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1. Dimensional Reduction Guides Electronic Structure Evolution in the A _n Cu _4–n SnS ₄ Semiconductor Series

   https://doi.org/10.1021/jacs.5c07366  

   Viti, Michael A; Li, Zhi; Wolverton, Christopher; Kanatzidis, Mercouri G (August 2025, Journal of the American Chemical Society)

   The search for new functional materials with tunable properties remains a central challenge in chemistry, particularly for applications in energy and electronics. In this work, we present a framework for predictive crystal design in alkali metal chalcogenides that enables controlled dimensional reduction of a parent covalent motif, yielding a broad range of electronic structures, which systematically evolve from one parent to the other. We present 11 new members of the AnCu4–nSnS4 family (A = alkali metal; n = 0–4), which reduce the three-dimensional (3D) covalent network of Cu4SnS4 into various 3D, 2D, 1D, and 0D [Cu4–nSnS4]n− motifs through the substitution of Cu with alkali metals of various radii. The end members of the family set the range in achievable band gaps at 0.99 eV for fully covalent Cu4SnS4 (n = 0) and 3.38 eV for K4SnS4 (n = 4) with 0D [SnS4]n− tetrahedra. As the dimensionality of [Cu4–nSnS4]n− systematically reduces within AnCu4–nSnS4 (n = 1–3), a stepwise increase in band gap energy occurs through a gradual decrease in the energy of the valence band maximum and an increase in the conduction band minimum, with an increase in the effective masses of charge carriers. Furthermore, irrespective of the alkali metal, the thermal stability decreases with decreasing [Cu4–nSnS4]n− dimensionality within the quaternary members. Most importantly, we demonstrate that predictable crystal structure and property evolution for a given composition space is possible by deriving a general formula based on substituting the covalent metals of a parent structure with alkali metals. 

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2. Rise and fall of Landau’s quasiparticles while approaching the Mott transition

   https://doi.org/10.1038/s41467-021-21741-z  

   Pustogow, Andrej; Saito, Yohei; Löhle, Anja; Sanz Alonso, Miriam; Kawamoto, Atsushi; Dobrosavljević, Vladimir; Dressel, Martin; Fratini, Simone (December 2021, Nature Communications)

   null (Ed.)

   Abstract Landau suggested that the low-temperature properties of metals can be understood in terms of long-lived quasiparticles with all complex interactions included in Fermi-liquid parameters, such as the effective mass m ⋆ . Despite its wide applicability, electronic transport in bad or strange metals and unconventional superconductors is controversially discussed towards a possible collapse of the quasiparticle concept. Here we explore the electrodynamic response of correlated metals at half filling for varying correlation strength upon approaching a Mott insulator. We reveal persistent Fermi-liquid behavior with pronounced quadratic dependences of the optical scattering rate on temperature and frequency, along with a puzzling elastic contribution to relaxation. The strong increase of the resistivity beyond the Ioffe–Regel–Mott limit is accompanied by a ‘displaced Drude peak’ in the optical conductivity. Our results, supported by a theoretical model for the optical response, demonstrate the emergence of a bad metal from resilient quasiparticles that are subject to dynamical localization and dissolve near the Mott transition. 

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3. Synthesis of Hybrid Nanocrystalline Alloys by Mechanical Bonding through High‐Pressure Torsion

   https://doi.org/10.1002/adem.201901289  

   Han, Jae-Kyung; Herndon, Taylor; Jang, Jae-il; Langdon, Terence_G; Kawasaki, Megumi (January 2020, Advanced Engineering Materials)

   An overview of the mechanical bonding of dissimilar bulk engineering metals through high‐pressure torsion (HPT) processing at room temperature is described in this Review. A recently developed procedure of mechanical bonding involves the application of conventional HPT processing to alternately stacked two or more disks of dissimilar metals. A macroscale microstructural evolution involves the concept of making tribomaterials and, for some dissimilar metal combinations, microscale microstructural changes demonstrate the synthesis of metal matrix nanocomposites (MMNCs) through the nucleation of nanoscale intermetallic compounds within the nanostructured metal matrix. Further straining by HPT during mechanical bonding provides an opportunity to introduce limited amorphous phases and a bulk metastable state. The mechanically bonded nanostructured hybrid alloys exhibit an exceptionally high specific strength and an enhanced plasticity. These experimental findings suggest a potential for using mechanical bonding for simply and expeditiously fabricating a wide range of new alloy systems by HPT processing. 

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4. Enzymatic synthesis of supported CdS quantum dot/reduced graphene oxide photocatalysts

   https://doi.org/10.1039/C9GC00097F  

   Spangler, Leah C.; Cline, Joseph P.; Sakizadeh, John D.; Kiely, Christopher J.; McIntosh, Steven (July 2019, Green Chemistry)

   Photocatalysis is an attractive, sustainable, and potentially low-cost route to capture solar energy as fuel. However, current photocatalytic materials synthesis routes are not easily scaled-up to the magnitude required to impact our energy consumption due to both economic and environmental concerns. While the elements utilized are often earth abundant, typical synthetic routes utilize organic solvents at elevated temperatures with relatively expensive precursors. Herein, we demonstrate the fully biomineralized synthesis of a quantum confined CdS/reduced graphene oxide (CdS/rGO) photocatalyst catalyzed by the single enzyme cystathionine γ-lyase (CSE). The synthesis is performed at pH 9 in a buffered aqueous solution, under ambient conditions, and utilizes the low-cost precursors Cd acetate, l -cysteine, graphene oxide, and a poly- l -lysine linker molecule. CSE actively decomposes l -cysteine to generate reactive HS − in aqueous solution at pH 9. Careful selection and control of the synthesis conditions enable both reduction of graphene oxide to rGO, and control over the mean CdS nanocrystal size. The CdS is conjugated to the rGO via a poly- l -lysine crosslinker molecule introduced during rGO formation. The completed CdS/rGO photocatalyst is capable of producing H 2 , without the aid of a noble metal co-catalyst, at a rate of 550 μmol h −1 g −1 for an optimized CdS/rGO ratio. This rate is double that measured for unsupported CdS and is comparable to CdS/rGO photocatalysts produced using more typical chemical synthesis routes. Single enzyme biomineralization by CSE can produce a range of metal chalcogenides without altering the enzyme or benign approach, making this an easily adaptable procedure for the sustainable production of a wide variety of important photocatalyst systems. 

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5. Identification of optimally stable nanocluster geometries via mathematical optimization and density-functional theory

   https://doi.org/10.1039/c9me00108e  

   Isenberg, Natalie M.; Taylor, Michael G.; Yan, Zihao; Hanselman, Christopher L.; Mpourmpakis, Giannis; Gounaris, Chrysanthos E. (January 2020, Molecular Systems Design & Engineering)

   null (Ed.)

   Small nanoparticles, a.k.a. nanoclusters, of transition metals have been studied extensively for a wide range of applications due to their highly tunable properties dependent on size, structure, and composition. For these small particles, there has been considerable effort towards theoretically predicting what is the most energetically favorable arrangement of atoms when forming a nanocluster. In this work, we develop a computational framework that couples density-functional theory calculations with mathematical optimization modeling to identify highly stable, mono-metallic transition metal nanoclusters of various sizes. This is accomplished by devising and solving a rigorous mathematical optimization model that maximizes a general cohesive energy function to obtain nanocluster structures of provably maximal cohesiveness. We then utilize density-functional theory calculations and error term regression to identify model corrections that are necessary to account with better accuracy for different transition metals. This allows us to encode metal-specific, analytical functions for cohesive energy into a mathematical optimization-based framework that can accurately predict which nanocluster geometries will be most cohesive according to density-functional theory calculations. We employ our framework in the context of Ag, Au, Cu, Pd and Pt, and we present sequences of highly cohesive nanoclusters for sizes up to 100 atoms, yielding insights into structures that might be experimentally accessible and/or structures that could be used as model nanoclusters for further study. 

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