Electrical response of ammonium-rich water ice

Abstract

The electrical properties of water ice impact the study of diverse frozen environments, in particular the radar sounding of ice masses. The high-frequency response of meteoric polar ice depends partly on the bulk concentration of ammonium (NH4 +), but the nature of this response has been unclear. Here we use broadband dielectric spectroscopy to investigate the electrical response of laboratoryfrozen solutions. By analyzing the relaxation frequency of these samples and its temperature dependence, we show that the mobility of Bjerrum D-defects formed in the ice lattice by ammonium is 1.40.810-9m2 V-1 s-1 at-208C, or about an order of magnitude smaller than that of Bjerrum L-defects formed by chloride. However, co-substitution of both ions increases the ice-lattice solubility of chloride by a factor of 7, causing an enhanced conductivity response due to greater concentrations of Bjerrum L-defects. Thus, despite its low mobility, ammonium can also affect the high-frequency electrical response of polar ice, but its covariance with chloride must be considered.