As it's known that the lattice parameter is the double of the bond lenght in the NaCl structure, I want to know how to calculate the bond lenght in the NiAs structure?
The bond length is the distance between the centres of the two kinds of atoms, and in NaCl it is half the axis of the cubic cell. In the NiAs structure the geometry is more complicated since the symmetry is hexagonal, meaning that the dimensions of two axes (a, c) take part. The structure may be described as derived from a formal hcp arrangement formed by the "anions" and then filling the octahedral holes by the cations". [N.B. since you imagine close-packing of atoms with the same charge, they are in fact not in contact with each other, but their coordinates are those from hcp.] To draw it on paper is a good help to realise what the structure looks like and then you apply simple geometry to calculate the distance expressed in both a and c. The ratio between these axes vary between different representatives of this structure type.
I am sorry that I do not calculate this for you but only show the direction of thought...
Thank you Mr Rolf Berger for your answer
I have found the formula to calculate the bond lenght for NiAs structure. The distance is related the both lattice parameters a and c. Thanks again
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