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Optically anisotropic materials are sought after for tailoring the polarization of light. Recently, colossal optical anisotropy (Δn = 2.1) was reported in a quasi-one-dimensional chalcogenide, Sr9/8TiS3. Compared to SrTiS3, the excess Sr in Sr9/8TiS3 leads to periodic structural modulations and introduces additional electrons, which undergo charge ordering on select Ti atoms to form a highly polarizable cloud oriented along the c-axis, hence resulting in the colossal optical anisotropy. Here, further enhancement of the colossal optical anisotropy to Δn = 2.5 in Sr8/7TiS3 is reported through control over the periodicity of the atomic-scale modulations. The role of structural modulations in tuning the optical properties in a series of SrxTiS3 compounds with x = [1, 9/8, 8/7, 6/5, 5/4, 4/3, 3/2] is investigated using density-functional-theory (DFT) calculations. The structural modulations arise from various stacking sequences of face-sharing TiS6 octahedra and twist-distorted trigonal prisms and are found to be thermodynamically stable for 1 < x < 1.5. As x increases, an indirect-to-direct band gap transition is predicted for x ≥ 8/7 along with an increased occupancy of Ti-dz2 states. Together, these two factors result in a theoretically predicted maximum birefringence of Δn = 2.5 for Sr8/7TiS3. Single crystals of Sr8/7TiS3 were grown using a molten-salt flux method. Single-crystal X-ray diffraction measurements confirm the presence of long-range order with a periodicity corresponding to Sr8/7TiS3, which is further corroborated by atomic-scale observations using scanning transmission electron microscopy. Polarization-resolved Fourier-transform infrared spectroscopy of Sr8/7TiS3 crystals shows Δn ≈ 2.5, in excellent agreement with the theoretical predictions. Overall, these findings demonstrate the compositional tunability of optical properties in SrxTiS3 compounds by control over atomic scale modulations and suggest that similar strategies could be extended to other compounds having modulated structures. 

Electrocatalytic nitrogen reduction (eNRR) offers a green pathway for NH3 production from N2 and H2O under ambient conditions. Transition metal oxynitrides (TMOxNy) are among the most promising catalysts but face challenges in achieving high yield and faradaic efficiency (FE). This work develops a hybrid WOxNy/WO3 catalyst with a unique heterogeneous interfacial complexion (HIC) structure. This design enables in situ generation and delivery of highly active hydrogen atoms (H*) in acidic electrolytes, promoting nitrogen hydrogenation and formation of nitrogen vacancies (Nv) on the WOxNy surface. This significantly enhances the selectivity of eNRR for NH3 synthesis while suppressing hydrogen evolution reaction (HER). A simple two-step fabrication process—microwave hydrothermal growth followed by plasma-assisted surface nitridation—was developed to fabricate the designed catalyst electrode, achieving an NH3 yield of 3.2 × 10-10 mol·cm-2·s-1 with 40.1% FE, outperforming most TMN/TMOxNy electrocatalysts. Multiple control experiments confirm that the eNRR follows a HIC-enhanced Mars-van Krevelen (MvK) mechanism. 

Abstract Noncollinear ferroic materials are sought after as testbeds to explore the intimate connections between topology and symmetry, which result in electronic, optical, and magnetic functionalities not observed in collinear ferroic materials. For example, ferroaxial materials have rotational structural distortions that break mirror symmetry and induce chirality. When ferroaxial order is coupled with ferroelectricity arising from a broken inversion symmetry, it offers the prospect of electric‐field‐control of the ferroaxial distortions and opens up new tunable functionalities. However, chiral multiferroics, especially ones stable at room temperature, are rare. A strain‐stabilized, room‐temperature chiral multiferroic phase in single crystals of BaTiS₃is reported here. Using first‐principles calculations, the stabilization of this multiferroic phase havingP6₃space group for biaxial tensile strains exceeding 1.5% applied on the basalab‐plane of the room temperatureP6₃cmphase of BaTiS₃is predicted. The chiral multiferroic phase is characterized by rotational distortions of TiS₆octahedra around the longc‐axis and polar displacement of Ti atoms along thec‐axis. The ferroaxial and ferroelectric distortions and their domains inP6₃‐BaTiS₃are directly resolved using atomic resolution scanning transmission electron microscopy. Landau‐based phenomenological modeling predicts a strong coupling between the ferroelectric and the ferroaxial order makingP6₃‐BaTiS₃an attractive test bed for achieving electric‐field‐control of chirality. 

Supported noble metal catalysts, ubiquitous in chemical technology, often undergo dynamic transformations between reduced and oxidized states—which influence the metal nuclearities, oxidation states, and catalytic properties. 

Abstract Porous carbons are the active materials of choice for supercapacitor applications because of their power capability, long-term cycle stability, and wide operating temperatures. However, the development of carbon active materials with improved physicochemical and electrochemical properties is generally carried out via time-consuming and cost-ineffective experimental processes. In this regard, machine-learning technology provides a data-driven approach to examine previously reported research works to find the critical features for developing ideal carbon materials for supercapacitors. Here, we report the design of a machine-learning-derived activation strategy that uses sodium amide and cross-linked polymer precursors to synthesize highly porous carbons (i.e., with specific surface areas > 4000 m²/g). Tuning the pore size and oxygen content of the carbonaceous materials, we report a highly porous carbon-base electrode with 0.7 mg/cm²of electrode mass loading that exhibits a high specific capacitance of 610 F/g in 1 M H₂SO₄. This result approaches the specific capacitance of a porous carbon electrode predicted by the machine learning approach. We also investigate the charge storage mechanism and electrolyte transport properties via step potential electrochemical spectroscopy and quasielastic neutron scattering measurements. 

A review highlights improvements in synthesizing and stabilizing multielement nanoparticles.