BaF2

Using:

F- = 117pm
Ba2+ = 135pm

As the radius of the two ions. I had to describe the structure etc. using the radius ratio. The ratio s 0.86, meaning that it has a 8,4 coordination, and a fluorite type structure. But my notes say that if the cation is 0.414 times bigger then the biggest radius (in this case is the cation anyway) then the anions will fill octahedral holes...

But then my notes also state that the fluorite structure has the anions in tetrahedral holes. I think its tetrahedral holes as there are 2n more octahedral holes, which can accommodate the anions as its BaF2. Does anyone know which is correct? Thanks!