The influence of different fabrication processes on characteristics of excess Bi2O3-doped 0.95 (Na0.5Bi0.5)TiO3–0.05 BaTiO3 ceramics

In this study, we will develop the influences of the excess x wt% (x=0, 1, 2, and 3) Bi₂O₃-doped and the different fabricating process on the sintering and dielectric characteristics of 0.95 (Na_0.5Bi_0.5)TiO₃–0.05 BaTiO₃ ferroelectric ceramics with the aid of SEM and X-ray diffraction patterns, and dielectric–temperature curves. The 0.95 (Na_0.5Bi_0.5)TiO₃–0.05 BaTiO₃+x wt% Bi₂O₃ ceramics are fabricated by two different processes. The first process is that (Na_0.5Bi_0.5)TiO₃ composition is calcined at 850 °C and BaTiO₃ composition is calcined at 1100 °C, then the calcined (Na_0.5Bi_0.5)TiO₃ and BaTiO₃ powders are mixed in according to 0.95 (Na_0.5Bi_0.5)TiO₃–0.05 BaTiO₃+x wt% Bi₂O₃ compositions. The second process is that the raw materials are mixed in accordance to the 0.95 (Na_0.5Bi_0.5)TiO₃–0.05 BaTiO₃+x wt% Bi₂O₃ compositions and then calcining at 900 °C. The sintering process is carried out in air for 2 h from 1120 to 1240 °C. After sintering, the effects of process parameters on the dielectric characteristics will be developed by the dielectric–temperature curves. Dielectric–temperature properties are also investigated at the temperatures of 30–350 °C and at the frequencies of 10 kHz–1 MHz.     

A higher conductivity Bi2O3-based electrolyte

We have developed a Bi₂O₃ electrolyte doped with Dy₂O₃ and WO₃ (DyWSB) that exhibits a higher conductivity than that of 20 mol% erbia stabilized bismuth oxide (20ESB), thus, giving it the highest conductivity of any known solid oxide electrolyte. Electrical conductivity results of the Dy–W stabilized bismuth oxide system are presented. The dopants were selected based on their polarizability and its effect on structural stability and conductivity. At 800 °C, the conductivity of (BiO_1.5)_0.88(DyO_1.5)_0.08(WO₃)_0.04 is 0.57 S/cm (1.5 times as high as that of 20ESB), and at 500 °C, the conductivity is 0.043 S/cm (2 times as high as that of 20ESB).     

Lithium extraction/insertion from LiMn2O4 — effect of crystallinity

Effect of host crystallinity on lithium extraction/insertion of LiMn₂O₄ was studied. LiMn₂O₄ powders with different crystallinity were prepared via lithium-manganese-tartrates by heat treatment at various temperatures above 300 °C. First charge-discharge capacity around 4 V depended on lattice parameter a₀ and lattice strain . On the other hand, the first discharge capacity around 3 V was found to be independent of these parameters.     

Superconducting oxide formation in the Yb---Ba---Cu---O system

Conditions for forming YbBa₂Cu₄O₈, Yb₂Ba₂Cu₃O_7−δ and YbBa₂Cu₃O_7−δ were determined in oxygen at 1.0 atm pressure by experiments with oxidized Yb---Ba---Cu---Ag alloys. YbBa₂Cu₃O_7−δ formed in less than 10 s when oxidized alloy ribbons were baked in the 805°C–890°C range. Large amounts of Ba₂Cu₃O₅ formed below 870°C. Yb₂Ba₄Cu₇O_15−δ and YbBa₂Cu₄O ₈ then formed in the 10²s–10³s range at temperatures in the 840°C–870°C and <840°C ranges, respectively. Ba₂Cu₃O₅ decomposition supplied Cu²⁺ and O²⁻ for the rapid transformation of YbBa₂Cu₃O_7−δ grains into Yb₂Ba₄Cu₇O_15−δ grains by intercalation. Intercalation was much slower in the absence of Ba₂Cu₃O₅. All of these transformation products underwent coarsening with increasing bake time. Rapid YbBa₂Cu₄O₈ and Yb₂Ba₄Cu₇O_15−δ formation, compared to the slow formation of these phase types when Yb was substituted by Y, Is due to the differing effects of Y and Yb on formation kinetics. Superconducting oxide-silver composite ribbons containing mainly YbBa₂Cu₃O_7−δ, Yb₂Ba₄Cu₇O_15−δ or YbBa₂Cu₄O₈ can be prepared from Yb---Ba ---Ba---Cu---Ag alloys.     

Structure of the Si(011)-(16 × 2) surface and hydrogen desorption kinetics investigated using temperature-programmed desorption

D₂ temperature-programmed desorption (TPD) was used to probe the structure of the Si(011)-(16 × 2) surface. Deuterium was adsorbed at 200°C to coverages θ_D ranging up to complete saturation (approximately 1.1 ML) and the sample heated at 5°C s⁻¹. TPD spectra exhibited three second-order desorption peaks labelled β₂, β*₁ and β₁ centered at 430, 520 and 550°C. Of the proposed models for the Si(011)-(16 × 2) reconstruction, the present TPD results as a function of θ_D provide support for the adatom/dimer model with the β₂ peak assigned to D₂ desorption from the dihydride phase, while the β*₁ and β₁ peaks arise from adatom and surface-atom monohydride phases.     

Relationship between electronic and crystal structure in Cu–Ni–Co–Mn–O spinels: Part A: Temperature-induced structural transformation

Local atomic and crystal structures around Cu and Mn atoms in Mn_1.68Cu_0.6Ni_0.48Co_0.24O₄ spinel samples fabricated by metal–organic decomposition synthesis at different annealing temperatures were investigated by X-ray absorption fine structure analysis. There are two distinct copper cations, Cu¹⁺ and Cu²⁺, both of which maintain tetrahedral coordination. The bond-length distances are Cu¹⁺–O = 2.00 Å and Cu²⁺–O = 1.80 Å. The manganese cations are for the most part octahedral. The spinels prepared at low temperature (600 °C) contain smaller (Mn⁴⁺–O = 1.88 Å) undistorted MnO₆ octahedrons corresponding to Mn⁴⁺ valence, whereas the manganese octahedrons in high-temperature materials (800 °C and higher) were larger and had a pronounced tetragonal distortion pertaining to Mn³⁺ oxidation state (Mn³⁺–O = 1.93 Å and 2.11 Å). By rising the fabrication temperatures, relative concentration of the species of Mn⁴⁺ and Mn³⁺ varies as a result of the reaction represented by Cu¹⁺ + Mn⁴⁺  Cu²⁺ + Mn³⁺, implying irreversible temperature-induced structural transformation. Atomic coordinates in the low-temperature phase are similar to those found in the ideal cubic spinel with oxygen parameter u = 0.27, whereas local environments of the Cu and Mn atom correspond to the tetragonal CuMn₂O₄ phase (space group I4₁/amd). Unlike in CuMn₂O₄, orientation of the lattice distortions is random, however, the long-range cubic spinel structure is retained at all time.     

The effects of substrate temperature on the superconducting properties of Tl2Ca2Ba2Cu3O10 films sputter-deposited from stoichiometric oxide targets

The annealing characteristics and the superconducting properties of Tl₂Ca₂Ba₂Cu₃O₁₀ thin films sputter-deposited onto yttrium- stabilized ZrO₂ substrate at up to 500°C from two stoichiometric oxide targets are reported. The films deposited at 400–500°C were found to require a lower post-annealing temperature than the films deposited at lower temperatures to attain the highest T_c superconducting state, due to a more pronounced Ba diffusion toward the substrate as indicated by their secondary ion mass spectrometry depth profiles. The highest T_c achieved tends to degrade with increasing substrate temperatures, a zero resistance T_c of 121 and ≈90 K, respectively, being observed for the films deposited at -ambient temperature and at 500°C. The formation of the highest T_c phase (Tl₂Ca₂Ba₂Cu₃O₁₀) generally is associated with a sheet type of crystal growth morphology with smooth and aligned surfaces which can be obtained only from the films capable of sustaining prolonged annealing at 900°C. Annealing at lower temperatures (≈860°C) results in the formation of rod or sphere type of morphologies with rough and randomly oriented crystals and the lower T_c phases such as Tl₂Ca₁Ba₂Cu₂O₈.     

The phase transition and optimal synthesis temperature of LiNiO2

The phase transition of LiNiO₂ has been studied by using impedance spectroscopy, DTA, and X-ray diffraction methods. At 720°C the hexagonal phase changes in air to the cubic phase. The phase transition process is rather slow and partially reversible. A peculiar conductivity behavior was observed. From 324°C the conductivity deviates from Arrhenius behavior and is temperature-invariant until 613°C. Subsequently, it decreases rapidly with increase of the temperature. This phenomenon is related to the occupation of Ni²⁺ in Li⁺ positions. The optimal sintering temperature for LiNiO₂ is suggested to be 700°C.     

A new procedure for the preparation of Tl2Ba2CaCu2O8-δ characterization by neutron diffraction, electron diffraction and HREM

A new procedure for the preparation of Tl₂Ba₂CaCu₂O_8-δ is presented. In the first step stoichiometric amounts of Cu(NO₃)₂·3H₂O, Ba(OH)₂·H₂O, CaO and Tl₂O₃ are reacted in a closed alumina crucible at 760°C to form a mixture of Tl- 2212, CuO, CaO and other oxide phases. In the second step this material is milled, pelletized and fired in a gold-sealed alumina crucible at 860–900°C for three to eight hours. Three batches of Tl-2212 prepared by this method were investigated showing less than 1% loss of thallium while T_c was close to 110 K. Rietveld refinements using time-of-flight neutron-diffraction data demonstrate that the method produces pure material in a reproducible way and that the materials are substoichiometric with respect to oxygen (δ=0.3). Investigations using electron diffraction and high-resolution electron microscopy indicate the absence of stacking faults.     

Eu,Dy共掺杂SrAl2O4长余辉材料制备新工艺

活化Al-Sr合金粉末水解制备SrAl₂O₄长余辉材料的前驱体,并采用高温固相反应法制备出Eu,Dy共掺杂的SrAl₂O₄长余辉材料,对其微观结构和发光特性进行了研究。实验结果表明:前驱体中Al、Sr元素在微观状态下分布均匀,所制成的长余辉发光材料的发射主峰位于520nm附近,为典型的Eu²⁺离子4f5d-4f的特征发射,初始亮度达到18cd/m²,余辉时间长达46h。     

Germanium and iron co-substituted SrCoO2.5+δ as oxygen permeable membrane

Germanium and iron co-doped SrCoO_2.5+δ was investigated in terms of phase stability, oxygen permeability and electrical conductivity. The favorable high-temperature cubic structure of SrCoO_2.5+δ was stabilized to lower temperatures by co-doping Ge (10 mol%) and Fe (10 mol%) that substituted for Co, which however could not be achieved by doping Ge (20 mol%) alone. In contrast to SrCo_0.8Ge_0.2O_2.5+δ sample which showed a sharp decrease in oxygen permeability at temperature of 875 °C upon cooling, SrGe_0.1Co_0.8Fe_0.1O_3−δ sample remained well-permeable to oxygen at lower temperatures down to at least 820 °C; an abrupt change in electrical conductivity in SrCo_0.8Ge_0.2O_2.5+δ also occurred accompanying the phase transition. The oxygen permeation flux for SrGe_0.1Co_0.8Fe_0.1O_3−δ increased significantly with the decrease of the membrane thickness, indicating the transport of oxygen ions in the bulk of the membrane as the rate-limiting step.     

多孔CeO2膜的制备及其光谱性能

以铈箔为原料,采用阳极氧化法和热处理法制备多孔的CeO₂膜。将阳极氧化铈膜分别在400,500和800 ℃下进行热处理,分别研究阳极氧化铈膜的晶体结构、组成和表面形貌,分别研究多孔的CeO₂膜红外光谱特征吸收和热膨胀性能。阳极氧化铈膜是Ce(OH)₃,CeF₃,Ce₂O₃,CeO₂和Ce的混合膜,并吸附水和乙二醇,其中Ce(OH)₃,CeF₃,Ce₂O₃分别为六方晶型结构,CeO₂和Ce分别为立方晶型结构。阳极氧化铈膜中的Ce(OH)₃,Ce₂O₃和Ce分别在400和500 ℃进行热处理时可能分别转变为CeO₂,分别在400和500 ℃热处理后的膜为CeF₃和CeO₂的混合膜。阳极氧化铈膜中的Ce(OH)₃,CeF₃,Ce₂O₃和Ce在800 ℃进行热处理时可能分别转变为CeO₂,在800 ℃热处理后的膜为CeO₂膜。该CeO₂膜是多孔的膜,且孔为直孔,在1 600～4 000 cm-1范围内具有强吸收。该CeO₂膜在170～900 ℃范围内热膨胀系数变化不大,该膜的热稳定性较好。     

X-ray diffraction studies of epitaxy in orthorhombic- DyMnO3/Er1Ba2Cu3O7-δ thin film heterostructures on LaAlO3 (100) substrates

The heteroepitaxy in DyMnO₃/Er₁Ba₂Cu₃O_7-δ bilayer thin films on LaAlO₃ (100) substates was characterized by four-circle X-ray diffractometry. The Er₁Ba₂Cu₃O_7-δ thin films on LaAlO₃ (100) substrates were prepared by molecular-beam deposition (MBD) and post-growth annealing in wet and dry O₂ at 880°C, whereas the DyMnO₃ thin films on the Er₁Ba₂Cu₃O_7-δ/LaAlO₃ (100) heterostructure were deposited by MBD and post-growth annealing in dry O₂ at 750°C. The conventional X-ray diffraction (XRD) patterns as well as pole figures (φ-scans) for specific (hkl) reflections were acquired. The Er₁Ba₂Cu₃O_7-δ thin film in the DyMnO₃/Er₁Ba₂Cu₃O_7-δ/LaAlO₃ (100) heterostructure showed [001] oriented epitaxial growth, as expected. The DyMnO₃ thin film on the Er₁Ba₂Cu₃O_7-δ epilayer in the heterostructure grew with (110) epitaxy in its metastable orthorhombic phase (lattice constants: a_o=5.272 Å, b_o=5.795 Å and c_o=7.38 Å). The heteroepitaxial relationships at the orthorhombic-DyMnO O₃ (110) /Er₁Ba₂Cu₃O_7-δ (001) interface was determined as the following: DyMnO₃ (110) Er₁Ba₂Cu₃O_7-δ (001), DyMnO₃ [1 0] ¶r; Er₁Ba₂Cu₃O_7-δ[100] or Er₁Ba₂Cu₃O_7-δ[010], and DyMnO₃ [001] ¶r; Er₁Ba₂Cu₃O _7-δ[010] or Er₁Ba₂Cu₃O_7-δ [100].     

In situ surface analytical investigation of the thermal oxidation of Ti–Al intermetallics up to 1000 °C

The low pressure high temperature oxidation behavior of Ti–Al intermetallics are of interest to power technology aiming to synthesize this material by sintering of powders. This paper presents in situ surface analytical studies of the composition of a two-phase TiAl/Ti₃Al bulk microcrystalline system after oxidizing the same (sputtered) reference surface for 30 min at various oxygen partial pressures and temperatures varying between room temperature (RT) and 1000 °C. The results show that oxidation already begins at very low (<5×10⁻¹⁰ mbar) oxygen pressure, producing Al₂O₃ and the lower oxidation states of Ti. As the oxygen pressure and oxidation temperature increases, TiO₂ becomes dominant up to 900 °C. No phase transition of Al₂O₃ has been observed in this range. No sign of a blocking behavior of the oxide layer is seen. At 1000 °C a new oxide phase, Al₂TiO₅ appears, changing the composition and behavior of the surface drastically. The observed results can be explained by qualitative thermodynamic arguments. The thickness and composition of the oxide overlayer is, however, primarily determined by the oxygen supply.     

Oxygen transfer processes in (La,Sr)MnO3/Y2O3-stabilized ZrO2 cathodes: an impedance spectroscopy study

Impedance spectroscopy was used to study the oxygen reaction kinetics of La_0.8Sr_0.2MnO₃ (LSM)-based electrodes on Y₂O₃-stabilized ZrO₂ (YSZ) electrolytes. Three types of electrodes were studied: pure LSM, LSM–YSZ composites, and LSM/LSM–YSZ bilayers. The electrodes were formed by spin coating and sintering on single-crystal YSZ substrates. Measurements were taken at temperatures ranging from 550 to 850°C and oxygen partial pressures from 1×10⁻³ to 1 atm. An arc whose resistance R_el had a high activation energy, E_a=1.61±0.05 eV, and a weak oxygen partial pressure dependence, (P_O2)^−1/6, was observed for the LSM electrodes. A similar arc was observed for LSM–YSZ electrodes, where R_el(P_O2)^−0.29 and the activation energy was 1.49±0.02 eV. The combination of a high activation energy and a weak P_O2 dependence was attributed to oxygen dissociation and adsorption rate-limiting steps for both types of electrodes. LSM–YSZ composite cathodes showed substantially lower overall interfacial resistance values than LSM, but exhibited an additional arc attributed to the resistance of YSZ grain boundaries within the LSM–YSZ. At 850°C and low P_O2, an additional arc was observed with size varying as (P_O2)^−0.80 for LSM and (P_O2)^−0.57 for LSM–YSZ, suggesting that diffusion had become an additional rate limiting step. Bilayer LSM/LSM–YSZ electrodes yielded results intermediate between LSM and LSM–YSZ. The results showed that most of the improvement in electrode performance was achieved for a LSM–YSZ layer only ≈2 μm thick. However, a decrease in the grain-boundary resistance would produce much better performance in thicker LSM–YSZ electrodes.     

Niobium based tetragonal tungsten bronzes as potential anodes for solid oxide fuel cells: synthesis and electrical characterisation

In this paper we report studies on a range of niobate based tungsten bronzes, with a view to analysing their potential as anode materials in SOFCs. Six systems were studied, (Sr_1−xBa_x)_0.6Ti_0.2Nb_0.8O₃, Sr_0.6−xLa_xTi_0.2+xNb_0.8−xO₃, (Sr_0.4−xBa_x)Na_0.2NbO₃, (Ba_1−xCa_x)_0.6Ti_0.2Nb_0.8O₃, Ba_0.5−xA_xNbO₃ (A=Ca, Sr), and Ba_0.3NbO_2.8, and the electrical conductivities were examined over a range of oxygen partial pressures (10⁻²⁰–1 bar). All the systems showed good conductivity in low oxygen partial pressures, with values as high as 8 S cm⁻¹ at 930°C (P(O₂)=10⁻²⁰ bar). As the oxygen partial pressure was raised the conductivity dropped showing in most cases an approximate [P(O₂)]^−1/4 dependence and good re-oxidation kinetics. Of all the samples studied the (Sr_1−xBa_x)_0.6Ti_0.2Nb_0.8O₃ and (Ba_1−xCa_x)_0.6Ti_0.2Nb_0.8O₃ systems appear most promising for potential use as anode materials in SOFCs.     

Low-temperature AC conductivity of Bi2Sr2CaCu2O8+δ

We report measurements of anamolously large dissipative conductivities, σ₁, in Bi₂Sr₂CaCu₂O_8+δ at low temperatures. We have measured the complex conductivity of Bi₂Sr₂CaCu₂O_8+δ thin films at 100–600 GHz as a function of doping from the underdoped to the overdoped state. At low temperatures there exists a residual σ₁ which scales with the T=0 superfluid density as the doping is varied. This residual σ₁ is larger than the possible contribution to σ₁ from a thermal population of quasiparticles (QP) at the d-wave gap nodes.     

Effect of lead addition to Bi-based 2222 superconducting cuprates Bi2-xPbxSr2(Y, Ce)2Cu2O10+δ

Bi_2-xPb_xSr₂(Y, Ce)₂Cu₂O_10+δ, a new family of lead containing Bi-2222 compounds has been synthesized and effects of annealing in high pressure of oxygen studied. Lead-free Bi₂Sr₂(Y, Ce)₂Cu₂O_10+δ synthesized under flowing oxygen is known to be non-superconducting, but annealing under high oxygen pressure (100 bar) at 500°C, induced superconductivity with T_c=25 K. On substitution of lead (x>0.4), the superconductivity appears even in samples synthesized under flowing oxygen (1 bar). T_c increases with oxygen annealing pressure for all compositions, and it also increases with Pb content at a given oxygen pressure. These findings are discussed.     

Formation of Mo and MoSx nanoparticles on Au(1 1 1) from Mo(CO)6 and S2 precursors: electronic and chemical properties

Mo(CO)₆ can be useful as a precursor for the preparation of Mo and MoS_x nanoparticles on a Au(1 1 1) substrate. On this surface the carbonyl adsorbs intact at 100 K and desorbs at temperatures lower than 300 K. Under these conditions, the dissociation of the Mo(CO)₆ molecule is negligible and a desorption channel clearly dominates. An efficient dissociation channel was found after dosing Mo(CO)₆ at high temperatures (>400 K). The decomposition of Mo(CO)₆ yields the small coverages of pure Mo that are necessary for the formation of Mo nanoclusters on the Au(1 1 1) substrate. At large coverages of Mo (>0.15 ML), the dissociation of Mo(CO)₆ produces also C and O adatoms. Mo nanoclusters bonded to Au(1 1 1) exhibit a surprising low reactivity towards CO. Mo/Au(1 1 1) surfaces with Mo coverages below 0.1 ML adsorb the CO molecule weakly (desorption temperature<400 K) and do not induce C–O bond cleavage. These systems, however, are able to induce the dissociation of thiophene at temperatures below 300 K and react with sulfur probably to form MoS_x nanoparticles. The formed MoS_x species are more reactive towards thiophene than extended MoS₂(0 0 0 2) surfaces, MoS_x films or MoS_x/Al₂O₃ catalysts. This could be a consequence of special adsorption sites and/or distinctive electronic properties that favor bonding interactions with sulfur-containing molecules.     

Effects of cation- or oxide ion-defect on conductivities of apatite-type La–Ge–O system ceramics

A series of apatite-type La–Ge–O ceramics were prepared and their cation-defect at the 4f+6h sites and oxide ion-defect at 2a site were investigated. In La_xGe₆O_12+1.5x ceramics of x=6–12, the higher conductivities were obtained in the region of apatite composition, La_x(GeO₄)₆O_1.5x−12 (x=8–9.33), and the highest conductivity was achieved for La₉(GeO₄)₆O_1.5 (x=9), where the number of cation (La³⁺) occupying the 4f+6h sites is 9 and the number of oxide ion occupying the 2a site is 1.5. The ceramics with cation- and oxide ion-defects were La_9−0.66xSr_x(GeO₄)₆O_1.5 (x=0–1), La_9−1.33xZr_x(GeO₄)₆O_1.5 (x=0–1), La_9−xSr_x(GeO₄)₆O_1.5−0.5x (x=0–3), La_9−xZr_x(GeO₄)₆O_1.5+0.5x (x=0–1), La_x(GeO₄)_3x−21(AsO₄)_27−3xO_1.5 (x=0–3), La_x(GeO₄)_33−3x(AlO₄)_3x−27O_1.5 (x=0–3), La₉(GeO₄)_6−x (AlO₄)_xO_1.5−0.5x (x=0–3), La₉(GeO₄)_6−x(AsO₄)_xO_1.5+0.5x (x=0–1), La_9.33−xSr_x(GeO₄)₆O_2−0.5x (x=0–1.2) and La_x(GeO₄)_4.5(AlO₄)_1.5O_1.5x−12.75 (x=8.8–9.83), which were prepared by the partial substitution of La³⁺and GeO₄⁴⁻of the basic apatite La₉(GeO₄)₆O_1.5 with Sr²⁺ or Zr⁴⁺ and AlO₄⁵⁻ or AsO₄³⁻. Such substitutions lowered the conductivity of La₉(GeO₄)₆O_1.5. These results were discussed by the electrostatic interaction between Sr²⁺, Zr⁴⁺, AlO₄⁵⁻ or AsO₄³⁻ and oxide ion as a conductive species.