RAMAN STUDY OF FERROELECTRIC BISMUTH LAYER-OXIDE ABi4Ti4O15 PREPARED BY THE MECHANOCHEMICAL SYNTHESIS

Ferroelectric materials have innumerable properties related totheir spontaneus polarization, for instance. pyre- and piezoelectricity, which are used for various sensors and actuators il 1. BaBi4Ti4O12 (BBT) is an r : 4 member of the Bi-layer structured ferroelecrtric oxide family (Auriviltius phase) [2]. Bi-layered structure ferroelectric material - bismuth titanate, Bi+Ti:Orz (BIT) and barium-bismuth titanate, BaBi+Ti+Ors (BBT) ceramic powders were prepared by mechanical synthesis possess. BaBi+TiaOrs was prepared from stoichometric quantities of barium titanate and bismuth titanate obtained via mechanochemical synthesis. Barium titanate, BaTiOt has been synthesised from mixture of BaO and TiGz and bismuth titanate, Bi+TirOr: was prepared starting from BiuO: and TiOz, comercialy available. The reaction mechanism of BBT and the preparation and characteristics of BBT ceramic powders u,ere studied using X-ray diffraction (XRD) and IR spectroscopy The phonon modes have been studied by Rarran spectroscopy. The Bi-layered perovskite structure of BBT cerantic fbrrns at ll00 "C. Microstructure of Bi+Ti:Or1 is in accordiance with the vierv that Bi,rTilOr:exhibits plate-like grains with thr average grain size increasing u,,ith the sintering temperature. lt is eviclent that Ba2- aclition leads to the change in the microstructure development, particularly in the change of the average grain size an; homogeneity of the grains of BaBi4Ti4O12

Effect of Y-doping on structure and properties of multiferroic BiFeO3 ceramics

Bismuth ferrite (BiFeO3) exhibits ferroelectric and antiferromagnetic properties up to very high temperatures, and is, consequently, considered one of the most promising single phase multiferroic materials. Doping with Y3+ was tested in terms of improving electrical and magnetic properties. Bi1-xYxFeO3 was synthesized by auto-combustion method using urea as a fuel. Precursor powders were annealed, pressed and sintered. Powders and ceramic samples were characterized by XRD, SEM, Raman, electrical and magnetic measurements. X-ray diffractograms and Raman spectra showed transition from rhombohedral to orthorhombic structure at 10 % Y3+ content. SEM images indicated reduction in grain size with higher concentration of Y3+

STRUCTURE AND CHARACTERIZATION OF BaTiO3-Ni(1-x)Zn(x)Fe2O4 COMPOSITES

NiZnFe2O4 (NZF) powder was prepared by auto-combustion method starting from nickel, zinc and iron nitrates. Thermal treatment was performed at 1000 oC for 1 h after which the nickel ferrite powder was formed. Barium titanate (BT) powder was prepared with same method using titanyl nitrate and barium nitrate as a starting reagents. Multiferroic composites with formula BaTiO3– Ni(1-x)ZnxFe2O4 (x = 0.3, 0.5, 0.7) were prepared by mixing chemically obtained NZF and BT powders in the planetary mill for 24 h. Powders were pressed and sintered at 1170 oC for 4 h. Samples were characterized by XRD, Raman, SEM, IR. Magnetic and electrical measurements were also carried out. X-ray and Raman measurements confirmed the presence of NZF, BT phases and the traces of barium ferrite phase. The microstructure of the ceramics shows (Fig. 1.) the formation of polygonal (NZF grains), rounded (BT grains) and plate like grains (barium ferrite phase). The impedance analyses of multifferoic composites at 200 ºC have shown the contribution of both, grain and grain boundary resistivity

Influence of Mg doping on structural, optical and photocatalytic performances of ceria nanopowders

Nanosized Mg-doped ceria powders were obtained by self-propagating room temperature reaction without using surfactants or templates. X-ray diffraction analysis and field emission scanning microscopy results showed that the doped samples are solid solutions with fluorite-type structure and spherical morphology. Raman spectra revealed an increase in the amount of oxygen vacancies with the increase of Mg concentration. This increasing results in a narrowing of the bandgap of CeO2. The photocatalytic performances of the Mg-doped ceria solid solutions were evaluated by decomposing an organic dye, crystal violet under UV irradiation. The Mg-doped ceria solid solutions exhibit significantly better photocatalytic activity than the pure CeO2 and commercial TiO2. The higher first rate constant of the Mg-doped samples demonstrated that they are much more efficient than TiO2 and CeO2 under UV light. Mg2+ dopant ions and oxygen vacancies play a significant role in the enhancement of photocatalytic performances of the Mg-doped ceria

IMPROVED ELECTRICAL AND MAGNETIC PROPERTIES IN Y DOPED BiFeO3 CERAMICS

Bismuth ferrite (BiFeO3) is considered one of the most promising single phase multiferroic materials thanks to the fact it exhibits ferroelectric and antiferromagnetic properties in the same time in very wide range of temperatures (up to 370 °C). Difficulties in obtaining pure BiFeO3 phase and dense ceramics, together with occurrence of leakage currents have prevented application of BiFeO3. Substitution of Bi3+ or Fe3+ ions with some transition metal or rare earth ions can improve both electrical and magnetic properties by reducing leakage currents and introducing weak ferromagnetism through structural changes. Y doped bismuth ferrite, Bi1-xYxFeO3, was synthesized by auto-combustion method using urea as a fuel. Precursor powders were annealed, pressed and sintered. Powders and ceramic samples were characterized by XRD, SEM, Raman, impedance spectroscopy, ferroelectric and magneticmeasurements. X-ray diffractograms and Raman spectra showed no presence of secondary phases. SEM images indicated lowering of grain size with higher concentration of Y3+. Electrical resistance is highly improved even at 1 % of Y, while 10 % of Y was necessary to break spiral spin structure, leading to weak ferromagnetism

Spectroscopic ellipsometry and polarimetry for materials and systems analysis at the nanometer scale: state-of-the-art, potential, and perspectives

This paper discusses the fundamentals, applications, potential, limitations, and future perspectives of polarized light reflection techniques for the characterization of materials and related systems and devices at the nanoscale. These techniques include spectroscopic ellipsometry, polarimetry, and reflectance anisotropy. We give an overview of the various ellipsometry strategies for the measurement and analysis of nanometric films, metal nanoparticles and nanowires, semiconductor nanocrystals, and submicron periodic structures. We show that ellipsometry is capable of more than the determination of thickness and optical properties, and it can be exploited to gain information about process control, geometry factors, anisotropy, defects, and quantum confinement effects of nanostructures

TiO2/WO3 photocatalytic composite coatings prepared by spray pyrolysis

TiO2/WO3 composites supported on a stainless steel foil were prepared by the spray pyrolysis technique. Content of WO3 was gradually increased from 1 wt% to 100 wt.%, while the coating thickness was limited to about 1 pm. The coatings were characterized by X-ray diffraction, scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. The photocatalytic activity of obtained coatings was investigated by degradation of methyl orange, used as model pollutant. The results show that with increasing WO3 content up to 10 wt.% photoactivity increases as result of better charge separation that could effectively prevent the recombination of photogenerated electrons and holes. Further increase of WO3 content led to decrease of photoactivity. (C) 2014 Elsevier B.V. All rights reserved

Theoretical and experimental study of octahedral tilting of Ca1-xGdxMnO3 (x=0.05, 0.1, 0.15, 0.2) nanometric powders

In order to estimate theoretical stability of the perovskite structure for synthesized Ca1-xGdxMnO3 (x = 0.05, 0.1, 0.15, 0.2) nanopowders, the Goldschmidt tolerance factor G(t) and global instability index GII were calculated. Furthermore, we have performed structure prediction of Ca1-xGdxMnO3 perovskites and found several possible perovskite-related phases. The influence of gadolinium amount on MneO bond angles and distances, tilting of MnO6 octahedra around all three axes and deformation due to the presence of the Jahn-Teller distortion around Mn3+ cation, as well as the influence of the amount of Mn3+ cation on Ca1-xGdxMnO3 compound, was examined. Ion Mn valence states were determined by bond valence calculations (BVC). Infrared active phonon modes in Ca1-xGdxMnO3 were studied by infrared reflection spectroscopy and magnetic properties were studied by using EPR (electron paramagnetic resonance) measurements. (C) 2016 Elsevier B.V. All rights reserved