I have seen that we have used the $h^2+k^2+l^2$ value for finding whether the lattice is BCC,FCC or simple cubic.Where is this factor coming from?Why can I not use the structure factor theorem expression for this?

  • $\begingroup$ This is really just geometry. The spacing of lattice planes (the $d$ in Bragg's law $\lambda = 2d\sin(\theta)$) depends on the factor you quote, thus its important in x-ray diffraction experiments. What part of the geometry is confusing to you? $\endgroup$
    – jacob1729
    Jul 2, 2019 at 23:22
  • $\begingroup$ Why are we using $h^2+k^2+l^2$ sometimes and a different form for hexagonal.Where does the intuition of the formula come from? $\endgroup$
    – gateprep
    Jul 3, 2019 at 7:22


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