A.L. Giorgi

High-pressure synthesis of yttrium-thorium sesquicarbide: A new high-temperature superconductor☆

Abstract A new, high-temperature superconductor, yttrium-thorium sesquicarbide, has been prepared by high-pressure-high-temperature techniques. The phase, crystallizing in the b.c.c., Pu2C3-type structure, exists over a wide ternary field. Lattice parameters are dependent on the Y Th metal and C M t carbon-total metal atomic ratios. The material is superconducting with a variable transition temperature, having a maximum at 17.0 °K. High-temperature ambient-pressure annealing results in the destruction of both the b.c.c. structure and the high-temperature superconductivity. A ternary b.c.t. phase, previously unreported, has been identified in a number of arc-melt preparations. This phase exists over a wide ternary field and is not superconducting down to 4 °K. Elements other than thorium have been incorporated in yttrium sesquicarbide with resultant enhancement of the superconducting temperature.

HIGH PRESSURE SYNTHESIS AND SUPERCONDUCTING PROPERTIES OF YTTRIUM SESQUICARBIDE.

Abstract The body-centered cubic Pu 2 C 3 -type structure of yttrium sesquicarbide, Y 2 C 3 , has been prepared in high yield by high pressure-high temperature techniques. Lattice parameter measurements indicate a homogeneity range for the compound. Magnetic susceptibility measurements show the material is superconducting over the entire homogeneity range with the superconducting transition temperature varying from a low of 6.0 °K to a high of 11.5 °K. High temperature-ambient pressure annealing of samples prepared by the high pressure-high temperature techniques destroyed the Pu 2 C 3 -type structure. No superconducting transition was observed on the annealed samples for measurements down to 2.0 °K.

Itinerant ferromagnetism in the C-15 Laves phase - TiBe2−xCux

Abstract By substituting copper for part of the beryllium in the C-15 Laves phase, TiBe2, the phase is converted into an itinerant electron ferromagnet. The stable C-15 phase forms over the general composition range, TiBe2−xCux where 0 ⩽ x

High pressure thorium-rare-earth carbide superconductors☆

Abstract The high pressure preparation of superconducting thorium sesquicarbide permitted its use as a matrix whereby the effects of the addition of incremental quantities of rare-earth elements on the transition temperature could be studied. Thorium -rare-earth carbide superconducting solid solutions of general formula (Th, R.E.) 2 C 3 ( R . E .  Ho , Er , Lu as well as Sc ) have been synthesized under conditions of high pressure and high temperature. Transition temperatures of 4.1 to 11.7 K were observed and are dependent upon the rare-earth element and the thorium/rare-earth atomic ratio. The occurrence of superconductivity in these systems is limited by the thermodynamic stability of the superconducting phase and the conversion from the superconducting state to one of paramagnetism. Light rare-earth elements such as Ce, Pr, and Nd also form superconducting solid solutions but with depressed transition temperatures. The intermediate rare-earth elements Gd, Tb and Dy form magnetic solid solutions at the concentration levels investigated. The (Th,R.E.) 2 C 3 solid solutions crystallize in the body-centered cubic Pu 2 C 3 ( D 5 c ) structure.

Enhancement of Superconductivity through Lattice Softening

The superconducting transition temperature of an iridium-yttrium eutectic is enhanced extraordinarily through lattice softening. This is shown by a drastically reduced Debye temperature.

The specific heat of two cubic laves compounds: TiBe2 and ThMg2

Abstract The low temperature specific heats of two isomorphous Laves compounds, TiBe2 and ThMg2, have been measured. The shape of the transition for the itinerant antiferromagnet TiBe2 is characteristic of magnetic ordering; the entropy of this transition is quite small, approximately 107 mJ/mole-K, a further indication of itinerancy. The γ, proportional to the density of states, is 42 mJ/mole-K2 for TiBe2, and the Debye temperature, θD, is 650 K. These numbers are compared to those for the itinerant ferromagnet, ZrZn2. The results for ThMg2 are γ=9.2 mJ/ mole-K2 and θD = 217 K. Results for both compounds are discussed in regards to the theory of Enz and Matthias.

Evidence for ferromagnetism in alloys formed between uranium tetraboride and yttrium tetraboride

Experimental results are presented showing an apparent inducement of ferromagnetism in UB/sub 4/ by alloying this compound with nonmagnetic YB/sub 4/. The appearance of ferromagnetism in the UB/sub 4/- YB/sub 4/ alloy may be the result of an effective increase in the average U-U atom spacing in the lattice due to dilution by YB/sub 4/. (JRD)

Preparation and superconductivity of germanium-stabilized Sc13C10☆

Abstract A new body-centered cubic scandium carbide phase having the approximate composition Sc13C10 has been prepared by high-temperature annealing of arc-melted samples containing small amounts of germanium. The lattice parameters of this new phase varied from a 0 = 8.514 A to a = 8.530 A suggesting a range of homogeneity. All compositions were found to be superconducting with the transition temperature ranging from 7.0 ° to 8.5 °K. Similar measurements on the previously reported Sc4C3 b.c.c. phase showed no superconducting transition for measurements down to 1 °K.

Ferromagnetism and heavy electron behavior in URu2−xMxSi2(M = Re, Tc and Mn)

Abstract The ferromagnetic state in URu 2−x Re x Si 2 has been confirmed with low field magnetization measurements and the Curie temperature found to be pressure independent up to 6.4 kbar. Substitution of Mn atoms for Ru in URu 2 Si 2 also leads to a ferromagnetic transition with a small saturation moment appearing at x ≳0.2. The ferromagnetism in URu 2− x M x Si 2 (M = Re, Tc or Mn) is apparently due to a sharp feature in the density of states of a band of strongly correlated electrons.

Suppression of spin fluctuations by alloying in UPt3

In order to investigate the normal state spin fluctuation behavior of UPt3, we have measured the low temperature resistivity and specific heat C of U(Pt0.8Pd0.2)3, which we find to be close to the phase stability boundary for the hexagonal UPt3 structure. The evidence for spin fluctuations observed in UPt3, aT3 ln (T/TSF) upturn inC/T below 10 K, is totally suppressed in U(Pt0.8Pd0.2)3, and the γ value, proportional to the dressed density of states, is decreased by 50% compared to pure UPt3. This extreme sensitivity to substitution by isoelectronic Pd for Pt indicates that the spin fluctuations in UPt3 depend critically on the hybridization of the U electrons, U-U separation equal to 4.2 Å, with the electrons of the intervening atoms.