Influence of pressure and temperature on the electrical conductivity of dolomite

Influence of temperature, pressure, and oxygen fugacity on the electrical conductivity of dry eclogite, and geophysical implications

“…The conduction mechanism of the hopping of small polarons between ferrous and ferric iron is characterized by low values of activation enthalpy (<2.0 eV) and a negative activation volume (i.e., the electrical conductivity decreased with increasing pressure) due to the greater difficulty in the formation and migration of vacancies at high pressures [Goddat et al, 1999;Ono and Mibe, 2015]. Our results give values for the activation enthalpy in the range 0.79-0.86 eV, and the activation volume is negative (22.51 cm 3 /mole), and therefore the hopping of small polarons can make a significant contribution to the electrical conductivity of eclogite at high temperatures and pressures, and with varying oxygen fugacities.…”

Electrical conductivity of siderite and its implication for high conductivity anomaly in the slab-mantle wedge interface

“…The notably diverse activation enthalpies obtained before and after the decomposition reaction imply the possible different conduction mechanisms respectively dominating the conductivity of the sample in the two processes. In the low temperature regime before sample decomposition, the electrical conductivities are reproducible and relatively high with the values of ~10 −3 -10 -6.5 S/m and can be nearly comparable to those of aragonite (Ono and Mibe, 2013) at similar temperatures, but higher than those of dolomite and magnesite (Mibe and Ono, 2011;Ono and Mibe, 2015) as indicated in Figure 6. All of the previous conductivity measurements on carbonate minerals are within their stability field at a temperatures no more than 727 °C.…”

“…The activation enthalpies obtained at low temperature decrease as pressure increases as shown in Figure 6; accordingly, the activation volume is −14.47 cm 3 /mole as indicated in Table 1. The negative pressure effect on the conductivity in siderite resembles that in dolomite and magnesite as shown in Figure 7, however, the much lower activation volume of siderite (−14.47 cm 3 /mole) compared to those of dolomite (−1.00 cm 3 /mole) and magnesite (−3.95 cm 3 /mole), is probably related to the iron of bivalence-variable metallic cation in the lattice position, unlike the unable oxidized cations in Ca-Mg carbonates, i.e., Ca, Mg. Due to the high activation energy of Ca-Mg carbonates (1.64 eV for dolomite and 1.76 eV for magnesite), the hopping conduction due to the large polarons process involving magnesium or/and calcium vacancies and a trapped hole is suggested to be the dominant mechanism in previous studies (Mibe and Ono, 2011;Ono and Mibe, 2015). For ironrich carbonate, resembling to other Fe-bearing silicate minerals, e.g., Fe-bearing olivine, garnet, pyroxene, pand erovskites (Xu et al, 2000;Romano et al, 2006;Yang and Heidelbach, 2012;Dai and Karato, 2014;Sinmyo et al, 2014), the small polaron that electron-hole hopping between ferrous (Fe 2+ ) and ferric (Fe 3+ ) ions are likely to be the predominant conduction mechanism.…”

“…Most of the previous conductivity measurements for carbonate minerals have been mainly performed on (Mg, Ca) CO 3 samples (e.g., calcite, magnesite, dolomite, aragonite, etc.) at high temperature and high pressure, and primarily focused on the discussion on the effect of temperature and pressure on conductivity in order to quantify their nature of transport mechanism (Papathanassiou and Grammatikakis, 1996;Papathanassiou, 1998;Ter Heege and Renner, 2007;Mibe and Ono, 2011;Ono and Mibe, 2013;Ono and Mibe, 2015). These experimental results have indicated that Mg-Ca carbonate minerals have a relatively low conductivity value within their stability and hardly make a pronounced contribution to the electrical structure of the surrounding mantle.…”

Diamond formation in an electric field under deep Earth conditions

“…Our work is based on the hypothesis that an electrochemical process may be involved in diamond formation in Earth's mantle, which is supported by the high electrical conductivity of mantle melts and fluids (31)(32)(33), in conjunction with electrochemical processes supposedly active in Earth's interior (34)(35)(36). We hypothesize that these chemically induced voltage gradients can be associated with both magnetic field variations (37,38) and lateral or vertical redox heterogeneity in the mantle (39,40).…”