Lidong Dai

Electrical conductivity of orthopyroxene: Implications for the water content of the asthenosphere

Electrical conductivity of minerals is sensitive to water content and hence can be used to infer the water content in the mantle. However, previous studies to infer the water content in the upper mantle were based on pure olivine model of the upper mantle. Influence of other minerals particularly that of orthopyroxene needs to be included to obtain a better estimate of water content in view of the high water solubility in this mineral. Here we report new results of electrical conductivity measurements on orthopyroxene, and apply these results to estimate the water content of the upper mantle of Earth. We found that the electrical conductivity of orthopyroxene is enhanced by the addition of water in a similar way as other minerals such as olivine and pyrope garnet. Using these new results, we calculate the electrical conductivity of pyrolite mantle as a function of water content and temperature incorporating the temperature and water fugacity-dependent hydrogen partitioning. Reported values of asthenosphere conductivity of 4 × 10−2−10−1 S/m corresponds to the water content of 0.01–0.04 wt%, a result in good agreement with the petrological model of the upper mantle.

The electrical conductivity of dry polycrystalline olivine compacts at high temperatures and pressures

Abstract The electrical conductivity of dry polycrystalline olivine compacts (hot-pressed and sintered pellets) was measured at pressures of 1.0-4.0 GPa, at temperatures of 1073-1423 K, and at different oxygen fugacities via the use of a YJ-3000t multi-anvil press. Oxygen fugacity was controlled successfully by means of five solid buffers: Fe3O4-Fe2O3, Ni-NiO, Fe-Fe3O4, Fe-FeO and Mo-MoO2. Within the selected frequency range of 102-106 Hz, the experimental results indicate that the grain interior conduction mechanism is characterized by a semi-circular curve on an impedance diagram. As a function of increasing pressure, the electrical conductivity of polycrystalline olivine compacts decreases, whereas the activation enthalpy and the temperature-independent pre-exponential factors increase slightly. The activation energy and activation volume of polycrystalline olivine compacts were determined to be 141.02±2.53 kJ/mol and 0.25±0.05 cm3/mol, respectively. At a pressure of 4.0 GPa, electrical conductivity was observed to increase as a function of increasing oxygen fugacity, and the relationship between electrical conductivity and oxygen fugacity can be described as log10 (σ) = (2.47±0.085) + (0.096±0.023) × log10 fO₂ + (-0.55±0.011)/T, which presents the exponential factor q (~0.096). Our observations demonstrate that the primary conduction mechanism for polycrystalline olivine compacts is a small polaron.

Electrical conductivity of albite at high temperatures and high pressures

Abstract The electrical conductivity of low albite has been measured using a complex impedance spectroscopic technique at 1.0-3.0 GPa and 773-1073 K in the frequency range of 10−1 to 106 Hz in a YJ-3000t multi-anvil press. Within this frequency range, the complex impedance plane displays a semi-circular arc that represents a grain interior conduction mechanism. The electrical conductivity of albite increases with increasing temperature, and the relationship between electrical conductivity and temperature fits the Arrhenius formula. Pressure has a weak effect on the electrical conductivity of albite in the experimental pressure-temperature (P-T) range in the present work. The pre-exponential factors decrease, and the activation enthalpy increases slightly with increasing pressure. The activation energy and activation volume of albite are 0.82 ± 0.04 eV and 1.45 ± 0.28 cm3/mol, respectively. Comparison with previous results with respect to albite indicates that our data are similar to previous data within the same temperature range. The dominant conduction mechanism in albite is suggested to be ionic conduction, where loosely bonded sodium cations, the dominant charge carriers, migrate into interstitial sites within the feldspar aluminosilicate framework. The Na diffusivity inferred from electrical conductivity of albite in this study using the Nernst-Einstein relation is consistent with that of previous studies on natural albite.

Influence of temperature, pressure, and chemical composition on the electrical conductivity of granite

Abstract The electrical conductivities of granites with different chemical compositions [XA = (Na2O + K2O + CaO)/SiO2 = 0.10, 0.13, 0.14, and 0.16 in weight percent] were measured at 623-1173 K and 0.5 GPa in a multi-anvil high-pressure apparatus using a Solartron-1260 Impedance/Gain Phase analyzer within a frequency range of 10-1-106 Hz. The conductivity of the granite sample with XA = 0.13 was also measured at 0.5-1.5 GPa. The results indicate that pressure has a very weak influence on the electrical conductivity in the stability field of granite, whereas increases in temperature and the value of XA produce dramatic increases in the electrical conductivity. For the granite samples with XA = 0.16 and 0.13, the activation enthalpies are 1.0 eV above 773 K and 0.5 eV below 773 K, suggesting that impurity conduction is the dominant conduction mechanism in the lower-temperature region. For the granites with XA = 0.14 and 0.10, the activation enthalpy is 1.0 eV over the whole temperature range, suggesting that only one conduction mechanism dominates the conductivity. Based on the value of activation enthalpy (~1.0 eV) and the dependence of electrical conductivity and activation enthalpy on XA at high temperatures, we propose that intrinsic conduction is the dominant conduction mechanism in all samples, and that K+, Na+, and Ca2+ in feldspar are the probable charge carriers controlling the conductivity. All conductivity data at high temperatures can be fitted to the general formula where σ0 is the pre-exponential factor; α, β, and γ are constants; ΔH0 is the activation enthalpy at very small values of XA; k is the Boltzmann constant; and T is the temperature. The present results suggest that the granite with various chemical compositions is unable to account for the high conductivity anomalies under stable mid- to lower-crust and southern Tibet.

Novel technique to control oxygen fugacity during high-pressure measurements of grain boundary conductivities of rocks.

This paper describes the development and application of a novel method for the measurement of grain boundary electrical conductivity of rock at high temperature and pressure. In this method, the metal electrodes, the corresponding metal shielding case, and the sleeves are altered in order to appropriately adjust and monitor the oxygen fugacity in a sample cavity in a high-pressure apparatus. As an example, a series of oxygen buffers including Fe(3)O(4) + Fe(2)O(3), Ni + NiO, Fe + Fe(3)O(4), Fe + FeO, and Mo + MoO(2) was selected and tested, and the oxygen fugacity was confirmed as adjusted during the process of electrical conductivity measurements. Application of this method provides a powerful means of restricting specific thermodynamic conditions at high temperature and pressure.

Evidence of the pressure-induced conductivity switching of yttrium-doped SrTiO3

The electrical transport properties of undoped and yttrium-doped strontium titanate (Sr(Ti1 - x Y x )O3 - δ , x  =  0, 0.02) under high pressure were investigated with in situ impedance spectroscopy measurements. A pressure-induced conductivity switching for undoped and 2 mole% Y-doped strontium titanate is observed at around ~10.0 and 7.0 GPa respectively, which are caused by a cubic to tetragonal I4/mcm phase transition. The decrease of the phase transition point of 2 mole% Y-doped strontium titanate can be attributed to larger Y(3+) atoms occupying the B-site and the creation of more oxygen vacancies, which lead to octahedra tilting and symmetry breaking. The results of the voltage-bias dependence of grain-boundary impedance of undoped and 2 mole% Y-doped strontium titanate at different pressures revealed that Schottky-type potential barriers formed at grain boundaries are the key factor for the accumulation of oxygen vacancy at the interface under pressure.

Experimental measurement of the electrical of the electrical conductivity of single crystal olivine at high temperature and high pressure under different oxygen fugacities

Abstract At 1.0–4.0 GPa and 11213–1473 K and under oxygen fugacity-controlled conditions (Bi + NiO, Fe + Fe3O4, Fe + FeO and Mo + MoO2 buffers), a YJ-3000t Model six-anvil solid high-pressure apparatus and a Sarltron-1260 Impedance/Gain-Phase analyzer were employed to conduct an in situ measurement of the electrical conductivity of single crystal olivine. Experimental results showed that: (1) within the range of experimentally selected frequencies (103–106 Hz), the electrical conductivity of the sample is of great dependence on the frequency; (2) with the rise of temperature (T); the electrical conductivity (σ) will increase, and the Arrenhius linear relationship is established between 1gσ and 1/T; (3) under the control of oxygen buffer Fe + Fe3O4, with the rise of pressure, the electrical conductivity tends to decrease whereas the activation enthalpy and independent-of-temperature preexponential factor tend to increase, with the activation energy and activation volume of the sample estimated at (1.25 + 0...

The bond ionicity of MB2 (M = Mg, Ti, V, Cr, Mn, Zr, Hf, Ta, Al and Y)

The bond ionicity in biborides MB2 (M = Mg, Ti, V, Cr, Mn, Zr, Hf, Ta, Al and?Y) has been studied by using the complex chemical bond theory based on a generalization of the Phillips-Van Vechten-Levine scheme. The ionicity of M-B bonds decreases in the following order: Mg, Al, Mn, Y, Cr, Zr, Hf, Nb, Ta, V and?Ti. The Mg-B bond in MgB2 has the largest value of ionicity of 96.8% among these examined diborides. Our calculations support the recent results of band structure calculations that Mg atoms are fully ionized so that they can donate valence electrons to the system. The observed superconductivity loss in the solid solution Mg1-xAlxB2 with x>0.1 can be understood in terms of the ionicity and the number of valence electrons.

Pressure-induced permanent metallization with reversible structural transition in molybdenum disulfide

This report presents a pressure-induced permanent metallization for MoS2 under non-hydrostatic conditions. Impedance and Raman spectra were measured to study the pressure-induced structural and electronic transformations of MoS2 at up to ∼25 GPa in diamond anvil cells under both non-hydrostatic and hydrostatic conditions. The results show evidence for isostructural hexagonal distortion from 2Hc to 2Ha and metallization at ∼17 GPa and ∼20 GPa under non-hydrostatic and hydrostatic conditions, respectively. Interestingly, the metallization is irreversible only under non-hydrostatic compression. We attribute this phenomenon to the incorporation of molecules of pressure medium between layers, which mitigate compressed stress and reduce interlayer interaction.

Pressure-induced improvement of grain boundary properties in yttrium-doped BaZrO3

Yttrium-doped BaZrO3 (BZY) is a promising electrolyte for intermediate-temperature protonic ceramic fuel cells. However, BZY exhibits a high resistance because of the blocking effect of the grain boundaries. In this study, the effect of pressure on undoped and 5% yttrium-doped BaZrO3 (BZY0 and BZY5) were investigated at 0.45–24.01 GPa and 273–673 K with a diamond anvil cell. Their bulk, grain boundary, and total electrical conductivities were determined by impedance spectroscopy and direct-current resistance measurement. Both samples tended to show increasing electrical conductivity with increasing pressure, although each showed a discontinuous inflexion point (at ~14.54 GPa for BZY0 and at ~11.11 GPa for BZY5) indicating a phase transition from a cubic to a tetragonal structure. The samples showed a 3.43 GPa difference in the onset pressure of the structure change. Characteristic parameters, including space charge potential, relaxation frequency, and transport activation energy, were obtained before and after the phase transition. The results suggest that pressure significantly improves oxygen ion conduction in acceptor-doped perovskites oxides.