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Small-angle x-ray scattering experiments conducted with compositionally asymmetric low molar mass poly(isoprene)-b-poly(lactide) diblock copolymers reveal an extraordinary thermal history dependence. The development of distinct periodic crystalline or aperiodic quasicrystalline states depends on how specimens are cooled from the disordered state to temperatures below the order-disorder transition temperature. Whereas direct cooling leads to the formation of documented morphologies, rapidly quenched samples that are then heated from low temperature form the hexagonal C14 and cubic C15 Laves phases commonly found in metal alloys. Self-consistent mean-field theory calculations show that these, and other associated Frank-Kasper phases, have nearly degenerate free energies, suggesting that processing history drives the material into long-lived metastable states defined by self-assembled particles with discrete populations of volumes and polyhedral shapes.

Charge density wave (CDW) correlations have been shown to universally exist in cuprate superconductors. However, their nature at high fields inferred from nuclear magnetic resonance is distinct from that measured with x-ray scattering at zero and low fields. We combined a pulsed magnet with an x-ray free-electron laser to characterize the CDW in YBa2Cu3O6.67 via x-ray scattering in fields of up to 28 tesla. While the zero-field CDW order, which develops at temperatures below ~150 kelvin, is essentially two dimensional, at lower temperature and beyond 15 tesla, another three-dimensionally ordered CDW emerges. The field-induced CDW appears around the zero-field superconducting transition temperature; in contrast, the incommensurate in-plane ordering vector is field-independent. This implies that the two forms of CDW and high-temperature superconductivity are intimately linked.

Ordered intermetallic nanoparticles are promising electrocatalysts with enhanced activity and durability for the oxygen-reduction reaction (ORR) in proton-exchange membrane fuel cells (PEMFCs). The ordered phase is generally identified based on the existence of superlattice ordering peaks in powder X-ray diffraction (PXRD). However, after employing a widely used postsynthesis annealing treatment, we have found that claims of “ordered” catalysts were possibly/likely mixed phases of ordered intermetallics and disordered solid solutions. Here, we employed in situ heating, synchrotron-based, X-ray diffraction to quantitatively investigate the impact of a variety of annealing conditions on the degree of ordering of large ensembles of Pt₃Co nanoparticles. Monte Carlo simulations suggest that Pt₃Co nanoparticles have a lower order–disorder phase transition (ODPT) temperature relative to the bulk counterpart. Furthermore, we employed microscopic-level in situ heating electron microscopy to directly visualize the morphological changes and the formation of both fully and partially ordered nanoparticles at the atomic scale. In general, a higher degree of ordering leads to more active and durable electrocatalysts. The annealed Pt₃Co/C with an optimal degree of ordering exhibited significantly enhanced durability, relative to the disordered counterpart, in practical membrane electrode assembly (MEA) measurements. The results highlight the importance of understanding the annealing process to maximize the degree of ordering in intermetallics to optimize electrocatalytic activity.

Many-body localization (MBL), the disorder-induced localization of interacting particles, signals a breakdown of conventional thermodynamics because MBL systems do not thermalize and show nonergodic time evolution. We experimentally observed this nonergodic evolution for interacting fermions in a one-dimensional quasirandom optical lattice and identified the MBL transition through the relaxation dynamics of an initially prepared charge density wave. For sufficiently weak disorder, the time evolution appears ergodic and thermalizing, erasing all initial ordering, whereas above a critical disorder strength, a substantial portion of the initial ordering persists. The critical disorder value shows a distinctive dependence on the interaction strength, which is in agreement with numerical simulations. Our experiment paves the way to further detailed studies of MBL, such as in noncorrelated disorder or higher dimensions.

Tourmalines form the most important boron rock-forming minerals on Earth. They belong to the cyclosilicates with a structure that may be regarded as a three-dimensional framework of octahedra ZO6 that encompass columns of structural \"islands\" made of XO9, YO6, BO3, and TO4 polyhedra. The overall structure of tourmaline is a result of short-range and long-range constraints resulting, respectively on the charge and size of ions. In this study, published data are reviewed and analyzed to achieve a synthesis of relevant experimental results and to construct a crystal-chemical model for describing tourmalines and their compositional miscibility over different length scales. Order-disorder substitution reactions involving cations and anions are controlled by short-range structural constraints, whereas order-disorder intracrystalline reaction involving only cations are controlled by long-range structural constraints. The chemical affinity of a certain cation to a specific structural site of the tourmaline structure has been established on the basis of structural data and crystal-chemical considerations. This has direct implications for the tourmaline nomenclature, as well as on petrogenetic and provenance information. Some assumptions behind the classification scheme of tourmaline have been reformulated, revealing major agreement and significant improvements compared to earlier proposed scheme.

Relaxor ferroelectrics were discovered almost 50 years ago among the complex oxides with perovskite structure. In recent years this field of research has experienced a revival of interest. In this paper we review the progress achieved. We consider the crystal structure including quenched compositional disorder and polar nanoregions (PNR), the phase transitions including compositional order-disorder transition, transition to nonergodic (probably spherical cluster glass) state and to ferroelectric phase. We discuss the lattice dynamics and the peculiar (especially dielectric) relaxation in relaxors. Modern theoretical models for the mechanisms of PNR formation and freezing into nonergodic glassy state are also presented.

Neutrino oscillations have become well-known phenomena; the measurements of neutrino mixing angles and mass squared differences are continuously improving. Future oscillation experiments will eventually determine the remaining unknown neutrino parameters, namely, the mass ordering, normal or inverted, and the CP-violating phase. On the other hand, the absolute mass scale of neutrinos could be probed by cosmological observations, single beta decay as well as by neutrinoless double beta decay experiments. Furthermore, the last one may shed light on the nature of neutrinos, Dirac or Majorana, by measuring the effective Majorana mass of neutrinos. However, the neutrino mass generation mechanism remains unknown. A well-motivated phenomenological approach to search for new physics, in the neutrino sector, is that of non-standard interactions. In this short review, the current constraints in this picture, as well as the perspectives from future experiments, are discussed.

Understanding the mineralogy of exoplanets is essential for unraveling their interior structures, dynamics, and evolution. For large super‐Earths, the post‐post spinel Mg2SiO4 ${\\text{Mg}}_{2}{\\text{SiO}}_{4}$, one of the major mantle phases, may undergo the order‐disorder transition (ODT) at high temperatures. However, the ODT phase boundary of Mg2SiO4 ${\\text{Mg}}_{2}{\\text{SiO}}_{4}$ has not been rigorously constrained. Additionally, fundamental thermodynamic properties of the disordered Mg2SiO4 ${\\text{Mg}}_{2}{\\text{SiO}}_{4}$ remain poorly investigated. Here, we develop a unified machine learning potential (MLP) for Mg2SiO4 ${\\text{Mg}}_{2}{\\text{SiO}}_{4}$ of ab initio accuracy under super‐Earth mantle conditions. With the efficient MLP, we extensively calculate the free energy of post‐post spinel Mg2SiO4 ${\\text{Mg}}_{2}{\\text{SiO}}_{4}$ via the thermodynamic integration method. The results are used to constrain the ODT phase boundary. Furthermore, we report the P‐V‐T equation of state and Grüneisen parameters for post‐post spinel Mg2SiO4 ${\\text{Mg}}_{2}{\\text{SiO}}_{4}$ across various degrees of disorder. These thermodynamic properties are further applied to update the adiabatic thermal profiles and the mass‐radius relation of super‐Earths.

Above 2 GPa the phase diagram of water simplifies considerably and exhibits only two solid phases up to 60 GPa, ice VII and ice VIII. The two phases are related to each other by hydrogen ordering, with the oxygen sublattice being essentially the same. Here we present neutron diffraction data to 15 GPa which reveal that the rate of hydrogen ordering at the ice VII–VIII transition decreases strongly with pressure to reach timescales of minutes at 10 GPa. Surprisingly, the ordering process becomes more rapid again upon further compression. We show that such an unusual change in transition rate can be explained by a slowing down of the rotational dynamics of water molecules with a simultaneous increase of translational motion of hydrogen under pressure, as previously suspected. The observed cross-over in the hydrogen dynamics in ice is likely the origin of various hitherto unexplained anomalies of ice VII in the 10–15 GPa range reported by Raman spectroscopy, X-ray diffraction, and proton conductivity.

The order-disorder transition (ODT) of A 2 B 2 O 7 compounds obtained enormous attention owing to the potential application for thermal barrier coating (TBC) design. In this work, the influence of ODT on the mechanical and thermophysical properties of dual-phase A 2 B 2 O 7 high-entropy ceramics was investigated by substituting Ce 4+ and Hf 4+ with different ionic radii on B-sites (Zr 4+ ). The X-ray diffraction (XRD), Raman, and transmission electron microscopy (TEM) results show that r A 3 + / r B 4 + = 1.47 is the critical value of ODT phase boundary with different doping B-site ion contents, and the energy dispersive spectroscopy (EDS) results further indicate the uniform distribution of elements. Interestingly, owing to the high intrinsic disorder derived from high-entropy effect, the A 2 B 2 O 7 high-entropy ceramics exhibit unreduced modulus ( E 0 ≈ 230 GPa) and enhanced mechanical properties ( HV ≈ 10 GPa, K IC ≈ 2.3 MPa·m 0.5 ). A 2 B 2 O 7 high-entropy ceramics exhibit excellent thermal stability with relatively high thermal expansion coefficients (TECs) (Hf0.25, 11.20×10 −6 K −1 , 1000 °C). Moreover, the matching calculation implied that the ODT further enhances the phonon scattering coefficient, leading to a relatively lower thermal conductivity of (La 0.25 Eu 0.25 Gd 0.25 Yb 0.25 ) 2 (Zr 0.85 Ce 0.15 ) 2 O 7 (1.48–1.51 W/(m·K), 100–500 °C) compared with other components. This present work provides a novel composition design principle for high-entropy ceramics, as well as a material selection rule for high-temperature insulation applications.