XRD nano-hydroxyapatite

Msl

Hello!

I would like to ask your help in the interpretation of Xrd data from hydroxyapatite nanopowder.
I know from the start that powders which I am analysing are already crystalline (another techniques were used to confirme that) but I keep having a characteristic spectrum of amorphous hydroxyapatite.
Why does this happen? What´s the influence of crystal size during in XRD procedure?

Thank you !