Element selection for crystalline inorganic solid discovery guided by unsupervised machine learning of experimentally explored chemistry

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.

How Li diffusion in spinel Li[Ni1/2Mn3/2]O4 is seen with μ ±SR

The diffusive behavior in a spinel-type Li+ ion battery material, Li[Ni1/2Mn3/2]O4, has been studied with positive and negative muon spin rotation and relaxation (μ ±SR) measurements in the temperature range between 200 and 400 K using a powder sample. The implanted μ + locates at an interstitial site near O2− ion so as to form a O–H like bond, while the implanted μ − is mainly captured by an oxygen nucleus, resulting in the formation of muonic oxygen. This means that local magnetic environments in Li[Ni1/2Mn3/2]O4 were investigated from the two different sites in the lattice, i.e., one is an interstitial site for μ +SR and the other is an oxygen site for μ −SR. Since both μ +SR and μ −SR detected an increase in the fluctuation rate of a nuclear magnetic field for temperatures above 200 K, the origin of this increase is clearly confirmed as Li diffusion. Assuming a random walk process with the hopping of thermally activated Li+ between a regular Li site and the nearest neighboring vacant octahedral sites, a self-diffusion coefficient of Li+ was found to range above 10−11 cm2/s at temperatures above 250 K with an activation energy of about 0.06 eV.

Significantly suppressing ion migration in metal halide perovskites via trace of multivalent interstitial doping

Cations with suitable sizes to occupy an interstitial site of perovskite crystals have been widely used to inhibit ion migration and promote performance and stability of perovskite optoelectronics. However, the interstitial doping accompanies inevitable lattice strain to impair long-range ordering and stability of the crystals to cause a sacrificial trade-off. Here, we unravel the evident influence of the valence states of the interstitial cations on their efficacy to suppress the ion migration. Incorporation of a trivalent neodymium cation (Nd3+) effectively mitigates the ion migration in the perovskite lattice with significantly reduced dosage (0.08%) compared to a widely used monovalent cation dopant (Na+, 0.45%). Less but better, the prototypical perovskite solar cells incorporated with Nd3+ exhibits significantly enhanced photovoltaic performance and operational stability.

Hydrogen Transportation Behaviour of V–Ni Solid Solution: A First-Principles Investigation

Hydrogen embrittlement causes deterioration of materials used in metal–hydrogen systems. Alloying is a good option for overcoming this issue. In the present work, first-principles calculations were performed to systematically study the effects of adding Ni on the stability, dissolution, trapping, and diffusion behaviour of interstitial/vacancy H atoms of pure V. The results of lattice dynamics and solution energy analyses showed that the V–Ni solid solutions are dynamically and thermodynamically stable, and adding Ni to pure V can reduce the structural stability of various VHx phases and enhance their resistance to H embrittlement. H atoms preferentially occupy the characteristic tetrahedral interstitial site (TIS) and the octahedral interstitial site (OIS), which are composed by different metal atoms, and rapidly diffuse along both the energetically favourable TIS → TIS and OIS → OIS paths. The trapping energy of monovacancy H atoms revealed that Ni addition could help minimise the H trapping ability of the vacancies and suppress the retention of H in V. Monovacancy defects block the diffusion of H atoms more than the interstitials, as determined from the calculated H-diffusion barrier energy data, whereas Ni doping contributes negligibly toward improving the H-diffusion coefficient.

Influence of Nickel Addition on the Stability, Trapping, and Diffusion Behaviour of Hydrogen in Vanadium: A First-Principles Investigation

Hydrogen embrittlement causes deterioration of materials used in hydrogen energy systems. Alloying is an effective means for overcoming this issue. In this study, the first-principles calculation method was used to investigate the effects of alloying Ni on the stability, dissolution, trapping, and diffusion behaviour of interstitial/vacancy H atoms in V. The calculated phonon spectra and solution energies of the vacancy/interstitial H atoms revealed that the V–Ni phase was dynamically and thermodynamically stable, and Ni addition could reduce the stability of V hydrides and improve their resistance to H embrittlement. H atoms in the interstitials and vacancies preferentially occupied the tetrahedral interstitial site (TIS) and octahedral interstitial site (OIS) with the lowest solution energies and diffused along the TIS → TIS and OIS → OIS paths with the minimum diffusion barrier energies. The trapping energy of the vacancy H atoms indicated that the addition of Ni could reduce the H trapping capability of the vacancies and suppress the retention of H in V. Detailed analysis of the calculated H diffusion barriers indicated that the presence of monovacancy defects blocked the diffusion of H atoms more than the presence of interstitials, and Ni doping did not enhance the H diffusion coefficient.

Electrochemical Stability and Performance of Li2OHCl Substituted by F or Br as Solid-State Electrolyte

Li2(OH)0.9F0.1Cl, Li2(OH)0.9Br0.1Cl, and Li2OHCl0.8Br0.2 solid electrolytes were synthesized and compared with Li2OHCl to analyze the exact improvement mechanism for Li+ conductivity and electrochemical stability of Li2OHX-type solid electrolyte. The substituted materials exhibit improved electrochemical stability and Li+ conductivity Li2OHCl. Among these materials, Li(OH)0.9F0.1Cl has improved Li+ conductivity due to a reduction of the OH– concentration and the conductivity of Li2OHCl0.8Br0.2 was also increased compared with Li2OHCl due to the large interstitial site. In the case of Li2(OH)0.9Br0.1Cl, it had the highest Li+ conductivity and good Li+ migration by both effects because of a larger interstitial site and low OH− concentration. Furthermore, the electrochemical stability of four materials was compared due to the different structural stabilities and strengths of binary chemical bonds such as Li–X, H–X, and O–X. Comparing the Li+ conductivity of Li2(OH)0.9F0.1Cl and Li2OHCl0.8Br0.2, the Li+ conductivity is influenced by the OH− concentration unlike the other mechanisms.

Magnetic Volume Effect of Hydrogen Diffusion in Palladium

The electronic and magnetic properties of palladium hydrogen are investigated using first-principles spin-polarized density functional theory. By studying the magnetic moments and electronic structures of hydrogen atoms diffusing in face-centered cubic structure of transition metal Pd, we found that the results of magnetic moments are exactly the same in the two direct octahedral interstitial site-octahedral interstitial site diffusion paths-i.e. the magnetic moments are the largest in the octahedral interstitial site, and the magnetic moments are the lowest in saddle point positions. We also studied on the density of states of some special points, with the result that the density of states near the Fermi level is mainly contributed by 4d electrons of Pd and the change of magnetic moments with the cell volume in the unit cell of transition metal Pd with a hydrogen atom.