共查询到20条相似文献,搜索用时 15 毫秒
1.
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
2.
A. Mogro-Campero L. G. Turner 《Physica C: Superconductivity and its Applications》1994,220(3-4):329-331
Although Ag and Au are commonly used to provide low-resistance contacts to YBa2Cu3O7 (YBCO), their effect on the electrical properties of the underlying YBCO has been largely neglected. Epitaxial YBCO thin films on LaAlO3 substrates were used in this study. Thin (50 nm) and thick (1 μm) layers of Ag or Au were deposited as overlayers, and in some cases annealed in oxygen at 550–650°C. Compared to samples with no metal overlayers, for both Ag and Au the normal-state parameters changed (resistivity, its temperature coefficient, and the transition width), whereas the transition temperature and critical current density remained unaltered. These results are encouraging for the use of these metals as contacts and/or conducting overlayers on YBCO. 相似文献
3.
Evidence that pinning on linear or planar defects dominates the vortex dynamics in YBa2Cu3O7−x (YBCO) films is provided by complex impedance measurements at temperature 8 K<T<T
c
and magnetic field 0<B<6 T. Below the vortex lattice melting transition Bg(T) but above a threshold field Bp≈8(1-T/T
c
) T, the inductance of vortices increases as B2, much less rapidly than predicted for collective pinning of vortices by point defects. Above the vortex melting line, critical
scaling persists over the region Bg(T<B<B*(T) where the vortex correlation length ξ exceeds a characteristic length scale ξ*≡ξ(B=B*)≈450?. The value of ξ* is not sensitive to Al-doping in the Cu sites in the lattice and is close to the size of twin domains in the film. The nature
of the observed crossovers is discussed in terms of available theoretical models for a glass-liquid transition at Bg. 相似文献
4.
H. Weyten G. Fransen R. Kemps A. Buekenhoudt J. Cornelis 《Physica C: Superconductivity and its Applications》1996,270(3-4):207-215
High-Tc superconducting thin films have been deposited in situ by means of a plasma assisted metal-organic chemical vapour deposition (PAMOCVD) process on LaAlO3. An EMCORE high-speed rotating disc reactor was used to deposit the films at a substrate temperature of 600°C to 800°C. The system is equipped with a (remote) 120 W microwave plasma generator. The oxidising plasma gas is N2O and/or O2 while Ar was used as the inert carrier gas for the different metal-organics. The influence of different process parameters (such as the temperatures of the metal-organics, substrate temperature, and plasma gas composition) on the superconductive properties and on the morphology of the films was investigated. Surface morphology and composition were studied by SEM/EDX or EPMA, and AC susceptibility measurements were used to investigate the superconductive properties (Tc and Jc). X-ray diffraction measurements indicated that single-phase YBa2Cu3O7−x films were epitaxially grown with the 00l orientation perpendicular to the substrate surface. The critical temperature (Tc) of the films is about 90 K and the critical current density (Jc) is higher than 106 A/cm2 at 77 K and zero field. 相似文献
5.
6.
J. Humli
ek J. Kircher H. -U. Habermeier M. Cardona 《Physica C: Superconductivity and its Applications》1992,190(4):383-395
Ellipsometry was used to study (110) and (001) oriented films of YBa2Cu3O7 and PrBa2Cu3O7 in the mid-and near-infrared spectral regions. Below a photon energy of 0.1 eV, the in-plane component of the dielectric tensor of YBa2Cu3O7 is dominated by a Drude term with a squared plasma energy of (3.0 ± 0.3) eV2. This “oscillator strength”, and the Lorentzian broadening energy of (0.104 ± 0.005) eV at room temperature, are confirmed by the changes induced in Pr-substituted material, and by low-temperature measurements in the near-infrared. The deviation from the Drude behavior observed above 0.1 eV is accounted for by a broad absorption band with an oscillator strength of (3.6 ± 0.1) eV2 in YBa2Cu3O7 which shifts to higher energies and takes over almost all of the oscillator strength of the Drude term when Y is substituted by Pr. The response to electric fields perpendicular to the planes is much weaker, with an upper bound of 0.63 eV2 for the squared plasma energy. The in-plane loss function computed from the measured dielectric function follows the Drude-like lineshape, modified by the bound-state absorption band, down to the lowest energy reached in our measurements (0.058 eV). 相似文献
7.
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
8.
Yuuji Horie Shun-ichi Kuroumaru Bai-ru Zhao
Xiang-gang Qiu
Yin-zi Zhang Yu-ying Zhao Po Xu Lin LiHiroshi Okubo
Shoichi Mase
《Physica C: Superconductivity and its Applications》1990,170(5-6):513-520We measured voltage V versus current I curves with a function of temperature T and magnetic field H for YBa2Cu3O7 single-crystalline thin films. The characteristics of the pinning type was found to be changed with the change in T, in contradiction to Kramer's scaling law. Furthermore, we analyzed I–V curves in terms of the flux creep model proposed by Anderson and Kim. In low H region the product of flux bundle volume vd and its jump distance l decreased with the increase of H, while in high H region the product increased rapidly with H, suggesting a rapid increased of interaction length between vortices. These results imply all evidence of an occurence of vortex liquid phase in the high H regime. We showed that the transition region between the above two regimes is located in the vicinity of H at which the critical current density begins to decrease rapidly with the increase of H. 相似文献
9.
R. Menegotto Costa L. Mendon?a Ferreira V. N. Vieira P. Pureur J. Schaf 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(2):107-113
We have studied experimentally the electrical magneto-conductivity near the
superconducting transition of YBa2Cu3O7-δ, YBa2
(Cu2.95Zn0.05)O7-δ and Y(Ba1.75Sr0.25)Cu3O7-δ polycrystalline samples. The measurements were performed in magnetic fields ranging from 0 to 400 Oe applied parallel to
the current orientation. The results show that the resistive transition of these systems proceeds in two stages. The pairing
transition occurs at the bulk critical temperature Tc, where superconductivity is stabilized within small and homogeneous regions of the
sample generically called grains. The regime of approach to the zero resistance state reveals the occurrence of a coherence
transition at a lower temperature Tc0. This transition is related to the connective nature of the granular samples and is controlled by fluctuations of the
order-parameter phase of individual grains. Our experiments show that the Zn-doping, besides depressing the pairing critical
temperature, strongly enlarges the temperature range dominated by effects related to the coherence transition. The substitution
of Ba by Sr causes only a small reduction of Tc, but also enhances significantly the effects related to the grain
coupling phenomenology. In general, our results indicate that these impurity substitutions in YBa2Cu3O7-δ produce or magnify the granularity at a microscopic level, enhancing the effects of phase fluctuations in the conductivity
near the transition. 相似文献
10.
V. Vaicikauskas G. N. Zhizhin V. A. Yakovlev 《International Journal of Infrared and Millimeter Waves》1991,12(11):1233-1240
The results of YBa2Cu3O7-x films on SrTiO3 investigation by far infrared surface electromagnetic waves (SEW) amplitude and phase spectroscopy at temperatures 80–350 K are presented. Strong SEW absorption at frequency 142 cm–1 has been observed. The origin of the observed absorbtion is proposed to be concerned with slab- phonons in YBa2Cu3O7-x. The optical constants of the films have been obtained. Also has been determined, that only the imaginary part of the SEW refraction index changes when the film transits into superconducting state, while the real part remains unchanged. 相似文献
11.
R. Durny M. Puri L. Kevan
Y. J. Zhao
W. K. Chu 《Physica C: Superconductivity and its Applications》1992,190(4):460-464The modulated microwave absorption in YBa2Cu3O7−δ thin films was studied as a function of temperature, modulation amplitude, and microwave power. The comparative nature of weak links in YBaCuO thin films, ceramics, and powders is discussed. 相似文献
12.
N. G. Trusevich L. G. Mamsurova A. A. Vishnev N. B. Butko 《Bulletin of the Russian Academy of Sciences: Physics》2012,76(3):312-314
The temperature dependences of normal state static magnet susceptibility χ(T) for high-temperature YBa2Cu3O7 superconductors (T
c ≤ T ≤ 400 K) measured for the same sample before and after 22 years of storage are compared. It is shown that during longime
storage of a maximally doped sample, its electronic system is more in equilibrium than it was in the initial state, while
a similar underdoped sample decomposed completely. Comparing the χ(T) curves for YBa2Cu3O7, we draw conclusions as to the nature of the Curie contribution and the fluctuation-induced contribution to the magnetic
susceptibility of the investigated sample, and the experimental procedure for determining T
c. 相似文献
13.
E.P. Kvam 《Physica C: Superconductivity and its Applications》1992,200(3-4):409-412
The pinning potential of the
031 type dislocation has been calculated. This dislocation bounds the excess Cu---O layer defect commonly observed in YBa2Cu3O7. It was found that there is a strong pinning anisotropy between edge dislocations lying along [100] and [010]. For the former, a repulsive potential of about 30 meV is found, while the latter exhibits an attractive interaction of less than
this magnitude. This potential is short-range (about 2ξ), indicating that these dislocations would act as distributed point-like pinning sites. 相似文献
14.
测量了在不同氧压下退火生长的YBa2Cu3O7-x(YBCO)薄膜中的激光感生热电电压(LITV)信号,发现随退火氧压的增大可使LITV信号的峰值有2—4倍的增强,并且变化趋势与薄膜热电势的各向异性随氧含量的变化规律相同.波长在473—808nm范围内的连续激光辐照,在5000Pa的氧压下退火生长的YBCO薄膜中探测到的LITV信号最大;而紫外脉冲激光辐照时,LITV信号的最大值出现在退火氧压为105Pa
关键词:
2Cu3O7-x薄膜')" href="#">YBa2Cu3O7-x薄膜
激光感生热电电压
各向异性的Seebeck系数
氧含量 相似文献
15.
This paper systematically investigates the intermediate phases of YBa2Cu3O7-x (YBCO) film prepared by metalorganic deposition method using trifluoroacetates (TFA-MOD). According to x-ray diffraction and Raman analyses, the precursor film decomposed in a mixture of BaF2, Y2O3 and CuO after the pyrolysis process. Then these intermediate phases converted into tetragonal YBa2Cu3O6.5 at about 725°C. The influence of water vapour pressure on the YBa2Cu3O7-x film growth on LaAlO3 single-crystal substrates was also studied. The films prepared at low water vapour pressures (40-140 hPa) showed poor electrical performance due to the a-axis grain structure and impurity phases. However, the films prepared at 190 hPa exhibited the highest critical temperature of 90 K and the highest Jc of 3.8 MA/cm2, which was attributed to the formation of a purer YBCO phase and stronger biaxial texture. 相似文献
16.
Meiya Li B. Ma B.L. Fisher V.A. Maroni U. Balachandran 《Solid State Communications》2004,131(2):101-105
Biaxially textured YBa2Cu3O7−x (YBCO) films were grown on non-textured metal substrates with inclined-substrate-deposited (ISD) MgO as template. The biaxial texture feature of the films was examined by X-ray pole-figure analysis, φ-scan, and 2θ-scan. A tilt angle of 32° of the MgO[001] with respect to the substrate normal was observed. Epitaxial growth of YBCO films with c-axis tilt angle of 32° with respect to the substrate normal was obtained on these substrates with SrTiO3(STO) as buffer layer. Whereas, by choosing yttria-stabilized ZrO2 and CeO2 instead of STO as buffer layer, a c-axis untilted YBCO film was obtained. Higher values of Tc=91 K and Jc=5.5×105 A/cm2 were obtained on the c-axis untilted YBCO films with 0.46 μm thickness at 77 K in zero field. Comparative studies revealed a unique role of CeO2 in controlling the orientation of the YBCO films grown on ISD-MgO buffered metal substrates. 相似文献
17.
T. K. Park B. J. Mean K. H. Lee S. W. Seo K. S. Han D. H. Kim Moohee Lee H. S. Lee H. B. Kim W. C. Lee Joung-Sook Cho 《Physica C: Superconductivity and its Applications》1999,320(3-4):245-252
We have prepared Zn-substituted YBa2Cu3−xZnxO7 (YBCO, x=0.0–0.09) and performed 63,65Cu nuclear quadrupole resonance (NQR) measurements for the plane site at 300 and 100 K as a function of Zn concentration. The substitutional effects are observed in resonant frequencies and linewidths of spectra, and relaxation times as well as in the superconducting transition temperature. The spin–lattice relaxation rate 1/T1 is reduced for the higher Zn concentration and the reduction is more significant at 100 K. The ratio of 63,65Cu spin–lattice relaxation rates suggests that a magnetic contribution due to the antiferromagnetic spin fluctuation becomes weak as the Zn concentration increases. These effects confirm that the antiferromagnetic spin fluctuation of Cu 3d spins is suppressed by the Zn substitution due to the absence of local moment at the zinc site. 相似文献
18.
19.
M. Ohkubo T. Kachi T. Noritake 《Physica C: Superconductivity and its Applications》1989,160(5-6):480-488
Rutherford backscattering/channeling has been applied to study structures of as-deposited epitaxial YBa2Cu3Ox thin films prepared on {100}SrTiO3 by laser deposition. The epitaxial growth has been proved by a planar channeling experiment and transmission electron microscopy. An axial angular yield profile for barium along the c-axis has ideal characters of compensating shoulders and of a flat region at the bottom of the channeling dip. The thermal vibration amplitude, which has been determined from a half-angle of the axial angular yield profile by using Gemmell's channeling model for polyatomic crystals, is compared to those from diffraction experiments. 相似文献
20.
The dependence of YBCO thin film properties on the deposition conditions was studied for different substrates. The deposition conditions were optimized for the epitaxial growth of high quality YBCO thin films of 1500 Å thickness onto single crystal (100-oriented) SrTiO3 (STO), MgO and LaAlO3 (LAO) substrates by DC Inverted Cylindrical Magnetron Sputtering (ICMS). The samples were investigated in detail by means of X-ray diffraction analysis (XRD), EDX, AFM, ρ-T, magnetic susceptibility and current-voltage (I-V) characterizations. The samples show strong diamagnetic behavior and sharp transition temperatures of 89-91 K with ΔT<0.5 K. XRD of the samples exhibited highly c-axis orientation. The full width at half maximum (FWHM) values of the rocking curves were ranging typically from 0.22 to 0.28°. The samples have smooth surfaces as shown from AFM micrographs. The surface roughness, Ra, changed between 5-7 nm. I-V characteristics were obtained from the 20 μm-wide microbridges, which were patterned by a laser writing technique. The critical current densities (Jc, 1.06×106 for LAO-based YBCO, 1.39×106 for MgO-based YBCO, 1.67×106 A/cm2 for STO based YBCO) of the microbridges were evaluated from I-V curves at 77 K. 相似文献