Showing papers on "Ionic radius published in 2003"
TL;DR: In this paper, Li3xLa(2/3)-x□(1/3)2xTiO3 (0 < x < 0.16) and its related structure materials, the x ≈ 0.1 member exhibits conductivity of 1 × 10-3 S/cm at room temperature with an activation energy of 0.40 eV.
Abstract: To date, the highest bulk lithium ion-conducting solid electrolyte is the perovskite (ABO3)-type lithium lanthanum titanate (LLT) Li3xLa(2/3)-x□(1/3)-2xTiO3 (0 < x < 0.16) and its related structure materials. The x ≈ 0.1 member exhibits conductivity of 1 × 10-3 S/cm at room temperature with an activation energy of 0.40 eV. The conductivity is comparable to that of commonly used polymer/liquid electrolytes. The ionic conductivity of LLT mainly depends on the size of the A-site ion cation (e.g., La or rare earth, alkali or alkaline earth), lithium and vacancy concentration, and the nature of the B−O bond. For example, replacement of La by other rare earth elements with smaller ionic radii than that of La decreases the lithium ion conductivity, while partial substitution of La by Sr (larger ionic radii than that of La) slightly increases the lithium ion conductivity. The high lithium ion conductivity of LLT is considered to be due to the large concentration of A-site vacancies, and the motion of lithium by a...
703 citations
TL;DR: The new compounds were found to have properties well-suited for use as precursors for atomic layer deposition (ALD) of thin films, and have high volatility, high thermal stability, and high and properly self-limited reactivity with molecular hydrogen, depositing pure metals, or water vapor, deposging metal oxides.
Abstract: A series of homoleptic metal amidinates of the general type [M(R-R'AMD)(n)](x) (R = (i)Pr, (t)Bu, R' = Me, (t)Bu) has been prepared and structurally characterized for the transition metals Ti, V, Mn, Fe, Co, Ni, Cu, Ag, and La. In oxidation state 3, monomeric structures were found for the metals Ti(III), V(III), and La(III). Bridging structures were observed for the metals in oxidation state 1. Cu(I) and Ag(I) are held in bridged dimers, and Ag(I) also formed a trimer that cocrystallized with the dimer. Metals in oxidation state 2 occurred in either monomeric or dimeric form. Metals with smaller ionic radii (Co, Ni) were monomeric. Larger metals (Fe, Mn) gave monomeric structures only with the bulkier tert-butyl-substituted amidinates, while the less bulky isopropyl-substituted amidinates formed dimers. The new compounds were found to have properties well-suited for use as precursors for atomic layer deposition (ALD) of thin films. They have high volatility, high thermal stability, and high and properly self-limited reactivity with molecular hydrogen, depositing pure metals, or water vapor, depositing metal oxides.
349 citations
TL;DR: In this article, the thermoelectric properties of Sr0.9R0.1TiO3 (R=Y, La, Sm, Gd, Dy) have been measured from room temperature to 1073 K.
256 citations
TL;DR: In this paper, the relationship between electrical conductivity and crystal structure was investigated for Ln2Zr2O7 (Ln=La, Nd, Sm, Eu, Gd, Y, or Yb) and (ln1−xLnx′) 2Zr 2O7 systems, where the crystal structure of both systems changed from fluorite (F)-type to pyrochlore (P)-type structure when the ionic radius ratios, r(Ln3+)/r(Zr4+), were larger than
212 citations
TL;DR: In this article, Li-doped ZnO with different compositions (Zn1-xLixOy, x=0.075, 0.125 and 0.15) have been prepared on heavily doped Si substrates by a pulsed laser deposition technique.
Abstract: Zinc oxide is a very important piezoelectric material with lower preparation temperature, simpler structure and composition. By doping with some elements having smaller ionic radii, such as lithium, to substitute the zinc ions, it is expected that the center of the positive charge in a unit cell will not overlap with that of the negative charge in the same unit cell, leading to the appearance of the spontaneous polarization. Thin films of Li-doped ZnO with different compositions (Zn1-xLixOy, x=0.075, 0.1, 0.125 and 0.15) have been prepared on heavily doped Si substrates by a pulsed laser deposition technique. In the films with x=0.1 and x=0.125, ferroelectric P–E hysteresis loops were successfully observed. The remanent polarization and the coercive field of Zn0.9Li0.1Oy and Zn0.875Li0.125Oy were (0.193 μC/cm2, 4.8 kV/cm) and (0.255 μC/cm2, 4.89 kV/cm), respectively. An anomalous point in the dielectric spectrum of the Li-doped ZnO ceramics is observed, showing that the ferroelectric phase transition occurs around 67 °C under 7.5 at. % Li-doped ZnO and 74 °C under 10 at. %. If the remanent polarization of this material can be further increased, it may be used as a ferroelectric material.
169 citations
TL;DR: A series of rare-earth iron borates having general formula LnFe 3 (BO 3 ) 4 (Ln =Y, La-Nd, Sm-Ho) were prepared and their magnetic properties have been investigated by the magnetic susceptibility, specific heat, and 57 Fe Mossbauer spectrum measurements.
147 citations
TL;DR: The structural evolution at 300 K of the series SrxBa1?xSnO3 and SrxCa 1?xsnO3 at 0.2 intervals has been determined by powder neutron diffraction.
Abstract: The structural evolution at 300 K of the series SrxBa1?xSnO3 and SrxCa1?xSnO3 at x = 0.2 intervals has been determined by powder neutron diffraction. All SrxCa1?xSnO3 samples (x = 0?1) have the Pbnm superstructure. In the series SrxBa1?xSnO3, the x = 1.0 and 0.8 samples have the Pbnm superstructure. The x = 0.6 sample has a second orthorhombic structure with space group Imma. There is a tetragonal I4/mcm phase at x = 0.4 and the undistorted cubic structure for x = 0.2 and BaSnO3. The octahedral tilt angles show a smooth variation with average A cation radius over the range of superstructures described by mean field theory close to the transition. The transitions are also analysed via the variation of spontaneous strains.
105 citations
TL;DR: In this paper, volume variation of dense LaMnO 3+ δ specimens was measured at elevated temperatures and in stepwise changes of oxygen partial pressure, and the measured expansion was in almost linear relationship with the oxygen nonstoichiometry.
100 citations
TL;DR: In this article, the authors carried out positron lifetime measurements in zinc ferrite (ZnFe2O4) samples of various grain sizes down to 5 nm, and the defect microstructures have been identified.
Abstract: By carrying out positron lifetime measurements in zinc ferrite (ZnFe2O4) samples of various grain sizes down to 5 nm, the defect microstructures have been identified. In the bulk samples composed of grains of large sizes, positrons were trapped by monovacancies in the crystalline structure. Upon reduction of the grain sizes to nanometer dimensions, positrons get trapped selectively at either the diffused vacancies on the grain surfaces and the intergranular regions. Below about 9 nm, the grains undergo the transformation from the normal spinel structure to the inverse phase. A concomitant lattice contraction results in substantial reduction of the octahedral site volume, and hence, a fraction of the Zn2+ ions with larger ionic radius fails to occupy these sites. This leaves vacancies at the octahedral sites which then turn out to be the major trapping sites for positrons. ZnFe2O4 samples prepared through different routes were investigated, which showed similar qualitative features, although those synthesi...
96 citations
TL;DR: A series of perovskite-like oxide in which the A-site cation was partially or totally substituted by calcium, samarium and neodymium has been used to produce in situ nanoparticles of Ru(Ni) well dispersed on a stable support for the carbon dioxide reforming of methane as discussed by the authors.
Abstract: A series of perovskite-like oxide in which the A-site cation of the precursor perovskite, LaRu08Ni02O3, was partially or totally substituted by calcium, samarium and neodymium have been used to produce in situ nanoparticles of Ru(Ni) well dispersed on a stable support for the carbon dioxide reforming of methane Perovskites of the type LnxCa1−xRu08Ni02O3 (Ln=La3+, Sm3+, Nd3+) were synthesized as catalysts precursors The reduced solids of nominal composition (Ru,Ni)/CaO and/or La2O3, Sm2O3, Nd2O3, were used as catalysts The La1−xCaxRu08Ni02O3 series showed a well-defined perovskite structure with surface areas between 3 and 10 m2/g However, when lanthanum was replaced by samarium and neodymium, the presence of pyrochlore structures, together with the perovskites, were obtained After reduction Ru(Ni) crystallites size between 9 and 17 nm were produced The substitution of La by cations of smaller ionic radii (Ca, Nd, Sm) decrease the stability of the perovskites and lower their reduction temperature Among the calcium series, La08Ca02Ru08Ni02O3 and La05Ca05Ru08Ni02O3, proved to be the most active catalysts with the highest selectivity to CO While samarium-containing perovskite was the best among the lanthanide series Correlations between the effect of partial or total substitution of A-site cations of the precursor perovskite and the catalytic activity and stability of in situ formed nickel and ruthenium particles were established
92 citations
TL;DR: This concept is demonstrated for complexes with bulky bis(trimethylsilyl)amido ligands [N(SiMe(3))(2)](-) and "slim" phosphoraneiminato ligands (NPR(3)(-)).
Abstract: Because of their large ionic radii and relatively low oxidation states rare-earth elements generally form complexes which have high coordination numbers and weak metal-ligand bonds. They are often not suitable for homogeneous catalysis on account of their instability of configuration in solution. Complexes of the corresponding metal atoms with low coordination numbers may be an improvement. This type of complex can be obtained in the classical way by the introduction of bulky ligands, and recently, they were also prepared in reactions with ligand groups which offer remarkable metal-ligand bond features. This concept is demonstrated for complexes with bulky bis(trimethylsilyl)amido ligands [N(SiMe(3))(2)](-) and "slim" phosphoraneiminato ligands (NPR(3)(-)). Their suitability as catalysts for the ring-opening polymerization of lactones is reported as well.
TL;DR: The structural properties and IR absorption spectra of Pb 4+ substituted Nickel ferrites having general formula Ni 1+ x Pb x Fe 2−2 x O 4 (where x = 0.0, 0.1, 0 2, 0 3, 0 4 and 0.5) were investigated in this paper.
TL;DR: In this article, the Li doping level in La0.7Ca0.3−yLiyMnO3 (0⩽y 0.3) was increased and the system was driven from a higher-conductivity regime to a lower-condivity regime, which is in sharp contrast with the behavior of Na or K doping.
Abstract: With increasing the Li doping level in La0.7Ca0.3−yLiyMnO3 (0⩽y⩽0.3), the system is driven from a higher-conductivity regime to a lower-conductivity regime, which is in sharp contrast with the behavior of Na or K doping. Compared to those of K or Na, the ionic radius of Li is much smaller than that of Ca. Therefore, substitution of Ca by Li results in a smaller average A-site radius, narrowing the bandwidth and hence enhancing the band gap and resistivity. The effect of random disorder of La3+ and A2+ also plays an important role leading to charge localization.
TL;DR: In this article, the photocatalytic activity of BaCrO4 and SrCrO 4 photocatalyst powders was characterized by powder X-ray diffraction, UV-Vis diffuse reflection spectroscopy and measurements in case of sacrificial reagents CH3OH and AgNO3 under UV and visible light irradiation (λ>420 nm), respectively.
TL;DR: The X-ray crystal structures of the title complexes showed that the differences between the U-O and Ln-O distances reflect the variation in the ionic radii of the trivalent uranium and lanthanide ions while the UI bond lengths are smaller than those predicted from a purely ionic bonding model as mentioned in this paper.
TL;DR: In this paper, the authors extended the hydration model to aquo species with covalent bonds and applied it to trivalent and tetravalent actinides.
Abstract: The hydration model that we proposed earlier has been extended to aquo species with covalent bonds. It has been applied successfully to the majority of monatomic ions with charges from −1 to +4. An evaluation of the permittivity in the vicinity of the ion, dipole and quadrupole moments and polarisability of the solvated water molecule is presented. In the case of trivalent and tetravalent actinides, the experimental cation–oxygen distance d, accurately measured by EXAFS, is shorter at the beginning of the series than the calculated values obtained in the ionic model. The observed decrease has been used to evaluate the effective charges, Zeff, of actinides. We discuss the evaluation of the ionic radius Ri, the coordination number N and the number of water molecules in a second hydration shell H. After defining the different parameters, which characterize the aquo ions, mainly, Zeff, Ri, N, H and d, the general hydration and entropy models is applied to evaluate the hydration energy and the entropy of different trivalent and tetravalent actinide aquo ions. We will also re-evaluate and discuss redox potentials corresponding to some 4+/3+ couples. Finally, we will define the radius of the aquo ions and deduce the ionic conductivity of trivalent and tetravalent actinides.
TL;DR: In this article, the relationship between electrical conductivity and crystal structure in Ln2Ce2O7 (Ln=La, Nd, Sm, Eu, Gd, Y and Yb) systems was investigated.
Abstract: The relationship between electrical conductivity and crystal structure in Ln2Ce2O7 (Ln=La, Nd, Sm, Eu, Gd, Y and Yb) systems was investigated. The crystal phases were assigned to a fluorite (F)-type phase accompanying the rare earth C-type superstructure, when the ionic radius ratio, r(Ln3+)/r(Ce4+) were larger than 1.17. On the other hand, La2Ce2O7 was the only F-type phase without the superstructure. The lattice constant increased linearly with increasing the ionic radius of Ln3+ independent of whether or not the superstructure was present. Oxygen partial pressure dependence of the electrical conductivity suggested that the charge carrier was oxide-ion, except for the Nd system. The electrical conductivity at 800°C in air for the Ln2Ce2O7 systems also increased with increasing the ionic radius ratio. The activation energy for the conduction decreased remarkably in the fluorite-type phase region. The compositional change of the oxide-ion conductivity was understood by the introduction of an unit cell free volume. This result was also supported by Raman spectra.
TL;DR: In this paper, a transport and magnetic measurements have been carried out on perovskite Co-oxides R 1- x A x CoO 3 (R = La, Pr, and Nd; A = Ba, Sr and Ca; 0≤ x ≤ 0.5).
Abstract: Transport and magnetic measurements have been carried out on perovskite Co-oxides R 1- x A x CoO 3 (R = La, Pr, and Nd; A = Ba, Sr and Ca; 0≤ x ≤0.5: All sets of the R and A species except Nd 1- x Ba x CoO 3 have been studied.). With increasing the Sr- or Ba-concentration x , the system becomes metallic ferromagnet with rather large magnetic moments. For R = Pr and Nd and A = Ca, the system approaches the metal–insulator phase boundary but does not become metallic. The magnetic moments of the Ca-doped systems measured with the magnetic field H =0.1 T are much smaller than those of the Ba- and Sr-doped systems. The thermoelectric powers of the Ba- and Sr-doped systems decrease from large positive values of lightly doped samples to negative ones with increasing doping level, while those of Ca-doped systems remain positive. These results can be understood by considering the relationship between the average ionic radius of R 1- x A x and the energy difference between the low spin and intermediate spin states....
TL;DR: This chapter describes the main features of solvent exchange on metal, taking into account developments and new results from the past 10 years, and determines exchange-rate constants by NMR using a variety of specific methods.
Abstract: Publisher Summary This chapter discusses the solvent exchange on metal ions. The solvent exchange is divided into categories of metal ions. The first category includes the main group ions that exhibit in general, for a given ionic charge, increasing exchange-rate constants with increasing ionic radius. The second category is the d -transition metal ions. Their solvent-exchange properties are strongly influenced by the electronic occupancy of their d orbitals. The third category is the high coordination number lanthanides and actinides. This chapter describes the main features of solvent exchange on metal, taking into account developments and new results from the past 10 years. Only a few experimental techniques are available to measure solvent-exchange rate constants directly. Nuclear magnetic resonance (NMR) spectroscopy has shown the widest range of applications. Most exchange-rate constants given in this chapter are determined by NMR using a variety of specific methods. A common method is the observation of NMR lineshape.
TL;DR: In this article, static lattice simulation techniques were used to calculate the energy of intrinsic defect generation, impurity incorporation and cation migration in the perovskite oxide LaGaO3.
Abstract: Static lattice simulation techniques were used to calculate the energetics of intrinsic defect generation, impurity incorporation and cation migration in the perovskite oxide LaGaO3. The calculations indicate that the formation of cation vacancies is energetically favoured over the formation of cation interstitials; expressions for the generation energies of lanthanum vacancies and of gallium vacancies are derived for several Brouwer regimes. Divalent and trivalent impurity cations with ionic radii smaller than 0.8 A in sixfold coordination are predicted to substitute preferentially for Ga3+. The migration energies of both native and impurity cations were determined. Simple models describing the migration energetics are proposed.
TL;DR: In this paper, a systematic study of the counterion layering phenomenon at high surface charge in a planar electric double layer is reported, where extensive canonical Monte Carlo simulations are performed on a 1:1 electrolyte to investigate the effect on layering due to a variation of electrode charge density, electrolyte concentration, and ionic size.
TL;DR: In this article, the dc electrical conductivity of (100−x)Na2B4O7−xWO3 (x = 5, 15, 20 and 30 mol%) glasses is reported in the temperature range 323 −473 K. The density and molar volume for these glasses are consistent with the ionic size, atomic weight and amount of different elements in the glasses.
Abstract: The dc electrical conductivity of (100−x)Na2B4O7−xWO3 (x = 5, 15, 20 and 30 mol%) glasses is reported in the temperature range 323–473 K. The density and molar volume for these glasses are consistent with the ionic size, atomic weight and amount of different elements in the glasses. At high temperatures the Mott model of phonon-assisted small polaron hopping between nearest neighbours is consistent with conductivity data, while at intermediate temperatures the Greaves variable-range hopping model is found to be appropriate. The estimated model parameters such as number of ions per unit volume, hopping distance, polaron radius and activation energy are found to be consistent with the formation of localized states in these glasses. The electrical conduction of these glasses is confirmed to be that of non-adiabatic small polaron hopping. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
TL;DR: In this article, the influence of the rare-earth dopant content and the ionic radius on the structural changes was undertaken on nanocrystalline-doped zirconia ceramics, which present the same microstructure.
TL;DR: In this article, the effect of substituted metal ions in the polymeric precursor on the gas separation performance of carbon molecular sieve (CMS) membranes containing alkali metal ions was determined.
TL;DR: The lattice parameters of Zr1−xMxW2O8−y (M=Sc, In and Y) solid solutions substituted up to x=0.04 for Zr(IV) sites by M(III) ions were synthesized by a solid-state reaction.
TL;DR: A careful scrutiny of the existing body of hydrated ionic radii data provide clear evidence that they are unreliable for polyatomic ions such as nitrate, nit...
Abstract: The existing body of experimental data in the open literature clearly indicate that reverse osmosis (RO) processes reject ions of identical valence (i.e., homovalent ions) to different degrees. For example, rejections (or relative permeations) of monovalent anions (such as Cl-, NO3-, Br-, CH2ClCOO-, ClO4-, etc.) during RO processes are different under otherwise identical conditions. The same is true for divalent anions (namely, SO42-, HPO42-, SeO42-) or monovalent cations (namely, Li+, Na+, K+, and NH4+). The solution diffusion model with the Nernst−Planck equation is unable to predict the differential permeation behaviors of homovalent ions. It is recognized that hydrated ionic radii data, if available, could be used to compute interdiffusion coefficients (or salt permeability coefficients) of permeating electrolytes. However, a careful scrutiny of the existing body of hydrated ionic radii data in the open literature provide clear evidence that they are unreliable for polyatomic ions such as nitrate, nit...
TL;DR: In this paper, an effective index was suggested to maximize the ionic conductivity in La2O3-CeO2 based oxides, and the index considers the fluorite structure, and combines the expected oxygen vacancy level with ionic radius mismatch between host and dopant cations.
Abstract: Doped ceria (CeO2) compounds are fluorite-type oxides which show oxide ionic conductivity higher than yttria-stabilized zirconia in oxidizing atmosphere. As a consequence of this, considerable interest has been shown in applications of these materials for low or intermediate temperature operation of solid-oxide fuel cells (SOFCs). In this study, the effective index was suggested to maximize the ionic conductivity in La2O3-CeO2 based oxides. The index considers the fluorite structure, and combines the expected oxygen vacancy level with the ionic radius mismatch between host and dopant cations. Using this approach, the ionic conductivity of this system has been optimized and tested under operating conditions of SOFCs. LaxCe1-xO2-delta (x = 0.125, 0.15, 0.175, and 0.20), (LaxSr1-x)(0.175)Ce0.825O2-delta (x = 0.1, 0.2, and 0.4), and (La1-xSr0.2Bax)(0.175)Ce0.825O2-delta (x 5 0.03, 0.05, and 0.07) were prepared and characterized as the specimens with low, intermediate, and high index, respectively. The ionic conductivity was increased with increasing suggested index. The transmission electron microscopy analysis suggested that partial substitution of alkaline earth elements in place of La into Ce site contributes to a decrease of microdomain size and an improvement of conductivity. (La0.75Sr0.2Ba0.05)(0.175)Ce0.825O1.891 with high index and small microdomains exhibited the highest conductivity, wide ionic domain, and good performance in SOFCs. (C) 2003 The Electrochemical Society.
TL;DR: In this article, the microwave dielectric properties of rare-earth titanium niobates can be tailored by preparing solid-solution phases between RETiNbO6 [RE = Pr, Nd, Sm] and RE′TiNbOn6 [Gd, Dy, Y] for different values of XRD, SEM, and microwave methods.
Abstract: The microwave dielectric properties of rare-earth titanium niobates can be tailored by preparing solid-solution phases between RETiNbO6 [RE = Pr, Nd, Sm] and RE′TiNbO6 [RE′= Gd, Dy, Y] microwave dielectric ceramics. Dielectric ceramics based on solid-solution phases RE1−xRE′xTiNbO6 are prepared by the conventional solid-state ceramic route for different values of x. The ceramic samples are characterized by XRD, SEM, and microwave methods. Ceramics based on RETiNbO6 belonging to aeschynite group show a positive value of τf, and those based on RE′TiNbO6 belonging to the euxenite group have a negative value of τf. The solid-solution phases between aeschynites and euxenites show intermediate dielectric constant and τf values. The results indicate the possibility of tailoring the microwave dielectric properties by varying the composition of solid-solution phases. The range of solid solubility of euxenites in aeschynites and aeschynites in euxenites are different for different rare-earth ions. The ceramics have low sinterability and a high dielectric loss factor near the vicinity of aeschynite to euxenite transition. The value of dielectric constant changes abruptly close to the transition point. The abrupt variation in microwave dielectric properties indicate a first-order phase transition at x= 0.86 in Pr1−x Gd xTiNbO6, x= 0.48 in Nd1−x Dy xTiNbO6 and x= 0.27 in Sm1−xY x TiNbO6 ceramics. The dielectric constant and the sign of τf of the solid-solution phases are found to depend on the average ionic radius of the rare-earth ions in RE1−xRE′xTiNbO6. The euxenite to aeschynite phase transition occurs at an average ionic radius of 0.945 A in all three systems of solid-solution phases.
TL;DR: In this article, the chiral Schiff base-Ln(III) complexes were determined using X-ray crystallography, and an effect of the ionic radius on the structure of the complexes was studied.