Palladium-rhodium Alloys Research Articles

The High Temperature Specific Heat of Palladium

The form of part of the electronic density of states curve for palladium is deduced from the low temperature specific heat coefficients γ of palladium-silver and palladium-rhodium alloys by means of the rigid band model of alloying. The curve, which shows a sharp maximum near the Fermi limit, is used to calculate the electronic contribution to the specific heat of palladium over the temperature range 0 °K to 1500 °K. Values of the electronic contribution in palladium are also deduced from the measured specific heat, and are shown to be in good agreement with the calculated values and to differ widely from the approximation Ce = γT. It is also suggested that the experimental specific heat results for palladium alone, without using the alloy data, indicate the occurrence of a maximum in the density of states curve near the Fermi limit.

Properties of Palladium–Rhodium Alloys

AN earlier communication1 from these laboratories gave preliminary results of an investigation into the magnetic susceptibilities of a series of palladium–rhodium alloys. A noteworthy finding was that alloying palladium with an element, rhodium, of a much lower susceptibility could, over a limited concentration-range, produce alloys having susceptibilities higher than those of either of the pure metals. This was more noticeable at low temperatures. More detailed investigations, since completed, have confirmed the general correctness of these results although minor adjustments of the absolute values previously given are required in some cases.

Thermoelectric Powers in Palladium-Silver and Palladium-Rhodium Alloys

Thermoelectric powers have been measured in the temperature range 77\ifmmode^\circ\else\textdegree\fi{}K to 273\ifmmode^\circ\else\textdegree\fi{}K in the alloys of palladium with silver. The absolute thermoelectric power is found to be highly sensitive to the presence of unoccupied $d$-band states, and a marked variation with composition is also found in alloys with more than 90% of either element. This latter behavior is ascribed to a departure of the Fermi surface from an accurately spherical form as the $s$-electron concentration increases above 0.9 per atom in the silver-rich alloys, and to a contribution to conduction from $d$-band holes in the palladium-rich alloys. The values of thermoelectric power obtained for the pure metals by extrapolation from the results for alloys where these effects are absent are in good agreement with estimates made on the basis of simple theoretical models. Results of measurements on some palladium-rich palladium-rhodium alloys are also presented and discussed briefly.

Magnetic Susceptibilities of Palladium–Rhodium Alloys from 20° to 300° K.

THE rapid, yet accurate, method of measurement and the results thereby obtained for the magnetic susceptibilities of platinum, rhodium and palladium between liquid hydrogen and room temperatures have been previously described by two of us1. The same measurement techniques were afterwards applied to a series of polycrystalline palladium–silver alloys; the specific heats of these alloys have also been investigated (both sets of results yet unpublished). The results, when interpreted through the collective electron theory, make possible an estimate of the size and shape of the normally unfilled portion of the d electronic energy-band of metallic palladium, on the assumption that the addition of small amounts of silver to palladium cause a reduction of the number of holes in the d-band without significantly modifying its shape. With the filling of the band, it would be expected that the magnetic susceptibility and its variation with temperature would be affected. It was actually found experimentally that both decreased monotonically with increased silver content.