Heating induced structural and chemical behavior of KD2PO4 in the 25 °C–215 °C temperature range

We have used powder x-ray diffraction (XRD) to investigate the structural and chemical modifications undergone by KD2PO4 (DKDP) upon heating from room temperature to 215 °C. Full-profile (Le Bail) analysis of our temperature-resolved data shows no evidence of polymorphic structural transitions or deuterium–hydrogen isotope exchange occurring below Ts = 185 °C. The lattice parameters of DKDP vary smoothly upon heating to Ts and are 0.2% to 0.6% greater than those of its isostructural hydrogenated counterpart KH2PO4 (KDP). In addition, XRD isotherms collected at Ts demonstrate the structural and chemical stability of the title compound at this temperature over a 10.5 h time period. Upon further heating, however, the tetragonal DKDP phase becomes unstable, as evidenced by its transition to a monoclinic DKDP modification and eventual chemical decomposition via dehydration.