High Pressure Electrical Conductivity Research Articles

High-pressure electrical conductivity and elasticity of iron-bearing δ-AlOOH

Abstract The electrical conductivity and elasticity of deep hydrous phases are essential to constraining water distribution, as well as deciphering the origins of conductivity anomalies in the lower mantle. To uncover the impact of iron-bearing δ-AlOOH on the geophysical properties of the lower mantle, we carried out synchrotron X-ray diffraction and electrical conductivity measurements on δ-(Al0.52Fe0.48)OOH and (Al0.95Fe0.05)OOH in diamond-anvil cells at pressures up to 75 GPa at room temperature. A sharp volume reduction of ~6.5% was observed in δ-(Al0.52Fe0.48)OOH across the spin transition at 40.8–43.3 GPa, where its electrical conductivity increases steadily without abrupt changes. The electrical conductivity of δ-(Al0.52Fe0.48)OOH is greater than that of pure δ-AlOOH at high pressure, suggesting that both small polaron and proton conduction mechanisms dominate in iron-bearing δ-AlOOH. Furthermore, the high-pressure electrical conductivity profiles are comparable between δ-(Al0.95Fe0.05)OOH and δ-(Al0.52Fe0.48)OOH, indicating that high-iron content only marginally influences the conductivity of iron-bearing δ-AlOOH. Notably, the electrical conductivity of iron-bearing δ-AlOOH along the North Philippine geotherm is greater than the average 1D electrical conductivity profile in the mantle (Ohta et al. 2010a). This result suggests that δ-(Al,Fe)OOH is a promising candidate to account for high conductivity in some subducting slabs.

High-Temperature and High-Pressure Phase Transition of Natural Barite Investigated by Raman Spectroscopy and Electrical Conductivity

We investigated the structural, vibrational, and electrical transport properties for natural barite under the conditions of 298–873 K and 1.5–35.0 GPa using a diamond anvil cell by virtue of Raman spectroscopy and electrical conductivity measurements. Upon compression, natural barite transformed into post-barite at 18.9 GPa and atmospheric temperature, which was evidenced by the emergence of υ5 Raman peak, the discontinuities in the pressure-dependent Raman shifts, FWHM of υ1 Raman peak and electrical conductivity under non-hydrostatic condition. The phase transition is of good reversibility, whereas a considerable pressure hysteresis was detected during the process of decompression. Under quasi-hydrostatic condition, the structural transition of natural barite occurred at a higher pressure of 21.4 GPa, which is possibly related to the influence of deviatoric stress. Furthermore, our high-temperature and high-pressure Raman spectra and electrical conductivity results for natural barite revealed that the phase transformation pressures decreased as temperatures enhanced and further, the phase boundary between barite and post-barite was described as P (GPa) = 24.00–0.0166 T (K). Our obtained phase diagram of natural barite can improve the knowledge about the structural and electrical properties for other barite-group minerals MSO4 (M = Sr and Pb) under high temperature and high pressure conditions.

Effect of pressure on the transport properties of 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide and 1-hexyl-3-methylimidazolium tetrafluoroborate

High-pressure self-diffusion and electrical conductivity data are reported for the ionic liquid reference material 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide. The data are used to calculate velocity cross-correlation coefficients and Laity resistance coefficients. High-pressure self-diffusion coefficients are also reported for 1-hexyl-3-methylimidazolium tetrafluoroborate. Comparisons are made with the viscosities using the Stokes-Einstein-Sutherland relation for the two ionic liquids. Density scaling is applied to the transport property measurements and comparison made with earlier studies on ionic liquid systems.

Some Remarks on the Electrical Conductivity of Hydrous Silicate Minerals in the Earth Crust, Upper Mantle and Subduction Zone at High Temperatures and High Pressures

As a dominant water carrier, hydrous silicate minerals and rocks are widespread throughout the representative regions of the mid-lower crust, upper mantle, and subduction zone of the deep Earth interior. Owing to the high sensitivity of electrical conductivity on the variation of water content, high-pressure laboratory-based electrical characterizations for hydrous silicate minerals and rocks have been paid more attention to by many researchers. With the improvement and development of experimental technique and measurement method for electrical conductivity, there are many related results to be reported on the electrical conductivity of hydrous silicate minerals and rocks at high-temperature and high-pressure conditions in the last several years. In this review paper, we concentrated on some recently reported electrical conductivity results for four typical hydrous silicate minerals (e.g., hydrous Ti-bearing olivine, epidote, amphibole, and kaolinite) investigated by the multi-anvil press and diamond anvil cell under conditions of high temperatures and pressures. Particularly, four potential influence factors including titanium-bearing content, dehydration effect, oxidation−dehydrogenation effect, and structural phase transition on the high-pressure electrical conductivity of these hydrous silicate minerals are deeply explored. Finally, some comprehensive remarks on the possible future research aspects are discussed in detail.

Equation of state and electrical transport properties of mixture of Li1.2Mn0.54Co0.13Ni0.13O2 and LiNi0.87Co0.09Mn0.03Al0.01O2 at high pressure

The equation of state (EOS) of mixture of Li[Formula: see text]Mn[Formula: see text]Co[Formula: see text]Ni[Formula: see text]O2 and LiNi[Formula: see text] Co[Formula: see text]Mn[Formula: see text]Al[Formula: see text]O2 was studied by synchrotron radiation X-ray diffraction (XRD) at room-temperature in a diamond anvil cell (DAC). The results showed that the hexagonal structure is maintained to the highest pressure of 23.1 GPa. The bulk modulus and its first derivative obtained from XRD data are [Formula: see text] GPa and [Formula: see text], respectively. In addition, we have investigated the high-pressure electrical conductivity of the mixture of Li[Formula: see text]Mn[Formula: see text]Co[Formula: see text]Ni[Formula: see text]O2 and LiNi[Formula: see text]Co[Formula: see text]Mn[Formula: see text]Al[Formula: see text]O2 to 22.9 GPa in a DAC. It is found that the resistance decreases with the increase of pressure and changes exponentially.

Pressure-induced structural phase transitions in natural kaolinite investigated by Raman spectroscopy and electrical conductivity

Abstract We investigated the structural, vibrational, and electrical transport properties of natural kaolinite and its high-pressure polymorphs by Raman scattering and electrical conductivity measurements at 293–673 K and up to 10.0 GPa using diamond-anvil cell. Upon compression, kaolinite underwent two structural transitions from kaolinite I to kaolinite II to kaolinite III phases at pressures of 2.9 and 6.5 GPa, respectively, which was disclosed by the inflection point in the pressure-dependent Raman shifts and electrical conductivity. Upon decompression, kaolinite III directly transformed to kaolinite I at 0.8 GPa without the appearance of kaolinite II. Additionally, the influence of temperature on the structural transformation of natural kaolinite was explored by high-temperature and high-pressure electrical conductivity measurements and negative temperature-dependent transition pressure correlations were obtained. A phase diagram of natural kaolinite was established for the first time and the kaolinite I-kaolinite II and kaolinite II-kaolinite III phase transition boundaries were determined: P (GPa) = 4.298–0.00462 T (K) and P (GPa) = 8.895–0.00799 T (K), respectively. Furthermore, our acquired phase diagram can be applied to understand the stability field of high-pressure polymorphs of kaolinite in the Earth’s interior and may provide a phase transition model for other kaolin-group minerals.

Pressure-Induced Structural Phase Transition and Metallization in Ga2Se3 Up to 40.2 GPa under Non-Hydrostatic and Hydrostatic Environments

A series of investigations on the structural, vibrational, and electrical transport characterizations for Ga2Se3 were conducted up to 40.2 GPa under different hydrostatic environments by virtue of Raman scattering, electrical conductivity, high-resolution transmission electron microscopy, and atomic force microscopy. Upon compression, Ga2Se3 underwent a phase transformation from the zinc-blende to NaCl-type structure at 10.6 GPa under non-hydrostatic conditions, which was manifested by the disappearance of an A mode and the noticeable discontinuities in the pressure-dependent Raman full width at half maximum (FWHMs) and electrical conductivity. Further increasing the pressure to 18.8 GPa, the semiconductor-to-metal phase transition occurred in Ga2Se3, which was evidenced by the high-pressure variable-temperature electrical conductivity measurements. However, the higher structural transition pressure point of 13.2 GPa was detected for Ga2Se3 under hydrostatic conditions, which was possibly related to the protective influence of the pressure medium. Upon decompression, the phase transformation and metallization were found to be reversible but existed in the large pressure hysteresis effect under different hydrostatic environments. Systematic research on the high-pressure structural and electrical transport properties for Ga2Se3 would be helpful to further explore the crystal structure evolution and electrical transport properties for other A2B3-type compounds.

Superionic iron oxide–hydroxide in Earth’s deep mantle

Water ice becomes a superionic phase under the high pressure and temperature conditions of deep planetary interiors of ice planets such as Neptune and Uranus, which affects interior structures and generates magnetic fields. The solid Earth, however, contains only hydrous minerals with a negligible amount of ice. Here we combine high pressure and temperature electrical conductivity experiments, Raman spectroscopy and first-principles simulations to investigate the state of hydrogen in the pyrite-type FeO2Hx (x ≤ 1), which is a potential H-bearing phase near the core–mantle boundary. We find that when the pressure increases beyond 73 GPa at room temperature, symmetric hydroxyl bonds are softened and the H+ (or proton) becomes diffusive within the vicinity of its crystallographic site. Increasing temperature under pressure, the diffusivity of hydrogen is extended beyond the individual unit cell to cover the entire solid, and the electrical conductivity soars, indicating a transition to the superionic state, which is characterized by freely moving protons and a solid FeO2 lattice. The highly diffusive hydrogen provides fresh transport mechanisms for charge and mass, which dictate the geophysical behaviours of electrical conductivity and magnetism, as well as geochemical processes of redox, hydrogen circulation and hydrogen isotopic mixing in Earth’s deep mantle.

Structural Phase Transition and Metallization of Nanocrystalline Rutile Investigated by High-Pressure Raman Spectroscopy and Electrical Conductivity

We investigate the structural, vibrational, and electrical transport properties of nanocrystalline rutile and its high-pressure polymorphs by Raman spectroscopy, and AC complex impedance spectroscopy in conjunction with the high-resolution transmission electron microscopy (HRTEM) up to ~25.0 GPa using the diamond anvil cell (DAC). Experimental results indicate that the structural phase transition and metallization for nanocrystalline rutile occurred with increasing pressure up to ~12.3 and ~14.5 GPa, respectively. The structural phase transition of sample at ~12.3 GPa is confirmed as a baddeleyite phase, which is verified by six new Raman characteristic peaks. The metallization of the baddeleyite phase is manifested by the temperature-dependent electrical conductivity measurements at ~14.5 GPa. However, upon decompression, the structural phase transition from the metallic baddeleyite to columbite phases at ~7.2 GPa is characterized by the inflexion point of the pressure coefficient and the pressure-dependent electrical conductivity. The recovered columbite phase is always retained to the atmospheric condition, which belongs to an irreversible phase transformation.

High–pressure electrical conductivity and Raman spectroscopy of chalcanthite

The phase transitions and dehydration of chalcanthite were investigated by electrical conductivity and Raman spectroscopy at 1.0–24.0 GPa and 293–673 K in a diamond anvil cell. At ambient temperature, two secondary phase transitions were observed according to discontinuous changes in the slope of Raman shifts, full width at half maximum and electrical conductivities at ∼7.3 and ∼10.3 GPa. The dehydration temperatures were determined by the splitting of Raman peaks and changes in electrical conductivity as ∼350 and ∼500 K at respective ∼3.0 and ∼6.0 GPa. A positive relationship for chalcanthite between dehydration temperature and pressure is established.

Giant magmatic water reservoirs at mid-crustal depth inferred from electrical conductivity and the growth of the continental crust

The formation of the continental crust at subduction zones involves the differentiation of hydrous mantle-derived magmas through a combination of crystallization and crustal melting. However, understanding the mechanisms by which differentiation occurs at depth is hampered by the inaccessibility of the deep crust in active continental arcs. Here we report new high-pressure electrical conductivity and petrological experiments on hydrated andesitic melt from Uturuncu volcano on the Bolivian Altiplano. By applying our results to regional magnetotelluric data, we show that giant conductive anomalies at mid-crustal levels in several arcs are characterized by relatively low amounts of intergranular andesitic partial melts with unusually high dissolved water contents (≥8 wt.% H2O). Below Uturuncu, the Altiplano-Puna Magma Body (APMB) displays an electrical conductivity that requires high water content (up to 10 wt.%) dissolved in the melt based on crystal-liquid equilibria and melt H2O solubility experiments. Such a super-hydrous andesitic melt must constitute about 10% of the APMB, the remaining 90% being a combination of magmatic cumulates and older crustal rocks. The crustal ponding level of these andesites at around 6 kbar pressure implies that on ascent through the crust hydrous magmas reach their water saturation pressure in the mid-crust, resulting in decompression-induced crystallization that increases magma viscosity and in turn leads to preferential stalling and differentiation. Similar high conductivity features are observed beneath the Cascades volcanic arc and Taupo Volcanic Zone. This suggests that large amounts of water in super-hydrous andesitic magmas could be a common feature of active continental arcs and may illustrate a key step in the structure and growth of the continental crust.One Sentence Summary: Geophysical, laboratory conductivity and petrological experiments reveal that deep electrical conductivity anomalies beneath the Central Andes, Cascades and Taupo Volcanic Zone image the ponding of super-hydrous andesitic melts which contributes to the growth of continental crust.

A combined theoretical and experimental investigation of uranium dioxide under high static pressure

We have investigated the behavior of uranium dioxide (UO2) under high static pressure using a combination of experimental and theoretical techniques. We have made Raman spectroscopic measurements up to 87 GPa, electrical transport measurements up to 50 GPa from 10 K to room temperature, and optical transmission measurements up to 28 GPa. We have also carried out theoretical calculations within the GGA + U framework. We find that Raman frequencies match to a large extent, theoretical predictions for the cotunnite (Pnma) structure above 30 GPa, but at higher pressures some behavior is not captured theoretically. The Raman measurements also imply that the low-pressure fluorite phase coexists with the cotunnite phase up to high pressures, consistent with earlier reports. Electrical transport measurements show that the resistivity decreases by more than six orders of magnitude with increasing pressure up to 50 GPa but that the material never adopts archetypal metallic behavior. Optical transmission spectra show that while UO2 becomes increasingly opaque with increasing pressure, a likely direct optical band gap of more than 1 eV exists up to at least 28 GPa. Together with the electrical transport measurements, we conclude that the high pressure electrical conductivity of UO2 is mediated by variable-range hopping.

Study of electrical conductivity response upon formation of ice and gas hydrates from salt solutions by a second generation high pressure electrical conductivity probe.

We recently reported the development of a high pressure electrical conductivity probe (HP-ECP) for experimental studies of formation of gas hydrates from electrolytes. The onset of the formation of methane-propane mixed gas hydrate from salt solutions was marked by a temporary upward spike in the electrical conductivity. To further understand hydrate formation a second generation of window-less HP-ECP (MkII), which has a much smaller heat capacity than the earlier version and allows access to faster cooling rates, has been constructed. Using the HP-ECP (MkII) the electrical conductivity signal responses of NaCl solutions upon the formation of ice, tetrahydrofuran hydrates, and methane-propane mixed gas hydrate has been measured. The concentration range of the NaCl solutions was from 1 mM to 3M and the driving AC frequency range was from 25 Hz to 5 kHz. This data has been used to construct an "electrical conductivity response phase diagrams" that summarize the electrical conductivity response signal upon solid formation in these systems. The general trend is that gas hydrate formation is marked by an upward spike in the conductivity at high concentrations and by a drop at low concentrations. This work shows that HP-ECP can be applied in automated measurements of hydrate formation probability distributions of optically opaque samples using the conductivity response signals as a trigger.

Development of a high pressure electrical conductivity probe for experimental studies of gas hydrates in electrolytes

We previously reported the development of a high pressure automated lag time apparatus and a high pressure video cell for experimental study of nucleation and growth of gas hydrates. Here we report the development of a high pressure electrical conductivity probe that monitors the electrical conductivity of an electrolyte that is subjected to a linear cooling ramp at elevated hydrate-forming-gas pressures. The electrical conductivity steadily decreases as the linear cooling progresses because of the increasing viscosity of the electrolyte and the consequently decreasing mobility of the ions. The onset of the formation of methane-propane mixed gas hydrate films at the gas-electrolyte interface is marked by an upward spike in the electrical conductivity. The physical mechanisms behind this phenomenon remain to be elucidated. Continued cooling of the electrolyte to, and subsequent holding of, the temperature at 273 K eventually results in decreased electrical conductivity. This conductivity signal can be used for the detection of the onset of the formation of gas hydrates in optically opaque samples that contain electrolytes.

New diamond anvil cell system for in situ resistance measurement under extreme conditions

We report an alumina-encapsulated microcircuit on a diamond anvil for high-pressure and high-temperature electrical conductivity measurement. An alumina thin film was deposited on a diamond anvil as a thermal insulation layer for laser heating, on which a molybdenum film was deposited and photolithographically fabricated to a van der Pauw circuit. The introduction of the alumina layer significantly improves the laser heating performance. This specially fabricated diamond anvil permits us to measure the resistivity of (Mg0.875Fe0.125)2SiO4 at 3450K and 35GPa in a laser-heated diamond anvil cell. We expect to substantially extend the pressure-temperature scale of in situ resistivity measurement.

Pressure-induced metallization of the Mott insulatorMnO

High-pressure electrical conductivity experiments have been performed on the Mott insulator MnO to a maximum pressure of 106 GPa. We observe a steady decrease in resistivity to 90 GPa, followed by a large, rapid decrease by a factor of 10{sup 5} between 90 and 106 GPa. Temperature cycling the sample at 87 and 106 GPa shows insulating and metallic behavior at these pressures, respectively. Our observations provide strong evidence for a pressure-induced Mott insulator-to-metal transition with an accompanying magnetic collapse beginning at 90 GPa.

Properties of electrolytes under pressure: PPG400 and PPG4000 complexed with LiCF 3SO 3

High-pressure electrical conductivity measurements and differential thermal analysis have been carried out on poly(propylene glycol) (PPG) complexed with LiCF 3SO 3 (composition O:Li=20:1) for pressures up to 1 GPa. The temperature and pressure dependence of the conductivity were analyzed in terms of the recently presented generalized Vogel equation as well as the well-known Vogel–Tamman–Fulcher equation, and the former provides an improved description of the data. The conductivity results show that the apparent activation volumes for the conduction process at room temperature and atmospheric pressure are 48 and 42 cm 3 mol −1 for electrolyte based on PPG4000 (molecular weight=4000) and PPG400, respectively. The temperature variation of the activation volume as well as the molecular weight dependence are described well within the free volume theory, which also provide a reasonable description of the pressure dependence. Differential thermal analysis was used to determine the pressure dependence of the glass transition temperature T g for the electrolyte based on PPG400. The result for the initial slope d T g/d p=140 K GPa −1 agrees well with that for the pure host PPG, but T g is shifted up 6 K.

The need to reconsider traditional free volume theory for polymer electrolytes

Pressure–temperature–volume ( PVT) data have been obtained for poly(propylene glycol) of molecular weight 1025 containing LiCF 3SO 3 in the mole ratio 20:1. The PVT data were used to calculate the specific volumes, V/ V P=0, T=296 K , associated with the pressures and temperatures for previously published variable temperature, high-pressure electrical conductivity data. It is found that the electrical conductivity depends strongly on temperature at a constant volume. Consequently, traditional free volume theory is not consistent with the data. Finally, it is shown that the features of the electrical conductivity data can be accounted for by a recently developed generalized Vogel theory.

High-pressure conductivity studies of blends of poly( p-phenylene)s with oxyethylene side-chains and lithium salts

High-pressure electrical conductivity studies have been carried out with poly( p-phenylene)s with oxyethylene side-chains (PPP(EO) x/ y ), which were blended with LiCF 3SO 3. Measurements were performed at pressures up to 280 MPa and at different temperatures. The influences of salt concentration, side-chain length, temperature, and plasticizer content on the relative conductance and activation volume are investigated. The temperature-dependent conductivity of the sample is non-Arrhenius and exhibits Williams–Landel–Ferry (WLF) behavior. The logarithm of relative conductance for PPP(EO) x/ y /LiCF 3SO 3 decreases almost linearly with increasing pressure but increases with salt concentration and side-chain length. As temperature increases, the activation volume becomes smaller but remains positive for PPP(EO) x/ y /LiCF 3SO 3. At higher salt concentrations and longer side-chain lengths, a smaller activation volume for the ion motion is found. These results can be interpreted such that PPP(EO) x/ y /LiCF 3SO 3 behaves like a true polymer electrolyte where ion transport is mediated by segmental motions of the EO side-chains. The addition of tetraethylene glycol dimethyl ether (TEGDME) as a plasticizer increases the activation volume but reduces the conductance.

NMR, DSC and high pressure electrical conductivity studies of liquid and hybrid electrolytes

Electrical conductivity, differential scanning calorimetry (DSC) and 7Li nuclear magnetic resonance (NMR) studies have been carried out on liquid electrolytes such as ethylene carbonate:propylene carbonate (EC:PC) and EC:dimethyl carbonate (DMC) containing LiPF6 (and LiCF3SO3 for NMR) and films plasticized using the same liquid electrolytes. The films are based on poly(vinylidene fluoride) (PVdF) copolymerized with hexafluoropropylene and contain fumed silica. All measurements were carried out at atmospheric pressure from room temperature to about −150°C and the electrical conductivity studies were performed at room temperature at pressures up to 0.3 GPa. The liquids and hybrid electrolytes are similar in that the electrical conductivity of the EC:PC-based substances exhibits Vogel–Tammann–Fulcher (VTF) behaviour while that for the EC:DMC-based substances does not. Part of the deviation from VTF behaviour for the EC:DMC-based materials is attributed to crystallization. Further, the glass transition temperatures as determined from NMR, DSC and electrical conductivity measurements are about the same for the liquids and hybrid electrolytes. However, substantial differences are found. The electrical conductivity of the hybrid electrolytes at room temperature is lower than expected and, more importantly, the relative change of conductivity with pressure is larger than for the liquids. In addition, above the glass transition temperature, the NMR T1 values are smaller and the NMR linewidths are larger for the hybrid electrolytes than for the liquids while at both low and high temperature the NMR linewidths are larger. Consequently, it is concluded that significant solid matrix–lithium ion interactions take place.