ch03 - Chapter 3 Structures of Metals and Ceramics Concept...

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Chapter 3 Structures of Metals and Ceramics Concept Check 3.1 Question: Table 3.4 gives the ionic radii for K + and O 2- as 0.138 and 0.140 nm, respectively. (a) What would be the coordination number for each O 2- ion? (b) Briefly describe the resulting crystal structure for K 2 O. (c) Explain why this is called the antifluorite structure. Answer: (a) First, let us find the coordination number of each O 2- ion for K 2 O. Taking the cation-anion radii ratio r K + r O 2- = 0.138 nm 0.140 nm = 0.986 From Table 3.3, the coordination number for oxygen is eight. (b) According to Table 3.5, for a coordination number of eight for both cations and anions, the crystal structure should be cesium chloride. However, there are twice as many K + as O 2- ions. Therefore, the centers of the K + ions are positioned at the corners of cubic unit cells, while half of the cube centers are occupied by O 2- ions. (c)
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ch03 - Chapter 3 Structures of Metals and Ceramics Concept...

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