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7 votes
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Two atoms exist in the same coordinate position in the lattice?

The paper states that four ligands of the iron are occupied by a 50:50 statistical mixture of water and fluoride (the double circles). They could have added the partial occupancy to the coordinates if ...
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6 votes

Two atoms exist in the same coordinate position in the lattice?

Ivan Neretin sums it up well in his comment. There can be either one type of atom or molecule or another at the relevant position in the unit cell. It's actually fairly commonplace. Consider an ...
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2 votes
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In calculating the radius ratio in a tetrahedral site in an FCC lattice, why do we take tetrahedral void in the middle of the body diagonal line?

That is not the center. The image shows 1/8 of the unit cell. It is unfortunate that they labelled the edge with $a$, conventionally used for the unit cell length. It does not matter for the result, ...
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4 votes

Why does density decrease when pressure is increased on an NaCl type lattice?

You've gotten a good answer from Oscar explaining the atomic details of what's actually happening. More broadly however, it is important to note that, irrespective of the atomic details, it's ...
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4 votes
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Why does density decrease when pressure is increased on an NaCl type lattice?

Two things to consider: Even though the sodium chloride crystal structure is face-centered cubic, it is not 12-coordinate. Face-centered cubic refers to the lattice formed by periodically equivalent ...
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