Homophase and Heterophase Interfaces

4 A full description of the DSC-lattice is given by Sutton and Balluffi [2], Note that the DSC-lattice of a single crystal is the crystal lattice itself. 

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 can also be classified as tilt boundaries, twist boundaries, and mixed boundaries. A tilt boundary s plane is parallel to the rotation axis used to define its crystal misorientation, as in Fig. B.4c. The crystals adjoining the boundary are related by a simple tilt around this axis. A twist boundary, as in Fig. B.56, is a boundary whose plane is perpendicular to the rotation axis. The two crystals adjoining the boundary are then related by a simple twist around this axis. All other types of boundaries are considered to be mixed. 

All sharp crystal/crystal homophase and heterophase interfaces can be classified as coherent, semicoherent, and incoherent. The structural features of these interfaces can be revealed by constructing them using a series of operations which always starts with a reference structure. 

In a further operation, these stresses can be eliminated by introducing an array of dislocations in the interface as in Fig. B.7c. The resulting interface consists of patches of coherent interface separated by dislocations. The cuts and displacements necessary to introduce the dislocations destroy the overall coherence of the interface, which is therefore considered to be semicoherent with respect to the reference 

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For crystalline-crystalline interfaces we further discriminate between homophase and heterophase interfaces. At a homophase interface, composition and lattice type are identical on both sides, only the relative orientation of the lattices differ. At a heterophase interface two phases with different composition or/and Bravias lattice structure meet. Heterophase interfaces are further classified according to the degree of atomic matching. If the atomic lattice is continuous across the interface, we talk about a fully coherent interface. At a semicoherent interface, the lattices only partially fit. This is compensated for by periodic dislocations. At an incoherent interface there is no matching of lattice structure across the interface. 

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... 

Interfaces may also be classified broadly into homophase interfaces and heterophase interfaces. A homophase interface separates two regions of the same phase, whereas a heterophase interface separates two dissimilar phases. Crystal/vapor and crys-tal/liquid interfaces are heterophase interfaces. Crystal/crystal interfaces can be either homophase or heterophase. Examples of crystal/crystal homophase interfaces are illustrated in Figs. B.2, B.4, and B.5. Examples of heterophase crystal/crystal interfaces are shown in Figs. B.6 and B.7. Figure B.6o shows an interface between f.c.c. and h.c.p. crystals where the small mismatch between close-packed lll fcc... 

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. 

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