The relation between normal state properties and Tc for some Zr2X compounds

Abstract We find that a certain feature of the normal state resistivity correlates with T c in a closely related group of superconductors.


(Received l8JuIy 1974 by H. SuM)
We fmd that a certain feature of the normal state resistivity correlates with in a closely related group of superconductors.
Zr2Ni (7, = 1.5°K),all crystallize in the tetragonal C16 structure.The first three compounds form an The resistance data are shown in Fig. 1.All the isoelectronic series, which is. especially interesting curves have a similar shape and we are interested because Zr2Rh has one of the highest 7,'s of all the particularly in the region of pronounced negative non-cubic inter-transition metal compounds.'The curvature.The negative curvature can be characterized investigation reported here was motivated by a desire by the inflection point which we shown in Table 1.

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For the isoelectronic compounds we note that as this  present temperature range of measurement and Zr2Rh exhibited two distinct transitions (Fig. 2), the d-band (electrons or holes for the almost empty or most of the bulk Tbeing at the higher temperature full cases, respectively); and 0R denotes the Debye 11.3 K.In these two cases ~yand 0D values were temperature.One simply assumes that the total deduced by simple extrapolation procedure of the density of states is dominated by the d-band and thus CIT vs T2 plots from above 7~.The data are given in s to d-state scattering dominates the electrical resistivity.
Table 2.It is interesting to note that °D varied only These parameters, as determined by the least-squares slightly from compound to compound whereas y fit, are given in Table 1.We notice that the fits, which changes considerably; but neither parameter seems are very good, show little variation in T 0 and a for to correlate with T,,.Similar anticorrelation has been the sequence Zr2Co-Zr2Rh-Zr2Ir, but that 0R varies pointed out in susceptibility measurements on these significantly.The fit for Zr 2Ni, with a = 0.3, indicates compounds earlier.
1 The origin of the second heat that the model is not as appropriate for this compound, capacity anomaly in Zr 2Rh iñot clear at present.since the d-density of states is not dominant.
What interests us here is that °R does not seem Low temperature heat capacity measurements to depend sensitively on °DThis suggests, therefore, have been made on the same specimens by an a.c. that there are groups of special phonons especially calorimetry technique.
34 The electronic heat capacity connected with both the resistance and the supercoefficient ~and Debye temperature °D of Zr 2Ir and conductivity.It is, of course, possible that the Cohen Zr2Co have been determined by equating the entropy model, which provides an accurate and convenient of normal and superconducting states below their parametrization, may not be particularly appropriate.
Printed in Great Britain THE RELATION BETWEEN NORMAL STATE PROPERTIES AND TF OR SOME Zr 2X COMPOUNDS Z. Fisk Institute for Pure and Applied Physical Sciences,* University of California, San Diego, La Jolla, California 92037, U.S.A. and R. Viswanathanf Department of Applied Physics and Information Science, University of California, San Diego, La Jolla, California 92037, U.S.A. and G.W. WebbD avid Sarnoff Research Center, RCA Laboratories, Princeton, New Jersey 08540, U.S.A.

FIG. 2 .
FIG. 2. Low temperature heat capacity of Zr2Rh.FIG. 1. Temperature dependence of the electrical resistivity of Zr2X compounds.All curves were scaled respective Ta's.The T,, for Zr2Ni was below the to make the room temperature values equal.presenttemperature range of measurement and Zr2Rh exhibited two distinct transitions (Fig.2), the d-band (electrons or holes for the almost empty or most of the bulk Tbeing at the higher temperature full cases, respectively); and

Table 1 .
Research supported in part by the Office of Naval region of negative curvature moves to high tempera-Research, Department of the Navy, Contract IPAPS/ tures the T~,decreases.Inflection point ofresistivity curves and best fit parameters to resistivity model of reference 2 * t Supported by U.S. Atomic Energy Commission under state properties of A-IS compounds, one assumes Contract USAEC-AT(04-3)-34.an almost empty or full d-band overlying a low density of states s-band.The ratio of s-density of :1: Research supported in part by the Air Force Office states to the total density of states at the Fermi level of Scientific Research under contract F446290-72-is called a; T0 is the effective Fermi temperature of RELATION BETWEEN NORMAL STATE PROPERTIES AND 7~Vol.15, No. 11/12