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1.
Electrical conductivity of orthopyroxene and plagioclase in the lower crust   总被引：4，自引：0，他引：4  
The electrical conductivities of lower crustal orthopyroxene and plagioclase, as well as their dependence on water content, were measured at 6–12 kbar and 300–1,000°C on both natural and pre-annealed samples prepared from fresh mafic xenolith granulites. The complex impedance was determined in an end-loaded piston cylinder apparatus by a Solarton-1260 Impedance/Gain Phase analyzer in the frequency range of 0.1–106 Hz. The spectra usually show an arc over the whole frequency range at low temperature and an arc plus a tail in the high and low frequency range, respectively, at high temperature. The arc is due to conduction in the sample interior, while the tails are probably due to electrode effects. Different conduction mechanisms have been identified under dry and hydrous conditions. For the dry orthopyroxene, the activation enthalpy is ~105 kJ/mol, and the conduction is likely due to small polarons, e.g., electrons hopping between Fe2+ and Fe3+. For the dry plagioclase, the activation enthalpy is ~161 kJ/mol, and the conduction may be related to the mobility of Na+. For the hydrous samples, the activation enthalpy is ~81 kJ/mol for orthopyroxene and ~77 kJ/mol for plagioclase, and the electrical conductivity is markedly enhanced, probably due to proton conduction. For each mineral, the conductivity increases with increasing water content, with an exponent of ~1, and the activation enthalpies are nearly independent of water content. Combining these data with our previous work on the conductivity of lower crustal clinopyroxene, the bulk conductivity of lower crustal granulites is modeled, which is usually >~10−4 S/m in the range of 600–1,000°C. We suggest that the high electrical conductivity in most regions of the lower crust, especially where it consists mostly of granulites, can be explained by the main constitutive minerals, particularly if they contain some water. Contributions from other highly conducting materials such as hydrous fluids, melts, or graphite films are not strictly necessary to explain the observed conductivities.  相似文献   

2.
Electrical conductivity of talc was measured at 0.5 GPa and ~473 to ~1,300 K by using impedance spectroscopy both before and after dehydration. Before dehydration, the electrical conductivity of talc increased with temperature and is ~10?4 S/m at 1,078 K. After dehydration, most of the talc changed to a mixture of enstatite and quartz and the total water content is reduced by a factor 6 or more. Despite this large reduction in the total water content, the electrical conductivity increased. The activation enthalpy of electrical conductivity (~125 kJ/mol) is too large for the conduction by free water but is consistent with conduction by small polaron. Our results show that a majority of hydrogen atoms in talc do not enhance electrical conductivity, implying the low mobility of the hydrogen atoms in talc. The observed small increase in conductivity after dehydration may be attributed to the increase in oxygen fugacity that enhances conductivity due to small polaron.  相似文献   

3.
大陆下地壳高电导率的起源：矿物中的结构水   总被引：5，自引：1，他引：5  
大地电磁学的测定结果显示，大陆下地壳可能具有异常高的电导率(10-4~10-2 S/m)。认识这种异常现象的起源，对于更好地理解地球内部的结构和一些典型的地质学过程具有重要的意义。虽然目前有多种机制试图对大陆下地壳高电导率现象进行解释，但是争论依然激烈，已有的模型(含水矿物模型、孔隙流体模型、颗粒边界石墨膜模型和正空穴电子对模型等)都不能提供令人信服的答案。对安徽女山下地壳麻粒岩包体中的主要组成矿物(斜长石、斜方辉石、单斜辉石)的Micro FTIR分析表明：这三种矿物普遍含有结构水，含量分别可以高至~1 700×10-6、~1 600×10-6和~2 400×10-6。麻粒岩中结构水的存在可能会对大陆下地壳的电导率分布产生重要的影响，从而可能为认识其起源提供一个新的解释方法。  相似文献   

4.
To investigate the solubility and the sites of incorporation of hydrogen in olivine as a function of point defect concentration, two-stage high-temperature annealing experiments have been carried out. The first annealing stage (the dry preannealing stage) was conducted at a total pressure of 0.1 MPa, a temperature of 1300° C and various oxygen fugacities in the range 10?11–10?4 MPa for times > 12 h. In these heat treatments, the samples were buffered against either orthopyroxene or magnesiowustite, or they remained unbuffered. The second annealing stage (the hydrothermal annealing stage) was performed at 300 MPa and 900–1050 ° C under a hydrogen fugacity of ～ 158 MPa for 1–5 h. Infrared spectra from the annealed samples revealed two distinct groups of bands. Group I bands occurred at wavenumbers in the range 3450–3650 cm?1, while Group II bands occurred in the range 3200–3450 cm?1. The hydrogen solubility associated with Group I bands is proportional to f O 2 to the 1/6 power for samples preannealed in contact with orthopyroxene, to the 1/3 power for samples preannealed in contact with magnesiowustite, and to the 1/13 power for samples preannealed in the absence of a solid-state buffer. The hydrogen concentration for Group II bands varies with f o 2 to the 1/3 power for opxbuffered samples, to the 1/2 power for mw-buffered samples, and to the 1/3 power for unbuffered samples. The dependence of hydrogen solubility on oxygen fugacity and orthopyroxene activity suggests that hydrogen is incorporated into the olivine structure via association with point defects. The presence of two distinct groups of absorption bands indicates that hydrogen is associated with two distinct lattice defects. The following point defect model for the mechanism of incorporation of hydrogen in olivine is consistent with these results: Hydrogen ions responsible for the Group I bands are associated with doubly charged oxygen interstitials, while hydrogen ions responsible for the Group II bands are associated with singly charged oxygen interstitials. Furthermore, the infrared bands observed in naturally derived olivines are present in spectra from our hydrothermally annealed crystals. Thus, the mechanisms of incorporation of hydrogen in olivine under geological conditions are the same as those operative under laboratory conditions. The maximum solubility reached in these experiments was ～ 360H/106Si, which corresponds to ～ 0.002 wt% of H2O. This value is a lower bound for the solubility of hydrogen in olivine under upper mantle conditions.  相似文献   

5.
1 Introduction recognized and accepted by more and more experts engaged in experimental research at high temperature and In-situ laboratory measurement of the electricity of high pressure. This method has been regardedgeological materials at high temperature and high pressure internationally as the most advanced one for the in-situis an important approach to revealing the composition, laboratory measurement of the electric properties ofstructure and properties of materials in the deep interior…  相似文献   

6.
Studies of mass transport and kinetics in minerals at high pressure often require a sample environment in which the stress is near-hydrostatic and the chemical environment is carefully controlled. We report here details of a multianvil sample assembly in which these requirements are fulfilled and which has been used to study the effect of pressure on the kinetics of dislocation recovery in olivine up to 10 GPa. Annealing experiments have been performed on single crystals of San Carlos olivine at 8.5 GPa and 1400° C in a 1200 tonne split-sphere multianvil apparatus. The sample assembly consists of an 18 mm MgO octahedron with a LaCrO3 heater of variable wall thickness to give a small temperature variation (20° C) along the 3 mm length of the sample capsule. To minimize the differential stress on the sample, the olivine single crystal is surrounded by NaCl and both pressurization and depressurization are performed slowly at a temperature of 600° C (to minimize the strength of the NaCl). The silica activity is buffered by orthopyroxene powder in contact with the olivine and the oxygen fugacity is buffered by Ni + NiO within the sample capsule. The H2O-content of the sample assembly is minimized by drying all components at 230° C under vacuum. Olivine single crystals recovered after annealing at 1400° C and 8.5 GPa show no evidence of deformation, either ductile or brittle. Dislocation densities of 109–1010 m-2 are similar to those observed prior to high-pressure annealing and indicate differential stresses of <10 mpa.=" infrared=" spectroscopy=" indicates=" that=" the=" hydrogen=" content=" of=" a=" sample=" annealed=" at=" 10=" gpa,=" 1500°=" c=" for=" 21=" h=" is=">13 H/106Si, which, although low, is higher than that of the crystals prior to high-pressure annealing. Finally, the effectiveness of the fO2 buffer has been verified by estimating the fO2 at the surface of the sample from the solubility of Fe in Pt metal in equilibrium with the olivine and orthopyroxene.  相似文献   

7.
The kinetics of hydrogen diffusion in enstatite was studied by hydrogen–deuterium exchange experiments in the range of 1–5,000 bar and 700–850°C using synthetic single crystals of pure and Cr-doped enstatites. The OH- and OD-content in the samples was quantified after each thermal treatment with Fourier transformed infrared spectroscopy. H–D-exchange rates were measured parallel to the three crystallographic axes. In addition, in order to visualize diffusion profiles, OH and OD were mapped for some samples, utilizing synchrotron IR micro-spectroscopy. Hydrogen self-diffusivities derived from D/H exchange experiments at one atmosphere are very similar to the chemical diffusivity of hydrogen in natural Fe-bearing orthopyroxene, which was reported previously (Stalder and Skogby 2003) to exhibit a small, but significant anisotropy (D[001] > D[100] > D[010]). Activation energies are estimated to be 211 (±31) kJ/mol for diffusion parallel [100] and 185 (±28) kJ/mol for diffusion parallel [010]. Lattice diffusion of hydrogen is decelerated by more than one order of magnitude when Cr is dissolved in enstatite. In comparison to the chemical composition, pressure seems to have only a minor influence on hydrogen diffusion. Compared to other minerals in the Earth’s upper mantle, enstatite exhibits the highest activation energy for hydrogen diffusion, suggesting faster diffusion than in other mafic minerals at mantle temperatures, but slower diffusion at crustal conditions. Thus under upper mantle conditions, physical properties that are expected to be influenced by hydrogen mobility, such as electrical conductivity, may in enstatite be more intensely affected by the presence of hydrogen than in other upper mantle minerals.  相似文献   

8.
  相似文献   

9.
To investigate the point defect chemistry and the kinetic properties of manganese olivine Mn2SiO4, the point defect relaxation time (τ) characterizing the rate of re-equilibration of electrical conductivity following a change in oxygen fugacity was measured for single crystals oriented for electrical conduction along the [010] direction. The experiments were carried out at temperatures T = 1173–1473 K and oxygen fugacities with the MnSiO3 activity controlled at unity. The value of τ, which ranges from 130 to 1463 s, increases with decreasing temperature. At 1273 K, the value of τ in the regime is a factor of ∼1.8 smaller than that in the regime. The point defect relaxation time was used to calculate the chemical diffusivity (). Values of lie in the range 2.2× 10− 10 − 2.5×10− 9 m2/s. For the regime, a semi-log plot of vs 1/T yields a concave downward curve. Based on these results combined with those from Part I of this work for the point defect structure and electrical conductivity in Mn-olivine, it is proposed that the relaxation rate of electrical conduction is determined by the coupled diffusion of manganese vacancies and electron holes which rate-control the relaxation process at low and high temperatures, respectively. Deconvolution of the curve into two straight-line segments yields values for the mobilities and the diffusivities for Mn vacancies and electron holes. These results, combined with the measured electrical conductivity data, were used to calculate the concentrations of Mn vacancies and electron holes. These results in conjunction with those published for other transition-metal silicate olivines reveal the following: The mobility of electron holes in Mn-olivine is about two orders of magnitude smaller than that in Fe-olivine and is somewhat larger than that in (Mg0.9Fe0.1)-olivine. The mobilities of metal vacancies in these three olivines are similar both in magnitude and in temperature dependence. The concentrations of the majority point defects are the highest in Fe-olivine crystals and the lowest in Co-olivine crystals, while those in Mn-olivine and (Mg0.9Fe0.1)-olivine crystals lie in between. The deviation from stoichiometry in the cation sublattice for a transition-metal silicate olivine is about two orders of magnitude lower than that for the corresponding transition-metal oxide. Received: 10 January 1996 / Revised, accepted: 29 May 1997  相似文献   

10.
Mechanisms of hydrogen incorporation and diffusion in iron-bearing olivine   总被引：1，自引：1，他引：0  
The incorporation and diffusion of hydrogen in San Carlos olivine (Fo90) single crystals were studied by performing experiments under hydrothermal conditions. The experiments were carried out either at 1.5 GPa, 1,000°C for 1.5 h in a piston cylinder apparatus or at 0.2 GPa, 900°C for 1 or 20 h in a cold-seal vessel. The oxygen fugacity was buffered using Ni–NiO, and the silica activity was buffered by adding San Carlos orthopyroxene powders. Polarized Fourier transform infrared (FTIR) spectroscopy was utilized to quantify the hydroxyl distributions in the samples after the experiments. The resulting infrared spectra reproduce the features of FTIR spectra that are observed in olivine from common mantle peridotite xenoliths. The hydrogen concentration at the edges of the hydrogenated olivine crystals corresponds to concentration levels calculated from published water solubility laws. Hydrogen diffusivities were determined for the three crystallographic axes from profiles of water content as a function of position. The chemical diffusion coefficients are comparable to those previously reported for natural iron-bearing olivine. At high temperature, hydrogenation is dominated by coupled diffusion of protons and octahedrally coordinated metal vacancies where the vacancy diffusion rate limits the process. From the experimental data, we determined the following diffusion laws (diffusivity in m2 s−1, activation energies in kJ mol−1): for diffusion along [100] and [010]; for diffusion along [001]. These diffusion rates are fast enough to modify significantly water contents within olivine grains in xenoliths ascending from the mantle.  相似文献   

11.
Grain boundary processes contribute significantly to electronic and ionic transports in materials within Earth’s interior. We report a novel experimental study of grain boundary conductivity in highly strained olivine aggregates that demonstrates the importance of misorientation angle between adjacent grains on aggregate transport properties. We performed electrical conductivity measurements of melt-free polycrystalline olivine (Fo90) samples that had been previously deformed at 1200 °C and 0.3 GPa to shear strains up to γ?=?7.3. The electrical conductivity and anisotropy were measured at 2.8 GPa over the temperature range 700–1400 °C. We observed that (1) the electrical conductivity of samples with a small grain size (3–6 µm) and strong crystallographic preferred orientation produced by dynamic recrystallization during large-strain shear deformation is a factor of 10 or more larger than that measured on coarse-grained samples, (2) the sample deformed to the highest strain is the most conductive even though it does not have the smallest grain size, and (3) conductivity is up to a factor of ~?4 larger in the direction of shear than normal to the shear plane. Based on these results combined with electrical conductivity data for coarse-grained, polycrystalline olivine and for single crystals, we propose that the electrical conductivity of our fine-grained samples is dominated by grain boundary paths. In addition, the electrical anisotropy results from preferential alignment of higher-conductivity grain boundaries associated with the development of a strong crystallographic preferred orientation of the grains.  相似文献   

12.
The Ballenera Creek has 160 km2 being a small catchment in the Pampa Plain in Argentina. This area has been deeply modified by human action through agricultural activities. From 2013 to 2017, electrical conductivity, stable isotopes of water and nitrate concentration monitoring program were conducted. The sampling included weekly and bimonthly samples in two sites along the stream, several groundwater wells and monthly precipitation. Chemical and isotopic tracers are used to discriminate the streamflow components and to evaluate their incidence in the nitrate concentration. The easiest conceptual model for gaining streams contemplates two main elements: direct runoff and groundwater (baseflow and pre-event water). The direct runoff has the lowest electrical conductivity and 18Ow variable content. The baseflow component is characterized by the highest electrical conductivity and isotope composition quite constant. Finally, pre-event water has an intermediate electrical conductivity and isotopic content close to the rainfall-weighted average composition. The nitrate concentration obtained was in general related to the different stream stages and was a useful indicator to evaluate the fertilization in agricultural zones.  相似文献   

13.
The electrical conductivity and polarization properties of calcite single crystals with three orientations, namely, a (00.1) plane perpendicular to the crystallographic c axis (10.0) plane parallel to the crystallographic c axis, and a (10.4) cleavage plane, were studied by both complex impedance and thermally stimulated depolarization current (TSDC) measurements. Conductivities for (00.1)-, (10.0)-, and (10.4)-oriented single calcite crystals at 400–600?°C were 1.16?×?10?7?–?1.05?×?10?5, 7.40?×?10?8?–?4.27?×?10?6, and 4.27?×?10?7?–?2.86?×?10?5 Ω?1 m?1, respectively, and the activation energies for conduction were 112, 103, and 101?kJ?mol?1, respectively. The TSDC spectra verified the electrical polarizability of calcite crystals. The activation energy for depolarization, estimated from TSDC spectra, of the (00.1)-, (10.0)-, and (10.4)-oriented calcite substrates were 112, 119, and 114?kJ?mol?1, respectively. Considering the correlation between the processes of conduction and electric polarization, we proposed the mechanisms of conduction and polarization in calcite on the assumption of oxide ion transport.  相似文献   

14.
The in situ electrical conductivity of hydrous garnet samples (Py20Alm76Grs4–Py73Alm14Grs13) was determined at pressures of 1.0–4.0 GPa and temperatures of 873–1273 K in the YJ-3000t apparatus using a Solartron-1260 impedance/gain-phase analyzer for various chemical compositions and oxygen fugacities. The oxygen fugacity was controlled by five solid-state oxygen buffers (Fe2O3 + Fe3O4, Ni + NiO, Fe + Fe3O4, Fe + FeO, and Mo + MoO2). Experimental results indicate that within a frequency range from 10−2 to 106 Hz, electrical conductivity is strongly dependent on signal frequency. Electrical conductivity shows an Arrhenius increase with temperature. At 2.0 GPa, the electrical conductivity of anhydrous garnet single crystals with various chemical compositions (Py20Alm76Grs4, Py30Alm67Grs3, Py56Alm43Grs1, and Py73Alm14Grs13) decreases with increasing pyrope component (Py). With increasing oxygen fugacity, the electrical conductivity of dry Py73Alm14Grs13 garnet single crystal shows an increase, whereas that of a hydrous sample with 465 ppm water shows a decrease, both following a power law (exponents of 0.061 and −0.071, respectively). With increasing pressure, the electrical conductivity of this hydrous garnet increases, along with the pre-exponential factors, and the activation energy and activation volume of hydrous samples are 0.7731 ± 0.0041 eV and −1.4 ± 0.15 cm3/mol, respectively. The results show that small hopping polarons ( \textFe\textMg · ) \left( {{\text{Fe}}_{\text{Mg}}^{ \cdot } } \right) and protons ( \textH · {\text{H}}^{ \cdot } ) are the dominant conduction mechanisms for dry and wet garnet single crystals, respectively. Based on these results and the effective medium theory, we established the electrical conductivity of an eclogite model with different mineral contents at high temperatures and high pressures, thereby providing constraints on the inversion of field magnetotelluric sounding results in future studies.  相似文献   

15.
About 30% of the chromite grains of variable sizes in a chromitite seam at the base of the Merensky Reef of the Bushveld Complex on the farm Vlakfontein contain abundant composite mineral inclusions. The inclusions are polygonal to circular with radial cracks that protrude into the enclosing chromite. They vary from a few microns to several millimeters in diameter and are concentrated in the cores and mantles of chromite crystals. Electron backscattered patterns indicate that the host chromites are single crystals and not amalgamations of multiple grains. Na-phlogopite and orthopyroxene are most abundant in the inclusions. Edenitic hornblende, K-phlogopite, oligoclase and quartz are less abundant. Cl-rich apatite, rutile, zircon and chalcopyrite are present at trace levels. Na-phlogopite is unique to the inclusions; it has not been found elsewhere in the Bushveld Complex. Other minerals in the inclusions are also present in the matrix of the chromitite seam, but their compositions are different. The Mg/(Mg+Fe2+) ratios of orthopyroxene in the inclusions are slightly higher than those of orthopyroxene in the matrix. K-phlogopite in the inclusions contains more Na than in the matrix. The average compositions of the inclusions are characterized by high MgO (26 wt%), Na2O (2.4 wt%) and H2O (2.6 wt%), and low CaO (1.1 wt%) and FeO (4.4 wt%). The δ18O value of the trapped melt, estimated by analysis of inclusion-rich and inclusion-poor chromites, is ∼7‰. This value is consistent with the previous estimates for the Bushveld magma and with the δ18O values of silicate minerals throughout the reef. The textural features and peculiar chemical compositions are consistent with entrapment of orthopyroxene with variable amounts of volatile-rich melts during chromite crystallization. The volatile-rich melts are thought to have resulted from variable degrees of mixing between the magma on the floor of the chamber and Na-K-rich fluids expelled from the underlying crystal pile. The addition of fluid to the magma is thought to have caused dissolution of orthpyroxene, leaving the system saturated only in chromite. Both oxygen and hydrogen isotopic values are consistent with the involvement of a magmatic fluid in the process of fluid addition and orthopyroxene dissolution. Most of the Cr and Al in the inclusions was contributed through wall dissolution of the host chromite. Dissolution of minor rutile trapped along with orthopyroxene provided most of the Ti in the inclusions. The Na- and K-rich hydrous silicate minerals in the inclusions were formed during cooling by reaction between pyroxene and the trapped volatile-rich melts.  相似文献   

16.
 We have determined the quenched cation ordering states of five orthopyroxene crystals collected from the marginal border group and the lower zone a and b of the Skaergaard intrusion, and modeled these data to retrieve their closure temperatures (T c) of Fe–Mg ordering and cooling rates. According to existing thermal models for the Skaergaard pluton, conductive cooling dominated the high and low temperature regimes, which were separated by an intermediate temperature regime in which the cooling was controlled primarily by convective fluid circulation. The cooling rates retrieved from the quenched cation ordering states of the orthopyroxene crystals strictly apply to temperatures around the closure temperatures of the ordering states, ∼340–400° C, which fall at the transition from convective to the lower temperature conductive cooling. The cooling rates obtained from the cation ordering states of orthopyroxene vary from ∼1 to 270 K/ka. These results agree well with a thermal model calculated using an assumed average permeability of 10-12 cm2 for the pluton, but not completely with a model calculated on the basis of an average permeability of 10-13 cm2, although both values produced shifts of δ18O that are comparable to those observed in the pluton. Received: 27 February 1995/Accepted: 20 July 1995  相似文献   

17.
The incorporation of hydrogen into ferrosilite, Fe-bearing enstatite and orthopyroxene containing different trivalent cations (Cr3+ and Al3+, Cr3+ and Fe3+) was investigated experimentally at 25 kbar. Hydrogen concentration was determined by FTIR-spectroscopy on oriented crystal sections and by secondary ion mass spectroscopy, whereas Mößbauer spectroscopy and optical spectroscopy were used to characterise the valence state of Fe in orthopyroxene. Results suggest that hydrogen incorporation in ferrosilite is achieved by a similar mechanism as in pure enstatite. In Cr-bearing samples, however, hydrogen incorporation is reduced by the presence of other trivalent cations by an increased tendency to form Tschermaks substitutions, e.g. Si T 4+ + Mg M1 2+ ? Al T 3+ + Cr M1 3+ . Thus, hydrogen solubility in natural orthopyroxenes from the Earth’s mantle, containing significant amounts of Cr3+, Al3+, and Fe3+, may be much more limited than expected from their trivalent cation content, as a large fraction of the trivalent cations does not participate in H-incorporating reactions as 2 Mg M1 2+ ? M M1 3+ + VM1 + H i + .  相似文献   

18.
Creep strength of oriented orthopyroxene single crystals was investigated via shear deformation experiments under lithospheric conditions [P (pressure) = 1.3 GPa and T (temperature) = 973–1,373 K]. For the A-orientation (shear direction [001] on (100) plane), the samples have transformed completely to clinoenstatite and much of the deformation occurred after transformation. In contrast, for the B-orientation (shear direction [001] on (010) plane), samples remained orthoenstatite and deformation occurred through dislocation motion in orthoenstatite. The strength of orthopyroxene with these orientations is smaller than for olivine aggregates under all experimental conditions. Flow of the B-orientation samples is described by a power-law, and the pre-exponential constant, the apparent activation energy, and the stress exponent are determined to be A = 10−9.5 s−1·MPa−4.2, Q = 114 kJ/mol and n = 4.2. However, for the A-orientation, the results cannot be fit by a single flow law and we obtained the following: A = 108.9 s−1·MPa−3.0, Q = 459 kJ/mol and n = 3.0 at high temperatures (≥1,173 K), and A = 10−27.4 s−1·MPa−14.3, Q = 296 kJ/mol and n = 14.3 at low temperatures (<1,173 K). The stress exponent for the low-temperature regime is high, suggesting that deformation involves some processes where the activation energy decreases with stress such as the Peierls mechanism. Our study shows that orthopyroxene with these orientations is significantly weaker than olivine under the lithospheric conditions suggesting that orthopyroxene may reduce the strength of the lithosphere, although the extent to which orthopyroxene weakens the lithosphere depends on its orientation and connectivity.  相似文献   

19.
The phase transition of K2SO4 has been investigated by measurements of the dielectric constant and electrical conductivity, correlated with the structural point of view. Using single crystals, the temperature dependences of the dielectric constants and electrical conductivities were measured at frequencies of 0.3, 1, 3, and 5 MHz in the temperature range from 20° to 640 °C. Within this range, the dielectric constant does not reach a maximum, but near the phase-transition temperature at 587° C, the dielectric constant along the c axis shows a larger discontinuity than those along the a and b axes. The temperature dependence of the dielectric constant is consistent with the disordered structure of the high temperature form. Based on the parabolic increase of the dielectric constant in the temperature range from 582° to 587° C, it is likely that the phase transition propagates through an intermediate state. The electrical conductivity coefficients of K2SO4 increase with increasing temperature, exhibiting semiconducting character above the phase-transition temperature. In the high-temperature form, the electrical conductivity along the a axis exceeds that along the c axis. Since the electrical conductivity of K2SO4 is mainly ionic in character, the migration of K+ ions makes a major contribution to the conduction process.  相似文献   

20.
Summary The hydrogen content of 29 quartz crystals originating from the Penninic series of the central and western Tauern Window (Tyrol, Austria) was determined by IR spectroscopy. The hydrogen contents are between 7 and 66 H/106 Si-atoms. In one sample showing a mimetic lamellar structure H-contents up to 140 H/106 Si-atoms could be found. In most cases no difference exists between the hydrogen contents of margins and cores of the crystals. No clear relationships between the hydrogen content of the quartz lattice and the metamorphic temperature ranging from about 600°C to about 450°C can be found.
Der H-Gehalt von Quarzen aus alpinen Klüften der Penninischen Gesteine des westlichen Tauernfensters (Österreich/Italien)
Zusammenfassung Der Wasserstoffgehalt von 29 Quarzkristallen aus den alpinen Zerrklüften der penninischen Gesteine des zentralen und westlichen Tauernfensters (Tirol, Österreich) wurde IR-spektroskopisch bestimmt. Der H-Gehalt schwankt zwischen 7 und 66 H/106 Si-Atome. In einer Quarzprobe, die auch eine Lamellenstruktur zeigt, wurde ein H-Gehalt bis zu 140 H/106 Si-Atome gemessen. In den meisten Quarzkristallen konnte kein Unterschied in den H-Gehalten des inneren und des äußeren Bereiches gefunden werden. Es konnte auch kein Zusammenhang zwischen den Metamorphosetemperaturen, die zwischen ca. 600 und 450°C liegen, und dem H-Gehalt der Quarzkristalle gefunden werden.
  相似文献   

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