Showing papers on "Ionic radius published in 2001"

Lithium Ionic Conductor Thio-LISICON: The Li2 S ­ GeS2 ­ P 2 S 5 System

Abstract: The new crystalline material family, lithium superionic conductor (thio-LISICON), was found in the Li 2 S-GeS 2 -P 2 S 5 system. The solid solution member x x 0.75 in Li 4-x Ge 1-x P x S 4 shows the highest conductivity of 2.2 x 10 -3 S cm -1 at 25°C of any sintered ceramic together with negligible electronic conductivity, high electrochemical stability, no reaction with lithium metal, and no phase transition up to 500°C. Its material design concepts of changing constituent ions with various ionic radii, valence, and polarizability are described.

High throughput fabrication of transition-metal-doped epitaxial ZnO thin films: A series of oxide-diluted magnetic semiconductors and their properties

Abstract: Combinatorial laser molecular-beam epitaxy method was employed to fabricate epitaxial ZnO thin films doped with all the 3d transition metal (TM) ions in a high throughput fashion The solubility behavior of TM ions was discussed from the viewpoints of the ionic radius and valence state The magneto-optical responses coincident with absorption spectra were observed for Mn- and Co-doped samples Cathodoluminescence spectra were studied for Cr-, Mn-, Fe-, and Co-doped samples, among which Cr-doped ZnO showed two sharp peaks at 297 eV and 371 eV, respectively, at the expense of the exciton emission peak of pure ZnO at 325 eV Different magnetoresistance behavior was observed for the samples codoped with n-type carriers Ferromagnetism was not observed for Cr- to Cu-doped samples down to 3 K

Rare earth element diffusion in diopside: influence of temperature, pressure, and ionic radius, and an elastic model for diffusion in silicates

Abstract: Volume diffusion rates for five rare earth elements (La, Ce, Nd, Dy, and Yb) have been measured in single crystals of natural diopside at pressures of 0.1 MPa to 2.5 GPa and temperatures of 1,050 to1,450 °C. Polished, pre-annealed crystals were coated with a thin film of rare earth element oxides, then held at constant temperature and pressure for times ranging from 20 to 882 h. Diffusion profiles in quenched samples were measured by SIMS (secondary ion mass spectrometry) depth profiling. At 1 atm pressure, with the oxygen fugacity controlled near the quartz–fayalite–magnetite buffer, the following Arrhenius relations were obtained for diffusion normal to (001) (diffusion coefficient D in m2/s): log10 D Yb =(–4.64±0.42)–(411±12 kJ/mol/2.303RT); log10 D Dy =(–3.31±1.44)–(461±41 kJ/mol/2.303RT); log10 D Nd =(–2.95±2.64)–(496±77 kJ/mol/2.303RT); log10 D Ce =(–4.10±1.08)–(463±31 kJ/mol/2.303RT); log10 D Lu =(–4.22±2.66)–(466±78 kJ/mol/2.303RT). Diffusion rates decrease significantly with increasing ionic radius, with La a factor of ~35 slower than Yb. The relationship between diffusivity and ionic radius is consistent with a model in which elastic strain plays a critical role in governing the motion of an ion through the crystal lattice. Activation volumes for Yb and Ce diffusion, at constant temperature and oxygen fugacity, are 9.0±2.0 cm3/mol and 8.9±3.2 cm3/mol, respectively, corresponding to an order of magnitude decrease in diffusivity as pressure is increased from 0 to 3 GPa at 1,200 °C. Diffusion of Nd is such that grain-scale isotopic equilibrium in the mantle can be achieved in ~1 My under conditions near the peridotite solidus (~1,450 °C at 2.5 GPa). The equilibration time is much longer under P, T conditions of the lithospheric mantle or at the eclogite solidus (~1 Gy at 1.5 GPa and 1,150 °C). Because of the relatively strong decrease in diffusivity with pressure (two orders of magnitude between 2.5 and 15 GPa along an adiabatic temperature gradient), Nd transport in clinopyroxene will be effectively frozen at pressures approaching the transition zone, on time scales less than 100 My. Rare earth element diffusion rates are slow enough that significant disequilibrium uptake of REE by growing clinopyroxene phenocrysts may be preserved under natural conditions of basalt crystallization. The relative abundances and spatial distributions of REE in such crystals may provide a sensitive record of the cooling and crystallization history of the host lava.

Site Occupancy of Rare-Earth Cations in BaTiO3

Abstract: A systematic study on the site occupancy of rare-earth cations in Ba-rich and Ti-rich BaTiO3 fired in reducing atmosphere is performed. The corresponding lattice relaxation is used as an indicator of site occupancy and, to a lesser extent, defect structures. Accurate lattice parameters are obtained from X-ray diffraction data that is analyzed with the maximum likelihood method to account for correlated errors in the c and a lattice parameters. Comparisons of lattice volume as a function of ionic radius of the dopant reveals three regimes, with the intermediate sized cations (0.087 nm \leqslantr \leqslant0.094 nm where r is the ionic radius in six-fold coordination) demonstrating amphoteric behavior (occupying A- or B-sites). Defect chemistry analysis of site occupancy links the importance of metal vacancy ratios and oxygen vacancy concentrations with site occupancy. The trends predicted from the defect chemistry analysis are consistent with the observed lattice relaxations.

Processing and Dielectric Properties of Sillenite Compounds Bi12MO20−δ (M = Si, Ge, Ti, Pb, Mn, B1/2P1/2)

Abstract: Six sillenite compounds Bi12MO20-δ (M = Si, Ge, Ti, Pb, Mn, B1/2P1/2) were synthesized, and the resulting single-phase powders were then sintered to obtain ∼97% dense ceramics. An analysis of their microwave dielectric properties, performed at ∼5.5 GHz, revealed a permittivity of ∼40 for all six compounds. The temperature coefficient of resonant frequency was the lowest for the Pb analogue (−84 ppm/K) and was found to increase with increasing ionic radius of the B-site ion to a value of −20 ppm/K for the Bi12SiO20 and Bi12(B1/2P1/2)O20 compounds. The Q×f value is a maximum for Bi12SiO20 and Bi12GeO20 with 8100 and 7800 GHz, respectively. The dielectric properties of the sillenites have been correlated with the structure of the oxygen network of the sillenite crystal lattice. As a result of its low sintering temperature (850°C), chemical compatibility with silver, low dielectric losses, and temperature-stable permittivity, the Bi12SiO20 compound is a suitable material for applications in low-temperature cofiring ceramic (LTCC) technology.

Doping effect in layer structured SrBi2Nb2O9 ferroelectrics

Abstract: This article reports a systematic study of doping effects on the crystal structure, microstructure, dielectric, and electrical properties of layer-structured strontium bismuth niobate, SrBi2Nb2O9 (SBN), ferroelectrics. Substitution in both the A site (Sr2+ by Ca2+ and Ba2+) and B site (Nb5+ by V5+) up to 30 at % were studied. It was found that crystal lattice constant, dielectric, and electrical properties of SBN ferroelectrics varied appreciably with the type and amount of dopants. The relationships among the ionic radii, structural constraint imposed by [Bi2O2]2+ interlayers, and properties were discussed.

Characteristic enhancement of emission from SrTiO3:Pr3+ by addition of group-IIIb ions

Abstract: Enhancement of the emission from SrTiO3:Pr3+ by addition of group-IIIb ions (IIIb3+) has been investigated. From the photoluminescence (PL) spectra and x-ray diffraction patterns, it is speculated that one of the origins of the enhancement is charge compensation of Pr3+ at the Sr2+ site by IIIb3+ substituting for Ti4+ around Pr3+, which results in a change in the crystal field around Pr3+. The IIIb3+-dependent PL spectra can be explained qualitatively by a local distortion around Pr3+ ions due to a difference in an ionic radius between Ti4+ and IIIb3+.

Effect of rare earth (Er, Gd, Eu, Nd and La) and bismuth additives on the mechanical and piezoelectric properties of lead zirconate titanate ceramics

Abstract: Mechanical, piezoelectric and dielectric properties of PZT ceramics (Pb 0.98 M 0.02 [(Zr 0.535 Ti 0.465 ) 0.995 ]O 3 , M=Er, Gd, Eu, Nd, La and Bi) have been studied. The fraction of A sites occupied by the different additives is estimated and is found to increase with the ionic radius of the additive ion. The density is high in Bi-, Gd- and Eu-PZT samples. Small amounts of the pyrochlore phase are present in Gd- and Eu-PZT. A maximum strength of 80–100 MPa and K IC of ∼1.5 MPa m 1/2 are obtained in Gd- and Eu-PZT. The R -curve behavior becomes more pronounced in Gd- and Eu-PZT, and it is observed that the strength and K IC increase with the slope of the K IC versus c 1/2 plot. Very good piezoelectric properties, i.e. d 33 of 410 PCN −1 , dielectric constant of 1005, κ p of 0.49 and the hydrophone figure of merit, d h g h , of 2760 are obtained for Nd-PZT. The piezoelectric properties in Bi-PZT are also higher than for the undoped composition, while for the Gd-PZT, these are slightly inferior. For all other compositions, the piezoelectric properties are not affected much.

Electrospray ionization tandem mass spectrometric study of salt cluster ions. Part 1? Investigations of alkali metal chloride and sodium salt cluster ions

Abstract: Salt cluster ions of alkali metal chlorides ACl (A = Li + ,N a + ,K + ,R b + and Cs + ) and sodium salts NaB (B = I , HCOO ,C H 3COO ,N O 2 ,a nd NO 3 ), formed by electrospray ionization, were studied systematically by mass spectrometry. The influences on the total positive ion and negative ion currents of variation of solvent, solution concentration, desolvation temperature, solution flow-rate, capillary voltage and cone voltage were investigated. Only cone voltage was found to influence dramatically the distribution of salt cluster ions in the mass spectra observed. Under conditions of normal cone voltage of70 V, cluster ions having magic numbers of molecules are detected with high relative signal intensity. Under conditions of low cone voltage of10 V, the distribution of cluster ions detected is characterized by a relatively low average mass/charge ratio due to the presence of multiply charged cluster ions; in addition, there is a marked reduction in cluster ions having a magic number of molecules. Product ion mass spectra obtained by tandem mass spectrometry of cluster ions are characterized by a base peak having a magic number of molecules that is less than and closest to the number of molecules in the precursor ion. Structures have been proposed for some dications and some quadruply charged ions. At pH 3 and 11, the mass spectra of NaCl clusters show the presence of mixed clusters of NaCl with HCl and NaOH, respectively. The effects of ionic radius on 20 distributions of cluster ions for 10 salts were investigated; however, the fine structure of these effects is not readily discerned. Copyright © 2001 John Wiley & Sons, Ltd.

Substitution Effects of In3+ by Al3+ and Ga3+ on the Photocatalytic and Structural Properties of the Bi2InNbO7 Photocatalyst

Abstract: A new series of photocatalysts, Bi2MNbO7 (M = Al3+, Ga3+, In3+), were synthesized by solid-state reaction and characterized by powder X-ray diffraction and Rietveld structure refinement. The substitution effect of In3+ by Al3+ and Ga3+ on the photocatalytic and structural properties of the Bi2InNbO7 photocatalyst was investigated. These photocatalysts crystallize in the same pyrochlore structure, but the lattice parameters decrease with decreasing M3+(M3+ = Al3+, Ga3+, In3+) ionic radii. The rates of H2 and O2 evolution from an aqueous methanol and cerium sulfate solution significantly increases with decreasing M3+ ionic radii under UV irradiation. The Bi2AlNbO7 photocatalyst exhibits much higher photocatalytic activity than the well-known TiO2 photocatalyst.

Occupational sites and dielectric properties of rare-earth and Mn substituted BaTiO3

Abstract: The effect of re-oxidation treatment on the solubility in dopants and the dielectric properties of La–Mn- and Ho–Mn-substituted BaTiO 3 ( AB O 3 ) was investigated. The lattice parameter and electrical resistivity results indicated that La ions occupied A -sites and Ho ions occupied both A - and B -sites. In the case of Ho–Mn-substituted samples, the decrease in lattice parameter and a shift of the Curie point ( T c ) to higher temperatures by re-oxidation treatment were observed in the range in which Ho ions predominantly occupy B -sites (act as acceptors). On the other hand, La–Mn-substituted samples showed little change. Electron spin resonance measurements revealed that these changes due to re-oxidation were based on the decrease of the ionic size of Mn due to the oxidation of Mn 2+ to Mn 3+ or Mn 4+ . The occupational sites of Ho ions strongly affected the valence state of Mn and the dielectric properties of BaTiO 3 .

Computer simulation studies of the structure and dynamics of ions and non–polar solutes in water

Abstract: The mobility of simple ions such as alkali–metal and halide ions at room temperature shows two anomalies. Firstly, there are maxima in mobilities as a function of ion size for both positive and negative ions and, secondly, the maximum for negative ions occurs at a larger ionic radius than the maximum for positive ions. Theoretical treatments of this problem are reviewed and it is concluded that a molecular treatment of the system is needed to understand the results. Computer simulation using the simple point charge model (SPC/E) for water reproduced the observations and is used to discuss the application of theories. In particular, the nature of the first solvation shell is correlated with ion mobility. Simulation reveals a further anomaly, namely that if the charge is removed from a large ion, then it moves more slowly. This is interpreted as the result of formation of a solvent cage around the hydrophobic solute. The changes in local structure resulting from changes in charge and size also affect the solvation thermodynamics. Simulations show that the solvation entropy has a double maximum when viewed as a function of charge. The local minimum near zero charge is interpreted as being due to hydrophobic order, and the maxima as the result of structure breaking. This double maximum in the entropy of solvation is a signature of the hydrophobic cage effect. Comparisons are made between ion mobilities in liquid water at ambient and supercritical conditions.

Density of Salt Solutions: Effect of Ions on the Apparent Density of Water

Abstract: The apparent density of water in aqueous solutions is analyzed by assuming that the volume occupied by the ions, in the absence of contact ion pairs, can be approximated reliably by spheres with appropriate ionic radii. X-ray data for ionic solutions are used to identify the ionic radii with crystal radii. Small corrections for the sizes of chloride and fluoride are made. Addition of ions to water changes the packing density of the water as well as the average hydrogen bond length. The slope of the apparent density of water versus concentration (taken at infinite dilution) varies from negative to positive for univalent electrolytes at 298 K, 1 atm. In the case of sucrose solutions, the apparent density of water does not change with sucrose concentration. For salts that have a positive slope of apparent water density with concentration, a maximum in apparent density as a function of concentration is generally observed depending on the solubility range. Apparent density maxima at room temperature are more f...

Infrared spectra and VUV excitation properties of BaLnB9O16:Re (Ln=La, Gd; Re=Eu, Tb)

Abstract: The infrared spectra of BaLnB(9)O(16):Re, along with the VUV excitation spectra, have been measured. The spectra were tentatively interpreted in terms of the data on absorptions of the borate groups and band structure. It was observed that there are absorption due to BO3 and BO4 groups, indicating that there are BO3 and BO4 groups in BaLnB(9)O(16). It is found that absorption of the borate groups is located in the range from 120 to 170 mn. This result reveals that there is an energy transfer from host to the rare earth ions. It also observed that the energy of charge transfer band, the host absorption, the total crystal field splitting of d-levels of Tb3+ increase with the decrease in the Ln(3+) radius. (C) 2001 Elsevier Science B.V. All rights reserved.

Influence of ionic size of rare-earth site on the thermoelectric properties of RCoO3-type perovskite cobalt oxides

Abstract: Thermoelectric properties of Ca-doped RCoO3 (R=Pr, Nd, Sm, Gd, Dy, Ho) perovskites were studied in the temperature range of 373–1173 K. Electrical conductivity increased and Seebeck coefficient decreased with increasing the ionic radius of rare-earth elements (Ho3+

Density functional theory studies on the dissociation energies of metallic salts: relationship between lattice and dissociation energies

Abstract: The formation and physicochemical properties of polymer electrolytes strongly depend on the lattice energy of metal salts. An indirect but efficient way to estimate the lattice energy through the relationship between the heterolytic bond dissociation and lattice energies is proposed in this work. The heterolytic bond dissociation energies for alkali metal compounds were calculated theoretically using the Density Functional Theory (DFT) of B3LYP level with 6-311+G(d,p) and 6-311+G(2df,p) basis sets. For transition metal compounds, the same method was employed except for using the effective core potential (ECP) of LANL2DZ and SDD on transition metals for 6-311+G(d,p) and 6-311+G(2df,p) calculations, respectively. The dissociation energies calculated by 6-311+G(2df,p) basis set combined with SDD basis set were better correlated with the experimental values with average error of ca. ±1.0% than those by 6-311+G* combined with the LANL2DZ basis set. The relationship between dissociation and lattice energies was found to be fairly linear (r>0.98). Thus, this method can be used to estimate the lattice energy of an unknown ionic compound with reasonably high accuracy. We also found that the dissociation energies of transition metal salts were relatively larger than those of alkaline metal salts for comparable ionic radii. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 827–834, 2001

Ion selectivities of the Ca2+ sensors for exocytosis in rat phaeochromocytoma cells

Abstract: 1. The ion selectivities of the Ca(2+) sensors for the two components of exocytosis in rat phaeochromocytoma (PC12) cells were examined by measurement of membrane capacitance and amperometry. The cytosolic concentrations of metal ions were increased by photolysis of caged-Ca(2+) compounds and measured with low-affinity indicators benzothiazole coumarin (BTC) or 5-nitrobenzothiazole coumarin (BTC-5N). 2. The Ca(2+)-induced increases in membrane capacitance comprised two phases with time constants of 30--100 ms and 5 s. Amperometric events reflecting the exocytosis of large dense-core vesicles occurred selectively in the slow phase, even with increases in the cytosolic Ca(2+) concentration of > 0.1 mM. 3. The slow component of exocytosis was activated by all metal ions investigated, including Cd(2+) (median effective concentration, 18 pM), Mn(2+) (500 nM), Co(2+) (900 nM), Ca(2+) (8 microM), Sr(2+) (180 microM), Ba(2+) (280 microM) and Mg(2+) (> 5 mM). In contrast, the fast component of exocytosis was activated by Cd(2+) (26 pM), Mn(2+) (620 nM), Ca(2+) (24 microM) and Sr(2+) (320 microM), but was only slightly increased by Ba(2+) (> 2 mM) and Co(2+) and not at all by Mg(2+). 4. The fast component, but not the slow component, was competitively blocked by Na(+) (median effective concentration, 44 mM) but not by Li(+), K(+) or Cs(+). Thus, the Ca(2+) sensor for the fast component of exocytosis is more selective than is that for the slow component; moreover, this selectivity appears to be based on ionic radius, with cations with radii of 0.84 to 1.13 A (1 A = 0.1 nm) being effective. 5. These data support a role for synaptotagmin--phospholipid as the Ca(2+) sensor for the exocytosis of large dense-core vesicles and they suggest that an additional Ca(2+)-sensing mechanism operates in the synchronous exocytosis of synaptic-like vesicles.

A spectroscopic study of the effect of the trivalent cation on the thermal decomposition behaviour of Co-based hydrotalcites

Abstract: Various correlations between the size of the trivalent cation (Al, Ga, Fe, and Cr) and the structural characteristics and decomposition behavior of Co-based hydrotalcites (Co/M3+ = 3) have been identified. In situ IR spectra (by the relative ratio of the amount of carbonate in low and high symmetry) and thermogravimetric analyses show that the larger the trivalent cation, the lower the relative amount of water in the interlayer space of the as-synthesized material. Removal of interlayer water upon decomposition induces a symmetry loss of the carbonate groups, leading to splitting of the ν3 vibrational mode of the carbonate groups at elevated temperatures. The extent of splitting was found to continuously decrease as a function of increasing cation size, which suggests a decreasing degree of interaction of the carbonate groups with remaining OH groups in the brucite-like layers. However, the stability of the carbonates in the temperature range of 200–250°C shows an opposite trend, and is apparently dependent on other factors, such as the stability of the hydroxides and the layered structure itself, as well as direct interactions of carbonate with the metal ions. Dehydroxylation of the brucite-like layers, followed by complete carbonate decomposition are the final stages leading to the formation of mixed metal oxides.

Mechanism of the piezoelectricity of langasite based on the crystal structures

Abstract: Langasite family crystals ( R 3 Ga 5 SiO 14, R= rare earth) are expected as the new piezoelectric material for SAW filter. La 3 Ga 5 SiO 14 has the largest piezoelectric modulus in these crystals. It is reported that the piezoelectric properties of these crystals improved with the increase of the ionic radius of R . In this work, we clarified the crystal structures of three kinds of langsite family crystals ( R =La, Pr and Nd) by X-ray diffraction analysis. We investigated the differences among these crystal structures and clarified the reason why the piezoelectric properties improved with the increase of the ionic radius of R on the basis of these structural differences.