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Doo-Sup Hwang Soon-Gul Lee Yong-Ki Park John-S Chun Jong-Chul Park 《Physica C: Superconductivity and its Applications》1995,250(3-4):375-381
We have investigated defects and in-plate orientations of YBa2Cu3Ox thin films prepared by pulsed laser deposition (PLD) with YSZ as a buffer layer. The films showed c-axis oriented growth with the transition temperature Tco up to 87 K. Several types of defects including thermally induced cracks, grain boundaries and outgrowths were observed by scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). The grain boundary provided a favorable path for crack propagation. The outgrowths nucleated on the YSZ surface grew with stoichiometric composition. According to X-ray diffraction (XRD) and HRTEM studies the YSZ buffer layer grew with the orientation relationship, YSZ110//Si110 and YSZ(001)//Si(001) up to the YBCO/YSZ interface. The superconducting YBCO films on top grew mainly with YBCO100//Si110 and YBCO(001)//Si(001), with some minor portions of YBCO110//Si110 and YBCO(001)//Si(001). 相似文献
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Rajneesh Mohan Kiran Singh Shovit Bhattacharya N.K. Gaur S.K. Gupta 《Solid State Communications》2007,141(11):605-609
Both oxygen and calcium play important roles in inducing superconductivity in Y Ba2Cu3Oy (YBCO), which is an antiferromagnetic insulator at low O and Ca content. O induces superconductivity in Ca-free YBCO, while Ca does similarly in oxygen-deficient YBCO. For doping oxygen HgO was used as it decomposes at 476 °C into Hg, which escapes from the matrix leaving the crystal unaltered, and O, which provide a way to dope O in YBCO. Considering these facts, polycrystalline samples of Y 1−xCaxBa2Cu3Oy with x=0, 0.1 and 0.2 with and without HgO addition were prepared through a solid-state reaction method. The samples were sintered at 950 °C in open atmosphere. These synthesized samples were characterized through using the X-ray diffraction technique (XRD) for phase evaluation, scanning electron microscopy (SEM) for grain morphology, energy dispersive X-ray analysis (EDX) for compositional analysis and the four-contact measurement technique for determining the superconducting transition temperature. 相似文献
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R.V. Shpanchenko M.G. Rozova A.M. Abakumov E.I. Ardashnikova M.L. Kovba S.N. Putilin E.V. Antipov O.I. Lebedev G. Van Tendeloo 《Physica C: Superconductivity and its Applications》1997,280(4):3652-280
Bulk superconductivity with Tc up to 94 K has been induced by fluorination of non-superconducting YBa2Cu3O6.11 using XeF2 as a fluorination agent. Strong changes on X-ray patterns were found after fluorination of reduced YBCO. High resolution electron microscopy of superconducting samples showed the presence of a new phase with c ≈ 13 Å which exists as noticeable areas included within a matrix of the 123 structure or which occurs as isolated defects with a limited extension. All fluorinated compounds exhibited a strong disorder along the c-direction resulting in a ‘loss’ of c-parameter on X-ray patterns. The present results demonstrate that fluorine indeed enters the YBCO structure with a significant structural rearrangement for the high level of fluorination. The structure of the fully fluorinated YBa2Cu3O6F2 phase, possibly responsible for superconductivity, has been deduced from high resolution electron microscopy. 相似文献
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G. B. Teitel’baum 《JETP Letters》2017,106(3):199-208
In the search for mechanisms of high-T c superconductivity it is critical to know the electronic spectrum in the pseudogap phase from which superconductivity evolves. The lack of ARPES data for every cuprate family precludes an agreement as to its structure, doping and temperature dependence and the role of charge ordering. No approach has been developed yet to address the issue theoretically, and we limit ourselves by the phenomenological analysis of the experimental data. We argue that, in the Fermi-liquid-like regime ubiquitous in underdoped cuprates, the spectrum consists of holes on the Fermi arcs and an electronic pocket in contrast to the idea of the Fermi surface reconstruction via charge ordering. At high temperatures, the electrons are dragged by holes while at lower temperatures they get decoupled. The longstanding issue of the origin of the negative Hall coefficient in YBCO and Hg1201 at low temperature is resolved: the electronic contribution prevails, as its mobility becomes temperature independent, while the mobility of holes, scattered by the shortwavelength charge density waves, decreases. 相似文献
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Electromagnetic transport measurements were combined with high-resolution electron microscopy observations to study the relation between structure and local critical currents in YBa2Cu3O7–x
(YBCO) Josephson junctions. The spatial variation of the critical current J(x) along the length of the boundary for interface engineered Josephson junctions and bicrystal grain boundary Josephson junctions was determined using a phase retrieval algorithm. The current distribution solutions were found to be highly uniform along the length of interface engineered junctions in contrast to solutions for grain boundary junctions. The latter showed significant spatial oscillations in the critical current as well as areas along the boundary that carried no current. Microstructural evaluation of interface engineered junctions fabricated using identical processing parameters to the junctions used for transport measurements suggest that the uniform current distribution is controlled by a highly uniform barrier layer formed between the superconducting electrodes. Microstructural evaluation of grain boundary junctions similar to the junctions used for transport measurements show considerable variations of the grain boundary structure within a single junction. 相似文献
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The grain boundary potential and interface state charge density at the grain boundaries of silver sulfide (Ag2S) thin films prepared by chemical conversion of cadmium sulfide (CdS) films have been determined from the dc resistance of the material and are found to be sensitive to annealing. A reduction in the grain boundary potential and the grain boundary charge density of the film has been noticed when the source CdS film is annealed at different temperatures prior to chemical conversion. The variation in the grain boundary charge density of the grown Ag2S film with source annealing temperature has been found to be similar to that of thin cadmium sulfide film, reported earlier. An additional low temperature heat treatment of the sample results in an enhancement in the charge density at the grain boundaries. The change in the silver vacancy and/or oxygen and sulfur content of the films as revealed from the energy dispersive spectra of the films suggests possible role of film composition on the grain boundary charge density. 相似文献
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本文介绍了沿c轴方向排布复层籽晶制备YBCO超导单畴的方法.该方法能够使123晶畴在不同深度进行生长.通过c轴方向籽晶的排布,研究了YBCO单畴中的(001)/(001)晶界.虽然由于压模中籽晶ab面的倾斜,造成部分(001)/(001)晶界出现大角晶界,使晶界上残余有液相,但仍有晶界连接良好、晶界上不存在残余液相和211粒子、错配角小于5°的(001)/(001)晶界的形成.对于制备有深度要求的单畴块材,复层籽晶法是一种有效的生长方法.在定向控制好籽晶方向的条件下,该方法可以提高超导单畴的生长深度.在77K,0.5T下,测试该样品磁悬浮力达到37N. 相似文献
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C. Trholt J.G. Wen H.W. Zandbergen Y. Shen J.W.M. Hilgenkamp 《Physica C: Superconductivity and its Applications》1994,230(3-4):425-434
YBa2Cu3O7 films in c-axis orientation on bicrystalline SrTiO3 substrates are investigated by TEM. The films and the substrates are examined in cross-section and in plane view. The grain boundary of the bicrystal substrate contains (110) faceted voids, but is otherwise straight on a nanometer scale. Contrary to this, the film grain boundary is not straight grain boundary can be up to 100 nm for a 100 nm thick film. The deviation from the intended position of the YBCO grain boundary can already occur at the film/substrate interface where it can be as much as ±50 nm. 相似文献
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本文用对靶溅射技术制备了La2/3Ca1/3MnO3/YBa2Cu4O8/La2/3Ca1/3MnO3薄膜.与YBCO单层薄膜相比,由于超导/铁磁系统中的磁性邻近效应,三层薄膜表现出较低的超导转变温度.薄膜的R~T测量曲线显示出超磁阻(CMR)效应和超导转变,预示着超导和铁磁特性共存于LCMO/YBCO/LCMO三文治结构. 相似文献
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The dust charge neutralization in a plasma with nonextensive ions is considered. The condition that the total current to a grain be zero is expressed in terms of the Lambert function. The fall-off of the net negative dust charge is then considered and a parameter study conducted, assuming hydrogen as well as argon plasma. Owing to ion nonextensivity, the dust charge reduction becomes much faster. Moreover, stronger is the ions correlation, more important is the involved electron depletion for a complete dust “decharging”. 相似文献
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针对低内禀噪声要求条件下HTcrf SQUID芯片制备成品率和优质率低等问题,通过对YBCO薄膜的PLD制备工艺参数及所制作的YBCO薄膜性能与微观形貌的观测分析,提出晶界结构的非均匀和不一致性可能是影响低噪声台阶边沿型晶界结制备质量的观点,进而以淀积温度为典型控制参数设计了一组实验,对实验获取的YBCO薄膜和SQUID芯片的性能测试表明:YBCO薄膜生长的三高条件(高淀积温度、高氧分压和高激光能量密度)易造成薄膜表面平整度恶化和晶界构型的不均匀,而选择合适的淀积温度可有效提高SQUID芯片的噪声性能。 相似文献
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R. Kita S. Kawamoto K. Ohata H. Izumi R. Itti T. Morishita S. Tanaka 《Physica C: Superconductivity and its Applications》1990,170(5-6):500-504
Ca-doped YBa2Cu4O8 (124) thin films are prepared on (100) SrTiO3 substrates by annealing the amorphous films deposited using a pulsed laser deposition technique. The X-ray diffraction measurements show that the Ca-doped YBa2Cu4O8 phase is formed by annealing below 800°C at a oxygen pressure of 1 atm. The 124 films have c-axis orientation normal to the substrates. As the Ca content increases, the proportion of the 123 impurity phase in the samples increases. The onset temperature of superconductivity of the Y(Ca)Ba2Cu4O8 films increases from 79 K to 88 K with an increase Ca-substitution for 5 to 10% of Y. 相似文献
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A. Del Vecchio C. Camerlingo F. De Riccardis H. Huang B. Ruggiero M. Russo E. Sarnelli M. A. Tagliente L. Tapfer G. Testa 《Il Nuovo Cimento D》1994,16(12):2025-2030
Summary We present a structural analysis of YBCO superconducting thin films fabricatedin situ by Inverted Cylindrical Magnetron (ICM) sputtering on commercial SrTiO3 single-crystal and bicrystal substrates. A detailed structural characterization of the superconductor films was performed
by using single-crystal X-ray diffractometry confirming that YBCO films have a strongc-axis orientation of the grains with a small mosaic spread. In the films grown on bicrystal substrates we observed a strong
correlation with the lattice structure of the substrate. In addition, a surface analysis of the region across the grain boundary
edge has been performed by using scanning electron microscopy.
Paper presented at the ?VII Congresso SATT?, Torino, 4–7 October 1994. 相似文献
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Functional complex-oxide materials show a wide variety of properties and behaviors that cannot be found in any other class of materials, including high-temperature superconductivity and colossal magneto resistance. Consequently, this group of oxide materials has become the focus of many experimental as well as theoretical studies, aiming at understanding the fundamental mechanisms and properties that govern these complex structures. Here, we will review our high-resolution Z-contrast imaging and electron energy-loss studies of two complex-oxide materials systems, more specifically low-angle tilt grain-boundaries in YBa(2)Cu(3)O(7) (YBCO), and the spin-state transition in LaCoO(3). It will be shown that the O K-edge pre-peak can be used to quantify the hole-concentration in the vicinity of the dislocation core in YBCO, as well as to determine the Co(3+) spin-state in LaCoO(3). 相似文献
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掺入BaCuO2杂相的YBa2Cu3O7-δ(YBCO)粉末样品采用固相反应方法制备获得。XRD的Rietveld精修显示BaCuO2杂相和YBCO并存。在YBCO+xBaCuO2(x=0,0.05,0.1,0.2,0.3)的一系列样品中,当x=0.05时,样品的临界电流密度最大。在磁场中,微量BaCuO2杂相的添加,使YBCO的临界电流(Jc)提高了,但超导转变温度(Tc)稍微有所下降。临界电流密度的这些特征行为来自于两方面的共同作用,一方面是超导性的变化,另一方面纳米尺寸范围内的空间分布的非均匀性。 相似文献