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Copyright of Romanian Journal of Materials / Revista Romana de Materiale is the property of Foundation for Materials Science & Engineering Serban Solacolu and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Thin films and crystalline powder of PbI2 intercalated with ammonia or pyridine have been studied by optical absorption, Raman scattering, photoluminescence, FTIR spectroscopy and thermo-gravimetric analysis. Ammonia intercalated PbI2 shows an increased optical band gap, of about 0.6 eV, with an intense broad emission band peaking at about 2.3 eV as signature in the photoluminescence spectrum. The intercalation of PbI2 with ammonia is noticed in the Raman spectrum by the appearance of new lines situated in low frequency range. The D3d coordination geometry of Pb2+ in the PbI2 crystal is reduced by compression to orthorhombic one, the distribution of the electronic states in valence band is also changed. Thus, the top of the valence band undergo a deformation inducing a weakness of the interaction between the lead and iodine ions within a layer. Also the PbI2 intercalated with pyridine is featured by optical and vibration properties different that of pure crystalline powder. Finally, the intercalation of PbI2 with different molecules changes the basic semiconducting properties of the crystal. Thermal analyses and infrared absorption spectra have been used to study the desorption of guests species from PbI2 in order to evaluate the stability range and morphological changes with temperature. [ABSTRACT FROM AUTHOR]

Abstract: Oxide ion conductors have been increasingly studied for many years because of their application in devices with high economical impact such as solid oxide fuel cells (SOFC), oxygen sensors, and dense ceramic membranes for oxygen separation, and membrane reactors for oxidative catalysis. New fast oxide ion conductors for low temperature applications (400–600°C) have been proposed during recent years. The influence of Sb2O3 and Ta2O5 as on the Bi2O3 structures and the corresponding electrical behavior were investigated. The powder products, obtained by solid state reactions, were characterized by XRD and SEM. They were sintered at different temperatures and the bulk ceramics were characterized and their electrical behavior versus temperature were recorded. This investigation underlines the influence of the nature of dopants on the structures and electrical performances bismuth based oxides. For microstructure analysis the theory of fractals was used. [Copyright &y& Elsevier]

Abstract: One of the most interesting category of multifunctional systems is the magnetoelectrics (ME), i.e., materials having simultaneous magnetic and ferroelectric activity. The present paper describes a simple low-temperature synthesis method of preparing bismuth ferrite thin films by a wet chemical route, using bismuth and iron nitrates and two chelating agents (citric acid and polyvinyl alcohol). The films were layer by layer deposited on substrate (silica glass) using the dip-coating technique. The thickness of the layers were controlled by viscosity of the solutions and withdrawing speed parameters. After specific annealing, in air, the samples were characterized by scanning electron microscopy SEM, spectroelipsometry SE, X-ray photoelectron spectroscopy XPS, Raman spectroscopy. A more thoroughly control of the processing parameters seems to be essential in obtaining BiFeO3 thin films. Solution chemistry variations (differences in precursor type) can have a significant impact on the film properties. [Copyright &y& Elsevier]

The paper describes a simple low-temperature synthesis route of preparing bismuth ferrite thin films through a wet chemical process, using nitrates of bismuth and iron and two chelating agents (citric acid and polyvinyl alcohol). The films were successively deposited on different type of substrates (silica glass, steel and sintered alumina) using the immersion technique. After specific annealing, in air, the samples were characterized by scanning electron microscopy (SEM), spectroellipsometry (SE), X-ray diffraction (XRD), X-ray photoelectron (XPS) and Raman spectroscopy. The influence of chelate agent and the nature of substrates on the mechanism formation of BiFeO3 is emphasized. [ABSTRACT FROM AUTHOR]

Abstract: From the technological point of view, the mutual control of electric and magnetic properties is an attractive possibility, but the number of candidate materials is limited. One of them, BiFeO3, has critical conditions for synthesizing single phase since the temperature stability range of the phase is very narrow. Hence, various aspects of BiFeO3 system have to be studied. Fine particles of BiFeO3 are obtained using a wet chemical route (combustion technique) and compared with the same product prepared by classic solid state reaction. The sintering programs have been varied in order to investigate the mechanism reactions and to show the relation between the microstructures and the magnetoelectric behavior. The samples are characterized by using various techniques: X-ray diffraction (XRD) study is carried out for phase determination and lattice parameter calculations; scanning electron microscopy (SEM-EDX) and TEM to find out grain size and morphology; differential thermal analysis (DTA) to determine transformations of the starting materials. The obtained bulk materials were characterized (density, porosity, etc.) and correlated with the phase composition present in the samples. Electric and magnetic properties were evaluated. This study underlines the role of the preparation route on the structural and morphological characteristic of the obtained materials and their influence on the magnetoelectric behavior. [Copyright &y& Elsevier]

Abstract: Multiferoic materials (having coupled electric, magnetic and structural order parameters that result in simultaneous ferroelectricity, ferromagnetism, and ferroelasticity) present opportunities for potential application in information storage, the emerging field of spinotronics and sensors. The perovskite BiFeO3 is ferroelectric [Curie temperature (T c) ∼1103K] and antiferromagnetic [Neél temperature (T N) ∼643K], exhibiting weak magnetism at room temperature. Conditions for synthesizing single BiFeO3 phase are critical since the temperature stability range of the phase is very narrow. Moreover, it is also difficult to control oxygen stoichiometry in the sample. In this work the preparation of BiFeO3 thin films by a specific wet chemical route is discussed. Respective influence of the precursors, thermal annealing condition, the substrate and, generally speaking, the preparation process of the films is presented. Results obtained by X-ray diffraction and spectroscopic elipsometer (SE) was used to characterize the obtained films. [Copyright &y& Elsevier]

Abstract: Oxide ion conductors have been increasingly studied for many years because of their application in devices with high economical interest such as solid oxide fuel cells (SOFC), oxygen sensors, dense ceramic membranes for oxygen separation, and membrane reactors for oxidative catalysis. Bismuth oxides present polymorph forms, such as δ-, β- or γ-Bi2O3, with great potential for such applications, alone or in combination with other oxides. The present study investigates the influence of selected ions (Fe3+, Sb3+/Sb5+, and Ta5+), introduced as dopant in α-Bi2O3 and their effect on the structure and properties of the oxide polymorph forms obtained at high temperature. The molar ratio was Bi2O3:M x O y 0.95:0.05 where M=Fe2O3, Sb2O3 or Ta2O5, respectively. The structural changes of α-Bi2O3 were analysed by powder X-ray diffraction, SEM/EDX analysis and infrared spectroscopy. The structural changes are correlated with bulk ceramic characteristics (density, porosity) and their electrical behaviour versus temperature. The presence of some dopants (antimony and tantalum) on bismuth sites enlarges and enhances the stability of the polymorph forms, which is relevant to potential application. [Copyright &y& Elsevier]

The paper presents a simple technique for synthesis of La1-xSrxCoO3 (x=0–0.3) nanopowders by calcining maleate-based precursors. The complex precursors were characterised by chemical analysis, electronic and FT-IR spectra and DTA–TG analysis. The XRD data for La1-xSrxCoO3 show that the samples are single phase with rhombohedral distorted perovskite structure. Specific surface area results of La1-xSrxCoO3 samples indicated values in the range 30–38 m2/g, which are high values for perovskite-type oxides. [Copyright &y& Elsevier]

Partial replacement of Bi by Pb and Sb produces materials of high-Tc pure phase, with antimony playing an important role in accelerating the formation of the phase with the higher superconductive transition in the Bi–Sr–Ca–Cu–O system. The influence of the antimony precursors on the superconducting phases mechanism formation was examined. Using a solid state reaction route, two nominal compositions Bi1.6Pb0.3Sb0.1Sr2Ca2Cu3Oy and Bi1.6Pb0.4Sb0.1Sr2Ca2Cu4Oy were investigated. The sources of antimony were Sb2O3, αSb2O4 and a prepared mixture Bi1.9Sb0.1Ox. The mechanism formation of the phases upon annealing was investigated using X-ray diffraction and simultaneous thermal analysis. Electrical properties of the obtained materials were evaluated. The presence of the antimony ions determined a higher reactivity of the system as well as the promotion of the superconducting high-Tc phase enhancement. [Copyright &y& Elsevier]

The present study investigates the influence of Sb ions, introduced as dopants in α-Bi2O3, on the structure of the oxide polymorph forms obtained at high temperature. The structural changes of α-Bi2O3 for compositions in the system Bi2-xSbxO3 (x=0, 0.05, 0.1, 0.15, 0.2), at different thermal treatment temperatures were analyzed by thermal analysis, powder X-ray diffraction and infrared transmission spectroscopy. A tendency of the structure to change to a higher symmetry (monoclinic → tetragonal → cubic) was observed, as the content in antimony increased and the temperature reached 850 °C. The presence of Sb2O3 in the Bi2O3 oxide system promotes an oxygen release from the oxide and enlarges the stabilization domain of the δ-phase. [Copyright &y& Elsevier]

We report the evolution of structural, dielectric, ferroelectric and ferromagnetic properties in novel (Pb 1 − 3x/2 Nd x )(Ti 0.98 − y Fe y Mn 0.02 )O 3 perovskite ceramics(x = 0.08, 0 < y < 0.05). We found room-temperature ferroelectric polarization and ferromagnetism for higher amount of iron ions(y ≥ 0.04). The paraelectric-ferroelectric phase transition occurred between 650 and 670 K for 0 ≤ y ≤ 0.05. Ferromagnetic hysteresis was measured at different temperatures on samples with y ≥ 0.04. Detailed structural analysis evidenced the variation of unit cell parameters with y increasing, confirming the substitution of the iron element in the lattice. 57 Fe Mössbauer spectroscopy evidenced that iron ions occupy Ti positions in the perovskite lattice, with the oxidation state Fe 3 + and two coordination types. X-ray photoelectron spectroscopy confirmed the presence of iron only as Fe 3 + and, moreover, evidenced the presence of a substantial amount of Ti 3 + ions in the structure. The presence of both Fe 3 + (spin 5/2) in different coordinations as well as Ti 3 + (spin 1/2) magnetic ions in B-site positions drives the occurrence of magnetic properties from low temperature to above room temperature, through superexchange Fe 3 + -O-Fe 3 + , Fe 3 + -O-Ti 3 + and Ti 3 + -O-Ti 3 + interactions. The finding of coexistent ferroelectric and ferromagnetic properties in these compounds ground the route to facile synthesis of multiferroics by simply doping a classical perovskite ferroelectric material like PbTiO 3 with an adequate amount of transition magnetic ions. [ABSTRACT FROM AUTHOR]

Abstract: Ce1−x Fe x O2−y (0≤x≤0.05) nanopowders were synthesized using hydrothermal method at low calcination temperature and low doping regime. Structural and morphological characterization has been carried out by the X-ray diffraction method and non-contact atomic force microscopy. Vibrational properties were investigated by Raman spectroscopy. It was observed that the content of oxygen vacancies increased significantly with Fe doping up to 3mol%. For higher dopant concentration, phase separation was detected. The optical properties of pure and Fe3+-doped CeO2−y samples were investigated by spectroscopic ellipsometry. Several analytical models were applied to analyze the optical absorption onset of ceria defective structure. It was found that, Cody–Lorentz model most suitably described the sub-band gap region of CeO2−y nanopowders and consequently gave more accurate band gap values, which are closer to the direct band gap transitions than to the indirect ones. The increased content of localized defect states in the ceria gap and corresponding shift of the optical absorption edge towards visible range in Fe-doped samples can significantly improve the optical activity of nanocrystalline ceria. [Copyright &y& Elsevier]

Abstract: Intercalation, i.e. the insertion of guest species in a crystalline layered structure, is an efficient route for generating new materials with novel properties. Thin films and crystalline powder of BiI3 layered semiconductor were intercalated by exposure to ammonia vapors at room temperature. The intercalated compound was studied by thermo-gravimetric analysis, differential scanning calorimetry, X-ray diffraction, UV–vis optical absorption, FTIR spectroscopy and Raman scattering. After exposure of BiI3 to ammonia the formation of a new phase, BiI3(NH3)3.83, was evidenced by thermal analysis. The intercalation process leads to a blue shift of the BiI3 optical absorption edge by 0.5eV. The appearance of new Raman lines at 135 and 353cm−1 in the Raman spectrum of intercalated BiI3 is considered as an evidence of the chemical interaction between the ammonia molecules and BiI3 lattice. [Copyright &y& Elsevier]