Decrease Of Ionic Radius Research Articles

Study of enhanced magnetism in Lu doped multiferroic bismuth ferrite

Abstract In this work, the enhancement in magnetic moment in Lu doped BiFeO 3 is reported. Sol–gel synthesized Bi 1− x Lu x FeO 3 ( x = 0, 0.02, 0.04 and 0.05) were characterized for their phase, magnetic properties, thermal analysis and Raman scattering studies. The X-ray diffraction study revealed the segregation of rare earth garnet as secondary phase. The presence of garnet phase was reiterated in the magnetization measurements with Curie temperature at 575 K. The DSC and the Raman spectrum once again ascertain the garnet phase in the compound. We believe that the instability in the structure with lower dopant ionic radii resulted in increase in segregation of garnet and hence enhanced the magnetic moment in rare earth doped BiFeO 3 samples. We suggest that the increase in magnetic moment with decrease in rare earth dopant ionic radii reported in the literature could have a strong correlation with the structural instability and the related secondary phase segregation.

Transport coefficients and the Stokes–Einstein relation in molten alkali halides with polarisable ion model

A polarisable ion model is parameterised for the whole series of molten alkali halides by using first-principles calculations based on density functional theory. Viscosity, electrical conductivity and thermal conductivity are determined using molecular dynamics simulations via the Green–Kubo formulae and confronted to experimental results. The calculated transport coefficients are generally in much better agreement than those obtained with the empirical Fumi–Tosi potentials. The inclusion of polarisation effects significantly decreases the viscosity and thermal conductivity, while it increases the electrical conductivity. The individual dynamics of the ions is analysed using the Stokes–Einstein relation. The anion behaviour is always well represented using the slip boundary condition, while for cations there is an apparent shift from slip to stick condition when the ionic radius decreases. This difference is interpreted by subtle changes in their coordinating environment, which are maximised in the case of Li+ cation.

Structure and Complexation Studies on 2,2′-Bipyridyl and Trivalent Lanthanides

Separation of trivalent lanthanides (Ln) and trivalent actinides (An) is important task in reprocessing high-level liquid waste. In this study, the relationship between structures of complexes of 2,2′-bipyridyl (Bpy) and Ln (Nd, Er) and coordination strengths were investigated by X-ray diffraction and UV titration. With the decrease in ionic radius from Nd to Er, the N(Bpy)-Ln distance and N(Bpy)-Ln-N(Bpy) angle decreased, the dihedral angle of the Bpy pyridines increased, and the stability constant increased. This information about structure and coordination strength is important for designing better ligands for separating Ln and An ions.

Effects of rare-earth size on the electronic structure of La1−xLuxVO3

The electronic structure of La1−xLuxVO3(x = 0, 0.2, 0.6 and 1) single crystals has been investigated using soft x-ray absorption spectroscopy, soft x-ray emission spectroscopy, and resonant soft x-ray inelastic scattering to study the effects of rare-earth size. The x-ray absorption and emission spectra at the O K-edge present a progressive evolution with R-site cation, in agreement with local spin density approximation calculations. This evolution with R, together with the temperature dependence of the O K-edge spectra, is attributed to changes in the crystal structure of La1−xLuxVO3. The crystal-field dd* excitations probed by resonant inelastic x-ray scattering at the V L3-edge exhibit an increase in energy and enhanced intensity with the decrease of R-site ionic radius, which is mainly attributed to the increased tilting magnitude of the VO6 octahedra. Upon cooling to ∼95 K, the dd* excitations are prominently enhanced in relative intensity, in agreement with the formation of the Jahn–Teller distortion in the orbital ordering phase. Additionally, the dd* transitions of the mixed compounds are noticeably suppressed with respect to those of the pure compounds, possibly owing to the formation of C-type orbital ordering induced by large R-site size variances.

Infra-red spectroscopic characteristics of naphthalocyanine in bis(naphthalocyaninato) rare earth complexes peripherally substituted with thiophenyl derivatives

The infra-red (IR) spectroscopic data for a series of eleven rare earth double-deckers MIII[Nc(SPh)8]2 (M=Y, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho and Er) have been collected and systematically investigated. For MIII[Nc(SPh)8]2, typical IR marker bands for the naphthalocyanine anion radical [Nc(SPh)8]− were observed at 1317–1325cm−1 as the most intense absorption bands, which can be attributed to the pyrrole stretching. As for Ce[Nc(SPh)8]2, the typical IR marker band was also observed at 1317cm−1, which shows that the cerium complex exists as the form of CeIII[Nc(SPh)8]2−[Nc(SPh)8]−. In addition, both the Q-bands of electronic absorption spectra and the typical IR absorption bands of naphthalocyanine radical anion [Nc(SPh)8]− move to the high energy as the decrease of rare earth metal ionic radius. These facts suggest that the π–π electron interaction in these double-deckers becomes stronger along with the lanthanide contraction.

Dielectric and ferroelectric properties of unfilled tungsten bronze KBa3RNb10O30 ceramics

Unfilled tungsten bronze ceramics with general formula KBa3RNb10O30 (R = La, Pr, Nd, Sm, Eu, Gd) were prepared by the conventional solid state reaction method. XRD patterns show that all ceramics are pure tungsten bronze phase. Dielectric characterization indicates that the ceramics except KBa3GdNb10O30 are relaxors with strong frequency dispersion, while KBa3GdNb10O30 shows diffuse phase transition and belongs to classical ferroelectrics. At room temperature, the KBa3RNb10O30 compounds (R = La, Pr, Nd) are paraelectrics while the KBa3RNb10O30 compounds (R = Sm, Eu, Gd) are ferroelectrics. Among them, KBa3GdNb10O30 has the highest remnant polarization (2Pr) of 8.2 μC/cm2. Phase transition temperature, remnant polarization (2Pr) and tetragonality of the compounds increase with the decrease of ionic radius of the rare earths.

Velocity auto-correlation function of ions and water molecules in different concentrations, anions and ion clusters

The characteristics of ion solvation are important for electrochemical and biophysical phenomena because all such phenomena occur under the presence of solvated ions. In this study, we performed an all-atom molecular dynamics simulation of aqueous NaCl ranging from 0.5 to 3.0 M, and aqueous NaF, NaBr and NaI in 2.0 M, to investigate the time-averaged velocity auto-correlation function (TAVAF) of ions and water molecules. By comparing the concentrations and ion pairs, we observed three behaviours: (i) in the case of NaCl, the velocity auto-correlation of Cl− becomes weaker as the concentration increases, whereas those of Na+ are not clearly different, (ii) the intensity of fluctuations of the TAVAF gradually decreases following the decrease in ionic radius and (iii) every TAVAF of water molecules in ionic solutions is clearly lower than that of bulk because of the cage effect. Furthermore, we observed that the first minimum of the TAVAF in the cluster is smaller than that of the isolated ions. These results indicate that the diffusion of ions and water molecules is affected by cage effect, and that the generation of ion cluster affects the diffusion of ions.

Study of structural effect on Eu-substituted LSMO manganite for high temperature coefficient of resistance

In this work, Eu substituted La0.7Sr0.3MnO3 (LSMO) is studied to achieve high temperature coefficient of resistance (TCR). The compounds La0.7−xEuxSr0.3MnO3 with x=0, 0.1 0.2 and 0.3 are prepared by solid state reaction route and their structural and transport properties are examined by different characterization techniques. The metal–semiconductor/insulator transition temperature (TMI) decreases from 390K (for x=0) to 240K (for x=0.3) with decrease in average ionic radius 〈rA〉 of A-site. The maximum TCR percentage of La0.7−xEuxSr0.3MnO3 compound is found to be increased for x=0.2 (1.9%) and for x=0.3 (3.36%) compared to its parent compound La0.7Sr0.3MnO3 (1.1%). The substitution of Eu increases the lattice distortion, which enhances the TCR value from 1.1% to 3.36%. The robustness of distortion increases with decreasing 〈rA〉 which is well correlated with the high magneto-resistance, and high TCR findings.

Self-assembly of surfactin in aqueous solution: Role of divalent counterions

Myriad applications of surfactin in environmental and biomedical field prompt understanding the self-assembly behaviour of surfactin in aqueous solution as well as its interaction with counterions. Effect of four divalent counterions namely, Ni2+, Zn2+, Cd2+, and Ca2+ on the self-assembly of the surfactin, a biosurfactant isolated from Bacillus subtilis YB7 is studied by fluorescence spectroscopy, dynamic light scattering, optical and electron microscopic studies. The critical micelle concentration (CMC) and aggregation number (Nagg) of surfactin are 96.76±15.49μM and 101.12±2.53, respectively. The degree of counterion association increases as its ionic radius decreases. Ni2+ exhibits the highest and Ca2+ the least degree of counterion association. Addition of counterion reduces the size of the microstructures, aggregation number (Nagg) and zeta potential. The reduction in the zeta potential indicates the neutralization of the negative charges on the electrical double layer of the microstructures. Differential interference contrast (DIC) and transmission electron microscopic (TEM) images of surfactin show the presence of vesicles and large aggregates including giant vesicles. On the addition of Ca2+, fusion of vesicles into large aggregates is predominantly observed. Ni2+ induces the transition of large spherical vesicles into small spherical, worm-like vesicles and multicompartment-like structures (vesosome). Such structures are the evidences for metal ion coordinated intervesicular interactions. This study reveals that the self-assembly process of surfactin can be controlled by the addition of metal ions according to the requirements.

The influence of ionic radii on the grain growth and sintering-resistance of Ln2Ce2O7 (Ln = La, Nd, Sm, Gd)

Rare earth cerium oxides (Ln2Ce2O7, Ln = La, Nd, Sm, and Gd) with cubic-fluorite structure were prepared by hydrothermal method using cetyltrimethyl ammonium bromide as surfactant. X-ray diffraction (XRD), thermogravimetric analysis/differential scanning calorimetry (TG/DSC), Raman spectroscopy, and field emission scanning electron microscopy (FESEM) were utilized to characterize the phase structure, thermal decomposition, and morphology of the products, respectively. Qualitative analyses indicate that the as-prepared products are fluorite-type structures. The lattice parameter and average crystallite size of the products are closely related to the ionic radii. The activation energy of crystal growth shows an increasing trend with the decrease in ionic radii. The sintering behavior of compacted body was also investigated, revealing that the sintering-resistance properties of Ln2Ce2O7 are descending as the order of La2Ce2O7, Nd2Ce2O7, Sm2Ce2O7, and Gd2Ce2O7.

Reaction Pathways and Energetics of Etheric C–O Bond Cleavage Catalyzed by Lanthanide Triflates

Efficient and selective cleavage of etheric C–O bonds is crucial for converting biomass into platform chemicals and liquid transportation fuels. In this contribution, computational methods at the DFT B3LYP level of theory are employed to understand the efficacy of lanthanide triflate catalysts (Ln(OTf)3, Ln = La, Ce, Sm, Gd, Yb, and Lu) in cleaving etheric C–O bonds. In agreement with experiment, the calculations indicate that the reaction pathway for C–O cleavage occurs via a C–H → O–H proton transfer in concert with weakening of the C–O bond of the coordinated ether substrate to ultimately yield a coordinated alkenol. The activation energy for this process falls as the lanthanide ionic radius decreases, reflecting enhanced metal ion electrophilicity. Details of the reaction mechanism for Yb(OTf)3-catalyzed ring opening are explored in depth, and for 1-methyl-d3-butyl phenyl ether, the computed primary kinetic isotope effect of 2.4 is in excellent agreement with experiment (2.7), confirming that etheric ...

Synthesis and structure of tris(dimethyldithiocarbamato)(1,10-phenanthroline)lanthanide complexes

Syntheses and structures of three new lanthanide coordination compounds with dithiocarbamate ligands are reported. The complexes [Ln(Me2dtc)3(phen)] (Ln = Pr (1), Nd (2) and Gd (3), Me2dtc = N,N-dimethyldithiocarbamate and phen = 1,10-phenanthroline) were synthetized by a simple metathesis between lanthanide(III) nitrate and sodium dimethyldithiocarbamate followed by addition of 1,10-phenanthroline without the exclusion of moisture. Single crystal X-ray analysis showed that all three complexes are isostructural, crystallizing in the triclinic space group P1̅. The Ln-S and Ln-N bond lengths decrease in agreement with the decrease in ionic radii across the lanthanide series. Similar structures with Et2dtc ligands show no significant effect on the changes of Ln-S bond lengths and also on the S-Ln-S bite angles. The crystal packing of described complexes is formed via π-π stacking interactions and C-H ... S non-covalent contacts.

Importance of exchange anisotropy and superexchange for the spin-state transitions inRCoO3(R=rare earth) cobaltates

Spin-state transitions are the hallmark of rare-earth cobaltates. In order to understand them, it is essential to identify all relevant parameters which shift the energy balance between spin states and determine their trends. We find that $\ensuremath{\Delta}$, the ${e}_{g}$-${t}_{2g}$ crystal-field splitting, increases by $\ensuremath{\sim}$250 meV when increasing pressure to 8 GPa and by about 150 meV when cooling from 1000 K to 5 K. It changes, however, by less than 100 meV when La is substituted with another rare earth. Moreover, the Hund's rule coupling ${\mathcal{J}}_{\mathrm{avg}}$ is about the same in systems with very different spin-state transition temperature, like LaCoO${}_{3}$ and EuCoO${}_{3}$. Consequently, in addition to $\ensuremath{\Delta}$ and ${\mathcal{J}}_{\mathrm{avg}}$, the Coulomb-exchange anisotropy $\ensuremath{\delta}{\mathcal{J}}_{\mathrm{avg}}$ and the superexchange energy gain $\ensuremath{\delta}{E}_{\mathrm{SE}}$ play a crucial role and are comparable with spin-state-dependent relaxation effects due to covalency. We show that in the LnCoO${}_{3}$ series, with $\mathrm{Ln}=\mathrm{Y}$ or another rare earth ($RE$), superexchange progressively stabilizes a low-spin ground state as the Ln${}^{3+}$ ionic radius decreases. We give a simple model to describe spin-state transitions and show that, at low temperature, the formation of isolated high-spin/low-spin pairs is favored, while in the high-temperature phase, the most likely homogeneous state is high spin rather than intermediate spin. An orbital-selective Mott state could be a fingerprint of such a state.

Neutron powder diffraction analysis of (Tm0.50Ca0.50)MnO3 and (Lu0.50Ca0.50)MnO3

The crystal and magnetic structures of (Tm0.50Ca0.50)MnO3 and (Lu0.50Ca0.50)MnO3 have been investigated between 5K and 300K by means of high resolution neutron powder diffraction followed by Rietveld refinement and dc magnetic measurements. During cooling orbital ordering at the Mn sub-lattice takes place at TOO∼280K in both compounds, inducing an orthorhombic to monoclinic phase transition. As the temperature is further decreased an antiferromagnetic CE-type structure occurs in both compounds at TN∼105K.The comparison with other (Ln0.50Ca0.50)MnO3 compounds reveals that at room temperature the average Jahn–Teller distortion increases sharply with the decrease of the ionic radius for lanthanides heavier than Sm. The ordered magnetic moment progressively decreases as the lanthanide ionic radius decreases on account of the decreased values of the Mn–O–Mn bond angles.

Effect of rare earth ions on transition temperature in perovskite materials by on-line ultrasonic studies

On-line measurements of ultrasonic longitudinal velocity, shear velocity and longitudinal attenuation were carried out on R1-xSrxMnO3 perovskites (R = La, Pr, Nd and Sm) for different compositions of Sr, at a fundamental frequency of 5 MHz over wide range of temperatures using the through-transmission method. The observed maxima/minima in velocities and attenuation have been discussed with decrease in ionic radii and composition. As a decrease in the ionic radii of rare earth elements leads to a decrease in transition temperature (Tc), the results that are observed show that measurement is one of the best tools to explore the structural/phase transition on-line velocity in perovskite manganese materials as a function of the ionic radii of rare earth elements.

Lanthanide N,N-Dimethylaminodiboranates as a New Class of Highly Volatile Chemical Vapor Deposition Precursors

New lanthanide N,N-dimethylaminodiboranate (DMADB) complexes of stoichiometry Ln(H(3)BNMe(2)BH(3))(3) and Ln(H(3)BNMe(2)BH(3))(3)(thf) have been prepared, where Ln = yttrium, lanthanum, cerium, praseodymium, neodymium, samarium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, and lutetium, except that isolation of the desolvated complexes proved difficult for Eu and Yb. The tetrahydrofuran (thf) complexes are all monomeric, and most of them adopt 13-coordinate structures in which each DMADB group chelates to the metal center by means of four B-H···Ln bridges (each BH(3) group is κ(2)H; i.e., forms two B-H···Ln interactions). For the smallest three lanthanides, Tm, Yb, and Lu, the metal center is 12 coordinate because one of the DMADB groups chelates to the metal center by means of only three B-H···Ln bridges. The structures of the base-free Ln(H(3)BNMe(2)BH(3))(3) complexes are highly dependent on the size of the lanthanide ions: as the ionic radius decreases, the coordination number decreases from 14 (Pr) to 13 (Sm) to 12 (Dy, Y, Er). The 14-coordinate complexes are polymeric: each metal center is bound to two chelating DMADB ligands and to two "ends" of two ligands that bridge in a Ln(κ(3)H-H(3)BNMe(2)BH(3)-κ(3)H)Ln fashion. In the 13-coordinate complexes, all three DMADB ligands are chelating, but the metal atom is also coordinated to one hydrogen atom from an adjacent molecule. The 12-coordinate complexes adopt a dinuclear structure in which each metal center is bound to two chelating DMADB ligands and to two ends of two ligands that bridge in a Ln(κ(2)H-H(3)BNMe(2)BH(3)-κ(2)H)Ln fashion. The complexes react with water, and the partial hydrolysis product [La(H(3)BNMe(2)BH(3))(2)(OH)](4) adopts a structure in which the lanthanum and oxygen atoms form a distorted cube; each lanthanum atom is connected to three bridging hydroxyl groups and to two chelating DMADB ligands. One B-H bond of each chelating DMADB ligand forms a bridge to an adjacent metal center. Field ionization MS data, melting and decomposition points, thermogravimetric data, and NMR data, including an analysis of the paramagnetic lanthanide induced shifts (LIS), are reported for all of the complexes. The Ln(H(3)BNMe(2)BH(3))(3) compounds, which are highly volatile and sublime at temperatures as low as 65 °C in vacuum, are suitable for use as chemical vapor deposition (CVD) and atomic layer deposition (ALD) precursors to thin films.

Rare Earth Elements: Their Importance in Understanding Soil Genesis

The rare earth elements (REEs) are commonly defined as lanthanum (La) and the 14 elements comprising the Lanthanide series. The REE’s typically exhibit trivalent oxidation states; however, Europium may also occur as Eu2+ and Cerium may occur as Ce4+. The REE’s ionic radii decrease on progression from La to Lu, which results in a slight but predictable change in their chemical affinity. Typically, the light REE (La to Sm) reside in trace minerals such as apatite, epidote and allanite, whereas the heavy REE (Gd to Lu) are associated with minerals such as zircon. Investigations typically show that the REE are depleted in near-surface horizons and accumulate in deeper horizons or the regolith as clay-oxyhydroxide adsorbates or REE-phosphate precipitates. Numerous studies show the heavy REE accumulating in the deeper soil regions to a greater extent than the light REE, whereas other studies show the light REE’s preferentially accumulating at greater soil depths. The degree of interhorizon transport has great potential to become an index of weather intensity. The various REE soil migration pathways have been isolated, including lessivage, soil organic matter complexation, leaching in percolating water, adsorption by inorganic colloids, and precipitated by phosphate-bearing minerals.

Ferrocene-Decorated (Phthalocyaninato)(Porphyrinato) Double- and Triple-Decker Rare Earth Complexes: Synthesis, Structure, and Electrochemical Properties

A series of four mixed (phthalocyaninato)(porphyrinato) rare earth double-decker complexes (Pc)M[Por(Fc)(2)] [Pc = phthalocyaninate; Por(Fc)(2) = 5,15-di(ferrocenyl)-porphyrinate; M = Eu (1), Y (2), Ho (3), Lu (4)] and their europium(III) triple-decker counterpart (Pc)Eu(Pc)Eu[Por(Fc)(2)] (5), each with two ferrocenyl units at the meso-positions of their porphyrin ligands, have been designed and prepared. The double- and triple-decker complexes 1-5 were characterized by elemental analysis and various spectroscopic methods. The molecular structures of two double-deckers 1 and 4 were also determined by single-crystal X-ray diffraction analysis. Electrochemical studies of these novel sandwich complexes revealed two consecutive ferrocene-based one-electron oxidation waves, suggesting the effective electronic coupling between the two ferrocenyl units. Nevertheless, the separation between the two consecutive ferrocene-based oxidation waves increases from 1 to 4, along with the decrease of rare earth ionic radius, indicating the effect of rare earth size on tuning the coupling between the two ferrocenyl units. Furthermore, the splitting between the two ferrocene-based one-electron oxidations for triple-decker 5 is even smaller than that for 1, showing that the electronic interaction between the two ferrocene centers can also be tuned through changing the linking sandwich framework from double-decker to triple-decker. For further understanding of the electronic coupling between ferrocenyl groups, DFT calculation is carried out to clarify the electronic delocalization and the molecular orbital distribution in these double-decker complexes.

Preparation and thermophysical properties of nano-sized Ln2Zr2O7 (Ln = La, Nd, Sm, and Gd) ceramics with pyrochlore structure

Rare earth zirconates (Ln2Zr2O7, Ln = La, Nd, Sm, and Gd) with pyrochlore structure were prepared by hydrothermal method with polyethylene glycol as surfactant. X-ray diffraction, thermogravimetric analysis/differential scanning calorimetry, Fourier transform infrared spectroscopy, Raman spectroscopy, and field emission scanning electron microscopy were utilized to characterize the phase structure, thermal decomposition, and morphology of the products. Qualitative analysis indicates that the as-prepared zirconates are pyrochlore-type structures. The specific surface area, lattice parameter, and average crystallite size of the as-prepared products are closely related to the ionic radius. The activation energy of crystal growth shows an increasing trend with the decrease in ionic radii. The sintering behavior of compacted body was also investigated, revealing that the sintering-resistance properties of Ln2Zr2O7 are descending as the order of La2Zr2O7, Nd2Zr2O7, Sm2Zr2O7, and Gd2Zr2O7.

A series of new rare earth sulfates based on lanthanide contraction and dual organic-amine templating effects

Five different types of dual organic-amine templated lanthanide sulfates, [(CH3)2NH2]6[H3N(CH2)2NH3][Nd2(SO4)7] (1), [(CH3)2NH2]3[Eu(SO4)3] (2), [(CH3)2NH2]2[H3N(CH2)2NH3]0.5[Ln(SO4)3] (3) (LnEu (3a), Gd (3b), Tb (3c)), [(CH3)2NH2]4[Dy2(SO4)5] (4) and [H3N(CH2)2NH3]5[Ln2(SO4)8] (5) (LnDy (5a), Ho (5b), Er (5c), Tm (5d), Yb (5e), Lu (5f)) have been solvothermally obtained by employing dimethylacetamide (DMAc) as solvent and characterized by single-crystal X-ray diffraction, IR spectroscopy, thermal analysis, fluorescent spectra and ICP. The zigzag chain structure of compound 1 is constructed from two types of 4-membered rings (4 MRs) which connect each other alternately by sulfate groups. The one-dimensional (1D) chainlike structure of compound 2 is alternately linked by tetramer [Eu2(SO4)2O10] and 4 MR units. Compounds 3a to 3c are isomorphous and have similar interesting two-dimensional (2D) frameworks fabricated through zigzag chains and 12 MRs, fully protonated ethylenediamine (en) are located in 12 MRs and protonated dimethylamine (dma) are located between the inorganic layers. Compound 4 exhibits a 2D layered structure and the plane layers consist of two types of double stranded chains and 12 MRs. Compounds 5a to 5f are also isomorphous and feature a binuclear lanthanide cluster structure. Although the 12 compounds were synthesized under the same conditions except the rare earth oxide types, they belong to five types of structures and we can clearly see obvious transitivity and uniformity, as the ionic radius decreases, the coordination number of the rare earth elements decreases from 9 to 8 and the lanthanide contraction supports crystal structures concerning a sterically hindered coordination atmosphere. The luminescent properties of compounds 2, 3a and 3c exhibit characteristic europium and terbium luminescence.