Question
Materials Science for Engineering-Quiz-2 (October 13, 2017) State True' or 'False', fill in the blanks, or draw 1. Frenkel defects are point defects 2. Schottky defects are equilibrium defects. 3. Vacancies are point defects in ionic crystals. 4. Interstitial defects are line defects. 5. Substitutional defects are point defects. 6. Frenkel defects are not thermodynamically equilibrium defects 7. Mathematically, point defects are zero-dimensional defects 8. Mathematically, dislocations are line defects. 9. An incomplete plane in a crystal creates an edge dislocation. 10. Draw a Burger's circuit and Burger vector around a negative edge dislocation in a simple cubic pt 1 pt 1 pt 1 pt 1 pt pt pt crystal 5 pt (i) Draw the Burger circuit around a vacancy in a simple cubic crystal.3pt (i) What is the magnitude of this Burger vector? pt 12. Dislocations are equilibrium defects since they always lower the crystal energy. 2 pt an a vacancy, interstitial and substitutional defect exists together in a crystal? 3 pt Given: A simple cubic crystal consists of two edge dislocations. One of them is a positive edge and another is a negative edge dislocation l0) Show Burger vector and its magnitude for the positive edge dislocation only. 2pt (i) Show Burger vector and its magnitude for the negative edge dislocation only. 2 pt ii) Show the Burger vector and its magnitude when the Burger circuit passes around both these dislocations 3 pt 3 pt 15. The number of vacancies at 0 K is exactly equal to one. 16. A missing group of atoms within a plane creates a stacking fault. sequence, point out ALL the stacking faults in a FCC crystal. Which stacking faults resemble a HCP sequence: ..ABCABCACACABCABCABABABCABC FCC crystal follow the sequence 10 pt
Explanation / Answer
1) A point defect is one where defect is encountered at one or more point or lattice point, whichnis somewhat different from the regular arrangement of the crystal. In Frenkel defect, one or more ion (in an ionic crystal say) leave their original lattice point and occupy interstitial position, creating hole in their original lattice point. Hence , Frenkel defect is a point defect.