Electrical conductivity of Ln2CuO4 compounds

Electrical conductivity of Ln₂CuO₄ compounds (where Ln = La, Pr, Nd, Sm, Eu and Gd) have been studied in air from 100° to 900°C. Results show that La₂CuO₄ is metallic showing an anomaly in its conductivity at about 310°C, while the conductivity of Pr₂CuO₄ enhances rapidly with temperature showing a saturation behaviour at high temperature. All other compounds are semiconducting. At high temperatures the Nd, Sm, Eu and Gd compounds have the same activation energy for conduction of 0.82 ± 0.02 eV.     

Poly(β-Styryl)-(1,2-Methanofullerene-C60)-61-Formo Hydroxamic Acid for the Solid Phase Extraction, Separation and Preconcentration of Rare Earth Elements

A new fullerene derivatives poly(β-styryl)-(12-methanofullerene-C₆₀)-61-formo hydroxamic acid has been synthesized and applied for the solid phase extraction, separation, preconcentration and ICP-MS determination of Ce, La, Pr, Nd, Sm and Gd. The introduction of the fullerene moiety into poly(β-styryl)-hydroxamic acid enhances its reactivity, chemical stability and recycled for their determination. The various parameter, viz. kinetics of sorption, breakthrough studies, effect of eluents, etc., have been studied. The influence of several diverse ions is also discussed. The proposed method has been applied for the sequential chromatographic separation of rare earths in the presence of each from rocks, monazite sand and in environmental samples.     

Extraction of Rare-Earth Elements and Americium from Nitric Acid Solutions with Polyphosphine Oxides

Extraction of HNO₃ and microamounts of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Am from solutions of NH₄NO₃ and HNO₃ with solutions of polyphosphine oxides containing o-oxyphenylenemethylene fragments in dichloroethane was studied. The stoichiometry of the extractable complexes was determined, and the apparent extraction constants were calculated. As the number of phosphoryl groups in the extractant molecule is increased, the extraction of cerium-group lanthanides increases and that of yttrium-group lanthanides decreases.     

Native point defects and oxygen migration of rare earth zirconate and stannate pyrochlores

Various excellent properties of rare earth zirconate and stannate pyrochlores are close related with their native point defects.First-principles calculations are performed to systematically investigate the point defect mechanism and the oxygen diffusion behavior of A2B2O7 (A=La,Ce,Pr,Nd,Pm,Sm,Eu,Gd;B=Zr,Sn).The possible defect complexes and their associated reactions under stoichiometric and nonstoichiometric conditions are explored.The O Frenkel pairs are the most stable defect structure in stoichiometric zirconates,whereas the cation antisite defects are the predominant one in stoichiometric stannates.In the case of BO2 excess zirconates and stannates,the BA cation antisite defect with the A vacancy and/or the oxygen interstitial is energetically favorable,whereas the AB antisite defect together with the oxygen vacancy and/or the A interstitial is preferable under the A2O3 excess condition.Meanwhile,the maximum point defect concentrations of zirconates are much higher than those of stannates.Furthermore,the oxygen migration barriers are similar in these compounds,ranging in 0.68 eV-0.80 eV.The predicted point defects and oxygen diffusion mechanisms play the critical role in their engineering applications and are expected to guide the future property improvement of pyrochlores through the control of point defects and/or composition.     

钙钛矿锰氧化物（La0.8Ln0.2）2/3Ca1/3MnO3（Ln=La，Ce，Pr，Nd，Sm，Eu）的低场电输运性能分析

用溶胶-凝胶法制备了系列掺杂（La0.8Ln0.2）2/3Ca1/3MnO3（Ln=La,Ce,Pr,Nd,Sm,Eu）纳米级晶体。对比在La被其它镧系元素部分替代后,引起的A位离子平均半径的改变和磁矩变化对电输运及磁阻性能的影响,实验分析表明,各个样品在同样大小磁场下的磁电阻存在较大的差别,样品的磁电阻随原子序数的增加而明显变大,由镧系收缩引起晶格畸变所产生的本征磁电阻占主导地位,随着外加磁场的增加,不同掺杂样品间的峰值电阻差异被弱化;各掺杂样品间的转变温度差与掺杂离子半径差和磁矩差密切相关,且离子半径的差异对转变温度的改变贡献更大。     

Catalytic activity of rare-earth orthoferrites and orthochromites

The catalytic activity of LnFeO₃ and LnCrO₃ (Ln=LaGd) for methanol oxidation has been studied by the measurement of conductivity change on methanol adsorption in the mixture gas (O₂(0.5%) + N₂(99.5%)); The activity of these compounds appeared above the Neel points. The sequence of the activity for LnFeO₃ was Gd > Eu > Sm > Nd > Pr > La, which was correlated with the Néel temperature; GdFeO₃, which has the lowest Néel temperature, showed the highest activity. However, a relationship between activity and Néel temperature was not clearly observed in LnCrO₃.     

Recovery of rare-earth elements from nitric acid solutions by fullerene black impregnated with diphenyl(dibutylcarbamoylmethyl)phosphine oxide

The distribution of microamounts of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y nitrates between aqueous HNO₃ solutions and fullerene black impregnated with diphenyl(dibutylcarbamoylmethyl)phosphine oxide (L) was studied. The influence exerted on the efficiency of REE recovery by the HNO₃ concentration in the aqueous phase and concentration of L in the sorbent phase was examined. The degree of REE recovery increases on adding HClO₄ to the aqueous phase.     

Synthesis and Study of Uranates of Rare-Earth Elements of Compositions LnU3O10.5·6H2O (Ln = La,Ce, Pr,Nd, Sm), LnU6O19.5·10H2O (Ln = Nd,Sm, Eu,Gd, Tb,Dy), and LnU2O7.5 (Ln = Dy,Ho, Er,Tm, Yb,Lu)

Radiochemistry - The interaction of synthetic skupite UO3·2.25H2O with aqueous solutions of La, Ce, Pr, Nd, Sm, Eu,Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu nitrates under hydrothermal conditions at a...     

Extraction of Rare-Earth Elements from Nitric Acid Solutions with Bidentate Phosphoryl-containing Compounds and Their Mixtures

Extraction of microamounts of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu from HNO₃ solutions with neutral bidentate phosphoryl-containing compounds was studied. Extraction with tetraphenylmethylenediphosphine dioxide increases in going from Lu to La, and extraction with methyleneoxyphenyldiphosphine dioxides increases in the opposite direction. The anomalous aryl strengthening effect varies in the same direction. Extraction with mixtures of diphosphine dioxides allows efficient concentration of the sum of rare-earth elements from nitric acid solutions.     

Catalytic properties of compounds between the rare earths and copper oxide

The catalytic properties of the rare earth-copper double oxides (Ln₂CuO₄, Ln=La ～ Gd) are dependent on the kind of rare earth included and reveal drastic changes on going from Pr to Nd. The sequence of activity for Ln₂CuO₄ was $\text{Eu > Gd > Pr ? La > Sm}$.     

Electrical conduction in light rare-earth tungstates

This paper reports the results of electrical conductivity (σ) and thermoelectric power (H) of light rare-earth tungstates in the temperature range 600–1200K. Holes are the dominant charge carriers over the whole studied temperature range for Nd, Sm and Gd tungstates. However, in the case of La, Ce and Pr tungstates, the conduction is dominated by electrons at lower temperatures, but above 950K in La, 800K in Ce and 950K in Pr the dominant charge carriers become holes. A sharp break and change in the log σ vs 1/T slope occurs in La, Ce and Pr tungstates around the same temperature at which the dominant charge carrier changes from electrons to holes. In the case of Nd, the conductivity anomaly occurs around 1020K without any change in the nature of the charge carrier. The data have been analysed using band theory.     

Efficient sorption of light rare-earth elements using resorcinol-formaldehyde polymeric resin

The sorption behavior of light rare-earth elements (La, Ce, Nd, Sm) on resorcinol-formaldehyde (RF) resin was studied. The effect of pH, shaking time, and temperature on the metal distribution coefficients was examined. The RF resin affinity for the examined lanthanides increases with a decrease in the ionic radius of the metal ion: Sm > Ce > Nd > La. The capacity of RF resins for the lanthanides shows the same trend. Because of the relatively high capacity of the resin, the presence of interfering ions affects the sorption percentage of the light REEs insignificantly. The thermodynamic functions of the sorption process were determined. They show that the adsorption of the light lanthanides on RF resin occurs spontaneously with the dehydrated metal ion.     

Rare earth niobium oxynitrides, LnNbON2−δ (Ln = Y, La, Pr, Nd, Gd, Dy): Synthesis, structure and properties

Ammonolysis of rare earth niobates of the type LnNbO₄ (Ln = Y, La, Pr, Nd, Gd, Dy) yields oxynitrides of different structures. When Ln = La, Nd and Pr, the structure is that of an orthorhombic perovskite of the general formula LnNbON₂. As the size of the rare earth decreases, the oxynitride has a nitrogen-deficient defect fluorite (Ln = Pr, Nd, Gd), or pyrochlore (Ln = Y) structure. The IR spectra of the oxynitrides and the corresponding oxides are significantly different. Thermogravimetric analysis suggests the formation of an intermediate phase wherein the N₂ molecule is attached to the oxide lattice above 400 °C and decomposes to give the oxide on heating in an oxygen atmosphere. Raman spectra of the intermediate phases show evidence for the NN stretching vibration. Gadolinium niobium oxynitride is found to be paramagnetic.     

PVC membrane potentiometric sensor based on 5-pyridino-2,8-dithia[9](2,9)-1,10-phenanthroline-phane for selective determination of neodymium(III)

Spectrofluorometric studies on the binding properties of 5-pyridino-2,8-dithia[9](2,9)-1,10-phenanthrolinephane (L) toward La3+, Sm3+, Gd3+, Yb3+, and Nd3+ in methanol solution revealed the occurrence of both 1:1 and 2:1 (ligand/metal) complexation with a stability order of Nd3+ > Yb3+ > Gd3+ > Sm3+ > La3+. Consequently, L was used as a suitable neutral ionophore for the preparation of a novel polymeric membrane-selective electrode for Nd3+ ion. The electrode exhibited a Nernstian response over a wide concentration range (1.0 x 10(-6)-1.0 x 10(-2) M) with a low limit of detection of 7.9 x 10(-7) M. The electrode possesses a fast response time of <5 s and can be used for at least 9 weeks without observing any considerable deviation. The proposed electrode revealed a very good selectivity for Nd3+ over a wide variety of alkali, alkaline earth, transition, and heavy metal ions, including members of the lanthanide family other than Nd3+. The potentiometric response of the electrode is independent of the pH of test solution in the pH range 4.0-6.5. The proposed electrode was successfully applied to the recovery of Nd3+ ion from tap water samples and, also, as an indicator electrode, in potentiometric titration of neodymium(III) ions.     

Gas-Phase Conversion of Oxide Phases of Lanthanides and Uranium to Water-Soluble Compounds

Radiochemistry - Gas-phase conversion to water-soluble compounds of individual rare-earth element (REE) (La, Ce, Pr, Nd, Sm, Eu, Dy, Ho, Er, Tm, Lu) oxides and oxide systems (U,Ce)Ox and (U,Nd)Ox...     

Hydrothermal phase equilibria studies in Ln2O3H2O systems and synthesis of cubic lanthanide oxides

Phase diagrams for the systems Ln₂O₃H₂O (Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Lu and Y) studied at 5000 to 10,000 psi and temperature range of 200–900°C, show that Ln(OH)₃ hexagonal and LnOOH monoclinic are the only stable phases from Nd to Ho. The cubic oxide phase (CLn₂O₃) is stable for systems of Er, Tm, Yb and Lu, with no evidence of its equilibrium in the systems of lighter lanthanides. Using strong acids, HNO₃ and HCOOH, as mineralisers the cubic oxides could be stabilised from Eu down to Lu. Solid solution phases of CeO₂Y₂O₃ and Eu₂O₃Y₂O₃ have also been synthesised with HNO₃ as mineraliser, since these compounds have promising use as solid electrolyte and phosphor materials respectively.     

Spherulitic growth of single (Gd & Pr) and mixed (Di) rare earth heptamolybdates in silica gels

Single (Gd and Pr) and mixed rare earth (Di—a mixture of four rare earths La, Pr, Nd & Sm) heptamolybdates grow as platelet, multifacetted crystals and spherulites when corresponding rare earth chloride ions are made to react with ammonium paramolybdate. Various spherulitic formations are illustrated. It is shown that the spherulitic formations may be due to either fibres radially diverging from multiple nuclei or agglomeration of tiny crystallites orienting and accommodating themselves in a spherical space or intergrowth of multiple crystals which may include multiple twinning of interpenetrating type.     

Stability field diagrams for <Emphasis Type="Italic">Ln</Emphasis>–O–Cl systems

Isothermal stability field diagrams for Ln?O?Cl systems (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb) are developed by taking partial pressures of volatile components oxygen and chlorine as variables. Thermodynamic properties of all the oxides and trichlorides (LnCl₃) are available in the literature. However, data for oxychlorides (LnOCl) and dichlorides (LnCl₂) are limited. Based on systematic trends in stability of these compounds across the lanthanide series, missing data are estimated to construct the diagrams for 13 Ln?O?Cl systems at 1000 K. All the lanthanide elements form stable LnCl₃ and LnOCl. Dichlorides of Nd, Sm, Eu, Dy, Tm and Yb are stable. For systems in which dichlorides are unstable (Ln = La, Ce, Pr, Gd, Tb, Ho, Er), the LnOCl is in equilibrium with the metal (Ln) and the stability field of LnOCl is sandwiched between those of oxides and trichlorides. Stability field diagrams of lanthanide systems forming stable LnCl₂ are of two kinds: in the first kind (Ln = Nd, Dy) the stability fields of Ln and LnOCl are in contact and the stability field of LnOCl separates the fields of chlorides and oxides. In diagrams of the second kind (Ln = Sm, Eu, Tm, Yb) there is a direct equilibrium between the oxides and dichlorides at low partial pressures of oxygen and chlorine. There is no contact between the stability fields of Ln and LnOCl; the stability field of LnOCl intervenes between the oxide and chloride phases only at higher partial pressures.     

A comparative study of DFT and XPS with reference to the adsorption of caesium ions in smectites

Chemical states of Cs ion adsorbed on dioctahedral smectites were studied using X-ray photoelectron spectroscopy (XPS) and molecular orbital calculations based on the density functional theory (DFT). Smectites investigated were montmorillonite, montmorillonite–beidellite, Fe–montmorillonite, and nontronite. It was found that montmorillonite samples kept approximately 50% of adsorbed Cs ions after a treatment by BaCl₂ aqueous solution, which were the highest values among the smectite samples. Cs(4d) binding energy was slightly shifted towards a lower energy by 0.2–0.8 eV after a BaCl₂ treatment, which suggests that plural adsorption sites exist on the smectite surface. Stable Cs adsorption sites and the adsorption energies were determined by DFT calculations. As a result, Cs ion is adsorbed strongly on a basal oxygen hexagonal hole. The chemical shift of the calculated Cs(4d) peak gave the same tendency as shown in the XPS measurements.     

Extraction of Rare-Earth Elements from Nitric Acid Solutions with Ethylenediphosphine Dioxides

Extraction of microamounts of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu from HNO₃ aqueous solutions with ethylenediphosphine dioxides in organic diluents was studied. The effect of the dioxide structure on its extractive power and selectivity was considered. The stoichiometry of extractable solvates was determined.