Transfer of protons through "pure" ice Ih single crystals. III. Extrinsic versus intrinsic polarization; surface versus volume conduction
Article
Maidique, MA, Von Hippel, A, Westphal, WB. (1971). Transfer of protons through "pure" ice Ih single crystals. III. Extrinsic versus intrinsic polarization; surface versus volume conduction
. JOURNAL OF CHEMICAL PHYSICS, 54(1), 26-33. 10.1063/1.1674585
Maidique, MA, Von Hippel, A, Westphal, WB. (1971). Transfer of protons through "pure" ice Ih single crystals. III. Extrinsic versus intrinsic polarization; surface versus volume conduction
. JOURNAL OF CHEMICAL PHYSICS, 54(1), 26-33. 10.1063/1.1674585
In order to analyze the charge transport through ice Ih single crystals and over their surfaces, the a-c polarization studies of Part I were supplemented by d-c and transient measurements ranging from 10 -2-4×104 V/cm, from nanoamperes to microamperes, and from 100/μec-3 h. After a brief description of techniques, the research focuses on "conductivity" as represented by an activation energy equation. In the literature, the activation energies quoted range from 33↔0 kcal/mole. Investigating the reasons for this confusion we found: (1) The value 33 kcal/mole is caused by surface conduction and can be reduced to ∼20 kcal/mole by pumping. (2) Zero activation energy characterizes the "initial" currents in the millisecond range. (3) Intermediate values (e.g., 12 kcal/mole) stem from apparent conductivities in spacecharge distorted fields. The saturation current at high fields, measured by Eigen and co-workers (activation energy ∼22 kcal/mole), seems to be an extrinsic current produced by multicrystallinity and internal surface conduction; the true volume current through ice single crystals proves orders of magnitude smaller and Ohmic in that range. Instead of a saturation current, an extrinsic saturation charge can be extracted from ice single crystals; our best fresh samples contained about 3×1011 of these carriers per cubic centimeter. Their mobility is about 5×10-3 cm2/V·sec. This mobility is only 2-3 times larger than that of protons in water and gives no evidence for a special proton transfer mechanism across hydrogen bridges. The polarization spectra in ice single-crystal samples change dramatically on aging; after 10 months we observed six clearly separated relaxation spectra, three of them connected with space-charge phenomena; in fresh samples, the space-charge polarization can be drastically reduced by a high-voltage pulse and needs hours to recover completely. The results can be understood on the basis of the theoretical concepts developed in Part II about the behavior of intrinsic and extrinsic defects in ice single crystals.
