Paramagnetic resonance evidence for anion fluctuations in the paraelectric phase of potassium dihydrogen phosphate

A marked nonlinear decrease of hyperfine splitting of the electron paramagnetic resonance spectrum of the I= 1/2 SeO3−4 radical doped into potassium dihydrogen phosphate and an increase in the linewidth is observed with increasing temperature above 40 °C. The effects are shown to be a result of slow tumbling of the radical in the lattice. The slow tumbling is believed to be driven by order–disorder fluctuations of the intrinsic phosphate anions which has been observed by NMR and neutron diffraction studies.