Rebecca W. Smaha

Nitride materials have many important technological applications, yet they remain underexplored compared to other classes of compounds, as reflected by the smaller number of reports in databases and literature. The primary reason for this is the difficulty of synthesizing nitrides, which must outcompete energetically stable molecular N ₂ and oxide compounds. As a result, bulk synthesis of nitrides often requires high pressure or corrosive fluxes in addition to oxygen-free conditions. We present our perspective on the metathesis technique as an accessible method for synthesizing nitrides at or below atmospheric pressure for the broader chemistry community. To highlight the advantages of this synthesis approach, we also review traditional methods for bulk nitride synthesis, including high pressure techniques, sodium and halide fluxes, and gas- and liquid-ammonia-based routes. We provide a brief tutorial on metathesis reactions including tips and tricks to help researchers get started. Finally, we discuss the future outlook for metathesis reactions, with an opportunity for precise structural selection during nitride synthesis through the controlled formation of stable and metastable polymorphs within the multidimensional potential-energy landscape of material nucleation and growth.

A metal selenide resulting from a mixed-site Fe/Cu solid solution was synthesized, Ba6Cu24-xFexSe27, in the composition range between Ba6Cu11Fe13Se27 (x = 13; 1) to Ba6Cu6Fe18Se27 (x = 18; 2). Its structure is derived from a parent mineral, i.e., naturally occurring bartonite K6Fe24-xS26(S,Cl), with the bartonite structure type in the I4/mmm space group and the general formula Ba6M24Se27 (M = Fe, Cu). In contrast to known low-dimensional iron selenides consisting of FeSe4 tetrahedra arranged in chains or layers, its structure is composed of a three-dimensional (3D) anionic framework of ∞3[M24Se26]10–. This 3D framework is constructed from fluorite-type clusters that link via shared-vertices. Open channels are filled by charge-compensating Ba(II) cations and isolated Se2– anions in all crystallographic directions. At the compositional end limits of the solid solution synthesized here, the Fe cations possess an average oxidation state between +2.32 in 1 and +2 in 2. Magnetic measurements reveal that 2 exhibits ferrimagnetic order at least up to 350 K, with a secondary magnetic transition at ∼170 K. In summary, these results demonstrate the utilization of a mixed Cu/Fe solid solution to stabilize a 3D metal–selenide framework, hence opening the door to wider investigations of their intriguing magnetic properties.

Hexagonal perovskite oxides with 12R stacking host well-separated face-sharing octahedral metal trimers with short metal–metal distances, leading in some cases to large degrees of magnetic frustration and cluster magnetism. Introducing magnetic ions in proximity to these trimers can influence the degree of frustration and cluster magnetism, but the extent to which the magnetism can be tuned by varying neighboring metal cations remains an open question. In this work, we test the impacts of using Nd in proximity to Mn trimers in the hexagonal perovskite 12R-Ba4NdMn3O12−γ. Given this stoichiometry, Nd should assume the 4+ oxidation state with a spin state of S = 1, which would be the first realization of Nd4+ in an oxide environment. Through detailed bulk magnetic, X-ray absorption spectroscopic, and powder neutron diffraction (PND) measurements, we find that Nd4+ is realized in this material, but there is also partial reduction to Nd3+, which is charge-balanced by O vacancies. Magnetometry measurements indicate an antiferromagnetic ordering temperature TN ≈ 16 K, and PND measurements reveal a surprising collinear antiferromagnetic structure with magnetic space group Pc2/m (no. 10.49 in BNS notation), which has not previously been seen in this class of materials. Our results represent a comprehensive analysis of the structural, electronic, and magnetic properties of 12R-Ba4NdMn3O12−γ, showing the first observation of partial Nd4+ in an oxide, and demonstrating that this structural class can host a broad range of magnetic structures which are not easily predicted based on compositional trends.

Experimental synthesis of theoretically predicted materials with controlled elemental coordination environments can lead to the realization of useful properties, such as facile ion transport or ferroelectric switching. Among such materials are ternary nitrides in the Mg−W−N composition space, where several stable and metastable compounds have been predicted and synthesized recently in bulk and film forms. Here, we report for the first time on the bulk synthesis of Mg₃WN₄ in a wurtzite-derived crystal structure via a solid-state metathesis reaction. In situ synchrotron powder X-ray diffraction shows how the ion exchange proceeds from Li₆WN₄ + MgCl₂ precursors to Mg₃WN₄ + LiCl products, with the reaction starting slowly near 380 °C and completing by 600 °C, including the presence of a competing disordered rocksalt-derived phase (Mg,W)N above 440 °C. The follow-up ex situ powder synthesis at 400 °C for 0.5 h with 10% excess MgCl₂ reveals the cation-ordered nature of the wurtzite-derived Mg₃WN₄ structure with polar symmetry confirmed by second-harmonic generation measurements. Optical absorption spectra, chemical composition analysis, and electron microscopy imaging suggest that bulk Mg₃WN₄ obtained via metathesis reaction is prone to defect formation. Overall, this study shows that selective ex situ synthesis of the phase-pure ternary nitrides, informed by in situ measurements, is possible by carefully controlling the thermal budget of the reaction and paves the way toward property characterization of the Mg₃WN₄ wurtzite-derived material.

Transition-metal nitrides in η-carbide-type structures exhibit unusual bonding motifs and proximity to magnetic instabilities. Yet they remain unexplored in thin-film form due to the difficulty of stabilizing nitrogen-poor ternaries among competing phases. Here, we report the thin-film synthesis and phase-stability mapping of the η-nitride systems Fe–W–N and Fe–Mo–N. Amorphous Fe–M–N (M = W, Mo) combinatorial libraries deposited by reactive cosputtering crystallize upon rapid thermal annealing, enabling systematic identification of synthesis windows as a function of composition and annealing temperature. Using laboratory powder X-ray diffraction and synchrotron grazing incidence wide-angle X-ray scattering, we establish that Fe₃Mo₃N-based η-carbide phases form over a substantially broader compositional and thermal range than W-based compositions, where η structures are stabilized only when the films are Fe-rich. These trends are rationalized using mixed chemical-potential vs composition phase diagrams that capture the narrow nitrogen chemical-potential stability of η-nitrides. Magnetic measurements reveal that ferromagnetism is induced in Fe-rich Fe_3.54Mo_2.46N with a small exchange-bias-like response that is absent in Fe₃W₃N-based compositions, highlighting the sensitivity of magnetic behavior to modest deviations from stoichiometry. This work establishes practical thin-film synthesis routes for η-nitride materials and demonstrates how composition can be tuned to access emergent magnetic phenomena in these complex nitrides.

Antiperovskite nitrides with the general formula M3AN have attracted significant attention due to their tunable electronic and magnetic properties. Among them are many cobalt-based compounds predicted to exhibit high thermodynamic stability and intriguing magnetic behavior. Here, we report the synthesis and magnetic characterization of epitaxial Co3ZnN thin films grown by radio frequency sputtering on SrTiO3 (STO) and MgO substrates. X-ray diffraction confirms phase-pure (00l)-oriented films with cube-on-cube epitaxy on STO, with a c-lattice parameter of 3.752 Å. Magnetic measurements reveal clear hysteresis at 2 K with a coercive field of ∼0.11 T and a small net moment of 0.108 μB/f.u., suggesting either a canted antiferromagnetic (AFM) or ferrimagnetic (FiM) configuration. Temperature-dependent magnetization measurements show a transition near 25 K, with strong AFM interactions with Curie–Weiss temperature (Θ) = −80.13 K. Complementary density functional theory and Monte Carlo simulations indicate a ferromagnetic (FM) ground state, with the FM–AFM energy difference decreasing systematically with increasing supercell size, consistent with competition between FM and AFM/FiM interactions. These results highlight Co3ZnN as a magnetically complex antiperovskite nitride with competing exchange interactions.

Synthetic variables can have an outsized influence on the crystal structure and magnetic properties of a material, particularly those of quantum materials. In this work, we investigate the impact of synthesis under a magnetic field (magnetosynthesis) on the crystal structure and magnetic properties of several Cu²⁺ (S = 1/2)-based materials with antiferromagnetic interactions and varying levels of magnetic frustration, from simple antiferromagnets to a quantum spin liquid. Here, we develop methods to apply small (0.09-0.37 T) magnetic fields during low-temperature hydrothermal, evaporative, and rehydration syntheses of the simple antiferromagnet CuCl₂·2H₂O, the canted antiferromagnet (Cu,Zn)₃Cl₄(OH)₂·2H₂O, the frustrated and canted antiferromagnet atacamite Cu₂(OH)₃Cl, and the highly frustrated quantum spin liquid herbertsmithite Cu₃Zn(OH)₆Cl₂. We report the first single-crystal X-ray structural determination of the Cu₃Cl₄(OH)₂·2H₂O structure type and probe the stability of this phase both experimentally and computationally. Atacamite Cu₂(OH)₃Cl synthesized under a 0.19 T field experiences a 0.15 K (∼3%) decrease in its Néel transition temperature. This result suggests that magnetosynthesis with small applied fields may have a very subtle influence upon the magnetic properties of moderately magnetically frustrated 3d materials.

Ternary nitride alloys based on wurtzite AlN are a promising platform to realize functional materials, particularly ferroelectrics and optical emitters, that can smoothly integrate with conventional microelectronics. Here, a strategic design is presented to enable multifunctional materials by substituting multiple elements into AlN to create quaternary nitride alloys. By combining computational predictions and combinatorial thin film synthesis, the phase diagram of these quaternary Al–Sc–Gd–N alloys (or pseudo‐ternary heterostructural AlN–ScN–GdN alloys) is successfully predicted as a function of effective temperature, and we experimentally grow thin films for the first time. It is revealed that crystallizes in a wurtzite‐derived structure for , consistent with the calculated phase diagram. The computational investigation explores whether co‐substitution induces cooperative effects on these alloys' piezoelectric and ferroelectric properties, finding that it is beneficial for reducing the polarization switching barrier. We calculate that thin films should display ferroelectric switching. This is supported by our experimental measurements of a high optical bandgap, enhanced piezoelectric coefficient, and a change in the calculated polarization switching mechanism, and we achieve preliminary ferroelectric switching that experimentally realizes the prediction. Overall, our work sets the foundation toward quaternary wurtzite‐nitride‐based multifunctional materials, including piezoelectrics, ferroelectrics, and possibly even multiferroics.

The advantageous properties of (pseudo)­halide argyrodite ion conductors of the formula Li₆PS₅ X (X = Cl^–, Br^–, I^–, CN^–) have motivated extensive studies of their structure-transport relationships, particularly as they pertain to the role of atomic site disorder. The argyrodite structure can accommodate additional configurational complexity to promote ion transport via extended three-anion site mixing and the potential for orientational disorder of molecular anions. In this work, we explore a ternary anion system including the cyanide anion, expanding site disorder and introducing dipolar orientations as an additional degree of freedom. We prepared the series Li₆PS₅(CN)_1–x Br _x , in which the dipolar cyanide anions are systematically diluted with bromide. We find that anion disorder, as determined by synchrotron and neutron diffraction and quantified by configurational entropy (S _config), is correlated with lowered activation barriers and increased lithium ion conductivity. We propose that S _config describes the electrostatic heterogeneity of the Li environments, flattening the energetic landscape for ion transport. While anion substitution strongly impacts the activation barrier for transport, the temperature-independent Arrhenius prefactor does not follow the same trend. Through heat-capacity measurements of attempt frequency and deconvolution of terms within the prefactor, we rationalize the apparent decoupling of activation energy and prefactor to strong cyanide-lithium interactions that increase the entropy of migration. Together, these results expand the structure–property relationships in the argyrodite family to encompass multiple facets of disorder and the subsequent impact on lithium ion transport.