Search results for "impur"
showing 10 items of 349 documents
Recycling of 3He from lung magnetic resonance imaging
2011
We have developed the means to recycle 3He exhaled by patients after imaging the lungs using magnetic resonance of hyperpolarized 3He. The exhaled gas is collected in a helium leak proof bag and further compressed into a steel bottle. The collected gas contains about 1–2% of 3He, depending on the amount administered and the number of breaths collected to wash out the 3He gas from the lungs. 3He is separated from the exhaled air using zeolite molecular sieve adsorbent at 77 K followed by a cold head at 8 K. Residual gaseous impurities are finally absorbed by a commercial nonevaporative getter. The recycled 3He gas features high purity, which is required for repolarization by metastability ex…
Co-doping with boron and nitrogen impurities in T-carbon
2020
Previously, Ren et al. [Chem. Phys. 518, 69–73, 2019] reported the failure of Boron-Nitrogen (B-N) co-doping as inter B-N bond in T-carbon. In present work, a B-N atom pair is introduced in T-carbon as p-n co-dopant to substitute two carbon atoms in the same carbon tetrahedron and form an intra B-N bond. The stability of this doping system is verified from energy, lattice dynamic, and thermodynamic aspects. According to our B3PW calculations, B-N impurities in this situation can reduce the band gap of T-carbon from 2.95 eV to 2.55 eV, making this material to be a promising photocatalyst. Through the study of its transport properties, we can also conclude that B-N co-doping cannot improve th…
Interaction Between Oxygen and Yttrium Impurity Atoms as well as Vacancies in fcc Iron Lattice: Ab Initio Modeling
2012
Synthesis of advanced radiation-resistant steels as construction materials for nuclear reactors, which contain the uniformly distributed yttria precipitates (ODS steels), is an important task for ecological security of nuclear plants. The initial stage of theoretical simulation on oxide cluster growth in the steel matrix is a large-scale ab initio modeling on pair- and triple-wise interaction between the Y and O impurity atoms as well as Fe vacancies, including their different combinations, in the paramagnetic face-centered-cubic (fcc) iron lattice. Calculations on the pair of Y atoms have shown that no bonding appears between them, whereas a certain attraction has been found between Y subs…
Mg impurity in helium droplets.
2011
Within the diffusion Monte Carlo approach, we have determined the structure of isotopically pure and mixed helium droplets doped with one magnesium atom. For pure 4He clusters, our results confirm those of M. Mella et al. [J. Chem. Phys. 123, 054328 (2005)] that the impurity experiences a transition from a surface to a bulk location as the number of helium atoms in the droplet increases. Contrarily, for pure 3He clusters Mg resides in the bulk of the droplet due to the smaller surface tension of this isotope. Results for mixed droplets are presented. We have also obtained the absorption spectrum of Mg around the 3s3p 1P_1 <-- 3s2 1S_0 transition.
Using the methods of radiospectroscopy (EPR, NMR) to study the nature of the defect structure of solid solutions based on lead zirconate titanate (PZ…
2014
The nature of intrinsic and impurity point defects in lead zirconate titanate (PZT) ceramics has been explored. Using electron paramagnetic resonance (EPR), nuclear magnetic resonance (NMR), and X-ray photoelectron spectroscopy (XPS) methods, several impurity sites have been identified in the materials, including the Fe 3+ -oxygen vacancy (VO) complex and Pb ions. Both of these centers are incorporated into the PZT lattice. The Fe 3+ -V paramagnetic complex serves as a sensitive probe of the local crystal field in the ceramic; the symmetry of this defect roughly correlates with PZT phase diagram as the composition is varied from PbTiO 3 to PbZrO 3 . NMR spectra 207 Pb in PbTiO 3 , PbZrO 3 ,…
Usability of Cr-Doped Alumina in Dosimetry
2019
Dosimetry is a widespread material science field dealing with detection and quantification of ionizing radiation using electronic processes in materials. One of the main aspects that determines the performance of dosimeters is the type of defects the material contains. Crystalline lattice imperfections are formed around impurity ions, which may have a smaller or larger size, or different oxidation states compared to host ions. In this study, we show what effects Cr impurities have on the luminescent properties of alumina. Porous Al 2 O 3 : Cr microceramics synthesized using the sol-gel method showed a higher thermoluminescence response than a single crystal ruby. We have found that Cr 2 O 3…
The nature of the defect structure of solid solutions based on lead zirconate titanate (PZT): Evidence from EPR and NMR
2013
The nature of intrinsic and impurity point defects in lead zirconate titanate (PZT) ceramics has been explored. Using electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) methods several impurity sites have been identified in the materials, including Fe3+-oxygen vacancy (VO) complex and Pb ions. Both of these centers are incorporated into the PZT lattice. The Fe3+-VO paramagnetic complex serves as a sensitive probe of the local crystalline field in the ceramic; the symmetry of this defect is roughly correlated with PZT phase diagram as composition is varied from PbTiO3 to PbZrO3. NMR spectra 207Pb in PbTiO3, PbZrO3 and PZT with iron content from 0 to 0.4 mol % showed t…
Atomic layer deposition and characterization of biocompatible hydroxyapatite thin films
2009
Abstract Atomic layer deposition (ALD) was used to produce hydroxyapatite from Ca(thd) 2 (thd = 2,2,6,6-tetramethyl-3,5-heptanedionato) and (CH 3 O) 3 PO onto Si(100) and Corning (0211). Film crystallinity, stoichiometry, possible impurities and surface morphology were determined. The as-deposited films contained significant amounts of carbonate impurities however, annealing at moist N 2 flow reduced the carbonate content even at 400 °C. The as-deposited Ca–P–O films were amorphous but rapid thermal annealing promoted the formation of the hydroxyapatite phase. Mouse MC 3T3-E1 cells were used for the cell culture experiments. According to the bioactivity studies cell proliferation was enhanc…
Density functional study of gold atoms and clusters on a graphite (0001) surface with defects
2006
Adsorption of gold atoms and clusters $(N=6)$ on a graphite (0001) surface with defects has been studied using density functional theory. In addition to perfect graphite (0001), three types of surface defects have been considered: a surface vacancy (hole), a pyridinelike defect comprising three grouped nitrogen atoms, and a substitutional doping by N or B. Results for Au and ${\mathrm{Au}}_{6}$ indicate that the surface vacancy can form chemical bonds with Au as the three nearby carbons align their dangling bonds towards the gold particle (binding energy 2.4--$2.6\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$). A similar chemically saturated holelike construction with three pyridinic N atoms resul…
Comparative Acoustic and Contact Studies of Elasticity of Ferroelectric LixNa1 - xTa0.1Nb0.9O3Solid Solutions at Nanometer Spatial Resolution
2009
Comparative acoustic and contact studies of elastic properties of the Li x Na 1−x Ta 0.1 Nb 0.9 O 3 (x = 0.015–0.135) ferroelectric solid solution ceramics are reported. A good agreement is obtained between the values of elastic modules determined by acoustic and contact methods at nano-scale spatial resolution.