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Effect of hydriding pressure on the superconducting transition temperature of palladium hydride and palladium rhodium hydride
Volume 45A, number 2
10 September 1973
PHYSICS LETTERS
EFFECT OF HYDRIDING PRESSURE ON THE SUPERCONDUCTING TRANSITION TEMPERATURE OF PALLADIUM HYDRIDE AND PALLADIUM RHODIUM HYDRIDE* J.E. SCHIRBER SandierLaboratories, Albuquerque, New Mexico 87115, USA Received 26 June 1973 A strong dependence of the superconducting transition temperature T, of Pd and RhPd hydrides on the hydriding pressure at - 24°C has been observed. H2 pressures to - 5 kbar were found to raise T, to over 7°K in PdH.
Pd hydrides [l] near room temperature to a hydrogen-to-metal ratio of -0.7 in a 1 bar atmosphere of H2. The superconducting transition temperature T, of PdH0.7 is below 1.2”K [2]. Skoskiewicz [2] was able to obtain transition temperatures up to 4°K in palladium hydrides prepared by electrolysis with H/Pd ratios up to about 0.9. Recent studies [3] using low temperature ion implantation techniques have shown PdH to have a T, near 9”K, presumably because of a substantial increase in H/Pd ratio. Harper et al. [4] also achieved a transition temperature near 9’K by low temperature (-SOY) electrolysis in acid solutions. In this letter we report preliminary results of studies of the effect of hydriding pressure on the superconducting transition temperature of palladium hydride and on dilute PdRh hydrides. Pressures to - 5 kbar were generated in H2 in a system similar to those described in detail earlier [5] except that all materials with any susceptibility to hydrogen embrittlement have been replaced with either BeCu or 3 16 stainless steel. Samples were initially 99.99+% powders. The alloys were prepared by pressing appropriate mixtures of the powders into pellets and arc melting several times in an argon atmosphere. The arc melted buttons were then cornminuted to -200 mesh by milling under toluene. The hydriding procedure was to place the powder in the pressure vessel and pump off the air in the system with a roughing pump. Next hydrogen was admitted at about 2000 psi. The pressure was increased to the maximum of -5.1 kbar at -24’C * Work supported by the U.S. Atomic Energy Commission.
0
I
I
I
I
I
I
2
3
4
5
P
tkkmr HJ
Fig. 1. Effect of hydriding pressure (at - 24°C) on the superconducting transition temperatures of PdH and RhPdH.
and held for about one hour. The sample was cooled slowly at pressure to near 77’K. At this temperature the pressure was reduced to the 2000 psi charge pressure and the system was cooled further to measure the superconducting transition. This same procedure was followed at the lower hydrogen pressures. The superconducting transition temperatures were determined using a conventional inductance bridge. The sensing coils were external to the pressure vessel. Temperatures above 4°K were measured with a Ge resistance thermometer. Below 4°K the temperature was obtained from the vapor pressure of the 4He bath. Results are shown in fig. 1. The transition temperature T, is plotted versus the pressure at which the hydriding took place near room temperature. The transition temperature was defined as midway between fully superconducting and completely normal. We 141
Volume 45A, number 2
PHYSICS LETTERS
observe a strong dependence of Tc for PdH with hydriding pressure from 2.2K at 0.15 kbar to 7.3K at our highest pressures of 5.1 kbar. Addition of Rh decreases the value of T, at all pressures, in spite of the fact that more H2 is taken up by the RhPd at a given pressure accoridng to the pressure-concentrationtemperature phase diagram of Green and Lewis [6]. This result suggests that the increased electron correlation in PdRh, over that observed in pure Pd [7], is not completely removed by the hydrogen. Furhtermore, this work (as do the studies of Harper ,et al. [4] ) indicates that damage induced in the ion implantation process is not an important influence on the superconducting transition temperature of PdH. Rather, the dominating effect is apparently the amount of hydrogen introduced.
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10 September 1973
We acknowledge the technical assistance of R.L. White and helpful conversations with A.C. Switendick and H.T. Weaver.
References [l] F.A. Lewis. The palladium hydrogen system (Academic Press, 1967), and references therein. [2] T. Skoskiewicz, Phys. Stat. Sol. (a) 11 (1972) K123. [3] B. Stritzker and W. Bickel, Z. Phys. 257 (1972) 1. [4] J.M.E. Harper, R. Hammond and T.H. GeBalJe, Bull. Am. Phys. Sot. 18 (1973) 326. [5] J.E. Schirber, Cryogenics 10 (1970) 418. [6] J.A.S. Green and F.A. Lewis, Trans. Faraday Sot. 62 (1966) 971. [7] K. Andres and M.A. Jensen, Phys. Rev. 165 (1968) 533.
10 September 1973
PHYSICS LETTERS
EFFECT OF HYDRIDING PRESSURE ON THE SUPERCONDUCTING TRANSITION TEMPERATURE OF PALLADIUM HYDRIDE AND PALLADIUM RHODIUM HYDRIDE* J.E. SCHIRBER SandierLaboratories, Albuquerque, New Mexico 87115, USA Received 26 June 1973 A strong dependence of the superconducting transition temperature T, of Pd and RhPd hydrides on the hydriding pressure at - 24°C has been observed. H2 pressures to - 5 kbar were found to raise T, to over 7°K in PdH.
Pd hydrides [l] near room temperature to a hydrogen-to-metal ratio of -0.7 in a 1 bar atmosphere of H2. The superconducting transition temperature T, of PdH0.7 is below 1.2”K [2]. Skoskiewicz [2] was able to obtain transition temperatures up to 4°K in palladium hydrides prepared by electrolysis with H/Pd ratios up to about 0.9. Recent studies [3] using low temperature ion implantation techniques have shown PdH to have a T, near 9”K, presumably because of a substantial increase in H/Pd ratio. Harper et al. [4] also achieved a transition temperature near 9’K by low temperature (-SOY) electrolysis in acid solutions. In this letter we report preliminary results of studies of the effect of hydriding pressure on the superconducting transition temperature of palladium hydride and on dilute PdRh hydrides. Pressures to - 5 kbar were generated in H2 in a system similar to those described in detail earlier [5] except that all materials with any susceptibility to hydrogen embrittlement have been replaced with either BeCu or 3 16 stainless steel. Samples were initially 99.99+% powders. The alloys were prepared by pressing appropriate mixtures of the powders into pellets and arc melting several times in an argon atmosphere. The arc melted buttons were then cornminuted to -200 mesh by milling under toluene. The hydriding procedure was to place the powder in the pressure vessel and pump off the air in the system with a roughing pump. Next hydrogen was admitted at about 2000 psi. The pressure was increased to the maximum of -5.1 kbar at -24’C * Work supported by the U.S. Atomic Energy Commission.
0
I
I
I
I
I
I
2
3
4
5
P
tkkmr HJ
Fig. 1. Effect of hydriding pressure (at - 24°C) on the superconducting transition temperatures of PdH and RhPdH.
and held for about one hour. The sample was cooled slowly at pressure to near 77’K. At this temperature the pressure was reduced to the 2000 psi charge pressure and the system was cooled further to measure the superconducting transition. This same procedure was followed at the lower hydrogen pressures. The superconducting transition temperatures were determined using a conventional inductance bridge. The sensing coils were external to the pressure vessel. Temperatures above 4°K were measured with a Ge resistance thermometer. Below 4°K the temperature was obtained from the vapor pressure of the 4He bath. Results are shown in fig. 1. The transition temperature T, is plotted versus the pressure at which the hydriding took place near room temperature. The transition temperature was defined as midway between fully superconducting and completely normal. We 141
Volume 45A, number 2
PHYSICS LETTERS
observe a strong dependence of Tc for PdH with hydriding pressure from 2.2K at 0.15 kbar to 7.3K at our highest pressures of 5.1 kbar. Addition of Rh decreases the value of T, at all pressures, in spite of the fact that more H2 is taken up by the RhPd at a given pressure accoridng to the pressure-concentrationtemperature phase diagram of Green and Lewis [6]. This result suggests that the increased electron correlation in PdRh, over that observed in pure Pd [7], is not completely removed by the hydrogen. Furhtermore, this work (as do the studies of Harper ,et al. [4] ) indicates that damage induced in the ion implantation process is not an important influence on the superconducting transition temperature of PdH. Rather, the dominating effect is apparently the amount of hydrogen introduced.
142
10 September 1973
We acknowledge the technical assistance of R.L. White and helpful conversations with A.C. Switendick and H.T. Weaver.
References [l] F.A. Lewis. The palladium hydrogen system (Academic Press, 1967), and references therein. [2] T. Skoskiewicz, Phys. Stat. Sol. (a) 11 (1972) K123. [3] B. Stritzker and W. Bickel, Z. Phys. 257 (1972) 1. [4] J.M.E. Harper, R. Hammond and T.H. GeBalJe, Bull. Am. Phys. Sot. 18 (1973) 326. [5] J.E. Schirber, Cryogenics 10 (1970) 418. [6] J.A.S. Green and F.A. Lewis, Trans. Faraday Sot. 62 (1966) 971. [7] K. Andres and M.A. Jensen, Phys. Rev. 165 (1968) 533.