... Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (1). [13] MG Ambia, MN Is... more ... Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (1). [13] MG Ambia, MN Islam and MO Hakim, J. Mater. Sci. 29 (1994), p. 6575. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (32). [14] T. Pauporte and D. Lincot, Electrochim. ...
Se caracterizaron mediante las tecnicas de difraccion de rayos-X y correlaciones angulares pertu... more Se caracterizaron mediante las tecnicas de difraccion de rayos-X y correlaciones angulares perturbadas diferenciales en tiempo (TDPAC), los siguientes compuestos intermetalicos con base circonio: Zr2Al, Zr3Al2 y Zr6NiAl2. Las medidas TDPAC fueron realizadas sobre las muestras irradiadas y luego de tratamientos tecnicos prolongados a 900°C en vacio dinamico. En todos los sistemas pudo observarse dano por radiacion el cual es removido luego de dichos tratamientos. Los sistemas analizados presentan mas de una interaccion cuadrupolar, las que se corresponden con los distintos sitios estructurales existentes en la red. Estos resultados son de especial interes para el analisis del orden local durante la cristalizacion en amorfos metalicos de Zr-Cu-Al-Ni con una amplia zona de liquido sobre enfriado.
Se analizo la produccion de nanodispersiones ceramico-metal (cermets) mediante el molido mecanico... more Se analizo la produccion de nanodispersiones ceramico-metal (cermets) mediante el molido mecanico de polvos a traves de la reaccion de sustitucion Fe2O3+2Al->2Fe+Al2O3. Se realizo un analisis del desarrollo progresivo de la reaccion en funcion del tiempo de molido, monitoreandose la temperatura y la presion durante el proceso. Los sistemas fueron caracterizados por difraccion de rayos X (DRX) obteniendose el tamano de grano de las fases involucradas. El orden local en torno del Fe fue analizado por espectroscopia Mossbauer (EM). Los polvos fueron tambien examinados por microscopia de transmision electronica (MTE). Se investigo la influencia de parametros tales como tamanos de grano, temperatura alcanzada en el cilindro, temperatura de ignicion e intensidad de trabajo mecanico en el desarrollo de la reaccion.
Abstract A combined experimental and novel theoretical ab initio structural and electronic study ... more Abstract A combined experimental and novel theoretical ab initio structural and electronic study was performed in order to characterize ZnO semiconductor nanopowders doped with Al atoms. For this, powder mixtures of ZnO and metallic Al in adequate proportions yielding different contents of Al (5, 10, and 30 at. %) were prepared by mechanical milling. The systems were characterized by X-ray diffraction and positron annihilation lifetime spectroscopy measurements. Additionally, combining two first-principles methods based on the Density Functional Theory (DFT) we calculated the final equilibrium structures for different concentrations of Al dopants and Zn vacancies in ZnO, predicting afterwards the characteristic positron annihilation lifetimes at these equilibrium structures. In addition to the structural relaxations, the ab initio predictions of the electronic properties in the studied systems help us to understand deeper the origin and characteristics of different positrons traps. This experimental and ab initio/DFT combined study allows to verify the dopant incorporation into the ZnO wurtzite structure and to extract the maximum information from the experimental data, giving an insight into the different defect complexes and their influence in the structural and electrical properties.
Fe and Co-doped ZnO powders obtained by mechanical milling from different starting materials are ... more Fe and Co-doped ZnO powders obtained by mechanical milling from different starting materials are presented. Both the local structural and the magnetic properties are investigated using X-ray diffraction, XAFS and magnetic measurements. The evolution of these properties with milling time, atomic content and milling atmosphere is analyzed. XAFS measurements revealed the progressive incorporation of doped atoms into the ZnO wurtzite crystalline structure. Also, the oxidation states of 2+ and 3+ for Fe atoms and 2+ for Co ones are confirmed. Furthermore, the presence of oxygen vacancies is predicted by EDAX and XAFS. These results, in combination with previous ones, will contribute to the comprehension of the controversial ferromagnetic behavior in these diluted semiconductor materials.
ABSTRACT Nanocolumnar ZnO films were prepared by electrodeposition (ED) on a glass substrate cove... more ABSTRACT Nanocolumnar ZnO films were prepared by electrodeposition (ED) on a glass substrate covered with a conductive layer of thin oxide doped with fluorine (FTO). After deposition the samples were annealed in oxidizing or reducing atmosphere, at temperatures between 100 to 500 ∘C, in order to follow the evolution of optical properties and morphology. The optical properties of these films were studied by means of photoluminescence spectroscopy (PL) and the morphology by scanning electron microscopy (SEM). Films annealed at 300 ∘C exhibit a higher ultraviolet emission peak, originating from exciton transitions. A green band related to deep-level emission centered at 500 nm, shows a drastic increase at 500 ∘C. These results are independent of the annealing atmosphere. An increase of coalescence is also observed after annealing at 500 ∘C. These results are explained taking into account the contribution of different point defects.
ABSTRACTMelt-spun Zr64Al7Cu17Ni10Fe2 amorphous ribbons were milled under nitrogen atmosphere for ... more ABSTRACTMelt-spun Zr64Al7Cu17Ni10Fe2 amorphous ribbons were milled under nitrogen atmosphere for different times. The resulting nitrided powders were studied by x-ray diffraction, Mössbauer spectroscopy and differential scanning calorimetry. The formation of nanosized crystalline particles, with cubic δ-ZrN structure, dispersed in the amorphous matrix was observed along with a change in the composition of the amorphous phase. Prolonged milling leads to the additional precipitation of late transition metals (Fe,Ni,Cu). The nitride particles affect the crystallization behavior and modify the thermal stability of the amorphous alloy.
ABSTRACT Cu Hf Ti ternary metallic alloys were prepared by melt spinning. The thermal stability o... more ABSTRACT Cu Hf Ti ternary metallic alloys were prepared by melt spinning. The thermal stability of the alloys with various Ti contents was studied by differential scanning calorimetry. The evolution of short range order with annealing treatment was also investigated by means of perturbed angular correlation. The results for the initial as-spun alloys indicate that the short range order can be described by a dense packing of atoms. The variation of electric field gradient with alloy composition is comparable to that previously observed in binary and multi-component Zr- and Hf-based amorphous alloys.
We have investigated the mechanically induced self-propagating reaction between Fe2O3 and Al. In ... more We have investigated the mechanically induced self-propagating reaction between Fe2O3 and Al. In this reaction the final phases, Al2O3 and Fe, are formed by an in situ chemical reaction. The evolution of the system was characterized as a function of the milling time using X-ray diffraction, magnetometry (300 and 5 K) and Mössbauer spectroscopy (300 and 77 K). After reaction, Fe particles in a crystalline Al2O3 matrix have been formed. At larger milling times, a rather wide Fe grain size distribution of around 20 nm was obtained according to the diffraction patterns. Mössbauer spectra were constituted of both paramagnetic and ferromagnetic contributions. The former was attributed to small grains of superparamagnetic Fe (within the Mössbauer characteristic time τM≈10−8 s) and FeAl2O4, whereas the latter was associated to larger Fe grains. Saturation magnetization, coercivity field and remanent magnetization rapidly reached a stationary value with the milling time. A correlation betwee...
The incorporation of suspensions of nanoparticles functionalized with gallic acid (GA) was used a... more The incorporation of suspensions of nanoparticles functionalized with gallic acid (GA) was used as a strategy to obtain nanocomposite active films with different both chitosan : tripolyphosphate (CH : TPP) and nanoparticles:chitosan (N : CH) ratios. The thermal analysis carried out by modulated differential scanning calorimetry (MDSC) allowed observing the shift of an endothermic event towards higher temperatures with a greater N : CH ratio. Analyzing ATR-FTIR spectra through principal component analysis (PCA) can be inferred that the incorporation of the nanoparticles produced a discrimination of the samples into clusters when the region 1400–1700 cm−1 was considered. The decrease in crystalline size with the inclusion of nanoparticles (NA and NB) proved the existence of interactions among CH, TPP, and GA, resulting in a more amorphous structure. The positron annihilation lifetime spectroscopy (PALS) technique was adequate to correlate the glass transition temperatures (Tg) obtaine...
Zr-Al-Cu-Ni-Fe belongs to the best glass forming systems known. These glasses present a high ther... more Zr-Al-Cu-Ni-Fe belongs to the best glass forming systems known. These glasses present a high thermal stability and are suitable as precursor material for nanocomposites containing a variety of particles. At this respect, the presence of a second phase embedded in the amorphous matrix improves their mechanical properties. Ball milling has already demonstrated to be a valuable processing route for producing
... Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (1). [13] MG Ambia, MN Is... more ... Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (1). [13] MG Ambia, MN Islam and MO Hakim, J. Mater. Sci. 29 (1994), p. 6575. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (32). [14] T. Pauporte and D. Lincot, Electrochim. ...
Se caracterizaron mediante las tecnicas de difraccion de rayos-X y correlaciones angulares pertu... more Se caracterizaron mediante las tecnicas de difraccion de rayos-X y correlaciones angulares perturbadas diferenciales en tiempo (TDPAC), los siguientes compuestos intermetalicos con base circonio: Zr2Al, Zr3Al2 y Zr6NiAl2. Las medidas TDPAC fueron realizadas sobre las muestras irradiadas y luego de tratamientos tecnicos prolongados a 900°C en vacio dinamico. En todos los sistemas pudo observarse dano por radiacion el cual es removido luego de dichos tratamientos. Los sistemas analizados presentan mas de una interaccion cuadrupolar, las que se corresponden con los distintos sitios estructurales existentes en la red. Estos resultados son de especial interes para el analisis del orden local durante la cristalizacion en amorfos metalicos de Zr-Cu-Al-Ni con una amplia zona de liquido sobre enfriado.
Se analizo la produccion de nanodispersiones ceramico-metal (cermets) mediante el molido mecanico... more Se analizo la produccion de nanodispersiones ceramico-metal (cermets) mediante el molido mecanico de polvos a traves de la reaccion de sustitucion Fe2O3+2Al->2Fe+Al2O3. Se realizo un analisis del desarrollo progresivo de la reaccion en funcion del tiempo de molido, monitoreandose la temperatura y la presion durante el proceso. Los sistemas fueron caracterizados por difraccion de rayos X (DRX) obteniendose el tamano de grano de las fases involucradas. El orden local en torno del Fe fue analizado por espectroscopia Mossbauer (EM). Los polvos fueron tambien examinados por microscopia de transmision electronica (MTE). Se investigo la influencia de parametros tales como tamanos de grano, temperatura alcanzada en el cilindro, temperatura de ignicion e intensidad de trabajo mecanico en el desarrollo de la reaccion.
Abstract A combined experimental and novel theoretical ab initio structural and electronic study ... more Abstract A combined experimental and novel theoretical ab initio structural and electronic study was performed in order to characterize ZnO semiconductor nanopowders doped with Al atoms. For this, powder mixtures of ZnO and metallic Al in adequate proportions yielding different contents of Al (5, 10, and 30 at. %) were prepared by mechanical milling. The systems were characterized by X-ray diffraction and positron annihilation lifetime spectroscopy measurements. Additionally, combining two first-principles methods based on the Density Functional Theory (DFT) we calculated the final equilibrium structures for different concentrations of Al dopants and Zn vacancies in ZnO, predicting afterwards the characteristic positron annihilation lifetimes at these equilibrium structures. In addition to the structural relaxations, the ab initio predictions of the electronic properties in the studied systems help us to understand deeper the origin and characteristics of different positrons traps. This experimental and ab initio/DFT combined study allows to verify the dopant incorporation into the ZnO wurtzite structure and to extract the maximum information from the experimental data, giving an insight into the different defect complexes and their influence in the structural and electrical properties.
Fe and Co-doped ZnO powders obtained by mechanical milling from different starting materials are ... more Fe and Co-doped ZnO powders obtained by mechanical milling from different starting materials are presented. Both the local structural and the magnetic properties are investigated using X-ray diffraction, XAFS and magnetic measurements. The evolution of these properties with milling time, atomic content and milling atmosphere is analyzed. XAFS measurements revealed the progressive incorporation of doped atoms into the ZnO wurtzite crystalline structure. Also, the oxidation states of 2+ and 3+ for Fe atoms and 2+ for Co ones are confirmed. Furthermore, the presence of oxygen vacancies is predicted by EDAX and XAFS. These results, in combination with previous ones, will contribute to the comprehension of the controversial ferromagnetic behavior in these diluted semiconductor materials.
ABSTRACT Nanocolumnar ZnO films were prepared by electrodeposition (ED) on a glass substrate cove... more ABSTRACT Nanocolumnar ZnO films were prepared by electrodeposition (ED) on a glass substrate covered with a conductive layer of thin oxide doped with fluorine (FTO). After deposition the samples were annealed in oxidizing or reducing atmosphere, at temperatures between 100 to 500 ∘C, in order to follow the evolution of optical properties and morphology. The optical properties of these films were studied by means of photoluminescence spectroscopy (PL) and the morphology by scanning electron microscopy (SEM). Films annealed at 300 ∘C exhibit a higher ultraviolet emission peak, originating from exciton transitions. A green band related to deep-level emission centered at 500 nm, shows a drastic increase at 500 ∘C. These results are independent of the annealing atmosphere. An increase of coalescence is also observed after annealing at 500 ∘C. These results are explained taking into account the contribution of different point defects.
ABSTRACTMelt-spun Zr64Al7Cu17Ni10Fe2 amorphous ribbons were milled under nitrogen atmosphere for ... more ABSTRACTMelt-spun Zr64Al7Cu17Ni10Fe2 amorphous ribbons were milled under nitrogen atmosphere for different times. The resulting nitrided powders were studied by x-ray diffraction, Mössbauer spectroscopy and differential scanning calorimetry. The formation of nanosized crystalline particles, with cubic δ-ZrN structure, dispersed in the amorphous matrix was observed along with a change in the composition of the amorphous phase. Prolonged milling leads to the additional precipitation of late transition metals (Fe,Ni,Cu). The nitride particles affect the crystallization behavior and modify the thermal stability of the amorphous alloy.
ABSTRACT Cu Hf Ti ternary metallic alloys were prepared by melt spinning. The thermal stability o... more ABSTRACT Cu Hf Ti ternary metallic alloys were prepared by melt spinning. The thermal stability of the alloys with various Ti contents was studied by differential scanning calorimetry. The evolution of short range order with annealing treatment was also investigated by means of perturbed angular correlation. The results for the initial as-spun alloys indicate that the short range order can be described by a dense packing of atoms. The variation of electric field gradient with alloy composition is comparable to that previously observed in binary and multi-component Zr- and Hf-based amorphous alloys.
We have investigated the mechanically induced self-propagating reaction between Fe2O3 and Al. In ... more We have investigated the mechanically induced self-propagating reaction between Fe2O3 and Al. In this reaction the final phases, Al2O3 and Fe, are formed by an in situ chemical reaction. The evolution of the system was characterized as a function of the milling time using X-ray diffraction, magnetometry (300 and 5 K) and Mössbauer spectroscopy (300 and 77 K). After reaction, Fe particles in a crystalline Al2O3 matrix have been formed. At larger milling times, a rather wide Fe grain size distribution of around 20 nm was obtained according to the diffraction patterns. Mössbauer spectra were constituted of both paramagnetic and ferromagnetic contributions. The former was attributed to small grains of superparamagnetic Fe (within the Mössbauer characteristic time τM≈10−8 s) and FeAl2O4, whereas the latter was associated to larger Fe grains. Saturation magnetization, coercivity field and remanent magnetization rapidly reached a stationary value with the milling time. A correlation betwee...
The incorporation of suspensions of nanoparticles functionalized with gallic acid (GA) was used a... more The incorporation of suspensions of nanoparticles functionalized with gallic acid (GA) was used as a strategy to obtain nanocomposite active films with different both chitosan : tripolyphosphate (CH : TPP) and nanoparticles:chitosan (N : CH) ratios. The thermal analysis carried out by modulated differential scanning calorimetry (MDSC) allowed observing the shift of an endothermic event towards higher temperatures with a greater N : CH ratio. Analyzing ATR-FTIR spectra through principal component analysis (PCA) can be inferred that the incorporation of the nanoparticles produced a discrimination of the samples into clusters when the region 1400–1700 cm−1 was considered. The decrease in crystalline size with the inclusion of nanoparticles (NA and NB) proved the existence of interactions among CH, TPP, and GA, resulting in a more amorphous structure. The positron annihilation lifetime spectroscopy (PALS) technique was adequate to correlate the glass transition temperatures (Tg) obtaine...
Zr-Al-Cu-Ni-Fe belongs to the best glass forming systems known. These glasses present a high ther... more Zr-Al-Cu-Ni-Fe belongs to the best glass forming systems known. These glasses present a high thermal stability and are suitable as precursor material for nanocomposites containing a variety of particles. At this respect, the presence of a second phase embedded in the amorphous matrix improves their mechanical properties. Ball milling has already demonstrated to be a valuable processing route for producing
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