1,721,170 research outputs found
Photophysical properties of samarium (II) doped in inorganic crystals: effect of chemical environment, external pressure and temperature
No full textThe effects of the surroundings on the emission properties of Sm2+ ion in inorganic crystals are probed by high pressure experiments as well as by chemical substitution. The sharp f-f emissions of Sm2+ under high external pressure enable us to study the pressure effect on the crystal field energy levels. A routine program allows to refine free ion and CFP by minimizing the differences between the observed and calculated energy levels. The variations of the F2, ξ parameters as a function of pressure were discussed relative to central field covalency and symmetry restricted covalency models. Using the formalism of the superposition model as a function of pressure, we have calculated intrinsic crystal field parameters. Emission lifetime measurements were performed as a function of temperature and pressure. The temperature dependent experiments can be described by a contribution of both radiative and non-radiative pathways which involve also the lowest f-d level
Experimental and theoretical studies of boron and hydrogen containing compounds in relation to potential hydrogen storage and ionic conduction applications
No full textThis thesis deals with the fundamental studies of some materials containing boron-hydrogen bonds which can potentially be used either as the hydrogen storage materials (M(BH4)2, M=Alkaline earth metal), as the solid electrolytes for batteries (Na2B12H12) or as reducing agents for CO2 (Mg(BH4)2). First part of thesis deals with borohydrides (BH4-). Synthesis and characterization of halide-free Sr(BH4)2, Ba(BH4)2 and Eu(BH4)2 is reported. Crystallographic study of these compounds helped in identifying several new phases and a new species metal borohydride hydride (M2(BH4)H3). In depth study of B-H bond breaking is reported via isotope exchange reaction in Ca(BH4)2.A practical example of borohydride as reducing agent is reported by showing the reduction of CO2 with gamma-Mg(BH4)2. The second part of the thesis focuses on closoboranes derived from the B12H122- ion. Compounds of this family have recently attracted great interest as solid ionic conductors for Li and Na ions.Results of DFT calculations on isolated B12H122- anions and halogen (F, Cl or Br) substituted anions were analysed in detail. Synthesis of Na2B12(SCN)H11 is reported.The measurement of the ionic conductivity of this sample shows that the conductivity at room temperature is much better (1000 fold) compared to pristine Na2B12H12
Novel and Scalable Synthesis of BnHxz- Boron Clusters as Solid-State Electrolytes for Sodium Batteries and their Detailed Study for Hydrogen Storage Applications
No full textAll-solid-state batteries (ASSBs) promise higher power and energy density compared to batteries based on liquid electrolytes. Recently, a stable 3V ASSB based on the super ionic conductor (1mS cm-1 near room temperature) Na4(B12H12)(B10H10) has demonstrated excellent cycling stability. This electrolyte Na4(B12H12)(B10H10) can be obtained directly using the 5 steps, scalable and solution-based synthesis shown in scheme 1 (TEA = Et4N+). The use of the wet chemistry in the final step allows the solution processing of the solid electrolyte and to improve the contacts with the cathode material during assembly of the battery. This new synthesis is a cost efficient synthesis for the precursors Na2B10H10 and Na2B12H12 which are commercially very expensive. Two key parameters to tune the kinetics and selectivity of this solvolthermal synthesis of closo-hydroborates were identified: the choice of the counter cation, tetraethylammonium ((C2H5)4N+, TEA+) vs tetrabutylammonium (TBA+), and the solvent
Combined computational and experimental study of inorganic fluorides, hydrides and borohydrides
No full textIn this thesis both computational (Density Functional Theory calculations on isolated systems and on crystals) and experimental (Infrared and Raman spectroscopy and Differential Thermal Analysis) methods were used to analyse insulating crystalline solids, with particular focus on their structural and vibrational properties. In the first part, the effects of physical and chemical pressure on the structure and the vibrational spectra of the Matlockite-type compounds MFX (M=Ba, Sr and X=Cl, Br) were studied using periodic-DFT calculations. Further studies concerned BaxFyClz compounds and the phase diagram BaCl2-BaF2. In the second part of this thesis A2TH6 systems, (A= alkaline earth and T=Fe, Ru) and borohydrides were considered. In particular, many borohydrides were studied both experimentally and theoretically. New insights on spectra-structure relations were obtained
Hydroborate Solid Electrolytes for High-Voltage All-Solid-State Batteries
No full textNext-generation all-solid-state batteries promise higher energy and power densities, and improved operational safety, compared to the state-of-the-art lithium-ion batteries. As their key component, several material classes of the ion-conducting solid electrolytes are currently under investigation. Among them, hydroborates draw attention as an emerging class, combining e.g. high Li+ and Na+ conductivity, compatibility with alkali metal anodes, low gravimetric density, low toxicity, and facile all-solid-state cell fabrication by cold pressing. To further improve energy density and interface compatibility, this thesis studies the electrochemical and thermal stability of hydroborate solid electrolytes and their cathode compatibility for high-voltage (>4 V) all-solid-state batteries. By introducing a self-passivating functionality into a solid electrolyte, it demonstrates the first 4 V hydroborate-based all-solid-state battery at room temperature with an excellent long-term capacity and energy retention. This work records the highest average discharge cell voltage and cathode-based specific energy among all reported all-solid-state sodium batteries so far
Development of a New closo-Borate Solid Electrolyte and Its Implementation in All-Solid-State Batteries
No full textAll-solid-state batteries promise to simultaneously yield higher energy and power density as well as improved safety as compared to state-of-the-art lithium-ion technologies based on organic liquid electrolytes. A competitive all-solid-state battery requires a solid-state electrolyte with high ionic conductivity near room temperature and high thermal and electrochemical stability. Meeting these requirements simultaneously represents a major challenge. Closo-borates represent a promising, yet underexplored, class of solid electrolytes. Specifically, their high-ionic conductivity, wide electrochemical stability window, and advantageous processing properties make them serious candidates to address the major challenges faced by all-solid-state batteries. This thesis presents the development and characterization of a new solid electrolyte within this family, namely Na4(B12H12)(B10H10). It demonstrates that this material possesses the appropriate combination of properties to develop a 3 V all-solid-state battery and discusses aspects related to the assembly and successful cycling of such a device
Strontium Aluminate Nanoparticles: Synthesis, Characterization, and Luminescence
No full textThe introduction of Eu2+ and Dy3+ co-doped SrAl2O4 phosphor as a bright long persistent phosphor (LPP) boosted the research in the field of LPPs. Soon, other members of the SrO-Al2O3 system attracted a lot of attention for different applications. Nevertheless, the applications are currently limited due to the large grain sizes of these materials. In this thesis, we present a novel method for the preparation of SrO-Al2O3 nanoparticles (NPs) in the range of 200-300 nm. CaO-Al2O3 NPs could be obtained with this method, as well. Luminescence properties of Eu3+-doped SrAl12O19 and CaAl12O19 nanocrystals were studied. Unlike the majority of Eu3+-based phosphors, in these NPs the strongest band originated from the 5D0→7F4 transition in the deep-red region of the spectrum. Emissions from the 5D1-3 states were also observed. Moreover, peculiarly strong 5D0→7F0 transition accompanied with a low-lying CT band was observed for Eu3+ in the amorphous phase of the SrO-Al2O3 NPs
Polydiacetylene-Peptide Interaction Mechanism in Mixed Lipid Systems
No full textThis thesis covers the theory, stimuli and interaction with peptides of (poly)diacetylenes (P/DA). PDA is employed as a sensor of its surrounding. The electronic and geometric structure of PDA is discussed. Different stimuli are presented and finally the interaction of various antimicrobial peptides with the P/DA are studied by UV-Vis-/transmission electron-/atomic force microscopy, DSC and ITC
Critical evaluation of the effect of anharmonicity and dispersion interactions using density functional theory on structural and spectroscopic properties of selected inorganic compounds
No full textDensity functional theory (DFT) in its modern Kohn-Sham formulation provides an efficient framework for the accurate characterization of the properties of many-electron systems in solid-state physics and in chemistry. In this thesis, DFT has been applied to the prediction of the structural and spectroscopic properties of selected inorganic compounds
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