Impurity Ions (impurity + ion)

Distribution by Scientific Domains


Selected Abstracts


Characterization of Phase Separation and Thermal History Effects in Magnesium Silicate Glass Fibers by Nuclear Magnetic Resonance Spectroscopy

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2009
Jonathan F. Stebbins
Liquid,liquid immiscibility, leading to the separation of silica-rich and silica-poor domains, is a common phenomenon in binary silicate glasses, but can be difficult to detect and characterize when rapid cooling results in nano-scale domain dimensions. 29Si nuclear magnetic resonance (NMR) spectroscopy can be very useful for detecting such phase separation, because the exclusion of paramagnetic impurity ions from the silica-rich regions can greatly slow their spin-lattice relaxation rates. Properly designed experiments can therefore largely isolate the NMR signals from high-silica and low-silica domains, and thus provide information about their proportions, compositions, and short- to intermediate-range structures. We demonstrate this approach here for fiber glasses that are predominantly magnesium, or calcium-magnesium silicates, with minor contents of alumina. For bulk compositions within the known region of stable liquid immiscibility, phase separation occurs even when extremely rapid cooling yields fibers less than 1 ,m in mean diameter. Slower cooling increases the extent of separation, while the addition of small amounts of alumina reduces it. [source]


Phase Morphology in Electrospun Zirconia Microfibers

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2008
Erin Davies
Electrospinning of sol,gels has been used to produce zirconium-doped polymer microfibers from zirconyl chloride and poly(vinylpyrollidone) precursors. Calcination of these structures between temperatures of 370 and 930C resulted in the formation of zirconia nanograined microfibers whose diameters ranged from 1200 to 800 nm at the higher temperatures and whose average grain size ranged from 9 to 33 nm. X-ray diffraction analysis revealed varying amounts of monoclinic and tetragonal zirconia present in the fibers and established how this varied with calcination temperature and time. The tetragonal phase was shown to be unstable and disappeared on heating the material beyond around 750C. The amount of zirconia yielded from the precursor material was measured and was found to be consistently greater than the theoretical yield. Average grain size within the microfibers increased with increasing calcination temperature and is effectively doubled when a 10 kPa pressure was applied. The effect of pressure also results in the creation of new crystal structures within the nanofibers and, as with traditional zirconia processing, the addition of impurity ions was found to stabilize the tetragonal phase. [source]


EPR study of Ni distribution in LaNiy Co1,yO3 solid solutions (0 , y , 0.25)

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2008
S. Ivanova
Abstract The distribution of Ni in LaNiy Co1,yO3 solid solutions was examined by means of EPR spectroscopy. For the assignment of the EPR signals, La1,xSrx CoO3 oxides were used as reference for Co3+,Co4+ magnetic clusters. For the oxides heated at 600 C, the EPR spectra of LaNiy Co1,yO3 consist of a signal due to magnetic Ni clusters, while the oxides prepared at 700 C display an EPR signal due to ferromagnetic coupled Co3+ and Co4+ impurity ions that do not form magnetic clusters. LaNiy Co1,yO3 samples prepared at T > 700 C are EPR "silent". The effect of the preparation method and the preparation temperature on the formation of Ni clusters is discussed. ( 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Fully relativistic analysis of the absorption spectra of Ca3Sc2Ge3O12:Ni2+

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2006
M. G. Brik
Abstract Systematic analysis of the energy level schemes, ground state absorption (GSA) and covalency effects for the Ni2+ ion in Ca3Sc2Ge3O12 was performed. The recently developed first-principles approach to the analysis of the absorption spectra of impurity ions in crystals based on the discrete variational multi-electron method (DV-ME) [K. Ogasawara et al., Phys. Rev. B 64, 115413 (2001)] was used in the calculations. As a result, complete energy level schemes of Ni2+ and its absorption spectra at both possible crystallographic positions (distorted octahedral Sc3+ and tetrahedral Ge4+ positions) were calculated, assigned and compared with experimental data. Energies of the charge transfer (CT) transitions for both positions are estimated. Numerical contributions of all possible electron configurations into the calculated energy states were determined. By performing analysis of the molecular orbitals (MO) population, it was shown that the covalency of the chemical bonds between the Ni2+ and O2, ions increases in passing from the hexa- to the tetra-coordinated complex. ( 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]