Superconductivity: Part 2


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  • Superconductivity of the Platinum Metals and Their Alloys?
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Supplier Name:. Note: Notes are optional and private. Electrical and magnetic measurements : Document History. IEC This document references:. Published by IEC on August 1, The electrical and magnetic behaviour of the platinum metals and their compounds has fascinated solid state chemists and physicists for many years.

Together with iron, cobalt and nickel the platinum metals belong to Group VIII of the Periodic Table, and one of the earliest problems was to consider why they did not show any magnetic ordering, in contrast to iron, cobalt and nickel. On the other hand, when in the form of solid solutions or compounds they exhibited very interesting magnetic behaviour, for example localised moments and spin glass behaviour.

The magnetic strengths of cobalt-platinum alloys even found industrial application. Matthias and others that superconductivity—that is the loss of any electrical resistance below a critical temperature, T c —and ferromagnetism exclude each other even though they are based on similar phenomena, the investigation of the low temperature electrical and magnetic behaviour of the platinum metals and their compounds became of special interest.


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Indirectly this work has led to new approaches in other areas, for example the growth and study of single crystals. Up to now superconductivity has found only limited application in high technology areas for example in magnets for fusion and atomic research at cern and Culham, and for electrical motors and generators. However, one can expect that the platinum metal compounds discussed here, with their unique properties, will in time find applications which cannot be envisaged at present, perhaps especially for solid state devices. It has been known for some time that three of the six platinum group metals in high purity form become superconducting, these being ruthenium, osmium and iridium.

In addition, many years ago, it was predicted from investigations made of rhodium alloy systems that the element rhodium might also become a superconductor at a temperature around 0. The superconductivity of the individual metals will now be considered. The superconducting transition temperature of ruthenium has been placed between 0. The dependence of critical temperature on its atomic mass M isotope effect is relatively small. For powdered and arc furnace melted samples of Ru 99 and Ru it was reported that the critical temperature coincides within the accuracy of measurements 8 and similar results were obtained later 9 , Measurements made on samples with an average atomic mass of The critical temperature of osmium as given in the literature ranges from 0.

An arc furnace melted sample of Isotope effect measurements do not agree, even when apparently identical samples are checked 10 , The critical field is At a pressure of 30, atm the critical temperature of osmium is reduced by 0. Iridium purified by electron beam melting until the total impurity content is below 10 ppm has a critical temperature curve with a mid point at 0.

Critical current density of superconductors with different fractal dimensions

Furthermore its transition curve is characterised by an uncommon hysteresis; the transition from the normal to the superconducting state occurs discontinuously but from the superconducting to the normal state it is continuous. Additionally, it is influenced by the applied magnetic field. The coherence length is 4. Small impurity concentrations reduce the critical temperature of iridium and make it a superconductor of the second kind. In the purities generally available commercially, rhodium is not superconducting at 0.

On solid solution samples of the alloy systems rhodium-osmium and rhodium-iridium the superconductivity was measured at compositions of up to 80 atomic per cent rhodium and an estimate then made of the behaviour of rhodium as an element 1. X-ray analysis suggested the samples were homogeneous, but microprobe investigations of the rhodium-iridium alloys showed some slight coring, but for the rhodium-osmium alloys the concentration varied by up to 20 atomic per cent. In order to avoid the introduction of impurities and segregation, the alloys had not been heat treated and therefore showed relatively broad transitions.

The superconducting transitions for the rhodium-iridium alloys were spread over a width of 1 mK while for the rhodium-osmium alloys, at the higher temperatures, the spread was very wide and sometimes incomplete. However, as mentioned earlier, it was deduced from these results that rhodium would become a superconductor at a temperature of 0.

Even extra purified palladium and platinum are not superconducting. The lowest test temperature published is 0. Apparently the disappearance of the strong paramagnetism of palladium is a prerequisite for the occurrence of superconductivity, as has been shown earlier for palladium-molybdenum and palladium-tungsten solid solutions Palladium with ion-implanted lithium, boron, carbon or nitrogen showed superconductivity only for the palladium-boron-hydrogen and palladium-carbon-hydrogen alloys at 3.

The lithium and nitrogen containing samples were not superconducting above 0. The effect of replacing part of the palladium by nickel, platinum or rhodium and silver in ion-implanted and pressure loaded palladium-hydrogen and palladium-deuterium alloys has been considered 25 , p. Up to 10 atomic per cent nickel suppresses the critical temperature rather strongly, but platinum has little influence on critical temperature at concentrations up to 25 atomic per cent 25 , p. There is no relationship between critical temperature, susceptibility and the coefficient of the low temperature specific heat for the rhodium-palladium-silver and nickel-palladium-platinum alloys investigated 25 , p.

None of the alloys of the platinum metals with lithium, sodium or potassium is superconducting above 2 K. This is valid for the solid solutions, as well as for the compounds at present known 7 , 13 , Electrolytically loading palladium-lithium solid solution samples with hydrogen did not produce superconductivity above 1.

Physica C: Superconductivity and its Applications - Journal - Elsevier

None of the alloys of the platinum metals with copper, gold or silver is superconducting above 2 K. Rhodium-copper samples, in the solid solution range, are not superconducting down to 0. Beryllium forms superconducting phases with four of the platinum metals but not with palladium and platinum; however sometimes it is culear to which phases superconductivity must be attributed 7 , 13 , Be 13 Ru and Be 2 Ru show critical temperatures of 1.

Of the many beryllium-rhodium compounds only Be 2 Rh is superconducting at 1. None of these three are known to form superconducting phases with the platinum metals, which is at least partially explained by the problems concerned with the formation of superconducting shields and the experimental difficulties due to the wide range of vapour pressures among the components The compound B 3 Ru is superconducting at 2.

None of the binary borides of platinum or palladium shows superconductivity above 1. Superconducting ternary palladium-hydrogenboron alloys can be prepared by ion-implantation techniques OsB 2 has a critical temperature of about 2 K 39 , but superconducting binary iridium borides are unknown. The hexagonal phases Ba 0. Among osmium-aluminium phases OsAl and Os 4 Al 13 become superconducting at 0. The critical temperature of 5. With the exception of palladium and platinum, the platinum metals together with lanthanum, scandium, yttrium and the rare earth elements form many superconductors 7 , 13 , 32 , 43 , 44 , 51 , 46 , It was first shown by V.

Compton and B.

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It drops down evenly to near 0 K at OsLu 2 The magnetic moments show two maxima at Ru 2 Pr and Ru 2 Dy and a minimum for europium compounds. This behaviour is equalled by that of the iridium and osmium rare earth Ctype phases In the system iridium-yttrium a maximum critical temperature of 0. Most likely this is caused by shields of Ir 3 Y or Ir 4 Y. Ir 2 Y 3 is superconducting at 1. The composition of the superconducting phase richest in iridium is near Ir 4 Y Nevertheless the behaviour is still somewhat unclear.

Scandium-rich rhodium alloys show superconductivity beginning partial superconductivity near 0.

In the systems consisting of platinum metals with yttrium, scandium and lanthanum superconductivity is explained by T. Geballe as most likely being of a filamentary nature In the lanthanum-rhodium system approximately 1 per cent lanthanum in the melt is enough to make the solidified alloy appear fully superconducting. Even 0. The ternary borides of the rare earth metals belong to a group of new superconducting compounds, which was discovered by B. Matthias and collaborators in The compounds are tetragonal in structure, of the CeCo 4 B 4 type 55 , As with the binary C15 phases of the rare earths, elements with an unfilled 4f shell, namely neodymium, samarium, erbium, thulium and lutetium, show superconductivity; those with the filled shell, that is gadolinium, terbium, dysprosium and holmium are ferromagnetic Up to now, it is impossible to prepare compounds with lanthanum, cerium, europium and ytterbium.

All superconducting phases exhibit long range magnetic ordering at a temperature T m which is below the superconducting transition temperature T c. The superconducting transition temperatures and the ferromagnetic Curie temperatures of the RERh 4 B 4 compounds are shown in Figure 1 Rhodium can be replaced at least partially by ruthenium 59 or iridium For the phase Ho Ir 0. Crystallographic, magnetic and superconducting properties of the system YRh 4 B 4 -LuRh 4 B 4 -ThRh 4 B 4 lead the authors to conclude that the lattice volume has relatively little influence on the electronic density of states.

Several reviews of the numerous investigations carried out on ternary borides have already been presented 59 — The primitive tetragonal crystal structure of the rare earth rhodium borides RERh 4 B 4 with the outline of the unit cell indicated by broken lines. For clarity, the Rh 4 B 4 -clusters are not drawn to scale, after reference Ternary silicides and germanides with ruthenium, rhodium and osmium and the rare earths, of the Sc 5 Co 4 Si 10 type of structure, show a similar behaviour 68 , 69 , The superconducting transition and magnetic ordering temperatures of Sc 5 Co 4 Si 10 type phases, having a primitive tetragonal lattice of a new structure type, are listed in Table III 68 , 68 , Phases I and II with Me being rare earth elements from the series lanthanum to gadolinium, and ytterbium, calcium, strontium and thorium are superconducting between 8.

Phase II of yttrium and scandium are superconducting at 3. Superconducting transition temperatures are YPd 2 Sn 3. Many alloys of titanium, zirconium and hafnium with even fairly small additions of other transition elements show a big increase in the transition temperature of their hexagonal close-packed a -phase 43 , 84 , see Figure 3. In these systems, a very careful definition of the state of the sample is necessary in order to obtain reliable results on their superconductivity.

For example oxygen impurities may play a role which is shown by the superconductivity of the ternary EO 3 -type phases Ti 0. Th 7 Pt 3 is not superconducting above 1. In the system titanium-platinum, depending on sample preparation, a critical temperature between 0. Ternary superconducting solid solutions based on body-centred cubic titanium-rhodium and zirconium-rhodium have been investigated 43 , 84 ; in all cases the critical temperature was reduced by the presence of platinum group metals.

Transition temperature versus concentration curves for titanium-iridium and titanium-rhodium alloys, after reference Superconductivity data for binary phosphides and arsenides of the platinum metals are listed in Table IV. It is interesting to note the difference between the critical temperature of the high and low temperature forms of Pd 7 P 3 and Pd 2 As, where the high temperature form always exhibits a slightly higher critical temperature. A review on the superconductivity of binary compounds of the platinum metals with elements of Groups IV, V and VI has been published elsewhere Ternary hexagonal phosphides and arsenides of ruthenium and osmium constitute a new class of ternary superconductors discovered in Transition temperatures and lattice parameters of the known superconducting ternary phosphides are listed in Table V and of the corresponding arsenides in Table VI 90 , The proposed structure of the hexagonal ternary phosphide ZrRuP is shown as Figure 4 The proposed structure of the hexagonal lernary phosphide ZrRuP.

Lines have been drawn to indicate the Ru 3 two-dimensional triangular clusters and also the linking of these clusters through zirconium-ruthenium bonds, after reference Depending on their preparation and heat treatment, some of the superconducting phosphides and arsenides show high or low temperature modifications, which in most cases have now been fully identified and reported The influence of oxygen on the critical temperature of ZrRuP has been investigated Oxygen is not taken into the lattice, but reduces the phosphorus concentration, which itself determines critical temperature.

The relatively low critical temperature of TiRuP may be caused by some kind of magnetic interaction Solid solutions of elements of Groups V and VI in the Periodic Table, when present in ruthenium and osmium reduce their critical temperatures In vanadium-rich solutions the presence of 10 atomic per cent palladium or platinum reduces the critical temperature of vanadium to below 1. Since the last review article on the superconductivity of the platinum metals and their alloys practically no new binary superconductors have been found Some work has been concerned with the influence of additions on the behaviour of pseudo-binary phases 7 , 13 , 32 , 43 , This may be caused by a very narrow homogeneity range.

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Aphases with the highest transition temperatures among these compounds are Nb 3 Pt and Mo 0. Special attention should be given to the peculiar Atype phase Os 0. A review of the superconductivity of sulphur, selenium and tellurium compounds has been presented Data on the latter are given in Table VII.

The decrease of the critical temperature of the B8 phase PdTe with tellurium concentration within its homogeneity range, is peculiar. Apparently there is a sharp peak in the density of states and energy at the stoichiometric composition.

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In the system ruthenium-chromium the critical temperature of the 20 atomic per cent chromium alloy is 0. Both RuCr 2 and RuCr 3 are superconducting, at 2. Further work on superconductivity in the ruthenium-molybdenum system has previously been summarised The Atype compound Nb 0. No superconducting phases are known between the platinum group metals and Group VII elements.

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