Neutron and Mössbauer effect measurements have been made as a function of Fe concentration in orthorhombic ( x = 0.01, 0.02) and tetragonal ( x ⩾ 0.05), YBa 2 (Cu 1 − x Fe x ) 3 O 7 + δ . A systematic Rietveld analysis of the neutron data for all concentrations shows that Fe principally occupies a site slightly displaced ( y , y , 0) from the Cul (0, 0, 0) site in order to approach tetrahedral coordination. Neutron data for the x = 0.05 compound at 10 K show no significant difference from those obtained at 297 K. Local ordering of oxygen about an Fe substituent is conducive to placement of a second Fe atom in an adjacent site leading to local aggregation into chains of various lengths. This clustering is reflected in the character of low temperature magnetic Mössbauer spectra and in specific heat measurements. The Mössbauer spectra yield the relative changes in oxygen configurations about Fe atoms as the Fe concentration changes.

Temperature dependent119Sn Mössbauer effect measurements on AuSn4, PdSn4, and PtSn4 compounds in the temperature range of 10 to 295 K shows the presence of a Sn4+ site. Variation of thermal shift and the Debye-Waller factor shows that the mean-squared displacement (lnf) and mean-squared velocity (δ) of the tin nuclei are both characterized by a Debye temperature of 238, 255, and 304 K in AuSn4, PdSn4, and PtSn4, respectively. No discernible evidence of a phonon mediated structural transition is observed in the temperature range studied.

57Fe Mössbauer effect measurements have been made on U x Fe100−x(x=32, 33.3, and 35) samples at 300 and 78 K. Laves phase structure was maintained for all three samples. Mössbauer spectra of the three samples were found to be a symmetric quadrupole doublet at 300 K. Such spectra were converted into a set of two overlapping six lines pattern at 78 K. The values of the hyperfine fields have been found to vary systematically with the iron content in the samples. The Curie temperatures, as determined by the ac susceptibility measurements, have been found to increase by increasing the amount of iron in the samples.

Mössbauer effect measurements have been made at 57Fe nuclei in PrxY1−xBa2(Cu0.9957Fe0.01)3Oy and in Y(Ba1−xSrx)2(Cu0.9957Fe0.01)3Oy as a function of x. For all Pr concentrations (0⩽x⩽0.7) studied, the Mössbauer spectra are nearly identical in character and comparison of Mössbauer shift and of quadrupole splitting EQ with composition indicates that oxygen order and electronic structure at the Cul site are virtually unaffected by changing the relative Y to Pr composition. Hence, the rapid depression of Tc with increasing x is inferred to be due to electronic changes caused by changes in the Pr bonding to the Cu2-O plane. In contrast to the behaviour of compounds with Pr substituted for Y, Mössbauer spectra for Y(Ba1−xSrx)2(Cu0.9957Fe0.01)3Oy show systematic pattern changes similar to those observed upon Fe substitutions for Cul in YBa2(Cu1−xFex)3O7+δ. That is, oxygen order and stoichiometry are strongly affected by Sr substitution for Ba.

Mössbauer effect studies have been made as a function of temperature for the orthorhombic (χ=0.01, 0.02) and tetragonal (χ=0.05) superconducting compounds YBa2(Cu1−χ57Feχ)3O7 + y. For Fe in or slightly displaced from the Cu1 (000) site, temperature dependent measurements yield Debye temperatures for the Mössbauer shift θδ in the range of 601 to 698 K and for the resonant fraction θf in the range from 333 to 568 K, depending on the local oxygen configuration. Very little change is observed in the region of the superconducting transition Tc for the orthorhombic phase samples, but both phonon and electronic changes occur near Tc in the tetragonal phase. The vibrational behavior of Fe in the Cu1 site shows a dramatic hardening near and below Tc in tetragonal YBa2(Cu0.95Fe0.05)3O7.1. The quadrupolar splitting EQ indicates a change in field gradient in this same temperature region. The Mössbauer shift also behaves anomalously near Tc.

Unit cell constants are reported for eight ternary compounds with the ZrPt2Al-type crystal structure. Compositions are (Gd, Tb, Y, Dy or Ho)Pt2In, and (Tb, Y or Tm)Pt2Sn. The crystal structure of YPt2In is hP8, P63/mmc, with Y in 2c, Pt in 4f, and In in 2a sites. The interatomic bonds which show the highest contraction are between a Pt atom and 3 In atoms. A comparison is made with the competing MnCu2Al-type structure in YPd2In.

The superconducting and magnetic properties of the compounds La1.85Sr0.15Cu1−xFexO4 and YBa2(Cu1−xFex)3O7−y with 0<x<0.1 are presented. The Fe substitution in the La-Sr compound rapidly depresses Tc, extrapolating to Tc=0 for x∼0.02. However, Tc is depressed much less rapidly in the Y-Ba compound, extrapolating to 0 K for x∼0.16. Mössbauer spectroscopy and magnetic data have been obtained to give information on the magnetic and structural properties of these materials. The results are compared with those for other dopants, both magnetic and non-magnetic, in the oxide superconductors.

The compounds EuPdGa and EuPtGa show lattice volume anomaly indicating the abnormal valence state of Eu. in these compounds. Magnetization studies reveal that these compounds are magnetically ordered with a moment of ∼7 μB/f.u. at 5K. The Curie temperatures obtained from the low field ac susceptibility measurements are 38K for EuPdGa and 36K for EuPtGa.151Eu Mössbauer studies at 300K gave large negative isomer shifts (relative to SmF3) and show a hyperfine split pattern at 4.2K in both the compounds. These results suggest that Eu is in a divalent state in EuPdGa and EuPtGa.

Mössbauer measurements have been made at 199Sn in the perovskite superconductors La1.85Sr0.15Cu1−xSnxO4. The Sn valence is 4+ for all concentrations. The temperature dependence of the mean-squared displacement for x=0.05 shows phonon softening near 75 and 170 K; θD=402 K above 180 K, between 77 and 160 K, and θD is temperature dependent below 77 K. Below 250 K the shift indicates electronic structure changes characteristic of a phase transformation.

The superconducting and magnetic properties of the compounds La/sub 1.85/Sr/sub 0.15/Cu/sub 1-x/Fe/sub x/O/sub 4/ and YBa/sub 2/(Cu/sub 1-x/Fe/sub x/)/sub 3/ with 0 < x < 0.1 are presented. The Fe substitution in the La-Sr compound rapidly depresses T/sub c/, extrapolating to T/sub c/ = 0 for x approx. 0.02. However, T/sub c/ is depressed much less rapidly in the Y-Ba compound, extrapolating to 0/sup 0/K for x approx. 0.12. Moessbauer spectroscopy and magnetic data have been obtained to give information on the magnetic and structural properties of these materials. The results are compared with those for other dopants, both magnetic and nonmagnetic, in the oxide superconductors. 10 refs., 2 figs.

A new alloy, having the formula, Co2ScSn, has been prepared. This is found to have the cubic Heusler L21 type structure (a = 6.19A). Magnetization measurements reveal a large drop in magnetization around 270K. Low field ac susceptibility also shows a transition at 268K which we take to be the Curie temperature of the alloy. The magnetic moment at 5K is found to be 0.55 μB per cobalt atom.119Sn Mössbauer measurements at 8K show a hyperfine split spectrum with a hyperfine field of about 40 kOe. Attempts to prepare other Co2RSn alloys particularly with R=Lu, were not successful.

There are 17 ScT2X intermetallic compounds, in which T is a member of the cobalt, nickel or copper group, and X is aluminium, gallium, indium or tin. Substitution of all or part of the lanthanoids (or yttrium) for scandium can be made in the series LnPd2In, LnNi2Sn, LnPd2Sn, LnCu2In, LnAg2In and LnAu2In. Unit cell constants are given and the role of atomic volume as a controlling factor is discussed.

Mössbauer and magnetic measurements have been made in the perovskite superconductors La1.85Sr0.15Cu1−x 57FexO4 for x=0.0025, 0.005, 0.01, 0.05 and 0.10. The superconducting transition temperature is rapidly depressed as x increases, reaching Tc=0 for x≈0.03. Mössbauer data for x=0.05 show behavior below ≈15 K which indicates magnetic ordering. Magnetic susceptibility data give an effective moment of 3–4 μB/Fe atom, and a hand-like susceptibility which increases with x.

The crystal structure of the equiatomic compounds EuPdGa and EuPt Ga is TiNiSi type, oP12, and the crystal structure of EuAgGa and EuAuGa is CeCu2 type, OI12. EuCuGa probably has CeCu2-type structure. The Eu atom is divalent in the five compounds, as shown by comparison of the unit cell volume with that of other lanthanide ternary compounds.

Superconductivity has been captivating humankind for more than a century—unimaginable breakthroughs were made and invaluable lessons were learned with perhaps the most important one being that this peculiar phenomenon still holds many surprises. When it comes to actinide-based superconductors, the number of known representatives is rather low. They have small energy scales, which restrict the upper bounds of critical temperatures, i.e., the highly sought-after room-temperature superconductor likely will not be an actinide-based one. However, the study of these peculiar materials can help fully understand what governs the magnitude of the critical temperature in other systems, allowing for a clever avenue toward improvement. In this review, a comprehensive analysis of actinide- and, in particular, uranium-based superconductors is presented, with an emphasis on the chemical bonding and its relation to the observed physical properties. Even more than 60 years after its discovery, the record value of the critical superconducting temperature among uranium-based materials is still being held by U6Fe with Tc = 3.8 K. This is particularly puzzling given much higher critical temperatures of ostensibly similar plutonium- and neptunium-based superconductors. It is therefore reasonable to assume that higher temperature uranium-based superconductors exist, but have not yet been discovered. When it comes to finding new materials and refining features that are responsible for the emergence of superconductivity in these systems, computational analyses are, unfortunately, not yet able to model such complex orbital configurations in a time- and cost-efficient way. The aspiration of this review is that perhaps a thorough empirical analysis can be used to discover new uranium-based superconductors and through this contribute to the general understanding of superconductivity. Due to the limited amount of data on uranium-based systems, just a rough direction is outlined below, with the hope that new members can be discovered and used to refine this approach over time.

Eu3Ni4Ga4 was found to have a b.c. cubic crystal structure, oI122, 143m, ao = 7.505 A. The compound is isostructural with Na3Pt4Ge4. Other lanthanide elements form ternary compounds of the TiNiSi-type (e.g., GdNiGa) instead of a 3:4:4 compound.