Structural Evolution and Photoluminescence Quenching across the FASnI3-xBrx (x = 0-3) Perovskites.

One of the primary methods for band gap tuning in metal halide perovskites has been halide (I/Br) mixing. Despite widespread usage of this type of chemical substitution in perovskite photovoltaics, there is still little understanding of the structural impacts of halide alloying, with the assumption being the formation of ideal solid solutions. The FASnI3-xBrx (x = 0-3) family of compounds provides the first example where the assumption breaks down, as the composition space is broken into two unique regimes (x = 0-2.9; x = 2.9-3) based on their average structure with the former having a 3D and the latter having an extended 3D (pseudo 0D) structure. Pair distribution function (PDF) analyses further suggest a dynamic 5s2 lone pair expression resulting in increasing levels of off-centering of the central Sn as the Br concentration is increased. These antiferroelectric distortions indicate that even the x = 0-2.9 phase space behaves as a nonideal solid-solution on a more local scale. Solid-state NMR confirms the difference in local structure yielding greater insight into the chemical nature and local distributions of the FA+ cation. In contrast to the FAPbI3-xBrx series, a drastic photoluminescence (PL) quenching is observed with x ≥ 1.9 compounds having no observable PL. Our detailed studies attribute this quenching to structural transitions induced by the distortions of the [SnBr6] octahedra in response to stereochemically expressed lone pairs of electrons. This is confirmed through density functional theory, having a direct impact on the electronic structure.

Artificial Intelligence Driving Materials Discovery? Perspective on the Article: Scaling Deep Learning for Materials Discovery.

The discovery of new crystalline inorganic compounds-novel compositions of matter within known structure types, or even compounds with completely new crystal structures-constitutes an important goal of solid-state and materials chemistry. Some fractions of new compounds can eventually lead to new structural and functional materials that enhance the efficiency of existing technologies or even enable completely new technologies. Materials researchers eagerly welcome new approaches to the discovery of new compounds, especially those that offer the promise of accelerated success. The recent report from a group of scientists at Google who employ a combination of existing data sets, high-throughput density functional theory calculations of structural stability, and the tools of artificial intelligence and machine learning (AI/ML) to propose new compounds is an exciting advance. We examine the claims of this work here, unfortunately finding scant evidence for compounds that fulfill the trifecta of novelty, credibility, and utility. While the methods adopted in this work appear to hold promise, there is clearly a great need to incorporate domain expertise in materials synthesis and crystallography.

Magnetic tunability in tetragonal Mn-Rh-Ir-Sn inverse Heusler compounds.

Gaining control over magnetic structure has been an ongoing challenge in materials that form complex, nanoscale, and non-collinear magnetic configurations. Recently, it was predicted that tuning the ratio of the Dzyaloshinskii-Moriya interaction to the uniaxial magnetic anisotropy in tetragonal inverse Heuslers through changes in composition could allow a range of interesting magnetic states to be accessed, from simple ferrimagnetism, to helical and antiskyrmionic phases. Here, we show tunability of the magnetic phase behavior in the Mn-Rh-Sn system through Ir substitution on the Rh substructure. Iridium substitution correlates to an increase in the strength of ferromagnetic exchange couplings, at the expense of antiferromagnetic exchange couplings. However, we do not observe the complex non-collinear magnetic phases proposed previously, likely due to the extremely narrow composition window where these phases are predicted to form in a bulk sample. This work highlights the sensitivity of complex magnetic structures to stoichiometry, which makes them difficult to discover empirically.

Hybrid Iodide Perovskites of Divalent Alkaline Earth and Lanthanide Elements.

Hybrid halide perovskites AMIIX3 (A = ammonium cation, MII = divalent cation, X = Cl, Br, I) have been extensively studied but have only previously been reported for the divalent carbon group elements Ge, Sn, and Pb. While they have displayed an impressive range of optoelectronic properties, the instability of GeII and SnII and the toxicity of Pb have stimulated significant interest in finding alternatives to these carbon group-based perovskites. Here, we describe the low-temperature solid-state synthesis of five new hybrid iodide perovskites centered around divalent alkaline earth and lanthanide elements, with the general formula AMIII3 (A = methylammonium, MA; MII = Sr, Sm, Eu, and A = formamidinium, FA; MII = Sr, Eu). Structural, calorimetric, optical, photoluminescence, and magnetic properties of these materials are reported.

Rapid and Reversible Lithium Insertion in the Wadsley-Roth-Derived Phase NaNb13O33.

The development of new high-performing battery materials is critical for meeting the energy storage requirements of portable electronics and electrified transportation applications. Owing to their exceptionally high rate capabilities, high volumetric capacities, and long cycle lives, Wadsley-Roth compounds are promising anode materials for fast-charging and high-power lithium-ion batteries. Here, we present a study of the Wadsley-Roth-derived NaNb13O33 phase and examine its structure and lithium insertion behavior. Structural insights from combined neutron and synchrotron diffraction as well as solid-state nuclear magnetic resonance (NMR) are presented. Solid-state NMR, in conjunction with neutron diffraction, reveals the presence of sodium ions in perovskite A-site-like block interior sites as well as square-planar block corner sites. Through combined experimental and computational studies, the high rate performance of this anode material is demonstrated and rationalized. A gravimetric capacity of 225 mA h g-1, indicating multielectron redox of Nb, is accessible at slow cycling rates. At a high rate, 100 mA h g-1 of capacity is accessible in 3 min for micrometer-scale particles. Bond-valence mapping suggests that this high-rate performance stems from fast multichannel lithium diffusion involving octahedral block interior sites. Differential capacity analysis is used to identify optimal cycling rates for long-term performance, and an 80% capacity retention is achieved over 600 cycles with 30 min charging and discharging intervals. These initial results place NaNb13O33 within the ranks of promising new high-rate lithium-ion battery anode materials that warrant further research.

Elusive Double Perovskite Iodides: Structural, Optical, and Magnetic Properties.

Halide double perovskites [A2 MI MIII X6 ] are an important class of materials that have garnered substantial interest as non-toxic alternatives to conventional lead iodide perovskites for optoelectronic applications. While numerous studies have examined chloride and bromide double perovskites, reports of iodide double perovskites are rare, and their definitive structural characterization has not been reported. Predictive models have aided us here in the synthesis and characterization of five iodide double perovskites of general formula Cs2 NaLnI6 (Ln=Ce, Nd, Gd, Tb, Dy). The complete crystal structures, structural phase transitions, optical, photoluminescent, and magnetic properties of these compounds are reported.

Electrochemical Cycling of Redox-Active Boron Cluster-Based Materials in the Solid State.

This work demonstrates the first successful electrochemical cycling of a redox-active boron cluster-based material in the solid state. Specifically, we designed and synthesized an ether-functionalized dodecaborate cluster, B12(OCH3)12, which is the smallest redox-active building block in the B12(OR)12 family. This species can reversibly access four oxidation states in solution, ranging from a dianion to a radical cation. We show that a chemically isolated and characterized neutral [B12(OCH3)12]0 cluster can be utilized as a cathode active material in a PEO-based rechargeable all-solid-state cell with a lithium metal anode. The cell exhibits an impressive active material utilization close to 95% at C/20 rate, a high Coulombic efficiency of 96%, and reversibility, with only 4% capacity fade after 16 days of cycling. This work represents a conceptual departure in the development of redox-active components for electrochemical storage and serves as an entry point to a broader class of borane-based materials.

[2,1,3]-Benzothiadiazole-Spaced Co-Porphyrin-Based Covalent Organic Frameworks for O2 Reduction.

Designing N-coordinated porous single-atom catalysts (SACs) for the oxygen reduction reaction (ORR) is a promising approach to achieve enhanced energy conversion due to maximized atom utilization and higher activity. Here, we report two Co(II)-porphyrin/ [2,1,3]-benzothiadiazole (BTD)-based covalent organic frameworks (COFs; Co@rhm-PorBTD and Co@sql-PorBTD), which are efficient SAC systems for O2 electrocatalysis (ORR). Experimental results demonstrate that these two COFs outperform the mass activity (at 0.85 V) of commercial Pt/C (20%) by 5.8 times (Co@rhm-PorBTD) and 1.3 times (Co@sql-PorBTD), respectively. The specific activities of Co@rhm-PorBTD and Co@sql-PorBTD were found to be 10 times and 2.5 times larger than that of Pt/C, respectively. These COFs also exhibit larger power density and recycling stability in Zn-air batteries compared with a Pt/C-based air cathode. A theoretical analysis demonstrates that the combination of Co-porphyrin with two different BTD ligands affords two crystalline porous electrocatalysts having different d-band center positions, which leads to reactivity differences toward alkaline ORR. The strategy, design, and electrochemical performance of these two COFs offer a pyrolysis-free bottom-up approach that avoids the creation of random atomic sites, significant metal aggregation, or unpredictable structural features.

Human ACE2 Peptide-Attached Plasmonic-Magnetic Heterostructure for Magnetic Separation, Surface Enhanced Raman Spectroscopy Identification, and Inhibition of Different Variants of SARS-CoV-2 Infections.

The emergence of Alpha, Beta, Gamma, Delta, and Omicron variants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is responsible for several million deaths up to now. Because of the huge amount of vaccine escape mutations in the spike (S) protein for different variants, the design of material for combating SARS-CoV-2 is very important for our society. Herein, we report on the design of a human angiotensin converting enzyme 2 (ACE2) peptide-conjugated plasmonic-magnetic heterostructure, which has the capability for magnetic separation, identification via surface enhanced Raman spectroscopy (SERS), and inhibition of different variant SARS-CoV-2 infections. In this work, plasmonic-magnetic heterostructures were developed using the initial synthesis of polyethylenimine (PEI)-coated Fe3O4-based magnetic nanoparticles, and then gold nanoparticles (GNPs) were grown onto the surface of the magnetic nanoparticles. Experimental binding data between ACE2-conjugated plasmonic-magnetic heterostructures and spike-receptor-binding domain (RBD) show that the Omicron variant has maximum binding ability, and it follows Alpha < Beta < Gamma < Delta < Omicron. Our finding shows that, due to the high magnetic moment (specific magnetization 40 emu/g), bioconjugated heterostructures are capable of effective magnetic separation of pseudotyped SARS-CoV-2 bearing the Delta variant spike from an infected artificial nasal mucus fluid sample using a simple bar magnet. Experimental data show that due to the formation of huge "hot spots" in the presence of SARS-CoV-2, Raman intensity for the 4-aminothiolphenol (4-ATP) Raman reporter was enhanced sharply, which has been used for the identification of separated virus. Theoretical calculations using finite-difference time-domain (FDTD) simulation indicate that, due to the "hot spots" formation, a six orders of magnitude Raman enhancement can be observed. A concentration-dependent inhibition efficiency investigation using a HEK293T-human cell line indicates that ACE2 peptide-conjugated plasmonic-magnetic heterostructures have the capability of complete inhibition of entry of different variants and original SARS-CoV-2 pseudovirions into host cells.

Synthesis and structural properties of a 2D Zn(II) dodecahydroxy-closo-dodecaborate coordination polymer.

In this work, we discuss the synthesis and characterization of a 2D coordination polymer composed of a dianionic perhydroxylated boron cluster, [B12(OH)122-], coordinated to Zn(II)-the first example of a transition metal-coordinated [B12(OH)12]2- compound. This material was synthesized via cation exchange from the starting cesium salt and then subjected to rigorous characterization prior to and after thermal activation. Numerous techniques, including XRD, FTIR, SEM, TGA, and solid-state NMR revealed a 2D coordination polymer composed of sheets of Zn(II) ions intercalated between planes of boron clusters. The as-synthesized material was then evacuated of solvent via thermal treatment, and atomic-level changes from this transformation were elucidated through a combination of 1D and 2D solid-state NMR analyses of 11B and 1H nuclei, suggesting the full removal of coordinated solvent molecules. Evidence also suggested that [B12(OH)122-] can adjust its coordination to Zn(II) in the solid-state through hemilability of its numerous -OH ligands.

Lattice Dynamics in the NASICON NaZr2(PO4)3 Solid Electrolyte from Temperature-Dependent Neutron Diffraction, NMR, and Ab Initio Computational Studies.

Natrium super ionic conductor (NASICON) compounds form a rich and highly chemically tunable family of crystalline materials that are of widespread interest because they include exemplars with high ionic conductivity, low thermal expansion, and redox tunability. This makes them suitable candidates for applications ranging from solid-state batteries to nuclear waste storage materials. The key to an understanding of these properties, including the origins of effective cation transport and low, anisotropic (and sometimes negative) thermal expansion, lies in the lattice dynamics associated with specific details of the crystal structure. Here we closely examine the prototypical NASICON compound, NaZr2(PO4)3, and obtain detailed insights into such behavior via variable-temperature neutron diffraction and 23Na and 31P solid-state NMR studies, coupled with comprehensive density functional theory-based calculations of NMR parameters. Temperature-dependent NMR studies yield some surprising trends in the chemical shifts and the quadrupolar coupling constants that are not captured by computation unless the underlying vibrational modes of the crystal are explicitly taken into account. Furthermore, the trajectories of the sodium, zirconium, and oxygen atoms in our dynamical simulations show good qualitative agreement with the anisotropic thermal parameters obtained at higher temperatures by neutron diffraction. The work presented here widens the utility of NMR crystallography to include thermal effects as a unique probe of interesting lattice dynamics in functional materials.

Hybrid Layered Double Perovskite Halides of Transition Metals.

Hybrid layered double perovskite (HLDP) halides comprise hexacoordinated 1+ and 3+ metals in the octahedral sites within a perovskite layer and organic amine cations between the layers. Progress on such materials has hitherto been limited to compounds containing main group 3+ ions isoelectronic with PbII (such as SbIII and BiIII). Here, we report eight HLDP halides from the A2MIMIIIX8 family, where A = para-phenylenediammonium (PPDA), 1,4-butanediammonium (1,4-BDA), or 1,3-propanediammonium (1,3-PDA); MI = Cu or Ag; MIII = Ru or Mo; X = Cl or Br. The optical band gaps, which lie in the range 1.55 to 2.05 eV, are tunable according to the layer composition, but are largely independent of the spacer. Magnetic measurements carried out for (PPDA)2AgIRuIIICl8 and (PPDA)2AgIMoIIICl8 show no obvious evidence of a magnetic ordering transition. While the t2g3 MoIII compound displays Curie-Weiss behavior for a spin-only d3 ion, the t2g5 RuIII compound displays marked deviations from the Kotani theory.

Chemistry, Structure, and Function of Lone Pairs in Extended Solids.

ConspectusThe lone pair has been a known feature of the electronic structure of molecules for over 100 years. Beginning with the pioneering work of Lewis and others that was later developed into useful guidelines for predicting molecular structure, lone pairs and their steric consequences are now taught at the very earliest stages of a chemistry education. In the crystalline solid state, lone pairs have perhaps had a less visible yet equally consequential role, with a significant impact on a range of properties and functionalities. Important properties associated with s2 electron-derived lone pairs include their role in creating conditions favorable for ion transport, in the formation and correlation of local dipoles and the resulting polar behavior leading to ferroics and multiferroics, in increasing the refractive index of glass, in reducing the thermal conductivity of thermoelectric materials, and in breaking local symmetry permitting second-harmonic light generation.. In recent years, the role of the lone pair in developing the electronic structure of some topological quantum materials has also been recognized. While structural distortions due to lone pairs have traditionally been characterized through their crystallography, recent advances in scattering and spectroscopy have revealed the presence of local lone pair-driven distortions that do not correlate over long length scales. The role of these crystallographically "hidden" lone pairs, their detection, and their impact on properties have become a growing body of work in the literature. Hidden lone pairs are an effective argument for considering a role for lone pairs that goes beyond their being objects that occupy space in the coordination polyhedra of cations. This Account introduces the chemistry of lone pairs in extended crystalline solids, including a discussion of when they are stereochemically active, how they manifest in the structure, and how their chemistry can be tuned by the chemical environment around them. Eventually, all of these factors work in unison to help develop and tune properties of interest. Certain specific examples of structure-property relationships in materials that are driven by lone pair behavior are described here, including the potential impact of lone pairs on the optical and electronic properties of hybrid halide perovskite compounds that are relevant to their photovoltaic applications. We highlight the role of lone pairs in the dielectric behavior of geometrically frustrated pyrochlores, the temperature-dependent optoelectronic behavior of halide perovskites, the polar phase transitions in lead-free ferroelectric perovskites, and the compositional insulator-to-metal transition in ruthenium pyrochlores. The theme underpinning this Account is that the lone pair can be considered to be a powerful design element for a broad range of material function.

Metal-Metal Bonding as an Electrode Design Principle in the Low-Strain Cluster Compound LiScMo3O8.

Electrode materials for Li+-ion batteries require optimization along several disparate axes related to cost, performance, and sustainability. One of the important performance axes is the ability to retain structural integrity though cycles of charge/discharge. Metal-metal bonding is a distinct feature of some refractory metal oxides that has been largely underutilized in electrochemical energy storage, but that could potentially impact structural integrity. Here LiScMo3O8, a compound containing triangular clusters of metal-metal bonded Mo atoms, is studied as a potential anode material in Li+-ion batteries. Electrons inserted though lithiation are localized across rigid Mo3 triangles (rather than on individual metal ions), resulting in minimal structural change as suggested by operando diffraction. The unusual chemical bonding allows this compound to be cycled with Mo atoms below a formally +4 valence state, resulting in an acceptable voltage regime that is appropriate for an anode material. Several characterization methods including potentiometric entropy measurements indicate two-phase regions, which are attributed through extensive first-principles modeling to Li+ ordering. This study of LiScMo3O8 provides valuable insights for design principles for structural motifs that stably and reversibly permit Li+ (de)insertion.

Tolerance Factor for Stabilizing 3D Hybrid Halide Perovskitoids Using Linear Diammonium Cations.

Three-dimensional (3D) halide perovskites have attracted enormous research interest, but the choice of the A-site cations is limited by the Goldschmidt tolerance factor. In order to accommodate cations that lie outside the acceptable range of the tolerance factor, low-dimensional structures usually form. To maintain the favorable 3D connection, the links among the metal-halide octahedra need to be rearranged to fit the large cations. This can result in a departure from the proper corner-sharing perovskite architectures and lead to distinctly different perovskitoid motifs with edge- and face-sharing. In this work, we report four new 3D bromide perovskitoids incorporating linear organic diammonium cations, A'Pb2Br6 (A' is a +2 cation). We propose a rule that can guide the further expansion of this class of compounds, analogous to the notion of Goldschmidt tolerance factor widely adopted for 3D AMX3 perovskites. The fundamental building blocks in A'Pb2Br6 consist of two edge-shared octahedra, which are then connected by corner-sharing to form a 3D network. Different compounds adopt different structural motifs, which can be transformed from one to another by symmetry operations. Electronic structure calculations suggest that they are direct bandgap semiconductors, with relatively large band dispersions created by octahedra connected by corner-sharing. They exhibit similar electronic band structures and dynamic lattice characteristics to the regular 3D AMX3 perovskites. Structures with smaller Pb-Br-Pb angles and larger octahedra distortion exhibit broad photoluminescence at room temperature. The emerging structure-property relationships in these 3D perovskitoids set the foundation for designing and investigating these compounds for a variety of optoelectronic applications.

Subtle Local Structural Details Influence Ion Transport in Glassy Li+ Thiophosphate Solid Electrolytes.

Many of the promising, high-performing solid electrolytes for lithium-ion batteries are amorphous or contain an amorphous component, particularly in the Li thiophosphate Li2S-P2S5 (LPS) compositional series. An explicit study of the local structure in four samples of ostensibly identically prepared 70Li2S-30P2S5 glass reveals substantial variation in the ratio between the two main local structural units in this system: PS43- tetrahedra and P2S74- corner-sharing tetrahedral pairs. Local structural and compositional probes including Raman spectroscopy, X-ray photoelectron spectroscopy, and X-ray pair distribution function analysis are employed here to arrive at a consistent description of the relative amounts of isolated tetrahedral units, which vary by 13% across the samples measured. This local structure variation translates to differences in the activation energies measured by electrochemical impedance spectroscopy in these samples, such that the higher concentration of isolated tetrahedra corresponds to a lower activation energy. The measured temperature-dependent ionic conductivity data are compared to conductivity results across the literature reported on the same compositions, highlighting the variation in the measured activation energy for nominally identical samples. These findings have implications for the critical need to play close attention to the local structure in solid electrolytes, particularly in systems that are glasses or glass ceramics, or those that comprise any amorphous contribution.

AB2X6 Compounds and the Stabilization of Trirutile Oxides.

The properties of crystalline materials tend to be strongly correlated with their structures, and the prediction of crystal structure from only the composition is a coveted goal in the field of inorganic materials. However, even for the simplest compositions, such prediction relies on a complex network of interactions, including atomic or ionic radii, ionicity, electronegativity, position in the periodic table, and magnetism, to name only a few important parameters. We focus here on the AB2X6 (AB2O6 and AB2F6) composition space with the specific goal of finding new oxide compounds in the trirutile family, which is known for unusual one-dimensional (1D) antiferromagnetic behavior. Through machine learning methods, we develop an understanding of how geometric and bonding constraints determine the crystallization of compounds in the trirutile structure as opposed to other ternary structures in this space. In combination with density functional theory (DFT) calculations, we predict 16 previously unreported candidate trirutile oxides. We successfully prepare one of these and show it forms in the disordered rutile structure, under the preparation conditions adopted here.

Tunable Broad Light Emission from 3D "Hollow" Bromide Perovskites through Defect Engineering.

Hybrid halide perovskites consisting of corner-sharing metal halide octahedra and small cuboctahedral cages filled with counter cations have proven to be prominent candidates for many high-performance optoelectronic devices. The stability limits of their three-dimensional perovskite framework are defined by the size range of the cations present in the cages of the structure. In some cases, the stability of the perovskite-type structure can be extended even when the counterions violate the size and shape requirements, as is the case in the so-called "hollow" perovskites. In this work, we engineered a new family of 3D highly defective yet crystalline "hollow" bromide perovskites with general formula (FA)1-x(en)x(Pb)1-0.7x(Br)3-0.4x (FA = formamidinium (FA+), en = ethylenediammonium (en2+), x = 0-0.44). Pair distribution function analysis shed light on the local structural coherence, revealing a wide distribution of Pb-Pb distances in the crystal structure as a consequence of the Pb/Br-deficient nature and en inclusion in the lattice. By manipulating the number of Pb/Br vacancies, we finely tune the optical properties of the pristine FAPbBr3 by blue shifting the band gap from 2.20 to 2.60 eV for the x = 0.42 en sample. A most unexpected outcome was that at x> 0.33 en incorporation, the material exhibits strong broad light emission (1% photoluminescence quantum yield (PLQY)) that is maintained after exposure to air for more than a year. This is the first example of strong broad light emission from a 3D hybrid halide perovskite, demonstrating that meticulous defect engineering is an excellent tool for customizing the optical properties of these semiconductors.

Glass Transition Temperature and Ion Binding Determine Conductivity and Lithium-Ion Transport in Polymer Electrolytes.

Polymer electrolytes with high Li+-ion conductivity provide a route toward improved safety and performance of Li+-ion batteries. However, most polymer electrolytes suffer from low ionic conduction and an even lower Li+-ion contribution to the conductivity (the transport number, t+), with the anion typically transporting over 80% of the charge. Here, we show that subtle and potentially undetected associations within a polymer electrolyte can entrain both the anion and the cation. When removed, the conductivity performance of the electrolyte can be improved by almost 2 orders of magnitude. Importantly, while some of this improvement can be attributed to a decreased glass transition temperature, Tg, the removal of the amide functional group reduces interactions between the polymer and the Li+ cations, doubling the Li+ t+ to 0.43, as measured using pulsed-field-gradient NMR. This work highlights the importance of strategic synthetic design and emphasizes the dual role of Tg and ion binding for the development of polymer electrolytes with increased total ionic conductivity and the Li+ ion contribution to it.