GATE 2021 MT – Question 63
An interstitial atom just fits an octahedral void in BCC iron without distorting the structure. If iron’s atomic radius is 0.124 nm, the interstitial radius is ______ nm (three decimal places).
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Correct answer: 0.017 to 0.023
Explanation
BCC host radius is R=√3a/4. The shorter octahedral-site distance to host centres is a/2, so r=a/2−R=(2/√3−1)R. With R=0.124 nm, r=0.01918 nm, rounding to **0.019 nm**.