title: Magic angle spinning NMR study of the ferroelectric transition of KH2PO4: definitive evidence of a displacive component.
abstract: Variable temperature magic angle spinning (MAS) NMR measurements are reported on1H and31P nuclei in KH2PO4(KDP) in the vicinity of its paraelectric-ferroelectric phase transition temperature, Tc, of 123 K, to examine the transition mechanism, in particular if this is a model order-disorder type or whether it also involves a displacive component. It has been well established that the temperature variation of the isotropic chemical shift, δiso, in NMR measurements of the nuclei directly involved in the transition should remain constant or change smoothly through Tcfor an order-disorder type transition but it should show an anomalous change for a displacive one. Here we demonstrate that the δisofor both31P and1H nuclei in KDP show clear anomalies as a function of temperature around KDP's Tc, providing direct evidence of a displacive component for the phase transition of KDP in contrast to the generally accepted notion that it is a model order-disorder type.
authors.affiliation: National High Magnetic Field Laboratory, Florida State University, 1800 E. Paul Dirac Drive, Tallahassee, FL 32310, United States of America.
authors.forename: Jin Jung
authors.initials: JJ
authors.lastname: Kweon
authors.forename: Riqiang
authors.initials: R
authors.lastname: Fu
authors.forename: Eun Sang
authors.initials: ES
authors.lastname: Choi
authors.forename: Naresh S
authors.initials: NS
authors.lastname: Dalal