Structure of the high-pressure phase IV of KH2PO4 (KDP)

Abstract

The high-pressure phase IV of potassium dihydrogen phosphate (KH₂PO₄, KDP) has been determined at 1.62 GPa/296 K. It is monoclinic, space group P2₁/c, Z = 12, and on decompression transforms into monoclinic phase I. The interplay of OH⋯O bonding networks and K⁺ coordination types leads to an exceptionally large number of KDP polymorphs, at least 13 according to the literature.