The effects of nonstoichiometry on optical properties of oxide nanopowders

In this paper we illustrate the change of optical properties of mechanically activated wurtzite ZnO powder and laser synthesized anatase TiO2 nanopowder due to the nonstoichiometry caused by mechanical activation and/or laser irradiation in vacuum. Both of the investigated materials are widely used in optoelectronics and the examination of their optical properties under different preparation and environmental conditions is of great practical interest

Characterization of Barium Titanate Ceramic Powders by Raman Spectroscopy

Barium titanate, BaTiO3 ceramic powders were prepared by mechanochemical synthesis and by the Pechini method. A powder mixture of BaO and TiO2 was treated in a planetary ball mill in an air atmosphere for Lip to 1 h, using zirconium oxide vial and zirconium oxide balls as the milling medium. After 60 min BaTiO3 phase was formed. In both ways BaTiO3 ceramics were sintered after 2 h on 1300 degrees C without pre-calcinations step. The heating rate was 10 degrees C min(-1). The formation of phase and crystal structure of BaTiO3 was approved by X-ray diffraction analysis and the Raman spectroscopy. The morphology and microstructure of obtained powders were examined by scanning electron microscopy method. Sharp phase transition from ferroelectric to paraelectric state was observed. The hysteresis loop is very well performed with regular sharp characteristic of ferroelectric materials

Characterization of mechanically activated ZnO powders by raman, luminescence and IR Spectroscopy

Commercial zinc oxide powder was mechanically treated by grinding in a high-energy vibro-mill in a continual regime in air up to 300 minutes. Original and modified ZnO samples were characterized by Raman, photoluminescence (PL) and infrared (IR) spectroscopy. This study confirms that change in defect structure of ZnO crystal lattice introduced by mechanical activation greatly affects the optical properties of this material

Study on bi-layered ceramics powders prepared by the mechanochemical synthesis

Bi-layered structured ferroelectric materials-bismuth titanate, Bi4Ti3O12 (BIT) and barium-bismuth titanate, BaBi4Ti4O15 (BBT) powders were prepared by homogenization and sintering of mixture of stehiometric quantities of bismuth titanate and barium titanate obtained via mechanochemical synthesis. The Bi4Ti3O12 ceramic was obtained at 1000 degrees C for 4 h and BaBi4Ti4O15 ceramic at 1100 degrees C for 4 h. The phase formation and properties of Bi4Ti3O12 and BaBi4Ti4O15 were studied using XRD, Raman spectroscopy, EDS and SEM. Microstructure of Bi4Ti3O12 and BaBi4Ti4O15 exhibits plate-like grains typical for the bi-layered structured material. The Ba2+ addition leads to the change in the microstructure development, particularly in the change of the average grain size. Crow

Corrosion study of ceria coatings on AA6060 aluminum alloy obtained by cathodic electrodeposition: Effect of deposition potential

Among potential replacements for chromates, cerium-based conversion coatings (CeCCs) have been identified as leading candidates, showing a good promise as environmentally compliant corrosion inhibitors on Al alloys. In this work, CeCCs were synthesized on M6060 by electrolytic deposition (ELD), a well-suited method for the fabrication of films with controllable properties, at low processing temperature and cost. The CeCCs were deposited at room temperature from Ce(NO3)(3) solution, applying different cathodic potentials (-1.1, -1.4 and -1.6 V vs. SCE) for different deposition times between 5 and 20 min. Structural, morphological and compositional properties of the films were characterized by X-ray diffraction, Raman spectroscopy and scanning electron microscopy coupled with energy dispersive spectroscopy. Ceria films were nanostructured, exhibiting a cubic fluorite structure. From corrosion perspective, the quality of CeCCs was evaluated in 0.5 M NaCI solution via electrochemical impedance spectroscopy and linear sweep voltammetry. As shown, the coating corrosion quality is the interplay between deposition potential and deposition time. The highest potential led to highly cracked films of poor adherence, even at the shortest deposition time, which disqualified them from any corrosion protection application. The lowest potential (-1.1 V) produced crack-free coatings, but longer times ( gt = 10 min) were needed to provide the protective layer formation. The best corrosion protection offered CeCCs prepared at -1.4 V. The highest R-p (582 k Omega cm(2)) and the smallest CPE (12.6 . 10(-6) s(n) Omega(-1) cm) were obtained at 20 min deposition time. However, from economical point of view, 10 min deposition is a promising choice. These CeCCs also improved pitting corrosion resistance owing to homogeneous microstructure and sufficient thickness

Comparative study of structural and electrical properties of Pr and Ce doped BiFeO3 ceramics synthesized by auto-combustion method

Polycrystalline Bi1-xPr(Ce)(x)FeO3 ceramics (x = 0, 0.03, 0.05 and 0.10) were prepared by auto-combustion method using urea as a fuel. The influence of Pr(Ce) doping on structural, vibrational, morphological, dielectric and ferroelectric properties of BiFeO3 polycrystalline ceramics was investigated. From X-ray diffraction (XRD) and scanning electron microscopy measurements it was observed that Pr(Ce) doping generated a reduction of the crystallite (grain) size of BiFeO3 and contraction of the rhombohedral cell due to the increased compressive strain. The changes seen in the XRD and Raman spectra of 10% Pr(Ce)doped samples, pointed to a probable appearance of orthorhombic (pseudotetragonal) crystal structure. The pristine BiFeO3 exhibited rounded shape, non-saturated ferroelectric hysteresis loop. The dielectric constant and dielectric loss have shown strong dispersion at lower frequencies, typical for conductive BiFeO3. Dielectric and ferroelectric properties at room temperature were improved with Pr doping. Concerning the Ce-doped samples, only the 3% Ce-doped sample exhibited a better shaped hysteresis loop and improved dielectric properties compared to the pristine BiFeO3. With further increase of Ce content the ferroelectric properties degraded

Improving of the electrical and magnetic properties of BiFeO3 by doping with yttrium

Bismuth ferrite is one of the most promising multiferroic materials, and the main barriers for exploiting all of its specific properties are difficulties in obtaining pure, high resistive material with nanosized grains. Doping of BiFeO3 with different transition metals and rare earth elements is often used way for overcoming these obstacles. Yttrium doped bismuth ferrite, Bi1-xYxFeO3 (x = 0; 0.01; 0.03; 0.05; 0.1), was prepared by auto-combustion method. X-ray diffraction patterns and Raman results showed that partial phase transition from rhombohedral to orthorhombic structure took place at around 10 mol% of Y. Effect of Y doping on microstructure was studied from SEM micrographies, showing the reduction of grain size in doped samples. Electrical measurements showed continuous improvement of resistivity with Y doping, whereas the values of saturation and remnant polarizations exhibit maximums at around 5 mol% of Y. Yttrium doping also enhanced magnetic properties, leading to weak ferromagnetism

Characterization of Barium Titanate Ceramic Powders by Raman Spectroscopy

Barium titanate, BaTiO3 ceramic powders were prepared by mechanochemical synthesis and by the Pechini method. A powder mixture of BaO and TiO2 was treated in a planetary ball mill in an air atmosphere for Lip to 1 h, using zirconium oxide vial and zirconium oxide balls as the milling medium. After 60 min BaTiO3 phase was formed. In both ways BaTiO3 ceramics were sintered after 2 h on 1300 degrees C without pre-calcinations step. The heating rate was 10 degrees C min(-1). The formation of phase and crystal structure of BaTiO3 was approved by X-ray diffraction analysis and the Raman spectroscopy. The morphology and microstructure of obtained powders were examined by scanning electron microscopy method. Sharp phase transition from ferroelectric to paraelectric state was observed. The hysteresis loop is very well performed with regular sharp characteristic of ferroelectric materials

The characterization of the barium titanate ceramic powders prepared by the Pechini type reaction route and mechanically assisted synthesis

BaTiO3 ceramic powders were prepared by a complex method based on the Pechini type reaction route and mechanically assisted synthesis. In both ways BaTiO3 ceramics were sintered after 120 min on 1300 degrees C without pre-calcination steps. The crystal structure was investigated by the XRD, IR and Raman spectroscopy. The particle size and morphology of BaTiO3 were examined by XRD and SEM. The XRD results of powders indicate the formation of cubic phase of BaTiO3. It can be observed that in the case of Pechini process BaTiO3 powder is well crystallized but in the case of mechanochemistry process, significant amount of amorphous phase was detected. The sintered BaTiO3 ceramic sample prepared by Pechini process, shows the formation of tetragonal phase. However, IR and Raman spectrum showed a mixture of cubic and tetragonal for BaTiO3 obtained by Pechini process and tetragonal for BaTiO3 obtained by mechanically assisted synthesis