Comparative Structural and Optical Properties of Different Ceria Nanoparticles

Herein a comparative study of five nanocrystalline cerium oxides (CeO2-delta) synthesised by different methods and calcined at 500 degrees C is reported. XRPD analysis showed that stoichiometry parameter delta, crystallite size/strain and lattice constant were only slightly affected by the method utilized. All ceria nanoparticles are nearly spherical in shape with faceted morphology, free of defects and with a relatively uniform size distribution. The average microstrain was found to be approximately 10 times higher than that of bulk counterpart. The absorption edge of nanocrystalline materials was shifted towards a higher wavelengths (red shift) in comparison with bulk counterpart, and band gap values were in the range 2.7-3.24 eV (3.33 eV for bulk counterpart)

Mossbauer Spectra and Crystallite Size Related Magnetic/Electric Properties of Yb Substituted Zn-Ferrite Nanoparticles

Influence of thermal-annealing-controlled crystallite size on the magnetic/electric properties of Yb substituted Zn-ferrite nanoparticles (ZnFe1.95Yb0.05O4) is studied, and results of the analysis are presented here. Room temperature Mossbauer spectrum of as-prepared sample shows coexistence of the sextet/doublet structure due to the particle size distribution. The central doublet originating from superparamagnetic relaxations of smaller particles is found to constitute the major fraction of the Fe-57 signal in samples obtained by thermal annealing of as-prepared sample at various temperatures in 300 degrees C-800 degrees C range. The determined quadrupole splitting (QS) parameters are significantly higher compared to corresponding bulk counterpart value and display decreasing trend with the crystallite size increase. The similar to 29 nm-sample, obtained by annealing at 800 degrees C, shows bulk-like properties, both in terms of the observed QS value and observed distribution of iron ions within the spinel lattice. Electric resistivity has non-monotonic dependence on crystallite-size, which could be attributed to enhanced disorder in as-prepared material. Partial substitution of iron by ytterbium in Zn-ferrite is found to increase the dielectric constant

X-ray powder diffraction line broadening analysis and magnetism of interacting ferrite nanoparticles obtained from acetylacetonato complexes

A study of the microstructures and magnetic properties of nanosize Zn ferrite (ZnFe2O4), Mn ferrite (MnFe2O4), and the cation deficit Zn-Mn ferrites Zn0.70Mn0.23Fe1.89O4 (S1), Zn0.41Mn0.50Fe1.84O4 (S2) and Zn0.18Mn0.67Fe1.85O4 (S3) was performed. The crystallite size for all samples was determined by x-ray powder diffraction (XRPD) analysis using four different methods, and was close to the particle size found from transmission electron microphotography. Among different methods of XRPD line broadening analysis it seems that the cubic harmonic function method is more precise and reliable than the Warren-Averbach and simplified integral breadth methods. M(T) and M(H) magnetization curves at different fields/temperatures indicate superparamagnetic behaviour of the samples. Asymmetric hysteresis loops and differences in coercive fields, H-C-(FC)-H-C- (ZFC), are discussed by both the core/shell model of nanoparticles and spin canting. The magnetic measurements with a maximum in the FC magnetization branches, the difference in M/M-S versus H/T curves above T-max, (temperature of maximum in ZFC magnetization), the nonlinearity in H-C versus T-1/2, the remanence/saturation ratio value, M-R/M-S and observation of the Almeida/Thouless line for low-field magnetization data (T-max versus H-2/3) indicate that the samples consist of an interacting ferrite nanoparticle ensemble

Formation of nanosize Li-ferrites from acetylacetonato complexes and their crystal structure, microstructure and order-disorder phase transition

Nanosize Li-ferrites were synthesised by the thermal decomposition of an appropriate mixture of complex compounds with acetylacetone - (2,4 pentadione) ligands ([M(AA)(x)]; M = Li and Fe) at 500 degrees C. The obtained sample is composed of three phases determined by the standard Rietveld procedure: Li0.5Fe2.5O4 (S. G. P4(3)32), Li1.16Fe3O4 (S.G. Fd (3) over barm) and LiFeO2 (S.G. Fm (3) over barm). Cation distribution in nanosize ordered spinel Li0.5Fe2.5O4 deviates from that of the bulk counterpart. Microstructure parameters (crystallite size of similar to 23 nm and strain of 3.2526(9) x 10(3)) were determined by the Rietveld refinement of the TCH-pV parameters. SEM microphotographs show a particle size of similar to 50-60 nm. An order disorder phase transition in ordered spinel Li0.5Fe2.5O4 was studied by DSC measurements and in situ XRPD technique. The temperature of phase transition was found to be 762 degrees C ( DSC) and (745 +/- 5) degrees C ( XRPD)

Magnetization enhancement in nanostructured random type MgFe2O4 spinel prepared by soft mechanochemical route

In this paper we report results of structural, spectroscopic, and magnetic investigations of MgFe2O4 nanoparticles prepared by soft mechanochemical synthesis. MgFe2O4 nanoparticles crystallize in Fd3m space group with mixed cation distribution and reduced percentage of Fe3+ at tetrahedral (8a) sites. Discrepancy in the cation distribution compared to that in the bulk Mg-ferrite is one of the highest known. X-ray line broadening analysis reveals crystallite size and strain anisotropy. The saturation magnetization, M-sat=62 emu/g measured at 5 K is twice higher than that found in the bulk counterparts. Such high value of M-sat is attributed to the low value of cation inversion parameter (delta=0.69), to the core/shell structure of the nanoparticles and to the surface/volume ratio. Moumlssbauer spectrum collected at room temperature reveals ferrimagnetic ordering between Fe3+ ions in 8a and 16d sites, while zero-field-cooled (ZFC) and field-cooled (FC) M(T) measurements were shown superparamagnetic state above 350 K

Investigation of nanocrystalline phases in Li-La-Fe-O system formed by the decomposition of acetylacetonato complexes

Applying a new synthesis route based on the thermal decomposition of a mixture acetylacetonato complexes, Li(AA), La(AA)(3) and Fe(AA)(3), Li, La ferrite (Li0.5La0.08Fe2.42O4) was formed. The element analysis performed by ICP technique and the Rietveld refinement data indicate that the sample is composed of three phases: Li0.5La0.008Fe2.42O4 (69%, SG P4(3)32, a = 8.3445(3) angstrom), La0.14Fe3O4 (16%, SG Fd (3) over barm, a = 8.403(1) angstrom) and LiFeO2 (15%, SG Fm (3) over barm, a = 4.2291(8) angstrom). A partial substitution Fe3+ - gt La3+ in Li ferrite and La insertion at 16c site in Fe3O4 occur at low concentrations. A partial cation ordering at 4b and 12d octahedral sites in Li0.5La0.08Fe2.42O4 was noticed. TEM micrograph shows that the nanoparticles are spherically shaped and that the particle distribution is in the range between 7 and 33 nm. The sample exhibits superparamagnetic behavior, thus the composite has potential industrial applications. (c) 2006 Elsevier B.V. All rights reserved

Temperature-induced structure and microstructure evolution of nanostructured Ni0.9Zn0.1O

The crystal structure and microstructure of as-prepared and annealed Ni0.9Zn0.1O were refined at room temperature in both the Fm (3) over barm and R (3) over barm space groups. It is shown that below the Neel point (458 K), where magnetic ordering triggers the presence of a trigonal strain, the common usage of a higher-symmetry non-admissible space group for crystal structure and microstructure analysis via the Rietveld method may result in both an incorrect structure description and incorrect microstructure parameters (size and strain). More realistic microstructure data can be obtained by whole powder pattern modelling of the powder diffraction data. Increasing the annealing temperature causes a reduction of the trigonal distortion as well as an increase in domain size. Simultaneously, the Raman spectra become less resolved, a clear indication of domain growth and structural evolution of the structure towards cubic symmetry (R (3) over barm - GT Fm (3) over barm)

Zn,Ni ferrite/NiO nanocomposite powder obtained from acetylacetonato complexes

The results on the synthesis, microstructure, structure and DC magnetization studies of nanocomposite Zn, Ni ferrite/NiO powder obtained by thermal decomposition of acetylacetonato complexes are reported in this paper. According to the results obtained by inductively coupled plasma optical emission spectroscopy (ICP-OES) element analysis and multiphase Rietveld refinement, the three samples made are composed of spinel-ferrite (86.7%-96.7%) and NiO (3.3%-13.3%) phases. The compositions of the spinel-ferrite (SP) phase in the investigated samples, S1-S3, are Zn0.72Ni0.24Fe1.98O4, Zn0.56Ni0.29Fe2.07O4 and Zn0.40Ni0.40Fe2.10O4, respectively. Due to the cation deficiency in spinels, created vacancies induce a partial change in the cation valence, Ni2+ - GT Ni3+. The vacancy distribution is found to be random at 8a and 16d cation sites, except in sample S3, where all vacancies are over octahedral sites. The x-ray line broadening due to crystallite size effect is found to be isotropic for all spinels, while the x-ray line broadening due to the strain effect is anisotropic. A correlation between the Zn2+ occupancy of the tetrahedral site and the 650 cm(-1) Raman peak intensities is shown. The observed coercivity decrease and shift in hysteresis loop in the samples are caused by the interaction between spinel and NiO phase. The results of M(H) measurements point to the properties of an ensemble of interacting nanoparticles. High saturation magnetization values and superparamagnetic behaviour at room temperature point to the technological significance of the title compounds

Optimization of photoluminescence of Y2O3:Eu and Gd2O3:Eu phosphors synthesized by thermolysis of 2,4-pentanedione complexes

Spherical shaped nanoparticles of series Y2-xEuxO3 (x = 0.06, 0.10, 0.20, and 2) and Gd2-xEuxO3 (x = 0.06, 0.10) were prepared by thermolysis of 2,4-pentanedione complexes of Y, Gd, and Eu. The bixbyite phase of Gd2-xEuxO3 samples was formed at 500 degrees C, whereas the thermal decomposition of Y and Eu complexes' mixtures occurred at higher temperatures. Linearity in the concentration dependence on lattice parameter confirmed the formation of solid solutions. The distribution of Eu3+ in Gd2-xEuxO3 was changed with thermal annealing: in the as-prepared sample (x = 0.10) the distribution was preferential at C-3i sites while in the annealed samples, Eu3+ were distributed at both C-2 and C-3i sites. Rietveld refinement of site occupancies as well as emission spectra showed a random distribution of cations in Y2-xEuxO3. The photoluminescence (PL) measurements of the sample showed red emission with the main peak at 614 nm (D-5(0)-F-7(2)). The PL intensity increased with increasing concentration of Eu3+ in both series. Infrared excitation was required to obtain good Raman spectra. The linear dependence of the main Raman peak wavenumber offers a non-destructive method for monitoring the substitution level and its homogeneity at the micron scale

HEBM synthesis of nanocrystalline LiZn0.5Ti1.5O4 spinel and thermally induced order-disorder phase transition(P4(3)32 - GT Fd(3)over-barm)

Nanocrystalline LiZn0.5Ti1.5O4 disordered spinel (S.G. Fd (3) over barm) was synthesized by high energy ball milling (HEBM). TEM analysis of the sample has shown that the particle size distribution is broad ranging from 10 to 60 nm. By X-ray line broadening analysis, the average apparent size of the crystallites is found to be 19(1) nm, while the average apparent strain is 26(4) x 10(-4). The cation distribution was found to be metastable, with Zn in octahedral 16d and Ti in tetrahedral 8a position, against their known site preference. After annealing the sample at 650 degrees C for 3 h and slow cooling down to room temperature, superstructure reflections (110), (210), (211) have been observed, indicating a cation ordering in the octahedral sublattice and a combined symmetry reduction (S.G. P4(3)32). The reverse symmetry change P4(3)32 - GT Fd (3) over barm caused by increasing the temperature was studied by in situ XRPD, DSC/DTA, Landaus theory of phase transitions and Raman spectroscopy. An analysis of the topology of the order parameter vector space indicates a biquadratic or linear-quadratic coupling between the order parameters Q(1) and Q(2). In LiZn0.5Ti1.5O4 dilatation expansion of crystal lattice as well as spontaneous strain values are rather small (order of 10(-4)), comparing to e.g. Li1.33xCo2-2xTi1+0.67xO4. (C) 2009 Elsevier B.V. All rights reserved