Electrical conductivity of synthetic iron-bearing olivine

Abstract

The electrical conduction in synthetic, dry polycrystalline, iron-bearing olivine (Fo 90 ) was investigated as a first-order approach to the electrical conductivity in the upper mantle. This fundamental study is of great importance to better understand the charge-transport mechanisms seen in olivine. Conduction processes in synthetic samples are not influenced by a complex geological history in contrast to conductivity in natural olivine. The experiments show that the apparent activation energy for conductivity for Fo 90 is 230 kJ mol -1 . In currently accepted defect modeling, natural and synthetic olivine requires a mechanism involving small polaron formation (Fe Á Mg and magnesium vacancies (V Mg ) as the dominant diffusing species to explain a fO 2 1/6 relation to electrical conduction. Here, Fo 90 shows no contribution of small polarons to conductivity at temperatures between 1,000 and 1,200°C and almost no dependence on fO 2 . Instead, under reducing conditions magnesium vacancies (and electrons) appear to be the major charge carriers.

Experimental investigation of the electrical behavior of olivine during partial melting under pressure and application to the lunar mantle

“…For each measurement, the electrical response of the samples was directly observed in the (Z', Z") plane, and the value of R was obtained from the intersection of the sample's response with the real impedance axis (Z'). For typically resistive systems like polycrystalline olivine, inductive effects are negligible compared to R and our data (semiarcs) are best fit with a RC or R-CPE (constant phase element) parallel circuit, as observed by previous studies of olivine aggregates (e.g., Yoshino et al, 2009;Farla et al, 2010). Relative errors on values of (Table 2) were calculated considering errors on the geometrical factor (i.e., considering errors on A and L) as well as propagated errors on each measured value of resistance R.…”

Electrical conductivity of continental lithospheric mantle from integrated geophysical and petrological modeling: Application to the Kaapvaal Craton and Rehoboth Terrane, southern Africa

“…As discussed by Jones et al [2009a], the effect of oxygen fugacity on the conductivity of mantle minerals is only of minor importance when compared with temperature or iron content (e.g., conductivity is only a function of f O 2 to the power 1/6 for the SEO3 model in equation (5) or 2/11 for the Du Frane et al [2005] model in equation (6)); therefore, we do not consider any fugacity dependence in this paper. A change in the conduction regime from small polaron to ionic conduction, related to Mg vacancies, at sublithospheric temperatures has been reported for olivine at T > 1300°C [ Schock et al , 1989; Constable , 2006; Yoshino et al , 2009; Farla et al , 2010] and garnet at T > 1530°C [ Yoshino et al , 2008b]. The ionic conduction is characterized by an activation enthalpy typically >2 eV in olivine [ Yoshino et al , 2009; Farla et al , 2010] and >1.6 eV in garnet [ Yoshino et al , 2008b].…”

“…A change in the conduction regime from small polaron to ionic conduction, related to Mg vacancies, at sublithospheric temperatures has been reported for olivine at T > 1300°C [ Schock et al , 1989; Constable , 2006; Yoshino et al , 2009; Farla et al , 2010] and garnet at T > 1530°C [ Yoshino et al , 2008b]. The ionic conduction is characterized by an activation enthalpy typically >2 eV in olivine [ Yoshino et al , 2009; Farla et al , 2010] and >1.6 eV in garnet [ Yoshino et al , 2008b]. In terms of the water content dependence, at least for olivine, two different proton conduction terms have been proposed by the different laboratory groups, as described in section 2.4.…”

“…The conduction mechanism in this temperature range changes at around 1300°C–1500°C from small polaron (electron hopping between ferric Fe 3+ and ferrous Fe 2+ ions) at T < 1300°C, to ionic conduction (charge carriers are magnesium vacancies) [e.g., Schock et al , 1989; Yoshino et al , 2008a]. In the case of the small polaron mechanism the activation enthalpies are around 1.6 eV, whereas for ionic conduction, values of >2 eV are typically expected [e.g., Yoshino et al , 2008a, 2009; Farla et al , 2010].…”

The effect of chemical composition and oxygen fugacity on the electrical conductivity of dry and hydrous garnet at high temperatures and pressures

“…The electrical properties of minerals and rocks are influenced mainly by temperature, pressure, oxygen fugacity, water content, grain boundary state, point-defect chemistry, chemical composition, the distribution of partial melting, and electronic spin-state transitions (Roberts and Tyburczy 1993;Lin et al 2007;Dai et al 2008aDai et al , b, 2010Gaillard et al 2008;Ohta et al 2008;Farla et al 2010;Watson et al 2010). Oxygen fugacity not only drives redox reactions, element partitioning, and structural phase transitions, but also controls certain transport electrical properties and rheological properties, especially in minerals such as silicates and oxides in which oxygen vacancies play a major role in these processes.…”