It was recalled that defects, especially interstitial impurities, were responsible for the degradation of resonator performance with time. In order to study the mobility of ionic impurities, measurements were made of thermionic currents (as a function of temperature) by using the thermally stimulated depolarization method. Several current maxima were observed in which each peak was due to the displacement of an impurity type from a given site. They were characterized by the associated activation energy. Impedance measurements revealed energies of about 1eV. Quartz crystals that were doped with various impurities were studied in order to identify the impurities that were responsible for a given current peak. The results confirmed the sensitivity of the thermally stimulated depolarization method.

C.Poignon, G.Jeandel, G.Morlot: Journal of Applied Physics, 1996, 80[11], 6192-7