Physics. - New superconducvors. The resistJance of alloys at the temperatures of liquid hydrogen and liquid helium. By W. J. DE HAAS, EDM. VAN AUBEL and J. VOOGD. (Communication N0. 197b from the Physical Laboratory at Leiden.)

(Communicatéd at the meeting of June 29, 1929.)

§ 1. In this communication we give the results of our investigations on the e1ectric resistance of some alloys at temperatures of liquid hydrogen and Iiquid helium. This research gave us the opportunity to investigate the influence of small admixtures of non-superconductive metals in super­conductors.

We examined the eutectic mixtures of the system :

Sn-Bi, Sn -Zn, Sn-Cd, Tl-Au, Tl-Cd, Pb-Ag, Pb-Cd, Pb-Sb and Pb-Bi.

The rods were prepared by one of us (VAN AUBEL) in the physical laboratory, Gent.

For 'the reslstance measurements, which were made in the usual way with a DIESSELHORST compensation-box, the required copper wires were fused to the rods, so that the use of solder was quite avoided.

§ 2. Sn-Bi. The rad, with which the measurements were made contained 42.0 %

Kahlbaum tin . The bismuth used was obtained from the firm J OHNSON MATTHEY & Co. Ltd., London. According to the melting point diagram the eutectic contains crystallized solid solutions of 1 Y2 % tin in bismuth and of a percentage bismuth in tin , for which we find different values 1) .

According to the last determination it is 15 % 2). In table I we give the results of the measurements. For a better mutual

comparison we give both the resiS'tance divided by the resistance at 0° (R/Ro) and the resistance divided by the resistance at the boiling point of helium (R/R4.2 ).

Fig. 1 represents the curve of R/R12 for the different tin alloys that were examined.

I) W . V. LEPKOWSKI, Zs. anorg. Chem. 59, 287, 1908. A. BUCHBR, Zs. anorg. Chem. 98, 117, 1916. A. STOPPEL, .. 53, 148, 1907. A. W . KAPP, Diss. Köningsbergen 1901.

2) HIKOZO ENDO, Science Reports of the Tohoku Imperia1 Universlty flrst series Vol. H, 1925, 479.

-46*

716

TABLE I.

Sn-Bi.

T I Ph.Uum in mm I R/Ro I R/Ro I I I

20.42 0.1677

16.79 0.1615

H.18 0 . 1582

4.231 785 0.H7 1.00 measurlng current 200 mA.

4.H9 723 0.H75 1.00 .. .. .. .. 3 .962 598 0.H75 1.00 .. .. .. .. 3.883 5 .. 8 0 . H7 1.00 . .. .. .. 3.865 538 0.H7 1.00 .. .. .. .. 3.850 529 0.146 0 .99 .. .. Ol .. 3.831 518 0.132 0.89 .. .. .. .. 3.813 508 0.071 0 . 48 " .. .. .

~791 .. 97 0 0 .. .. " .. I

For comparison the thermal transition curve of pure ' tin has also been plotted in the figure 1) .

The Sn-Bi eutectic eVidently becomes more easily superconductive thall pure tin. Though of course it is not a fact established by these measurements it seems to us very probable, that the solid solution of bismuth in tin first becomes superconductive. If th is is true, it is of this solution that we determined the therm al transition curve.

The vanishing of the resistance takes place in a temperature interval of 0 .07°. For pure tin this interval is 0.04° .

In earlier researches on the influence of superconductive admixtures we found , that the vanishing of the resistance took place in a considerably greater tempera tu re interval.

Because of the small temperature interval of 0 .07° it does not seem probable to us , that the superconductivity is due to the solid solution of 1 Y2 % tin in bismuth.

§ 3. Sn-Zn. The rod was prepared from Kahlbaum tin and Kahlbaum zinc and

contained 90.0 % tin. According to determinations of the melting point diagram the eutectic contains crystallized pure tin and zinco According to T AMMANN however I % zinc is dissolved in the tin.

I) Leiden, Comm. NO. 181. W. TUYN and H. KAMERLINCH ONNES.

717

Our measurements render it probable. th at a small quantity of zinc IS

dissolved in the tin and that the solid solution becomes superconductive.

ê 1.0 -. .,.

..

f ~ -~

r r 0.8

0.6

0.4

VJ Sn 0.2

0 Sn-Bi A Sn-Zn

Al j D Sn-C .. 3 .7 3 .8 3.9 4.0

Fig. I.

The thermal transition curve faHs over a temperature interval of 0.06° and is displaced with respect to the pure tin over 0.06° towards the low temperatures (TabIe Il . fig . 1).

In the aHoy the intensity of the measuring current was of the same order of magnitude as that in the case of pure tin. In the latter case however the intensity of the total current was rather high. As the intensity of the magnetic field caused by the current is highest near the surface of the wir!!

718

and depends on the total current, we calculated wh ether the magnetic field was due to a too strong current.

The displacement however cannot be ascribed to too strong a current. This is moreover evident from the measurement with a weaker measuring

current (tabIe 11) .

TABLE Il.

Sn-Zn.

T I Phelium in mm I R/Ro I R/R~. 2 I 20 .40 I 0.0238

19.13 0.0215

16.54 0.0178

14.08 0.0150

4.23· 785 0.0093 0.99 measurlng current 200 mA.

3.96° 596 0.0097 1.03 .. · · .. 3.786 492 O.OO9i 1.00 H H .. .. 3.742 468 0.0093 0.99 .. · .. .. 3.733 463 0.0096 1.02 .. .. · " 3.71' 454 0.009i 1.00 .. .. · .. 3.696 i43 0.0088 0.94 .. .. .. .. 3.686 438 0.0072 0.77 .. .. .. .. 3.673 H4 0.0042 0 .i5 .. .. .. .. . .. 0.0025 0.27 .. .. 100 ..

3.667 428 0.0010 0.11 H · 200 "

3.659 424 0 0 . .. · ..

§ 4. Sn~Cd.

The rod was prepared from KahIbaum tin and KahIbaum cadmium and contained 71 .9 % tin.

Opinions differ as to the melting point diagram. For our purpose it

suffices however to know that tin is not or very Iittle soIubIe in cadmium and that cadmium is soIubIe in tin to a few percent. The eutectic is 3

mixture of these two soIutions 1) . Like the other tin alloys this eutectic becomes superconductive. The fall

of the resistance takes place in a temperature interval of 0.05°, which has

1) A. BUCHER, Zs. anorg. Chem. 98, 106, 1916. G. TAMMANN, Lehrbuch der Metallographie, 1923.

719

been displaced over 0.100 (tabie III fig. 1) towards the low temperatures with respect to the thermal transition curve of pure tin.

TABLE 111 .

Sn-Cd. --

T I Phelium In mm I R/Ro I R/R1.2 I 20.'10 0.0727

19.13 0 .0697

16.54 0.0637

14.08 0.0590

4.231 785 0.0441 1.000 measuring current 200 mA.

3.960 596 0.OH4 1.000 .. .. .. .. 3.786 492 0.OH8 1.008 .. .. .. .. 3. ]42 468 0.0449 1.012 .. .. .. .. 3.733 463 0.0447 1.006 .. .. .. .. 3 .7J1 451 0.OH8 1.008 .. . , .. .. 3.696 H3 0.OH7 1.006 .. .. " .. 3.686 438 0.0415 1.002 .. .. .. .. 3.678 434 0.0444 1.000 .. .. .. ..

.. .. 0.0440 0.990 .. .. 100 .. 3.667 428 0 .0432 0.972 .. .. 200 .. 3.659 424 0.0403 0.907 .. .. .. "

3.646 417 0.0315 0.708 w .. .. .. 3.639 414 0 .0203 0.458 .. .. .. ..

0.0160 0.361 .. .. 100 .. 3.628 408 0.0047 0.107 .. .. 200 .. 3.618 403 0 0 .. .. .. ..

Here also this displacement cannot be ascribed to too strong measuring currents.

Our experience has taught us, that non-superconductors that are rendered superconductive by a small admixture of a superconductor, show a much slower fall of the resistance with the temperature than the "true" super­conductors. While for the first group this fall is completed within O.2 c ,

this happens within about 1/30 0 for the second (true superconductor ) group. In relation with the steep fall, we assume therefore, that the thermal

720

transition curve is not due to the cadmium containing a Iittle tin , but to thc tin in which a low percentage of cadmium is dissolved. 50 we come to the condusion, that the presence of the cadmium in the tin hinders the occurrence of the superconductivity.

§ 5. Tl~Cd.

For the preparation of the eutectic Kahlbaum thallium and Kahlbaum cadmium we re used. The rod contained 81.7 % thallium. The melting point diagram is not completely known with certainty.

According to the existing data the eutectic consists of pure cadmium and of asolid solution of cadmium in thallium.

The percentage of th is solution is uncertain 1) . The results of our measurements are to be found in table IV :

TABLE IV. Tl-Cd.

T I Phel/.rn in mm I R/Ro I RIRu I 20.oH 0.0984

19 .08 0.0942

16.51 0.0871

14.18 0.0817

4.234 785 0.0656 1.000 measuring current 200 mA.

3.11 4 198 0.0660 1.007 .. .. .. . 2.576 73 .7 0.0659 1.005 .. .. .. . 2.549 69.5 0.0588 0.897 .. .. .. .. 2.529 66.4 0.0122 0.187 .. .. .. .. 2.51s 64.6 0.0013 0.020 .. . .. .. 2.502 62.6 0 0 .. .. .. ..

Fig. 11 represents the thermal transition curve of our thallium alloys and of pure thallium. Those of pure thallium are taken from the measurements of H. KAMERLINGH ONNES and W. TUYN 2).

It is evident, that the Cd~Tl~eutectic becomes more easily superconductive than pure thallium.

The thermal transition curve falls within a temperature interval of 0.06° and the displacement with respect to pure thallium is 0.06°.

I) KURNAKOW and PUSCHIN. Zs. anorg. Chemie 30, 106, 1902. G. TAMMANN, loc. cito

3) Comm. 160a. Leiden H. KAMERLINGH ONNES and W. TUYN.

721

As in preceding cases we must ascribe the thermal transition curve wc obtained to the solid solution of cadmium in thallium.

1D

\-j Tl [:] TI-C4

0.8 o Tl-Au

I

/ 0.6

0.4

0.2

I ~~4.2

Ucr 2.1

r. ,...

14"'" ,

~ 2.3 2.5 2.7

Fig. 2.

The presence of the cadmium in thallium is therefore advantageous for the occurrence of superconductivity.

§ 6. Tl-Au. For the preparation Heraeus gold and Kahlbaum thallium were used.

The rod contained 73 .0 % thallium.

722

According to LEVIN the pure componen'ts are crystalLized separately 1) . According to T AMMANN we are here concerned with a mixture of pure gold and asolid solution of a low percentage of gold in thallium. The limit of solubility is given as not known with certainty 2).

Table V and fig . 11 contain our results. In contradiction to the ot her

TABLE V. Tt-Au.

T I Phelium in mm I R/Ro I RI R1.2 I 20 .H 0.0720

19.08 0.0663

16.51 0.0573

H.18 0.0498

4 .23i 785 0.0305 1.000 measurlng current 200 mA.

3.618 198 0.0308 1.011 .. . .. .. 2.549 69 . 5 0.0306 1.004 .. .. .. .. 2.51 5 64.6 0.0307 1.008 .. .. .. .. 2 . 502 62.6 0.0305 1.000 .. .. .. .. 2. 475 59.1 0.0308 1.011 .. .. .. .. 2.Hi 55.0 0.0305 1.000 .. .. .. .. 2.352 44.4 0.0305 1.000 .. .. .. .,

2.238 33.7 0.0301 0.988 .. .. .. " 2.178 28.8 0 .0280 0.920 .. .. .. .. 2 . 116 24.4 0 .0248 0 . 812 .. .. .. .. I 2.028 19.2 0.0079 0.261 .. .. .. ..

I 1.927 14.6 0 0 .. .. .. ..

transition curves obtained by us, the temperature interval in which the resistance vanished is considerably larger viz. 0.3°. Also the displacement towards the low temperatures (-+- 0.5° ) is larger than those found for othereutectics.

Perhaps both phenomena are intimately connected and form together a transition to the complete destruction of the superconductivity by a non­superconductive admixture, in the same way as that found earlier for CU3Sn 3).

I) M. LEV IN, Zs. anorg. Chemie iS, 34, 1905. 2) G. TAMMANN, loc. clt. 3) EDM. VAN Au BEL, W. J. DE HAAS and J. VOOGD, Proc. Amsterdam, Vol. 32,

NO. 2, 1929. Comm. Leiden. NO. 193c.

723

§ 7. Eutectics with lead. We investigated the eutectics of the systems : Pb-Ag. Pb-Cd. Pb-Sb

and Pb-Bi. As the experiments at temperatures in the neigbourhood of the transition

point of lead are still very difficult. we measured the resistances at 4.20 K. only. At this temperature all rods we re already superconductive.

The results of the further measurements are to be found in table VI.

TABLE VI.

RIRo·

T I Pb-Ag I Pb-Cd I Pb-Sb j Pb-Bi

20 .42 0.0374 0.0596

20.40 0.0081 0.455

19 . 13 0.0076 0.451

16.79 0 .0242 0.0469

16.54 0.0067 0.444

14.18 0.0180 0.0397

14 .08 0.0059 0. 437

§ 8. From these measurements it is evident. that the temperature at which the superconductivity sets in. is influenced by non-superconducting admixtures. The thermal transition curve (R/Ri.d generally becomes a little less steep than in the case of pure superc~nductors . The thermal transition curve is most displaced towards the low temperatures for Tl-Au and at the same time the temperature interval. over which the fall of the resistance extends. is largest.

It would be intéresting. to investigate with systems chosen for this purpose. whether these phenomena always occur together and form a transition to the complete destruction of the superconductivity. Then those systems might be of importance for the temperature measurements in the helium reg ion.

The question. why the transition point is displaced and what will be the direction of th is displacement in every particular case. cannot yet be answered.

Therefore we want more material in combination with röntgenographic data . We are inclined to seek a solution . which treats th is ph en omen on as an analogue to that of the influence of pressure and stress on super­conductivity 1) . It is however dubious. whether this view point alone suffices to interpret the phenomena .

I) Comm. Leiden. NO. 180.