Low-temperature superconductivity has been known since 1957 to be described by BCS theory for effective single-band metals controlled by the density of states at the Fermi level, very far from band edges, the electron–phonon coupling constant l, and the energy of the boson in the pairing interaction w0, but BCS has failed to predict high-temperature superconductivity in different materials above about 23 K. High-temperature superconductivity above 35 K, since 1986, has been a matter of materials science, where manipulating the lattice complexity of high-temperature superconducting ceramic oxides (HTSCs) has driven materials scientists to grow new HTSC quantum materials up to 138 K in HgBa2Ca2Cu3O8 (Hg1223) at ambient pressure and near room temperature in pressurized hydrides. This perspective covers the major results of materials scientists over the last 39 years in terms of investigating the role of lattice inhomogeneity detected in these new quantum complex materials. We highlight the nanoscale heterogeneity in these complex materials and elucidate their special role played in the physics of HTSCs. Especially, it is highlighted that the geometry of lattice and charge complex heterogeneity at the nanoscale is essential and intrinsic in the mechanism of rising quantum coherence at high temperatures.

A plutonium-rich carbide, (U,Pu)(Al,Fe)3C3, was discovered in a hot particle from the Maralinga nuclear testing site in South Australia. The particle was produced between 1960 and 1963 and has been exposed to ambient conditions since then. The new phase belongs to a group of ternary carbides known as 'derivative-MAX phases'. It formed at high temperature within an explosion cloud via rapid eutectic crystallisation from a complex Al–Fe–U–Pu–C–O melt, and is the major Pu host in this particle. Despite signs of volume expansion due to radiation damage, (U,Pu)(Al,Fe)3C3 remains highly X-ray crystalline 60 years after its formation, with no evidence of Pu leaching from the crystals. Our results highlight that the high-energy conditions of (sub-)critical explosions can create unexpected species. Even micro-particles of a derivative-MAX phase can effectively retain low-valence (metallic-like character) Pu under environmental conditions; the slow physical and chemical weathering of these particles may contribute to the slow release of radionuclides over decades, explaining constant low-levels of radionuclides observed in fauna. This study further suggests that rapidly quenched eutectic melts may be engineered to stabilise actinides in nuclear waste products, removing the need for hydrometallurgical processing.

Cu K edge X-ray absorption spectra of overdoped superconducting YSr_2Cu_2.75Mo_0.25O_7.54 and Sr_2CuO_3.3 show a remarkably strong correlation of their superconductivity with the local dynamics of their Cu-Sr and Cu-apical-O pairs. This finding that the entire alkaline earth cation-apical O "dielectric" layer has an active role in the unusual electronic properties of cuprates has not been previously considered and has far reaching implications. We develop this idea of a possible role for the apical oxygen charge dynamics via a soft mode of the Sr by applying Kuramoto's synchronization technique to exact diagonalization calculations of two neighboring Cu-apical O pairs bridged by Sr and a planar O atom. These calculations show a first order phase transition to a synchronized state of the Internal Quantum Tunneling Polarons (IQTPs) in which a fraction of the hole originally confined to the apical O atoms of the cluster is transferred onto the planar O. This combination of experimental results and theory demonstrates that the Sr-O dielectric layer of cuprates most likely plays an important role in high temperature superconductivity via its collective charge dynamics that extends into the CuO_2 conducting planes.

The defect chemistry and thermal oxidation of lanthanide (Ln) incorporated-UO2 are critical for understanding and predicting their behavior as enhanced fuels, mixed oxide (MOX) fuels, spent nuclear fuels (SNF), and particles for safeguard purposes. In this study, we independently controlled the Ln type (Ce4+, Nd3+, and Gd3+) and the preparation condition (reduced and nonreduced) to investigate their correlations to the generated non-equilibrated defects correspondingly. From early to late lanthanides: Ce and U formed close-to-ideal solid solutions in Fm-3m and oxidized to (Ce, U)4O9, Nd and U mixing under the reducing condition formed solid solutions with oxygen vacancies aggregating near Nd, and the mixing of smaller Gd with U resulted in short-range subnano-domain segregations with Ia-3 region embedded in the global Fm-3m matrix. Both trivalent Ln-incorporated UO2 oxidized to a mixture of (Ln, U)4O9 and (Ln, U)3O8. From these signature defect structures resulting from both Ln type and preparation condition, we proposed kinetic model and thermodynamic hypothesis for explaining the oxidation resistance of (Ln, U)O2. Although originated from f-block oxides, the discovery of long-range disorder short-range ordering may be not uncommon in other metal oxide systems, which can strongly influence their functionalities and properties.

The different structures and behaviors of UO2+x observed in crystallographic and local structure measurements were examined by extended X-ray absorption fine structure (EXAFS) measurements of pristine UO2.0, p+ and He2+ irradiated UO2.0, and, at multiple temperatures, bulk U4O9 and U3O7 and thin film U4O9-δ on an epitaxial substrate. The disorder caused by irradiation is mostly limited to increased widths of the existing U–O/U pair distributions, with any new neighbor shells being minor. As has been previously reported, the disorder caused by oxidative addition to U4O9 and U3O7 is much more extensive, resulting in multisite U–O distributions and greater reduction of the U–U amplitude with different distributions in bulk and thin-film U4O9. This includes the significant spectral feature near R = 1.2 Å for all U4O9 and U3O7 samples fit with a U-oxo type moiety with a U–O distance around 1.7 Å. In addition to indicating that these anomalies only occur in mixed valence materials, this work confirms the continuous rearrangement of the U–O distributions from 10 to 250 K. Although these variations of the structure are not observed in crystallography, their prominence in the EXAFS indicates that the dynamic structure underlying these effects is an essential factor of these materials.

The interaction of electrons with the lattice in metals can lead to reduction of their kinetic energy to the point where they may form heavy, dressed quasiparticles-polarons. Unfortunately, polaronic lattice distortions are difficult to distinguish from more conventional charge- and spin-ordering phenomena at low temperatures. Here we present a study of local symmetry breaking of the lattice structure on the picosecond timescale in the prototype layered dichalcogenide Mott insulator 1T-TaS2 using X-ray pair-distribution function measurements. We clearly identify symmetry-breaking polaronic lattice distortions at temperatures well above the ordered phases, and record the evolution of broken symmetry states from 915 K to 15 K. The data imply that charge ordering is driven by polaron crystallization into a Wigner crystal-like state, rather than Fermi surface nesting or conventional electron-phonon coupling. At intermediate temperatures the local lattice distortions are found to be consistent with a quantum spin liquid state.

In order to elucidate the unusual superconducting properties of cuprates in the strongly overdoped region, i.e., at hole-doping levels p≳0.4/Cu in the CuO2 plane, we study the structural and superconducting properties of a series of Cu0.75Mo0.25Sr2YCu2O7+x powder samples oxygenated under high pressure using different concentrations of KClO3 up to 35 mol %. The analysis of X-ray diffraction data indicates a high purity ∼90% of all samples and suggests that the concentration, x, of extra oxygen atoms increases with increasing KClO3 concentration. Surprisingly, the Tc values remain nearly constant within the 80–85 K range independent of KClO3 concentration, which suggests a scenario of Tc saturation. In order to account for this unexpected behaviour, we put forward the hypothesis that overdoping enhances the density of unpaired holes, which is supported by the observation of large values of the Sommerfeld coefficient in all samples. We therefore propose a scenario of electronic phase separation between normal and superconducting holes.

Abstract Interesting emergent behavior in quantum materials arises when the interaction of electrons with the lattice leads to localization and ordering. The triangular lattice of some transition metal dichalcogenides results in additional interplay of interactions involving spin, localized charge and lattice degrees of freedom. In the light of such complexity, the dominant mechanism that drives the formation of different orders is quite difficult to ascertain. Here we present a study of local symmetry breaking of the lattice structure in the prototype layered dichalcogenide material 1T-TaS2 to investigate the origin of the multiple charge and spin ordered phases. Remarkably, x-ray pair-distribution function measurements show symmetry-breaking polaronic distortions of the lattice structure around individual localized electrons at temperatures well above any of the known long-range ordered phases. The characteristic polaronic broken symmetry signatures remain present on cooling from 800 K to 15 K, through the purported quantum spin liquid (QSL) and charge ordered states, additionally revealing a new transition near 50 K to a state displaying partially restored symmetry and significant inter-layer dimerization. The appearance of locally broken symmetry and the associated order parameter at temperatures well above the appearance of long range order implies that charge ordering is driven by the Wigner crystallization of polarons, rather than Fermi surface nesting or conventional electron-phonon coupling. The local lattice distortions are consistent with a QSL state at intermediate temperatures where interlayer dimerization is incomplete. The breakup of the QSL state below 50 K is concurrent with the disappearance of domains in the charge order.

Interesting emergent behavior in quantum materials arises when the interaction of electrons with the lattice leads to partial localization and ordering of charge at low temperatures. The triangular lattice of some transition metal dichalcogenides additionally presents an interesting case, where spin order is frustrated, leading to an additional complex interplay of interactions involving spin, charge and lattice degrees of freedom. Here we present a study of local symmetry breaking of the lattice structure in the layered dichalcogenide material 1T-TaS$_{2}$ using x-ray pair-distribution function measurements. Remarkably, we observe symmetry-breaking polaronic distortions of the lattice structure around individual localized electrons at temperatures well above any of the known long-range ordered phases. These characteristic polaronic signatures remain on cooling through the spin and charge ordered states, eventually revealing a new transition near 50 K to a state displaying partially restored symmetry and significant inter-layer dimerization. The order parameter associated with the observed local atomic displacements and symmetry-allowed polaron spin structure in the ground state suggests that charge ordering is driven by the crystallization of polarons, rather than conventional Fermi surface nesting. Symmetry analysis shows that the distorted structure is consistent with a breakup of the QSL phase at low temperature, concurrent with the disappearance of domains in the charge order.

The capture of palladium from spent nuclear fuel is crucial for the sustainable development of nuclear energy and resource recovery. One of the most challenging issues in this direction is the survival of adsorbents under extreme reprocessing conditions such as strongly acidic media and high radiation fields while still maintaining high extraction ability and selectivity. Herein, an approach to addressing this issue is reported by incorporating macrocycle into nitrogen‐rich covalent organic polymers (COPs). Dramatically outperforming current adsorbing materials, pillar[5]arene‐based COPs with pyridyl and triazolyl functionalities display record adsorption capacity for Pd(II) at 3 M HNO 3 (403 mg g −1 ), extraordinary stability under 500 kGy gamma irradiation, and ultra‐high selectivity toward Pd(II) over both 17 coexisting cations and six anions. In particular, the material P5COP‐ m ‐BPT with the best performance also shows remarkable dynamic adsorption efficiency for Pd(II). This study not only provides a strategy to enhance all‐sided adsorption performance in palladium separation with nitrogen‐rich COPs materials but also demonstrates the superiority of customizing advanced materials with macrocycles.

A major open topic in cuprates is the interplay between the lattice and electronic dynamics and the importance of their coupling to the mechanism of high-temperature superconductivity (HTSC). As evidenced by Extended X-ray Absorption Fine Structure experiments (EXAFS), anharmonic structural effects are correlated with the charge dynamics and the transition to a superconducting phase in different HTSC compounds. Here we describe how structural anharmonic effects can be coupled to electronic and lattice dynamics in cuprate systems by performing the exact diagonalization of a prototype anharmonic many-body Hamiltonian on a relevant six-atom cluster and show that the EXAFS results can be understood as a Kuramoto synchronization between coupled internal quantum tunneling polarons associated with the two-site distribution of the copper-apical-oxygen ($Cu-O_{ap}$) pair in the dynamic structure. Furthermore, we find that this first order, anti-phase synchronization transition can be fine tuned by temperature and anharmonicity of the lattice vibrations, and promotes the pumping of charge, initially stored at the apical oxygen reservoirs, into the copper-oxide planes. Simultaneously, the internal quantum tunneling polaron extends to the copper-planar-oxygen ($Cu-O_{pl}$) pair. All these findings support an interpretation of the EXAFS data in terms of an effective, quantum mechanical triple-well-potential, which accurately represents the anti-phase synchronization of apical oxygens displacements and lattice-assisted charge transfer to the $CuO_2$ plane.

Because of its sensitivity to the instantaneous structure factor, S(Q,t = 0), Extended X-ray Absorption Fine Structure (EXAFS) is a powerful tool for probing the dynamic structure of condensed matter systems in which the charge and lattice dynamics are coupled. When applied to hole-doped cuprate superconductors, EXAFS has revealed the presence of internal quantum tunneling polarons (IQTPs). An IQTP arises in EXAFS as a two-site distribution for certain Cu–O pairs, which is also duplicated in inelastic scattering but not observed in standard diffraction measurements. The Cu–Sr pair distribution has been found to be highly anharmonic and strongly correlated to both the IQTPs and to superconductivity, as, for example, in YSr2Cu2.75Mo0.25O7.54(Tc=84 K). In order to describe such nontrivial, anharmonic charge-lattice dynamics, we have proposed a model Hamiltonian for a prototype six-atom cluster, in which two Cu-apical-O IQTPs are charge-transfer bridged through Cu atoms by an O atom in the CuO2 plane and are anharmonically coupled via a Sr atom. By applying an exact diagonalization procedure to this cluster, we have verified that our model indeed produces an intricate interplay between charge and lattice dynamics. Then, by using the Kuramoto model for the synchronization of coupled quantum oscillators, we have found a first-order phase transition for the IQTPs into a synchronized, phase-locked phase. Most importantly, we have shown that this transition results specifically from the anharmonicity. Finally, we have provided a phase diagram showing the onset of the phase-locking of IQTPs as a function of the charge-lattice and anharmonic couplings in our model. We have found that the charge, initially confined to the apical oxygens, is partially pumped into the CuO2 plane in the synchronized phase, which suggests a possible connection between the synchronized dynamic structure and high-temperature superconductivity (HTSC) in doped cuprates.

Within the cuprate constellation, one fixed star has been the superconducting dome in the quantum phase diagram of transition temperature vs. the excess charge on the Cu in the CuO2-planes, p, resulting from O-doping or cation substitution. However, a more extensive search of the literature shows that the loss of the superconductivity in favor of a normal Fermi liquid on the overdoped side should not be assumed. Many experimental results from cuprates prepared by high-pressure oxygenation show Tc converging to a fixed value or continuing to slowly increase past the upper limit of the dome of p = 0.26–0.27, up to the maximum amounts of excess oxygen corresponding to p values of 0.3 to > 0.6. These reports have been met with disinterest or disregard. Our review shows that dome-breaking trends for Tc are, in fact, the result of careful, accurate experimental work on a large number of compounds. This behavior most likely mandates a revision of the theoretical basis for high-temperature superconductivity. That excess O atoms located in specific, metastable sites in the crystal, attainable only with extreme O chemical activity under HPO conditions, cause such a radical extension of the superconductivity points to a much more substantial role for the lattice in terms of internal chemistry and bonding.

Steven D. Conradson, Victor Velasco, Marcello B. Silva Neto, Theodore H. Geballe, Chang-Qing Jin, Wen-Min Li, Li-Peng Cao†, Andrea Gauzzi, Maarit Karppinen, Andrea Perali, Sandro Wimberger, Alan R. Bishop, Gianguido Baldinozzi, Matthew Latimer, Edmondo Gilioli Department of Complex Matter, Josef Stefan Institute, 1000 Ljubljana, Slovenia Department of Chemistry, Washington State University, Pullman, WA 90164, U.S.A. Instituto de Física, Universidade Federal do Rio de Janeiro, Caixa Postal 68528, Rio de Janeiro, Brazil.

Selective extraction of highly radiotoxic actinides(III) is an important and challenging task in nuclear wastewater treatment. Many proposed ligands containing S or P atoms have drawbacks including high reagent consumption and possible secondary pollution after incineration. The present work reports five novel pillar[5]arene-based extractants that are anchored with picolinamide substituents of different electronic nature by varying spacer. These ligands reveal highly efficient separation of actinides(III) over lanthanides(III). Specifically, almost all of these ligands could extract Am(III) over Eu(III) selectively at around pH 3.0 (SFAm/Eu > 11) with fast extraction kinetics. Variation of the pyridine nitrogen basicity via changing para-substitution leads to an increase in the distribution ratios by a factor of over 300 times for Am(III) with an electron-withdrawing group compared to those with an electron donating group. Investigation of complexation mechanism by slope analysis, NMR, IR, EXAFS, and DFT techniques indicates that each ligand binds two metal ions by pyridine nitrogen and amide oxygen. Finally, these ligands do not show obvious decrease in both extraction and separation ability after being exposed to 250 kGy absorbed gamma radiation. These results demonstrate the potential application of pillar[5] arene-picolinamides for actinide(III) separation.

The high-energy release of plutonium (Pu) and uranium (U) during the Maralinga nuclear trials (1955–1963) in Australia, designed to simulate high temperature, non-critical nuclear accidents, resulted in wide dispersion µm-sized, radioactive, Pu–U-bearing ‘hot’ particles that persist in soils. By combining non-destructive, multi-technique synchrotron-based micro-characterization with the first nano-scale imagining of the composition and textures of six Maralinga particles, we find that all particles display intricate physical and chemical make-ups consistent with formation via condensation and cooling of polymetallic melts (immiscible Fe–Al–Pu–U; and Pb ± Pu–U) within the detonation plumes. Plutonium and U are present predominantly in micro- to nano-particulate forms, and most hot particles contain low valence Pu–U–C compounds; these chemically reactive phases are protected by their inclusion in metallic alloys. Plutonium reworking was observed within an oxidised rim in a Pb-rich particle; however overall Pu remained immobile in the studied particles, while small-scale oxidation and mobility of U is widespread. It is notoriously difficult to predict the long-term environmental behaviour of hot particles. Nano-scale characterization of the hot particles suggests that long-term, slow release of Pu from the hot particles may take place via a range of chemical and physical processes, likely contributing to on-going Pu uptake by wildlife at Maralinga.

Exploring nitrogen-containing extractants for recovering hazardous minor actinides that are workable in solutions of high acidity has been a challenge in nuclear waste treatment. Herein, we report our findings that 2,6-bistriazolyl-pyridine (PyTri), which is ineffective as a hydrophobic ligand for minor actinide separation, turns into an excellent extractant that exhibits unexpectedly high efficiency and selectivity (SFAm/Eu = 172, 1 M HNO3) when attaching to pillar[5]arene platform. Surprisingly, the distribution ratio of Am(III) (DAm) is 4300 times higher than that of the acyclic PyTri ligand. The solvent extraction performance of this pillar[5]arene-achored PyTri not only far exceeds the best known pillar[5]arene ligands reported to date, but also stays comparable to other reported outstanding extractants. Slope analysis indicates that each P[5]A-PyTri can bind two metal ions, which is further corroborated by spectroscopic characterizations. Thermodynamic studies imply that the extraction process is exothermic and spontaneous in nature. Complexation investigation via EXAFS technique and DFT calculations strongly suggest that each Eu(III) ion is coordinated to three PyTri arms through a ninecoordination mode. This work provides a N-donor extractant that can operate at high acidity for minor actinide partitioning and implicates a promising approach for transforming poor extractants into superior ones.

Closure of the Mott gap and formation of a superthermal metal in the Fröhlich-type nonequilibrium polaron Bose-Einstein condensate in UO2+x Conradson, S.; Durakiewicz, T.; Tayal, A.; Andersson, D.; Bagus, P.; Baldinozzi, G.; Bishop, A.; Boland, K.; Bradley, J.; Byler, D.; Clark, D.; Conradson, D.; Espinosa-Faller, F.; Gilbertson, S. M.; Kas, J.; Kozimor, S.; Kvashnina, K.; Lezama-Pacheco, J.; Martucci, M.; Nordlund, D.; Rehr, J.; Rodriguez, G.; Seidler, G.; Valdez, J.;