In mineral A2B, atoms B form CCP structure while A atoms occupy the voids within this structure. What are the coordination numbers of atoms A and B ? Name the voids in which atoms A are present and what fraction of these voids they occupy?
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2 Answers
1I guess this represents an anti-flourite structure.
coordination numbers of A and B are 4 and 8 respectively.
A occupies all the tetahedral voids .
now, if around B , 8 tetrahedral voids are filled by A, then der would be four octahedral voids.
thus, the fraction of voids occupied = 8/12 = 2/3
1B atoms form CCP structure
Number of octahedral voids = Number of B atoms
Number of tetrahedral voids = 2 x Number of B atoms.
Since the number of A atoms = 2 x Number of B atoms therefore they occupy all of tetrahedral voids.
Coordination number of A atoms = Four as they occupy tetrahedral voids
Coordination number of B atoms = Twice the coordination number of A
Since B atoms are half of A atoms therefore their coordination number is twice the coordination number of A.Coordination number of B = 8.