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# Structure.homework-#9 answer - at its melting point T=2800...

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MTLE-2100 Structure of Engineering Materials, Homework #9 -Answer 1. MgO (rock salt structure) and Li 2 O (antifluorite structure) both are based on cubic close-packed oxygen, with cations occupying interstices in the array. Yet predominant point defect in MgO is of the Schooky type; that in Li 2 O is the Frenkel type. Explain why. Li 2 O has a space in the body center position which can accommodate an interstitial ion, while MgO does not have such space. It is, therefore, difficult for MgO to produce an interstitial, which is a part of Frenkel defect. Therefore, Schottky defect formation is easier for MgO. 2. Calculate the Schottky defect concentration, n/N, for MgO

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Unformatted text preview: at its melting point, T=2800 ° C. Its energy for the formation of one pair of defect is 6 eV. Assume n/N = exp (-Q/2kT). 1 eV = 1.602x10-19 J, k=13.81x10-24 J/K= 86.20x10-6 eV/K n/N = exp [- 6/(2x86.20 x10-6 x 3073)]= exp (-11.325)=1.2x10-5 3. A dislocation loop shown below was observed. Indicate the portions of edge dislocation, screw dislocation and mixed dislocation. edge edge Direction of Scre Mix Edg Edg Scre 4. Two dimensional crystals of bubbles are shown below. Identify an irregularity of this “crystal”, which appears to be an extra-half plane....
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