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1.
The surface resistanceR s of Tl2Ba2CaCu2O8 films fabricated on LaAlO3 wafers up to 3 inches (7.6 cm) in diameter through a post-deposition anneal process was measured over the frequency range 5.55–94.1 GHz by the following techniques: 5.55 and 27.5 GHz high-temperature superconductor (HTS)-sapphire resonators, 10 GHz parallel plate resonator, and 94.1 GHz scanning confocal resonator.R s was found to exhibit a quadratic dependence on frequencyf at 77 K:R s f 2.0±0.1. The highest-quality films yieldR s =145±15 at 10 GHz and 77 K. Scanning confocal resonator mapping ofR s across a 2-inch (5.1 cm) diameter wafer yielded a base value forR s of 16±1 m at 77 K and 94.1 GHz (equivalent to 180±10 at 10 GHz) and good uniformity inR s across the wafer. HTS-sapphire resonator measurements ofR s for fifteen 1.2 cm square parts cut from a 3-inch diameter wafer yieldedR s values scaled to 10 GHz of 196±10 at 80 K. Similar values were measured for Tl2Ba2CaCu2O8 films prepared on both sides of a 2-inch diameter wafer.Rs values at 10 GHz and 80 K of 147–214 were maintained over the course of 40 independent and successive deposition runs and corresponding anneals under nominally identical film fabrication conditions. Surface resistance at 5.55 GHz remained below 80 for maximum rf magnetic fields up to 85 Oe at 4.2 K and 7 Oe at 80 K, respectively. Results are compared with predictions of the two-fluid model. The relative advantages and disadvantages of the different techniques for measuring surface resistance are discussed.  相似文献   

2.
This paper describes a TE013 mode dielectric resonator at 36.098 GHz. The dielectric resonator was formed by sandwiching a cylindrical piece of polished dielectric (sapphire) rod between two GdBa2Cu3O7?x (GBCO) High Temperature Superconductor (HTS) thin films. The resonator was tested as a two-port device at a temperature of 77 K. A 62700 unload quality factor Q 0 was obtained. The surface resistance (Rs) of the HTS film had been determined as 9.4 mΩ at 77 K and 36 GHz.  相似文献   

3.
We have performed millimeter-wave frequency (94 GHz) measurements on high-quality YBa2Cu3O7- superconducting films on yttrium-stabilized (100) ZrO2 and MgO substrates. The 0.2m thin films fabricated by magnetron sputteringin situ with the YBa2Cu3O7- powders as target exhibit superconducting transition temperatures up to 88 K. The critical current density of 6×105 A/cm2 at 77 K and the X-ray diffraction spectrum as well as scanning electron microscope photographs indicate these thin films are fullyc-axis oriented, extremely high in density, and universally homogeneous. Millimeter-wave surface resistances have been measured on a hemisphere open resonator in the temperature range of 20 K toT c and beyond. The surface resistance at 94 GHz and 77 K for these films is found to be about 30 m, nearly 1/4 that for copper, and a drop of two orders in the surface resistance within 4 K is observed, which indicates that these films are good materials for applications in the millimeter-wave range, especially for fabricating microwave devices. We observed such low surface resistance in these thin films due to the near absence of grain and phase boundaries coupled with a high degree of crystalline orientation.  相似文献   

4.
Measurements of microwave surface impedance of high-T c films at gigahertz frequencies and nitrogen temperature are performed. A simple technique employing a parallel-plate resonator with liquid nitrogen as a dielectric spaces is suggested. The use of a precise mechanical device provides smooth changing of distance between films from 200m down to zero. Coupling to the resonator is accomplished by means of two small antennas-half-wave vibrators for frequency 10 GHz. The method for determining resistivity and magnetic field penetration depth was based on the analysis of spacer thickness dependences of the resonator quality factor and frequency. YBa2Cu3O7 films produced by a laser deposition technique on CaNdAlO4 substrates withT c =91 K andj c =107 A/cm2 and on NdGaO3 substrates withT c =91 K andj c =106 A/cm2 are examined, and the valuesR s =0.6 m,=348 nm atf=8.97 GHz andR s =0.5 m,=250 nm atf=10.12 GHz, respectively, are obtained at 77 K.  相似文献   

5.
A microwave superconducting magnetometer is described in which a microstrip resonator is coupled to a two-hole high-T c thin-film SQUID device. Both the microstrip circuit and the thin-film SQUID were fabricated by photolithography techniques. The YBCO thin film was deposited on single-crystal substrate of yttria-stabilized zirconia [YSZ(100)] by an ion beam sputtering technique producing a superconducting transition measured at a critical temperature ofT c =92 K to within T 3 K. Non linear oscillatory behavior was observed in the microstrip resonator when inductively coupled to the SQUID. This nonlinear behavior yielded a microwave device in which the reflected microwave power varied with applied DC magnetic flux.  相似文献   

6.
    
In order to apply highT c superconductivity to general microwave cavities and to shielding devices for quasistationary magnetic fields, we have developed an electrophoretic coating technique. This work reports about the continuation of our experiments. More than 60 samples of electrophoretic layers deposited on silver substrates were fabricated by systematically varying the processing parameters. The r.f. surface resistance measured at 21.5 GHz and 77 K at low excitation fields is found to be a sensitive measure of the quality of the samples and falls rapidly with increasing average grain size. Textured electrophoretic layers of large grain size show the smallest sensitivity ofR s against the r.f. surface magnetic fieldH s. The magnetic sensitivitydR s /dH s is found to be in direct proportion toR s (77 K). After optimizing the sintering procedure the electrodes of the prototype cavity for a compact hydrogen maser were coated. The cavity was successfully operated at 1.42 GHz, and a surface resistance of 1 m was achieved at 77 K. This compares to 4 m for copper at the same temperature.  相似文献   

7.
The in situ process—laser ablation in combination with thermal evaporation of Tl2O—has turned out to be a preparation method for single-phase and epitaxial TlBa2Ca2Cu3O9 (1223) thin films with T c values up to 109 K. It was found by several groups that a partial substitution of Tl by Bi simplifies the phase development of the 1223 compound in the usual two-step process. We have investigated the influence of the Bi doping on the in situ growth. X-ray measurements show that the films consisted mainly of the 1223 compound. In 300-nm thin films there was no evidence of a Bi amount in the crystal structure, but thinner films (80 nm) show a small amount of Bi. We concluded that Bi doping supports the phase development of the 1223 compound only in an early stage of the film growth. The Bi-doped films have higher T c values up to 114 K, higher j c values up to 6 × 105 A/cm2 (77 K, 0 T), and lower surface resistances of 56 m (77 K, 87 GHz) than the undoped films.  相似文献   

8.
Crack-free thick YBa2Cu3O7 – x films are prepared on CeO2 buffered r-cut sapphire (2 inch in diameter) with thickness up to 700 nm, smooth surfaces (peak-to-valley roughness <10 nm), high critical currents (J C > 2 MA/cm2 at 77 K and 0 T), and low microwave surface resistances (R s(77K) .4m and R s(4.2K) .110 at 19.15GHz) comparable to the best values reported in the literature for YBCO films on structurally better matched substrates. These thick YBCO films were able to handle high microwave power corresponding to magnetic field amplitudes (B HF) up to 54, 37, and 17.4 mT at 4.2, 50, and 77 K, respectively, which for the lower temperatures were limited by the available power of the 25-W HF amplifier. The high-power performance, which to our knowledge belongs to the best reported so far for unpatterned YBa2Cu3O7 – x films, was achieved without any degradation of the samples despite frequent thermal cycling.  相似文献   

9.
A millimeter wave spectrometer for frequencies between 100 and 350 GHz consisting of continuously tunable backward wave oscillators as sources and a quasioptical interferometer in the Mach-Zehnder configuration was used to measure the transmittivity in phase and amplitude of YBa2Cu3O7 thin films on NdGaO3 substrates. From the measured spectra we derived the real and imaginary part of the dynamic conductivity= 1+i 2 in the superconducting state as a function of temperature. The 1(T) and 2(T) values at 300 GHz were compared to corresponding values at 19 GHz determined by surface impedance measurements of the same films using a shielded dielectric resonator. Our observed frequency dependence of both 1(T) and 2(T) is consistent with a strong reduction of the quasiparticle scattering rate –1(T) with decreasing temperature belowT c .  相似文献   

10.
We measure the relative permittivity r and dielectric loss tangent tan of substrate materials for high-T c superconducting films at 18–300 K and at 5–10 GHz using the cavity-resonator method. The materials measured are single crystals of MgO, LaAlO3, YAlO3, LaSrGaO4, NdGaO3, sapphire, and ZrO2 ceramic. The r values are 10–30 and become almost constant below about 50 K. The tan values decrease with decreasing temperature and are below 1×10–5 at 77 K except for those of NdGaO3 and ZrO2 ceramic. This suggests that the tan values of MgO, LaAlO3, YAlO3, LaSrGaO4, and sapphire do not limit the quality factors of microwave passive components fabricated using high-T c superconducting films. It is also demonstrated that the tan of the substrate material is strongly affected by impurities.  相似文献   

11.
High-T c superconductivity has generated a great deal of interest because of the challenges it presents in the fields of material science, condensed matter physics, and electrical engineering, and because of the potential applications which may result from these research efforts. Thin-film passive microwave components may become the first high-temperature superconducting (HTS) devices available for widespread use and commercialization. In this article, we review aspects of material science, physics, and engineering which directly impact high-T c superconducting microwave devices and discuss issues which determine the performance of these devices. Methods of growing HTS thin films on large-area substrates, techniques for fabricating single-level HTS passive microwave components, and the relevant properties of high-T c superconducting films are discussed, with a focus on thin films of the HTS material YBa2Cu3O7–. Several known mechanisms for microwave loss in both the superconductor and the dielectric substrate are presented. An overview of the general classes of superconducting passive microwave devices is given, and representative microwave devices which have been recently demonstrated are described in detail. Examples of a select few HTS active microwave components are also presented. Potential microwave applications are illustrated with comparisons to current technology.  相似文献   

12.
The variation of critical current density at 77 K as a function of film thickness was studied for YBa2Cu3O7 films on (100) LaAlO3 substrates. Film thicknesses were in the range 0.2–1.6m. The films were deposited by co-evaporation and post-annealed under conditions which have previously resulted in high-quality films (750°C and an oxygen partial pressure of 29 Pa). The critical current density at 77 K exceeds 1 MA cm–2 for the thinner films, and decreases with increasing film thickness in excess of about 0.4m. The decrease is in rough agreement with a switch fromc-axis toa-axis growth at about this critical thickness. A good anticorrelation was found between room temperature resistivity and critical current density at 77 K. The results are compared to those obtained before by post-annealing at 850°C in 1 atm of oxygen.  相似文献   

13.
Physical mechanisms which limit the power handling of YBa2Cu3O7–x films and devices are discussed in terms of a quantitative classification scheme. The possible limitations are devided into magnetic or thermal, and global or local in nature. Analytical estimations are compared with measurements of YBa2Cu3O7–x films (Ø = 1–2) using a niobium-shielded sapphire resonator at 19 GHz, and disk resonators at 2 GHz. Magnetic effects are found to play an essential role in nonoptimized films in terms of weak-links, and in high-quality films if the lower critical field Bcl is reached. The majority of films and disk resonators appear to suffer from microwave heating. Global heating appears predominantly at CW operation. Local heating results mainly from defects in films of medium quality. Defect-induced quenches are observed at moderate field levels, sometimes resulting in an irreversible degradation of the power handling.  相似文献   

14.
Growth-induced linear defects are shown to strongly affect the microwave surface resistance, Rs, of highly biaxially oriented high temperature superconductor (HTS) YBa2Cu3O7– (YBCO) films. Measured Rs(77 K) turned out to be 4–5 times higher than in single crystals. The films were deposited by modified pulse-laser technique, Jc(77 K) = (3-6) × 106 A/cm2, onto LaAlO3 substrates. Rs(T) was measured at 134 GHz and 20–100 K. TEM/HREM study of YBCO films deposited at Ts = 750°C–780°C revealed a reduction of edge dislocation density with Ts increase (from 2 · 1011 to 1010 lines/cm2). YBCO films deposited at Ts = 780°C exhibited the smallest Rs(77 K, 134 GHz) < 120 m and the lowest density of dislocations detected by HREM and X-ray analysis. A nature of the dislocation effect is discussed within a model of local anisotropic elastic deformation in a vicinity of dislocation cores, where Tc variation and an enhancement of normal quasiparticle density are significant.  相似文献   

15.
We have measured magnetic penetration depth(0) of high-T c YBCO samples of different density by the cavity resonant frequency shift method at 10, 16.65, and 22.3 GHz microwave frequencies. The value of(0) at 10 GHz is found to decrease from 5850 Å to 2550 Å as the density of the sample increases from 4.4 to 5.3 g/cm3. The results of the frequency response of the penetration depth show a fairly constant value of(0) for all the three samples in the frequency range 10–22.3 GHz. The wide variation observed in the value of(0) for different density samples has been explained in terms of varying Josephson coupling strength in these ceramics.  相似文献   

16.
    
The diffusion of the excess oxygen during phase separation in La2CuO4+ was studied using thermal history-dependent normal state magnetic susceptibility(T, t) measurements versus temperatureT and timet as a probe. A large thermal hysteresis of(T) was observed for La2CuO4.044 between data obtained after quenching to 5 K and then warming, and data obtained while or after slowly cooling from 300 K. A model for the excess oxygen diffusion is presented, from which the(T, t) data yield aT-independent activation energy of 0.24(3) eV for the diffusion coefficient of the excess oxygen from 150 to 220 K. In related work, we have used139La NQR andSR measurements to probe the antiferromagnetic (AF) region (x<0.02) of the La2–x Sr x CuO4 system below the Néel temperatureT N(x), from which we extract the Cu+2 staggered magnetizationM (x, T). M(x, T=0), extrapolated from above 30 K, was successfully modeled with spin-wave theory, assuming that the doped holes are mobile and are situated in walls in the CuO2 plane which uncouple undoped AF domains; these domains are coupled to those in adjacent CuO2 planes. This agreement supports the previous hypothesis that microsegregation of the (mobile) doped holes into domain walls occurs above 30 K, consistent with the phenomenology of Emery and Kivelson. Below 30 K, an anomalous increase inM (x, T) is observed, such thatM (x, T=0) is nearly independent ofx. We interpret this effect as arising from localization of the doped holes below 30 K.Deceased.  相似文献   

17.
Measurements of the microwave surface resistance Rs and reactance Xs of GdBa2Cu3O7– and Sr2RuO4 single crystals are reported in the temperature range 0.4 to 25 K at frequencies from 10 to 20 GHz, using a hollow dielectric resonator technique. The GdBa2Cu3O7– measurements are interpreted in terms of antiferromagnetic alignment of the Gd spins, resulting in a Nèel transition at 2.25 K, with a strongly temperature spin relaxation time both above and below the transition. Above Tc = 1.45 K, the normal state surface impedance of the suspected p-wave superconductor Sr2RuO4 agrees rather well with that expected from dc measurements; however, below Tc, we observe an unusual increase in the surface reactance, which we attribute to a long electron relaxation time. Using a two-fluid model, we obtain a normal fluid component that decreases almost linearly with temperature and extrapolates to a finite low-temperature value.  相似文献   

18.
Bi2O3–ZnO–Nb2O5 system has emerged as a good low sintering (1050 °C) microwave material because it exhibits high dielectric constant and low temperature coefficient of resonance frequency (τf). We have lowered the sintering temperature of Bi1.5Zn0.92Nb1.5O6.92 (BZN) below 900 °C by using 3 wt.% of CuO-based dopants, such as 0.21BaCO3–0.79CuO (BC) and 0.81MoO3–0.19CuO (MC). The doped BZN exhibits high microwave dielectric constant at 2.3 GHz (k  120). The interfacial behavior between BZN and silver was investigated by using X-ray diffractometer, scanning electronic microscope, and electronic probe microanalyzer. The extent of silver migration of MC and BC dopants is reduced at least by one order of magnitude as compared with V2O5 dopant when the samples was prepared at 900 °C for 4 h. Thus, CuO-based dopants can replace V2O5 to lower the sintering temperature of BZN and to be cofired with silver.  相似文献   

19.
The nominal composition of YBa2–x M x Cu3O y (M = K, Na) cuprates with x 0.30 were synthesized by the standard solid-state reaction technique. X-ray diffraction (XRD) and the resistivity measurements were used to characterize the structure and the superconductivity of the doped cuprates. There was no impurity phase detected within the whole doping range. The structure of the main phase (123) has the orthorhombic with P mmm symmetry. With increasing the content of dopants, the lattice constants and some other structural parameters are almost unchanged for M = K, whereas they changed for M = Na. The refined contents of dopants are consistent with that of the nominal ones. The zero resistance temperature T c0 decreases sharply with the increase of the content of potassium in potassium-doped samples as x 0.20. For sodium-doped YBa2–z Na x Cu3O y cuprates, T c0 varies very little. The difference in superconductivity depression may result from the shift oxygen, which transfers conducting carriers from Cu-O chains to Cu-O2 sheets or the structural stress effect.  相似文献   

20.
The compressibility behavior of three mixtures of the CH4 C2 H6, system has been investigated experimentally by means of the dielectric constant method. Precise ( ± 1 ppm) measurements of the dielectric constant () as a function of the pressure (P) along one isotherm (T) are combined with the first three dielectric virial coefficients (A,B, andC) in order to obtain accurate values of the molar density (p). The compressibility factorZ=P/( p RT) was obtained from the measured values ofp,P, andT. The coefficientA, is determined from the measurements of as a function ofP, while the higher-order coefficients (B, andC,) are obtained by an expansion technique. We report the measured values ofZ at 295.15 K up to 12 MPa for three mixtures of CH4-C2-H6 containing, respectively. 9.54, 35.3, and 75.4% (molar) of ethane. Their exact composition was determined by weighing during the mixing process. The first three dielectric virial coefficients and the mixed second dielectric virial coefficient for the CH4,-C2, H6 system agree with the calculated or the literature values within the limits of uncertainties. For the mixture containing 90.46% CH4+C2H6, deviations in compressibility are of the order of 0.4% from GERG.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.  相似文献   

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