Nenad Ivanović

ELECTRONIC PRINCIPLES OF SOME TRENDS IN PROPERTIES OF METALLIC HYDRIDES

Due to their extensive present, important and versatile potential applications, metal hydrides (MH) are among the most investigated solid-state systems. Theoretical, numerical and experimental studies have provided a considerable knowledge about their structure and properties, but in spite of that, the basic electronic principles of various interactions present in MH have not yet been completely resolved. Even in the simplest MH, i.e. alkali hydrides (Alk-H), some trends in physical properties, and especially their deviations, are not well understood. Similar doubts exist for the alkaline-earth hydride (AlkE-H) series, and are even more pronounced for complex systems, like transition metal-doped AlkE-H, alanates and borohydrides. This work is an attempt of explaining some trends in the physical properties of Alk-H and AlkE-H, employing the Bader analysis of the charge distribution topology evaluated by first-principle all-electron calculations. These results are related to some variables commonly used in the explanation of experimental and calculated results, and are also accompanied by simple tight-binding estimations. Such an approach provides a valuable insight in the characteristics of M-H and H-H interactions in these hydrides, and their possible changes along with external parameters, like temperature, pressure, defect or impurity introduction. The knowledge of these basic interactions and processes taking place in simple MH are essential for the design and optimisation of complex MH-systems interesting for practical hydrogen storage applications.

Laser interaction with carbon-type materials

It is well known that application of stimulated light may influence phase modifications and changes of carbon structure. These effects of laser irradiation, in different working regimes and atmospheres, are widely investigated for fullerenes and diamond structure, but for many other carbon materials, are not. In the presented experiments, we treated by Q-switch ruby and Nd3+ YAG laser beams different carbon clothes, produced by pyrolysis (T <EQ 1000 degree(s)C) of cellulose materials in inert atmosphere. The materials are interesting for many applications, including medical. The laser pulse energy was of order of 0.1 - 1 J, in one, or multi-pulse regime. Focused and unfocused beams were used to induce damages and oxidation of sample surfaces. the damages were analyzed by scanning electron microscopy and specific area is measured by Brunauer, Emmet and Teller method, before and after the interaction. Materials exhibited differences in the damaging level and the fiber breaking thresholds. Mechanisms of laser interaction leading to oxidation of carbon type materials are discussed, and the necessary experimental conditions for intended changes are analyzed.

Specific heat of the Hf2Fe, Hf2Co, and Hf2Rh intermetallic compounds

The specific heat under constant pressure, Cp, of intermetallic compounds Hf2Fe, Hf2Co and Hf2Rh with the Ti2Ni structure was obtained by means of differential thermal analysis in the temperature range 275–740 K. The results differ significantly from the Debye theory, even when a correction for optical phonons in Einstein approximation is considered, which indicates existence of a defect contribution to the specific heat. Relative entropy has been determined and the obtained results were fitted and analysed. The anomalous temperature behaviour of Cp is discussed, having in mind results of previous investigations of these and similar systems, obtained by other methods.

Minimally invasive surgery for benign esophageal disorders: first 200 cases

SummaryBackgroundTo evaluate the method of introduction, feasibility, and early results of a laparoscopic surgery for benign foregut disorders in a single high volume center.MethodsA retrospective clinical study included consecutively laparoscopically operated patients due to benign foregut disorders. The study was conducted at the Department of Esophagogastric Surgery, First Surgical University Hospital, School of Medicine, University of Belgrade from March 2010 until July 2014. Complete preoperative diagnostics data, details of surgical procedures, and follow-up results are included.ResultsOverall, 200 consecutive patients were enrolled in the study. GERD and achalasia were the most common indications for laparoscopic surgery, with 81 and 72 patients respectively. Due to giant hiatal hernia, 37 patients were operated on, while the rest were less common indications. There were no conversions to open procedures. In three patients, pneumothorax resulted from intraoperative pleural lesion. One mucosal perforation occurred in an achalasia patient. One reoperation was conducted due to excessive port site bleeding. Short term follow-up results are highly satisfactory, and are presented in detail for every patient group.ConclusionIntroduction of laparoscopy in a foregut surgery high volume center for the treatment of benign foregut disorders can be obtained with low incidence of complications, and satisfactory short term functional results.

Experimental and Theoretical Investigations of Cured and Uncured Disiloxane Bisbenzocyclobutene Thin Films

The main challenge in the large-scale commercial applications of benzocyclobutene (BCB) dielectrics is to perform their curing rapidly and efficiently at low temperatures, and in the same time, to obtain large area, high quality, pinhole free dielectric thin films. For that purpose, we investigated numerous uncured and cured BCB films, approximately 2 µm thick, spin-coated on glass/ITO surface, using optical and AFM microscopy, infrared (IR) and Raman spectroscopy, and complete these results with appropriate Linear Combination of Atomic Orbitals (LCAO) calculations. That way we relate microscopic characteristics of the involved molecules, and macroscopic properties of the cured and uncured polymers, which is important for their practical applications.

Influence on Cr and Ni doping on PbTe local structural properties

Structural aspects of Cr and Ni incorporation into the PbTe lattice are studied by means of Extended X-ray Absorption Fine Structure (EXAFS). EXAFS measurements enabled to get exact information on Pb and Te local structural features and their thermal evolution. The obtained results also revealed that by distorting their local environment, impurity atoms (Cr, Ni) add to high inherent disorder already present in the host PbTe. Larger anharmonicity of the Pb–Te bond and larger atomic thermal parameters observed in PbTe(Cr, Ni) could be of interest for thermoelectronics applications since they are both expected to reduce the thermal conductivity.

Local and electronic structure around manganese in Cd0.98Mn0.02Te0.97Se0.03 studied by XAFS

X-ray Absorption Fine Structure (XAFS) technique was employed to study local electronic and structural features of Mn ions incorporated in Cd0.98Mn0.02Te0.97Se0.03. XAFS measurements performed at Mn K edge revealed that manganese Mn(II) ions are well incorporated into the host CdTe lattice (cubic zinc-blende structure type) and their immediate surrounding is found to be composed exclusively of Te atoms. The observed preference of Mn ions distribution around Te opposes earlier observations on the similar systems, where preferential Mn-Se over Mn-Te paring was found.

Reduction of Nanometric Magnetite Powder

The investigated nanometric magnetite powders were synthesized electrochemically, and examined by XRD and SEM techniques. Their reduction was conducted through the isothermal heating in hydrogen in the temperature range from 600 to 860 K. Kinetics of the hydrogen recovery process during oxidation of freshly formed Fe powders in a water vapor stream was also studied. It was assumed that the solid-gas reaction is diffusion controlled, and Jander’s model was applied to describe it. The experimental data suggest that the reoxidation process proceeds in two stages, at various activation energies. By changing the conditions of the electrochemical (EC) process we were able to produce the iron oxide powders with optimal particle size and activity, for pure hydrogen production through appropriate reduction/oxidation processes.

Structural, Magnetic, and Electrical Characteristics of Metastable Iron Oxide Nano-Sized Powders

Structural, magnetic and electrical properties of iron oxide nano-sized powders synthesised electrochemically under various conditions are presented. The influence of the temperature and current density of synthesis on particular powder characteristics is established. Possibilities for co-existence of various phases and their impact on powder properties, as well as feasible paths of phase relaxation and transition during non-isothermal heating are investigated, too. In this way, optimal procedures for the preparation and stabilisation of iron oxides nano-sized powders of different characteristics are evaluated.

Changes in Structure and Properties of Oligophenylenes under Selected External Influences

Effects induced by uniaxial compression and external electric field in P2P to P6P oligophenylene molecules are investigated by versatile calculations. In this way some useful relations between particular values of compression or field directions and intensities to specific changes in molecular structure and properties have been established, enabling estimation of possibilities for tuning the materials characteristics and their spectroscopic analyses. The results are compared to the existing experimental data and similar calculations, and some consequences for applications of oligophenylenes-based materials are discussed.