Abstract :
The characteristics of E′ centers detected from natural deformed quartz samples have been examined in comparison with the standard quartz sample prepared by heavy γ-irradiation. The most deformed quartz sample with a polygonized structure shows a sharp E′ center, whereas other deformed quartz samples show very weak ones, although they have almost the same concentrations of radioactive elements. E′ centers, which are intrinsic ESR signals in quartz, are of two different types: One type is the E′1 center as a complementary center of a Frenkel or Schottky pair formed by radiation. Another type is the E′ center on the surface of a crystal (surface E′ center) which is a non-bridging silicon electron center formed by mechanical fracture. According to the results from the lineshapes, peak-to-peak widths, g-values, microwave power dependence and thermal stability, the E′ center detected from the most deformed quartz has the characteristics of the E′1 center rather than the surface E′ center. Presumably oxygen vacancies are formed by alpha or alpha-recoil particles from the radioactive elements concentrated along the subgrain boundaries which were developed with plastic deformation. The number of defects formed along alpha tracks estimated from the concentrations of the U-and Th-series corresponds reasonably to the concentration of oxygen vacancies calculated from the E′ center. On the other hand, X-ray powder diffraction patterns show that natural quartz samples have been more or less deformed by stress in the crust. A peroxy center that is often detected from deformed quartz is another complementary center of a Frenkel or Schottky pair, and may be formed by dislocation slip under plastic condition. Then, the E′ center can not be formed together because the vacancies are crushed by dislocation slip.
