E.J. Olivier

The role of surface and deep-level defects on the emission of tin oxide quantum dots

This paper reports on the role of surface and deep-level defects on the blue emission of tin oxide quantum dots (SnO₂ QDs) synthesized by the solution-combustion method at different combustion temperatures. X-ray diffraction studies showed the formation of a single rutile SnO₂ phase with a tetragonal lattice structure. High resolution transmission electron microscopy studies revealed an increase in the average dot size from 2.2 to 3.6 nm with an increase of the combustion temperature from 350 to 550 °C. A decrease in the band gap value from 3.37 to 2.76 eV was observed with the increase in dot size due to the quantum confinement effect. The photoluminescence emission was measured for excitation at 325 nm and it showed a broad blue emission band for all the combustion temperatures studied. This was due to the creation of various oxygen and tin vacancies/defects as confirmed by x-ray photoelectron spectroscopy data. The origin of the blue emission in the SnO₂ QDs is discussed with the help of an energy band diagram.

Critical behavior of the ferromagnetic-paramagnetic phase transition in Fe90−xNixZr10 alloy ribbons

This work presents a detailed study on the critical behavior of the ferromagnetic-paramagnetic (FM-PM) phase transition in Fe90−xNixZr10 (x = 0 and 5) alloy ribbons. Basing on field dependences of magnetization (M-H), M2 versus H/M plots prove the alloys exhibiting a second-order magnetic phase transition. To investigate the nature of the FM-PM phase transition at TC = 245 and 306 K for x = 0 and 5, respectively, we performed a critical-exponent study. The values of critical components β, γ, and δ determined by using the modified Arrott plots, Kouvel-Fisher (KF), and critical isotherm analyses agree with each other. For x = 0, the critical parameters β = 0.365 ± 0.013 and γ = 1.615 ± 0.033 are obtained by modified Arrott plots while β = 0.368 ± 0.008 and γ = 1.612 ± 0.016 are obtained by the KF method. These values are close to those expected for the 3D-Heisenberg model, revealing short-range FM interactions in Fe90Zr10. Meanwhile, for x = 5, the values of the critical parameters β = 0.423 ± 0.008 and γ =...

Structural and magnetic properties of ferrihydrite nanoparticles

Ferrihydrite is a short range ordered iron(III) oxyhydroxide that has been recently recognized as a good catalyst for Fischer–Tropsch synthesis of liquid hydrocarbons. Despite the critical role of ferrihydrite in many disciplines, its mineral structure remains a topic of debate. The main aspect of its structure which has been debated is the presence or absence of tetrahedrally coordinated Fe3+ in its mineral structure. In this work, electron energy-loss spectroscopy (EELS) was used to probe the Fe L2,3 edges of ferrihydrite and reference spectra of different iron oxide compounds and the percentage of Fe3+ in Td symmetry was estimated from non-linear least squares (NLLS) fitting coefficients. EELS results demonstrate that Fe3+ in Td coordination is present in substantial amounts in the structure of ferrihydrite. These findings were supported by Mossbauer spectroscopy results performed on the same ferrihydrite samples.

Imaging the atomic structure and local chemistry of platelets in natural type Ia diamond

In the past decades, many efforts have been devoted to characterizing {001} platelet defects in type Ia diamond. It is known that N is concentrated at the defect core. However, an accurate description of the atomic structure of the defect and the role that N plays in it is still unknown. Here, by using aberration-corrected transmission electron microscopy and electron energy-loss spectroscopy we have determined the atomic arrangement within platelet defects in a natural type Ia diamond and matched it to a prevalent theoretical model. The platelet has an anisotropic atomic structure with a zigzag ordering of defect pairs along the defect line. The electron energy-loss near-edge fine structure of both carbon K- and nitrogen K-edges obtained from the platelet core is consistent with a trigonal bonding arrangement at interstitial sites. The experimental observations support an interstitial aggregate mode of formation for platelet defects in natural diamond.The accurate structure of the platelet defects in diamond is now resolved by transmission electron microscopy, and, out of all the proposed models, it agrees well with the zigzag atomic model.

The Effect of Granulated Nickel Converter Matte Mineralogy on Phase-Specific Hardness and Associated Breakage Characteristics

There is very little in-depth study on the processing behavior of granulated nickel converter matte as an intermediate product, particularly related to downstream comminution and hydrometallurgical processing. The measurement of fundamental phase-specific physical properties would assist in understanding grinding and leaching processing behavior. The aim of this study was to investigate a possible dependence between phase-specific hardness, microstructures, and breakage characteristics. Relevant to the investigation is the application of a novel combination of micro-analytical techniques. The phase-specific hardness and breakage characteristics were sequentially tested with a CSM Nano-Indentation Tester. Phase-breakage characteristics were further tested in a laboratory ball mill at a specific energy input. Comparative phase-breakage analysis was additionally performed using a field-emission scanning electron microscope. It was found that the softest phase is copper sulfide with an average hardness of 1975 MPa. The harder phases are NiCu-alloy and nickel sulfide with average hardness values of 4981 MPa and 4456 MPa, respectively. Indentation-induced micro-cracks are common along curving copper-sulfide phase boundaries while there is a notable smaller degree of breakage attainable with respect to the harder nickel-sulfide phases. In addition, there is a comparative lack of breakage attainable with respect to NiCu-alloy phases, suggesting possible ductility under both the compressive indentation loads and during grinding events in a laboratory ball mill.