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The application of machine learning models to predict material properties is determined by the availability of high-quality data. We present an expert-curated dataset of lithium ion conductors and associated lithium ion conductivities measured by a.c. impedance spectroscopy. This dataset has 820 entries collected from 214 sources; entries contain a chemical composition, an expert-assigned structural label, and ionic conductivity at a specific temperature (from 5 to 873 °C). There are 403 unique chemical compositions with an associated ionic conductivity near room temperature (15–35 °C). The materials contained in this dataset are placed in the context of compounds reported in the Inorganic Crystal Structure Database with unsupervised machine learning and the Element Movers Distance. This dataset is used to train a CrabNet-based classifier to estimate whether a chemical composition has high or low ionic conductivity. This classifier is a practical tool to aid experimentalists in prioritizing candidates for further investigation as lithium ion conductors.

The selection of the elements to combine delimits the possible outcomes of synthetic chemistry because it determines the range of compositions and structures, and thus properties, that can arise. For example, in the solid state, the elemental components of a phase field will determine the likelihood of finding a new crystalline material. Researchers make these choices based on their understanding of chemical structure and bonding. Extensive data are available on those element combinations that produce synthetically isolable materials, but it is difficult to assimilate the scale of this information to guide selection from the diversity of potential new chemistries. Here, we show that unsupervised machine learning captures the complex patterns of similarity between element combinations that afford reported crystalline inorganic materials. This model guides prioritisation of quaternary phase fields containing two anions for synthetic exploration to identify lithium solid electrolytes in a collaborative workflow that leads to the discovery of Li3.3SnS3.3Cl0.7. The interstitial site occupancy combination in this defect stuffed wurtzite enables a low-barrier ion transport pathway in hexagonal close-packing., Machine learning has the potential to significantly speed-up the discovery of new materials in synthetic materials chemistry. Here the authors combine unsupervised machine learning and crystal structure prediction to predict a novel quaternary lithium solid electrolyte that is then synthesized.

Molecular solids with cooperative electronic properties based purely on π electrons from carbon atoms offer a fertile ground in the search for exotic states of matter, including unconventional superconductivity and quantum magnetism. The field was ignited by reports of high-temperature superconductivity in materials obtained by the reaction of alkali metals with polyaromatic hydrocarbons, such as phenanthrene and picene, but the composition and structure of any compound in this family remained unknown. Here we isolate the binary caesium salts of phenanthrene, Cs(C

Electrode materials for intermediate temperature (500–700 ∘C) solid oxide fuel cells require electrical and mechanical stability to maintain performance during the cell lifetime. This has proven difficult to achieve for many candidate cathode materials and their derivatives with good transport and electrocatalytic properties because of reactivity towards cell components, and the fuels and oxidants. Here we present Ba0.5Sr0.5(Co0.7Fe0.3)0.6875W0.3125O3−δ (BSCFW), a self-assembled composite prepared through simple solid state synthesis, consisting of B-site cation ordered double perovskite and disordered single perovskite oxide phases, as a candidate cathode material. These phases interact by dynamic compositional change at the operating temperature, promoting both chemical stability through the increased amount of W in the catalytically active single perovskite provided from the W-reservoir double perovskite, and microstructural stability through reduced sintering of the supported catalytically active phase. This interactive catalyst-support system enabled stable high electrochemical activity through the synergic integration of the distinct properties of the two phases. Electrodes of solid oxide fuel cells need to be stable during operation. Here, the authors use tungsten as a substituent to stabilize a perovskite oxide as a two-phase composite. The resulting material dynamically adjusts the phase compositions to keep a high catalytic activity at operation conditions.

The crystal structure of a solid controls the interactions between the electronically active units and thus its electronic properties. In the high-temperature superconducting copper oxides, only one spatial arrangement of the electronically active Cu(2+) units-a two-dimensional square lattice-is available to study the competition between the cooperative electronic states of magnetic order and superconductivity. Crystals of the spherical molecular C(60)(3-) anion support both superconductivity and magnetism but can consist of fundamentally distinct three-dimensional arrangements of the anions. Superconductivity in the A(3)C(60) (A = alkali metal) fullerides has been exclusively associated with face-centred cubic (f.c.c.) packing of C(60)(3-) (refs 2, 3), but recently the most expanded (and thus having the highest superconducting transition temperature, T(c); ref. 4) composition Cs(3)C(60) has been isolated as a body-centred cubic (b.c.c.) packing, which supports both superconductivity and magnetic order. Here we isolate the f.c.c. polymorph of Cs(3)C(60) to show how the spatial arrangement of the electronically active units controls the competing superconducting and magnetic electronic ground states. Unlike all the other f.c.c. A(3)C(60) fullerides, f.c.c. Cs(3)C(60) is not a superconductor but a magnetic insulator at ambient pressure, and becomes superconducting under pressure. The magnetic ordering occurs at an order of magnitude lower temperature in the geometrically frustrated f.c.c. polymorph (Néel temperature T(N) = 2.2 K) than in the b.c.c.-based packing (T(N) = 46 K). The different lattice packings of C(60)(3-) change T(c) from 38 K in b.c.c. Cs(3)C(60) to 35 K in f.c.c. Cs(3)C(60) (the highest found in the f.c.c. A(3)C(60) family). The existence of two superconducting packings of the same electronically active unit reveals that T(c) scales universally in a structure-independent dome-like relationship with proximity to the Mott metal-insulator transition, which is governed by the role of electron correlations characteristic of high-temperature superconducting materials other than fullerides.

High-conductivity oxide ion electrolytes are needed to reduce the operating temperature of solid-oxide fuel cells. Oxide mobility in solids is associated with defects. Although anion vacancies are the charge carriers in most cases, excess (interstitial) oxide anions give high conductivities in isolated polyhedral anion structures such as the apatites. The development of new families of interstitial oxide conductors with less restrictive structural constraints requires an understanding of the mechanisms enabling both incorporation and mobility of the excess oxide. Here, we show how the two-dimensionally connected tetrahedral gallium oxide network in the melilite structure La1.54Sr0.46Ga3O7.27 stabilizes oxygen interstitials by local relaxation around them, affording an oxide ion conductivity of 0.02–0.1 S cm−1 over the 600–900 ∘C temperature range. Polyhedral frameworks with central elements exhibiting variable coordination number can have the flexibility needed to accommodate mobile interstitial oxide ions if non-bridging oxides are present to favour cooperative network distortions. Fast-ion conductors are needed to reduce the operating temperature of solid-oxide fuel cells. The identification of the conduction mechanism in electrolytes where conduction is based on mobile oxygen interstitials rather than the usual anion vacancies offers a generic design principle for novel solid electrolytes.

C(60)-based solids are archetypal molecular superconductors with transition temperatures (Tc) as high as 33 K (refs 2-4). Tc of face-centred-cubic (f.c.c.) A(3)C(60) (A=alkali metal) increases monotonically with inter C(60) separation, which is controlled by the A(+) cation size. As Cs(+) is the largest such ion, Cs(3)C(60) is a key material in this family. Previous studies revealing trace superconductivity in Cs(x)C(60) materials have not identified the structure or composition of the superconducting phase owing to extremely small shielding fractions and low crystallinity. Here, we show that superconducting Cs(3)C(60) can be reproducibly isolated by solvent-controlled synthesis and has the highest Tc of any molecular material at 38 K. In contrast to other A(3)C(60) materials, two distinct cubic Cs(3)C(60) structures are accessible. Although f.c.c. Cs(3)C(60) can be synthesized, the superconducting phase has the A15 structure based uniquely among fullerides on body-centred-cubic packing. Application of hydrostatic pressure controllably tunes A15 Cs(3)C(60) from insulating at ambient pressure to superconducting without crystal structure change and reveals a broad maximum in Tc at approximately 7 kbar. We attribute the observed Tc maximum as a function of inter C(60)separation--unprecedented in fullerides but reminiscent of the atom-based cuprate superconductors--to the role of strong electronic correlations near the metal-insulator transition onset.

Superconductivity has been discovered in the materials that form when alkali metals react with a solid hydrocarbon. This is the first new class of organic, high-temperature superconductor in a decade.

We report μSR measurements on a series of compounds with composition La2-xSrxNiO4+\delta where the net hole concentration x+2\delta is greater than 0.4. A magnetic transition is found in all the samples studied which occurs at a composition‐dependent temperature TM. Below TM, clear precession signals are observed in zero applied magnetic field. The possible muon sites are discussed within the context of dipole‐field calculations.

Expanded alkali fullerides are molecular superconductors with a Mott parent insulating state. Klupp et al. use infrared spectroscopy to detect the molecular Jahn–Teller distortion of fulleride ions and establish its relevance to strongly correlated superconductivity.

Thin transparent conducting oxide (TCO) films of gallium-doped zinc oxide have been deposited on glass substrates by atomic layer deposition (ALD) using diethyl zinc, triethyl gallium and water vapour as precursors. The gallium-doped zinc oxide films were deposited over the temperature range 100-350°C. Transmission electron microscopy reveals that the as-deposited films are polycrystalline in character. The electrical resistivity of the gallium-doped zinc oxide films was evaluated using four-point probe and contactless measurement methods as a function of film thickness. The lowest sheet resistance of 16 Ω/☐ was measured from a film thickness of 400nm and a gallium content of 5 atomic percent. The electron Hall mobility of this film was 12.3 cm2/Vs. The visible transmittance of the films was 78% with a haze of 0.2%.

INTEREST in the alkali-intercalated AxC60 fullerides (where A is an alkali metal and x = 2, 3, 4, 6)1,2 has been greatly enhanced by the discovery of a family of superconducting phases for x = 3 with transition temperatures (Tcs) that are exceeded only by the copper oxide materials3–9. An early structure refinement5 identified K3C60 as a face-centred-cubic (f.c.c.) intercalation phase with two tetra-hedral (T) and one octahedral (O) potassium ion per C60. The other superconducting A3C60 systems are isostructural7. Here we report 87Rb NMR studies of Rb3C60 which show the expected T: O ratio of 2:1 at 440 K. Below 370 K, however, an additional resonance appears; spin-echo double-resonance NMR experiments11,12 show that this arises from a second type of tetrahedral Rb+ site (T′). Thus the bulk of this material has a local symmetry lower than that of the f.c.c. structure derived from X-ray refinements. Models that could account for this include a rotational orientation of C60 that places a C5 ring adjacent to the T′ Rb+ ions. Alternatively, the symmetry lowering might be due to a Jahn-Teller distortion on C3−60, carrier-density modulation or Rb+ clustering. Each of these models could lead to a degree of charge localization and consequent reduction in the density of states and hence in Tc.

A WIDE variety of alkali-metal fullerides (AxC60) have been prepared, with stoichiometries varying between 1⩽=x⩽=11 (refs 1,2). Most of the compounds with x = 3 are superconductors with unusually high transition temperatures (Tc) which increase with the size of the face-centred cubic unit cell3. The increase in Tc on lattice expansion is attributed to a decrease in the conduction band width, and therefore one ultimately expects a saturation or downturn of Tc followed by a metal–insulator transition. We have sought to explore this regime by expanding the A3C60 structure through intercalation of neutral molecules capable of solvating the A+ ions. Here we report that the reaction of ammonia with Na2CsC60 (Tc = 10.5K; lattice constant α = 14.132 A) produces the compound (NH3)4Na2CsC60, which has an expanded unit cell (a = 14.473 A) and an increased Tc of 29.6 K. The structure contains the Na(NH3)+4 cation on the octahedral site.

The functionalization of crystalline porous materials is frequently limited to groups inert to the microscopic structure. Photoconversion of dormant precursors into highly reactive species shines light on the problem.

ALKALI metal fuller ides exhibit superconductivity1–4 at temperatures surpassed only by the copper-oxide-based ceramics. Three types of stoichiometry and structure have been identified: A3C60 (ref. 5) (where A is K or Rb) with A+ cations intercalated in the face-centred cubic (f.c.c.) C60 structure, and A6C60 (ref. 6) or A4C60 (ref. 7) (where A is K, Rb or Cs) with body-centred arrays of C60 molecules. All A3C60 compounds reported so far are superconductors with transition temperatures that increase with unit cell size8,9. No successful preparation of bulk NaxC60 has been reported, although measurements of electrical conductivity10 and Raman11, ESR11 and photoemission12 spectra of thin films have given clear indications of NaxC60 formation. Here we report the synthesis and initial characterization of bulk NaxC60 (2≤x≤6) and mixed alkali phases Na2AC60 (where A is K, Rb, or Cs). All of these phases have intercalated f.c.c. structures. The Na6C60 structure has a Na4 cluster centred on the octahedral site. The Na2AC60 compounds superconduct for the larger A cations, but a crossover to nonsuperconducting behaviour occurs with decreasing cation size and correlates with a minimum in the unit cell volume.

A drying procedure using supercritical carbon dioxide gives greater access to the pores of metal–organic frameworks, affording larger surface areas for applications.

SUPERCONDUCTING K3C60 (ref. 1) has been shown2 to have an intercalated face-centred cubic (f.c.c.) structure, and other A3C60 compounds (where A is K, Rb or mixtures of K, Rb and/or Cs) form an isostructural series with superconducting transition temperatures up to 31.3 K (ref. 3). Recently we reported413C NMR studies of KxC60 for x

THE recent syntheses1,2 of macroscopic quantities of C60 have suggested possible applications in host–guest and organic chemistry, tribology, electrochemistry and semiconductor tech-nology. Here we report the preparation of alkali-metal-doped films of C60 and C70 which have electrical conductivities at room temperature that are comparable to those attained by n-type doped polyacetylene. The highest conductivities observed in the doped films are: 4Scm−1 (Cs/C60), 100 (Rb/C60), 500 (K/C60), 20 (Na/C60), 10 (Li/C60), 2 (K/C70). The doping process is reversed on exposure of the films to the atmosphere. At high doping levels, the films become more resistive. We attribute the conductivity induced in these films to the formation of energy bands from the π orbitals of C60 or C70, which become partially filled with carriers on doping. The smaller alkali metal ions should be able to fit into the interstices in the lattice without disrupting the network of contacts between the carbon spheroids. In the case of C60, this would allow the development of an isotropic band structure, and we therefore propose that these materials may constitute the first three-dimensional 'organic' conductors.

A complex iron oxide has been made that has an unusual crystal structure suggesting that the oxide ions are surprisingly mobile. This finding could pave the way to other metal-oxide materials with useful properties.

Retention of the void space upon loss of the solvent template is directly demonstrated using single-crystal X-ray diffraction for molecular frameworks constructed using both hydrogen and co-ordinate bonds. While the co-ordination polymer remains rigid upon desolvation, the extra flexibility in the hydrogen-bonded framework, due both to the large number of redundant hydrogen-bonding donor and acceptor groups and the possibility of significant φ-φ stacking interactions within the framework, lead to a significant structural and symmetry change while retaining significant void volume. Molecular modelling techniques are used to understand and predict the guest uptake chemistry of these host frameworks.

The crystallography and electronic properties of the Ln2-xSr1+xMn2O7 manganese oxides adopting the n = 2 Ruddlesden-Popper (RP) structure are discussed, focusing on the structural phase diagrams and electronic properties in the vicinity of the Mn +3.5 oxidation state and in particular the ease of synthesis of single phases of these materials.

The Na based mixed alkali doped C60 superconductors show anomalous behavior with respect to the “universal” superconducting transition temperature Tc vs lattice constant ao relation followed by most of the fcc A3C60 superconductors. We have measured dTc/dP for Na2CsC60 and (NH3)4Na2CsC60 using solid He as the pressure medium to ∼ 6 kbar finding dTc/dP equal to −0.88±(0.01) K/kbar and −1.0(±0.1) K/kbar for Na2CsC60 and Na2(NH3)4C60 respectively. Our value for Na2CsC60 differs markedly from that obtained by Mizuki et al of about −1.3 K/kbar. However, using N2 or Ar, we obtain values for dTc/dP in substantial agreement with Mizuki et al who used fluorinert to generate their pressure. This work emphasizes the need for compressibility measurements with the same pressure medium in the appropriate temperature range so that meaningful comparisons can be made between various pressure measurements and models which are based on lattice spacing.

The phonon spectra of pristine fullerene, superconducting K3C60 and saturation-doped Rb6C60 measured by inelastic neutron scatteringin the energy range 2.5 - 200 meV at low temperatures reveal substantial broadening of five-fold degenerate Hg intramolecular vibrational modes both in the low-energy radial and the high-energy tangential part of the spectrum. This provides strong evidence for a traditional phonon-mediated mechanism of superconductivity in the fullerides but with an electron-phonon coupling strength distributed over a wide range of energies (33-195 meV) as a result of the finite curvature of the fullerene spherical cage.

INTERCALATION of C60 (buckminsterfullerene1,2) by alkali metals3 leads to superconducting compounds of stoichiometry A3C60 (refs 4–6) with transition temperatures Tc as high as 33 K (ref. 7). These transition temperatures are considerably higher than those for alkali-metal-intercalated graphite (

THE discovery of conductivity1 in AxC60 (where A represents an alkali metal) and superconductivity2 in KxC60 has been followed by reports of superconductivity in other alkali-metal-doped full-erides with transition temperatures as high as 33 K (ref. 3). Elucidation of phase diagrams and understanding the relationship between structure and superconducting properties is essential to a detailed understanding of superconductivity in these systems. So far, structural data have been reported only for the non-conducting, intercalated body-centred cubic (b.c.c.) structures A6C60 (where A is K or Cs; ref. 4), a body-centred tetragonal structure for A6C60 (where A is K, Rb, Cs; ref. 5) and the superconducting, intercalated face-centred cubic (f.c.c.) material K3C60 (ref. 6). Here we report the preparation of a series of single-phase, isostructural f.c.c. superconductors with composition A3C60 (where A is K, Rb, Cs or a mixture of these), and show that Tcc increases monotonically with the size of the unit cell. Extended Hiickel band-structure calcula-tions also show a monotonic increase in the density of states at the Fermi level, N(EF), with lattice parameter. The primary impli-cation of these results is that all A3C60 superconductors have the same structure and that changes in Tc can be accounted for by changes in N(EF).

THE magnetic susceptibility of C60 and the possibility of magnetic-field-induced π-electron ring currents in this carbon spheroid have been of interest since the initial experiments on carbon clusters1. If the molecule is regarded as a sphere with a radius of 3.5 A, on which 60 electrons are free to move, the Pauling ring-current model predicts a ring-current diamagnetic susceptibility 41 times the π-electron ring-current magnetic susceptibility of benzene with the field normal to the plane of the six-membered ring2,3. London theory predicts, however, that the π-electron ring currents in C60 should be weakly paramagnetic or diamagnetic, depending on the relative bond strengths used in the calculation2,3. With the availability of macroscopic quantities of C60 (ref. 4), it is now possible to study experimentally the magnetic properties of the molecule. Here we report on such measurements. We find that the diamagnetism of C60 is small, a result that we attribute to excited-state paramagnetic contributions to the π-electron ring-current magnetic susceptibility. Thus C60 seems to be an aromatic molecule with a vanishingly small π-electron ring-current magnetic susceptibility. We have performed similar measurements on C70, which indicate an appreciable π-electron diamagnetism, consistent with theoretical calculations. We attribute the differences in magnetic properties of these two molecules to their different fractions of five-membered ring structures. The fullerenes may thus constitute a class of compounds of 'ambiguous' aromatic character, traditional measures of which will not provide an adequate classification.

Nature 352, 701-703 (1991). THE positions of the alkali atoms, originally reported as (0,0.5, z) with z = 0.28, should read (x,0.5,0) with x = 0.22. These are the positions used in the calculations for Table 1 and the positions illustrated in Fig. 2.