1. The problem statement, all variables and given/known data A wavelength of 0.7107 Angstroms is used to analyse a polycrystalline sample with a known FCC lattice structure. The interplanar spacing of the first peak is 0.3 A. Calculate 2θ for the first 3 peaks on the XRD pattern. First 3 peaks occur at (111), (200) and (220). 2. Relevant equations nλ = 2dsinθ. d = a/sqrt(h^2 + k^2 + l^2) 3. The attempt at a solution I used d = a/sqrt(h^2 + k^2 + l^2) to find the lattice parameter. You're given d for the (111) plane. I then used this value for a to find d for the remaining planes, followed by the diffraction angle for these planes. Was I correct in assuming that a is the same for each and every set of miller indices? I can't see any other way of doing this than this way.