[en] In recent years many synchrotron radiation facilities are built around the world. The properties of this radiation, it's intensity and tuneability, are leading to exciting new experiments in chemistry, physics, biology and material sciences. In X-ray crystallographic studies, data can be collected on very small samples of only a few microns in size and time as short as one millisecond. Other techniques allow us to probe the local structures of impurities in technologically important materials. In the present paper unique properties of synchrotron radiation will be described. X-ray diffraction (XRD) and X-ray Absorption Fine Structure (XAFS) spectroscopic techniques are now routinely used for materials characterization. X-ray Absorption Fine Structure (XAFS) spectroscopic techniques have been applied to study the local structural environment of host and dopant cations in complex systems. X-ray Absorption Near Edge Structure (XANES) spectroscopy is useful to determine the valence state of different cations. To examine the local structure around different cations Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy is the most appropriate technique. A review of these methodologies and the results on Yba/sub 2/ Cu/sub 3-x/ Sb/sub x/O/sub 7/, and SrFe/sub 1-x/ Nb/sub x/O/sub 3/ (where x = 0.0 and 0.5) will be presented. The Synchrotron light for Experimental Science and Applications in the Middle East (SESAME) is under construction in jordan, Pakistan in one of the member states of SESAME project, therefore a brief review of SESAME will be presented. (author)

[en] Solid state preparation method has been employed to prepare Ni/sub 1-x/ Cu/sub x/ Fe/sub 2/O/sub 4/ (where x=0.0-1.0). X-ray Absorption Spectroscopic (XAS) techniques have been employed to investigate the effects of dopants on the structural properties of these materials. X-ray Absorption Near Edge Structure (XANES) spectroscopy has been employed to investigate the valence state of Fe; whereas Extended X-ray Absorption Fine Structure (EXAFS) Spectroscopy was used to determine the effects of doping on the local structure around Fe in these materials. X-ray diffraction investigations of all the compositions confirm the formation of single-phase ferrite. The patterns are similar in the composition range 0.0-1.0. (author)

[en] A polycrystalline ceramic oxide La/sub 0.50/ Ca/sub 0.50/MnO/sub 3/ was synthesized using the powders of respective oxides by conventional solid-state reaction route. The single phase of the material has been confirmed using conventional XRD. Resistivity of the sample shows metal-insulator transition with increase in resistance at liquid nitrogen temperature with thermal cycling. Impedance studies have been carried out in the Frequency range of 1 x 10/sup 2/ Hz to 1 x 10/sup 7/ Hz at 77 K. An equivalent circuit model, R/sub 1/(R/sub 2/ C/sub 2/)(R/sub 3/C/sub 3/) i.e., a resistor-capacitor network, has been proposed to explain the impedance results. With time, grain boundary resistance increases, showing canted spin nature of the material. However, after 150 hours the grain boundary resistance becomes saturated, indicating that most of the metastable states have relaxed and transformed into stable charge ordered, most probably of antiferromagnetic nature. (author)

[en] X-ray Absorption Fine Structure (XAFS) spectroscopy is a powerful technique to investigate the local structural environment of different cations in complex materials. In the present study, XAFS spectroscopy has been employed to determine the local structural environment of bulk and nanosized spinel ferrites (ZnFe/sub 2/O/sub 4/ CuFe/sub 2/O/sub 4/ and NiFe/sub 2/O/sub 4/). XAFS data have been collected, at the Elettra Synchrotrone, Trieste, Italy, for the K-edges of Zn, Cu, Ni and Fe in transmission mode. These results show that for ZnFe/sub 2/O/sub 4/ the local structure changes when particles size is below 20 nm. However, when particle size > 26 nm the local structural environment of nanoparticles are identical to that of bulk ZnFe/sub 2/O/sub 4/. For CuFe/sub 2/O/sub 4/ and NiFe/sub 2/O/sub 4/ we do not observe any appreciable change in the local structural environment of bulk and nanoparticles. (author)

[en] Energy Dispersive X-ray diffraction (EDXRD) techniques are described for high pressure studies. A detailed structural investigation of high Tc ceramic oxides La/sub 2-x/(Ba,Sr)/sub x/CuO/sub 4/YBa/sub 2/Cu/sub 3/O/sub 7/, pure and doped BaBiO/sub 3/ and Bi/sub 2/Sr/sub 2/Ca/sub n-1/Cu/sub n/O/sub 4+2n/(n=1,2 and 3)) under high pressures using EDXRD techniques is reviewed. These materials show three different types of response to high pressures: (i) structure remain stable with isotropic compression (e.g. La/sub 2-x/(Ba,Sr) /sub x/CuO/sub 4/ and BaBiO doped with Pb and K), (ii) crystalline structural phase transformation (e.g., YBa/sub 2/Cu/sub 3/O/sub 7/ and Bi/sub 2/SR/sub 2/CuO ) and amorphization, where crystalline phase changes to non crystalline (e.g., Bi/sub 2/Sr/sub 2/Ca/sub 2/CuO/sub 8/ octahedral to square planar the structure becomes more unstable to pressure. (author)

[en] Atomistic simulation techniques have been applied to investigate the perfect and defect properties of ionic solid using the energy minimization procedures. First of all, potential parameters are derived to reproduce the crystal structure and lattice properties (lattice energy, elastic and dielectric constant). After deriving reliable potentials, defect energies are calculated using the two region approach based on the Mott-littleton approximation. The materials investigated are perovskite type, ABO/sub 3/ structured (SrTiO/sub 3/) and high T/sub c/ superconducting (La/sub 2/CuO/sub 4/) oxides. Among the properties considered are the fundamental isolated defects and defect structure associated with cation impurities. Solution and related defect energies are calculated for the dopant cations to be substituted at the lattice sites. From these energies we can predict the most favourable site to be occupied by the dopant ions in the host lattice and related defects for charge compensation mechanism. (author)

[en] The effects of partially replacing Mn with Fe ions in the La_0.85Ca_0.15MnO₃ system are reported. On replacing 5% of the Mn with Fe ions the system exhibits a transition to a re-entrant spin glass like phase with a ferromagnetic transition at 170 K and spin freezing transition at T∼100 K. The system remains insulating throughout both the ferromagnetic and glassy phases with however a sharp resistivity increase at low temperature (T∼150 K). The spin freezing temperature shifts upwards with increasing frequency and magnetic relaxation effects are observed. However conventional spin glass features such as a memory effect are not observed and the spin freezing temperature is relatively insensitive to applied magnetic fields

[en] The application of Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy for the study of local structural environment of different ions in a material is described. The technique is particularly useful for materials when parent compounds are doped with small amount of dopant impurities, because the local environment of individual atomic species can be determined. EXAFS results of Nb/sub 5+/ doped alkaline earth ferrates (BaFe/sub 1-x/Nb/sub x/O/sub 3/ and SrFe/sub 1-x/Nb/sub x/O/sub 3/) are illustrated as a example. These results show that the local environment of the dopant ion is different from that of the host atoms. This variation in local structure depends on the concentration of the dopant ion. The Fe-O bond lengths increase as the concentration of the dopant ion (Nb/sup 5+/) is increased. However, the Nb-O bond lengths do not vary significantly with the Nb/sup 5+/ concentration, indicting that the dopant local environment is independent of its concentration. In the case of BaFe/sup 1-x/Nb/sub x/O/sub 3/ a local structural change was observed around the Fe. (author)

[en] X-ray absorption spectroscopy is an ideal technique the local environment of different cations in electronic ceramic oxides by virtue of its inherent chemical selectivity and sensitivity to impurity species. In this study x-ray absorption near edge structure and extended x-ray absorption fine structure spectroscopy measurements have been employed to determine the valence state and local environment of different cations in high Tc-superconducting and toxic gas sensor ceramic oxides, using synchrotron radiation as x-ray source. The materials studied include pure and doped (Pb,K) BaBiO/sub 3/, Bi/sub 2/Sr/sub 2/Ca/sub n-1/Cu/sub n/O/sub 2n+4/, La/sub 2-x/(Ba,Sr)/sub x/CuO4, Nd/sub 2-x/Ce/sub x/CuO/sub 4/5+ and Nd/sup 5+/ doped alkaline earth ferrates (SrFeO/sub 3/ and BaFeO/sub 3/). XANES spectroscopy has been used to determine the valence state of Bi, Pb and Cu in these materials. The valence state of Bi and Pb in pure and doped BaBiO/sub 3/ is close to (IV). In Bi based cuprate superconductors the formal valence states of Bi and Cu are slightly higher than their stoichiometric values of (III). EXAFS spectroscopy has been applied to determine the local structural ordering values of (III) and (II). EXAFS spectroscopy has been applied to determine the local structural ordering in these materials. These results show that local environment of dopant and host cations are different. This vibration in local structure depends on the concentration of the dopant ions. (author) 4 figs.; 24 refs

[en] Glyphosate (GLX) is a crucial organophosphonate herbicide applied to eliminate unwanted, grasses and herbaceous plants in various vegetation management situations. Its widespread and consequently application is causing environmental pollution, there is a need to remove it from the environment using an eco-friendly and cost-effective method. Biodegradation is an effective method for the removal of GLX. But various environmental factor effecting is degradation after its applications such as aerobic and anaerobic environment, different pH and temperature, soil water contents and soil textures. Glyphosate resistant bacterial strains have been isolated from GLX-contaminated soil which were proficient to utilize GLX as a carbon source. High Pressure Liquid Chromatography instrument was used to determine the rate of GLX biodegradation in liquid media and soil under different environmental conditions. The five out of eleven strains such as WAG2 (Serratia liquefaciens), WAG4 (Klebsiella variicola), WAG45 (Enterobacter cloacae), WAG9 (Pseudomonas aeruginosa), and WAG11 (Enterobacter ludwigii) were proficient in average degraded 95 to 98 mg kg-1 glyphosate in soil followed by liquid media 93 to 96 mg kg-1 within 28 days of incubation in different environmental factors. The optimal circumstances for the degradation of GLX were found to be aerobic, pH 7, 40 degree C, soil water content at 10% and sandy loam texture showed maximum degradation at 100 mg kg-1 compared to 200 mg kg-1 concentration of GLX. This study demonstrates the potential of isolated bacterial strains for efficient degradation of GLX, which can be exploited for remediation of GLX in contaminated soil. (author)