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1.
The properties of Be films, quench-condensed upon a3He cooled substrate, have been investigated by resistance and tunneling measurements. The superconducting transition temperature,T c , of Be films increased with thickness and a thick film limit of 9.95 K could be estimated. Alloying with Al or Pb decreasedT c. The ratios between energy gaps andT c 's indicated that Be is a weak coupling superconductor, and no phonon induced structure could be traced in tunneling curves neither in pure Be nor in the Be based alloys. Resistance change during annealing as well as superconducting data indicated that the vapour quenched Be films were amorphous as deposited.  相似文献   

2.
Thin films of Ge-Cu, Ge-Ag and Ge-Au alloys have been condensed onto substrates held at 4 K. An amorphous, metallic phase has been obtained. The superconductivity of this phase is believed to be due to Ge which is forced into a liquidlike structure with a higher coordination number than that of the semiconducting diamond structure. The maximum transition temperatures of the Ge-Cu and Ge-Au films are 3.3 and 3.6 K, respectively, whereas Ge-Ag films show a maximumT c of 1.2 K. The difference inT c is explained by the band structure of the noble metals.  相似文献   

3.
The volume dependence of the superconducting transition temperatureT c of quench-condensed Be films is investigated by bending the substrate of the film. Tensile strain causes an increase, compressive strain a decrease ofT c . The volume coefficientd lnT c /d lnV is about 0.8, a value which is small compared with those of other weakcopling non-transition metals. In addition to pure films, Be films stabilized by codeposition of noble metals or Ge are investigated.Paper based in part on a Habilitationsschrift submitted to the Fakultät für Physik, Universität Karlsruhe (TH), FRG  相似文献   

4.
Quench condensed binary alloy films are produced by evaporation from two separated furnaces. The films contain the whole composition range of the respective alloy system in well defined arrangement.T c is measured as a function of concentration. Eight predominantly amorphous alloy systems are studied: Bi—Ga, Pb—Ga, Pb—Bi, Be—Bi, Be—Pb, Be—Ga, Be—Al, Be—Li. In Bi—Ga and Pb—GaT c is a linear function of concentration in the amorphous composition range. In Pb—BiT c has a maximum. All Be-alloys show lower transition temperatures than pure quench condensed Be. Except for Be—Li all systems have aT c minimum. The experiments are compared to aT c calculation using tunelling spectroscopy data. Except for the Be-alloys the agreement is satisfying.  相似文献   

5.
本文对Ge/An,Ge/Ag,双层膜和Ge-An,Ge-Ag合金膜的退火过程进行了透射电子显微镜观测,对Ge/多晶Au(或Ag)还进行了加热过程的原位观测。观测表明,多晶Au和单晶Au膜的存在使非晶Ge的晶化温度Tc的下降显著不同,可由晶界三叉点等处为非晶Ge的有利形核位置来解释,双层膜的缩聚区中由于局域优先晶化的影响,不仅Tc(=100℃)比非缩聚区中(Tc=150℃)低,而且形成直径为1—2μm的Ge大晶粒,而Ge/多晶Ag和Ge/单晶Ag膜的Tc均约为280℃,合金膜中金属含量较低时(CAu<17at%,CAg<18at%),Tc高于相应的Ge/多晶Au(Ag)膜;金属含量较高时,Tc低于Ge/多晶Au(Ag)膜。这说明过饱和金属原子的存在使得非晶Ge的晶化势垒大大降低。 关键词:  相似文献   

6.
Tc for vapour quenched Be is depressed in thin films. In the limit of infinite thickness we measure Tc = 9.95 ± 0.06 K.  相似文献   

7.
To determine the reproductibility in the measurement of Tc a round-robin experiment was conducted. The samples consisted of five high Tc “Nb3Ge” thin films. The results of this experiment show that only the midpoint of the Tc curve is reproducible to within ≈±0.2 K.  相似文献   

8.
The upper critical field Hc2(T) of the highest Tc(~23K) Nb3Ge superconducting films has been found to be ≈370kG at 4.2K. Measurements on lower Tc films show very broad transitions reflecting nonuniformity. The Hc2(T) characteristics are consistent with other Nb3X type II superconductors.  相似文献   

9.
This is a report on a cooperative research carried out in Stanford University to investigate the possibility of using epitaxy to prepare the high Tc superconductor Nb3Ge in an A15 crystalline structure at the 3:1 stoichiometry.Nb3Ir polycrystalline films with the A15 structure deposited on sapphire were used as substrates for the epitaxial growth of Nb3Ge because of the favorable lattice parameter match. The experimental results clearly show that epitaxial growth indeed occurs and helps to extend the range of homogeneity of the A15 phase up to 26.3 at.% Ge as compared with the thermodynamic equilibrium boundary at 19 at.% Ge. We also used Nb3Rh films as substrates and found them inferior to Nb3Ir because of the multiphase nature of the films.In addition to extending the A15 phase boundary epitaxy results in a considerable rise in the superconducting transition temperature for Ge-rich samples together with a reduction in the transition width. The work suggests that polycrystalline epitaxy can be an important tool in the synthesis of thin-film intermetallic compounds.  相似文献   

10.
We have performed Extended X-ray Absorption Fine Structure (EXAFS) studies of the high-Tc ternary superconducting alloy Nb3Ge0.26Al0.74 above the Ge K-edge. The EXAFS indicates that the local environment surrounding the Ge atoms is characterized by a high degree of structural order, similar to that found in previous investigations of high-Tc Nb3Ge thin films. We also present direct “microscopic” structural evidence that this material is a solid solution of Nb3Ge and Nb3Al. No evidence of Nb3Ge microcrystals is observed.  相似文献   

11.
The temperature dependence of the superconducting critical current density Jc(T) in zero applied field from 4.2 K to Tc has been measured for 15 films of Nb-Ge with varying composition, deposition conditions, and radiation damage. The results show (i) the enhanced superconductivity observed in stoichiometric Nb3Ge as well as nonstoichiometric films is “bulk like” rather than filamentary, (ii) a simple correlation of the form Jc(0)∝eTcT0 which is reasonably independent of how the Tc has been achieved, and (iii) some additional evidence that the enhanced Tc of the films is not due to their chemical composition alone.  相似文献   

12.
Annealed and quench condensed indium films have been implanted with 150 keV-In ions. It is found thatTc can be increased, even in the disordered films, to a maximum value of 4.54 K.  相似文献   

13.
Sputtered films of nominal composition Nb3Ge deposited onto hot substrates, of the type recently found by Gavaler to have superconductivity onsets at 22.3° K, have now been obtained with a maximum onset temperature of 23.2 ± 0.2° K and a transition width of ~ 1.2° K. The sputtering conditions necessary to achieve these results are discussed and suggest that the high Tc phase may be detrimentally affected by the presence of high energy particles present under normal sputtering conditions.  相似文献   

14.
The effect of short-term low-temperature annealing in air and in vacuum on the properties of HTSC films of YBCO is studied. It is shown that, under certain conditions of preparation of initial samples, a transition from the HTSC phase with the superconducting transition temperature Tc=90 K to a phase with Tc=60 K occurs without a noticeable change in the oxygen content. It is found that, as a result of short-term annealings, a transition from the HTSC phase with Tc=60 K to the phase with Tc=90 K can occur only through the vacuum annealing stage, which converts the sample into the superconducting state. Short-term annealings lead to multiple reversible “switching” of the films from one phase to another. The obtained results are of practical interest, since the proposed method can be used to quickly obtain superconducting YBCO films in various phase states. It is shown, in addition, that the annealing procedure makes it possible not only to increase the oxygen concentration but also to produce a structural rearrangement of a YBCO film.  相似文献   

15.
Thin Tl/Te-films are condensed onto a cooled substrate at 4 K. An amorphous phase is obtained. The maximum superconducting transition temperature of the amorphous Tl/Te-films is 4.2 K. Measurements of the energy gap by superconducting tunneling yield a ratio 2Δ/k T c =4.6 for amorphous Tl/Te-films and 2Δ/k T c =3.8 for disordered, pure Tl-films.  相似文献   

16.
Bulk material of Nb3 (Ge0.8Nb0.2) with A15 structure and a superconducting transition temperature Tc of 6.5 K has been implanted with Ge, Si, Ar and O ions and subsequently annealed at high temperatures. After annealing between 700 and 750°C the Ge implanted samples showed a strong increase in Tc up to 16.2 K. With Si ions only a Tc of 13 K was obtained, with Ar and O ions Tc remained below 9 K. From X-ray measurements carried out on high Tc Ge implanted samples it could be concluded that the implanted surface layer grows up to a high degree epitaxially on the single crystallites of the bulk material. The lattice constant a0 of the implanted film was reduced by 0.02 Å with respect to the bulk material. This reduction in a0 is stronger than expected from the transition temperature of the implanted surface layer.  相似文献   

17.
The superconducting transition temperature (Tc) of amorphous Nb3Ge was studied under both hydrostatic and quasihydrostatic pressure to 3.5 and 13 GPa, respectively. Whereas hydrostatic pressure causes Tc to initially decrease, Tc is found to increase under higher quasihydrostatic pressures. Tc(p) was also studied on an A-15 crystalline Nb3Ge sample obtained from the amorphous sample by annealing.  相似文献   

18.
A mechanism for the degradation of superconducting transition temperatures Tc by high energy nuclear irradiation in A-15 materials is proposed. The radiation is supposed to produce small “disordered” regions having a very low Tc, in a matrix having the original Tc of the material. The composite system has a well defined but lower Tc due to the proximity effect of the “disordered” regions.  相似文献   

19.
Resistive superconducting zero-field transition in amorphous In-O films in the states in the vicinity of the insulator-superconductor transition is analyzed in terms of two characteristic temperatures: the upper T c0 , where the finite amplitude of the order parameter is established, and the lower T c , where the phase ordering takes place. It follows from the magnetoresistance measurements that the resistance in between, T c <T< T c0 , cannot be ascribed to the dissipation by thermally dissociated vortex pairs. So, it is not a Kosterlitz-Thouless-Berezinskii transition that occurs at T c .  相似文献   

20.
Thin and pure Tl-films and In-films with different impurities (Ag, Te, Ge, Sb) are condensed onto a cooled substrate at 4 K. Measurements of the energy gap by means of the tunnel effect and the transition temperature of the weak-coupling superconductor thallium are carried out as a function of the degree of disorder of the films. The ratioα=2Δ 0/kT c increases proportional to the reciprocal mean free path from 3.5 for the annealed film up to 3.8 for the highly disordered film. For In-films condensed by quenching with impurity additions, one finds a linear relation between energy gap and transition temperature. In-films with Sb-additive are obtained in an amorphous phase with a ratioα=2Δ 0/kT c of 4.4. The amorphous state of the In/Sb-films is confirmed by measurements of the electric conductivity and the Hall-effect.  相似文献   

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