High temperature a.c. electrical properties of olivine single crystal with varying oxygen partial pressure: implications for the point defect chemistry

Abstract

The electrical conductivity and dielectric constant of a natural olivine single crystal were measured as a function of frequency over 0.1–1000 Hz. The measurements were made at temperatures of 1000–1400°C under a controlled oxygen partial pressure that was varied within the range of the olivine stability field. The observed dielectric constant of olivine increased with increasing oxygen pressure, and the change was greater at higher temperature and lower frequency. When the oxygen pressure Po 2 was relatively high, the dielectric constants measured at 0.1 Hz were proportional to P o 2 1 6 . This observation can be interpreted as a polarization effect of magnesium vacancies that are partially blocked at the specimen electrodes. The conductivity value and the frequency dependence of the dielectric constant indicate that holes as well as magnesium vacancies contribute to electrical properties of olivine. At lower oxygen pressure, the conductivity and dielectric constant are less dependent on oxygen pressure, suggesting that magnesium interstitial ions and/or electrons also contribute to the electrical conduction in olivine.