Extended X-ray absorption fine structure (EXAFS) experiments at the Zr K-edge were carried out on... more Extended X-ray absorption fine structure (EXAFS) experiments at the Zr K-edge were carried out on perovskite relaxor ferroelectrics BaTi1−xZrxO3 (BTZ) (x = 0.25, 0.30, 0.35), and on BaZrO3 for comparison. Structural information up to 4.5Å around the Zr atoms is obtained, revealing that the local structure differs notably from the average Pm3m cubic structure deduced from X-ray diffraction. In particular, our results show that the distance between Zr atoms and their first oxygen neighbors is independent of the Zr substitution rate x and equal to that measured in BaZrO3, while the X-ray cubic cell parameter increases linearly with x. Furthermore, we show that the Zr atoms tend to segregate in Zr-rich regions. We propose that the relaxor behavior in BTZ is linked to random elastic fields generated by this particular chemical arrangement, rather than to random electric fields as is the case in most relaxors.
X-ray absorption spectroscopy experiments were performed on a set of xenon implanted uranium diox... more X-ray absorption spectroscopy experiments were performed on a set of xenon implanted uranium dioxide samples. Results indicate that the gas forms highly pressurised inclusions as a result of temperature anneals or an external ion irradiation. Estimated bubble pressures were found to be in the region of 2-5 GPa at low temperature. The consequences of such high pressures developing within intra-granular bubbles in irradiated fuels are discussed. A model is given enabling the computation of the sink strengths of bubbles as a function of the pressure of the rare-gas they contain. The model predicts that for pressure values found in the experiments, fission gas bubbles do not act as sinks for diffusing rare-gas atoms.
The deep subsurface is characterized by hostile conditions in terms of temperature, pressure and ... more The deep subsurface is characterized by hostile conditions in terms of temperature, pressure and nutrient availability. Our current view of the biosphere extension is restricted to depths shallower than the isotherm associated to the highest observed temperature for life, i.e. 122°C. At this temperature, depending on the geological setting, pressure varies between ambient pressure at geothermal springs and 350 MPa in cold subduction zones. In this high-pressure biosphere, biological iron reduction is an important process linked to carbon oxidation. Among the factors governing reaction rates and yields in the deep subsurface, pressure could be of importance due its effects on kinetic and equilibrium reactions. The understanding and modelling of Fe reduction in natural environments, especially in the subsurface, can be first comprehended thanks to studies of Fe reduction in pure cultures; indeed the study of the effects of high pressure on Fe-reducing bacteria in pure cultures can serve as a basic model for the effects of pressure on Fe reduction in the subsurface. We investigated the effects of pressure on the reduction of Fe(III) to Fe(II) by the bacterial model Shewanella oneidensis MR-1. This strain is a mesophilic and piezosensitive counterpart of the psychrophilic and piezophilic Shewanella representatives that have been frequently isolated from deep-sea environments. Kinetics of Fe(III) reduction to Fe(II) were monitored in situ by X-ray Absorption Spectroscopy (XAS) in an appropriate pressure vessel dedicated to in situ XAS measurements (Testemale et al. 2005). Measurements were performed at the BM30B beamline of the European Synchrotron Radiation Facilty (Grenoble, France). Experiments were conducted from 0.1 MPa to 100 MPa at MR-1 optimal temperature (30°C). Iron reduction was monitored until 100 MPa in cultures of MR-1 at a concentration of 10 8 cells/ml. This shows that the metabolic activity of a piezosensitive microbe extends far beyond its pressure limits for growth (0-50 MPa) and consequently that considering only the ability to grow in the conditions of the deep subsurface as a proof of metabolic activity may lead to an underestimation of the impact of the biosphere in deep environments. Even if some experimental factors prevent the exact reproduction of subsurface conditions, we show here that the metabolic activity of a surface microbe potentially brought to the deep subsurface can affect important biogeochemical cycles as those of iron and carbon. cited as : Picard, A., Daniel, I., Testemale, D., Hazemann, J., and Oger, P. Microbial iron reduction under deep subsurface pressure conditions (2009), Title, Eos Trans. AGU, 90(52), Fall Meet. Suppl., Abstract B22A-06
... 100, 985 (1994) [SPIN][INSPEC][ADS]. Y. Ito, T. Mukoyama, S. Emura, M. Takahashi, S. Yoshikad... more ... 100, 985 (1994) [SPIN][INSPEC][ADS]. Y. Ito, T. Mukoyama, S. Emura, M. Takahashi, S. Yoshikado, and K. Omote, Phys. Rev. ... 93, 1157 (1993) [CAS]. G. Ferlat, A. San Miguel, PA Bopp, I. Daniel, S. Guillot, and R. Argoud, J.-F. Jal, J.-C. Soetens, J.-L. Hazemann (unpublished). ...
We report the first observation of a weak ferromagnetic state of Cr in Cr/Ru(0001) superlattices,... more We report the first observation of a weak ferromagnetic state of Cr in Cr/Ru(0001) superlattices, based on magnetic hysteresis and corroborated by x-ray magnetic circular dichroism at the CrL(2,3) edges. In situ reflection high-energy electron diffraction, x-ray diffraction, and Cr K-edge polarized x-ray absorption investigations have shown that the Cr layers thinner than 8 angstroms adopt a slightly distorted hcp structure, accompanied by a large atomic volume expansion of up to 14% compared to the bcc packing volume. The expanded hcp structure clearly induces the observed ferromagnetism, in agreement with theory.
Extended X-ray absorption fine structure (EXAFS) experiments at the Zr K-edge were carried out on... more Extended X-ray absorption fine structure (EXAFS) experiments at the Zr K-edge were carried out on perovskite relaxor ferroelectrics BaTi1−xZrxO3 (BTZ) (x = 0.25, 0.30, 0.35), and on BaZrO3 for comparison. Structural information up to 4.5Å around the Zr atoms is obtained, revealing that the local structure differs notably from the average Pm3m cubic structure deduced from X-ray diffraction. In particular, our results show that the distance between Zr atoms and their first oxygen neighbors is independent of the Zr substitution rate x and equal to that measured in BaZrO3, while the X-ray cubic cell parameter increases linearly with x. Furthermore, we show that the Zr atoms tend to segregate in Zr-rich regions. We propose that the relaxor behavior in BTZ is linked to random elastic fields generated by this particular chemical arrangement, rather than to random electric fields as is the case in most relaxors.
In this paper, small-angle X-ray scattering measurements are used to determine the different comp... more In this paper, small-angle X-ray scattering measurements are used to determine the different compressibility contributions, as well as the isothermal compressibility, χ 0 T , in thermal equilibrium in silica glasses having different thermal histories. Using two different methods of analysis, in the supercooled liquid and in the glassy state, we obtain respectively the temperature and fictive temperature dependences of χ 0 T . The values obtained in the glass and supercooled liquid states are very close to each other. They agree with previous determinations of the literature. The compressibility in the glass state slightly decreases with increasing fictive temperature. The relaxational part of the compressibility is also calculated and compared to previous determinations. We discussed the small differences between the different determinations.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2008
ABSTRACT X-ray absorption spectroscopy experiments were performed on a set of uranium dioxide sam... more ABSTRACT X-ray absorption spectroscopy experiments were performed on a set of uranium dioxide samples implanted with 1017 xenoncm−2 at 800keV (8at.% at 140nm). EXAFS measurements performed at 12K showed that during implantation the gas forms highly pressurised nanometre size inclusions. Bubble pressures were estimated at 2.8±0.3GPa at low temperature. Following the low energy xenon implantation, samples were annealed between 1073 and 1773K for several hours. Stability of nanometre size highly pressurized xenon aggregates in UO2 is demonstrated up to 1073K as for this temperature almost no modification of the xenon environment was observed. Above this temperature, bubbles will trap migrating vacancies and their inner pressure is seen to decrease substantially.
X-ray absorption spectroscopy experiments were performed on a set of xenon implanted uranium diox... more X-ray absorption spectroscopy experiments were performed on a set of xenon implanted uranium dioxide samples. Results indicate that the gas forms highly pressurised inclusions as a result of temperature anneals or an external ion irradiation. Estimated bubble pressures were found to be in the region of 2-5 GPa at low temperature. The consequences of such high pressures developing within intra-granular bubbles in irradiated fuels are discussed. A model is given enabling the computation of the sink strengths of bubbles as a function of the pressure of the rare-gas they contain. The model predicts that for pressure values found in the experiments, fission gas bubbles do not act as sinks for diffusing rare-gas atoms.
Andosols on the island of Réunion have high nickel (Ni) concentrations due to the natural pedo-ge... more Andosols on the island of Réunion have high nickel (Ni) concentrations due to the natural pedo-geochemical background. Enhanced knowledge of Ni speciation is necessary to predict the bioavailability and potential toxicity of this element. Ni spe-ciation in these andosols, marked by the presence of high amounts of natural aluminosilicate nanoparticles, was investigated in two complementary systems: (i) In a soil sample—densimetric fractionation was first performed in order to separate the potential bearing phases, prior to Ni speciation characterization. (ii) In a synthetic sample—Ni reactivity with synthetic alu-minosilicate nanoparticle analogs were studied. In both cases, Ni speciation was determined using X-ray absorption spectros-copy (XAS). The results revealed that Ni had the same local environment in both systems (natural and synthetic systems), and Ni was chemically linked to natural short-range ordered aluminosilicates or analogs. This complex represented about 75% of the total Ni in the studied soil.
Extended X-ray absorption fine structure (EXAFS) experiments at the Zr K-edge were carried out on... more Extended X-ray absorption fine structure (EXAFS) experiments at the Zr K-edge were carried out on perovskite relaxor ferroelectrics BaTi1−xZrxO3 (BTZ) (x = 0.25, 0.30, 0.35), and on BaZrO3 for comparison. Structural information up to 4.5Å around the Zr atoms is obtained, revealing that the local structure differs notably from the average Pm3m cubic structure deduced from X-ray diffraction. In particular, our results show that the distance between Zr atoms and their first oxygen neighbors is independent of the Zr substitution rate x and equal to that measured in BaZrO3, while the X-ray cubic cell parameter increases linearly with x. Furthermore, we show that the Zr atoms tend to segregate in Zr-rich regions. We propose that the relaxor behavior in BTZ is linked to random elastic fields generated by this particular chemical arrangement, rather than to random electric fields as is the case in most relaxors.
X-ray absorption spectroscopy experiments were performed on a set of xenon implanted uranium diox... more X-ray absorption spectroscopy experiments were performed on a set of xenon implanted uranium dioxide samples. Results indicate that the gas forms highly pressurised inclusions as a result of temperature anneals or an external ion irradiation. Estimated bubble pressures were found to be in the region of 2-5 GPa at low temperature. The consequences of such high pressures developing within intra-granular bubbles in irradiated fuels are discussed. A model is given enabling the computation of the sink strengths of bubbles as a function of the pressure of the rare-gas they contain. The model predicts that for pressure values found in the experiments, fission gas bubbles do not act as sinks for diffusing rare-gas atoms.
The deep subsurface is characterized by hostile conditions in terms of temperature, pressure and ... more The deep subsurface is characterized by hostile conditions in terms of temperature, pressure and nutrient availability. Our current view of the biosphere extension is restricted to depths shallower than the isotherm associated to the highest observed temperature for life, i.e. 122°C. At this temperature, depending on the geological setting, pressure varies between ambient pressure at geothermal springs and 350 MPa in cold subduction zones. In this high-pressure biosphere, biological iron reduction is an important process linked to carbon oxidation. Among the factors governing reaction rates and yields in the deep subsurface, pressure could be of importance due its effects on kinetic and equilibrium reactions. The understanding and modelling of Fe reduction in natural environments, especially in the subsurface, can be first comprehended thanks to studies of Fe reduction in pure cultures; indeed the study of the effects of high pressure on Fe-reducing bacteria in pure cultures can serve as a basic model for the effects of pressure on Fe reduction in the subsurface. We investigated the effects of pressure on the reduction of Fe(III) to Fe(II) by the bacterial model Shewanella oneidensis MR-1. This strain is a mesophilic and piezosensitive counterpart of the psychrophilic and piezophilic Shewanella representatives that have been frequently isolated from deep-sea environments. Kinetics of Fe(III) reduction to Fe(II) were monitored in situ by X-ray Absorption Spectroscopy (XAS) in an appropriate pressure vessel dedicated to in situ XAS measurements (Testemale et al. 2005). Measurements were performed at the BM30B beamline of the European Synchrotron Radiation Facilty (Grenoble, France). Experiments were conducted from 0.1 MPa to 100 MPa at MR-1 optimal temperature (30°C). Iron reduction was monitored until 100 MPa in cultures of MR-1 at a concentration of 10 8 cells/ml. This shows that the metabolic activity of a piezosensitive microbe extends far beyond its pressure limits for growth (0-50 MPa) and consequently that considering only the ability to grow in the conditions of the deep subsurface as a proof of metabolic activity may lead to an underestimation of the impact of the biosphere in deep environments. Even if some experimental factors prevent the exact reproduction of subsurface conditions, we show here that the metabolic activity of a surface microbe potentially brought to the deep subsurface can affect important biogeochemical cycles as those of iron and carbon. cited as : Picard, A., Daniel, I., Testemale, D., Hazemann, J., and Oger, P. Microbial iron reduction under deep subsurface pressure conditions (2009), Title, Eos Trans. AGU, 90(52), Fall Meet. Suppl., Abstract B22A-06
... 100, 985 (1994) [SPIN][INSPEC][ADS]. Y. Ito, T. Mukoyama, S. Emura, M. Takahashi, S. Yoshikad... more ... 100, 985 (1994) [SPIN][INSPEC][ADS]. Y. Ito, T. Mukoyama, S. Emura, M. Takahashi, S. Yoshikado, and K. Omote, Phys. Rev. ... 93, 1157 (1993) [CAS]. G. Ferlat, A. San Miguel, PA Bopp, I. Daniel, S. Guillot, and R. Argoud, J.-F. Jal, J.-C. Soetens, J.-L. Hazemann (unpublished). ...
We report the first observation of a weak ferromagnetic state of Cr in Cr/Ru(0001) superlattices,... more We report the first observation of a weak ferromagnetic state of Cr in Cr/Ru(0001) superlattices, based on magnetic hysteresis and corroborated by x-ray magnetic circular dichroism at the CrL(2,3) edges. In situ reflection high-energy electron diffraction, x-ray diffraction, and Cr K-edge polarized x-ray absorption investigations have shown that the Cr layers thinner than 8 angstroms adopt a slightly distorted hcp structure, accompanied by a large atomic volume expansion of up to 14% compared to the bcc packing volume. The expanded hcp structure clearly induces the observed ferromagnetism, in agreement with theory.
Extended X-ray absorption fine structure (EXAFS) experiments at the Zr K-edge were carried out on... more Extended X-ray absorption fine structure (EXAFS) experiments at the Zr K-edge were carried out on perovskite relaxor ferroelectrics BaTi1−xZrxO3 (BTZ) (x = 0.25, 0.30, 0.35), and on BaZrO3 for comparison. Structural information up to 4.5Å around the Zr atoms is obtained, revealing that the local structure differs notably from the average Pm3m cubic structure deduced from X-ray diffraction. In particular, our results show that the distance between Zr atoms and their first oxygen neighbors is independent of the Zr substitution rate x and equal to that measured in BaZrO3, while the X-ray cubic cell parameter increases linearly with x. Furthermore, we show that the Zr atoms tend to segregate in Zr-rich regions. We propose that the relaxor behavior in BTZ is linked to random elastic fields generated by this particular chemical arrangement, rather than to random electric fields as is the case in most relaxors.
In this paper, small-angle X-ray scattering measurements are used to determine the different comp... more In this paper, small-angle X-ray scattering measurements are used to determine the different compressibility contributions, as well as the isothermal compressibility, χ 0 T , in thermal equilibrium in silica glasses having different thermal histories. Using two different methods of analysis, in the supercooled liquid and in the glassy state, we obtain respectively the temperature and fictive temperature dependences of χ 0 T . The values obtained in the glass and supercooled liquid states are very close to each other. They agree with previous determinations of the literature. The compressibility in the glass state slightly decreases with increasing fictive temperature. The relaxational part of the compressibility is also calculated and compared to previous determinations. We discussed the small differences between the different determinations.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2008
ABSTRACT X-ray absorption spectroscopy experiments were performed on a set of uranium dioxide sam... more ABSTRACT X-ray absorption spectroscopy experiments were performed on a set of uranium dioxide samples implanted with 1017 xenoncm−2 at 800keV (8at.% at 140nm). EXAFS measurements performed at 12K showed that during implantation the gas forms highly pressurised nanometre size inclusions. Bubble pressures were estimated at 2.8±0.3GPa at low temperature. Following the low energy xenon implantation, samples were annealed between 1073 and 1773K for several hours. Stability of nanometre size highly pressurized xenon aggregates in UO2 is demonstrated up to 1073K as for this temperature almost no modification of the xenon environment was observed. Above this temperature, bubbles will trap migrating vacancies and their inner pressure is seen to decrease substantially.
X-ray absorption spectroscopy experiments were performed on a set of xenon implanted uranium diox... more X-ray absorption spectroscopy experiments were performed on a set of xenon implanted uranium dioxide samples. Results indicate that the gas forms highly pressurised inclusions as a result of temperature anneals or an external ion irradiation. Estimated bubble pressures were found to be in the region of 2-5 GPa at low temperature. The consequences of such high pressures developing within intra-granular bubbles in irradiated fuels are discussed. A model is given enabling the computation of the sink strengths of bubbles as a function of the pressure of the rare-gas they contain. The model predicts that for pressure values found in the experiments, fission gas bubbles do not act as sinks for diffusing rare-gas atoms.
Andosols on the island of Réunion have high nickel (Ni) concentrations due to the natural pedo-ge... more Andosols on the island of Réunion have high nickel (Ni) concentrations due to the natural pedo-geochemical background. Enhanced knowledge of Ni speciation is necessary to predict the bioavailability and potential toxicity of this element. Ni spe-ciation in these andosols, marked by the presence of high amounts of natural aluminosilicate nanoparticles, was investigated in two complementary systems: (i) In a soil sample—densimetric fractionation was first performed in order to separate the potential bearing phases, prior to Ni speciation characterization. (ii) In a synthetic sample—Ni reactivity with synthetic alu-minosilicate nanoparticle analogs were studied. In both cases, Ni speciation was determined using X-ray absorption spectros-copy (XAS). The results revealed that Ni had the same local environment in both systems (natural and synthetic systems), and Ni was chemically linked to natural short-range ordered aluminosilicates or analogs. This complex represented about 75% of the total Ni in the studied soil.
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Papers by J-l. Hazemann