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Evolution of Bonding and Magnetism via Changes in Valence Electron Count in CuFe 2– x Co x Ge 2
A series of solid solutions, CuFe 2–x Co x Ge 2 (x = 0, 0.2, 0.4, 0.8, and 1.0), have been synthesized by arc-melting and characterized by powder X-ray and neutron diffraction, magnetic measurements, Mössbauer spectroscopy, and electronic band structure calculations. All compounds crystallize in the CuFe 2 Ge 2 structure type, which can be considered as a three-dimensional framework built of fused MGe6 octahedra and MGe 5 trigonal bipyramids (M = Fe and Co), with channels filled by rows of Cu atoms. As the Co content (x) increases, the unit cell volume decreases in an anisotropic fashion: the b and c lattice parameters decrease while the a parameter increases. The changes in all the parameters are nearly linear, thus following Vegard’s law. CuFe 2 Ge 2 exhibits two successive antiferromagnetic (AFM) orderings, corresponding to the formation of a commensurate AFM structure, followed by an incommensurate AFM structure observed at lower temperatures. Additionally, as the Co content increases, the AFM ordering temperature (TN) gradually decreases, and only one AFM transition is observed for x ≥ 0.2. The magnetic behavior of unsubstituted CuFe 2 Ge 2 was found to be sensitive to the preparation method. The temperature-dependent zero-field 57 Fe Mössbauer spectra reveal two hyperfine split components that evolve in agreement with the two consecutive AFM orderings observed in magnetic measurements. In contrast, the field-dependent spectra obtained for fields ≥ 2 T reveal a parallel arrangement of the moments associated with the two crystallographically unique metal sites. Electronic band structure calculations and chemical bonding analysis reveal a mix of strong M–M antibonding and non-bonding states at the Fermi level, in support of the overall AFM ordering observed in zero field. The substitution of Co for Fe reduces the population of the M–M antibonding states and the overall density of states at the Fermi level, thus suppressing the T N value.
Elasticity of Nonstoichiometric Alumina-Rich Spinel Determined by Bond Valence Theory and Brillouin
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Complexation of High-Valency Mid-Actinides by a Lipophilic Schiff Base Ligand: Synthesis, Structural Characterization, and Progress toward Selective Extraction
We report that separation of U, Np, and Pu from used nuclear fuel (UNF) would result in lower long-term radiotoxicity, alleviating constraints on the storage and handling of the material. The complexity of UNF requires several industrial-scale processes with multiple waste streams. A one-step solution to the group removal of the elements, U–Pu, is desirable. Here we present a possible solution to group actinide separation utilizing the unique dioxy conformation of An(V/VI) cations and demonstrate the ability of a tetradentate lipophilic Schiff base ligand (L) to yield isostructural complexes of the general formula [(An VI O 2 )(L)(CH 3 CN)] (where An = U, Np, or Pu). Extraction of An(VI) with the ligand follows the order U > Pu > Np, likely reflecting the decreased stability of the hexavalent actinide across the series. Lastly, while the results indicate a promising path toward a one-step process, further improvement in the ligand stability and control of the redox chemistry is required.
Attosecond X-ray Diffraction Triggered by Core or Valence Ionization of a Dipeptide
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Spatial Mapping of Valence Excited-State Landscapes Using Time-Resolved Shake-Down Spectroscopy
Time-resolved X-ray photoelectron spectroscopy (XPS) is used to track the photodissociation dynamics of 2-iodothiophene following 262 nm excitation. The transient XPS features include both direct ionization of the initially populated excited states and pronounced satellite peaks arising from shake-down processes. While the direct ionization signals exhibit only minimal energy shifts during C−I bond cleavage, the shake-down transitions undergo a substantial, 5 eV, shift over the reaction coordinate. By correlating these shifts with simulated C−I bond lengths, a direct structural mapping is established that reveals the exceptional sensitivity of shake-down channels to molecular geometry. These results demonstrate that shake-down transitions provide a new and powerful probe of ultrafast structural dynamics.
Valence-Shell Photoionization of C 4 H 5 : The 2-Butyn-1-yl Radical
We present here new high-resolution data on the photoionization of the 2-butyn-1-yl radical (CH 3 C≡C–•CH 2 ) formed by H atom abstraction from 2-butyne by F atoms. The spectra were recorded from 7.7 to 11 eV by using double-imaging, photoelectron–photoion coincidence spectroscopy, which allows the unambiguous correlation of photoelectron data and the mass of the species. The photoionization spectrum shows significant resonant autoionizing structure converging to excited states of the C 4 H 5 + cation, similar to what is observed in the closely related propargyl radical (HC≡C–•CH 2 ). The threshold photoelectron spectrum, obtained with a resolution of 17 meV, is also reported. This spectrum is consistent with previous measurements of the first photoionization band but has been extended to higher energy to allow the observation of bands corresponding to excited electronic states of the ion. A refined value of the adiabatic ionization energy is extracted: IE(C 4 H 5 ) = 7.93 ± 0.01 eV. A determination of the absolute photoionization cross section of the 2-butyn-1-yl radical at 9.7 eV is also reported: σ ion (C 4 H 5 ) = 6.1 ± 1.8 Mb.