Ionic Radius Of RE3 Research Articles

Study of variation in thermophysical properties of RE6UO12(s) along the lanthanide series

The variation in thermophysical properties along the lanthanide series for RE6UO12(s) was investigated. Structural characterization of Er6UO12(s) was carried out by Rietveld refinement method. The trend in heat capacity along the rare earth series for RE6UO12(s) and RE2O3(s) as function of ionic radius of RE3+ was found to be similar. Hence, the sole cause of excess heat capacity in rare earth uranates was concluded to be the rare earth ion. Linear relation was found between the thermal expansion coefficient of RE6UO12(s) (RE = La, Gd, Lu) and the ionic radii of rare earth ion.

Effect of chemical state and occupation site of RE (RE = Yb, Y, Eu, Sm, Nd) on crystal structure and optical property of BaCe1-xRExO3-δ —Analyses of origin of peculiar crystal structure and property of BaCe1-xNdxO3-δ

Crystal structure, temperature dependence of molar volume and optical property of single phase BaCe1-xRExO3-δ were investigated. The crystal structure of BaCe1-xRExO3-δ (RE; Yb, Y, Eu, and Sm) and BaCe1-xNdxO3-δ changes from primitive orthorhombic to monoclinic and body-centered orthorhombic, respectively, by increasing x. Almost linear relationship between ionic radius of RE3+ and the molar volume are observed for BaCe1-xRExO3-δ with RE of Yb, Y, Eu, Sm; however, that of BaCe1-xNdxO3-δ is smaller than the relationship. As one of the origins, proposed is that Nd in BaCe1-xNdxO3-δ is near 4+, showing agreement with reported oxygen nonstoichiometry, in-situ X-ray absorption spectra and reduction expansion observed in this work. As another origin, partial Ba-site mixing of Nd3+ is proposed from separation of BaCO3 from BaCe0.9Nd0.1O3-δ by high temperature sintering. The lower optical band gap of BaCe0.9Nd0.1O3-δ observed by reflectance spectroscopy, can also be explained by the partial mixing.

Structural, electronic and magnetic properties of RE3+-doping in CoFe2O4: A first-principles study

RE3+(RE=La, Ce, Pr, Nd, Eu, Gd) doped cobalt ferrite (CoFe2O4) have been studied systematically by the first-principles calculations based on density functional theory within the generalized gradient approximation with Hubbard corrections (GGA+U) . The significant effects of RE3+doping on the crystal structure, electronic and magnetic properties of CoFe2O4 have been explored. The calculated results show that the RE ions prefer substituting Fe3+ located at the octahedral sites. And the lattice constant of CoFe1.875RE0.125O4 (RE=La, Ce, Pr, Nd, Eu and Gd) decreases due to the decreasing ionic radius of RE as the atomic number increases. The magnetic properties depend on the unpaired 4f electrons of RE3+ ions. The net magnetic moment of CoFe2O4 increases by doping with Eu and Gd, the reason is that there are more unpaired 4f electrons for Eu3+and Gd3+. However, the net magnetic moment of CoFe2O4 decreases by doping with La, Ce, Pr, and Nd, due to the reason that these RE ions prefer their low spin configurations.

Properties of rare-earth orthoferrites perovskite driven by steric hindrance

REFeO3 (RE = La, Pr, Nd, Sm) perovskites present interesting properties and are studied for their potential applications as smart devices and the requirement of miniaturization and low power consumption in such electronic components has led to the development of thin films. The understanding of crystallization mechanisms and the characterization of such perovskites are thus important to understand their properties. In this study, we purpose a systematic comparison of structural, optical and electrical properties of REFeO3 thin films, and we investigate the direct link between properties and crystallographic distortion. The as-deposited films are annealed in air under XRD measurements in order to investigate their complete crystallization kinetic, using Johnson Mehl Avrami Kolmogorov model. TEM observations of films are in agreement with this model. Then, optical and electrical characterization of films were performed by using UV–visible spectroscopy, Fourier Transform Infrared spectroscopy (FTIR), and 4-probes measurements. We found that the activation energy of crystallization, the infrared vibration mode position and the activation energy of conduction mechanism are driven by distortion of the perovskite, which can be described by the Goldschmidt tolerance factor. All the studied properties are shifted due to decrease of RE ionic radius and the direct relationship between structural distortion and physical properties shifting is discussed.

Structural characteristics, magnetic properties of Re2NiMnO6 (Re = La, Pr, Nd, Sm, Y) thin films on (001) LaAlO3 by simple polymer assisted deposition

Re2NiMnO6 (Re=La, Pr, Nd, Sm, Y) epitaxial thin films grown on (001) LaAlO3 substrates were obtained via a simple polymer assisted deposition method. The XRD θ/2θ scans, ω scans, and φ scans indicate that the films are single-phase epitaxial films. It is found that there is a ferromagnetic (FM) transition with the temperature decreasing from room temperature for all the films. The Raman mode positions shift toward the low frequency with the substitution of La by a smaller rare earth element. The FM transition temperature Tc decreases as the A-site ionic radius decreasing. Moreover, all the FM transition temperatures (Tc) of the Re2NiMnO6 films are lower than those corresponding values of the bulks, indicating the ferromagnetic interaction weakening. It is suggested that the ferromagnetic interaction is affected by the strain existing in the film through affecting the B(B′)O6 octahedra and the cation disorder related to the ionic radius of Re, which can be used as an effective way to improve the magnetic properties of the film and obtain the higher Tc functional materials.

Theoretical study on the influence of rare earth doping on the electronic structure and magnetic properties of cobalt ferrite

Spinel ferrite is one of the very important magnetic materials, having the unique physical properties, chemical properties, magnetic properties, and electronic properties. CoFe2O4 is widely used due to their good electromagnetic properties. We have studied the electronic structure and magnetic properties of CoRE0.125Fe1.875O4 (RE = Nd, Eu, Gd)by first-principles plane-wave pseudopotential method based on density functional theory (DFT), combined with the generalized gradient approximation (GGA + U) in this paper. Results show that the lattice constants of the compunds CoFe1.875RE0.125O4 (RE=Nd, Eu and Gd) will decrease due to the decreasing ionic radius of RE as the atomic number increases. Their magnetic properties depend on the unpaired 4f electrons of RE3+ ions, and the net magnetic moment of CoFe2O4 will increase with Eu and Gd doping, mainly because there are more unpaired 4f electrons in Eu3+ and Gd3+. Thus the doping of Eu3+ and Gd3+ may have a greater impact on the magnetic properties of cobalt ferrite. The contribution from the doping of Nd is not remarkable on the magnetic properties, since the Nd3 + ion, having a larger ionic radius, could distort the crystal structure of CoFe2O4.

Structural, hyperfine and Raman properties of RE2FeSbO7 compounds

Pyrochlores of the RE2FeSbO7 type were synthesized by ball-milling followed by annealing in free atmosphere at high temperatures. The samples prepared were characterized by X-ray diffraction, Raman spectroscopy and 57Fe Mössbauer spectroscopy, at room temperature. The results showed that RE2FeSbO7 compounds have a cubic structure, i.e., Fd-3m (#227) space group, and that a site disorder takes place for the RE’s of larger ionic radii. Lattice parameters, Raman bands and quadrupole splittings were shown to depend correlatedly on the RE ionic radius. This behavior is discussed in terms of the pyrochlore crystallographic structure.

Study on structural, dielectric, thermal and chemical characteristics of aluminoborosilicate glasses doped by rare earth oxides

Glasses in SiO2–Al2O3–B2O3–RO system doped with different Re2O3 (Re = La, Ce, Nd and Sm) at 4·5 mol.-% were prepared by conventional melt quenching technique. Structural, thermal durability and dielectric properties were investigated by using differential thermal analysis, Fourier transform infrared spectroscopy and precision impedance analyser respectively. Chemical durability was evaluated by weight losses of samples after immersion in HCl solution for varying times. The results showed that with increasing ionic radius of Re3+ ions (La3+<Ce3+<Nd3+<Sm3+), it was found that the fraction of non-bridging oxides and BO3 units increased. Dielectric constant and loss of doped different Re2O3 glasses decreased with the increase in frequency ranging from 40 Hz to 1 MHz, and possessed the lowest values of dielectric properties of ϵr = 3·83, tan δ = 7·93×10−4. In addition, the results of acid resistance showed that doping Re2O3 could improve the chemical durability in the order of La2O3>Ce2O3>Nd2O3>Sm2O3.

Polymorph (C2N2H10)0.5RE3F10·xH2O (RE = Ho-Lu, Y) and REF3 nanocrystals: Hydrothermal synthesis, characterization and luminescence

In this paper, a solvents-thermal system is developed to prepare one new polymorph of (C2N2H10)0.5Ho3F10·xH2O and rare earth fluorides REF3 nanocrystals under mild condition. It is found that the ionic radius of RE3+ is the key factor responsible for the shape evolution and phase control for rare earth fluorides nanocrystals at selected temperatures, which has an influence on the microstructure and morphology of the products to some extent. With the increase of the atomic number, the shape of fluoride changes from hexagonal REF3 phase (RE=La, Sm) to orthorhombic REF3 phase (RE=Eu-Dy), and finally to diamond structure (C2N2H10)0.5Ho3F10·xH2O (RE=Ho, Er, Tm, Yb, Lu, Y). In addition, the characteristic energy level transition 5D0–7F1 of Eu3+ splits into 585 and 591nm emission peaks, and the dominant peak is the orange emission at 591nm.

Fabrication of Ca-doped REBa2Cu4O8 films by the molten hydroxide method

Abstract In order to improve a critical current density (Jc) under applied magnetic fields, it is well known that the RE-Ba-Cu-O superconductors are required an improvement of a critical temperature (Tc). Although the Tc of REBa2Cu4O8 (RE124) is inferior to REBa2Cu3Oy (RE123), RE124 has rigorous stability of oxygen stoichiometry. Furthermore, the RE124 has an important advantage that the Tc was improved by Ca-doping. In this study, in order to improve Tc of RE124, we fabricated the Ca-doped RE124 (RECa124) films by using molten hydroxide method. The orientation of Y124 and YCa124 films showed a c-axis orientation completely and the Tc of YCa124 film showed 10 K higher than that of the Y124 film. However, GdCa124 and SmCa124 films contained RE123 phase by much compare with YCa124 films and the Tc were decreased with increasing of RE ionic radius over YCa124.

Extraordinary role of rare-earth elements on the transport properties of barium W-type hexaferrite

The influence of R2O3 substitution on the electrical properties and the thermoelectric power on the W-type hexaferrite Ba0.95R0.05 Mg0.5 Zn0.5 Co Fe16 O27; R = Y3+, Er3+, Ho3+, Sm3+, Nd3+, Gd3+, and Ce3+ ions as a function of the absolute temperature and frequency in the ranges 300–750 K and 100 kHz–4 MHz, respectively have been studied. The results obtained reveal that, by introducing a relatively small amount of R2O3 instead of Fe2O3, an important modification of both structure and physical properties can be obtained. The dielectric constant ɛ′, the dielectric loss factor ɛ″ and AC conductivity σ of the investigating samples have highest values in the case of Sm3+. The values of the calculated activation energy varied between (0.335 and 0.553 eV) and (0.106 and 0.232 eV), above and below the transition temperature, respectively which indicate the semiconducting properties of the prepared samples. The conduction mechanism for Ho3+ sample is associated with the small polaron whereas the hopping conduction mechanism is predominant mechanism for the samples doped with the rest of rare-earth ions. The thermoelectric power measurements indicated that the samples are n-type semiconductors except Er3+ and Y3+ samples, where the thermoelectric power of them is positive at low temperature but nearly above 480 and 375 K, respectively transits to negative. The charge carriers concentration n increases with slightly increasing RE ionic radius to critical value (≈1.04 Å), after that n becomes nearly constant.

Enthalpies of Formation of Rare Earth Orthovanadates, REVO4.

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Systematic research on RE 2Zr 2O 7 (RE = La, Nd, Eu and Y) nanocrystals: Preparation, structure and photoluminescence characterization

A series of rare-earth zirconate RE 2Zr 2O 7 nanocrystals (RE = La, Nd, Eu and Y) were prepared by a simple combustion method. These compounds possess either a pyrochlore structure (P-RE 2Zr 2O 7) or a defect fluorite structure (F-RE 2Zr 2O 7), which depends on the ionic radius of RE 3+. The photoluminescence (PL) property of the as-prepared RE 2Zr 2O 7 nanocrystals was studied, and the observed emissions in the UV and visible range were attributed to different transition mechanisms for RE 2Zr 2O 7 with different RE ion. A PL mechanism has been proposed, associated with the transition between the valence band and a mid-gap state related to oxygen vacancies. Divalent Pb ions were introduced into RE 2Zr 2O 7 nanocrystals and the luminescence of the Pb 2+-doped samples was also recorded for comparison. The PL property of RE 2Zr 2O 7 was found to be intimately related to their intrinsic defect structure, and PL was thought as a new method to estimate the degree of disorder in the A 2B 2O 7 structure (from pyrochlore structure to defect fluorite structure).

Magnetoelastic coupling inRTiO3(R=La,Nd,Sm,Gd,Y)investigated with diffraction techniques and thermal expansion measurements

A detailed analysis of the crystal structure in RETiO3 with RE = La, Nd, Sm, Gd, and Y reveals an intrinsic coupling between orbital degrees of freedom and the lattice which cannot be fully attributed to the structural deformation arising from bond-length mismatch. The TiO6 octahedra in this series are all irregular with the shape of the distortion depending on the RE ionic radius. These octahedron distortions vary more strongly with temperature than the tilt and rotation angles. Around the Ti magnetic ordering all compounds exhibit strong anomalies in the thermal-expansion coefficients, these anomalies exhibit opposite signs for the antiferromagnetic and ferromagnetic compounds. Furthermore the strongest effects are observed in the materials close to the magnetic cross-over from antiferromagnetic to ferromagnetic order.

Enthalpies of formation of rare earth orthovanadates, REVO 4

Rare earth orthovanadates, REVO 4, having the zircon structure, form a series of materials interesting for magnetic, optical, sensor, and electronic applications. Enthalpies of formation of REVO 4 compounds ( RE=Sc, Y, Ce–Nd, Sm–Tm, Lu) were determined by oxide melt solution calorimetry in lead borate (2PbO·2B 2O 3) solvent at 1075 K. The enthalpies of formation from oxide components become more negative with increasing RE ionic radius. This trend is similar to that obtained for the rare earth phosphates.

Charge transfer gap for T′-RE2CuO4 and T-La2CuO4 as estimated from Madelung potential calculations

T′-RE2CuO4 (RE: rare-earth element), after appropriate “reduction”, has fairly high conductivity and also exhibits clear Fermi edge in photoemission spectroscopy. To clarify the origin of conductivity in the T′ mother compounds, we evaluated the unscreened charge-transfer gap (Δ0) for T′-RE2CuO4 and T-La2CuO4. The Δ0 value for T′-compounds almost linearly decreases with increasing the ionic radius of RE from 12.24eV for T′-Tm2CuO4 to 9.90eV for T′-La2CuO4. The results qualitatively explain metallic conductivity in T′-RE2CuO4 for large RE.

Strain effects on point defects and chain-oxygen order-disorder transition in 123 cuprate compounds

The energetics of Schottky defects in 123 cuprate superconductor series, $\rm REBa_2Cu_3O_7$ (where RE = lanthandies) and $\rm YAE_2Cu_3O_7$ (AE = alkali-earths), were found to have unusual relations if one considers only the volumetric strain. Our calculations reveal the effect of non-uniform changes of interatomic distances within the RE-123 structures, introduced by doping homovalent elements, on the Schottky defect formation energy. The energy of formation of Frenkel Pair defects, which is an elementary disordering event, in 123 compounds can be substantially altered under both stress and chemical doping. Scaling the oxygen-oxygen short-range repulsive parameter using the calculated formation energy of Frenkel pair defects, the transition temperature between orthorhombic and tetragonal phases is computed by quasi-chemical approximations (QCA). The theoretical results illustrate the same trend as the experimental measurements in that the larger the ionic radius of RE, the lower the orthorhombic/tetragonal phase transition temperature. This study provides strong evidence of the strain effects on order-disorder transition due to oxygens in the CuO chain sites.

Thermochemistry of the alkali rare-earth double phosphates, A3RE(PO4)2

The formation enthalpies for alkali rare-earth compounds of the type K3RE(PO4)2where RE = Sc, Y, Lu, Er, Ho, Dy, Gd, Nd, or Ce and for A3Lu(PO4)2compounds with A = K, Rb, or Cs were determined using high-temperature oxide-melt solution calorimetry. Structural phase transitions were observed and characterized using differential scanning calorimetry and high-temperature x-ray diffraction. The formation enthalpy of the K3RE(PO4)2phases from oxides becomes more exothermic with increasing rare-earth radius for the K3RE(PO4)2series and with increasing alkali radius for the A3Lu(PO4)2compounds. The K3RE(PO4)2phases are stable with respect to anhydrous K3PO4and REPO4. The monoclinic K3RE(PO4)2compounds undergo a reversible phase transition to a hexagonal (glaserite-type) structure with a phase transition temperature that increases from −99 to 1197 °C with increasing RE ionic radius going from Lu to Ce.

Systematic enhancement of in-field critical current density with rare-earth ion size variance in superconducting rare-earth barium cuprate films

Enhanced in-field critical current densities (Jc’s) have been obtained in epitaxial superconducting (RE1,RE2)Ba2Cu3O7−x (RE1=rare-earthion 1, and RE2=rare earth ion 2) films grown on both single crystal and buffered metallic substrates. For a constant average RE ionic radius (equal to that of yttrium), there is a systematic dependence of the in-field Jc on the RE ion size variance, with a small, but nonzero, variance being optimum. Compared to the standard YBa2Cu3O7−x composition, a factor of two improvement in Jc(75.5K) is reproducibly observed at 0.2T(‖c) for the composition Dy1∕3Ho2∕3Ba2Cu3O7−x on both single crystal and buffered-metallic substrates. Angular dependent magnetic field studies and transmission electron microscopy indicate the presence of additional pointlike random defects.

A new group of microwave dielectric ceramics in the RE(Ti0.5W0.5)O4 [RE=Pr, Nd, Sm, Gd, Tb, Dy, and Y] system

RE(Ti0.5W0.5)O4 [RE=Pr, Nd, Sm, Gd, Tb, Dy, and Y] ceramics have been prepared as single-phase materials by a conventional solid-state ceramic route. The ceramics have been characterized by X-ray diffraction and microwave methods. The RE(Ti0.5W0.5)O4 ceramics showed an increase in cell volume and a corresponding decrease in density with ionic radius of RE3+ ions. The dielectric constant varies from 21 to 25, Qu×f from 6000 to 11 000 GHz and τf from −5 to −22 ppm °C−1. The microwave dielectric properties indicate that these materials are possible candidates for dielectric resonator as well as substrate applications in microwave integrated circuits.