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Papers by Béatrice Hannoyer

Materials Science and Engineering: A, 2003

... Permissions & Reprints. Interlamellar boundary characterization in Ni-based alloy thermal... more ... Permissions & Reprints. Interlamellar boundary characterization in Ni-based alloy thermally sprayed coating. R. Molins a , B. Normand Corresponding Author Contact Information , E-mail The Corresponding Author , b , c , G. Rannou d , B. Hannoyer e and H. Liao c. ...

International Thermal Spray Conference

Investigations have been carried out to study the influence of Atmospheric Plasma Spray process (... more Investigations have been carried out to study the influence of Atmospheric Plasma Spray process (APS) on the in-flight oxidation of pure iron particles. After collecting the molten droplets in-flight, XRD, SEM and Mössbauer spectroscopy are used to determine the amount and distribution of formed oxides. The results indicate that the Wüstite, Fe0.95O, is the only oxide formed during the APS. In the jet core and at the beginning of its plume, oxidation is controlled by convection within molten droplets and then for the downstream of the plasma by diffusion where the solubility of oxygen through the external oxide layer governs the growth of Wüstite. Calculations have shown that the convective movement is due to the drastic velocity difference between the plasma jet and particles. Wüstite granules can be distinguished within the particles due to the immiscibility between Fe and FeO in liquid phase. This oxide phase represents about 13 wt% of the collected particles at 100 mm stand-off ...

Revue de Métallurgie, 1999

La preoxydation, par le panache d’un plasma d’arc, d’un acier inoxydable austenitique 304L a ete ... more La preoxydation, par le panache d’un plasma d’arc, d’un acier inoxydable austenitique 304L a ete etudiee sur trois etats de surface differents, l’etat poli diamant 1 μm (A), l’etat poli SiC grade 1000 (B) et l’etat sable (C). L’acier laisse apparaitre une martensite d’ecrouissage apres le traitement B et des microcontraintes notables sur l’etat C. Les oxydes formes sont principalement de type Fe2-x Crx O3 a partir des etats A et C, et de type spinelle Nix Cry Fe3-x-y O4 a partir de l’etat B, avec apparition dans les cas B et C d’une phase ferritique en surface du substrat metallique.

Materials Chemistry and Physics, 1998

Mixed hydroxide suspensions with a molar ratio of NiO:Fe203 = 1:1 were aged at 25, 90 or 120°C fo... more Mixed hydroxide suspensions with a molar ratio of NiO:Fe203 = 1:1 were aged at 25, 90 or 120°C for various times. Ferritization of Ni 2 + ions in these suspensions was studied by analysis of the solid products separated from the mother liquor. X-ray powder diffraction indicated that in one sample, a maximum of three crystalline phases were detected: NiFe20,,, oe-Ni(OH)2.0.75HaO and ee-FeOOH. The actual phase composition of the samples was very dependent on the experimental conditions. FT-IR spectroscopy indicated the Ni 2+ ferritization in the samples obtained at 90 and 120°C, and provided evidence that this process was possible even at 25°C. The Ni 2+ ferritization was also monitored by 57Fe M6ssbauer spectroscopy. The relative intensity of the hyperfine magnetic splitting component increased with the aging time at 90°C. The effect of particle size on the shape of these spectra was suggested. The superposition of two central quadrupole doublets was discussed in the sense of the presence of the NiFe,O4 precursor and in some samples of ferrihydrite. The visible and near-infrared diffuse reflectance spectra also gave evidence of Ni 2+ ferritization in the samples investigated. The characteristic bands, which supported this conclusion, were interpreted.

Physica Status Solidi (a), 1987

ABSTRACT

Physica C: Superconductivity, 1998

Ž. A superconductive Bi Pb Sr Ca Cu Fe O compound with x s 0.02 has been investigated by means of... more Ž. A superconductive Bi Pb Sr Ca Cu Fe O compound with x s 0.02 has been investigated by means of X-ray 1.7 0.3 2 2 1yx x 3 10 diffraction technique and Mossbauer spectroscopy. Its electrical resistance did not show anomaly in the transition region around 110 K, and, even at 77 K, no magnetic behavior was put in evidence. Mossbauer data have proved that the samplë contained other phases than the 2223-phase while it was difficult to distinguish these impurity phases in the X-ray pattern. Ž. The evolution of the Mossbauer components as a function of the temperature shows that the oxygen environments of Fe Cü atoms are modified when the sample is cooled down at temperatures lower than the onset temperature.

Materials Science and Engineering: B, 2000

Ferrite ceramics were prepared utilizing solid state reactions between CuO and Fe 3 O 4 or a-Fe 2... more Ferrite ceramics were prepared utilizing solid state reactions between CuO and Fe 3 O 4 or a-Fe 2 O 3. The samples were analyzed with X-ray diffraction, 57 Fe Mö ssbauer and FT-IR spectroscopies. For the solid state reaction between CuO and Fe 3 O 4 , the initial atomic ratios of Cu:Fe varied between 1:299 and 1:2. With an increase in the amount of CuO in the initial reaction mixture, there was a corresponding increase in cuprospinel (cubic CuFe 2 O 4) in the final products of the synthesis. For the initial molar ratio of Cu:Fe = 1:2, cuprospinel phase (0.85) and CuFeO 2 phase (0.15) were found by XRD, as the result of solid state reaction between CuO and Fe 3 O 4. In this sample, a small amount of CuO was also detected. For the solid state reaction between CuO and a-Fe 2 O 3 , the initial molar ratio of 1:1 was used. The samples prepared at a maximum temperature of 800°C, contained similar fractions of tetragonal and cubic CuFe 2 O 4 phases, and also minor phases of CuO and a-Fe 2 O 3 as found by XRD. In the samples prepared at between 1000 and 1350°C, the cubic CuFe 2 O 4 phase was found together with small amounts of CuFeO 2 and CuO. Mö ssbauer spectra showed hyperfine field distributions and on the basis of these spectra, calculated parameters, the possible presence of Cu + and Fe 2 + ions in the samples was discussed. For the samples prepared at 1350°C the FT-IR spectrum suggested a significant increase in Fe 2 + ions, whereas the Mö ssbauer spectrum and calculated parameters were similar to those for the compound Cu 0.7 Fe 2.3 O 4 .

Materials Research Bulletin, 1983

Chemical shifts of L~ 1 2' K~I ~" KS~ emission bands and X-ray absorption spectra near the K edge... more Chemical shifts of L~ 1 2' K~I ~" KS~ emission bands and X-ray absorption spectra near the K edge have been measured in several iron spinels oxides with the metal in the formal oxidation states +2 and +3. The first high resolution XANES spectra for these materials were performed at the DCI storage ring at LURE, Orsay. Two transitions in the range 15-20 eV above the Is ~ 3d observed on the derivative XANES spectra are very sensitive to the iron oxidation state. The analysis of the X-ray absorption fine structure in the near edge region and the measurements of the chemical shift of FeK85 are more adapted than Mossbauer effect to disclosing FeII in mixed ferrites.

Materials Research Bulletin, 1990

Oxidation products formed on stainless steels of the type 18 Cr, 10 Ni, ~ 2 Mn have been studied ... more Oxidation products formed on stainless steels of the type 18 Cr, 10 Ni, ~ 2 Mn have been studied by X-ray diffraction, C.E.M.S. and FTIR reflectance spectroscopy. Oxidation was performed in air between 900°C and 1100°C. The layer contains chromium oxides Cr203 and MnCr204 and mostly iron oxides ~Fe203 even at short oxidation times of a few minutes. The formation of Fe203 is probably preceded by the formation of an Fe304 layer. No nickel has been detected in the oxide layer. FTIR specular spectroscopy at different angles of incidence is very useful to understand the mechanisms and kinetics of oxidation processes (o_Fe203 is characterized by main bands at 510 and-430 cm-1). INDEX: stainless steel, oxides.

Materials Research Bulletin, 1982

The devolopment of new physical methods as photoelectron spectroscopy (ESCA), X-ray emission and ... more The devolopment of new physical methods as photoelectron spectroscopy (ESCA), X-ray emission and absorption spectroscopies is needful to characterize the chemical bonding in materials like Cu0.5Fe2.504 and CuMn204 • The K-absorption edges of copper in oxides CuM02 and CuM204 have been studied with a view to further analytical applications. La caract4risation de la liaison chimique dans des mat~riaux tels Cu0,5Fe2,504, CuMn204 n4cessite le d~veloppement de nouvelles m~thodes physiques telles la spectrom4trie de photoelectrons (ESCA), la spectrom~trie d'~mission et d'absorption X. Cet article est consacr~ & l'4tude des seuils d'absorption K du cuivre dans des oxydes en vue d'applications analytiques ult~rieures. Conditions ex~rimentales

Materials Research Bulletin, 1993

The crystallographic structure of 7-MnO 2 is an important factor of its electrochemical reactivit... more The crystallographic structure of 7-MnO 2 is an important factor of its electrochemical reactivity in primary battery cathods. In order to characterize two industrial samples (EMD and CMD), the structural evolution induced by static thermal treatment in air up to 450°C has been studied using FTIR spectroscopy in diffuse reflectance and EXAFS spectroscopy. Diffuse reflectance FTIR spectra, which can not be correlated to transmittance spectra, show that 7-MnO 2 samples are progressively transformed into ~-MnO 2 with increasing temperature, but that increasing treatment duration at 450°C of up to 60 days does not allow to complete it. EXAFS spectroscopy allows to describe quantitatively the short-range order in such poorly crystallized compounds, and give precise informations on the breadth of the "tunnels" of the structure, which plays a significant part in proton insertion.

Materials Chemistry and Physics, 1985

The effects of oxygen loss on the crystallographic and magnetic properties of CuFe204 ferrite hav... more The effects of oxygen loss on the crystallographic and magnetic properties of CuFe204 ferrite have been studied by high-temperature X-ray diffraction, X-ray absorption spectrometry and Mdssbauer spectrometry. In the heat-treatment under nitrogen, formation of a ferrimagnetic phase is observed with an increased content of Fe2+ and precipitation of CuFe02. Quenching after sintering leads to a mixture containing CuO and a spine1 ferrimagnetic phase in which the oxygen deficiency involves the formation of Cu+. mkonnaissance des phenom&nes d'oxydo-reduction accompagnant le processus de dt?composition [3,4].

Journal of Solid State Chemistry, 1981

XI'S study of copper ferrite oxide spinels Cu,-,Fq,O, with 0 < x I 0.5 gives information about va... more XI'S study of copper ferrite oxide spinels Cu,-,Fq,O, with 0 < x I 0.5 gives information about valence states and cationic distribution of copper in the spine1 matrix. It appears that copper is monovalent and divalent and that Cu*+ and Cu+ cations are found in the tetrahedral and octahedral Wanion environments. X-Ray irradiation induces reduction of tetrahedral Cu*+ to tetrahedral Cu+. The different copper types give shifted Cu zg312 lines, the intensity ratios of which can be used to evaluate the relative proportions of one type on each site. There is satisfactory agreement between our results, Miissbauer snectrosco~)~ studies. and statistical calculations of cationic distribution. The transformation under' X-ray &adiatiod is attributed CU$&

Journal of Non-Crystalline Solids, 1992

ABSTRACT

Journal of Nanoscience and Nanotechnology, 2010

Rutile TiO 2 nanoneedle flowers (representing concurrent nano-micro hierarchical morphology) with... more Rutile TiO 2 nanoneedle flowers (representing concurrent nano-micro hierarchical morphology) with high shape anisotropy ratio are synthesized at room temperature by using a simple and efficient one step electrochemical process of anodic dissolution. This process employs highly acidic bath of perchloric acid (pH < 2) and a large current density on the surface of Titanium foil to form nanostructures. The diameter and length of rutile TiO 2 nanoneedle is ∼8 nm and 100 nm respectively (aspect ratio >10). Dye sensitized solar cell (DSSC) configured using such rutile TiO 2 flowers is shown to exhibit IPCE of 30% and power conversion efficiency of ∼3.6%.

Journal of Materials Science, 1996

The solid solutions (Cr• 0 ~< x ~< 1, were prepared by traditional ceramic procedures. The sample... more The solid solutions (Cr• 0 ~< x ~< 1, were prepared by traditional ceramic procedures. The samples were characterized using X-ray diffraction, M6ssbauer, Fourier transform infra-red (FT-IR) and optical spectroscopic measurements. In the whole concentration range two phases exist phase F, 0~-(CrxFel_• which is isostructural with 0~-Fe203 and phase C, which is closely related to Cr203. Phase F exists in samples heated up to 900~ for 0 ~< x~<0.95. Phase C exists from x~>0.27 to x=l for samples heated up to 900~ and from x~>0.65to x=l for samples heated up to 1200~ For samples heated up to 900~ the solubility limits were 27.5 _+ 0.5 mol % of Cr203 in 0~-Fe203 and 4.0_+ 0.5 mol % of ~-Fe203 in Cr203. For the samples heated at 1200~ the diffraction peaks for the F and C phases in the two phase region were severely overlapped and thus the solubility limits could not be determined accurately as for previous samples. 57Fe M6ssbauer spectra of the samples heated up to 1200 ~ showed significant broadening of spectral lines and a gradual decrease of the hyperfine magnetic field with increase of x up to 0.50. For x>0.7, a paramagnetic doublet with collapsing sextet was observed. The spectra were interpreted in terms of an electronic relaxation effect; however, an agglomeration of iron ions which would contribute to the superparamagnetic effect could not be excluded. The FT-IR spectra showed transition effects in accordance with the X-ray diffraction results. The most intense absorption bands, observed for the samples heated up to 1200 ~ were located at ,-~ 460 and 370 nm (22 000 and 27000cm-1) for x~> 0.5, ,-~500 and 360 nm for x< 0.3, and might be correlated with the strong enhancement of the pair transitions through antiferromagnetic interactions. The intensification of the 6A1 ~ 4T1 Fe 3+ ions in all spectra and the development of the absorption at 13000 cm-~ due to a metal-metal charge transfer (Or 3+ ~ Fe 3+) transition, might be explained by exchange coupling which has been observed in some spinel compounds.

Journal of Applied Physics, 2003

Epitaxial thin films of La0.67Ca0.33MnO3 were implanted with 30 and 100 keV Fe57 ions at differen... more Epitaxial thin films of La0.67Ca0.33MnO3 were implanted with 30 and 100 keV Fe57 ions at different fluence values to achieve a uniform implant distribution. The resistivity of the film increases as fluence increases, but the peak resistivity temperature Tp does not change significantly for the as-implanted sample. Annealing of the implanted samples at 950 °C allows recovery of the structural properties of the films and leads to interesting properties: increase of the peak resistivity and of the colossal magnetoresistance values, and decrease of Tp. The decrease in Tp is of ∼130 K, and the increase in resistivity is almost a factor of 28 as compared to the as-implanted sample.

Journal of Applied Physics, 1996

Thin Fe2O3 layers (44 and 55 nm) were deposited by pulsed excimer laser ablation on single-crysta... more Thin Fe2O3 layers (44 and 55 nm) were deposited by pulsed excimer laser ablation on single-crystal alumina (α-Al2O3) substrates heated at 675 °C. The ion beam mixing of these α-Fe2O3/α-Al2O3 couples was carried out using 300 keV Kr3+ ions at a fluence of 2×1016 ions/cm2. The mixing effect was followed by Rutherford backscattering spectrometry (RBS), conversion electron Mössbauer spectroscopy, and grazing incidence x-ray diffraction method. RBS spectra do not show any evidence of mixing at the interface, whereas the data obtained with the two other techniques display phases like oxygen deficient Fe3O4, Fe3−yAlyO4, and Fe1+xAl2−xO4. For this last phase, x is determined as being equal to about 0.5. It is shown that ion beam mixing is more efficient for the thinner Fe2O3 layer, in accordance with the projected range of the Kr3+ ions.

Hyperfine Interactions, 1986

Conclusion The formation of heterovalent pairs seems to be proved for the compounds rich in Fe2+ ... more Conclusion The formation of heterovalent pairs seems to be proved for the compounds rich in Fe2+ ions (x⩾0.5) and the electron-phonon coupling seems to change with decreasing concentration of Fe2+ ions.

Materials Science and Engineering: A, 2003

... Permissions & Reprints. Interlamellar boundary characterization in Ni-based alloy thermal... more ... Permissions & Reprints. Interlamellar boundary characterization in Ni-based alloy thermally sprayed coating. R. Molins a , B. Normand Corresponding Author Contact Information , E-mail The Corresponding Author , b , c , G. Rannou d , B. Hannoyer e and H. Liao c. ...

International Thermal Spray Conference

Investigations have been carried out to study the influence of Atmospheric Plasma Spray process (... more Investigations have been carried out to study the influence of Atmospheric Plasma Spray process (APS) on the in-flight oxidation of pure iron particles. After collecting the molten droplets in-flight, XRD, SEM and Mössbauer spectroscopy are used to determine the amount and distribution of formed oxides. The results indicate that the Wüstite, Fe0.95O, is the only oxide formed during the APS. In the jet core and at the beginning of its plume, oxidation is controlled by convection within molten droplets and then for the downstream of the plasma by diffusion where the solubility of oxygen through the external oxide layer governs the growth of Wüstite. Calculations have shown that the convective movement is due to the drastic velocity difference between the plasma jet and particles. Wüstite granules can be distinguished within the particles due to the immiscibility between Fe and FeO in liquid phase. This oxide phase represents about 13 wt% of the collected particles at 100 mm stand-off ...

Revue de Métallurgie, 1999

La preoxydation, par le panache d’un plasma d’arc, d’un acier inoxydable austenitique 304L a ete ... more La preoxydation, par le panache d’un plasma d’arc, d’un acier inoxydable austenitique 304L a ete etudiee sur trois etats de surface differents, l’etat poli diamant 1 μm (A), l’etat poli SiC grade 1000 (B) et l’etat sable (C). L’acier laisse apparaitre une martensite d’ecrouissage apres le traitement B et des microcontraintes notables sur l’etat C. Les oxydes formes sont principalement de type Fe2-x Crx O3 a partir des etats A et C, et de type spinelle Nix Cry Fe3-x-y O4 a partir de l’etat B, avec apparition dans les cas B et C d’une phase ferritique en surface du substrat metallique.

Materials Chemistry and Physics, 1998

Mixed hydroxide suspensions with a molar ratio of NiO:Fe203 = 1:1 were aged at 25, 90 or 120°C fo... more Mixed hydroxide suspensions with a molar ratio of NiO:Fe203 = 1:1 were aged at 25, 90 or 120°C for various times. Ferritization of Ni 2 + ions in these suspensions was studied by analysis of the solid products separated from the mother liquor. X-ray powder diffraction indicated that in one sample, a maximum of three crystalline phases were detected: NiFe20,,, oe-Ni(OH)2.0.75HaO and ee-FeOOH. The actual phase composition of the samples was very dependent on the experimental conditions. FT-IR spectroscopy indicated the Ni 2+ ferritization in the samples obtained at 90 and 120°C, and provided evidence that this process was possible even at 25°C. The Ni 2+ ferritization was also monitored by 57Fe M6ssbauer spectroscopy. The relative intensity of the hyperfine magnetic splitting component increased with the aging time at 90°C. The effect of particle size on the shape of these spectra was suggested. The superposition of two central quadrupole doublets was discussed in the sense of the presence of the NiFe,O4 precursor and in some samples of ferrihydrite. The visible and near-infrared diffuse reflectance spectra also gave evidence of Ni 2+ ferritization in the samples investigated. The characteristic bands, which supported this conclusion, were interpreted.

Physica Status Solidi (a), 1987

ABSTRACT

Physica C: Superconductivity, 1998

Ž. A superconductive Bi Pb Sr Ca Cu Fe O compound with x s 0.02 has been investigated by means of... more Ž. A superconductive Bi Pb Sr Ca Cu Fe O compound with x s 0.02 has been investigated by means of X-ray 1.7 0.3 2 2 1yx x 3 10 diffraction technique and Mossbauer spectroscopy. Its electrical resistance did not show anomaly in the transition region around 110 K, and, even at 77 K, no magnetic behavior was put in evidence. Mossbauer data have proved that the samplë contained other phases than the 2223-phase while it was difficult to distinguish these impurity phases in the X-ray pattern. Ž. The evolution of the Mossbauer components as a function of the temperature shows that the oxygen environments of Fe Cü atoms are modified when the sample is cooled down at temperatures lower than the onset temperature.

Materials Science and Engineering: B, 2000

Ferrite ceramics were prepared utilizing solid state reactions between CuO and Fe 3 O 4 or a-Fe 2... more Ferrite ceramics were prepared utilizing solid state reactions between CuO and Fe 3 O 4 or a-Fe 2 O 3. The samples were analyzed with X-ray diffraction, 57 Fe Mö ssbauer and FT-IR spectroscopies. For the solid state reaction between CuO and Fe 3 O 4 , the initial atomic ratios of Cu:Fe varied between 1:299 and 1:2. With an increase in the amount of CuO in the initial reaction mixture, there was a corresponding increase in cuprospinel (cubic CuFe 2 O 4) in the final products of the synthesis. For the initial molar ratio of Cu:Fe = 1:2, cuprospinel phase (0.85) and CuFeO 2 phase (0.15) were found by XRD, as the result of solid state reaction between CuO and Fe 3 O 4. In this sample, a small amount of CuO was also detected. For the solid state reaction between CuO and a-Fe 2 O 3 , the initial molar ratio of 1:1 was used. The samples prepared at a maximum temperature of 800°C, contained similar fractions of tetragonal and cubic CuFe 2 O 4 phases, and also minor phases of CuO and a-Fe 2 O 3 as found by XRD. In the samples prepared at between 1000 and 1350°C, the cubic CuFe 2 O 4 phase was found together with small amounts of CuFeO 2 and CuO. Mö ssbauer spectra showed hyperfine field distributions and on the basis of these spectra, calculated parameters, the possible presence of Cu + and Fe 2 + ions in the samples was discussed. For the samples prepared at 1350°C the FT-IR spectrum suggested a significant increase in Fe 2 + ions, whereas the Mö ssbauer spectrum and calculated parameters were similar to those for the compound Cu 0.7 Fe 2.3 O 4 .

Materials Research Bulletin, 1983

Chemical shifts of L~ 1 2' K~I ~" KS~ emission bands and X-ray absorption spectra near the K edge... more Chemical shifts of L~ 1 2' K~I ~" KS~ emission bands and X-ray absorption spectra near the K edge have been measured in several iron spinels oxides with the metal in the formal oxidation states +2 and +3. The first high resolution XANES spectra for these materials were performed at the DCI storage ring at LURE, Orsay. Two transitions in the range 15-20 eV above the Is ~ 3d observed on the derivative XANES spectra are very sensitive to the iron oxidation state. The analysis of the X-ray absorption fine structure in the near edge region and the measurements of the chemical shift of FeK85 are more adapted than Mossbauer effect to disclosing FeII in mixed ferrites.

Materials Research Bulletin, 1990

Oxidation products formed on stainless steels of the type 18 Cr, 10 Ni, ~ 2 Mn have been studied ... more Oxidation products formed on stainless steels of the type 18 Cr, 10 Ni, ~ 2 Mn have been studied by X-ray diffraction, C.E.M.S. and FTIR reflectance spectroscopy. Oxidation was performed in air between 900°C and 1100°C. The layer contains chromium oxides Cr203 and MnCr204 and mostly iron oxides ~Fe203 even at short oxidation times of a few minutes. The formation of Fe203 is probably preceded by the formation of an Fe304 layer. No nickel has been detected in the oxide layer. FTIR specular spectroscopy at different angles of incidence is very useful to understand the mechanisms and kinetics of oxidation processes (o_Fe203 is characterized by main bands at 510 and-430 cm-1). INDEX: stainless steel, oxides.

Materials Research Bulletin, 1982

The devolopment of new physical methods as photoelectron spectroscopy (ESCA), X-ray emission and ... more The devolopment of new physical methods as photoelectron spectroscopy (ESCA), X-ray emission and absorption spectroscopies is needful to characterize the chemical bonding in materials like Cu0.5Fe2.504 and CuMn204 • The K-absorption edges of copper in oxides CuM02 and CuM204 have been studied with a view to further analytical applications. La caract4risation de la liaison chimique dans des mat~riaux tels Cu0,5Fe2,504, CuMn204 n4cessite le d~veloppement de nouvelles m~thodes physiques telles la spectrom4trie de photoelectrons (ESCA), la spectrom~trie d'~mission et d'absorption X. Cet article est consacr~ & l'4tude des seuils d'absorption K du cuivre dans des oxydes en vue d'applications analytiques ult~rieures. Conditions ex~rimentales

Materials Research Bulletin, 1993

The crystallographic structure of 7-MnO 2 is an important factor of its electrochemical reactivit... more The crystallographic structure of 7-MnO 2 is an important factor of its electrochemical reactivity in primary battery cathods. In order to characterize two industrial samples (EMD and CMD), the structural evolution induced by static thermal treatment in air up to 450°C has been studied using FTIR spectroscopy in diffuse reflectance and EXAFS spectroscopy. Diffuse reflectance FTIR spectra, which can not be correlated to transmittance spectra, show that 7-MnO 2 samples are progressively transformed into ~-MnO 2 with increasing temperature, but that increasing treatment duration at 450°C of up to 60 days does not allow to complete it. EXAFS spectroscopy allows to describe quantitatively the short-range order in such poorly crystallized compounds, and give precise informations on the breadth of the "tunnels" of the structure, which plays a significant part in proton insertion.

Materials Chemistry and Physics, 1985

The effects of oxygen loss on the crystallographic and magnetic properties of CuFe204 ferrite hav... more The effects of oxygen loss on the crystallographic and magnetic properties of CuFe204 ferrite have been studied by high-temperature X-ray diffraction, X-ray absorption spectrometry and Mdssbauer spectrometry. In the heat-treatment under nitrogen, formation of a ferrimagnetic phase is observed with an increased content of Fe2+ and precipitation of CuFe02. Quenching after sintering leads to a mixture containing CuO and a spine1 ferrimagnetic phase in which the oxygen deficiency involves the formation of Cu+. mkonnaissance des phenom&nes d'oxydo-reduction accompagnant le processus de dt?composition [3,4].

Journal of Solid State Chemistry, 1981

XI'S study of copper ferrite oxide spinels Cu,-,Fq,O, with 0 < x I 0.5 gives information about va... more XI'S study of copper ferrite oxide spinels Cu,-,Fq,O, with 0 < x I 0.5 gives information about valence states and cationic distribution of copper in the spine1 matrix. It appears that copper is monovalent and divalent and that Cu*+ and Cu+ cations are found in the tetrahedral and octahedral Wanion environments. X-Ray irradiation induces reduction of tetrahedral Cu*+ to tetrahedral Cu+. The different copper types give shifted Cu zg312 lines, the intensity ratios of which can be used to evaluate the relative proportions of one type on each site. There is satisfactory agreement between our results, Miissbauer snectrosco~)~ studies. and statistical calculations of cationic distribution. The transformation under' X-ray &adiatiod is attributed CU$&

Journal of Non-Crystalline Solids, 1992

ABSTRACT

Journal of Nanoscience and Nanotechnology, 2010

Rutile TiO 2 nanoneedle flowers (representing concurrent nano-micro hierarchical morphology) with... more Rutile TiO 2 nanoneedle flowers (representing concurrent nano-micro hierarchical morphology) with high shape anisotropy ratio are synthesized at room temperature by using a simple and efficient one step electrochemical process of anodic dissolution. This process employs highly acidic bath of perchloric acid (pH < 2) and a large current density on the surface of Titanium foil to form nanostructures. The diameter and length of rutile TiO 2 nanoneedle is ∼8 nm and 100 nm respectively (aspect ratio >10). Dye sensitized solar cell (DSSC) configured using such rutile TiO 2 flowers is shown to exhibit IPCE of 30% and power conversion efficiency of ∼3.6%.

Journal of Materials Science, 1996

The solid solutions (Cr• 0 ~< x ~< 1, were prepared by traditional ceramic procedures. The sample... more The solid solutions (Cr• 0 ~< x ~< 1, were prepared by traditional ceramic procedures. The samples were characterized using X-ray diffraction, M6ssbauer, Fourier transform infra-red (FT-IR) and optical spectroscopic measurements. In the whole concentration range two phases exist phase F, 0~-(CrxFel_• which is isostructural with 0~-Fe203 and phase C, which is closely related to Cr203. Phase F exists in samples heated up to 900~ for 0 ~< x~<0.95. Phase C exists from x~>0.27 to x=l for samples heated up to 900~ and from x~>0.65to x=l for samples heated up to 1200~ For samples heated up to 900~ the solubility limits were 27.5 _+ 0.5 mol % of Cr203 in 0~-Fe203 and 4.0_+ 0.5 mol % of ~-Fe203 in Cr203. For the samples heated at 1200~ the diffraction peaks for the F and C phases in the two phase region were severely overlapped and thus the solubility limits could not be determined accurately as for previous samples. 57Fe M6ssbauer spectra of the samples heated up to 1200 ~ showed significant broadening of spectral lines and a gradual decrease of the hyperfine magnetic field with increase of x up to 0.50. For x>0.7, a paramagnetic doublet with collapsing sextet was observed. The spectra were interpreted in terms of an electronic relaxation effect; however, an agglomeration of iron ions which would contribute to the superparamagnetic effect could not be excluded. The FT-IR spectra showed transition effects in accordance with the X-ray diffraction results. The most intense absorption bands, observed for the samples heated up to 1200 ~ were located at ,-~ 460 and 370 nm (22 000 and 27000cm-1) for x~> 0.5, ,-~500 and 360 nm for x< 0.3, and might be correlated with the strong enhancement of the pair transitions through antiferromagnetic interactions. The intensification of the 6A1 ~ 4T1 Fe 3+ ions in all spectra and the development of the absorption at 13000 cm-~ due to a metal-metal charge transfer (Or 3+ ~ Fe 3+) transition, might be explained by exchange coupling which has been observed in some spinel compounds.

Journal of Applied Physics, 2003

Epitaxial thin films of La0.67Ca0.33MnO3 were implanted with 30 and 100 keV Fe57 ions at differen... more Epitaxial thin films of La0.67Ca0.33MnO3 were implanted with 30 and 100 keV Fe57 ions at different fluence values to achieve a uniform implant distribution. The resistivity of the film increases as fluence increases, but the peak resistivity temperature Tp does not change significantly for the as-implanted sample. Annealing of the implanted samples at 950 °C allows recovery of the structural properties of the films and leads to interesting properties: increase of the peak resistivity and of the colossal magnetoresistance values, and decrease of Tp. The decrease in Tp is of ∼130 K, and the increase in resistivity is almost a factor of 28 as compared to the as-implanted sample.

Journal of Applied Physics, 1996

Thin Fe2O3 layers (44 and 55 nm) were deposited by pulsed excimer laser ablation on single-crysta... more Thin Fe2O3 layers (44 and 55 nm) were deposited by pulsed excimer laser ablation on single-crystal alumina (α-Al2O3) substrates heated at 675 °C. The ion beam mixing of these α-Fe2O3/α-Al2O3 couples was carried out using 300 keV Kr3+ ions at a fluence of 2×1016 ions/cm2. The mixing effect was followed by Rutherford backscattering spectrometry (RBS), conversion electron Mössbauer spectroscopy, and grazing incidence x-ray diffraction method. RBS spectra do not show any evidence of mixing at the interface, whereas the data obtained with the two other techniques display phases like oxygen deficient Fe3O4, Fe3−yAlyO4, and Fe1+xAl2−xO4. For this last phase, x is determined as being equal to about 0.5. It is shown that ion beam mixing is more efficient for the thinner Fe2O3 layer, in accordance with the projected range of the Kr3+ ions.

Hyperfine Interactions, 1986

Conclusion The formation of heterovalent pairs seems to be proved for the compounds rich in Fe2+ ... more Conclusion The formation of heterovalent pairs seems to be proved for the compounds rich in Fe2+ ions (x⩾0.5) and the electron-phonon coupling seems to change with decreasing concentration of Fe2+ ions.