Transitions superconducting

Figure C 1.2.7. Superconducting transition temperature plotted as a function of the a lattice parameter for a variety of A Cgg phases [55].

Rhenium hexafluoride is a cosdy (ca 3000/kg) material and is often used as a small percentage composite with tungsten or molybdenum. The addition of rhenium to tungsten metal improves the ductility and high temperature properties of metal films or parts (11). Tungsten—rhenium alloys produced by CVD processes exhibit higher superconducting transition temperatures than those alloys produced by arc-melt processes (12). 

Titanium alloyed with niobium exhibits superconductivity, and a lack of electrical resistance below 10 K. Composition ranges from 25 to 50 wt % Ti. These alloys are P-phase alloys having superconducting transitional temperatures at ca 10 K. Thek use is of interest for power generation, propulsion devices, fusion research, and electronic devices (52). 

Isotope Effects on Superconductivity. Substitution of hydrogen by deuterium affects the superconducting transition temperature of palladium hydride [26929-60-2] PdH2 (54,55), palladium silver hydride, Pd Ag H D ( 6), and vanadium—2itconium—hydride, N(57). 

Fig. 12. Normalized dc electrical resistivity p(T) of single crystal KsCeo. The inset shows the p(T) behavior near the superconducting transition temperature Tc = 19.8 K [114]. The curvature in p(T) for T > Tc is due to the volume expansion of the sample [7, 4.3],...

It will be intriguing to theoretically examine the possibility of superconductivity in CNT prior to the actual experimental assessment. A preliminary estimation of superconducting transition temperature (T ) for metallic CNT has been performed considering the electron-phonon coupling within the framework of the BCS theory [31]. It is important to note that there can generally exist the competition between Peierls- and superconductivity (BCS-type) transitions in lowdimensional materials. However, as has been described in Sec. 2.3, the Peierls transition can probably be suppressed in the metallic tube (a, a) due to small Fermi integrals as a whole [20]. 

Electrical Resistivity 75 oDcm Superconductive Transition Temperature <1.2K Hall Constant -0.47x10"4 cm /A s... 

Electrical Resistivity 37-45 pDcm Superconductive Transition Temperature < 1.2K Hall Constant -12.4 x lO " cm A s Magnetic Susceptibility -23 x 10 emu/mol... 

Electrical Resistivity 35 pGcm Superconductive Transition Temperature 6K Hall Constant -1.3 x 10 " cmVA s Magnetic Susceptibility +15.3 x 10 emu/mol... 

Electrical Resistivity 17-22pDcm Superconductive Transition Temperature lO.OK Hall Constant - 21.8 x 10 " cm /A s at20°C Magnetic Susceptibility + 10 x 10 emu/mol... 

Superconductive Transition Temperature 2-8.7 K (varies with composition)... 

The idea that new phenomena could be present in 3He at very low temperatures arose from thermal measurements. The first observation was the anomaly in the specific heat at the normal superfluid transition which reminded the behaviour of specific heat at the superconductive transition in metals (Fig. 2.11) [34-36]. 

We notice from Fig. 3.4(b) that the lattice specific heat cph is not modified by the superconducting transition cph = /3T3 with the same of the normal state. 

Melting temperatures Tm and superconducting transition temperatures Tc of some solders [14-21]... 

In 1968, an international agreement was reached about the definition of an official (practical) scale of temperature for T> 14 K. This temperature scale IPTS-68, corrected in 1975 [11], was defined by reference fixed points given by transitions of pure substances. To extend the low-temperature range of IPTS-68, the EPT 76 [12-13] gave nine reference temperatures defined by phase transition of pure substances in particular the superconductive transition (between 0.5 and 9K) of five pure metals was introduced. Moreover,... 

Fig. 8.4. Superconductive transition of pure Be showing the dependence on the magnetic field. Data in die...

External fields must be shielded to about 10-7T, i.e. well below earth magnetic field ( 50 jlT). The maximum recommended field is 10 6T and the dTc/dH (about lOOK/Tesla) is supplied around H = 0. The maximum power which may be supplied to the coils is between 10-9 and 10-1°W. The sweep rate used to trace out the superconducting transitions should be less than O.lmK/min (for W and Be) to avoid hysteresis effects. Unfortunately, nowadays SRM-767a and SRM-768 are no longer produced. 

A very attractive feature of the SRD1000 device is the presence of the electronics to trace out the superconducting transitions of the samples, of the magnetic shields and of... 

APPENDIX Superconductive transitions and influence of purity and magnetic fields... 

Fig. 8.7. Superconductive transitions of four Ti samples of different purity sample Ap Tc = 246.4 mK,...

In superconducting transitions, the purity of materials and the shielding from magnetic fields are fundamental to obtain steep transitions (see Figs 8.6-8.8). 

Figure 8.6 shows the definition of transition temperature Tc and transition width Wc. To remark how the purity of the material and the magnetic field influence the two parameters, we will report hereafter the measurements of the superconducting transition of titanium samples of different purity and in the presence of different magnetic fields. The transitions of four Ti samples, whose characteristics are reported in Table 8.12, are shown in Fig. 8.7 where a change of only 0.2% in purity dramatically moves both the transition... 

Fig. 8.8. Superconductive transitions of die Ti sample D of Table 8.12 in a magnetic Field (0-148G).

Nevertheless deviations from eq. (9.19) have been observed for the intermetallic compound Auln2 [108,109] and for T1 [110,111], Requirements for the validity of eq. (9.19) are the absence of changing internal fields due to nuclear magnetic or electronic magnetic ordering in the relevant temperature range, the absence of nuclear electronic quadrupole interactions and no superconductive transition. 

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