Question

Given an alloy of Cu, Ag and Au in which Cu atoms
constitute the ccp arrangement. If the hypothetical
formula of the alloy is Cu,Ag,Au. What are the
probable locations of Ag & Au atoms.​

Answer 1

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The question says that Copper atoms (Cu) form CCP (Cubic Closed Packed) arrangement which is similar to FCC (Face Centered Cubic) arrangement.

Number of atoms of Cu present in unit cell = $\frac{1}{8}$ (number of corners of a cube) x 8 x $\frac{1}{2}$ x 6 = 1+3 =  4 copper atoms

No. of octahedral voids (spaces) = No. of atoms in FCC arrangement = 4

Since the arrangement is centered, the Ag atoms tend to be at the centres of the sides of the cube

There are three atoms of Ag, and 8 corners of a cube, so, the fraction will be

3/8 of tetrahedral voids for Ag and 1/4 octahedral voids for Au