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Tomoo Katsura - One of the best experts on this subject based on the ideXlab platform.
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electrical conductivity of enstatite as a function of water Content implications for the electrical structure in the upper mantle
Earth and Planetary Science Letters, 2012Co-Authors: Tomoo Katsura, Takashi Yoshino, Shuangming Shan, Takuya Matsuzaki, Baohua ZhangAbstract:Abstract The electrical conductivity of Ca-free aluminous enstatite with various water Contents has been determined at a pressure of 3 GPa in a Kawai-type multi-anvil apparatus. Impedance spectroscopy was performed for both hydrogen-doped and -undoped samples in a frequency range from 0.1 Hz to 1 MHz to examine the effect of water on conductivity. Two conduction mechanisms were identified for hydrogen-undoped samples at temperature of 1000–1723 K and for hydrogen-doped samples at relatively lower temperature range of 500–900 K to minimize dehydration of samples. For the hydrogen-undoped samples, the activation enthalpy is around 1.9 eV at the higher temperatures range (>1300 K) suggesting that the dominant charge transfer mechanism is Fe 2+ −Fe 3+ hopping (small polaron) conduction. For the hydrogen-doped samples measured below 900 K, the activation enthalpy decreases from 1.11 to 0.70 eV, and the conductivity values systematically increase with increasing water Content, suggesting that proton conduction is the dominant conduction mechanism. Taking hopping conduction and water Content Dependence of activation enthalpy for proton conduction into account, all electrical conductivity data were fitted to the formula σ = σ 0 h exp( −H h / kT )+ σ 0 p C w exp[−( H p 0 − αC w 1/3 )/ kT ], where σ 0 is pre-exponential factor, C w is the water Content in weight percent, H is the activation enthalpy, H p 0 is the activation enthalpy for proton conduction at very low water concentration, α is the geometrical factor, k is the Boltzmann constant, T is absolution temperature and subscripts h and p represent hopping and proton conductions, respectively. Using the present results, a laboratory-based conductivity-depth profile in the Earth's upper mantle has been constructed as a function of water Content. Comparison of our model with the currently available geophysical observations beneath the Eastern Pacific Rise indicates that hydrous aluminous enstatite cannot account for the high conductivity anomaly at the top of the asthenosphere as well as hydrous olivine.
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effect of iron Content on electrical conductivity of ringwoodite with implications for electrical structure in the transition zone
Physics of the Earth and Planetary Interiors, 2009Co-Authors: Takashi Yoshino, Tomoo KatsuraAbstract:Abstract Electrical conductivity of ringwoodite with various iron Contents [Fe/(Fe + Mg) = 0.09, 0.2 and 0.3] was measured at pressure (20 GPa) and temperature (up to 1900 K) conditions of the lower part of the mantle transition zone in a Kawai-type multi-anvil apparatus. The conductivity increased with increasing total iron Content. All electrical conductivity data were fitted to the formula of electrical conductivity σ = σ0 XFe exp(−H/kT), where σ0 is the pre-exponential term, XFe is the mole fraction of iron Content in the Mg site, H is the activation enthalpy, k is the Boltzmann constant and T is absolute temperature. The activation enthalpy becomes higher at a certain temperature. At high temperatures, the activation enthalpy decreased from 1.44 to 0.92 eV with increasing total Fe Content. At low temperatures less than 1000 K, the activation enthalpy also decreases from 1.15 to 0.74 eV with total Fe Content. Dependence of the activation enthalpy on Fe Content suggests that the dominant mechanism of charge transport is Fe2+–Fe3+ hopping (small polaron). Recent electrical conductivity-depth profiles of the transition zone beneath the Pacific Ocean obtained from the electromagnetic induction study shows that the conductivity values between 520 and 660 km depths may be explained by ringwoodite with Fe/(Fe + Mg) = 0.10. On the other hand, assuming a normal geotherm, conductivity values beneath the continent or stable craton are considerably lower than those of ringwoodite with Fe/(Fe + Mg) = 0.10. Taking into consideration results from the global seismic tomographic studies, relatively low conductivity in these regions can be explained by the existence of a cooler region compared with the surrounding mantle, rather than the presence of iron-poor ringwoodite, or a combination of both.
T F Kuech - One of the best experts on this subject based on the ideXlab platform.
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epitaxial gan1 yasy layers with high as Content grown by metalorganic vapor phase epitaxy and their band gap energy
Applied Physics Letters, 2004Co-Authors: Akitaka Kimura, C A Paulson, H F Tang, T F KuechAbstract:GaN1−yAsy epitaxial alloy samples with [N]≫[As] were grown by metalorganic vapor phase epitaxy. The range of As Content achieved, up to y=0.067, greatly extends the range of achievable As levels to values that are well within the miscibility gap of the GaN–GaAs system. The single-phase epitaxial nature of the alloy samples was confirmed by x-ray diffraction. The As-Content Dependence of the band gap was determined by optical absorption measurements. A highly-bowed bandgap was observed as a function of the As Content, and a refined value of the bowing parameter of 16.9±1.1 eV was determined.
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n rich ganas with high as Content grown by metalorganic vapor phase epitaxy
MRS Proceedings, 2003Co-Authors: Akitaka Kimura, C A Paulson, H F Tang, T F KuechAbstract:GaN1−yAsy epitaxial alloys on the N-rich side with high As Content were grown by metalorganic vapor phase epitaxy. They had specular surfaces and the single-phase epitaxial nature was confirmed by X-ray diffraction. The As incorporation increased through both a decrease in the growth temperature and V/III ratio. These trends were similar to that found in other III–V alloy systems which exhibit a large miscibility gap and the anion incorporation was considered to have been limited kinetically under the conditions of the low V/III ratio. The range of achieved As Content was extended up to y=0.067, which is a composition well within the miscibility gap. The As-Content Dependence of the band gap energy was determined by optical absorption measurements and large bowing parameter of 16.8 ± 0.9 eV was determined.
Shunichiro Karato - One of the best experts on this subject based on the ideXlab platform.
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some notes on hydrogen related point defects and their role in the isotope exchange and electrical conductivity in olivine
Physics of the Earth and Planetary Interiors, 2015Co-Authors: Shunichiro KaratoAbstract:Abstract Nominally anhydrous minerals such as olivine dissolve hydrogen in a variety of forms including free (or interstitial) proton (H ) and two protons trapped at the M-site ( ( 2 H ) M × ). The strength of chemical bonding between protons and the surrounding atoms are different among different species, and consequently protons belonging to different species likely have different mobility (diffusion coefficients). I discuss the role of diffusion of protons in different species in the isotope exchange and hydrogen-assisted electrical conductivity adding a few notes to the previous work by Karato (2013) including a new way to test the model. I conclude that in the case of isotope exchange, the interaction among these species is strong because diffusion is heterogeneous, whereas there is no strong interaction among different species in electrical conduction where diffusion is homogeneous (in an infinite crystal). Consequently, the slowest diffusing species controls the rate of isotope exchange, whereas the fastest diffusing species controls electrical conductivity leading to a different temperature Dependence of activation energy and anisotropy. This model explains the differences in the activation energy and anisotropy between isotope diffusion and electrical conductivity, and predicts that the mechanism of electrical conductivity changes with temperature providing an explanation for most of the discrepancies among different experimental observations at different temperatures except for those by Poe et al. (2010) who reported anomalously high water Content Dependence and highly anisotropic activation energy. When the results obtained at high temperatures are used, most of the geophysically observed high and highly anisotropic electrical conductivity in the asthenosphere can be explained without invoking partial melting.
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the effect of water on the electrical conductivity of olivine
Nature, 2006Co-Authors: Duojun Wang, Mainak Mookherjee, Shunichiro KaratoAbstract:It is well known that water (as a source of hydrogen) affects the physical and chemical properties of minerals--for example, plastic deformation and melting temperature--and accordingly plays an important role in the dynamics and geochemical evolution of the Earth. Estimating the water Content of the Earth's mantle by direct sampling provides only a limited data set from shallow regions (<200 km depth). Geophysical observations such as electrical conductivity are considered to be sensitive to water Content, but there has been no experimental study to determine the effect of water on the electrical conductivity of olivine, the most abundant mineral in the Earth's mantle. Here we report a laboratory study of the Dependence of the electrical conductivity of olivine aggregates on water Content at high temperature and pressure. The electrical conductivity of synthetic polycrystalline olivine was determined from a.c. impedance measurements at a pressure of 4 GPa for a temperature range of 873-1,273 K for water Contents of 0.01-0.08 wt%. The results show that the electrical conductivity is strongly dependent on water Content but depends only modestly on temperature. The water Content Dependence of conductivity is best explained by a model in which electrical conduction is due to the motion of free protons. A comparison of the laboratory data with geophysical observations suggests that the typical oceanic asthenosphere contains approximately 10(-2) wt% water, whereas the water Content in the continental upper mantle is less than approximately 10(-3) wt%.
Akitaka Kimura - One of the best experts on this subject based on the ideXlab platform.
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epitaxial gan1 yasy layers with high as Content grown by metalorganic vapor phase epitaxy and their band gap energy
Applied Physics Letters, 2004Co-Authors: Akitaka Kimura, C A Paulson, H F Tang, T F KuechAbstract:GaN1−yAsy epitaxial alloy samples with [N]≫[As] were grown by metalorganic vapor phase epitaxy. The range of As Content achieved, up to y=0.067, greatly extends the range of achievable As levels to values that are well within the miscibility gap of the GaN–GaAs system. The single-phase epitaxial nature of the alloy samples was confirmed by x-ray diffraction. The As-Content Dependence of the band gap was determined by optical absorption measurements. A highly-bowed bandgap was observed as a function of the As Content, and a refined value of the bowing parameter of 16.9±1.1 eV was determined.
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n rich ganas with high as Content grown by metalorganic vapor phase epitaxy
MRS Proceedings, 2003Co-Authors: Akitaka Kimura, C A Paulson, H F Tang, T F KuechAbstract:GaN1−yAsy epitaxial alloys on the N-rich side with high As Content were grown by metalorganic vapor phase epitaxy. They had specular surfaces and the single-phase epitaxial nature was confirmed by X-ray diffraction. The As incorporation increased through both a decrease in the growth temperature and V/III ratio. These trends were similar to that found in other III–V alloy systems which exhibit a large miscibility gap and the anion incorporation was considered to have been limited kinetically under the conditions of the low V/III ratio. The range of achieved As Content was extended up to y=0.067, which is a composition well within the miscibility gap. The As-Content Dependence of the band gap energy was determined by optical absorption measurements and large bowing parameter of 16.8 ± 0.9 eV was determined.
Dominique Baillis - One of the best experts on this subject based on the ideXlab platform.
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granular cork Content Dependence of thermal diffusivity thermal conductivity and heat capacity of the composite material granular cork bound with plaster
Energy Procedia, 2013Co-Authors: Aboubakr Cherki, Abdelhamid Khabbazi, Benjamin Remy, Dominique BaillisAbstract:This work is a contribution to understand the thermal behavior of the composite material based on granular cork embedded in plaster. An experimental investigation of its thermal properties was mainly performed using the Flash method and the tiny Hot Plate method in steady state regime. This will allow compare its thermal properties with those of plaster for motivate the proposal that this composite will be used as false ceiling. A comparison of the energy performances of the composite material and plaster was made; it allows deducing a very interesting energy gain. The preliminary findings indicate the composite is better than plaster in term of thermal insulation, energy storage capacity and lightness.