Preparation of YBa2Cu3O7–x high-Tcceramic superconductors from melt

Fabrication of high-T _c ceramic superconductor in the system Y₂O₃-BaO-CuO by melting a mixture of component oxides has been investigated. The compositions of the resulting specimens and the effects of heat treatment have been investigated. It was determined that molten material was composed of phases including BaCuO₂, CuO, Y₂O₃, and Y₂BaCuO₅. A subsequent heat treatment in air produced a nominal amount of the high-T _c phase, while heat treatment in an O₂ atmosphere resulted in a significantly large percentage of the superconducting phase.     

Investigations of chemical interaction between Bi-based 2212 and (RE)Ba2Cu3O7 high Tc superconducting materials

Composite materials have been synthesized by mixing 90% (or 95%) YBa₂Cu₃O₇ and 10% (or 5%) Bi₂Sr₂Ca₁Cu₂O₈ by weight, and firing at 900°C to promote grain growth by inducing a liquid phase (Bi₂Sr₂Ca₁Cu₂O₈) in the system. The influence of the amount of liquid phase on the X-ray diffraction data and electrical properties is reported. Energy dispersive X-ray (EDX) analyses are also reported. The YBiBa₂O₆ phase is formed during the heat treatment and introduces additional chemical heterogeneities at the grain boundaries. A previously reported 2212-related superconducting phase, Bi₂(Sr,Ba)₂(Ca,Y)Cu₂O_8+y, could also be formed during the synthesis process, and its effect on the electrical resistance versus temperature measurements is discussed. Attempts to substitute RE ions (Dy³⁺, Er³⁺, Ho³⁺) for Y³⁺ in YBiBa₂O₆ have been successful and are reported in an appendix section. X-ray diffraction data are also reported. EDX analyses have been performed specifically for a typical ErBiBa₂O₆ compound and reveal the presence of a new Er₂Ba₄O₇ phase.     

Solution-sol-gel processing of superconductors

Bulk materials and thin films of pure and homogeneous YBa₂Cu₃O_7−x and Bi₂Sr₂CaCu₂O_8+x compounds were prepared by a nanocomposite solution-sol-gel (SSG) method. The superconducting oxides of YBa₂Cu₃O_7−x and Bi₂Sr₂CaCu₂O_8+x were prepared at very low temperatures i.e. 750°C and 850°C, respectively by SSG method. Pellets sintered from these nanophasic sol powders showed sharp resistivity drops atT _c ∼ 90°K for YBa₂Cu₃O_7−x andT _c∼67°K for Bi₂Sr₂CaCu₂O_8+x . Thin films were prepared using triphasic sol of Y, Ba, Cu and tetraphasic sol of Bi, Sr, Ca and Cu on MgO and SrTiO₃ substrates. The triphasic sol coated on SrTiO₃ substrates and calcined at 800°C for 12h showed the formation of superconducting phase, YBa₂Cu₃O_7−x with preferred orientation along theC-axis. X-ray diffraction patterns of the Bi₂Sr₂CaCu₂O_8+x films on MgO substrate showed the formation of the superconducting phase with preferential orientation along the C-axis and the microwave absorption data as a function of temperature of this film revealed the onset temperature to be 90°K.     

Investigations of Bi substitution in NdBa2Cu3Oy

Attempts to substitute Bi for Nd in orthorhombic NdBa₂Cu₃O _y , prepared in air or oxygen at about 950°C led instead to formation of Ba₂NdBiO₆, a new cubic compound witha=0.8703 nm. The possibility was then explored of preparing superconducting (Nd_1–x Bi _x )Ba₂Cu₃O _y , by first forming the tetragonal phase at 880–950°C in nitrogen or argon followed by reheating in oxygen or air at 250–500°C in order to insert the additional oxygen required to yield the orthorhombic form while avoiding oxidation of Bi³⁺ to Bi⁵⁺. X-ray diffraction studies, electrical conductivity measurements, and thermogravimetric analysis of products indicate that Bi does not enter the NdBa₂Cu₃O _y , lattice in either the tetragonal or the orthorhombic phase. Ba₂NdBiO₆ clearly forms on reheating in oxygen or air even at low temperatures, and evidence is presented that a poorly crystallized oxygen-deficient form of this compound is already present prior to the reheating.     

High-capacity superconducting current leads of Y1Ba2Cu3O7?x

We have fabricated and measured a high-capacity superconducting current lead composed of a Y₁Ba₂Cu₃O_7–x cylinder, 20 cm long and 0.9 cm² cross section. A steady-state, d.c., critical current of 225 A at a temperature of 77 K was measured in this sample, using a voltage criterion of 2×10^–7 V/cm (p = 8×10^–10 ohm-cm). This current was limited by the currentinduced, self magnetic field. To our knowledge this is the largest d.c. critical current so far reported in a Y₁Ba₂Cu₃O_7–x sample and demonstrates the possibility of using hightemperature superconducting HTS materials for current leads to low-temperature superconducting LTS magnets or in power distribution systems.     

Preparation of Y<Subscript>2</Subscript>O<Subscript>3</Subscript> Buffer Layer on LaAlO<Subscript>3</Subscript> Substrate by TFA-MOD Method

Chemical solution deposition is a promising technique for fabrication of high-temperature superconducting films and oxide buffer layers due to its reproducibility and low cost. In this work, Y₂O₃ buffer layers were prepared on (100) LaAlO₃ substrates by mental organic deposition method using trifluoroacetate. The resulting Y₂O₃ films crystallized as a single phase at 900°C and showed a low degree ofc-axis orientation. The scanning electron micrography showed that the surface of the films was smooth with a uniform grain size of approximately 10 nm.     

Superconducting Properties of Iodine-Intercalated Bi<Subscript>2</Subscript>Sr<Subscript>2</Subscript>Ca<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>10+<Emphasis Type="Italic">x</Emphasis></Subscript>

The superconducting properties of iodine-intercalated high-temperature superconducting Bi₂Sr₂Ca₂Cu₃O_10+x phase (Bi-2223) were systematically studied. It was found that for samples containing a significant amount of Bi₂Sr₂CaCu₂O_8+x , iodine intercalation results in the dramatic decrease of the inter-granular critical current density, as well as a significant decrease of the critical temperature (T _c), the critical current density in the grains (J _cg), and of the amount of Bi-2223. For samples with a large amount of Bi-2223, T _c changes insignificantly, whereas J _cg can even increase. We argue that the different behavior of the superconducting parameters is the result of various oxygen concentrations, and we explain the effect of iodine intercalation based on the parabolic dependence between T _c and the number of holes per CuO₂ layer. The H(T) curves (determined from the peak position in the loss signal of ac susceptibility) for intercalated samples deviate significantly from the quasi 2D-like behavior, pointing toward an enhancement of the 3D fluctuations of vortices. For the change in the values and dimensionality of the flux pinning in the process of the intercalation, we attempted a qualitative explanation based on the models proposed in literature.     

Electrical characteristics and reheat-treatment effects in a ZnO varistor fabricated by two-stage heat-treatment

Conventional ZnO varistors are generally fabricated by sintering ZnO powder mixed with additives such as Bi₂O₃, Sb₂O₃, Cr₂O₃, Co₂O₃, and MnO₂. To reduce abnormal grain growth and change in electrical characteristics in the conventional ZnO varistors caused by volatilization of Bi₂O₃, the ZnO powder with all additive oxides except Bi₂O₃ was pressed into disc form and sintered. The disc was then painted with metal oxide paste containing Bi₂O₃ and again fired. The ZnO varistor fabricated by this process, i.e. a two-stage heat-treatment process, showed typical non-linearI-V characteristics with higher breakdown voltage exceeding 800 V mm^–1. It was also observed that the non-linearI-V coefficient change rate, , in the ZnO varistor due to reheat-treatment is almost linearly proportional to the sintered density.     

Vortex motion in coupled DyBa2Cu3O7/(Y0.6Pr0.4)Ba2Cu3O7 heterostructures

Multilayer structures containing 24 Å thick DyBa₂Cu₃O₇ layers, separated by 96 Å of an (Y_0.6Pr_0.4)Ba₂Cu₃O₇ alloy, are studied to investigate the effect of coupling on vortex dynamics. With the magnetic field perpendicular to theab plane, and as a function of the number of superconducting layers in the structure, we find that the activation energy for flux motion increases, first linearly, and then saturates. This linear increase is taken as evidence that pancake vortices belonging to different DyBa₂Cu₃O₇ layers are stacked and have a coupled motion. Above a characteristic number of superconducting layers,N _c , shear of the vortex structures becomes important and the thermally activated process only displaces a stack ofN _c pancake vortices, meaning that the vortex lattice is turning three dimensional. In these structures we findN _c to be 2 to 3.     

Thermal-stress stability of yttrium oxide as a buffer layer of metal-ferroelectric-insulator-semiconductor field effect transistor

The effect of thermal stress on the electrical properties of ferroelectric/semiconductor structure was investigated when introducing Y₂O₃ film as a barrier layer in the structure. Two different thermal stress states could be obtained by fast (400 °C/min) or slow (30 °C/min) cooling of sputter-deposited Y₂O₃ films on silicon wafer from 800 °C. The formation of interfacial layer containing Y-Si-O and SiO₂ layers while annealing could be characterized by using a spectroscopic ellipsometry. The introduction of strain-induced defects from thermal stress of the fast cooled sample showed a soft breakdown at low applying voltage. In the capacitance-voltage relation, a flat band voltage shift, hysteresis, and stretch-out phenomena were also observed. Nd₂Ti₂O₇ was spin deposited using sol-gel procedure on the Y₂O₃/Si to form a metal-ferroelectric-insulator field effect transistor structured sample. These Nd₂Ti₂O₇/Y₂O₃/Si samples were also furnace-annealed at 800 °C and cooled down to room temperature fast or slowly. One order lower value of leakage current, 1E−8 A/cm² was observed with these samples when comparing with the Y₂O₃/Si samples. A soft breakdown of the fast cooled sample seemed to have the same origin as the fast cooled Y₂O₃/Si sample, i.e., the strain-induced defects in the interfacial layer containing Y-Si-O and SiO₂ phases. Hysteretic gaps of the Nd₂Ti₂O₇/Y₂O₃/Si samples showed a possibility to be used as a memory window for ferroelectric gate.     

Luminescence properties of Ca4Y6(SiO4)6O:RE (RE = Eu, Tb, Dy, Sm and Tm) under vacuum ultraviolet excitation

The vacuum ultraviolet excited luminescent properties of Eu³⁺, Tb³⁺, Dy³⁺, Sm³⁺ and Tm³⁺ in the matrices of Ca₄Y₆(SiO₄)₆O were investigated. The bands at about 173 nm in the vacuum ultraviolet excited spectra were attributed to host lattice absorption of the matrix Ca₄Y₆(SiO₄)₆O. For Eu³⁺-doped samples, the O²⁻ → Eu³⁺ CTB was identified at 258 nm. Typical 4f-5d absorption bands in the region of 195-300 nm were observed in Tb³⁺-doped samples. For Dy³⁺-doped and Sm³⁺-doped samples, the broad excitation bands consisted of host absorptions, CTB and f-d transition. For Tm³⁺-doped samples, the O²⁻ → Tm³⁺ CTB was located at 191 nm. About the color purity and emission intensity, Ca₄Y₆(SiO₄)₆O:Tb³⁺ is an attractive candidate of green light PDP phosphor, and Ca₄Y₆(SiO₄)₆O:Dy³⁺ has potential application in the field of mercury-free lamps.     

Superconductivity at 103 K in CdBa2(Ca0.7Y0.3)Cu2Oy

A cadmium analogue of the mercury system with nominal composition CdBa₂(Ca_1–xY_x)Cu₂O_y has been synthesized. Thex=0 samples contain about 12 vol.% of the 1212 phase but are not superconducting. Thex=0.3 samples are superconducting atT _on = 103 K. The EDX analysis of 18 microcrystals shows a broad cationic distribution of the different components. The observed broad superconducting transition is attributed to the variousT _c of the different microcrystals.     

超声协同微球型Bi2O2CO3降解罗丹明B的研究

Bi_2O_2CO_3是一种Bi类半导体催化剂,文章研究了它的超声催化性能。首先,采用水热法制备了微球型的Bi_2O_2CO_3,利用X射线衍射(X-ray Diffraction, XRD)、扫描电子显微镜(Scanning Electron Microscope, SEM)、紫外-可见漫反射光谱对样品的晶体结构、微观形貌、光学特性进行了表征。然后,以罗丹明B(Rh B)作为模型污染物,通过研究超声催化降解罗丹明B来评测Bi_2O_2CO_3的超声催化性能。研究了催化剂的浓度(Ccatalytic)、初始罗丹明B染料的浓度(CRhB)和超声功率(P)等实验因素对超声催化降解效率的影响。得出在Ccatalytic=3 g·L-1,CRhB=10 mg·L-1和P=400 W条件下降解罗丹明B的效率最高,其最高降解效率可以达到91.7%。     

Mechanism of the Dynamic Thermal Expansion of Bismuth-Based High-T c Superconductors1

The dynamic process of thermal expansion (DPTE) of Bi-based high-T _c (HTC) superconductor samples (Bi₂ Sr₂ Ca₂ Cu₃ O₁₀, T _c=105K) is studied theoretically. The abnormal expansion behavior in the superconducting and normal states are of relevance to the energy absorption and pairing mechanisms.     

Effect of Cd and Cd-Ca Substitution on the Superconductivity in Y1−xPrxBa2Cu3O7−δ Superconductor

The structural and superconducting properties of Y_1−v−η Pr_NCd{η}¨zCa _z Ba₂Cu₃O_7−δ system are investigated using X-ray diffraction, ac susceptibility, dc resistivity, and oxygen content measurements. The effect of increasing Cd concentration substituting the Y-site in Y_0.8Pr_0.2Ba₂Cu₃O_7-δ suppresses the superconducting transition temperature and lowers the hole concentration, unlike that of Ca substitution in Y_0.8Pr_0.2Ba₂Cu₃O_7-δ which increasesT _c due to hole doping by Ca. The suppression ofT _c due to Cd substitution can be counterbalanced by simultaneous hole doping by Ca which increases the T_c with increasing Ca concentration. In spite of similarity in the ionic radii and valency, the role played by Cd and Ca substitution at the Y-site in the Y_0.8Pr_0.2Ba₂Cu₃O_7-δ system is opposite in nature as Cd doping helps in T_c suppression due to the Pr effect, suggesting that Cd does not provide the necessary holes like Ca substitution which helps to increase the T_c by the hole doping mechanism.     

Luminescence enhancement of Y2O3:Eu and Y2SiO5:Ce,Tb core particles with SiO2 shells

This paper reports on the luminescence and microstructural features of oxide nano-crystalline (Y₂O₃:Eu³⁺) and submicron-sized (Y₂SiO₅:Ce³⁺,Tb³⁺) phosphor cores, produced by two different synthesis techniques, and subsequently coated by an inert shell of SiO₂ using a sol-gel process. The shells mitigate the detrimental effect of the phosphor particle surfaces on the photoluminescence emission properties, thereby increasing luminous output by 20-90%, depending on the core composition and shell thickness. For Y₂O₃:Eu³⁺, uniformly shaped, narrow particle size distribution core/shell particles were successfully fabricated. The photoluminescence emission intensity of core nanoparticles increased with increasing Eu³⁺ activator concentration and the luminescence emission intensity of the core/shell particles was 20-50% higher than that of the core particles alone. For Y₂SiO₅:Ce³⁺,Tb³⁺, the core/shell particles showed enhancement of the luminescence emission intensity of 35-90% that of the core particles, depending on the SiO₂ shell thickness.     

Influence of ZnO additive on the properties of Y-doped BaSnO3 proton conductor

The effects of ZnO additive on the phase formation, microstructure and electrical conduction of Y-doped BaSnO₃ have been investigated. The single-phase and dense BaSn_0.75Y_0.25O_3−δ compound with 4 mol% ZnO additive was successfully prepared after sintering at 1300 °C, which significantly reduces the sintering temperature. The conductivities measured under dry and wet air atmospheres reveal that the bulk conductivity of BaSn_0.71Y_0.25Zn_0.04O_3−δ is much lower than that of BaSn_0.75Y_0.25O_3−δ. However, ZnO as a sintering aid does not affect the bulk conductivity. The total conductivity of BaSn_0.75Y_0.25O_3−δ with ZnO as the sintering aid is slightly higher than that of unmodified BaSn_0.75Y_0.25O_3−δ, and reaches 2.4 × 10⁻³ S cm⁻¹ at 621 °C. Therefore, this material can be used as a proton-conducting electrolyte for intermediate temperature solid oxide fuel cells.     

Low-field magnetic properties of high-TcGdxY1?xBa2Cu3Oy superconductor

The magnetization of Gd_0.85Y_0.15Ba₂Cu₃O _y high-T _c superconductor was measured at low fields (<100 Oe) and at a constant temperature of 77 K. The magnetization curves deviate from linearity at 25 Oe, causing the destruction of the weak couplings of the superconducting grains. The hysteresis due to granular superconductivity was also observed.     

Interplay of YBCO and Embedded 211 Particles in Melt-Textured YBCO Superconductors

Local orientations of superconducting YBa₂Cu₃O _x (123) and embedded Y₂BaCuO₅ (211) particles within bulk, melt-textured 123 samples are studied on a local scale by means of electron backscatter diffraction (EBSD). The embedded Y₂BaCuO₅ (211) particles do not show any preferred texture, but their presence within the 123-matrix alters the growth of the 123-phase, independent of the orientation. EBSD enables to analyse the interactions between the 123- and 211-phases in detail.