Crystal morphology of ADP (NH4H2PO4) : A qualitative approach

Abstract

The Hartman-Perdok theory enables one to establish the order of morphological importance of the ADP (NH4H2PO4) crystal faces from its crystal structure. Periodic Bond Chains (PBC's) have been obtained using the N−HN…O strong bonds between the ionic [NH4]+ and [H2PO4]- crystallization units. The PBC's are parallel to 100, [001], and . The F faces which grow slowly according to a layer mechanism, are {011} and {010}. The elementary growth layer of {011} is not uniquely determined. Two layers bounded by either [H2PO4]- or [NH4]+ ions are possible. Hence the growth form of ADP is prismatic. S forms are {112} and {110}. Although the {0kl} are theoretically expected to be S faces, they nevertheless exhibit for >k < l K face characteristics. Only the {0kl} with k l, which are typical of the so-called tapering, are S faces.