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Van der Waals (vdW) magnets offer unique opportunities for exploring magnetism in the 2D limit. Metal–organic magnets (MOM) are of particular interest as the functionalisation of organic ligands can control their physical properties. Here, we demonstrate tuning of mechanical and magnetic function of a noncollinear vdW ferromagnet, NiCl2(btd) (btd = 2,1,3-benzothiadiazole), through creating solid-solutions with the oxygen-substituted analogue ligand 2,1,3-benzoxadiazole (bod). We synthesise NiCl2(btd)1−x(bod)x up to x = 0.33, above which we find mixtures primarily composed of 1D NiCl2(bod)2. Magnetometry reveals bod incorporation reduces the coercivity significantly (up to 60%), without altering the ordering temperatures. High pressure synchrotron diffraction measurements up to 0.4 GPa demonstrate that the stiffest axis is the b axis, through the Ni–N–(O/S)–N–Ni bonds, and the softest is the interlayer direction. Doping with bod fine-tunes this compressibility, softening the layers, but stiffening the interlayer axis. This demonstrates that substitution of organic ligands in vdW MOMs can be used to realise targeted magnetic and mechanical properties. [ABSTRACT FROM AUTHOR]

The substitution of atoms with molecular building blocks to form hybrid organic–inorganic networks has been an important research theme for several decades. ABX3 molecular perovskites (MolPs) are a subclass of hybrid networks, adopting the perovskite structure with cationic and anionic molecules on the A-site and X-site. MolPs such as ((CH3)2NH2)Zn(HCOO)3 or ((n-C3H7)4N)Mn(C2N3)3 show a range of fascinating structure–chemical properties, including temperature-driven phase transitions that include a change of polarity as interesting for ferroelectrics, pressure-driven order–disorder phase transitions as interesting for barocaloric solid-state refrigeration, and most recently, melting-behaviour before decomposition with subsequent glass formation after cooling. In this feature article, we take a more personal perspective, overviewing the field's current state and outlining future directions. We start by comparing the MolPs' structural chemistry with their inorganic parents, a comparison that helps us identify opportunities for material design. After discussing the MolPs' potential as barocalorics, ferroelectrics, and in the area of glasses, we outline some challenges that lie ahead. Beyond their relevance as a hybrid analogue of inorganic perovskites, we find that MolPs' chemical parameter space provides exciting opportunities for systematically developing design guidelines for functional materials. [ABSTRACT FROM AUTHOR]

Eutectic systems design requires an in-depth understanding of their solid–liquid equilibria (SLE). Modeling SLE in eutectic systems has as prerequisites, the melting properties and activity coefficients of components in the liquid phase. Thus, due to the unavailable melting properties of thermally unstable substances, it is impossible to estimate their activity coefficients from experimental SLE data and model the SLE phase diagram of their eutectic systems. Here, we evaluate the activity coefficients of thermally unstable constituents in the liquid phase, which were calculated independent of their melting properties by correlating the SLE data of their cocrystals. Differential scanning calorimetry and powder x-ray diffraction were employed to obtain the SLE phase diagram of three eutectic systems, i.e., tetramethylammonium chloride/catechol, tetraethylammonium chloride/catechol, and betaine/catechol systems, and identify the formation of nine cocrystals. The non-random, two-liquid equation was used to calculate the activity coefficients of the components in the liquid phase. The substantial negative deviation from ideality in the three studied systems indicated strong hydrogen bonding interactions in the liquid solution. Furthermore, modeling ion–ion interactions in eutectic systems containing ionic constituents is of utmost importance for understanding their nonideality. [ABSTRACT FROM AUTHOR]

Ternary nitride semiconductors are rapidly emerging as a promising class of materials for energy conversion applications, offering an appealing combination of strong light absorption in the visible range, desirable charge transport characteristics, and good chemical stability. In this work, it is shown that finite‐temperature lattice dynamics in CuTaN2 – a prototypical ternary nitride displaying particularly strong visible light absorption – exhibit a pronounced anharmonic character that plays an essential role in defining its macroscopic optoelectronic and thermal properties. Low‐frequency vibrational modes that are Raman‐inactive from symmetry considerations of the average crystal structure and unstable in harmonic phonon calculations are found to appear as intensive Raman features near room temperature. The atomic contributions to the anharmonic vibrations are characterized by combining Raman measurements with molecular dynamics and density functional theory calculations. This analysis reveals that anharmonic lattice dynamics have large ramifications on the fundamental properties of this compound, resulting in uniaxial negative thermal expansion and the opening of its bandgap to a near‐optimal value for solar energy harvesting. The atomic‐level understanding of anharmonic lattice dynamics, as well as the finding that they strongly influence key properties of this semiconductor at room temperature, have important implications for design of new functional materials, especially within the emerging class of ternary nitride semiconductors. [ABSTRACT FROM AUTHOR]

Coordination polymer (CP) glasses have recently emerged as a new glass state. Given the young state of the field, the discovery of concepts that guide the synthesis of CP glasses with targeted thermal and macroscopic properties is at the center of ongoing research. In our work, we draw inspiration from research on inorganic glasses, investigating the impact of Li(C2N3) as a modifier on the thermal properties of the new molecular perovskite [(C3H7)3N(C4H9)]Mn(C2N3)3 (with [C2N3]− = dicyanamide, DCA). We derive the phase diagram and show that Li(C2N3) and [(C3H7)3N(C4H9)]Mn(C2N3)3 form a eutectic mixture, in which the melting temperature is decreased by 30 K. Additionally, for the eutectic mixture at xLiDCA ≈ 0.4, a CP glass forms under slow cooling, opening interesting pathways for scalable synthesis routes of CP glasses. Given the virtually unlimited parameter space of hybrid modifiers, they will play a major role in the future to alter the glass' properties where the availability of rigorously derived phase diagrams will be important to identify material class overarching trends. [ABSTRACT FROM AUTHOR]

In the article "The Critical Role of Anharmonic Lattice Dynamics for Macroscopic Properties of the Visible Light Absorbing Nitride Semiconductor CuTaN2," researchers Omer Yaffe, Ian D. Sharp, David A. Egger, and their colleagues investigate the impact of anharmonic vibrational effects on the properties of the nitride semiconductor CuTaN2. They find that these dynamic structural characteristics significantly influence the compound's bandgap, resulting in an optimal value for solar energy harvesting. The study sheds light on the importance of anharmonic lattice dynamics in understanding and manipulating the properties of materials for renewable energy applications. [Extracted from the article]

Van der Waals (vdW) magnets offer unique opportunities for exploring magnetism in the 2D limit. Metal–organic magnets (MOM) are of particular interest as the functionalisation of organic ligands can control their physical properties. Here, we demonstrate tuning of mechanical and magnetic function of a noncollinear vdW ferromagnet, NiCl2(btd) (btd = 2,1,3-benzothiadiazole), through creating solid-solutions with the oxygen-substituted analogue ligand 2,1,3-benzoxadiazole (bod). We synthesise NiCl2(btd)1−x(bod)x up to x = 0.33, above which we find mixtures primarily composed of 1D NiCl2(bod)2. Magnetometry reveals bod incorporation reduces the coercivity significantly (up to 60%), without altering the ordering temperatures. High pressure synchrotron diffraction measurements up to 0.4 GPa demonstrate that the stiffest axis is the b axis, through the Ni–N–(O/S)–N–Ni bonds, and the softest is the interlayer direction. Doping with bod fine-tunes this compressibility, softening the layers, but stiffening the interlayer axis. This demonstrates that substitution of organic ligands in vdW MOMs can be used to realise targeted magnetic and mechanical properties. [ABSTRACT FROM AUTHOR]

Ternary nitride semiconductors are rapidly emerging as a promising class of materials for energy conversion applications, offering an appealing combination of strong light absorption in the visible range, desirable charge transport characteristics, and good chemical stability. In this work, it is shown that finite‐temperature lattice dynamics in CuTaN2 – a prototypical ternary nitride displaying particularly strong visible light absorption – exhibit a pronounced anharmonic character that plays an essential role in defining its macroscopic optoelectronic and thermal properties. Low‐frequency vibrational modes that are Raman‐inactive from symmetry considerations of the average crystal structure and unstable in harmonic phonon calculations are found to appear as intensive Raman features near room temperature. The atomic contributions to the anharmonic vibrations are characterized by combining Raman measurements with molecular dynamics and density functional theory calculations. This analysis reveals that anharmonic lattice dynamics have large ramifications on the fundamental properties of this compound, resulting in uniaxial negative thermal expansion and the opening of its bandgap to a near‐optimal value for solar energy harvesting. The atomic‐level understanding of anharmonic lattice dynamics, as well as the finding that they strongly influence key properties of this semiconductor at room temperature, have important implications for design of new functional materials, especially within the emerging class of ternary nitride semiconductors. [ABSTRACT FROM AUTHOR]

Van der Waals (vdW) magnets offer unique opportunities for exploring magnetism in the 2D limit. Metal-organic magnets (MOM) are of particular interest as the functionalisation of organic ligands can control their physical properties. Here, we demonstrate tuning of mechanical and magnetic function of a noncollinear vdW ferromagnet, NiCl 2 (btd) (btd = 2,1,3-benzothiadiazole), through creating solid-solutions with the oxygen-substituted analogue ligand 2,1,3-benzoxadiazole (bod). We synthesise NiCl 2 (btd) 1- x (bod) x up to x = 0.33, above which we find mixtures primarily composed of 1D NiCl 2 (bod) 2 . Magnetometry reveals bod incorporation reduces the coercivity significantly (up to 60%), without altering the ordering temperatures. High pressure synchrotron diffraction measurements up to 0.4 GPa demonstrate that the stiffest axis is the b axis, through the Ni-N-(O/S)-N-Ni bonds, and the softest is the interlayer direction. Doping with bod fine-tunes this compressibility, softening the layers, but stiffening the interlayer axis. This demonstrates that substitution of organic ligands in vdW MOMs can be used to realise targeted magnetic and mechanical properties.

The substitution of atoms with molecular building blocks to form hybrid organic-inorganic networks has been an important research theme for several decades. ABX 3 molecular perovskites (MolPs) are a subclass of hybrid networks, adopting the perovskite structure with cationic and anionic molecules on the A-site and X-site. MolPs such as ((CH 3 ) 2 NH 2 )Zn(HCOO) 3 or (( n -C 3 H 7 ) 4 N)Mn(C 2 N 3 ) 3 show a range of fascinating structure-chemical properties, including temperature-driven phase transitions that include a change of polarity as interesting for ferroelectrics, pressure-driven order-disorder phase transitions as interesting for barocaloric solid-state refrigeration, and most recently, melting-behaviour before decomposition with subsequent glass formation after cooling. In this feature article, we take a more personal perspective, overviewing the field's current state and outlining future directions. We start by comparing the MolPs' structural chemistry with their inorganic parents, a comparison that helps us identify opportunities for material design. After discussing the MolPs' potential as barocalorics, ferroelectrics, and in the area of glasses, we outline some challenges that lie ahead. Beyond their relevance as a hybrid analogue of inorganic perovskites, we find that MolPs' chemical parameter space provides exciting opportunities for systematically developing design guidelines for functional materials.