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1. Predicting failure in disordered solids from structural metrics

   https://doi.org/10.1103/PhysRevMaterials.00.003600  

   Richard, D; Ozawa, M; Patinet, S; Stanifer, E; Shang, B; Ridout, S; Xu, B; Zhang, G; Morse, P; Barrat, J-L; et al (November 2020, Physical review materials)

   null (Ed.)

   Amorphous solids lack long-range order. Therefore identifying structural defects—akin to dislocations in crystalline solids—that carry plastic flow in these systems remains a daunting challenge. By comparing many different structural indicators in computational models of glasses, under a variety of conditions we carefully assess which of these indicators are able to robustly identify the structural defects responsible for plastic flow in amorphous solids. We further demonstrate that the density of defects changes as a function of material preparation and strain in a manner that is highly correlated with the macroscopic material response. Our work represents an important step towards predicting how and when an amorphous solid will fail from its microscopic structure. 

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2. Scaling of relaxation and excess entropy in plastically deformed amorphous solids

   https://doi.org/10.1073/pnas.2000698117  

   Galloway, K. Lawrence; Ma, Xiaoguang; Keim, Nathan C.; Jerolmack, Douglas J.; Yodh, Arjun G.; Arratia, Paulo E. (May 2020, Proceedings of the National Academy of Sciences)

   When stressed sufficiently, solid materials yield and deform plastically via reorganization of microscopic constituents. Indeed, it is possible to alter the microstructure of materials by judicious application of stress, an empirical process utilized in practice to enhance the mechanical properties of metals. Understanding the interdependence of plastic flow and microscopic structure in these nonequilibrium states, however, remains a major challenge. Here, we experimentally investigate this relationship, between the relaxation dynamics and microscopic structure of disordered colloidal solids during plastic deformation. We apply oscillatory shear to solid colloidal monolayers and study their particle trajectories as a function of shear rate in the plastic regime. Under these circumstances, the strain rate, the relaxation rate associated with plastic flow, and the sample microscopic structure oscillate together, but with different phases. Interestingly, the experiments reveal that the relaxation rate associated with plastic flow at time t is correlated with the strain rate and sample microscopic structure measured at earlier and later times, respectively. The relaxation rate, in this nonstationary condition, exhibits power-law, shear-thinning behavior and scales exponentially with sample excess entropy. Thus, measurement of sample static structure (excess entropy) provides insight about both strain rate and constituent rearrangement dynamics in the sample at earlier times. 

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3. High frequency atomic tunneling yields ultralow and glass-like thermal conductivity in chalcogenide single crystals

   https://doi.org/10.1038/s41467-020-19872-w  

   Sun, Bo; Niu, Shanyuan; Hermann, Raphael P.; Moon, Jaeyun; Shulumba, Nina; Page, Katharine; Zhao, Boyang; Thind, Arashdeep S.; Mahalingam, Krishnamurthy; Milam-Guerrero, JoAnna; et al (December 2020, Nature Communications)

   null (Ed.)

   Abstract Crystalline solids exhibiting glass-like thermal conductivity have attracted substantial attention both for fundamental interest and applications such as thermoelectrics. In most crystals, the competition of phonon scattering by anharmonic interactions and crystalline imperfections leads to a non-monotonic trend of thermal conductivity with temperature. Defect-free crystals that exhibit the glassy trend of low thermal conductivity with a monotonic increase with temperature are desirable because they are intrinsically thermally insulating while retaining useful properties of perfect crystals. However, this behavior is rare, and its microscopic origin remains unclear. Here, we report the observation of ultralow and glass-like thermal conductivity in a hexagonal perovskite chalcogenide single crystal, BaTiS 3 , despite its highly symmetric and simple primitive cell. Elastic and inelastic scattering measurements reveal the quantum mechanical origin of this unusual trend. A two-level atomic tunneling system exists in a shallow double-well potential of the Ti atom and is of sufficiently high frequency to scatter heat-carrying phonons up to room temperature. While atomic tunneling has been invoked to explain the low-temperature thermal conductivity of solids for decades, our study establishes the presence of sub-THz frequency tunneling systems even in high-quality, electrically insulating single crystals, leading to anomalous transport properties well above cryogenic temperatures. 

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4. Hyperuniformity and phase enrichment in vortex and rotor assemblies

   https://doi.org/10.1038/s41467-022-28375-9  

   Oppenheimer, Naomi; Stein, David B.; Zion, Matan Yah Ben; Shelley, Michael J. (February 2022, Nature Communications)

   Abstract Ensembles of particles rotating in a two-dimensional fluid can exhibit chaotic dynamics yet develop signatures of hidden order. Such rotors are found in the natural world spanning vastly disparate length scales — from the rotor proteins in cellular membranes to models of atmospheric dynamics. Here we show that an initially random distribution of either driven rotors in a viscous membrane, or ideal vortices with minute perturbations, spontaneously self assemble into a distinct arrangement. Despite arising from drastically different physics, these systems share a Hamiltonian structure that sets geometrical conservation laws resulting in prominent structural states. We find that the rotationally invariant interactions isotropically suppress long-wavelength fluctuations — a hallmark of a disordered hyperuniform material. With increasing area fraction, the system orders into a hexagonal lattice. In mixtures of two co-rotating populations, the stronger population will gain order from the other and both will become phase enriched. Finally, we show that classical 2D point vortex systems arise as exact limits of the experimentally accessible microscopic membrane rotors, yielding a new system through which to study topological defects. 

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5. Effect of composition and thermal history on deformation behavior and cluster connections in model bulk metallic glasses

   https://doi.org/10.1038/s41598-022-20938-6  

   Neuber, Nico; Sadeghilaridjani, Maryam; Ghodki, Nandita; Gross, Oliver; Adam, Bastian; Ruschel, Lucas; Frey, Maximilian; Muskeri, Saideep; Blankenburg, Malte; Gallino, Isabella; et al (October 2022, Scientific Reports)

   Abstract The compositional dependence and influence of relaxation state on the deformation behavior of a Pt–Pd-based bulk metallic glasses model system was investigated, where platinum is systematically replaced by topologically equivalent palladium atoms. The hardness and modulus increased with rising Pd content as well as by annealing below the glass transition temperature. Decreasing strain-rate sensitivity and increasing serration length are observed in nano indentation with increase in Pd content as well as thermal relaxation. Micro-pillar compression for alloys with different Pt/Pd ratios validated the greater tendency for shear localization and brittle behavior of the Pd-rich alloys. Based on total scattering experiments with synchrotron X-ray radiation, a correlation between the increase in stiffer 3-atom cluster connections and reduction in strain-rate sensitivity, as a measure of ductility, with Pd content and thermal history is suggested. 

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