O17 nuclear-quadrupole-resonance measurements in the ferroelectric phase of potassium dihydrogen phosphate: Evidence for proton tunneling

The pure nuclear-quadrupole-resonance spectra of naturally abundant O17 in potassium dihydrogen phosphate (KDP) in the ferroelectric phase was obtained by a double-resonance-sensitive detection method. Fine structure due to dipolar interaction with the protons was resolved. From the best fit between the calculated and experimental spectra it is deduced that proton motion along the hydrogen bond prevails in the ferroelectric phase. The ordering parameter for the proton along the hydrogen bond is estimated.