Superconductivity of osmium and ruthenium under pressure

Superconductivity of osmium and ruthenium under pressure

LETTER TO THE EDITORS Table 2 Superconductivity of Osmium and Ruthenium Under Pressure WE have pointed out previously 1-3 that there is a connection...

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LETTER TO THE EDITORS Table 2

Superconductivity of Osmium and Ruthenium Under Pressure

WE have pointed out previously 1-3 that there is a connection between the magnitude of the isotope effect in a superconductor and the rate of change with volume of the parameter K in the Bardeen-CooperSchrieffer expression for the transition temperature Te = 0 e x p ( - K

-1)

The experimental data are, unfortunately, sparse, and there is need for more information. We have therefore measured the pressure effect in two metals for which isotope effect data exist. 4,s For osmium no pressure

÷0OI

I

F.P

-0.0~

~

-

I

~

/

~

-0.0~ -

-0.0~

-oo

,

10

20 p .

30

.

(katm)

Figure J. The change it: transition temperature as a fimction o f pressure in osmium attd ruthenium

Table 1

Ru

1.0_+ o-1 (a)

Zr Os Mo Re Cd, Hg, P b ) Sn, Zn

t + 0-1 (b)

(a) (b) (c) (d)

0-3 + 0"3 - 2.2 __.0.8 (f) 1.1 ___0.4 0"6 + 0-4 (g) 1.1 + 0"5 (h)

0.55 + 0.05 (c) 0-33 + 0"2 (d) 0.24 + 0.05 (e) 0+0"1

Reference 5 Reference 11 Reference 4 Reference 12

1-8 to 3.7

(e) (f) (g) (h)

Reference 13 Reference 14 Reference 2 Reference 15

impurity. The pressures were generated using a modification 7 of the fixed clamp technique of Chester and Jones. s They were calibrated by observing the change in Te of a superconductor of known bTe/~p enclosed with the specimen to be investigated. Araldite was used as pressure transfer medium. The sharpness of the observed transitions indicated a homogeneous pressure distribution. Superconductivity was detected by recording the effective susceptibility as a function of temperature. The observed changes in Te as a function of pressure are shown in Figure 1. The resulting values of bTe/bp and also of the derived quantity @ = b In K/b In o (where v is the volume) are shown in Table 1, together with the values of the physical constants required for its calculation. In Table 2 we have collected the experimental data at present available for the parameter ~o and for the deviation ~ from the isotope effect. ¢ is defined by the relation

To oc M - ½ o - o Te ('°K)

Osmium Ruthenium

b Te/bp (deg/atm)

x.lO 7 (cm2/kg)

0"65 ( - 0"18 + 0"06). 10-5

3"6

I "1 + 0"4

0"48

3"4

0"3 + 0"3

(0 + 0"03). 10-s

measurements exist, while for ruthenium only provisional results on a single rather impure specimen at a pressure of 2,000 atm have been reported. 6 Our present results indicate that the correlation between isotope effect and pressure effect is less simple than we have previously suggested. Measurements up to 30,000 atm were made on electron-beam-melted samples of osmium and ruthenium, both stated to contain less than 0.001 per cent CRYOGENICS" OCTOBER 1965

It will be noticed that a certain trend from positive to negative ¢# with increasing ( exists. This may be understood in the light of the treatment by Morel and Anderson 9 and by Garland 1° of the isotope effect. The interaction K is understood as made up of a phonon and a Coulomb contribution. As the Coulomb contribution increases, the deviation ( from the pure phonon isotope effect increases from zero to unity. As this happens ~ In K/b In v will change from its value corresponding to pure phonon interaction to a value dominated by the volume dependence of the Coulomb interaction. The fact that the values in Table 2 do not fall on a single curve shows that the logarithmic volume dependence of the Coulomb interaction varies from metal to metal. 283

This research was supported by a grant from the Eidgen0ssische Kommission zur F/Srderung der wissenschaftlichen Forschung.

lnstitut de Physique Exdprimentale, University of Geneva, Switzerland.

E. BUCHER J. MOLLER

Institut far kalorische Apparate J.L. OLSEN und Kiiltetechnik. C. PALMY Swiss Federal Institute of Technology, Ziirich, Switzerland. (25 August 1965) REFERENCES 1. ANDRES,K., OLSEN, J. L., and ROHRER, H. IBMJ. Res. Dev. 6, 84 (1962) 2. OLSEN, J. L., BUCHER, E., LEVY, M., MOLLER, J., CORENzwrr, E., and GEBALLE, T. Rev. mad. Phys. 36, 168

(1964)

3. LEVY, M., and OLSEN,J. L. Physics of High Pressure and the Condensed Phase, p. 525 (Ed. A. Van Itterbeek) (NorthHolland, Amsterdam, 1965) 4. HEIN, R. A., and GIBSON, J. W. Phys. Rev. 131, 1105 (1963) 5. GEBALLE, T. H., MA'[-FHIAS, B. T., HULL, G. W., and CORENZWIT,E. Phys. Rev. Lett. 6, 275 (1961) 6. BUCHER, E., GROSS, D., and OLSEN, J. L. Helo. phys. acta 34, 775 (1961) 7. LEvy, M., and OLSEN, J. L. Rev. sci. Instrum. 36, 233 (1965) 8. CHESTER,P. F., and JONES,G. O. Phil. Mag. 44, 1281 (1953) 9. MOREL, P., and ANDERSON, P. W. Phys, Rev. 125, 1263 (1962) 10. GARLAND,J. W. Phys. Reo. Lett. I1, 114 (1963) !1. BUCHER, E., MOLLER, J., OLSEN, J. L., and PALMY, C. Physics Lett. 15, 303 (1965) 12. MATTHIAS, B. T., GEBALLE, T. H., CORENZWIT, E., and HULL, G. W. Phys. Rev. 129, 1025 (1963) 13. MAXWELL,E. Reo. mad. Phys. 36, 144 (1964) 14. BRANDT,N. B., and GINZBURG,N. I. J. exp. theor. Phys. 46, 1216 (1964) 15. OMEN, J. L. ANDRES, K., MEIER, H., and DE SALABERRY, H. Z. Naturf. 18a, 125 (1963)

BOOK REVIEWS Technology and Uses of Liquid Hydrogen---Edited by R. B. Scott (Pergamon Press, 1965) 120s. THXS book is-an excellent illustration of the way in which liquid hydrogen has progressed from a laboratory curiosity to a material with a fast growing range of technological uses. Its most striking use of course is in space research as a rocket fuel. This activity in the last ten years has, more than any other, initiated the development of the technology of liquid hydrogen and low temperature engineering. This book gathers together a well balanced group of experts and is recommended to those using liquid hydrogen or engaged in low temperature design work. Sources of hydrogen gas suitable for liquefaction are discussed, such as electolysis of water, steam-iron reaction, catalytic conversion of hydrocarbons, and the clean-up plant required prior to liquefaction. A rather limited volume of cost data is provided to enable the most economic choice to be made but conditions will vary widely depending on location, scale, and demand pattern so that each case would probably need a detailed cost study. The basic design of hydrogen liquefiers and refrigerators is discussed with emphasis on power requirements; some indication of the most suitable type for varying demand patterns and 284

ranges would have been most helpful. A good summary is given of some of the liquefiers which have been built in the range 10-500 1/hr. mainly for l'aboratory uses. This particular chapter is very helpful to those concerned with the problem of buying a commercial liquefier but some mention I feel should have been made that liquid hydrogen is now an off-the-shelf chemical and in many cases it may be difficult to justify the capital expenditure, running cost, and trouble of running a liquefier facility in a laboratory. In the U.S.A. tonnage liquid hydrogen is required in ever-increasing quantities and by 1966 consumption is expected to rise to about 4,000 tons/month. A well illustrated chapter gives an appreciation of the problems and complexity of these large American plants which look more like part of an oil refinery than a cryogenic installation. The chapter on the transport, transfer, storage, and insulation contains much valuable design information and concepts, The problem of predicting cool-down losses and times is considered and the difficult problem of two-phase pressure drop is discussed. Much of the work on liquid hydrogen as a propellant was carried out by the Pratt and Witney Aircraft Corporation in the U.S.A., and a review of their work since 1958 is given. To date more than 30,000,000 CRYOGENICS" OCTOBER 1965