PROTON SPIN-LATTICE RELAXATION IN HEXAGONAL ICE

Proton spin-lattice relaxation times T1 in hexagonal ice have been measured from -10 to -80°C for different external Zeeman fields HR from 0.125 to 6.57 kOe. The results can be described by T1∼HR2 exp(ΔEc/kT) (ΔEc=activation energy). In pure ice (HR ∥c-axis)ΔEc is 0.62 eV, whereas relaxation due to impurities gives ΔE′c≈0.25 eV. The analysis of these results including additional data of the dielectric relaxation and the self-diffusion coefficient yields that T1 in pure ice is determined mainly by the motion of Schottky defects. Bjerrum faults give an additional but small contribution. Setting T1=C·τc (τc=molecular correlation time which is proportional to exp(ΔEc/kT), C=constant depending on HR and molecular distances) we calculated C with the model mentioned above and found e.g. 0.88 · 106 at HR=6.57 kOe. E′c≈0.25 eV is assumed to be the energy of migration of Bjerrum and ionic faults. © 1969 Springer-Verlag.