Highlighting of structural units of B2O3–Li2O–P2O5 system under heat treatment

As technology evolves towards the design of small size – high efficiency devices there is a necessity for the development of solid, stable electrolytes that can be fabricated in various shapes. Accordingly, a glass system of xB₂O₃·0.4Li₂O·(0.6 − x)P₂O₅ with 0 ≤ x ≤ 0.6 mol%, was prepared by melting the raw materials at 1200 °C and rapidly cooling the melts at room temperature. The samples were afterwards heat treated to develop crystalline structures, for better identification of the units that build up the network.     

Enhancement of the Current Density J C for Bi2Sr2CaCu2O8 by?Means of Carbon and NbSe2 Nanotubes

Three polycrystalline Bi₂Sr₂CaCu₂O₈, Bi₂Sr₂CaCu₂O₈ with carbon nanotubes, Bi₂Sr₂CaCu₂O₈ with NbSe₂ nanotubes were synthesized by solid state reaction method and studied by scanning electron microscopy, X-ray diffraction, magnetization measurements, and high resolution transmission electron microscopy. The critical temperature T _C for the three compounds was about 85 K. There is an enhancement in the critical current density, J _C for samples with carbon and NbSe₂ nanotubes as compared with pure Bi₂Sr₂CaCu₂O₈. The enhancement provides evidence that wetting exists for the two doped samples investigated.      

Characterization of epitaxial Bi2Sr2CaCu2O8+δ thin films

We report a dc sputtering method for the fullin situ preparation of Bi₂Sr₂CaCu₂O₈₊ thin films on SrTiO₃ and LaAlO₃.T _c values of more than 90 K can be achieved by oxidizing annealing below the melting point, followed by a reducing anneal at 500°C. The structural properties of the films are revealed by X-ray diffraction in Bragg-Brentano geometry (strongc-axis orientation with FWHM (0 0 10)=0.3) and also by scans (epitaxy within the substrate plane). Rutherford backscattering and channeling confirmed the correct composition of the cations while the minimum yield, _min, is 23%. Depth profiles by SNMS show a very homogeneous distribution of the cations with no detectable loss of bismuth near the surface. The surface morphology of the films was studied by SEM and by STM. Patterning of the films in lateral geometry can be performed by photolithographic techniques without degradation ofT _c .     

Microstructures formed during devitrification of Na2O·Al2O3·B2O3·SiO2·Fe2O3 glasses

Soda alumina borosilicate glasses of composition (24-y)Na₂O·yAl₂O₃·14B₂O₃·37SiO₂·25Fe₂O₃, y = 8, 12, 14, 16 mol%, were melted using Fe₂O₃ as raw material. Besides, samples with y = 12 and Fe₂O₃ concentrations of 14.32, 17.8, and 25.0 mol% were prepared from FeC₂O₄·2H₂O as raw material. The X-ray diffraction analyses showed the presence of magnetite for the samples from all the investigated compositions. Transmission electron microscopy (TEM) evidenced that all the samples are phase separated and droplets in the diameter range 100–1000 nm, enriched in iron, are formed. Inside these droplets, numerous small magnetite particles, with size in the 25–40 nm interval, are crystallized.     

Improvement of the Irreversibility Line of the 1212 Compound Tl0.5Pb0.5Sr2CaCu2O7?δ

The superconducting properties and the irreversibility line of the Tl_0.5Pb_0.5Sr₂CaCu₂O_7– were studied by ac susceptibility on both ceramic and powder samples prepared in sealed quartz tube at 960°C. In parallel, carefull investigations by DTA/Tg, X rays diffraction and plasma emission spectroscopy were performed on each sample after each thermal treatment. It is shown that the superconducting properties are strongly dependent on further heat treatments and that the irreversibility line may be optimized. Nevertheless, the results obtained suggest that further improvement of the irreversibility line might be expected.     

Systematics of the thermopower below Tc in Tl2Ba2CaCu2O8+δ

A systematic study of the mixed-state thermopower in Tl₂Ba₂CaCu₂O₈₊ indicates a that there are two contributions to the total signal. The largest contribution is accurately proportional to the resistivity, as previously reported. We have also identified a new, additional contribution to the thermopower. The source of the excess thermopower is not presently determined, and may be related to vortex fluctuations or d-wave superconductivity.This work is supported in part by USAFOSR F49620-93-1-0310, NSF Grant No. DMR 91-22043, ARPA Grant MDA 972-90-J-1001, the Texas Center for Superconductivity at the University of Houston, and the T.L.L. Temple Foundation.     

Theory of the Phase-Sensitive Bi2Sr2CaCu2O8+δc-Axis Twist Josephson Junction Experiments

We studied theoretically the phase-sensitive c-axis Bi₂Sr₂CaCu₂O₈₊ (BSCCO) bicrystal twist Josephson junction experiments of Li et al. (Phys. Rev. Lett. 83, 4160 (1999)), calculating the critical current as a function of the twist angle in a wide variety of models. The data provide strong evidence that the c-axis tunneling in BSCCO is incoherent, and that the order parameter is s-wave for T T _c.     

Optical properties and structure of R2O–Ga2O3–SiO2 and RO–Ga2O3–SiO2 glasses

Refractive index and molar refraction of Li₂O–, Na₂O–, CaO–, and BaO–Ga₂O₃–SiO₂ glasses have been used to test the validity of a structural model of silicate glasses containing Ga₂O₃ glasses. Ga₂O₃ enters these types of glass in a similar manner as Al₂O₃. It is assumed that, for (SiO₂/Ga₂O₃) >1 and (Ga₂O₃/R₂O) ≤1, Ga₂O₃ associates primarily with modifier oxides to form GaO₄ units. The rest of modifier oxide forms silicate units with non-bridging oxygen ions. Silicate structural units have the same factors as found for binary alkali- and alkaline earth silicate glasses. Differences between experimental and model values suggest another structure for (Ga₂O₃/SiO₂) ≥1.     

Effects of copper and Al2O3 particles on characteristics of Cu–Al2O3 composites

High-energy milling was used for production of Cu–Al₂O₃ composites. The inert gas-atomized prealloyed copper powder containing 2 wt.%Al and the mixture of the different sized electrolytic copper powders with 4 wt.% commercial Al₂O₃ powders served as starting materials. Milling of prealloyed copper powders promotes formation of nano-sized Al₂O₃ particles by internal oxidation with oxygen from air. Hot-pressed compacts of composites obtained from 5 and 20 h milled powders were additionally subjected to the high-temperature exposure in argon at 800 °C for 1 and 5 h. Characterization of processed material was performed by optical and scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), microhardness, as well as density and electrical conductivity measurements. Due to nano-sized Al₂O₃ particles microhardness and thermal stability of composite processed from milled prealloyed powders are higher than corresponding properties of composites processed from the milled powder mixtures. The results were discussed in terms of the effects of different size of starting copper powders and Al₂O₃ particles on the structure, strengthening of copper matrix, thermal stability and electrical conductivity of Cu–Al₂O₃ composites.     

MgO-Al2O3-SiO2-TiO2-Y2O3玻璃的弹性模量

根据硬盘基板用材料的要求，制备了MgO-Al2O3-SiO2-TiO2-Y2O3高弹性模量玻璃（120GPa)，玻璃的弹性模量随组成的变化服从Makishima-Mackenzie理论，MgO,Al2O3,TiO2,Y2O3等具有较高单位体积离解能的氧化物有利于提高玻璃的弹性模量，但玻璃弹性模量的理论计算值低于测试值，这是因为Makishima-Mackenzie理论没有考虑玻璃内阳离子的具体配位，对MgO,Y2O3堆积密度因子的堆导存在误差，因此利用Makishima-Mackenzie理论发展高弹性模量玻璃时应对MgO,Y2O3等氧化物的计算进行修正。     

Anisotropic Ultrafast Dynamics of Quasiparticles on CuO2 Planes of Y0.7Ca0.3Ba2Cu3O7?δ

The orientation-resolved femtosecond spectroscopy, combined with the well-textured (110)- and (001)-Y_0.7Ca_0.3Ba₂Cu₃O_7−δ thin films, serves as an effective probe to quasiparticle relaxation dynamics on the ab planes and along the diagonal orientations. The significant divergences in the temperature-dependent relaxation time (τ) associated with the opening of superconducting gap were observed along the nodal directions and on the CuO₂ planes which are dominated by the a axis and b axis in the overdoped region. Moreover, the divergence in the temperature-dependent τ along the nodal direction disappears around optimal doped region. This implies that the superconducting gap evolves from the dominant s-wave symmetry in overdoped region into the dominant d-wave symmetry in optimal doped region.     

Preparation of Ca-α SiAlON hollow spheres by carbothermal reduction-nitridation of CaO-Al2O3-SiO2 glass

Ca-α SiAlON powders were prepared by carbothermal reduction-nitridation of CaO-Al₂O₃-SiO₂ glasses at 1450 °C for 2 h in nitrogen. The content of Ca-α SiAlON phase was 65-81% in the products, and the other phases were AlN and β-SiAlON. The products contained hollow spheres with the size of around 5 μm in diameter. The particle morphology was almost identical to that of Ca-α SiAlON prepared from CaCO₃-Al₂O₃-SiO₂ powder mixtures.     

Ultrafast Phase-Coherence in Normal State of Underdoped Bi2Sr2CaCu2O8 + δ Thin Film

A phase-sensitive time-domain terahertz-transmission spectroscopy was carried out on a c-axis oriented underdoped Bi₂Sr₂CaCu₂O_{8 +} thin film. We directly extracted the complex refractive index and conductivity at frequencies from 0.3 to 1.5 THz by numerically solving the observed complex transmittance without Kramers–Kronig analysis. The frequency-resolved real and imaginary part of the conductivity (1.0 THz < f) showed a measurable increase below the characteristic temperature of T* 210 K because of the appearance of partial phase-coherence with an ultrashort lifetime less than about 1 ps.     

The effect of Sm substitution on properties of Bi1.6Pb0.4Sr2Ca2? x Sm x Cu3O y superconductors

The effect of the partial substitution of Ca by Sm in the Bi-2223 superconducting samples have been investigated in terms of X-ray diffraction (XRD), EDXRF (Energy Dispersive X-ray Fluorescent), magnetoresistivity, critical temperature, transport critical current density, and ac susceptibility measurements. The samples were prepared by the conventional solid-state reaction method. XRD patterns are used to calculate lattice parameters and phase ratio of the Bi-2223 samples. The volume fraction was determined from the intensities of Bi-2223 and Bi-2212 peaks. The room temperature XRD patterns of the samples showed the presence of Bi-2223 phase decreases with increasing the Sm content. We estimated the transition temperature of the samples from the resistivity versus temperature measurements in dc magnetic fields up to 0.6 T. We observed that transition temperature, T _c , and transport critical current density, , depend on the Sm substitution. They both decrease with increasing the Sm substitution. We extracted the peak temperature, T _p , and the pinning force density from our previous ac susceptibility measurements. The pinning force density decreased with increasing the Sm content. The possible reasons for the observed decreases in critical temperature and critical current density due to Sm substitution were discussed.     

Li2O/K2O物质的量比对P2O5-Al2O3-BaO-Li2O-K2O磷酸盐玻璃热光性能的影响

通过高温熔融法制备了不同Li_2O/K_2O物质的量比的磷酸盐玻璃,研究了其热学性能和热光性能。采用干涉仪法测试了玻璃的折射率温度系数dn/dT,并进一步计算获得了热光系数。结果表明:随着Li_2O/K_2O物质的量比的增大,玻璃的转变温度Tg、软化温度Tf、热膨胀系数α皆出现极值点,呈现明显的混合碱效应;而玻璃的热光系数dS/dT随着Li_2O含量增加而增大,当Li_2O/K_2O物质的量比为9∶6时,玻璃的dS/dT为0.08×10~(-6)/K;在磷酸盐体系中可获得具有零热畸变的光学玻璃。     

Percolation Behavior of the Normal-State Resistivity and Superconductivity of the YBa2Cu3O7?δ-Ba2GdNbO6 Composite System

The percolation behavior of the normal-state resistivity and superconductivity of the YBa₂Cu₃O_7–Ba₂GdNbO₆ composite system were studied by X-ray diffraction and temperature-resistivity measurements. No detectable chemical reaction was observed between the YBa₂Cu₃O_7– superconductor and the ceramic insulator Ba₂GdNbO₆, even after severe heat treatment above 950°C. The normal-state and superconducting percolation threshold values were found to be 17 vol.% and 30 vol.% of YBa₂Cu₃O_7– respectively in the YBa₂Cu₃O_7–-Ba₂GdNbO₆ composite system. The values obtained for the critical exponents describing the normal-state pecolation behavior of the system matched fairly well with the theoretically expected values for an ideal metal-insulator composite system.     

Sc2O3-Y2O3-ZrO2陶瓷材料热物理性能

采用固相合成法制备了6.3%Sc_2O_3-1.3%Y2O3-92.4%ZrO_2(摩尔分数)陶瓷材料。分别利用X射线衍射、示差扫描量热法、高温热膨胀仪和激光导热法对陶瓷材料的物相组成、高温相稳定性、热膨胀系数和热扩散等性能进行了表征。结果表明,经1600℃烧结6h,该陶瓷材料由单一的立方相结构组成,具有良好的高温相稳定性,热导率低于传统的6~8YSZ,是一种良好的热障涂层候选材料。     

Thermo-mechanical properties of La2NiO4+δ

Elastic and fracture behavior of La₂NiO_4+δ have been assessed. Fracture stress and elastic modulus of porous La₂NiO_4+δ were evaluated from room temperature (RT) up to 900 °C on the basis of 4-point bending tests. Both parameters increase slightly from RT to 700 °C. However, at higher temperatures the elastic modulus decreases, whereas the fracture stress increases. In addition, elastic modulus and damping/internal friction of dense specimens were measured by a resonance method. A strong change of elastic modulus and internal friction between RT and 100 °C appears to be related to an orthorhombic-tetragonal phase transition. No indications of phase transition can be observed at higher temperatures. Although thermogravimetric measurements suggest that oxygen was continuously released from the lattice up to 1000 °C with increasing temperature, the thermal expansion coefficient showed a rather stable value from RT up to 1000 °C.     

Room-temperature synthesis of nanometric α-Bi2O3

Nanometric Bi₂O₃ powder was successfully synthesized by applying the method based on self-propagating room temperature reaction (SPRT) between bismuth nitrates and sodium hydroxide. X-ray powder diffraction (XRPD) and Rietveld's structure refinement method were applied to characterize prepared powder. It revealed that synthesized material is a single phase monoclinic α-Bi₂O₃ (space group P2₁/c with cell parameters a = 5.84605(4)Å, b = 8.16339(6) Å, c = 7.50788(6) Å and β = 112.9883(8)). Powder particles were of nanometric size (about 50 nm). Raman spectral studies conformed that the obtained powder is single phase α-Bi₂O₃. Specific surface area of obtained powder was measured by Brunauer-Emmet-Teller (BET) method.     

La2O3在MgO-Al2O3-SiO2-TiO2微晶玻璃中的作用

在MgO-Al2O3-SiO2-TiO2玻璃中添加不同数量的氧化镧，采用差热分析，X射线衍射及电子显微镜等技术研究了氧化镧对玻璃析晶过程与力学性能的影响。氧化镧的加入使玻璃中析出α－堇青石相的温度降低，同时避免了高膨胀方石英相的析出。随着氧化镧加入量的增加，玻璃整体析晶能力下降，微晶玻璃中晶相含量减少，晶粒尺寸增大，微晶玻璃的弹性模量与硬度减小，断裂韧性增加，体现出大尺寸长柱状金红石晶粒的增韧作用。