Crystal structure analysis of Nd-doped ceria solid solutions

This paper deals with Nd-doped ceria solid solutions: Ce1-xNdxO2-d with "x" ranging from 0 to 0.25. Six different powders were synthesized by applying the method based on selfpropagating room temperature reaction (SPRT) between metallic nitrates and sodium hydroxide. The method is known to assure very precise stoichiometry of the final product in comparison with a tailored composition. Rietveld refinement was employed to get structural information on the synthesized powder. An increase of Nd ion concentration increases the unit cell parameters and average bond distances. We have shown that all obtained powders were solid solutions with a fluorite-type crystal structure and all powder particles were of nanometric size (about 3 nm)

Far-infrared spectroscopy of PbTe doped with iron

Far infrared reflection spectra, at room and liquid nitrogen temperature, of PbTe single crystals doped with iron are presented. Plasma minima were observed at about 160 cm–1 and 180 cm–1 for room and liquid nitrogen temperature, respectively. Using the reflectivity diagrams and their minima the values of the hole concentrations and their mobility at both temperatures were calculated and compared with galvanomagnetic measurements. All these results indicated that when PbTe is doped with a small concentration of Fe, the hole concentration is reduced by one order of magnitude and the free carrier mobility is larger when compared to pure PbTe

Nanometric solid solutions of the fluorite and perovskite type crystal structures: Synthesis and properties

In this paper a short review of our results on the synthesis of nanosized CeO2, CaMnO3 and BaCeO3 solid solutions are presented. The nanopowders were prepared by two innovative methods: self propagating room temperature synthesis (SPRT) and modified glycine/nitrate procedure (MGNP). Different types of solid solutions with rare earth dopants in concentrations ranging from 0–0.25 mol% were synthesized. The reactions forming solid solutions were studied. In addition, the characteristics of prepared nanopowders, phenomena during sintering and the properties of sintered samples are discussed

Comprehensive characterization of BiFeO3 powder synthesized by the hydrothermal procedure

In this paper, bismuth ferrite (BFO) particles synthesized by controlled hydrothermal process, where the particles of small sizes and with high purity were obtained. Structural analysis showed that non-annealed powder can be perfectly fitted to rhombohedral space group R3c and contains a very small amount of secondary phase, whereas the final product (annealed at 800 °C) represents single-phase perovskite powder with high crystallinity. HRTEM analysis confirmed existence of twin stacking faults, which are responsible for enhanced magnetic properties. EPR measurements suggested existence of electrons trapped by vacancies or defects. It has been proposed that existence of Fe3+ −OV defect complex could be generated at elevated temperatures followed by formation of trivalent Fe ions, which intensely provide local 3d moments

Influence of Gd-doping on electrical properties in Ca1-xGdxMnO3 (x=0.05, 0.1, 0.15, 0.2) perovskites

Ca1-xGdxMnO3 (x = 0.05–0.20) nanostructured perovskites were successfully synthesized by modified glycine nitrate procedure (MGNP). Temperature intervals of sintering and phase transition during heating were revealed during dilatometric measurements. In order to determine the band gap values of the tested samples, ellipsometric measurements were performed in the UV-VIS spectral range. Decrease of band gap values with increase of Gd dopant content was attributed to n-type doping and upward shifting of the Fermi level in the conduction band. The investigation of the crystal structure and phase content of nanocrystalline Ca1- xGdxMnO3 powders was continued using micro-Raman spectroscopy. The electrical conductivity of Gd3+ doped sintered samples CaMnO3 as a function of temperature was measured by electrochemical impedance spectroscopy (EIS), in the temperature range of 400–700 °C. The corresponding activation energies of conductivity, measured in the investigated temperature range, were also discussed. The obtained research results showed that the highest hardness values of 7.58 GPa respectively, were achieved and that these nanostructured materials can be used as a high-density ceramic material for various industrial applications

Influence of Gd-doping on electrical properties in Ca1-xGdxMnO3 (x=0.05, 0.1, 0.15, 0.2) perovskites

Ca1-xGdxMnO3 (x = 0.05–0.20) nanostructured perovskites were successfully synthesized by modified glycine nitrate procedure (MGNP). Temperature intervals of sintering and phase transition during heating were revealed during dilatometric measurements. In order to determine the band gap values of the tested samples, ellipsometric measurements were performed in the UV-VIS spectral range. Decrease of band gap values with increase of Gd dopant content was attributed to n-type doping and upward shifting of the Fermi level in the conduction band. The investigation of the crystal structure and phase content of nanocrystalline Ca1- xGdxMnO3 powders was continued using micro-Raman spectroscopy. The electrical conductivity of Gd3+ doped sintered samples CaMnO3 as a function of temperature was measured by electrochemical impedance spectroscopy (EIS), in the temperature range of 400–700 °C. The corresponding activation energies of conductivity, measured in the investigated temperature range, were also discussed. The obtained research results showed that the highest hardness values of 7.58 GPa respectively, were achieved and that these nanostructured materials can be used as a high-density ceramic material for various industrial applications

Far infrared and transport properties of single crystal PBTE samples doped with Ce

Single crystal samples of lead telluride doped with cerium were made using the Bridgman technique. Single crystals could be easily cleaved parallel to the (002) plane. Room temperature far infrared reflectivity was measured on single crystal samples and a plasma minimum at about 180 cm(-1) and local modes of Ce were observed. A fitting procedure based on a modified four parameter model of plasmon - phonon interaction, was used to determine the values of optical parameters. Carrier concentration and their mobility were measured at room and liquid nitrogen temperatures.Romanian Conference on Advanced Materials (ROCAM 2000), Bucharest, ROMANIA, october 23-25th, 2000

Cerium neodymium oxide solid solution synthesis as a potential analogue for substoichiometric AmO 2 for radioisotope power systems

The European Space Agency (ESA) is sponsoring a research programme on the development of americium oxides for radioisotope generators and heater units. Cubic AmO2-(x/2) with an O/Am ratio between 1.65 and 1.75 is a potentially suitable compound for pellet sintering. C-type (Ia-3) Ce1-xNdxO2-(x/2) oxides with 0.5 &lt; x &lt; 0.7 could be used as a surrogate for some Ia-3 AmO2-(x/2). A new Ce1-xNdxO2-(x/2) production process has been investigated where a nominally selected x value of 0.6 was targeted: Ce and Nd nitrates and oxalic acid were added drop-wise into a vessel, where they continuously reacted to create oxalate precipitates. The effect of temperature (25 °C, 60 °C) of the reactants (mixed at 250 revolutions per minute) on oxalate particle shape and size were investigated. Oxalates were calcined at 900 °C to produce oxide particles. Oxalate particle properties were characterised as these are expected to influence oxides particle properties and fuel pellet sintering.</p

Spectroscopic ellipsometry and polarimetry for materials and systems analysis at the nanometer scale: state-of-the-art, potential, and perspectives

This paper discusses the fundamentals, applications, potential, limitations, and future perspectives of polarized light reflection techniques for the characterization of materials and related systems and devices at the nanoscale. These techniques include spectroscopic ellipsometry, polarimetry, and reflectance anisotropy. We give an overview of the various ellipsometry strategies for the measurement and analysis of nanometric films, metal nanoparticles and nanowires, semiconductor nanocrystals, and submicron periodic structures. We show that ellipsometry is capable of more than the determination of thickness and optical properties, and it can be exploited to gain information about process control, geometry factors, anisotropy, defects, and quantum confinement effects of nanostructures