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The Auger and XPS technique has been used for investigation in the surface of bismuth titanate (Bi4Ti3O12) (BIT) ceramics obtained by reactive sintering from Bi2O3 and TiO2 oxides. All peaks characteristic for bismuth, titanium and oxygen are clearly visible in the spectrum. Oxygen vacancies are preferentially sited in the vicinity of bismuth ions observed by our X-ray photoemission data. The variation in the valence state of titanium ions is also possible. The XPS and AES measurements confirm that the surface elemental composition of bismuth titanate ceramics does not deviate from nominal bulk composition. © 2008 Elsevier B.V. All rights reserved.

The Auger and XPS technique has been used for investigation in the surface of bismuth titanate (Bi4Ti3O12) (BIT) ceramics obtained by reactive sintering from Bi2O3 and TiO2 oxides. All peaks characteristic for bismuth, titanium and oxygen are clearly visible in the spectrum. Oxygen vacancies are preferentially sited in the vicinity of bismuth ions observed by our X-ray photoemission data. The variation in the valence state of titanium ions is also possible. The XPS and AES measurements confirm that the surface elemental composition of bismuth titanate ceramics does not deviate from nominal bulk composition. © 2008 Elsevier B.V. All rights reserved.

Manganese ferrite, MnFe2O4 have been prepared by a soft mechanochemical route from mixture of (a) Mn(OH)(2) and alpha-Fe2O3 and (b) Mn(OH)(2) and Fe(OH)(3) powders in a planetary ball mill. The mixture was activated for varying duration. Soft mechanochemical reaction leading to formation of the MnFe2O4 spinel phase was followed by X-ray diffraction, Raman spectroscopy, scanning and transmission microscopy and magnetization measurements. The spinel phase formation was first observed after 12 h of milling and its formation was completed after 25 h in both cases. The synthesized MnFe2O4 ferrite has a nanocrystalline structure with a crystallite size of about 40 and 50 nm respectively for cases (a) and (b). There are five Raman active modes. Measurements after 25 h of milling show magnetization values of 70.4 emu/g and 71.1 emu/g respectively for cases (a) and (b). In order to understand better the whole process of phase formation, Mossbauer measurements were done. (C) 2011 Elsevier B.V. All rights reserved.

Manganese ferrite, MnFe2O4 have been prepared by a soft mechanochemical route from mixture of (a) Mn(OH)(2) and alpha-Fe2O3 and (b) Mn(OH)(2) and Fe(OH)(3) powders in a planetary ball mill. The mixture was activated for varying duration. Soft mechanochemical reaction leading to formation of the MnFe2O4 spinel phase was followed by X-ray diffraction, Raman spectroscopy, scanning and transmission microscopy and magnetization measurements. The spinel phase formation was first observed after 12 h of milling and its formation was completed after 25 h in both cases. The synthesized MnFe2O4 ferrite has a nanocrystalline structure with a crystallite size of about 40 and 50 nm respectively for cases (a) and (b). There are five Raman active modes. Measurements after 25 h of milling show magnetization values of 70.4 emu/g and 71.1 emu/g respectively for cases (a) and (b). In order to understand better the whole process of phase formation, Mossbauer measurements were done. (C) 2011 Elsevier B.V. All rights reserved.

In this work we report results on the influence of heavy rare earth ions substitution on microstructure and magnetism of nanocrystalline magnetite. A series of Fe(2.85)RE(0.15)O(4) (RE = Gd, Dy, Ho, Tm and Yb) samples have been prepared by high energy ball milling. Structure/microstructure investigations of two selected samples Fe(2.85)Gd(0.15)O(4) and Fe(2.85)Tm(0.15)O(4), represent an extension of the previously published results on Fe(3)O(4)/gamma-Fe(2)O(3), Fe(2.85)Y(0.15)O(4) and Fe(2.55)In(0.45)O(4) [Z. Cvejic, S. Rakic, A. Kremenovic, B. Antic, C. Jovalekic. Ph. Colomban, Sol. State Sciences 8 (2006) 908], while magnetic characterization has been done for all the samples. Crystallite/particle size and strain determined by X-ray diffractometry and Transmission electron microscopy (TEM) confirmed the nanostructured nature of the mechanosynthesized materials. X-ray powder diffraction was used to analyze anisotropic line broadening effects through the Rietveld method. The size anisotropy was found to be small while strain anisotropy was large, indicating nonuniform distribution of deffects in the presence of Gd and Tm in the crystal structure. Superparamagnetic(SPM) behavior at room temperature was observed for all samples studied. The Y-substituted Fe(3)O(4) had the largest He and the lowest M(S). We discuss the changes in magnetic properties in relation to their magnetic anisotropy and microstructure. High field irreversibility (H GT 20kOe) in ZFC/FC magnetization versus temperature indicates the existence of high magnetocrystalline and/or strain induced anisotropy. (C) 2008 Elsevier B.V. All rights reserved.

In this work we report results on the influence of heavy rare earth ions substitution on microstructure and magnetism of nanocrystalline magnetite. A series of Fe(2.85)RE(0.15)O(4) (RE = Gd, Dy, Ho, Tm and Yb) samples have been prepared by high energy ball milling. Structure/microstructure investigations of two selected samples Fe(2.85)Gd(0.15)O(4) and Fe(2.85)Tm(0.15)O(4), represent an extension of the previously published results on Fe(3)O(4)/gamma-Fe(2)O(3), Fe(2.85)Y(0.15)O(4) and Fe(2.55)In(0.45)O(4) [Z. Cvejic, S. Rakic, A. Kremenovic, B. Antic, C. Jovalekic. Ph. Colomban, Sol. State Sciences 8 (2006) 908], while magnetic characterization has been done for all the samples. Crystallite/particle size and strain determined by X-ray diffractometry and Transmission electron microscopy (TEM) confirmed the nanostructured nature of the mechanosynthesized materials. X-ray powder diffraction was used to analyze anisotropic line broadening effects through the Rietveld method. The size anisotropy was found to be small while strain anisotropy was large, indicating nonuniform distribution of deffects in the presence of Gd and Tm in the crystal structure. Superparamagnetic(SPM) behavior at room temperature was observed for all samples studied. The Y-substituted Fe(3)O(4) had the largest He and the lowest M(S). We discuss the changes in magnetic properties in relation to their magnetic anisotropy and microstructure. High field irreversibility (H GT 20kOe) in ZFC/FC magnetization versus temperature indicates the existence of high magnetocrystalline and/or strain induced anisotropy. (C) 2008 Elsevier B.V. All rights reserved.

Bismuth titanate, Bi4Ti3O12 powders were prepared by mechanically assisted synthesis from their oxides. The diameter of obtained particles depends on time of milling. In order to understand the grain size effects on the crystal structure we measured X-ray, TEM analysis and Raman spectra. The effect of mechanical treatment on the grain size is quite evident: as the milling time increases (3, 6, 12 h), the powder becomes more activated and grain size decrease (7.3, 7.2, 6.9 nm). With reducing the grain size, quantum effects at the Raman spectra, is reflected in the mode position change against balk crystal. And also, coagulation of each line appears, as well as a significant asymmetry of certain modes. (c) 2006 Elsevier B.V. All rights reserved.

Bismuth titanate, Bi4Ti3O12 powders were prepared by mechanically assisted synthesis from their oxides. The diameter of obtained particles depends on time of milling. In order to understand the grain size effects on the crystal structure we measured X-ray, TEM analysis and Raman spectra. The effect of mechanical treatment on the grain size is quite evident: as the milling time increases (3, 6, 12 h), the powder becomes more activated and grain size decrease (7.3, 7.2, 6.9 nm). With reducing the grain size, quantum effects at the Raman spectra, is reflected in the mode position change against balk crystal. And also, coagulation of each line appears, as well as a significant asymmetry of certain modes. (c) 2006 Elsevier B.V. All rights reserved.