HR: 1340h
AN: MR13C-1413    [Abstracts]
TI: High Pressure Electrochemistry: Application to silver halides
AU: * Havens, K
EM: klhavens@ucla.edu
AF: UCLA, Earth & Space Science Department 595 Charles Young Drive, East, Los Angeles, CA 90095, United States
AU: Kavner, A
EM: akavner@ucla.edu
AF: UCLA, Earth & Space Science Department 595 Charles Young Drive, East, Los Angeles, CA 90095, United States
AB: Electron and ion charge transfer processes help govern electrical conductivity and diffusive mass and heat transport properties in deep Earth minerals. In an attempt to understand how pressure influences charge transfer behavior, the halide silver bromide (AgBr) was studied under the influence of an electric potential difference applied across two electrodes in a diamond anvil cell. This study follows our previous work on AgI, which was found to dissociate to molecular iodine and silver metal due to pressure and voltage influences. We performed two sets of experiments on AgBr at high pressure in a diamond anvil cell: electrochemical dissociation and electrical resistance measurements. In our study, we were able to electrochemically dissociate AgBr at pressures of 0.25-1.6 GPa by applying a voltage across the electrodes in the diamond cell sample chamber. Ag metal grew visibly on the negatively-charged electrode when voltages varying from 0.1 V to 5 V were applied. Additionally, a dark blue color appeared in low pressure areas of the diamond cell and grew darker from both voltage application and light exposure, indicating photochemical effects. We found that the reaction area and growth rate of both metal and dark blue color strongly increased as voltage increased, but tended to decrease with greater pressure. The resistance across the cell was observed to be influenced by both pressure and light exposure. As the AgBr sample was exposed to visible light, the resistance dropped instantaneously, and after the light was turned off, the resistance increased on a timescale of 10's of seconds to minutes. Notably, at higher pressures, the AgBr showed less photosensitivity. Exploration of these metal halide systems has many potential applications. First, these experiments explore the pressure-dependence of photochemical and photovoltaic processes, and may spur development of pressure-tuned microscale electronic devices. Second, these experimental results can be used to constrain thermodynamic models of pressure-dependent electrochemical behavior of materials, which may then be applied to the high temperature, high pressure mineral phases of the deep Earth and planets.
DE: 1012 Reactions and phase equilibria (3612, 8412)
DE: 3611 Thermodynamics (0766, 1011, 8411)
DE: 3630 Experimental mineralogy and petrology
DE: 5109 Magnetic and electrical properties (0925)
DE: 5139 Transport properties
SC: Mineral and Rock Physics [MR]
MN: 2007 Fall Meeting