RE Doping Research Articles

Pressure-induced insulating state inBa1−xRxIrO3(R=Gd, Eu) single crystals

BaIrO3 is a novel insulator with coexistent weak ferromagnetism, charge and spin density wave. Dilute RE doping for Ba induces a metallic state, whereas application of modest pressure readily restores an insulating state characterized by a three-order-of-magnitude increase of resistivity. Since pressure generally increases orbital overlap and broadens energy bands, a pressure-induced insulating state is not commonplace. The profoundly dissimilar responses of the ground state to light doping and low hydrostatic pressures signal an unusual, delicate interplay between structural and electronic degrees of freedom in BaIrO3.

RE (RE = Sm, Eu, Gd)‐doped CeO2 single buffer layers for coated conductors prepared by chemical solution deposition

AbstractTextured RE (RE = Sm, Eu, Gd)‐doped CeO2 single buffer layers for coated conductors were prepared by a polymer assisted chemical solution deposition (PACSD) approach. The as‐grown buffer layers on biaxially textured NiW(5%) alloy tapes were characterized by X‐ray diffraction (XRD) and scanning electron microscopy (SEM) as well as atomic force microscopy (AFM). The thicknesses of these buffer layers have been determined to be over 150 nm, on which a YBCO film has been deposited with an onset transition temperature above 90 K and a critical current density of 1 MA cm–2. These results indicate that RE doping can increase the critical thickness of CeO2 and PACSD may be a cost‐effective way to deposit CeO2. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

First-principles study on defect chemistry and migration of oxide ions in ceria doped with rare-earth cations

Oxygen transport in rare-earth oxide (RE(2)O(3)) doped CeO(2) with fluorite structure has attracted considerable attention owing to both the range of practical usage (e.g., fuel cells, sensors, etc.) and the fundamental fascination of fast oxide ion transport in crystalline solids. Using density-functional theory, we have calculated the formation energies of point defects and their migration properties in RE(2)O(3) doped CeO(2)(RE = Sc, Y, La, Nd, Sm, Gd, Dy, and Lu). The calculated results show that oxygen vacancies are the dominant defect species obtained by RE(3+) doping. They form associates with the RE(3+) ions, and the corresponding defect association energy is a strong function of the ionic radii of the RE(3+) dopants. The migration of an oxygen vacancy was investigated using the nudged elastic band method. The lowest activation energy for oxygen vacancy hopping is obtained for a straightforward migration path between two adjacent oxygen sites. The migration energy of an oxygen vacancy also strongly depends on the ionic radii of the neighbouring dopant cations. Accordingly, we have identified two factors that affect the oxygen vacancy migration; (1) trapping (or repelling) of an oxygen vacancy at the NN site of the RE(3+) dopant, and (2) reduction (or enlargement) of the migration barrier by RE(3+) doping. These findings provide insight for atomistic level understanding of ionic conductivity in doped ceria and would be beneficial for optimizing ionic conductivity.

Sm-doped CeO2 single buffer layer for YBCO coated conductors by polymer assisted chemical solution deposition (PACSD) method

An over 150 nm thick Sm 0.2 Ce 0.8 O 1.9− x (SCO) single buffer layer has been deposited on bi-axially textured NiW (2 0 0) alloy substrate. Highly in-plane and out-of-plane oriented, dense, smooth and crack free SCO single layer has been obtained via a polymer-assisted chemical solution deposition (PACSD) approach. YBCO thin film has been deposited equally via a PACSD route on the SCO-buffered NiW, the as grown YBCO yielding a sharp transition at T c0 = 87 K as well as J c (0 T, 77 K) ∼ 1 MA/cm 2 . These results indicates that RE (lanthanides other than Ce) doping may be an effective approach to improve the critical thickness of solution derived CeO 2 film, which renders it a promising candidate as single buffer layer for YBCO coated conductors.

Magnetic properties of amorphous Si films doped with rare-earth elements

Amorphous silicon films doped with Y, La, Gd, Er, and Lu rare-earth elements $(a$-Si:RE) have been prepared by cosputtering and studied by means of electron-spin resonance (ESR) and dc magnetization. For comparison purposes the magnetic properties of laser-crystallized and hydrogenated a-Si:RE films were also studied. It was found that the rare-earth species are incorporated in the a-Si:RE films in the ${\mathrm{RE}}^{3+}$ form and that the RE doping depletes the neutral dangling bond ${(D}^{0})$ density. The reduction of ${D}^{0}$ density is significantly larger for the magnetic RE's $({\mathrm{Gd}}^{3+}$ and ${\mathrm{Er}}^{3+})$ than for the nonmagnetic ones ${(Y}^{3+},$ ${\mathrm{La}}^{3+},$ ${\mathrm{Lu}}^{3+}).$ These results are interpreted in terms of an exchangelike interaction ${H}_{\mathrm{int}}\ensuremath{\sim}\ensuremath{-}{J}_{\mathrm{RE}\ensuremath{-}\mathrm{DB}}{\mathbf{S}}_{\mathrm{RE}}{\mathbf{S}}_{\mathrm{DB}}$ between the spin of the magnetic RE's and that of the ${D}^{0}.$ All our Gd-doped Si films showed basically the same broad ESR ${\mathrm{Gd}}^{3+}$ resonance $(\ensuremath{\Delta}{H}_{\mathrm{pp}}\ensuremath{\approx}850\mathrm{Oe})$ at $g\ensuremath{\approx}2.01,$ suggesting the formation of a rather stable RE-Si complex in these films.

Synthesis, crystal growth and second harmonic generation properties of trivalent rare-earth-doped non-linear tungsten–bronze-type structure Ba 2Na 1−3 xRE xNb 5O 15 (RE=Sc, Y, La, Gd, Yb and Lu)

A new compound filled tungsten–bronze-type structure Ba 2Na 1−3 x RE x Nb 5O 15 (trivalent rare-earth ions: RE 3+=Sc 3+, Y 3+, La 3+, Gd 3+, Yb 3+ and Lu 3+, with x=0.02) has been prepared by selecting RE 3+ ions without any absorption in the visible range. The effect of rare-earth addition on micro-twin formation, that is to say, tetragonal–orthorhombic ferroelastic phase transition in barium sodium niobate was investigated and micro-twin formation could be suppressed by doping of smaller RE 3+ ions such as Yb 3+ and Lu 3+. All the samples exhibit an intense second harmonic generation signal under tunable IR pumping laser source, due to both the high values of the non-linear optical coefficients and the absence of absorption of additional RE ions in the visible range.

The Preparation, Characterization, and their Photocatalytic Activities of Rare-Earth-Doped TiO2 Nanoparticles

RE/TiO2 photocatalysts were prepared by the sol–gel method using rare earth (RE=La3+, Ce3+, Er3+, Pr3+, Gd3+, Nd3+, Sm3+) metal salts and tetra-n-butyl titanate as precursors, and were characterized by XRD, IR, UV–vis diffuse reflection, and transient absorption spectra. Their photocatalytic activities were evaluated using nitrite as a decomposition objective. As a result, suitable content of doping rare earth in TiO2 can efficiently extend the light absorption properties to the visible region. At the same time, it is beneficial to NO2− adsorption over the catalysts due to rare earth doping. RE/TiO2 samples can enhance the photocatalytic activity to some extent as compared with naked TiO2. The increase in photoactivity is probably due to the higher adsorption, red shifts to a longer wavelength, and the increase in the interfacial electron transfer rate. Nitrite is almost completely degraded over RE/TiO2 catalysts after longer irradiation, which is different from Degussa P-25 with a plateau of activity after ca. 20 min irradiation. Gd3+-doped TiO2 showed the highest reaction activity among all concerned RE-doped samples because of its specific characteristics. The amount of RE doping was an important factor affecting photocatalytic activity; the optimum amount of RE doping is ca. 0.5 wt%, at which each RE/TiO2 sample shows the most reactivity. The photocatalytic degradation reaction of nitrite over Gd3+-doped samples and P-25 follows apparent first order kinetics, which is different from that of Sm3+, Ce3+, Er3+, Pr3+, La3+, and Nd3+-doped TiO2 catalysts, which obey zero-order kinetics, indicating that these processes were dominated by electron–hole recombination.

Phase stabilisation and structural disorder in Ln 1.85Ce 0.15CuO 4 (Ln=Pr, Nd, Sm, Eu and Gd)

A systematic FTIR study of electron doped compounds of the T′-series are presented in this paper. Rare-earth substituted phases of composition Ln 1.85Ce 0.15CuO 4 (Ln=Pr, Nd, Sm, Eu and Gd) have been synthesised. Single-phase formation is achieved up to RE=Gd, beyond which T′-structure is not stable. Disorder due to RE doping is exhibited in the FTIR spectra of as-prepared materials. The origin of disorder is due to non-matching of LnO/CuO bonds in the T′-structure. The built-in internal pressure is responsible for the change of CuO polyhedron (CuO 6 octahedra to CuO 2 planar) as relaxing mechanism in the formation of T′-compounds from T-structured compounds. This is well established from the appearance or disappearance of CuO vibration peaks in the FTIR spectra.

Lanthanum Alkaline‐Earth Manganites as a Cathode Material in High‐Temperature Solid Oxide Fuel Cells

The effect of RE (RE = Ce and Pr) doping perovskite on crystallographic properties, phase relationships, conductivity, thermal expansion, sintering, and reaction with electrolyte is presented. showed a single perovskite phase in the region 0 ≤ x ≤ 0.05 for Ce substitution and over the entire composition range of Pr content. No effect of RE doping of on conductivity was observed. A decrease in thermal expansion coefficients of accompanied RE doping. Ce doping of increased its morphological stability and suppressed its reaction with the electrolyte. (Ln: lanthanum concentration with La, Ce, and Pr, AE = Sr, Ca) materials were examined as cathodes in solid oxide fuel cells. X‐ray diffraction analysis indicated that (0 ≤ x ≤ 0.3) 7:19 AM 7/22/01 showed a single perovskite phase. Conductivities of these oxides increased with AE content and ranged from 80 to 200 S/cm at 1000°C in air, and thermal expansion coefficients ranged from 9.5 to . showed less reactivity with the electrolyte compared with . The cathodic polarization of the at 1000°C was 60 mV at in air. © 1999 The Electrochemical Society. All rights reserved.

Preparation and characterization of RE doped La 2- xSr xCuO 4

We report on the systhesis of (La,RE) 2- x Sr x CuO 4 for various RE=Pr, Nd, Sm, Eu, Gd, Dy, Ho and Er as a function of the RE and Sr concentrations. The sample characterization by means of powder X-ray diffraction and EDX is described. We present our results on the solubility limit of the various RE in the T structure of La 2- x Sr x CuO 4 and discuss the systematic influence of RE and Sr doping on the structural properties. We furthermore show that doping with RE does not influence the charge carrier concentration of the samples.