Duck Young Chung

Instead of infinite tellurium chains, LaCu _x Te ₂ intrinsically forms a statistically disordered collinear arrangement of monotelluride and oligotelluride species, yielding semiconducting transport and quasi-linear magnetoresistance at low temperatures.

CsPbBr3 single-crystal perovskites have emerged as promising room-temperature radiation detectors due to their high energy resolution, balanced charge transport, and low-cost crystal growth. However, long-term stability under high electric fields remains a key challenge, driven by ion migration and interfacial electrochemical degradation. This work examines degradation mechanisms in CsPbBr3 detectors and evaluates organic and inorganic encapsulation strategies to mitigate environmental ingress and suppress interfacial reactions. While organic coatings such as paraffin wax extend operational lifetime under continuous bias, inorganic Al2O3 encapsulation via atomic layer deposition enables stable high-field operation with improved spectral performance, providing practical pathways toward reliable perovskite-based γ-ray detectors.

The relationship between local coordination, framework connectivity, and lattice scattering, electronic structure, and quantum transport in complex pnictides remains poorly understood. Here, we show that Cu–As polyhedral architecture provides a structural route to tuning scattering and quantum magnetotransport in Ba–Cu–As pnictide single crystals. The clearest example is BaCu ₄ As ₂ , which undergoes a first-order transition near 225 K from a trigonal to a triclinic structure. This symmetry lowering converts the Cu–As framework into a more distorted mixed-coordination network and is accompanied by a sharp resistive anomaly, thermal hysteresis, heat-capacity feature, Hall-response changes, and reconstruction of the low-temperature electronic structure. High-field measurements further reveal light carriers associated with small three-dimensional Fermi pockets in the reconstructed phase. A broader comparison with Ba ₂ Cu _18−x As ₁₀ , BaCu ₈ As ₄ , BaCu ₆ As ₂ , and BaCu ₂ As ₂ shows that the characteristic electron–phonon scattering scale extracted from Bloch–Grüneisen fits follows the dimensionality and connectivity of the Cu–As polyhedral networks. BaCu ₈ As ₄ , a three-dimensional mixed-coordination framework, additionally exhibits low-field magnetoconductance consistent with weak-antilocalization-like behavior and symmetry-indicator evidence suggestive of nontrivial topology. These results underscore the Ba–Cu–As family as a platform in which Cu coordination, framework dimensionality, and metal or pnictogen bonding provide chemical handles for controlling metallic scattering, Fermi-surface reconstruction, and quantum magnetotransport.

Methods of elucidating the mechanisms of fast-ion conduction in solid-state materials are pivotal for advancements in energy technologies such as batteries, fuel cells, sensors, and supercapacitors. In this study, we examine the ionic conduction pathways in single crystal Sr Cl 2 , which is a fast-ion conductor above 900 K, using four-dimensional quasielastic neutron scattering (4D-QENS). We explore both coherent and incoherent neutron scattering at temperatures above the transition temperature into the superionic phase to explore the correlated motion of hopping anions. Refinements of the incoherent QENS yield residence times and jump probabilities between lattice sites in good agreement with previous studies, confirming that ionic hopping along nearest-neighbor directions is the most probable conduction pathway. However, the coherent QENS reveals evidence of de Gennes narrowing, indicating the importance of ionic correlations in the conduction mechanism. This highlights the need for improvements both in the theory of ionic transport in fluorite compounds and the modeling of coherent 4D-QENS in single crystals.

Understanding how unusual oxidation states influence material properties is important for both fundamental science and energy applications. AgSnSe2 is particularly intriguing because it stabilizes the rare and long-debated Sn3+ oxidation state, whose true existence and role have remained enigmatic for many years. In this work, we employ X-ray photoelectron spectroscopy, Mössbauer spectroscopy, and X-ray absorption spectroscopy to directly probe the oxidation state of Sn and its evolution under chemical substitution. All experimental evidence consistently confirms the presence of Sn in the +3 oxidation state in AgSnSe2. Complementary density functional theory calculations further corroborate this assignment. By substituting Sn with Sb, we systematically control the electronic state and its impact on the material’s physical properties. At low Sb concentrations, AgSnSe2 retains superconductivity with a transition temperature of ~5 K, while increasing Sb content deterministically drives a metallic-to-semiconducting transition through progressive suppression of superconductivity. Spectroscopic analyses show that Sb substitution provides deterministic control of the Sn oxidation state, evolving from a uniform +3 configuration in AgSnSe2 to a mixed +2/+4 valence-skipping regime at higher Sb levels, thereby establishing a direct chemical handle over the material’s electronic phase. This tunability demonstrates that the Sn oxidation state in AgSnSe2 can be precisely engineered through Sb substitution, enabling controlled electronic phase transitions and establishing AgSnSe2 as a promising platform for quantum and energy-related applications.

We describe a compositionally guided structural evolution within a stoichiometrically conserved framework, BaSbQ ₃ (Q = Te _{1− x} S _x ), where each value of x gives rise to a distinct phase. The fundamental building blocks, A ₁ (BaSbSTe ₂ ) and B _n (Ba _n Sb _n S _{n −1} Te _{2 n +1} ), were composed of modular double rocksalt slabs stacked with functional polytelluride zigzag chains, with each phase differing only in the size and assembly of these blocks. Ten compounds were synthesized that maintained a coherent chemical identity that arose from this isovalent, isoelectronic substitution of Te and S. We envision that the phase formation at a molecular level unfolds in stages of extension, termination, and assembly and propose a design concept of “anionic disparity,” where phase homologies and polytelluride hierarchical networks can be controlled by leveraging differences in anion electron affinity and sizes.

Perovskite materials have recently attracted significant attention for hard X-ray and gamma-ray detection. Cherenkov light generated by fast electrons due to gamma-ray interaction with the material can be used to provide fast timing information. Here, we report Geant4 simulation results of Cherenkov photon generation, transport, and detection within perovskite CsPbBr3. The Cherenkov photon yield, energy spectrum and temporal distribution are investigated under different gamma-ray energy deposition within CsPbBr3. CsPbBr3 has a similar Cherenkov photon yield as of TlBr that has demonstrated fast-timing capability based on Cherenkov light. The effect of crystal volume, surface finish and SiPM photon detection efficiency on the Cherenkov detection is also discussed. This work provides insights into Cherenkov processes of CsPbBr3.

Iron-based superconductors exhibit various magnetic and electronic phases that are highly sensitive to structural and chemical modifications. Elucidating the origins of these phases remains a central challenge. Here, using neutron and x-ray diffraction, we uncover a universal phase diagram that identifies disorder as a hidden tuning parameter governing these phase transitions. By analyzing nine hole-doped phase diagrams, we observe the emergence of a double-Q tetragonal magnetic phase in proximity to ideal FeAs₄ tetrahedral configurations, thereby demonstrating a strong link between bond-angle stabilization and magnetic transitions. Beyond stabilizing the double-Q phase, atomic disorder also influences charge doping and magnetic anisotropy. We further observe similar scaling behavior of the transition temperatures of the double-Q and the more prevalent orthorhombic single-Q magnetic phases, evidencing a unified origin of structural and magnetic properties linked to itinerant nesting instability. Our findings establish a comprehensive basis for understanding how chemical disorder, charge doping, and structural features collectively shape the magnetic and superconducting properties of iron-based superconductors.

The functionality of materials is intrinsically linked to their structures, an axiom encapsulated in the principle of structure-property relationships. The pinnacle of materials design is the tailoring of its structure for a specific function, which requires the ability of rational synthesis and the development of synthesis science. This idea, however, remains elusive for the synthesis of complex extended solids. A major obstacle is the difficulty in using established chemical principles selectively to control reaction paths and favor certain structural patterns over numerous other possible results. In this context, we are developing a synthesis science approach that facilitates the control of the structure and bonding to create new structures. This is achieved by employing a two-component flux consisting of mixed hydroxides and halides as the reaction medium. This enables reaction conditions that allow better control of the structure dimensionality and composition by manipulating the temperature and solvent basicity (via the flux component ratio). We demonstrate the efficacy of this method in controlling their structural motifs to arrive at 23 unreported compositions and 6 unique structure types. These materials are expected to exhibit a broad range of properties, from metallic to semiconducting, with calculations suggesting the potential for emergent phenomena such as Dirac semimetals. The reaction paths afforded by these mixed fluxes establish a direct correlation between the synthetic variables and properties, providing significant insight into a broadly applicable approach for new materials.