Effect Of Y-doping Research Articles

Investigation of Mixed Conductor BaCo0.7Fe0.3−xYxO3−δ with High Oxygen Permeability

Cubic BaCo0.7Fe0.3−xYxO3−δ (BCFY, x = 0.08−0.2) was prepared by the conventional solid state reaction route as oxygen permeation membranes. The effects of Y-doping on the crystal structure, electrical conductivity, and oxygen permeability are investigated, and the factors influencing the activation energy of oxygen migration are discussed from the viewpoints of metal−oxygen bonding energy and geometric lattice structure. Y-substitution decreases the electrical conductivity but increases the oxygen vacancy concentration of BCFY samples. Nevertheless, the oxygen permeability decreases with increasing Y-doping level. Both the strong Y−O bonding energy and the decreased critical radius (rC) with Y-doping should be responsible for the increased activation energy. First principle calculation reveals that Y-doping results in the nonequivalent positions of the mobile oxygen ions and thus limits the oxygen ion diffusion passages. BaCo0.7Fe0.22Y0.08O3−δ membrane exhibits a high oxygen permeability of 1.73 mL min−1 ...

Multiferroicity and magnetoelectric coupling in polycrystalline Y-doped EuMnO 3

The effects of Y-doping on the magnetic, dielectric and ferroelectric properties of EuMnO 3 were carefully investigated through a series of polycrystalline Eu 1 − x Y x MnO 3 ( x = 0, 0.15, 0.25, 0.3 and 0.5) samples prepared by solid state reaction. The Y-doping reduces the A-site ionic size and then the Mn–O–Mn bond angle. It is postulated that upon the doping, the magnetic ground state firstly changes to a conical spin order at x = 0.15 and then a spiral spin order for higher doping. The ferroelectric transitions appear at the conical and spiral spin order transition points ∼ 25 K, and a polarization ∼ 90 μC/m 2 is achieved in sample with x = 0.25.

Oxygen grain-boundary transport in polycrystalline alumina using wedge-geometry bilayer samples: Effect of Y-doping

Novel wedge-geometry, dual-layer alumina samples, both undoped and 500 ppm Y 3+-doped, were studied in the temperature regime 1250–1400 °C to determine the effect of Y 3+ on oxygen grain-boundary transport in alumina. The samples consisted of a wedge-shaped, single-phase alumina top layer, diffusion bonded to an alumina/Ni substrate containing a fine, uniform dispersion of Ni marker particles (0.5 vol.%). The extent of the alumina spinel oxidation layer was measured as a function of the wedge thickness for a series of heat-treatment conditions. Models of the transport behavior were used to derive values for the rate constants ( k) in both the alumina top layer and the alumina/Ni substrate. It was found that the presence of yttrium slows oxygen grain-boundary diffusion in alumina by a factor of ∼5 (at 1300 °C), and increases the corresponding activation enthalpy for oxidation from 407 ± 20 to 486 ± 34 kJ mol −1. Microstructural observations suggested that yttrium also slows Ni outward diffusion. A comparison of the different k values revealed that, at 1300 °C, the presence of Ni alone enhances transport by a factor of ∼2 relative to undoped alumina.

Low temperature heat capacity of Nd2/3Ca1/3MnO3 and (Nd0.9 Y0.1)2/3Ca1/3MnO3 manganites: transformation of the Schottky-like anomaly

Effect of Y-doping on interactions in the spin system of the colossal magnetoresistance compound Nd2/3Ca1/3MnO3 has been studied by the thermal relaxation heat capacity and neutron diffraction techniques in the 2 — 30 K temperature range. In 5 K temperature region a broadened Schottky-like specific heat anomaly Csch(T) has been foDnd both in the parent Nd2/3Ca1/3MnO3 and in the doped (Nd0.9Y0.1)2/3Ca1/3MnO3 compounds. The experimental data were successfully fitted by a set of three two-level Schottky contributions, implying a broadening of the exited level in the system with randomly distributed Y ions. Replacement of 10 % Nd ions by nonmagnetic Y ions leads to the about 10 % enlargement of the splitting of the ground state doublet of Nd3+ ion.

New Insight into the Properties of Proton‐Conducting Oxides from Neutron Total Scattering

In recent years there has been a growing interest in searching for new proton conducting materials that could be successfully used in medium temperature solid oxide fuel cells (SOFC). In particular, proton conducting oxides have been the subject of a massive research activity. Among the most promising oxide the acceptor doped cerates appears to be those most appealing in view of practical applications. A relevant aspect of these materials is the investigation of the local distortion of the structure arising from water incorporation. This kind of study is of great help in defining how the structure changes in order to accommodate the proton which is usually thought to enter the structure in form of hydroxyl group where the oxygen vacancy results from the acceptor doping on the Ce site. Atomistic simulation work confirmed that the preferential location of dopant ions is on the Ce site. To the best of our knowledge the only experimental work addressing the role of dopant and water incorporation on the local structure of V-doped cerates is a X-ray absorption spectroscopy (XAS) work carried out by Longo and coworkers at the Y K-edge. The main conclusion of that work was the observation that Y-doping induces amore » distortion of the parent BaCe0{sub 3} structure resulting in a significantly distorted Y local environment. However, local structure information derived from XAS study does not provide a direct structural information and depends strongly upon the model used to calcualte theoretical {chi}(k) which is not unique. Moreover, the XAS analysis usually provide significant information only up to the second shell. As a consequence, a more reliable and useful technique to investigate the local arrangement in these proton conducting oxides appears to be the Pair Distribution Function (PDF) analysis derived from total neutron scattering measurements. In the present work we investigated the pure BaCeO{sub 3} and the acceptor doped BaCe{sub 0.90}Y{sub 0.10}O{sub 2.85} compounds. In both cases the samples have been measured at room temperature and after being exposed to dry and wet air (humidification attained through bubbling air in D{sub 2}O). Aim of this work is to look at the effect of Y-doping and water doping on the local structure of the above mentioned samples.« less

Effect of Y-doping on the magnetic and charge orderings in Nd 2/3Ca 1/3MnO 3

The shifts of the magnetic and charge ordering transition temperatures caused by Nd substitution for Y in Nd 2/3Ca 1/3MnO 3 CMR narrow-band perovskite manganite have been studied. At low temperatures, three different long-range magnetic orderings consistent with a phase separation scenario have been observed in the doped compound (Nd 0.9Y 0.1) 2/3Ca 1/3MnO 3 by neutron-diffraction study: the antiferromagnetic orderings of PCE and DE types existing below ∼110 and ∼60 K, respectively, and the ferromagnetic one of B type existing below ∼42. Magnetic phase transformations temperatures as well as those of charge ordering have been found to be structural-dependent. Y-doping leads to the decrease of the anisotropy of the orthorhombic Pnma crystal lattice b/√2 c, which causes a decrease of the indirect exchange parameters in the system and thus a decrease in the magnetic transformation temperatures for 20–30 K in the doped compound. Doping leads as well to the higher level of the coherent Jahn–Teller distortions of the MnO 6 octahedra in the 200–300 K temperature region, which results in the increase of the charge ordering temperature for ∼80 K.

Synthesis and properties of Y-doped SrTiO 3 as an anode material for SOFCs

Y-doped SrTiO 3 was synthesized via solid-state reaction. The effects of Y-doping on the sinterability and the electrical conductivity of Y x Sr 1− x TiO 3 were investigated. Y-doping can increase the sintering activity and the electrical conductivity of SrTiO 3 when yttrium amount is less than 0.09 in Y x Sr 1− x TiO 3. Excessive yttrium will cause the generation of an insulating phase Y 2Ti 2O 7, which impedes the densification process and decreases the electrical conductivity of Y x Sr 1− x TiO 3 material. With the increased temperature, the electrical conductivity of Y-doped SrTiO 3 increases first and then decreases gradually, showing a mixed conduction behavior of semi-conductors and metals. The optimized Y 0.09Sr 0.91TiO 3 possesses an electrical conductivity on the order of 32.5–195.8 S cm −1 in the temperature range of 25–1000 °C and being 73.7 S cm −1 at 800 °C in forming gas. The thermal cycling in air does not remarkably affect the electrical conductivity and the conduction behavior of Y 0.09Sr 0.91TiO 3 at high temperatures. Y 0.09Sr 0.91TiO 3 displays a relatively stable electrical conductivity at different oxygen partial pressures and excellent chemical compatibility with YSZ at temperatures lower than 1300 °C.

Processing and physical properties of La 0.8− zY zSr 0.2MnO 3 bulk, thick films and single crystal

Bulk and thick film manganese perovskite La 0.8− z Y z Sr 0.2MnO 3 (LYSMO) with 0⩽ z⩽0.8 have been processed by standard ceramic process. A single crystal of La 0.78Y 0.02Sr 0.2MnO 3 made by floating zone method had been prepared and thick films were deposited on (001) MgO substrates using an air-brushing method. The structure and microstructure were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electron paramagnetic resonance (EPR) and the magneto-transport properties have been performed to determine the paramagnetism–ferromagnetism transition temperature ( T C). The insulator-to-metal transition (I–M) occurs at about room temperature ( T IM) and T C is in range of 311–355 K. The magnetoresistance of 70% at 300 K has been observed. Effects of Y-doping are also discussed.

Influence of A-site cation size on the magnetic and transport properties of (Nd 1− yY y) 0.7Sr 0.3MnO 3 (0⩽ y⩽0.42)

The effects of Y-doping on the Nd-sites in the perovskite (Nd 1− y Y y ) 0.7Sr 0.3MnO 3 have been investigated by means of magnetic AC-susceptibility and resistivity measurements. With increasing y, corresponding to decreasing the A-site average ionic radius 〈 r A〉, the ferromagnetism and metallicity are strongly suppressed. Increasing y in the range 0⩽ y⩽0.21 rapidly lowers T C, however, there still exists a metallic–insulating transition at temperatures close to T C. Although the ferromagnetic-state conductivity is strongly depressed, within 0⩽ y⩽0.14, the paramagnetic-state conductivity is not significantly affected and seems to follow the variable-range hopping model. The nearest-neighbor hopping mechanism becomes dominant at higher doping levels. At the critical average cation size 〈 r A〉=1.19 Å (according to y=0.28) and lower, the ferromagnetic–paramagnetic as well as the metallic–insulating transitions are no longer observed, but spin-glass-like and insulating behavior are observed instead. These results are discussed in terms of the double-exchange mechanism and the GdFeO 3-type lattice distortion.

Effect of Y-Doping on Resistance Degradation of Multilayer Ceramic Capacitors with Ni Electrodes under the Highly Accelerated Life Test

The effect of Y-doping on the degradation behavior of insulation resistance for multilayer ceramic capacitors with Ni electrodes has been studied using electrical measurement techniques such as admittance spectroscopy, thermally stimulated current (TSC), and electrical conductivity measurements. TSC measurements show that a strong internal bias field remained after applying an electrical field at a high temperature, like during highly accelerated life testing. This internal bias field originated from the migration of positive carriers. Admittance spectroscopy indicated three types of relaxation, with activation energies of 0.4, 0.8, and 0.8–1.0 eV. The intensity of the 0.4 eV relaxation peak increased with Y3+ doping and disappeared at low oxygen partial pressure ( PO2) annealing. The existence of holes was also observed from the temperature dependence of insulation resistance. The 0.4 eV relaxation is considered to be due to the transition of electrons from the valence band to barium vacancy states. These results suggest that Y3+ acts as a donor and creates barium vacancies, which compensate for the oxygen vacancies and thereby improve the resistance to degradation.

Effects of Y-doping on the formation, structure and properties of iron oxide

The effects of Y-doping on the phase formation in an FeSO 4Na 2CO 3 suspension system were determined. The phase, microstructure and thermal stability of the samples were studied by XRD, TEM and TG-DTA. It was found that Y appears to restrain the nucleation and growth of α-FeOOH, but facilitates the formation of γ-FeOOH. Partly due to Y-doping, tetragonal γ-Fe 2O 3 from direct dehydration of γ-FeOOH has high thermal stability, and the phase transition temperature of γ-Fe 2O 3→α-Fe 2O 3 is increased to 725 °C. The properties of cubic γ-Fe 2O 3 obtained from Y-doped α-FeOOH were also investigated.

Angle-resolved photoemission of Y-doped Bi 2Sr 2CaCu 2O 8+ δ

An angle-resolved photoemission study of a single crystal of the Y-doped BCSCO 2212 phase, of composition (Bi 1.87Pb 0.13)(Sr 1.92Y 0.08)(Ca 0.52Y 0.41)(Cu 1.97Al 0.02Bi 0.01)O x has been undertaken using line 6.2 at the CLRC D Laboratory. This superconducting material undergoes a poorly understood metal-to-non-metal transition when roughly half the Ca is replaced by Y. The dispersion of the valence band and Fermi level states in the (001) ( ab) plane of the structure has been studied. Results for the high symmetry directions in the 2D Brillouin zone, ГX, ГY and ГZ, are presented. We compare the ab-plane band structure of this material with band-structure calculations, and with photoemission results from the well-studied undoped 2212 phase. The effect of Y-doping on the band structure close to the metal-to-non-metal transition is discussed.