Mobilité des impuretés ioniques dans le quartz

Abstract
In order to produce very high quality oscillators of quartz, crystals which include a minimum of impurities are necessary. "Sweeping" is used in industry to purify synthetic crystals. An electric field is applied to a quartz sample at a given temperature to move ionic impurities nearer to the electrodes. After a lapse of time, the crystal is cooled and the field is removed and subsequently the extremities are either cut off or removed by polishing. The technique T.S.D. (Thermally Stimulated Depolarization) is used to better know the effects of "sweeping". Current densities are measured as a function of temperature. Two qualities of quartz, furnished by the S.I.C.N. (Société Industrielle de Combustible Nucléaire à Annecy) have been studied. Samples, purified or not, cut either perpendicular to the Z axis or to the Y axis, were extracted from various places in the crystal. The results obtained vary according to the origin of the studied samples and their treatment. In order to determine the influence of different parameters which occur at the time of "sweeping", we varied the intensity of the applied tension and the polarization time. Effects on the measurements of the thermoionic current were observed for a high quality sample.