[MUSIC] Hello everyone. In this lecture, we are going to talk about two-dimensional and three-dimensional defect structures. Two-dimensional defects are interfaces. It include three different types of free surfaces, intercrystalline boundaries and internal interfaces. The free surfaces are external surfaces, which terminate at a vapor or liquid. Intercrystalline boundaries separate grains, sometimes these things phases. The internal interfaces disrupt the crystalline patterns. The free surface affect the shape of the solid and governs the interaction between the solid and vapor, sometimes liquid, and also influences the behavior of the solids. The atom in the free surface are bonded on one side that this indicates that the presence of dangling bond. Dangling bond that provide the favorable sites for the adsorption of atoms, as shown in left side of here. And sometimes we can find the dislike the stepped morphology as shown in right sided figure, and increase the surface area and we can obtain the low surface tension of the close-packed steps. And the most common form of bulk material is polycrystalline. So polycrystalline is composed of many small crystallized grains, and sometimes contains several these things constituent. It is piece of different composition and crystal structure. So grain boundary, the boundary between grains are interfaces that separate the grains. Structure of grain boundary depends on the misorientation of the crystal grain. So small misorientation means low-angle grain boundary with planar array of dislocations. So low-angle tilt boundary and twist boundary are low angle grain boundaries. And large misorientation resulted in the complicate microstructure of polycrystalline material. Let's think about the interface between crystals. It is piece boundary that separated phases. We can find three different characteristic features including coherent, semi-coherent and incoherent. The coherent is two crystals match perfectly at the interface plane. And semi-coherent is associated with coherent interface with total energy more favorable to replace the coherent interface in which either this registry is periodically taken up by misfit dislocation, as shown in the center figure. And incoherent is the interface plane has a very different atomic configuration. And another type of interface which can be found in crystalline material is stacking fault. This like structure is found in closer factor structure. You remember that the stacking sequence of face centered cubic is ABCABC, and we can find the three different types of stacking for it. The first is extrinsic stacking fault, to which can be generated by inserting an extra plane. So the stacking sequence of this extrinsic stacking for it is ABCBABC. So this like a stacking faults can be generated by the interstitialcies after irradiation treatment. And the second is intrinsic stacking fault, to which it can be generated by removing a plane of atoms. So the stacking sequence of intrinsic stacking fault is ABCBCABC by missing A plane. So for example, this like intrinsic stacking fault can be generated by condensation of vacancies onto a close-packed plane. And partial slip of the crystal to the rights of the fault that carries A-site to B-site, B-site to C-site, and C-site to A-site. And the third is twin boundary. The stacking sequence of twin boundary is ABCAB, CBACBA, to which it separates two volumes of crystal that are mirror images. So stacking fault creates a new crystal structure. For example, in mixture of face centered cubic and hexagonal close packed structure, we can find these like sequences. ABC ABC ABC ABC ABC and ABABABC. And then three-dimensional defects or volume defect. So three-dimensional aggregates of atoms or vacancies, so it can be classified into several categories. The first precipitate of fraction of a Micron in size and decorates the crystal by introduction the into the matrix with the small size particles. For example, that this precipitates can be incorporated in order to increase the strength because the introduced inclusion can be accessed as on obstacle to the motion of dislocations. And the second is dispersant, a fraction of a micron inside intentionally introduced the two-matrix material. So for example, larger precipitate grains and polygranular particles. And the third is inclusion, normally the inclusions are undesirable particles, such as the foreign particles or large precipitate particles. And the first is void, the holes formed by trapped gases or accumulation of vacancies. Normally the dislike of voids are undesirable defects increased materials. And we already discussed about the three-dimensional nanomaterials, the nanocomposite. And the dislike nanocomposites has the different defect structures. For example, as shown Figure B, be the nanograin composite as two-dimensional grain boundary defect structure. And in C, the nano inclusion composite you can find the two-dimensional defect, it is the pieces boundary between nanoinclusion and matrix material. And also find the three-dimensional defect, it is nanoinclusion. And indeed, the composite with modified grain boundaries that you can find the two different types of defect structure. One is one-dimensional dislocation, and the other one is two-dimensional modified grain boundary. And in E, the hetero nanograin composite you can find the mixture of two-dimensional defect structure the piece boundary between material A and material B. And also find the three-dimensional defect structure, the nano-sized grains. And anyway, you can find so many keywords, which is related with the defect structures and electrical and thermal properties of materials. For example, the Zero Dimensional Point defect or solute makes strain and disorder destruction. So by doping, intercalation, modulation doping. And sometimes we can induce the band engineering effects, such as band flattening, band convergence and resonant state formation by the generation of Zero Dimensional Point effect. And also we can reduce the lattice thermal conductivity of material by intensifying pointed effect phonon patterning due to or lowering effect. And one-dimensional defect dislocation is related to with some keyword of core actually screw and mixed. And this like defect structure can also make a strain field, and this is related with the semicoherent interface between two different material. And two-dimensional defect, such as interface surface boundary can also induce the strain field and the coherent semi-coherent incoherent. And heterostructure core shell is the keyword, which is later with the two dimensional defect structure. And three-dimensional defect, the precipitates, inclusion, pores can also generate the strain field, and nanocomposite, nanograin, nanoprecipitate there. Nanoinclusion and carrier filtering is the keyword which is related with three-dimensional defect structure. So in this lecture, we talked about the two-dimensional and three-dimensional defect structures. In the next we are going to talk about some important relationship between the defect structure and the physical property of inorganic materials. Thank you.
