Showing papers on "Ionic radius published in 1990"
TL;DR: In this article, Li1+xMxTi2−x(PO4)3 systems with various metal ions of M3+ (M=Al, Cr, Ga, Fe, Sc, In, Lu, Y, or La) were prepared, and their properties were investigated.
196 citations
TL;DR: In this paper, a synthetic goethite prepared under highly alkaline conditions incorporates Co3+, Ni2+, Cu2+, Zn2+, Cd2+, and Pb4+ into its structure by isomorphous substitution.
159 citations
TL;DR: In this paper, the phase relationships in the CuO-rich region of these ternary diagrams progressively change from the La system through the Nd, Sm, Eu, Gd, Y, Ho systems to the Er system.
129 citations
TL;DR: Results indicate that the single Ca(II) site of the Escherichia coli receptor for D-galactose and D-glucose selects metal ions on the basis of both charge and size.
Abstract: The molecular mechanisms by which protein Ca(II) sites selectively bind Ca(II) even in the presence of high concentrations of other metals, particularly Na(I), K(I), and Mg(II), have not been fully described. The single Ca(II) site of the Escherichia coli receptor for D-galactose and D-glucose (GGR) is structurally related to the eukaryotic EF-hand Ca(II) sites and is ideally suited as a model for understanding the structural and electrostatic basis of Ca(II) specificity. Metal binding to the bacterial site was monitored by a Tb(III) phosphorescence assay: Ca(II) in the site was replaced with Tb(III), which was then selectively excited by energy transfer from protein tryptophans. Photons emitted from the bound Tb(III) enabled specific detection of this substrate; for other metals binding was detected by competitive displacement of Tb(III). Representative spherical metal ions from groups IA, IIA, and IIIA and the lanthanides were chosen to study the effects of metal ion size and charge on the affinity of metal binding. A dissociation constant was measured for each metal, yielding a range of KD's spanning over 6 orders of magnitude. Monovalent metal ions of group IA exhibited very low affinities. Divalent group IIA metal ions exhibited affinities related to their size, with optimal binding at an effective ionic radius between those of Mg(II) (0.81 A) and Ca(II) (1.06 A). Trivalent metal ions of group IIIA and the lanthanides also exhibited size-dependent affinities, with an optimal effective ionic radius between those of Sc(III) (0.81 A) and Yb(III) (0.925 A). The results indicate that the GGR site selects metal ions on the basis of both charge and size.(ABSTRACT TRUNCATED AT 250 WORDS)
95 citations
TL;DR: In this article, rare earth (Nd, Sm, Er, Yb, Sc)-doped zirconia was melted using an arc-imaging furnace, and rapidly quenched with a hammer and anvil apparatus (cooling rate >105 K sec−1).
Abstract: Rare-earth (Nd, Sm, Er, Yb, Sc)-doped zirconia was melted using an arc-imaging furnace, and rapidly quenched with a hammer and anvil apparatus (cooling rate >105 K sec−1). These ZrO2-RO1.5 samples were investigated by X-ray diffraction and transmission electron microscopy. The existing region of metastable tetragonal zirconia is from 2 to 14 mol% of RO1.5 regardless of the species of dopants, RO1.5. In the lattice parameters of the tetragonal phases, the unit cell volume corresponds to the ionic radii of dopants, whereas the tetragonality (c/a) is independent of the species of dopants, but dependent on the content of dopants.
87 citations
TL;DR: For the main group elements in their highest oxidation state, this article showed that a scale of Lewis acid strenght derived from observed structures correlates with the scale of electronegativity derived from electron energies in the free atom.
Abstract: For main group elements in their highest oxidation state we show that a scale of Lewis acid strenght derived from observed structures correlates with a scale of electronegativity derived from electron energies in the free atom. If the bonding geometry is also explicitly taken into account the same correlation holds for the same atoms in their next lower oxidation state. Although the two scales are conceptually quite distinct they correlate because both have a similar dependence on the screened nuclear charge and the ionic radius
77 citations
TL;DR: In this article, the rate of ion transfer across the polarized nitrobenzene/water interface has been determined for twelve homologous alkylammonium ions by using phase-selective ac polarography.
60 citations
TL;DR: In this article, the thermodynamic properties of double oxides in rare earth transition metal (V and Mn)-oxygen ternary systems have been collected and evaluated to examine their stability using chemical potential diagrams plotted as log (αA/αB) vs log (P(O2)).
Abstract: The thermodynamic properties of double oxides in rare earth-transition metal (V and Mn)-oxygen ternary systems have been collected and evaluated to examine their stability using chemical potential diagrams plotted as log (αA/αB) vs log (P(O2)). The thermodynamic regularities of perovskites, pyrochlores, and other compounds have been discussed in terms of the effective ionic radii across a series of rare earths. The obtained regularities have been used to estimate tentatively the thermodynamic properties of some rare-earth vanadium and manganese oxides.
59 citations
TL;DR: The existence and ionic conductivity of Na3ln2(PO4)3 with Nasicon-like structure have been investigated and the results compared with literature data as mentioned in this paper.
Abstract: The existence and ionic conductivity of solid solutions Na1+xM
x
III
Zr2−x(PO4)3 with Nasicon-like structure have been investigated and the results compared with literature data. A limited range of solid solutions is formed with MIII = aluminium, gallium, yttrium, ytterbium, whereas a continuous series is obtained for MIII = chromium, iron, scandium, indium. The pure end member Na3ln2(PO4)3 is reported for the first time; according to powder diffraction data, it is hexagonal witha = 0.8966(1) andc = 2.2104(4) nm. The small monoclinic distortion already known for MIII = chromium, iron and scandium is restricted tox values very close to 2. Ionic conductivity measurements show that for a given value ofx, the mobility of the Na+ ions is strongly influenced both by the ionic radius and the type of electronic structure of the MIII ion. However, no simple correlation can be found.
58 citations
TL;DR: In this paper, the effect of Pr substitution in suppressing T c in LaCaBaCu 3 O 7− d and Y 0.8 Ca 0.2 Ba 2 Cu 3 O 6+ d has been studied.
Abstract: The effect of Pr substitution in suppressing T c in LaCaBaCu 3 O 7− d and Y 0.8 Ca 0.2 Ba 2 Cu 3 O 6+ d has been studied. Infrared spectroscopy and a model based on ionic radii considerations were used to examine the location of Pr ions and the influence of Pr and Ca ions on hole localisation on chains and planes. For this purpose the series PrBa 2− x Ca x Cu 3 O 7− d was also studied. The main conclusions are that Pr ions play a role in suppressing T c by exchange scattering, and to some extent by the hole filling mechanism involving the formation of Pr 4+ . The Pr ions in La 1− x Pr x CaBaCu 3 O 7− d exist in both the Y and Ba sites. The magnitude of the resistivity at the insulator-metal transition for the polycrystalline samples is consistent with an anisotropic superconductor in which superconductivity accompanies metallisation. The rate of suppression of T c is similar to that of Y 1− x Pr x Ba 2 Cu 3 O 7− d but it is suggested that a percolation model may explain the results more adequately than the Abrikosov-Gorkov theory.
56 citations
TL;DR: The crystal structure refinements of Sr3(PO4)2 [a=53901(8), c=19785(5)A; space group R-3m] and Ba3PO42 as discussed by the authors have been carried out by means of the single-crystal diffraction data and the final R(Rw) factors have been converged to 00299 (00309) and 00296 (00335), respectively.
Abstract: The crystal structure refinements of Sr3(PO4)2 [a=53901(8), c=19785(5)A; space group R-3m] and Ba3(PO4)2 [a=56038(7), c=21000(5)A; space group R-3m] have been carried out by means of the single-crystal diffraction data and the final R(Rw) factors have been converged to 00299 (00309) and 00296 (00335), respectively The rod sequence of coordination polyhedra, PO4–M(2)O10–M(1)O12–M(2)O10–PO4, where M = Sr or Ba, is characteristic in these structures The M(1)O12 and M(2)O10 polyhedra show smaller distortion with increase in the ionic radius of the constituent elements
TL;DR: In this article, the electron-phonon coupling constants of the bending and stretching vibrations of the apex oxygen in RBa 2 Cu 3 O 7−δ were determined by Raman scattering.
TL;DR: In this article, the Raman spectra were measured on pyrochlore and fluorite-type Zr2Gd7 (x = 0.50) in the system (1−x)ZrO2−xGdO 1.5 and structure refinements were carried out for both structure types with a composition of x=0.43 by means of single crystal X-ray diffraction.
TL;DR: In this article, the superconducting transition temperature, T c, was measured for the 2212-phase BiSr-Ca-Cu-O compounds with varying a rare-earth atom (R) which was partially substituted for Ca by 20% to optimize hole concentrations and T c.
Abstract: The superconducting transition temperature, T c , was measured for the 2212-phase Bi-Sr-Ca-Cu-O compounds with varying a rare-earth atom (R) which was partially substituted for Ca by 20% to optimize hole concentrations and T c . We found that T c was varied systematically with the ionic radius of the rare earth; T c was increased with decreasing the ionic radius. These results are compared with the results in the RBa 2 Cu 3 O 7 system, which has a double pyramidal layer structure similar to that of the 2212-phase BSCCO.
TL;DR: The results support the alternative conjecture, that the relative insensitivity of the longitudinal waves to temperature is a characteristic of oxygen-bearing minerals at high pressure.
Abstract: Many-body effects in the binding energy of oxides can be incorporated efficiently in empirical Hamiltonians by including terms that describe the response of the ionic charge density to the crystalline environment. It is assumed that the effect of the ionic response on interionic interactions is completely characterized by the dependence of the ionic radius on the crystal field, which in turn is given by the positions of all the ions in the system. The model is particularly suitable for oxides, where the field is necessary to stabilize the ${\mathrm{O}}^{2\mathrm{\ensuremath{-}}}$ ion. This scheme has allowed ab initio electron-gas models to predict elasticity and phase transitions in oxides. Here we propose simple parametric expressions for the dependence of the ionic radius on the crystal field, and the dependence of the energy on the former. By parametrizing the Hamiltonian, and solving for harmonic phonon spectra without approximations, we obtain accurate volume-dependent thermodynamic properties at the experimentally accessible range of pressure and temperature. Predictions of thermoelastic properties at conditions beyond experimental capabilities are readily obtained. Of particular interest is our finding that the sensitivity of the compressibility to temperature decreases significantly at high compressions. Reduction of thermal effects at high pressures is plausible from a theoretical standpoint. However, the only physical manifestation of our prediction comes from the geophysical data on the Earth's interior. Seismic studies find that the transverse-acoustic velocity in the Earth's oxide mantle is significantly more sensitive to temperature than the longitudinal velocities. Partial melting has been suggested for reconciling this observation with the behavior of relevant minerals under laboratory conditions. Our results support the alternative conjecture, that the relative insensitivity of the longitudinal waves to temperature is a characteristic of oxygen-bearing minerals at high pressure.
TL;DR: YbBa2Cu3O7−δ with a Tc (zero-resistance) of 89K has been prepared without contamination of Yb2BaCuO5 as mentioned in this paper.
TL;DR: In this article, the conductivity of a series of alkali metal ions such as Li +, Na +, K +, Rb +, and Cs + is measured, and the results are summarized with the reduced temperature (T - T g: T g=glass transition temperature ) to neutralize the effect of segmental motion on the relative conductivity.
TL;DR: Raman spectra have been measured on carefully synthesized and characterized sesquisulfides of the rare earth ions plus yttrium and scandium as mentioned in this paper, and six structure types are represented.
TL;DR: In this article, the optical properties of the system CaF2:Eu2+ to Mn2+ have been analyzed in order to obtain a better characterisation of optical properties.
Abstract: The optical properties (emission, excitation and lifetime data) of CaF2 slightly contaminated with Eu2+ and Mn2+ ions have been analysed in the present investigation. The optical properties of the systems CaF2:Eu2+ and CaF2:Mn2+ have also been studied in order to obtain a better characterisation of the optical properties of the CaF2:Eu:Mn phosphor material. The spectroscopic data obtained clearly indicate that energy transfer from the donor Eu2+ ions to the acceptor Mn2+ ions takes place in CaF2 even at the very low impurity concentrations employed in the authors' samples, suggesting therefore that the impurities are not randomly distributed in the lattice but rather occur as impurity clusters of Eu2+ to Mn2+. Some insight into the possible nature of the impurity complexes as well as of the Eu to Mn energy transfer mechanism taking place inside them were gathered with the help of Dexter's theory for energy transfer phenomena. The results presented in this paper give support to the ionic radius criterion proposed by Rubio et al. (1985-9) to predict impurity pairing in a solid material.
TL;DR: In this article, the lattice parameters, resistivity and Cu-K absorption spectra were measured for the rare Earth (RE) ionic radius scales linearly with lattice parameter, but also with the superconducting transition temperature and with the position of the CuK absorption edge.
TL;DR: In this article, the parameters of the pair potentials have been obtained from MO calculation by using a 3-21 G basis set, and the difference in predominant position of the cations with respect to the neighbouring anion may be explained in terms of the differences in the ionic radii of cations, and some dynamic properties such as selfdiffusion and rotational motion of the anion are also discussed in relation to the structures.
Abstract: Molecular dynamics simulation of molten Li2CO3 and Na2CO3 has been performed. The parameters of the pair potentials have been obtained from MO calculation by using a 3–21 G basis set. Comparison of structure of Li2CO3 with Na2CO3 reveals that the difference in predominant position of the cations with respect to the neighbouring anion may be explained in terms of the difference in the ionic radii of the cations. Some dynamic properties such as self-diffusion and rotational motion of the anion are also discussed in relation to the structures.
TL;DR: Strontium and barium l-aspartate are obtained by neutralization of aqueous solutions of l -aspartic acid with strontium or barium hydroxide, respectively, and the crystal structure of the two compounds has been determined by single crystal X-ray diffraction as mentioned in this paper.
Abstract: Strontium and barium l-aspartate are obtained by neutralization of aqueous solutions of l-aspartic acid with strontium or barium hydroxide, respectively. Slow crystallization from hot water affords the crystalline trihydrates, saturated solutions of which show pH values of 11.0 and 10.8 at ambient temperature. – The crystal structure of the two compounds has been determined by single crystal X-ray diffraction. The compounds are isomorphous (orthorhombic, space group P212121), and the structural parameters are very similar as expected from the small differences in the ionic radii of the two metals. – The cations are arranged in double strings parallel to the b axis. The l-aspartate dianions are bridging these double strings by chelating contacts of the two carboxylate groups with the metal atoms of different strings to give layers. While the α-carboxylate groups are only bidentate and associated with one metal atom each, the β-carboxylate oxygen atoms are also each bridging two adjacent metals of the neighbouring string. The three water molecules are all coordinated to the metal atoms, which attain coordination number 9. The amino groups are not engaged in metal coordination, but are part of a system of hydrogen bonds cross-linking the layers.
01 Apr 1990
TL;DR: In this paper, the self-diffusion coefficients of acetonitrile, methanol and ions in salt free acetitrile-methanol mixtures and in solutions of NaI have been measured at 25°C for the whole composition range of the binary solvent, for the salt molarity ranging from 1· 10−4 to 1 · 10−2.
Abstract: The self-diffusion coefficients of acetonitrile, methanol and ions in salt free acetonitrile-methanol mixtures and in solutions of NaI have been measured at 25°C for the whole composition range of the binary solvent, for the salt molarity ranging from 1 · 10−4 to 1 · 10−2. The limiting self-diffusion coefficients of sodium and iodide ions increase monotonously with increasing concentration of acetonitrile. The composition dependences of the ionic radii allow to postulate a preferential solvation of iodide ions by acetonitrile. That phenomenon has been found for those compositions of the mixed solvent, for which a microheterogeneity of the system has been observed. In methanol rich solvents (xAN < 0.5) the observed microheterogeneity results from the self-association of methanol. The preferential solvation of iodide ions causes an enlargement of acetonitrile aggregates resulting in enhancement of microheterogeneity of the system. These results confirm a hypothesis that if interactions between ions and components of the mixed solvent are similar the preferential solvation of ions is promoted by the structure of solvent.
TL;DR: In this paper, a systematic investigation of the direct synthesis of several quarternary compounds of the form MgMeAl 10 O 17 in which Me is a divalent cation, was carried out.
TL;DR: In this article, the stability of metastable tetragonal (mt)-ZrO2 particles depends on the Young's modulus of the SiO2 matrix and transition metal oxides existing on the interface.
Abstract: ZrO2-SiO2 (1∶1) mixtures and ZrO2 particles were prepared by a sol-gel method from the solutions of ZrOCl2·8H2O (ZOC) + Si(OC2H5)4 (TEOS) + C2H5OH and ZOC + C2H5OH + H2O + NH4Cl systems, respectively. Quantitative changes of phase crystallized by heating were compared with those of ZOC + TEOS + H2O and/or ZrO(NO3)2 · 2H2O + H2O systems, respectively. The stability of metastable tetragonal (mt)-ZrO2 particles depends on the Young's modulus of the SiO2 matrix. Transition metal oxides existing on the interface assisted in stabilizing mt-ZrO2. The order of the assistance agreed with that of the relative field strengths of their oxides. A relationship between the ionic radius and the volatility of anionic groups, and the difficulty of nucleation for the martensitic transformation accompanying a shear stress, is suggested.
TL;DR: In this article, the formation mechanisms of M-type calcium ferrite were further assessed by doping Y2O3, BaCO3 and SrCO3, and it was found that the ionic radius, rather than the valence, is the predominant factor in the formation of the magnetoplumbite phase of calcite, and the defect structures based on substitution of Ca2+ by La3+, the charge compensation by Fe2+, and release of oxygen were supported by DTA-TGA and conductivity data.
Abstract: The formation mechanisms of M-type calcium ferrite were further assessed by doping Y2O3, BaCO3 and SrCO3. It was found that the ionic radius, rather than the valence is the predominant factor in the formation of the magnetoplumbite phase of calcium ferrite. The CaO/sd2Fe2O3 phase which played a precursor role in the formation of the M-type calcium ferrite was further verified. The defect structures based on the substitution of Ca2+ by La3+, the charge compensation by Fe2+, and release of oxygen were supported by DTA-TGA and conductivity data. The conductivity was assumed to, occur through a hopping mechanism as it increased with increasing temperature. The estimated values of the activation energy based on the small-polaron conduction were 0.35 to 0.40 eV in the high temperature region and 0.027 to 0.054 eV in the low temperature region. Moreover, the preexponential factor in the conductivity equation is an exponential function of the fraction of the M phase in the specimen.
Patent•
25 Jan 1990
TL;DR: In this article, a monocrystalline lanthanum orthogallate is described in the form of a single crystal of a size greater than 1 cm in diameter/width and at least 10 cm in length.
Abstract: Monocrystalline lanthanum orthogallate compositions grown along a predetermined crystallographic direction in the form of a single crystal of a size greater than 1 cm in diameter/width and at least 10 cm in length are described. Such compositions include mixed crystal monocrystalline lanthanum orthogallates wherein a portion of the lanthanum is replaced with a rare earth element of smaller ionic radius than lanthanum and/or a portion of the gallium is replaced with Al, Sc or In. The foregoing monocrystalline compositions are particularly suited as superconductor substrates.
TL;DR: Ammonium plutonium double sulphate tetrahydrate NH4Pu(SO4)2·4H2O and some of its lanthanide isomorphs were synthesized and characterized by chemical, thermal and X-ray diffraction methods.
Abstract: Ammonium plutonium double sulphate tetrahydrate NH4Pu(SO4)2·4H2O and some of its lanthanide isomorphs, i.e. NH4Ln(SO4)2·4H2O (Ln ≡ Y, Dy, Ho and Er) were synthesized and characterized by chemical, thermal and X-ray diffraction methods. The powder data of NH4Pu(SO4)2·4H2O obtained in the present work showed it to be isostructural to NH4Sm(SO4)2·4H2O reported in the literature. All these compounds belonged to the same structural family where the Pu3+ or Ln3+ ion is coordinated to nine oxygen atoms. The unit cells of dysprosium, holmium and erbium compounds showed regular contraction with atomic number. The linear plot of ν 1 3 vs. ionic radii of the lanthanide compounds was used to obtain empirical ionic radii of U3+ and Pu3+ for nine coordination.
TL;DR: In this article, all ten oxygen atoms of the acyclic oligomer 1 c participate in the coordination of Ba2⊕ in the "scorpion" complex 1c · Ba(SCN)2 · Me2CO.
Abstract: All ten oxygen atoms of the acyclic oligomer 1 c participate in the coordination of Ba2⊕ in the “scorpion” complex 1c · Ba(SCN)2 · Me2CO. The eleventh coordination site is occupied by the acetone molecule. A further characteristic of the complex are strong OHċN hydrogen bonds to the thiocyanate counterion. The ligands 1 also exhibit a high selectivity for cations with ionic radii of 1.2–1.3 A, which could be explained with the help of molecular modeling studies. (Figure Presented.) Copyright © 1990 by VCH Verlagsgesellschaft mbH, Germany
TL;DR: In this article, cubic pyrochlore oxides of the type (RM)(BiPb)O7 (M = Ba, Sr, Ca; R = rare earth) were prepared by solid state reactions at 850°C under 3 kbar pressure.