Electron spin resonance studies of doped synthetic kaolinite. I

Synthetic kaolinites of varying crystallinity, and in some instances with ideal morphology, have been produced by hydrothermal reaction of aluminiosilicate gels. Synthetic kaolinites doped with Mg 2+ and Fe 3+ were also obtained. Synthetic kaolinite doped with Fe 3+ produced an ESR spectrum at g = 4 identical to spectra observed in natural kaolinites. Following X-irradiation and annealing at ~200°C, synthetic kaolinite doped with Mg 2+ exhibited an ESR signal at g = 2·0 identical to a resonance observed in natural kaolinites. It is concluded that the g = 2·0 signal in kaolinite is due to a defect centre stabilized by Mg 2+ substitution. All synthetic and natural kaolinites exhibit an additional resonance at g = 2·0 following X-irradiation which can be repeatedly created and destroyed by irradiation and annealing. This resonance is attributed to defects possibly associated either with the substitution of Al 3+ for Si 4+ in kaolinite or with lattice vacancies.