Residual resistance ratio p

For experimentalists, measurements of the transport properties of metals are also of great practical interest, since they are very sensitive to the purity of the studied materials. It is known that the residual resistivity ratio p(300 K)/p(4.2 K) is commonly used as a global purity test. Values as high as 1000 have been obtained for ultra-pure thorium refined by electro-transport (Peterson et al. 1967). Even in the purest lanthanides this ratio is below 300. A value of 50 has been reached for electro-refined plutonium (Arko et al. 1972) and one of 65 for electro-refined neptunium (Fournier and Amanowicz 1992). 

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... 

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. 

Table 7.3 Summaty of electrical transport parameters calculated from the resistivity ( ), Hall coefficient (Rh) and magnetoresistance coefficient (a), for select MAX phases. Unless otherwise noted, = [ip = is assumed. Note that this approach can, and does, result in slightly different values than assuming n—p. The residual resistivity ratio is listed in column 4. 

In the clean limit, on the other hand, the transport is dominated by the carriers with the longest life times, i.e., by the quasiparticles far away from the hot regions on the Fermi surface yielding p T) T. Equation (60) is valid only at very low temperatures T/F < I/po where po denotes the residual resistivity ratio po = p(0)/p(273 K). At intermediate temperatures 1/po < < 1/v the resistivity rises linearly with temperature... 

The 7). values of the Ar-irradiated ZrN film and the He-irradiated HfN film are shown as a function of the irradiation fluence and the deposited energy in Fig. 7. They decrease continuously with increasing irradiation fluence from 9.2 K down to 3.8 K for ZrN and from 8.3 K down to 3.0 K for HfN. The widths of the transition temperature (temperature difference between 10% and 90% drops in the resistivity) were maintained within 0.4 K during the irradiations. The residual resistivities at 11 K (po) and the residual resistivity ratios (RRR = Prt/Po) were measured before and after the irradiation procedures. The residual resistivities increase continuously from the initial value of po = 30 aQ cm to 200 p.Q cm in ZrN and from the initial value of Po = 230 p.Q cm to 490 iQ cm in HfN. The residual resistivity ratios decrease continuously from the initial value of RRR = 3.0 to 1.15 in ZrN and from the initial value of RRR =1.15 to 1.05 in HfN. 

Figure 5.13 Isotropic residual resistivity p (left), and spontaneous magnetoresistance anisotropy ratio A p/p (right) of disordered BCC-Fe Coj alloys calculated in four different...

Table 3.1-203 Residual electrical resistivity ratio (RRR) of pure noble metals [1.217, p. 156]...

Figure 5.12 Left residual isotropic resistivity p of disordered CojcPdi- ( ) and Co Pti- (o) alloys. Full lines, calculated including vertex corrections broken lines, calculated omitting vertex corrections. Right calculated anomalous magnetoresistance (AMR) ratio Ap/p of CojPdi- ( ) and Co Pti- (o) alloys. Experimental data denoted by open squares, white diamonds, triangles and crosses arise from various sources (Ebert et al. 1996b).

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