Structure.questions_II-answer - MTLE-2100 Structure of...

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MTLE-2100 Structure of Engineering Materials, Questions II-Answers 1. Estimate the coordination number of Li + (number of oxygen around Li + ) in Li 2 O from the radius ratio. r Li+ = 0.060 (or 0.076)nm, R O2- = 0.140 nm. Answer--C.N.=4, exception to the rule. r/R = 0.4286 or 0.5428 CN = 6 is expected since it is in the range of 0.414—0.732. But Li takes the tetrahedral sites. CN = 4. An exception to the rule. 2. Using Pauling’s rule 2, find out how many Li surround one oxygen in Li 2 O. Strength of Li—O bond: Since Li +1 is surrounded by four oxygens, the strength of the bond is ¼. Valence of oxygen is 2. According to Pauling rule 2, 2 = (number of bonds to oxygen) x ¼ (number of bonds to oxygen = 8 3. Li 2 O takes anti-fluorite structure: O 2- , fcc positions; Li + in all of the tetrahedral sites. Compare the above-estimated coordination numbers with those in this structure. Li is in tetrahedral sites. O is surrounded by 8 Li; consistent with Pauling rule 2.
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This note was uploaded on 04/29/2008 for the course MTLE 2100 taught by Professor Tomozawa during the Spring '08 term at Rensselaer Polytechnic Institute.

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Structure.questions_II-answer - MTLE-2100 Structure of...

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