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Abdul Sami.pptx

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Defects Engineering ABDUL SAMI PhD Student Department of Chemical Engineering Outline of Presentation: Defects with classifications Case study Graphene & Perovskite Crystal: IDEAL vs. Reality Ideal Crystal: An ideal crystal can be described in terms a three- dimensionally periodic arrangement of points called lattice and an atom or group of atoms associated with each lattice point called motif: Crystal = Lattice + Motif (basis) Real Crystal: Deviations from this ideali
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  Defects Engineering ABDUL SAMI PhD Student Department of Chemical Engineering   Outline of Presentation: Defects with classifications Case study Graphene & Perovskite  Crystal: IDEAL vs. Reality Ideal Crystal:  An ideal crystal can be described in terms a three-dimensionally periodic arrangement of points called lattice and an atom or group of atoms associated with each lattice point called motif: Crystal = Lattice + Motif (basis) Real Crystal: Deviations from this ideality. These deviations are known as crystal defects. Therefore, defects engineering is major field of novel research. Diffused atoms Vacancy Extrinsic Defects Intrinsic Defects  0D (Point defects)    CLASSIFICATION OF DEFECTS BASED ON DIMENSIONALITY 1D (Line defects)    2D (Surface / Interface) 3D (Volume defects) Vacancy Impurity Frenkel defect Schottky defect Dislocation Surface Interphase  boundary Grain  boundary Twin  boundary Twins Precipitate Faulted region Voids / Cracks Stacking faults Disclination Dispiration Thermal vibration  Guess: There may   be some vacant sites in a crystal Surprising   Fact There must   be a certain fraction of vacant sites in a crystal in equilibrium. Equilibrium means Minimum Gibbs free energy G   at constant T   and P A crystal with vacancies has a lower free energy G   than a perfect crystal What is the equilibrium concentration of vacancies? Point Defects: Vacancy Gibbs Free Energy G G  =  H     –    T    S 1.Enthalpy  H  =  E  +  PV 2.Entropy S=k   ln W T   Absolute temperature  E internal energy  P   pressure V   volume k   Boltzmann constant W   number of microstates
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