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Charge Compensation (charge + compensation)
Selected AbstractsHigh-saturation-current InGaAs/InAlAs charge-compensated uni-traveling-carrier photodiodePHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 13 2004Ning Li Abstract Charge compensation is utilized to reduce space charge compression in a photodiode. Here we demonstrate an InGaAs/InAlAs uni-traveling-carrier photodiode with a charge compensated InAlAs depletion layer. A bandwidth of 20 GHz and saturation current of 45 mA are demonstrated. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Theoretical studies of the spin Hamiltonian parameters and the local structure for the orthorhombic V4+ in CaYAlO4PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 6 2008Chuan-Ji Fu Abstract The spin Hamiltonian parameters (g -factors and the hyperfine structure constants) and the local structure for the orthorhombic V4+ in CaYAlO4 are theoretically studied from the perturbation formulas of these parameters for a 3d1 ion in orthorhombically distorted octahedra. Based on the present studies, this center is explicitly assigned to V4+ occupying the Al3+ site, associated with one next-nearest-neighbor Mg2+ replacing the host Al3+ (i.e. MgAl) in the ab -plane due to the charge compensation. Since the effective charge of the compensator is negative (,e), the ligand O2, intervening in the impurity V4+ and the MgAl would undergo a small displacement (,0.08 Å) towards the central ion because of the electrostatic repulsion. The local structure of this center can be described as elongation of the oxygen octahedron along the c- axis and the slight orthorhombic distortion in the perpendicular direction. The theoretical spin Hamiltonian parameters and the optical transitions based on the above local structure show reasonable agreement with the experimental data. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Voltage-activated proton currents in human lymphocytesTHE JOURNAL OF PHYSIOLOGY, Issue 1 2002Tom Schilling Voltage-activated proton currents are reported for the first time in human peripheral blood T and B lymphocytes and in the human leukaemic T cell line Jurkat E6-1. The properties of H+ currents studied using tight-seal voltage-clamp recording techniques were similar in all cells. Changing the pH gradient by one unit caused a 47 mV shift in the reversal potential, demonstrating high selectivity of the channels for protons. H+ current activation upon membrane depolarisation had a sigmoidal time course that could be fitted by a single exponential function after a brief delay. Increasing pHo shifted the activation threshold to more negative potentials, and increased both the H+ current amplitude and the rate of activation. In lymphocytes studied at pHi 6.0, the activation threshold was more negative and the H+ current density was three times larger than at pHi 7.0. Increasing the intracellular Ca2+ concentration to 1 ,m did not change H+ current amplitude or kinetics detectably. Extracellularly applied Zn2+ and Cd2+ inhibited proton currents, slowing activation and shifting the voltage-activation curve to more positive potentials. The H+ current amplitude was 100 times larger in CD19+ B lymphocytes and in Jurkat E6-1 cells than in CD3+ T lymphocytes. Following stimulation with the phorbol ester PMA, the H+ current density in peripheral blood T lymphocytes and Jurkat T cells increased. In contrast, the H+ current density of phorbol ester (PMA)-stimulated B lymphocytes was reduced and activation became slower. The pattern of expression of H+ channels in lymphocytes appears well suited to their proposed role of charge compensation during the respiratory burst. [source] Structural derivation and crystal chemistry of apatitesACTA CRYSTALLOGRAPHICA SECTION B, Issue 1 2003T. J. White The crystal structures of the [A(1)2][A(2)3](BO4)3X apatites and the related compounds [A(1)2][A(2)3](BO5)3X and [A(1)2][A(2)3](BO3)3X are collated and reviewed. The structural aristotype for this family is Mn5Si3 (D88 type, P63/mcm symmetry), whose cation array approximates that of all derivatives and from which related structures arise through the systematic insertion of anions into tetrahedral, triangular or linear interstices. The construction of a hierarchy of space-groups leads to three apatite families whose high-symmetry members are P63/m, Cmcm and P63cm. Alternatively, systematic crystallographic changes in apatite solid-solution series may be practically described as deviations from regular anion nets, with particular focus on the O(1),A(1),O(2) twist angle , projected on (001) of the A(1)O6 metaprism. For apatites that contain the same A cation, it is shown that , decreases linearly as a function of increasing average ionic radius of the formula unit. Large deviations from this simple relationship may indicate departures from P63/m symmetry or cation ordering. The inclusion of A(1)O6 metaprisms in structure drawings is useful for comparing apatites and condensed-apatites such as Sr5(BO3)3Br. The most common symmetry for the 74 chemically distinct [A(1)2][A(2)3](BO4)3X apatites that were surveyed was P63/m (57%), with progressively more complex chemistries adopting P63 (21%), P (9%), P (4.3%), P21/m (4.3%) and P21 (4.3%). In chemically complex apatites, charge balance is usually maintained through charge-coupled cation substitutions, or through appropriate mixing of monovalent and divalent X anions or X -site vacancies. More rarely, charge compensation is achieved through insertion/removal of oxygen to produce BO5 square pyramidal units (as in ReO5) or BO3 triangular coordination (as in AsO3). Polysomatism arises through the ordered filling of [001] BO4 tetrahedral strings to generate the apatite,nasonite family of structures. [source] Disordered structure of ZrW1.8V0.2O7.9 from a combined X-ray and neutron powder diffraction study at 530 KACTA CRYSTALLOGRAPHICA SECTION C, Issue 10 2009Xi Chen A novel compound, vanadium aliovalent substituted zirconium tungstate, ZrW1.8V0.2O7.9, was prepared with vanadium substituting tungsten rather than the common zirconium substitution. The structure of the high-temperature phase was refined from combined neutron and X-ray powder diffraction data gathered at 530,K. This phase is the disordered centric modification (space group Pa) and the average crystal structure is similar to that of ,-ZrW2O8. The V atom occupies only a W2 site and charge compensation is achieved through oxygen vacancy, i.e. the oxygen vacancy occurs at only the O4 site. [Atom names follow the established scheme; Evans et al. (1996). Chem. Mater.8, 2809,2823.] [source] New organically templated vanadium tellurites: (H2pn)[V2TeO8] (pn is propane-1,3-diamine)ACTA CRYSTALLOGRAPHICA SECTION C, Issue 10 2009Xihe Huang The title compound, poly[propane-1,3-diaminium hexa-,-oxido-dioxidotellurium(IV)divanadium(V)], (C3H12N2)[V2O8Te] or (H2pn)[V2TeO8] (pn is propane-1,3-diamine), contains a two-dimensional anionic layer and the diprotonated pn cation for charge compensation. The anionic layer consists of pyrovanadates and [TeO3] pyramids, which are linked alternately through corner-sharing to form a one-dimensional chain. These one-dimensional chains are crosslinked through two weak Te,O bonds, constructing an anionic layer. Hydrogen bonds are observed involving the diprotonated pn cation and the O atoms of the anionic framework. [source] Coordination behaviour and two-dimensional-network formation in poly[[,-aqua-diaqua(,5 -propane-1,3-diyldinitrilotetraacetato)dilithium(I)cobalt(II)] dihydrate]: the first example of an MII,1,3-pdta complex with a monovalent metal counter-ionACTA CRYSTALLOGRAPHICA SECTION C, Issue 6 2008Urszula Rychlewska The title compound, {[CoLi2(C11H14N2O8)(H2O)3]·2H2O}n, constitutes the first example of a salt of the [MII(1,3-pdta)]2, complex (1,3-pdta is propane-1,3-diyldinitrilotetraacetate) with a monopositive cation as counter-ion. Insertion of the Li+ cation could only be achieved through application of the ion-exchange column technique which, however, appeared unsuccessful with other alkali metals and the ammonium cation. The structure contains two tetrahedrally coordinated Li+ cations, an octahedral [Co(1,3-pdta)]2, anion and five water molecules, two of which are uncoordinated, and is built of two-dimensional layers extending parallel to the (010) lattice plane, the constituents of which are connected by the coordinate bonds. O,Hwater...O hydrogen bonds operate both within and between these layers. The crystal investigated belongs to the enantiomeric space group P21 with only one (,) of two possible optical isomers of the [Co(1,3-pdta)]2, complex. A possible cause of enantiomer separation during crystallization might be the rigidification and polarization of the [M(1,3-pdta)]2, core, resulting from direct coordination of Li+ cations to three out of four carboxylate groups constituting the 1,3-pdta ligand. The structure of (I) differs considerably from those of the other [MII(1,3-pdta)]2, complexes, in which the charge compensation is realized by means of divalent hexaaqua complex cations. This finding demonstrates a significant structure-determining role of the counter-ions. [source] Optimizing the formula of rare earth-bearing materials: A computational chemistry investigationINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 3 2007Marjorie Bertolus Abstract We present a computational investigation into the nature of bonds formed by rare earth elements (REE) in materials. This study focuses on the incorporation of neodymium in minerals called apatites, which are derived from fluorapatite: Ca10(PO4)6F2. These minerals, which allow many substitutions on all three Ca, P, and F sites, are considered as potential host phases for radioactive elements separated from nuclear waste. Nd and trivalent actinides have very similar physical and chemical properties, and Nd is not radioactive and much more easily handled. It is therefore very often used as a surrogate for actinides with oxidation degree three in experimental studies. Several formulas can be considered to substitute Nd3+ to Ca2+ and maintain charge balance of the apatite. Existing experimental and theoretical studies, however, mostly concern the Ca9Nd(PO4)5SiO4F2 formula, where the Nd incorporation is compensated by the replacement of one PO by a SiO group. Moreover, only the cation position has been studied, whereas the silicate position and its influence on stability are unknown. We present a more general investigation of possible charge compensations on the one hand, and of the various resulting configurations on the other. All possible configurations of the two formulas Ca9Nd(PO4)5 SiO4F2 and Ca8NdNa(PO4)6F2 have been considered. Calculations have been performed within the framework of density functional theory (DFT). A computation scheme that permits good accuracy in these systems within reasonable computation times is determined. The results obtained for cohesion energies, geometries, and electronic densities are discussed. As for the formulation, it is shown that the Ca8NdNa(PO4)6F2 formula is less stable than the fluorapatite, while Ca9Nd(PO4)5 SiO4F2 is more stable. For the structures, it is found that Nd substitutes preferably in the second cationic site. Moreover, the most stable structures exhibit the shortest Na,Nd or Nd,Si distances. Local charge balance therefore seems favorable. Then, it is shown that Nd forms covalent bonds both in apatite and in britholite, while Na forms ionic bonds. Finally, a first correlation between the material stability and the covalent character of the bonds formed is established. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source] | |||||||||||||