase system (see insets of Fig. 8.5). The elementary mode of fluctuations of the degree of order is localized at the phase boundary between the wetting layer and the bulk phase and it corresponds to fiuctuations of the thickness of the central part of the slab. The next mode, which is also localized at the nematic-isotropic interface, represents fluctuations of the position of the core. The relaxation rates of these two modes are the same as long as the two wetting layers are effectively uncoupled. 

The first conception (or microheterogeneous model) is based on the assumption that the main contribution to the kinetics of the process in the initial state does not lead to homophaseous polymerization in the liquid monomer/polymeric solution, but the heterophaseous one, proceeding on the solid polymer-liquid monomer boundary under the gel-effect conditions. 

Fig. 39. Micro-EDX analysis of Ndl23 crystals grown by the modified TSSG method in low-Po, atmosphere from contamination-firee Nd Oj crucibles with different post-growth heat treatments. In all the cases final oxygenation at 340°C in oxygen was applied. The picture demonstrates (a) tweed structure formation and (b) nanoscale composition fluctuations in crystals with the anomalous peak effect on a magnetization curve. Note that the composition profile for heavy atoms (Ba/Nd ratio) is similar to wave-like fluctuations typical for demixing behavior or a spinodal homophase decomposition rather than for a heterophase decomposition with the formation of a boundary between the crystal matrix and the precipitated phase (M. Nakamura et al. 1996c).

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