Double resonance study of the 17O quadrupole coupling in paraelectric and ferroelectric KH 2PO 4

Abstract

The pure quadrupole resonance spectrum of 17O has been measured in a 10% enriched KH 2PO 4 sample at 190°K at at 77°K. In the paraelectric phase all oxygen sites are chemically equivalent with e 2 qQ/h = 5.16 MHz and η = 0.55, whereas there are two chemically non-equivalent 17O sites in the ferroelectric phase: ( e 2 qQ/h) 1 = 5.96 MHz, η t = 0.72 and ( e 2qQ/h) II = 4.85 MHz, η II = 0.18. The results can be interpreted in terms of a double minimum type O-H—O hydrogen bond potential, where the protons above T c rapidly fluctuate between the two equilibrium sites. In contrast with the neutron scattering results in KD 2PO 4, the present data show no evidence for any anomalous oxygen ferroelectric mode displacements in KH 2PO 4, which would not condense out below T c.