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See detailEffect of different technological approaches on the optical properties of ZnO sol-gel thin films
Ivanova, T.; Harizanova, A.; Koutzarova, T. et al

in Journal of Physics: Conference Series (2014), 514

The work presents a sol-gel approach with two types of solvents for ZnO films deposition in view of varying the films' structural and optical properties. The ZnO films were characterized by X-Ray ... [more ▼]

The work presents a sol-gel approach with two types of solvents for ZnO films deposition in view of varying the films' structural and optical properties. The ZnO films were characterized by X-Ray diffraction (XRD) and found to have a polycrystalline wurtzite phase structure. The grain sizes and the lattice parameters were determined; it was established that the ZnO crystallites' size increases with the annealing temperatures from 25 nm to 36 nm. The ZnO films possess high transmittance in the visible spectral range. Further, the optical band gap values were estimated. The material's vibration properties were analyzed by Fourier Transform Infrared (FTIR) spectroscopy. The two technological sol-gel approaches for deposition of ZnO films, using two different solvents, proved to be successful in producing structures with different structural and optical properties. The thin films fabricated were very smooth and uniform and exhibited a high transparency in the visible spectral range. [less ▲]

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See detailSol-gel nanocrystalline ZnO:Ag films: Structural and optical properties
Ivanova, T.; Harizanova, A.; Koutzarova, T. et al

in Superlattices & Microstructures (2014), 70

The paper presents a sol-gel approach for deposition of ZnO:Ag composite films. The films are obtained by spin coating method on quartz and Si substrates. The effect of the annealing temperatures (500-800 ... [more ▼]

The paper presents a sol-gel approach for deposition of ZnO:Ag composite films. The films are obtained by spin coating method on quartz and Si substrates. The effect of the annealing temperatures (500-800 °C) and the gas ambient (oxygen and nitrogen) has been studied by X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR). Optical properties are investigated by UV-VIS spectroscopy. The transmittance spectra of ZnO:Ag films are differed from ZnO spectra and manifest absorption features due to silver nanoparticles formation. © 2014 Elsevier Ltd. All rights reserved. [less ▲]

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See detailStudy of quasi-monophase Y-type hexaferrite Ba2Mg2Fe12O22 powder
Koutzarova, T.; Kolev, S.; Nedkov, I. et al

in Micro and Nanosystems (2014), 6(1), 14-20

We present the structural and magnetic properties of a multiferroic Ba2Mg2Fe12O22 hexaferrite composite containing a small amount of MgFe2O4. The composite material was obtained by auto-combustion ... [more ▼]

We present the structural and magnetic properties of a multiferroic Ba2Mg2Fe12O22 hexaferrite composite containing a small amount of MgFe2O4. The composite material was obtained by auto-combustion synthesis and, alternatively, by co-precipitation. The Ba2Mg2Fe12O22 particles obtained by co-precipitation have an almost perfect hexagonal shape in contrast with those prepared by auto-combustion. Two magnetic phase transitions, responsible for the composite’s multiferroic properties, were observed, namely, at 183 K and 40 K for the material produced by auto-combustion, and at 196 K and 30 K for the sample prepared by co-precipitation. No magnetic phase transitions in these temperature ranges were observed for a MgFe2O4 sample, which shows that the magnesium ferrite does not affect the multiferroic properties of this type of multiferroic metarials. [less ▲]

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See detailStudy of sol-gel Cu-doped Al2O3 thin films: Structural and optical properties
Ivanova, T.; Harizanova, A.; Koutzarova, T. et al

in Journal of Physics: Conference Series (2014), 514

We present a study of of copper-doped Al2O3 films prepared by sol-gel deposition. The films were spin-coated on Si and quartz substrates and a high-temperature treatment was conducted in the range 500-800 ... [more ▼]

We present a study of of copper-doped Al2O3 films prepared by sol-gel deposition. The films were spin-coated on Si and quartz substrates and a high-temperature treatment was conducted in the range 500-800 °C in oxygen or nitrogen. The impact was followed of the annealing procedures on the AlxCu1-xO3 films's properties. XRD was used to determine the films' structure; it revealed a mixture of amorphous and crystalline phases. Optical characterization was performed by UV-VIS spectroscopy. The sol-gel films prepared are very transparent. The band gaps of the Al-Cu-O films were estimated from the optical data, with the values ranging from 3.4 to 4.8 eV depending on the Cu content, the annealing and the gas ambients. [less ▲]

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See detailQuadrupole splitting and isomer shifts in Te oxides investigated using nuclear forward scattering
Klobes, B.; Barrier, N.; Vertruyen, Bénédicte ULg et al

in Hyperfine Interactions (2014), 226(1-3), 713-719

Nuclear forward scattering by 125Te is a viable alternative to conventional 125Te Mössbauer spectroscopy avoiding all source related issues. Using reference compounds with known hyperfine parameters and ... [more ▼]

Nuclear forward scattering by 125Te is a viable alternative to conventional 125Te Mössbauer spectroscopy avoiding all source related issues. Using reference compounds with known hyperfine parameters and Te oxides exhibiting stereochemically active lone pairs, we show that nuclear forward scattering by 125Te can be reliably used to extract quadrupole splitting energy and relative isomer shift. The rough correlation between Te-Ocoordination and quadrupole splitting energy as put forward by Takeda and Greenwood (J. Chem. Soc. Dalton, 2207, 1975), is corroborated by the presented results. © 2014 Springer Science+Business Media Dordrecht. [less ▲]

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See detailSurfactant-assisted ultrasonic spray pyrolysis of nickel oxide and lithium-doped nickel oxide thin films, towards electrochromic applications
Denayer, Jessica ULg; Bister, Geoffroy; Simonis, Priscilla et al

in Applied Surface Science (2014), 321

Lithium-doped nickel oxide and undoped nickel oxide thin films have been deposited on FTO/glass substrates by a surfactant-assisted ultrasonic spray pyrolysis. The addition of polyethylene glycol in the ... [more ▼]

Lithium-doped nickel oxide and undoped nickel oxide thin films have been deposited on FTO/glass substrates by a surfactant-assisted ultrasonic spray pyrolysis. The addition of polyethylene glycol in the sprayed solution has led to improved uniformity and reduced light scattering compared to films made without surfactant. Furthermore, the presence of lithium ions in NiO films has resulted in improved electrochromic performances (coloration contrast and efficiency), but with a slight decrease of the electrochromic switching kinetics. [less ▲]

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See detailImproved coloration contrast and electrochromic efficiency of tungsten oxide films thanks to a surfactant-assisted ultrasonic spray pyrolysis process
Denayer, Jessica ULg; Aubry, Philippe; Bister, Geoffroy et al

in Solar Energy Materials & Solar Cells (2014), 130

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See detailSpray-drying synthesis of Na2FePO4F/carbon powders for lithium-ion batteries
Brisbois, Magali ULg; Krins, Natacha ULg; Hermann, Raphael et al

in Materials Letters (2014), 130

Sodium iron fluorophosphate Na2FePO4F is a candidate positive electrode material for both lithium-ion batteries and sodium-ion batteries. We report the synthesis of Na2FePO4F/carbon powders by the simple ... [more ▼]

Sodium iron fluorophosphate Na2FePO4F is a candidate positive electrode material for both lithium-ion batteries and sodium-ion batteries. We report the synthesis of Na2FePO4F/carbon powders by the simple and easily up-scalable technique of spray-drying. An aqueous solution containing citric acid as a carbon source was sprayed in a pilot-scale spray-dryer. Heat treatment at 600°C in argon for 12 hours was found appropriate to obtain single-phase Na2FePO4F; only 1.8% of Fe (III) were detected by iron-57 Mössbauer spectroscopy. When cycled against lithium, the discharge capacity reached 110 mAh g-1 at C/15 rate. (C) 2014 Elsevier B.V. All rights reserved. [less ▲]

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See detailMesoporous Lithium Vanadium Oxide as Thin Film Electrode for Lithium-Ion Batteries: Comparison between Direct Synthesis of LiV2O5 and Electrochemical Lithium Intercalation in V2O5
Caes, Sébastien ULg; Arrebola, Jose Carlos; Krins, Natacha ULg et al

in Journal of Materials Chemistry A (2014), 2

Research in the field of lithium-ion batteries favours electrode materials with high surface area. In this context, this paper is dedicated to mesoporous thin films (MTFs) and compares the electrochemical ... [more ▼]

Research in the field of lithium-ion batteries favours electrode materials with high surface area. In this context, this paper is dedicated to mesoporous thin films (MTFs) and compares the electrochemical performance of g-LiV2O5 MTFs with post-synthesis electrochemical lithium intercalation in a-V2O5 MTFs. Formation of vanadium oxide MTFs by soft-chemistry is notoriously difficult. However, it is shown that wormlike vanadium oxide (V–O) and lithium vanadium oxide (Li–V–O) MTFs can be obtained on silicon substrates by a direct sol–gel soft-templating route (evaporation-induced micelle assembly) using a polystyrene-block-poly(ethylene oxide) (PS-b-PEO) structuring agent. Heat treatment for 1 minute at 400 C (Li–V–O system) or 30 minutes at 350 C (V–O system) leads to the crystallization of g-LiV2O5 or a-V2O5, respectively. These calcination conditions ensure the degradation of the structuring agent while preventing the collapse of the mesostructure, yielding MTFs with pore size diameter in the 30–35 nm range. Using the same set of synthesis conditions, films can be deposited on conductive glass substrates for electrochemical investigation: the a-V2O5 films display better specific capacities, while the cyclability is good for both compositions, even at a current density as high as 30 C-rate. [less ▲]

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See detailLow temperature crystallization of yttrium orthoferrite by organic acid-assisted sol-gel synthesis
Stevens, Frédéric ULg; Cloots, Rudi ULg; Poelman, D. et al

in Materials Letters (2014), 114

Yttrium orthoferrite (YFeO3) is a promising material for visible light photocatalytic applications due to its band gap of 2.2-2.6 eV. However, during the synthesis of YFeO3, unwanted composition can be ... [more ▼]

Yttrium orthoferrite (YFeO3) is a promising material for visible light photocatalytic applications due to its band gap of 2.2-2.6 eV. However, during the synthesis of YFeO3, unwanted composition can be obtained and the crystallization requires temperatures as high as 850 C. Powders of YFeO3 were prepared using a sol-gel method with and without organic acids (citric acid, tartaric acid, malonic acid and oxalic acid) used as organic modifiers. The band gap of these powders was measured by diffuse reflection spectroscopy, and the crystallinity and crystalline phase content were characterized by X-ray diffraction. Organic acids allow a higher purity and facilitate crystallization. This work aims to produce YFeO3 powders at the lowest possible temperature. Citric acid was found to be the best additive: it reduces the crystallization temperature below 450 C. This opens new perspectives such as the deposition of crystalline YFeO3 thin films onto conductive glass for water-splitting applications. © 2013 Elsevier B.V. [less ▲]

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See detailStudies on the Influence of Different Grain-sized Titania Scattering Layers for Dye Sensitized Solar Cells
Thalluri, Venkata Visveswara Gopala Kris ULg; Henrist, Catherine ULg; Vertruyen, Bénédicte ULg et al

Poster (2013, July)

The efficiencies of dye sensitized solar cells (DSCs) are boosted up to 12% by NIR light harvesting dyes and with the usage of scattering layer in the device preparation.The importance of Titania ... [more ▼]

The efficiencies of dye sensitized solar cells (DSCs) are boosted up to 12% by NIR light harvesting dyes and with the usage of scattering layer in the device preparation.The importance of Titania scattering layers was studied as a part of this work. These scattering layers were prepared from two different grain-sizes (100 nm & 500 nm) for SQ2-NIR and N3-UV/Vis DSCs. The 100 nm grain-sized Titania paste was commercially supplied and 500 nm grain-sized Titania paste was prepared according to literature. The morphological and structural properties of these bigger grain-sized Titania layers were deliberated by using and Scanning Electron Microscope (SEM) and X-Ray diffraction (XRD) measurements. The influence of these bigger grain-sized Titania scattering layers in SQ2-NIR and N3-UV/Vis DSCs were expounded by using various electro-optical characterization techniques such as light I-V, electrochemical impedance spectroscopy (EIS) shown in Figure 1 and external quantum efficiency (EQE) measurements. The importance of understanding the influence of these bigger grain-sized scattering Titania layers could pave a way for future design and optimizing of DSCs for increasing the amount of light harvesting. [less ▲]

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See detailYBCO superconducting thick films: electrophoretic deposition (EPD) on non-planar silver substrates
Namburi, Devendra Kumar ULg; Closset, Raphaël ULg; Fagnard, Jean-François ULg et al

Conference (2013, January 30)

A new formulation of a stable YBa2Cu3O7-δ (YBCO) suspension is proposed in which butanol is preferred to the commonly-used acetone as the suspension medium. Appropriate surfactant has been used to develop ... [more ▼]

A new formulation of a stable YBa2Cu3O7-δ (YBCO) suspension is proposed in which butanol is preferred to the commonly-used acetone as the suspension medium. Appropriate surfactant has been used to develop the superficial charge on the YBCO particles in order to promote migration during the process of electrophoresis. YBCO thick films were deposited on silver tubes and half-tubes by electrophoretic deposition (EPD). The EPD parameters (deposition voltage, deposition time, number of layers etc.) were optimized with respect to the microstructural properties of the YBCO layers after an intermediate heat treatment at 920°C. An essential criterion is the minimization of macrocracks after the 920°C heat treatment, since it was found to favour good superconducting properties after the final heat treatment. This final heat treatment involves (i) partial melting above the peritectic temperature, (ii) peritectic recombination at lower temperature and (iii) reoxygenation at 500°C. Finally, the superconducting properties of the best films are discussed. A uniformly coated 55μm-thick YBCO film on a curved Ag substrate showed excellent superconducting properties with the onset of critical temperature at 92.2 K and an associated sharp resistive transition with transition width < 1 K. [less ▲]

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See detailLithium transition metal (Ti, Nb, V) oxide mesoporous thin films: contrasting results when attempting direct synthesis by evaporation-induced self assembly
Caes, Sébastien ULg; Malherbe, Cédric ULg; Krins, Natacha ULg et al

in Microporous and Mesoporous Materials (2013), 172

This work investigates the possibility to prepare mesoporous thin films of Li-Ti, Li-Nb, Li-Nb-V and Li-V oxides through a direct sol-gel EISA route by dissolving a lithium salt in the precursor solution ... [more ▼]

This work investigates the possibility to prepare mesoporous thin films of Li-Ti, Li-Nb, Li-Nb-V and Li-V oxides through a direct sol-gel EISA route by dissolving a lithium salt in the precursor solution. Experimental conditions involve a hydrolysis molar ratio H2O/TM ~10 (TM = Ti,Nb,V) and the common Pluronic structuring agent P123 (EO20-PO70-EO20). Systematic formation of lithium-containing oxides as first-crystallizing phases points to a significant intermixture of lithium and transition metal ions in the inorganic network. In the case of Ti-based and Nb-based oxide films, addition of lithium to the precursor solution is compatible with the formation of amorphous mesoporous films at 350°C. On the contrary, addition of lithium has a detrimental effect on the notoriously difficult formation of vanadium-based mesostructured films: even when replacing half of the vanadium by niobium as a stabilizer, formation of mesostructured films has not been possible in the investigated range of experimental conditions. [less ▲]

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See detailOptical and structural characterization of TiO2 films doped with silver nanoparticles obtained by sol-gel method
Ivanova, T.; Harizanova, A.; Koutzarova, T. et al

in Optical Materials (2013), 36

Nanostructured titanium oxide films with incorporated Ag nanoparticles were deposited by sol-gel spin coating method. The films were annealed at 300 °C, 400 °C, 500 °C and 600 °C in oxygen and nitrogen ... [more ▼]

Nanostructured titanium oxide films with incorporated Ag nanoparticles were deposited by sol-gel spin coating method. The films were annealed at 300 °C, 400 °C, 500 °C and 600 °C in oxygen and nitrogen ambient. X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and UV-VIS spectroscopy had been applied for studying the influence of the thermal treatments and the gas ambient on the structural and optical properties of TiO2 and TiO2:Ag films. The XRD analysis revealed the presence of metallic Ag phase without traces of silver oxides and these results were confirmed by FTIR spectra. It has been revealed that the annealing temperatures and the ambient, where the annealing is carried out is crucial for TiO2 crystallization, when there is Ag incorporation and especially for appearance of anatase and rutile phase. The nitrogen and oxygen ambient influences quite different the crystallization of TiO2:Ag films. Transmission and absorption spectra have been analyzed. Optical band gap values were evaluated for pure titania and Ag incorporated TiO2 films. © 2013 Elsevier B.V. All rights reserved. [less ▲]

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See detailMullite plasma spraying for in situ repair of cracks in mullite refractories: Simultaneous optimization of porosity and thickness by statistical design of experiments
Schrijnemakers, Audrey ULg; Francq, B. G.; Cloots, Rudi ULg et al

in Journal of Thermal Spray Technology (2013), 22(7), 1133-1139

We report a laboratory-scale study about the suitability of the plasma spraying process for "in situ" repair of cracks in mullite refractories of industrial furnaces. The "design of experiments" approach ... [more ▼]

We report a laboratory-scale study about the suitability of the plasma spraying process for "in situ" repair of cracks in mullite refractories of industrial furnaces. The "design of experiments" approach is used to investigate how the coating porosity and thickness are influenced by six experimental parameters. Arc current, secondary gas (H 2) flow rate, and stand-off distance are the most significant parameters for both responses. Several interaction terms also affect significantly the thickness response. The validity of the model equations is discussed both from a statistical point of view and regarding the physical credibility of the main model terms. Additional experiments confirm that the measured properties lie into the prediction intervals provided by the model. Using a set of parameters optimized for minimal porosity and high thickness (relevant for the crack repair application), coatings with 6% porosity and 1070 μm thickness can be prepared reproducibly. © 2013 ASM International. [less ▲]

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See detailDifferences in the structural and magnetic properties of nanosized barium hexaferrite powders prepared by single and double microemulsion techniques
Koutzarova, T.; Kolev, S.; Ghelev, Ch et al

in Journal of Alloys & Compounds (2013), 579

Barium hexaferrite powders of nanometer particle size synthesized via two variants of the microemulsion technique, namely, single microemulsion and double microemulsion, were studied. The influence was ... [more ▼]

Barium hexaferrite powders of nanometer particle size synthesized via two variants of the microemulsion technique, namely, single microemulsion and double microemulsion, were studied. The influence was explored of the type of microemulsion technique on the microstructure and on the magnetic properties of the barium hexaferrite powders. The average particle size of the barium hexaferrite powders was in the range from 110 nm to 442 nm depending on the method and conditions of synthesis. The particles with size below 150 nm had irregular shapes between spherical and platehexagonal; the bigger ones had an almost perfect hexagonal shape. The powders obtained by single microemulsion had better magnetic characteristics (saturation magnetization of 65.12 emu/g and coercivity field of 3.6 × 105 A/m) than those obtained by double microemulsion. © 2013 Elsevier B.V. All rights reserved. [less ▲]

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See detailEffect of freeze-drying and self-ignition process on the microstructural and electrochemical properties of Li4Ti5O12
Jamin, Claire ULg; Traina, Karl; Eskenazi, David ULg et al

in Materials Research Bulletin (2013), 48

Crystalline Li4Ti5O12 is synthesized by a method involving the freeze-drying and self-ignition of a gel prepared from titanium isopropoxide, lithium nitrate and hydroxypropylmethylcellulose (HPMC). This ... [more ▼]

Crystalline Li4Ti5O12 is synthesized by a method involving the freeze-drying and self-ignition of a gel prepared from titanium isopropoxide, lithium nitrate and hydroxypropylmethylcellulose (HPMC). This synthesis route yields crystalline Li4Ti5O12 particles after calcination at 800°C for 2 h. In an alternative route, addition of ammonium nitrate shifts the self-ignition mode from wave-like propagation to simultaneous. Powders with different microstructures are thereby obtained. Electrochemical characterization shows that the best results for Li+ intercalation/desintercalation are obtained for the powder prepared without ammonium nitrate addition. These results highlight the necessity for a control of the self-ignition mode to obtain adequate properties. [less ▲]

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See detailThe influence of a grain boundary on the thermal transport properties of bulk, melt-processed Y-Ba-Cu-O
Marchal, C.; Fagnard, Jean-François ULg; Shi, Y. H. et al

in Superconductor Science and Technology (2013), 26

We report the dependence of thermal conductivity, thermoelectric power and electrical resistivity on temperature for a bulk, large grain melt-processed Y-Ba-Cu-O (YBCO) high temperature superconductor ... [more ▼]

We report the dependence of thermal conductivity, thermoelectric power and electrical resistivity on temperature for a bulk, large grain melt-processed Y-Ba-Cu-O (YBCO) high temperature superconductor (HTS) containing two grains separated by a well-defined grain boundary. Transport measurements at temperatures between 10 and 300 K were carried out both within one single grain (intra-granular properties) and across the grain boundary (inter-granular properties). The influence of an applied external magnetic field of up to 8 T on the measured sample properties was also investigated. The presence of the grain boundary is found to affect strongly the electrical resistivity of the melt-processed bulk sample, but has almost no effect on its thermoelectric power and thermal conductivity, within experimental error. The results of this study provide direct evidence that the heat flow in multi-granular melt-processed YBCO bulk samples should be virtually unaffected by the presence of grain boundaries in the material. © 2013 IOP Publishing Ltd. [less ▲]

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