Содержание
- 2. PROPERTIES Structure sensitive Structure Insensitive E.g. Yield stress, Fracture toughness E.g. Density, elastic modulus
- 3. 0D (Point defects) CLASSIFICATION OF DEFECTS BASED ON DIMENSIONALITY 1D (Line defects) 2D (Surface / Interface)
- 4. Translation SYMMETRY ASSOCIATED DEFECTS Rotation Screw Atomic Level Dislocation Disclination Dispiration Mirror SYMMETRY ASSOCIATED DEFECTS Rotation
- 5. Topological DEFECTS Non-topological Based on symmetry breaking Hence association with symmetry
- 6. Random DEFECTS Structural Random DEFECTS Ordered Based on origin Based on position Vacancies, dislocations, interface ledges…
- 7. THE ENTITY IN QUESTION GEOMETRICAL PHYSICAL E.g. atoms, clusters etc. E.g. spin, magnetic moment
- 8. THE OPERATION DEFINING A DEFECT CANNOT BE A SYMMETRY OPERATION OF THE CRYSTAL A DEFECT “ASSOCIATED”
- 9. 0D (Point defects) Vacancy Impurity Frenkel defect Schottky defect Non-ionic crystals Ionic crystals Imperfect point-like regions
- 10. Vacancy Missing atom from an atomic site Atoms around the vacancy displaced Tensile stress field produced
- 11. Impurity Interstitial Substitutional SUBSTITUTIONAL IMPURITY ∙ Foreign atom replacing the parent atom in the crystal ∙
- 12. Interstitial C sitting in the octahedral void in HT FCC-Fe rOctahedral void / rFCC atom =
- 13. ENTHALPY OF FORMATION OF VACANCIES Formation of a vacancy leads to missing bonds and distortion of
- 14. ΔG = ΔH − T ΔS ΔG (putting n vacancies) = nΔHf − T ΔSconfig Let
- 15. Considering only configurational entropy ⇒ User R instead of k if ΔHf is in J/mole Assuming
- 16. Certain equilibrium number of vacancies are preferred at T > 0K At a given T
- 17. Ionic Crystals Overall electrical neutrality has to be maintained Frenkel defect Cation (being smaller get displaced
- 18. Schottky defect Pair of anion and cation vacancies E.g. Alkali halides
- 19. Other defects due to charge balance If Cd2+ replaces Na+ → one cation vacancy is created
- 20. FeO heated in oxygen atmosphere → FexO (x Vacant cation sites are present Charge is compensated
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