17O NQR and the Mechanism of the Phase Transition in KH2PO4 Type H-bonded Systems

Abstract

17O quadrupole and 17O-proton magnetic dipolar coupling data are used to discriminate between three alternative phase transition driving mechanisms in KH2PO4 type H-bonded systems: (i) the proton order-disorder model; (ii) the P (or Se) ion order-disorder model, and (iii) the PO4 (or SeO3) orientational order-disorder model.The data for KH3(SeO3)2, CsH2PO4 and KH2PO4 definitely exclude models (ii) and (iii) and agree with the predictions of model (i).