Question

How to calculate lattice parameter for orthorhombic?

Answer 1

First you have to index the diffractogram and then you preferable use the h00, 0k0 and 00l reflections to determine the d-value using Braggs law. The lattice parameter are then given by h*d00h, k*d0k0, and l*d00l. Of course there are programs which can do this for you, but you can do everything also manually. If you have a good approach for the lattice parameters you can refine them by full-pattern refinement software.