Residual Resistance Ratio

Fig. 3.20. Thermal conductivity of copper samples with residual resistivity ratio (RRR) ranging from 3000...

The experiments were carried out on high purity aluminium from different producers (Table I) and Al-Ga alloys. The impurity concentration in the used materials was determined by glow discharge mass-spectrometry. The total impurity content in pure aluminium (0.4 - 7.7 ppm) was defined as the sum of the concentration of all found elements.The residual resistivity ratio RRR=p(273K)/p(4.2K) of the materials was measuredby the method prescribed by the U.S. National Bureau of Standards. 

Here we will summarize, from the previous subsections as well as from literature, some typical properties and representative parameters (see table 6) of the superconducting state of YNi2B2C and LuNi2B2C where completeness is not attempted. These materials are usually clean-limit type II superconductors. However by substitutional disorder on the rare earth site in (Y,Lu)Ni2B2C or on the transition-metal site in Lu(Ni,Co)2B2C the residual resistance ratio RRR = p(300 K)/p(Tc), where p(T) is the normal state resistivity, and the mean free path / of the electrons in the normal state can be considerably reduced... 

In this work the results for two kinds of samples are surveyed. The first type of sample is thin c-axis oriented films with a thickness of about several hundred nanometers [18]. The residual resistance is about several tens of /xQ cm with the residual resistance ratio (RRR) of 2.2 pointing out that films have a disorder between crystallites. This does not preclude the fact that, on some spots, the films contain clean, small, single crystals on which we occasionally may fabricate a point contact (PC). Normally, the contacts were prepared by touching the film surface with a noble metal counter electrode (Cu, Au, Ag) in the direction perpendicular to the substrate. Thus, nominally, the preferential current direction in the PC is along the c axis. Nevertheless, since the surface of the films contains terraces with small crystallites, a PC to the ab plane of these crystallites is also possible. 

HFS heavy-fermion state RRR residual resistance ratio... 

In the fictive gray system the value of Tc would be on the upper curve in Figure 6 with a value between the values of both parent compounds. However, in the real pseudoquaternary system YxLui xNi2B2C, Tc has a considerably lower value than expected from a linear interpolation, i.e. the gray system. As shown in Figure 60 the concentration dependence of Tc is non-monotonic with a minimum near x = 0.5. A similar behavior was found also for other quantities characterizing the electronic state of the system as the upper critical field H 2 and the parameter a [from Hc2(T) = H 2( 1 - T/Tc)1+ ] which is a measure for the positive curvature of Hc2(T), the residual resistance ratio RRR = pn(300 K)/pn(Tc), where pn(T) is the normal-state resistivity, and the two parameters kn and describing the field... 

By using an anodic plate of technically pure aluminum (A1 = 99.99%), metal with a residual content of impurities < 5 ppm and a residual resistance ratio RR of 8.000-20.000 can be obtained after electrolytical refining in Na[Et3Al-F-AlEt3] 1... 

Thermal conductivity and diffusivity [1.35,1.80,1.81]. At room temperature, the thermal conductivity coefficient X is about 1.75 W cm K . Its temperature dependence is shown in Fig. 1.19. Some typical data are given in Table 1.14. In the low-temperature range, it is strongly dependent on the RRR (residual resistivity ratio Po/PrX which is also an indication of the purity. Table 1.15 shows the differences between samples of varying purity. 

TABLE 1.15. Thermal Conductivity Coefficient in the Low-Tenqrerature Range and Dependence on the Residual Resistivity Ratio [1.35,1.80]... 

A number of phases have been measured 18) using a probeless technique 48). The results are plotted and compared with the pure elements Rb and Cs in Fig. 20. The earlier data of Brauer 49) differ by less than 10% of the absolute values. The metallic nature of all samples (at least qualitatively) verifies the bond model. The specific resistivity p of an alkali metal suboxide is in the same order of magnitude as with the pure elements Rb and Cs (JO). The compound CS7O exhibits a residual resistivity ratio (rrr) defined as p (260 K)/p (T -> 0 K) in the order of 200, near to the value found for Cs (JO). The value for the compound CsnOa is approximately 50. The temperature dependence of the ideal resistivity (corrected for the residual resistivity) of e.g. CS7O is very similar to that of Rb and Cs. 

K with a slope of 352 x 10 ohm/ohm-°K. The linear extrapolation of the corrected unstrained curve to 4.2°K yields a resistance ratio of 0.9061 further extrapolation to 0°K yields a residual resistance ratio of 0.8945. 

RRR = residual resistivity ratio (ratio of electrical resistivity at 273 K to that at 4 K)... 

Fig. 7. Degradation of the residual resistance ratio (/ 295k/ 9k) of the copper matrix as a function of the number of fatigue cycles. Ae refers to the peak-to-peak cyclic strain amplitude, as defined in Fig. 4.

Four aluminum specimens were tested under cyclic strains of 0.1 and 0.2% and up to 0.6% tensile strain. Under these deformations, the increase of the magnetoresistivity for the four specimens behaved differently. The residual resistivities ranged from 0.39 to 0.54nfl-cm, with residual resistivity ratios (RRR = P3oo/P4.2 at zero field) of about 5000 to 6000. The error in the resistivity data was about 10% at zero field and about 1% for R > 2 T. 

B = magnetic flux density H = magnetic field strength N = number of cycles RRR = residual resistivity ratio... 

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