Crystallite growth in magnesium oxide under applied electric fields

An electrolysis cell is described for use in conjunction with a high-temperature X-ray furnace, which permits X-ray diffraction studies to be made of solids during the course of their high temperature electrolysis. The technique is applied to an investigation of the effect of electric fields on crystallite growth in MgO at 600°C in air, argon and reducing atmospheres. In all cases crystallite growth is greatest at the positive electrode face, suggesting that the charge carriers are anions. The efficiency of the electrolysis process depends both on the concentration of charge carriers and on the concentration of anion vacancies by which the charge carriers migrate. The defect concentration is increased under reducing conditions. In MgO samples containing a high concentration of protons, the conduction is protonic, with the greatest crystallite growth occurring at the cathode due to the catalytic action of the water vapour formed in that region by recombination of protons with hydroxyl ions.