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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.

The stellar optoelectronic properties of metal halide perovskites provide enormous promise for next-generation optical devices with excellent conversion efficiencies and lower manufacturing costs. However, there is a long-standing ambiguity as to whether the perovskite surface/interface (e.g. structure, charge transfer or source of off-target recombination) or bulk properties are the more determining factor in device performance. Here we fabricate an array of CsPbI3 crystal and hybrid glass composites by sintering and globally visualise the property-performance landscape. Our findings reveal that the interface is the primary determinant of the crystal phases, optoelectronic quality, and stability of CsPbI3. In particular, the presence of a diffusion alloying layer is discovered to be critical for passivating surface traps, and beneficially altering the energy landscape of crystal phases. However, high-temperature sintering results in the promotion of a non-stoichiometric perovskite and excess traps at the interface, despite the short-range structure of halide is retained within the alloying layer. By shedding light on functional hetero-interfaces, our research offers the key factors for engineering high-performance perovskite devices.

Electrocatalytic synthesis under mild conditions has become increasingly important as one of the practical alternatives for industrial applications, especially for the green ammonia (NH3) industry. A properly engineered electrocatalyst plays a vital role in the realization of superior catalytic performance. Among various types of promising nanomaterials, metal-organic frameworks (MOFs) are competitive candidates for developing efficient electrocatalytic NH3 synthesis from simple nitrogen-containing molecules or ions, such as N2 and NO3-. In this review, recent advances in the development of electrocatalysts derived from MOFs for the electrosynthesis of NH3 are collected, categorized, and discussed, including their application in the N2 reduction reaction (NRR) and the NO3- reduction reaction (NO3RR). Firstly, the fundamental principles are illustrated, such as plausible mechanisms of NH3 generation from N2 and NO3-, the apparatus of corresponding electrocatalysis, parameters for evaluation of reaction efficiency, and detection methods of yielding NH3. Then, the electrocatalysts for NRR processes are discussed in detail, including pristine MOFs, MOF-hybrids, MOF-derived N-doped porous carbons, single atomic catalysts from pyrolysis of MOFs, and other MOF-related materials. Subsequently, MOF-related NO3RR processes are also listed and discussed. Finally, the existing challenges and prospects for the rational design and fabrication of electrocatalysts from MOFs for electrochemical NH3 synthesis are presented, such as the evolution of investigation methods with artificial intelligence, innovation in synthetic methods of MOF-related catalysts, advancement of characterization techniques, and extended electrocatalytic reactions.

Imines are important intermediates for synthesizing various fine chemicals, with the disadvantage of requiring the use of expensive metal-containing catalysts. We report that the dehydrogenative cross-coupling of phenylmethanol and benzylamine (or aniline) directly forms the corresponding imine with a yield of up to 98%, and water as the sole by-product, in the presence of a stoichiometric base, using carbon nanostructures as the "green" metal-free carbon catalysts with high spin concentrations, which is synthesized by C(sp2)-C(sp3) free radical coupling reactions. The catalytic mechanism is attributed to the unpaired electrons of carbon catalysts to reduce O2 to O2·-, which triggers the oxidative coupling reaction to form imines, whereas the holes in the carbon catalysts receive electrons from the amine to restore the spin states. This is supported by density functional theory calculations. This work will open up an avenue for synthesizing carbon catalysts and offer great potential for industrial applications.

Perovskite-related materials show very promising properties in many fields. Pb-free perovskites are particularly interesting, because of the toxicity of Pb. In this study, hybrid double perovskite MA2KBiCl6 (MA = methylammonium cation) was found to have interesting variable temperature behaviours. Both variable temperature single crystal X-ray diffraction, synchrotron powder diffraction, and Raman spectroscopy were conducted to reveal a rhombohedral to cubic phase transition at around 330 K and an order to disorder transition for inorganic cage below 210 K.

A combination of gas adsorption and gas breakthrough measurements show that the metal-organic framework, Al(HCOO)3 (ALF), which can be made inexpensively from commodity chemicals, exhibits excellent CO2 adsorption capacities and outstanding CO2/N2 selectivity that enable it to remove CO2 from dried CO2-containing gas streams at elevated temperatures (323 kelvin). Notably, ALF is scalable, readily pelletized, stable to SO2 and NO, and simple to regenerate. Density functional theory calculations and in situ neutron diffraction studies reveal that the preferential adsorption of CO2 is a size-selective separation that depends on the subtle difference between the kinetic diameters of CO2 and N2. The findings are supported by additional measurements, including Fourier transform infrared spectroscopy, thermogravimetric analysis, and variable temperature powder and single-crystal x-ray diffraction.

In the pursuit of urgently needed, energy dense solid-state batteries for electric vehicle and portable electronics applications, halide solid electrolytes offer a promising path forward with exceptional compatibility against high-voltage oxide electrodes, tunable ionic conductivities, and facile processing. For this family of compounds, synthesis protocols strongly affect cation site disorder and modulate Li+ mobility. In this work, we reveal the presence of a high concentration of stacking faults in the superionic conductor Li3YCl6 and demonstrate a method of controlling its Li+ conductivity by tuning the defect concentration with synthesis and heat treatments at select temperatures. Leveraging complementary insights from variable temperature synchrotron X-ray diffraction, neutron diffraction, cryogenic transmission electron microscopy, solid-state nuclear magnetic resonance, density functional theory, and electrochemical impedance spectroscopy, we identify the nature of planar defects and the role of nonstoichiometry in lowering Li+ migration barriers and increasing Li site connectivity in mechanochemically synthesized Li3YCl6. We harness paramagnetic relaxation enhancement to enable 89Y solid-state NMR and directly contrast the Y cation site disorder resulting from different preparation methods, demonstrating a potent tool for other researchers studying Y-containing compositions. With heat treatments at temperatures as low as 333 K (60 °C), we decrease the concentration of planar defects, demonstrating a simple method for tuning the Li+ conductivity. Findings from this work are expected to be generalizable to other halide solid electrolyte candidates and provide an improved understanding of defect-enabled Li+ conduction in this class of Li-ion conductors.

Lithium and sodium (Na) mixed polyanion solid electrolytes for all-solid-state batteries display some of the highest ionic conductivities reported to date. However, the effect of polyanion mixing on the ion-transport properties is still not fully understood. Here, we focus on Na1+xZr2SixP3-xO12 (0 ≤ x ≤ 3) NASICON electrolyte to elucidate the role of polyanion mixing on the Na-ion transport properties. Although NASICON is a widely investigated system, transport properties derived from experiments or theory vary by orders of magnitude. We use more than 2000 distinct ab initio-based kinetic Monte Carlo simulations to map the compositional space of NASICON over various time ranges, spatial resolutions and temperatures. Via electrochemical impedance spectroscopy measurements on samples with different sodium content, we find that the highest ionic conductivity (i.e., about 0.165 S cm-1 at 473 K) is experimentally achieved in Na3.4Zr2Si2.4P0.6O12, in line with simulations (i.e., about 0.170 S cm-1 at 473 K). The theoretical studies indicate that doped NASICON compounds (especially those with a silicon content x ≥ 2.4) can improve the Na-ion mobility compared to undoped NASICON compositions.

The guest-dependent flexibility of the pillared-layered metal-organic framework (MOF), Zn2bdc2dabco·X(guest), where guest = EtOH, DMF or benzene, has been examined by high-pressure single crystal X-ray diffraction. A pressure-induced structural phase transition is found for the EtOH- and DMF-included frameworks during compression in a hydrostatic medium of the guest species, which is dependent upon the nature and quantity of the guest in the channels. The EtOH-included material undergoes a phase transition from P4/mmm to C2/m at 0.69 GPa, which is accompanied by a change in the pore shape from square to rhombus via super-filling of the pores. The DMF-included material undergoes a guest-mediated phase transition from I4/mcm to P4/mmm at 0.33 GPa via disordering of the DMF guest. In contrast, the benzene-included framework features a structure with rhombus-shaped channels at ambient pressure and shows direct compression under hydrostatic pressure. These results demonstrate the large influence of guest molecules on the high-pressure phase behavior of flexible MOFs. Guest-mediated framework flexibility is useful for engineering MOFs with bespoke pore shapes and compressibility.

Although metal-organic frameworks (MOFs) are being widely used to derive functional nanomaterials through pyrolysis, the actual mechanisms involved remain unclear. In the limited studies to date, elemental metallic species are found to be the initial products, which limits the variety of MOF-derived nanomaterials. Here, the pyrolysis of a manganese triazolate MOF is examined carefully in terms of phase transformation, reaction pathways, and morphology evolution in different conditions. Surprisingly, the formation of metal is not detected when manganese triazolate is pyrolyzed in an oxygen-free environment. Instead, a direct transformation into nanoparticles of manganese nitride, Mn2N x embedded in N-doped graphitic carbon took place. The electrically conductive Mn2N x nanoparticles show much better air stability than bulk samples and exhibit promising electrocatalytic performance for the oxygen reduction reaction. The findings on pyrolysis mechanisms expand the potential of MOF as a precursor to derive more functional nanomaterials.

Phosphorene, monolayer or few-layer black phosphorus, exhibits fascinating anisotropic properties and shows interesting semiconducting behavior. The synthesis of phosphorene nanosheets is still a hot topic, including the shaping of its two-dimensional structure into nanoribbons or nanobelts. Here we report electrochemical unzipping of single crystalline black phosphorus into zigzag-phosphorene nanobelts, as well as nanosheets and quantum dots, via an oxygen-driven mechanism. The experimental results agree well with our theoretical calculations. The calculation for the unzipping mechanism study suggests that interstitial oxygen-pairs are the critical intermediate species for generating zigzag-phosphorene nanobelts. Although phosphorene oxidation has been reported, lengthwise cutting is hitherto unreported. Our discovery of phosphorene cut upon oxidation represents a previously unknown mechanism for the formation of various dimensions of phosphorene nanostructures, especially zigzag-phosphorene nanobelts. It opens up a way for studying the quantum effects and electronic properties of zigzag-phosphorene nanobelts.

Geometric or electronic confinement of guests inside nanoporous hosts promises to deliver unusual catalytic or opto-electronic functionality from existing materials but is challenging to obtain particularly using metastable hosts, such as metal-organic frameworks (MOFs). Reagents (e.g. precursor) may be too large for impregnation and synthesis conditions may also destroy the hosts. Here we use thermodynamic Pourbaix diagrams (favorable redox and pH conditions) to describe a general method for metal-compound guest synthesis by rationally selecting reaction agents and conditions. Specifically we demonstrate a MOF-confined RuO2 catalyst (RuO2@MOF-808-P) with exceptionally high catalytic CO oxidation below 150 °C as compared to the conventionally made SiO2-supported RuO2 (RuO2/SiO2). This can be caused by weaker interactions between CO/O and the MOF-encapsulated RuO2 surface thus avoiding adsorption-induced catalytic surface passivation. We further describe applications of the Pourbaix-enabled guest synthesis (PEGS) strategy with tutorial examples for the general synthesis of arbitrary guests (e.g. metals, oxides, hydroxides, sulfides).

Three-dimensional carbon-based structures have proven useful for tailoring material properties in structural mechanical and energy storage applications. One approach to obtain them has been by carbonization of selected metal-organic frameworks (MOFs) with catalytic metals, but this is not applicable to most common MOF structures. Here, we present a strategy to transform common MOFs, by guest inclusions and high-temperature MOF-guest interactions, into complex carbon-based, diatom-like, hierarchical structures (named for the morphological similarities with the naturally existing diatomaceous species). As an example, we introduce metal salt guests into HKUST-1-type MOFs to generate a family of carbon-based nano-diatoms with two to four levels of structural hierarchy. We report control of the morphology by simple changes in the chemistry of the MOF and guest, with implications for the formation mechanisms. We demonstrate that one of these structures has unique advantages as a fast-charging lithium-ion battery anode. The tunability of composition should enable further studies of reaction mechanisms and result in the growth of a myriad of unprecedented carbon-based structures from the enormous variety of currently available MOF-guest candidates.

We investigate the pressure-dependent mechanical behaviour of the zeolitic imidazolate framework ZIF-4 (M(im)2; M2+ = Co2+ or Zn2+, im- = imidazolate) with high pressure, synchrotron powder X-ray diffraction and mercury intrusion measurements. A displacive phase transition from a highly compressible open pore (op) phase with continuous porosity (space group Pbca, bulk modulus ∼1.4 GPa) to a closed pore (cp) phase with inaccessible porosity (space group P21/c, bulk modulus ∼3.3-4.9 GPa) is triggered by the application of mechanical pressure. Over the course of the transitions, both ZIF-4 materials contract by about 20% in volume. However, the threshold pressure, the reversibility and the immediate repeatability of the phase transition depend on the metal cation. ZIF-4(Zn) undergoes the op-cp phase transition at a hydrostatic mechanical pressure of only 28 MPa, while ZIF-4(Co) requires about 50 MPa to initiate the transition. Interestingly, ZIF-4(Co) fully returns to the op phase after decompression, whereas ZIF-4(Zn) remains in the cp phase after pressure release and requires subsequent heating to switch back to the op phase. These variations in high pressure behaviour can be rationalised on the basis of the different electron configurations of the respective M2+ ions (3d10 for Zn2+ and 3d7 for Co2+). Our results present the first examples of op-cp phase transitions (i.e. breathing transitions) of ZIFs driven by mechanical pressure and suggest potential applications of these functional materials as shock absorbers, nanodampers, or in mechanocalorics.

Hybrid organic-inorganic perovskites represent a special class of metal-organic framework where a molecular cation is encased in an anionic cage. The molecule-cage interaction influences phase stability, phase transformations, and the molecular dynamics. We examine the hydrogen bonding in four AmBX3 formate perovskites: [Am]Zn(HCOO)3, with Am+ = hydrazinium (NH2NH3+), guanidinium (C(NH2)3+), dimethylammonium (CH3)2NH2+, and azetidinium (CH2)3NH2+. We develop a scheme to quantify the strength of hydrogen bonding in these systems from first-principles, which separates the electrostatic interactions between the amine (Am+) and the BX3- cage. The hydrogen-bonding strengths of formate perovskites range from 0.36 to 1.40 eV/cation (8-32 kcalmol-1). Complementary solid-state nuclear magnetic resonance spectroscopy confirms that strong hydrogen bonding hinders cation mobility. Application of the procedure to hybrid lead halide perovskites (X = Cl, Br, I, Am+ = CH3NH3+, CH(NH2)2+) shows that these compounds have significantly weaker hydrogen-bonding energies of 0.09 to 0.27 eV/cation (2-6 kcalmol-1), correlating with lower order-disorder transition temperatures.

The physicochemical properties of the potassium neptunate K2NpO4 have been investigated in this work using X-ray diffraction, X-ray absorption near edge structure (XANES) spectroscopy at the Np-L3 edge, and low-temperature heat capacity measurements. A Rietveld refinement of the crystal structure is reported for the first time. The Np(VI) valence state has been confirmed by the XANES data, and the absorption edge threshold of the XANES spectrum has been correlated to the Mössbauer isomer shift value reported in the literature. The standard entropy and heat capacity of K2NpO4 have been derived at 298.15 K from the low-temperature heat capacity data. The latter suggest the existence of a magnetic ordering transition around 25.9 K, most probably of the ferromagnetic type.

Inorganic zeolites have excellent molecular sieving properties, but they are difficult to process into macroscopic structures. In this work, we use metal–organic framework (MOF) glass as substrates to engineer the interface with inorganic zeolites, and then assemble the discrete crystalline zeolite powders into monolithic structures. The zeolites are well dispersed and stabilized within the MOF glass matrix, and the monolith has satisfactory mechanical stabilities for membrane applications. We demonstrate the effective separation performance of the membrane for 1,3‐butadiene (C4H6) from other C4 hydrocarbons, which is a crucial and challenging separation in the chemical industry. The membrane achieves a high permeance of C4H6 (693.00±21.83 GPU) and a high selectivity over n‐butene, n‐butane, isobutene, and isobutane (9.72, 9.94, 10.31, and 11.94, respectively). This strategy opens up new possibilities for developing advanced membrane materials for difficult hydrocarbon separations. [ABSTRACT FROM AUTHOR]

The Giant Magellan Telescope (GMT) consists of seven 8.365 m segments with a separation of 0.345 m. A uniquechallenge for GMT lies in phasing these segments and, in particular, how to measure segment piston optically.In this paper, we present a results of a phasing strategy using a non-redundant pupil mask. We show how thismethod can be extended to measure segment piston differences of more than half a wave by using broadbandlight.