From the view of crystal chemistry, the growth units and forming mechanism
of KDP crystal were investigated. The thickness of boundary layers changing
with lattice faces was studied by in-situ observation with Raman spectra,
where the solution structure during crystal growth could be well observed.
It was found that the solution structure at the boundary layer is similar t
o that of the crystal, so that the growth units are proposed as [H2PO4](-).
The difference of growth rates of lattice faces is determined by the combi
nation of growth units, which is mainly dominated by the angular orientatio
n of K-O and H-O bonds. Consequently the reason about the difference of gro
wth rates of lattice faces and the influence of pH value on the crystal mor
phology can be well elucidated.