Title: Anisotropic Dielectric Relaxation in Single Crystal H$_{2}$O Ice Ih from 80-250 K,
Abstract: Three properties of the dielectric relaxation in ultra-pure single
crystalline H$_{2}$O ice Ih were probed at temperatures between 80-250 K; the
thermally stimulated depolarization current, static electrical conductivity,
and dielectric relaxation time. The measurements were made with a guarded
parallel-plate capacitor constructed of fused quartz with Au electrodes. The
data agree with relaxation-based models and provide for the determination of
activation energies, which suggest that relaxation in ice is dominated by
Bjerrum defects below 140 K. Furthermore, anisotropy in the dielectric
relaxation data reveals that molecular reorientations along the
crystallographic $c$-axis are energetically favored over those along the
$a$-axis between 80-140 K. These results lend support for the postulate of a
shared origin between the dielectric relaxation dynamics and the thermodynamic
partial proton-ordering in ice near 100 K, and suggest a preference for
ordering along the $c$-axis.