Zein K. Heiba

X-ray structure and microstructure determination of the mixed sesquioxides (Eu1-xYbx)2O3 prepared by a sol-gel process

Polycrystalline samples of (Eu1−xYbx)2O3 (x = 0.0, 0.1, 0.2, 0.5, 0.8, 0.9 and 1.0) were synthesized by a sol–gel process. X-ray diffraction data were collected and the crystal structures were refined by the Rietveld method. All samples are found to have the same crystal system and formed solid solutions over the whole range of x. The lattice parameters are found to vary linearly with the composition x. The cationic distribution over the two non-equivalent sites 8b and 24d of the space group Ia{\bar 3} is found to be random in the range 0.0 < x ≤ 0.5 and preferential in the range 0.5 < x ≤ 1.0. Replacing Eu3+ and Yb3+ by each other introduces slight changes in the atomic coordinates. Crystallite size and microstrain analysis are performed on single and multiple orders for each sample using profile fitting and the Warren–Averbach method. The obtained values of microstrain are correlated with the distribution of the rare earth (RE) ions over the two cationic sites of the structure. The average crystallite size ranges from 35 to 96 nm and the mean-square strain from 0.052 to 0.225 × 10−2.

Structure and microstructure characterization of the mixed sesquioxides (Gd1−xYbx)2O3 and (Gd1−xHox)2O3 prepared by sol–gel process

Polycrystalline samples of (Gd 1-x Yb x ) 2 O 3 and (Gd 1-x HO x ) 2 O 3 (0.0 ≤ x ≤ 1.0) were synthesized by a sol-gel process. X-ray diffraction data were collected and crystal structure and microstructure analyses were performed using the Rietveld refinement method. All samples were found to have the same crystal system and formed solid solutions over the whole range of x. For the system (Gd 1-x HO x ) 2 O 3 , the cationic distribution over the two non-equivalent sites 8b and 24d of the space group Ia3 were found to be random for all values of x. For (Gd 1-x Yb x ) 2 O 3 , the distribution is random in the range 0.0 < x ≤ 0.5 and preferential in the range 0.5 < x ≤ 1.0. The lattice parameters are found to vary linearly with the composition x. Replacing Gd 3+ and Yb 3+ , or Gd 3+ and Ho 3+ , by each other introduces slight changes in relative atomic coordinates. Crystallite size and microstrain analyses were performed along different crystallographic directions and both are found to vary anisotropically with the composition parameter (x). The obtained values of microstrain are correlated with the distribution of the rare earth ions over the two cationic sites of the structure. The average crystallite size ranges from 45 to 144 nm and the root mean square (r.m.s.) strain from 0.018 to 0.409 × 10 -2 .

Synthesis and characterization of highly conductive charge-transfer complexes using positron annihilation spectroscopy.

Molecular charge-transfer complexes of the tetramethylethylenediamine (TMEDA) with picric acid (Pi-OH), benzene-1,4-diol (QL), tin(IV) tetrachloride (SnCl(4)), iodine, bromine, and zinc chloride (ZnCl(2)) have been synthesized and investigated by elemental and thermal analysis, electronic, infrared, Raman and proton-NMR, energy-dispersive X-ray spectroscopy, X-ray powder diffraction and positron annihilation lifetime spectroscopy, and scanning electron microscopy. In this work, three types of acceptors π-acceptors (Pi-OH and QL), σ-acceptors (iodine and bromine), and vacant orbital acceptors (SnCl(4) and ZnCl(2)) were covered. The results of elemental analysis indicated that the CT complexes were formed with ratios 1:1 and 1:2 for QL, SnCl(4), and ZnCl(2) acceptors and iodine, Pi-OH, and Br(2) acceptors, respectively. The type of chelating between the TMEDA donor and the mentioned acceptors depends upon the behavior of both items. The positron annihilation lifetime parameters were found to be dependent on the structure, electronic configuration, and the power of acceptors. The correlation between these parameters and the molecular weight and biological activities of studied complexes was also observed. Regarding the electrical properties, the AC conductivity and the dielectric coefficients were measured as a function of frequency at room temperature. The TMEDA charge-transfer complexes were screened against antibacterial (Escherichia coli, Staphylococcus aureus, Bacillus subtilis, and Pseudomonas aeruginosa) and antifungal (Aspergillus flavus and Candida albicans) activities.

Development of 100% lattice match buffer layers on RABiTS Ni tapes by sol-gel

Gd/sub 2/O/sub 3/-Yb/sub 2/O/sub 3/ and Gd/sub 2/O/sub 3/-Ho/sub 2/O/sub 3/ mixed RE oxides were used to produce buffer layers with a perfect lattice match with superconducting layer. Since these RE oxides are 100% miscible in each other, pseudocubic lattice parameter of the buffer layers can be modified by changing the ratio of components to perfectly match with any superconducting RE-123. Texture and the microstructure of the buffer layers were studied by XRD, Pole Figure and ESEM.

Structural and anisotropic thermal expansion correlation of Li2ZrO3 at different temperatures

Structural and thermal expansion studies of Li2ZrO3 were carried out by recording X-ray powder diffraction patterns at five temperatures, 82, 198, 300, 423 and 573 K. The Rietveld refinement method was used for the analysis. There were large anisotropic changes in the lattice parameters as a function of temperature, slight changes in the fractional coordinates of the different atoms, and anisotropic changes in the interatomic distances between the different cations. The correlation of these anisotropies with the structure is considered.

Y-and Yb-123 coated conductor development by PLD and sol-gel on (Gd/sub 1-x/Er/sub x/)/sub 2/O/sub 3/ buffered Ni tapes

YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// and YbBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// layers were coated by sol-gel and PLD on Gd/sub 1.91/Er/sub 0.09/O/sub 3/ (100% lattice match with Y- and Yb-123) textured buffer layer on Ni substrates. Different thickness of buffer layers and superconducting layer were tried to see the thickness effect on superconducting properties. Buffer layers were prepared with different lattice parameters for Y-123 and Yb-123. Coated conductors were characterized by means of XRD, ESEM and T/sub c/ and J/sub c/ measurement. Since the perfect lattice match can be achieved between buffer layer and superconducting layer, texture of superconducting film was improved, and consequently critical current density of Y- and Yb-123 were improved.

The effect of the partial substitution of sulfur on the structural and microstructural properties of selenium

.These discrepancies are being discussed in terms of the peak shifts in both the amorphous andcrystalline state, the percentage of sulfur compositional variations, and finally in terms of theprobable site occupancy of the sulfur atoms in the selenium structure.

Effect of partial substitution of Cr or Mn for Ga or Fe on crystal-structure and microstructures of GaFeO3

Gallium iron oxide GaFeO 3 and the substituted GaFeO 3 with Cr and Mn, i.e., Ga(Fe 0.95 M e 0.05 )O 3 , and (Ga 0.95 M e 0.05 )FeO 3 ; M e =Cr and Mn, have been synthesized and investigated by X-ray powder diffraction. The refined structural parameters of the considered samples using the Rietveld technique showed a considerable distortion in the polyhedron around different cations, which may have an effect on the piezoelectricity of the studied samples. There are also changes in the interatomic distances between different cations, which may have a direct influence on the ferromagnetic properties of the samples. Crystallite size and microstrain are anisotropic and the largest along the b axis, which may be responsible for the piezoelectricity. The correlations between all these changeable parameters will be discussed.

Optical and Structural Characteristics of CdSe/PMMA Nanocomposites

Abstract Nanocomposites of polymethylmethacrylate (PMMA) and CdSe were fabricated by a casting technique. The result showed that CdSe@PMMA can be used in white and green light emitting devices. 0.01CdSe@PMMA exhibits monochromatic green color emission with the highest fluorescent quantum yield and lowest optical band gap value, while CdSe@PMMA with other ratios shows a multicolor emission. The band-edge emits in the vicinity of 280 – 296 nm but a more stable intensive green color emission at 553 nm is found for 0.01CdSe@PMMA. The change in Eg (4.18 to 4.4) eV values is due to the interaction between the PMMA polymer and CdSe.

Crystal Structure Determination and Biological Activity of C20H20O6 and C19H16O6Br2 (abstract)

Crystal structures for methyl 2‐(3‐(3,4‐dimethoxyphenyl)‐1‐1oxopropan‐2‐yl) benzoate (C20H20O6) and methyl 4‐bromo‐3‐(2‐bromo‐4,5‐dimethoxyphenyl)‐1‐oxoisochroman‐4‐carboxylate (C19H16O6Br2) were prepared and characterized by single‐crystal x‐ray diffraction technique to establish their three‐dimensional structures. Both were crystallized from acetone by a slow evaporation method. The results showed that the first crystal (C20H20O6) is monoclinic with space group P21, lattice parameters a = 7.8839 (4)A, b = 8.1087 (4)A, c = 14.4840 (10)A, β = 97.447 (2)°, V = 918.13 (9)A3, Z = 2, and Dx = 1.289 g/m3. The final discrepancy factor is R = 0.034 for 2,917 significant reflections. The second crystal (C19H16O6Br2) is monoclinic with space group P21/c, lattice parameters 20.1043 (7)A, b = 8.7046 (2)A, c = 11.0497 (3)A, β = 97.0923 (11)°, V = 1918.90 (10)A3, Z = 4, and Dx = 1.690 g/m3. The final discrepancy factor is R = 0.064 for 9,619 significant reflections. Projection of structure, connectivity of the molecul...