Chemistry of Materials最新文献

Hybrid molecular ferroelectrics necessitate switchable components, either organic or inorganic, capable of altering polarity under a reversing electric field. Isothiocyanate (NCS^–) ligands display such behavior through nonlinear coordination with metal ions. Homoleptic complexes of lanthanide ions exhibit variable coordination numbers, which can be controlled by the size of the counterions. We harnessed these properties to achieve polar order and ferroelectricity in hybrid [Er(III)(NCS)_x]^3-x complexes. The incorporation of triethyl methylammonium (TEMA) cations yields the complex [TEMA]₄[Er(NCS)₇], which exhibits polarity at low temperatures with a Curie temperature (T_c) of 203 K. Notably, the use of bulkier and more rigid ethyltriphenyl phosphonium (ETPP) cations gave a room-temperature stable ferroelectric complex [ETPP]₃[Er(NCS)₆]. In contrast, flexible cations, such as tripropylmethylammonium (TPMA), tributylmethylammonium (TBMA), and tetraethyl phosphonium (TEP) ions, yielded only centrosymmetric complexes. The polar structural symmetries in [TEMA]₄[Er(NCS)₇] and [ETPP]₃[Er(NCS)₆] are attributed to pronounced distortions of the Er(III)-NCS coordination, driven by the rigid nature of organic counterions. The ferroelectric measurements on [ETPP]₃[Er(NCS)₆] gave a saturation polarization (P_s) of 1.6 μC cm^–2. Remarkably, [ETPP]₃[Er(NCS)₆] exhibits a high piezoelectric charge coefficient (d₃₃) of 22.7 pCN^–1 and an electrostrictive coefficient (Q₃₃) of 4.11 m⁴C^–2, enabling its application for piezoelectric energy harvesting.

Photopolymerization-driven additive manufacturing (AM) is a well-established technique to generate polymeric 3D structures with both high resolution and formation in complex geometries. Recent approaches focus on AM techniques that enable multiproperty architectures using wavelength orthogonal photochemistry. Herein, a dual-cure, single-vat resin was developed, based on the radical photopolymerization of a thiol-methacrylate monomer system containing covalently bound chalcone moieties as dimerizable cross-linkers. Thermo-mechanical properties were spatially and systematically controlled via the wavelength-selective [2 + 2] cycloaddition reaction of the chalcone groups. Reaction kinetics were studied with infrared and ultraviolet–visible spectroscopy to ensure sequence-dependent λ-orthogonality during the two-stage illumination process. 3D-structures were fabricated by dynamic light processing (DLP), imprinting, and two-photon lithography (TPL). In particular, the ability to excite both the radical photoinitiator and the chalcone groups separately with TPL in high spatial resolution enabled the production of multifunctional microstructures and represents a versatile concept for the fabrication of soft active devices along various length scales.

Diamond, with its extraordinary physical and electrical properties, has emerged as a transformative material for next-generation electronics. Its ultrawide bandgap, superior thermal conductivity, high carrier mobility, and excellent mechanical characteristics uniquely position it to address the limitations of traditional semiconductor materials. However, realizing the full potential of diamond in electronic applications requires overcoming significant challenges in its synthesis scalability, defect and dislocation control, and advanced device fabrication. In this Perspective, we discuss strategies and recent advancements in the synthesis of single-crystalline diamond in wafer scales as well as the reduction of defects and dislocations. The development of new diamond morphologies is also reviewed, underscoring their potential to modify properties and broaden application domains. Furthermore, we highlight the progress in engineering diamond-based electronic devices, particularly, field-effect transistors (FETs). Innovations in surface conductivity optimization and the realization of stable, normally off-device operation have enhanced the performance and reliability of diamond devices. Key areas for future research are proposed throughout, offering insights into the opportunities and challenges that remain in diamond synthesis and harnessing diamond’s full potential for next-generation electronic applications.

In this paper, we build on previous work to characterize a phase with stoichiometry Li₃(OH)₂Br existing between ∼225 and ∼275 °C in the LiBr-LiOH phase diagram. Diffraction studies indicate that the phase takes a hexagonal unit cell, and theoretical modeling is used to suggest a possible crystal structure. Nuclear magnetic resonance spectroscopy and electrochemical impedance spectroscopy measurements demonstrate excellent lithium-ion dynamics in this phase, with an ionic conductivity of 0.12 S cm^–1 at 250 °C. Initial attempts to stabilize this phase at room temperature through quenching were not successful. Instead, a metastable state demonstrating poor ionic conductivity is found to form. This is an important consideration for the synthesis of Li₂OHBr solid-state electrolytes (also found in the LiBr-LiOH phase diagram) which are synthesized by cooling through phase fields containing Li₃(OH)₂Br, and are hence susceptible to these impurities.

A major drawback to the implementation of metal–organic frameworks (MOFs) on scale is the vast quantity of organic solvents, typically N,N-dimethylformamide (DMF), required to synthesize even small quantities of MOF under traditional dilute (∼0.01 M) solvothermal conditions. High-concentration solvothermal methods offer the opportunity to synthesize MOFs with minimal solvent use but are currently limited by a lack of understanding of how dynamic self-assembly operates under these conditions. Herein, we systematically investigate the crystallization of a series of MOFs under variable concentration (0.01–0.2 M) and temperature (80–160 °C) conditions based on the dilute synthesis of the canonical framework Mg₂(dobdc) (dobdc^4– = 2,5-dioxido-1,4-terephthalate). Through this analysis, we identify controlling factors that lead to isolation of the highly photoluminescent phases Mg(DHT)(DMF)₂ (DHT = dihydroxyterephthalate) and CORN-MOF-1 (Mg) (CORN = Cornell University) or Mg₂(dobdc). Ultimately, we connect the preference for specific MOF phases to the extent of acid-catalyzed DMF hydrolysis and the competing influences of dimethylamine (Me₂NH) and formate (HCO₂^–) at high concentrations, which is likewise affected by temperature, pH, and solvent composition. We use the insights gained to synthesize the Fe, Co, Ni, and Zn analogs of CORN-MOF-1 for the first time, as well as a second series of related MOFs, CORN-MOF-6 (M) (M = Mg, Mn, Fe, Co, Ni), based on the linker 2-hydroxyterephthalic acid (H₃hbdc). Both series exhibit tunable luminescence properties based on the metal composition and crystal structure, making them potentially useful materials for optoelectronic applications. Overall, this work contributes to a clearer understanding of the factors that control MOF formation under high-concentration conditions.