The La for Pr substitution in the Ruddlesden-Popper (RP) n = 2 La3Ni2O7 +/-delta nickelates was investigated for the first time in the whole possible substitution range for their use as oxygen electrodes in Solid Oxide Fuel Cells (SOFCs) and Electrolyzers (SOECs). In this work we evidenced that the solid solution is restricted up to the composition La1.5Pr1.5Ni2O7 +/-delta. The synthesis conditions (temperature, atmosphere), the oxygen stoichiometry including its variation with temperature in air, as well as the corresponding cell parameters of the prepared materials were thoroughly determined. Long-term ageing experiments were performed both on pure materials and on mixtures prepared with gadolinium doped ceria (GDC20) powders, to determine the stability of the phases under the operating conditions of temperature and the chemical reactivity at the interface with GDC20, which is used as a barrier layer between the 8YSZ electrolyte and the nickelate. The latter acts as accelerated degradation conditions. Using XRD and TEM-EDX analysis, we were able to evidence the diffusion of Pr and La into GDC20 after the ageing of the nickelate/GDC mixture. The electrochemical performances measured on symmetrical cells are among the best reported in the literature, with a polarisation resistance, Rp, of 36 m Omega cm2 at 800 degrees C for La1.5Pr1.5Ni2O7 +/-delta, close to that of the reference La0.6Sr0.4Co0.2Fe0.8O3-delta perovskite material (Rp = 10 m Omega cm2) and state of the art n = 1 RP Pr2NiO4+delta (Rp = 10 m Omega cm2). Although the extent of the impact of La/Pr diffusion into the barrier layer on the performances still needs to be determined, the slow degradation rate compared to Pr2NiO4+delta along with the low polarisation resistance of La1.5Pr1.5Ni2O7 +/-delta makes this RP n = 2 nickelate compound an attractive alternative for oxygen electrode materials in SOFC/SOEC application.

F-doped La0.6Sr0.4Co0.2Fe0.8O3-x-delta Fx (LSCFFx, x = 0.05, 0.10, and 0.20) materials are evaluated as oxygen electrodes for solid oxide fuel and electrolyser cell application. Materials have been prepared via low-temperature topotactic route by fluorination of the parent oxide with polyvinylidene fluorine (PVDF). A decrease in the polarisation resistance (R-p) is observed for the "LSCFFx" symmetric cells. However, the improved electrochemical behavior for the symmetric cells cannot be explained by the presence of fluorine, as post mortem chemical analysis shows that fluorine is absent from the materials after the calcination treatment, contradicting previous results from the literature and calling for deeper understanding. The presence of fluorine is proved to result in a sluggish surface exchange rate compared with the LSCF oxide via pulsed isotopic exchange technique. Despite the absence of fluorine in the fabricated symmetric cell, annealing with PVDF at low temperatures prior to the electrode fabrication is proven to be a beneficial step to improve the electrochemical performance of LSCF material with applications for solid oxide cells. Studies with room temperature X-ray diffraction, X-ray photoelectron spectroscopy, and M & ouml;ssbauer spectroscopy suggest that increased oxygen vacancy concentration, structural disorder and changes in the cobalt/iron valence state distribution are potential explanations for the reduced R-p.

Sr2FeO3F, an oxyfluoride compound with an n = 1 Ruddlesden-Popper structure, was identified as a potential interesting mixed ionic and electronic conductor (MIEC). The phase can be synthesized under a range of different pO2 atmospheres, leading to various degrees of fluorine for oxygen substitution and Fe4+ content. A structural investigation and thorough comparison of both argon- and air-synthesized compounds were performed by combining high-resolution X-ray and electron diffraction, high-resolution scanning transmission electron microscopy, Mössbauer spectroscopy, and DFT calculations. While the argon-synthesized phase shows a well-behaved O/F ordered structure, this study revealed that oxidation leads to averaged large-scale anionic disorder on the apical site. In the more oxidized Sr2FeO3.2F0.8 oxyfluoride, containing 20% of Fe4+, two different Fe positions can be identified with a 32%/68% occupancy (P4/nmm space group). This originates due to the presence of antiphase boundaries between ordered domains within the grains. Relations between site distortion and valence states as well as stability of apical anionic sites (O vs F) are discussed. This study paves the way for further studies on both ionic and electronic transport properties of Sr2FeO3.2F0.8 and its use in MIEC-based devices, such as solid oxide fuel cells.

Mixed ionic electronic conductors (MIECs) oxides are used as electrode materials for solid oxide cell (SOC) application, as they combine high electronic conductivity as well as high oxygen diffusivity and oxygen surface exchange coefficients. The ionic transport properties can be directly determined thanks to the isotopic exchange depth profiling (IEDP) method. To date, the reported measurements have been performed at ambient pressure and below. However, for a higher efficiency of hydrogen production at the system level, it is envisaged to operate the cell between 10 and 60 bar. To characterize the MIEC oxides properties in such conditions, an innovative setup able to operate up to a total pressure of 50 bar and 900 & DEG;C has been developed. The main goal of this study was to compare the behavior of two types of reference materials: the oxygen deficient La-Sr-Fe-Co perovskites, and the overstoichiometric lanthanide nickelates Ln2NiO4+& delta; (Ln = La, Pr, Nd). Diffusion and surface exchange coefficients obtained under 6.3 bar of oxygen are measured and their evolution discussed in light of the change in oxygen stoichiometries. This analysis allows better understanding of the dependency of the surface exchange coefficient with the oxygen partial pressure.

This study systematically investigates the vacancy formation energy, diffusivity, and ionic conductivity of the Ln2NiO4+δ (δ=0.125) compound using the ab initio approach. Specifically, we consider the impact of thermal expansion on the oxygen transport properties, using a combination of quasi-harmonic approximation (QHA) and a linear regression model to study and reproduce the temperature-dependent properties of Ln2NiO4+δ. Our predictions are in excellent agreement with previous theoretical studies in the literature. We confirm that oxygen vacancy diffusion does not dominate the ionic transport properties of the Ln2NiO4+δ due to the high vacancy formation energy. Moreover, we confirm that the more favorable diffusion path involves interstitial O2- hopping parallel to the a-b plane with the rocksalt layer (known as the interstitialcy mechanism). Meanwhile, the predicted energy barrier, diffusion coefficient, and ionic conductivity of Ln2NiO4+δ show reasonable agreement with experimental data, with Pr2NiO4+δ exhibiting the lowest activation energy barrier and the highest thermal expansion, diffusivity, and ionic conductivity. Overall, this study presents an efficient and computationally facile tool for predicting ionic transport properties in materials where thermal expansion is the main driving force for temperature-dependent properties.

Li-containing materials providing fast ion transport pathways are fundamental in Li solid electrolytes and the future of all-solid-state batteries. Understanding these pathways, which usually benefit from structural disorder and cation/anion substitution, is paramount for further developments in next-generation Li solid electrolytes. Here, we exploit a range of variable temperature 6Li and 7Li nuclear magnetic resonance approaches to determine Li-ion mobility pathways, quantify Li-ion jump rates, and subsequently identify the limiting factors for Li-ion diffusion in Li3AlS3 and chlorine-doped analogue Li4.3AlS3.3Cl0.7. Static 7Li NMR line narrowing spectra of Li3AlS3 show the existence of both mobile and immobile Li ions, with the latter limiting long-range translational ion diffusion, while in Li4.3AlS3.3Cl0.7, a single type of fast-moving ion is present and responsible for the higher conductivity of this phase. 6Li-6Li exchange spectroscopy spectra of Li3AlS3 reveal that the slower moving ions hop between non-equivalent Li positions in different structural layers. The absence of the immobile ions in Li4.3AlS3.3Cl0.7, as revealed from 7Li line narrowing experiments, suggests an increased rate of ion exchange between the layers in this phase compared with Li3AlS3. Detailed analysis of spin-lattice relaxation data allows extraction of Li-ion jump rates that are significantly increased for the doped material and identify Li mobility pathways in both materials to be three-dimensional. The identification of factors limiting long-range translational Li diffusion and understanding the effects of structural modification (such as anion substitution) on Li-ion mobility provide a framework for the further development of more highly conductive Li solid electrolytes.

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.

An entry from the Inorganic Crystal Structure Database, the world’s repository for inorganic crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the joint CCDC and FIZ Karlsruhe Access Structures service and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

The piezoelectric devices widespread in society use noncentrosymmetric Pb-based oxides because of their outstanding functional properties. The highest figures of merit reported are for perovskites based on the parent Pb(Mg1/3Nb2/3)O3 (PMN), which is a relaxor: a centrosymmetric material with local symmetry breaking that enables functional properties, which resemble those of a noncentrosymmetric material. We present the Pb-free relaxor (K1/2Bi1/2)(Mg1/3Nb2/3)O3 (KBMN), where the thermal and (di)electric behavior emerges from the discrete structural roles of the s0 K+ and s2 Bi3+ cations occupying the same A site in the perovskite structure, as revealed by diffraction methods. This opens a distinctive route to Pb-free piezoelectrics based on relaxor parents, which we demonstrate in a solid solution of KBMN with the Pb-free ferroelectric (K1/2Bi1/2)TiO3, where the structure and function evolve together, revealing a morphotropic phase boundary, as seen in PMN-derived systems. The detailed multiple-length-scale understanding of the functional behavior of KBMN suggests that precise chemical manipulation of the more diverse local displacements in the Pb-free relaxor will enhance performance.

Mixed anion materials and anion doping are verypromising strategies to improve solid-state electrolyte properties by enablingan optimized balance between good electrochemical stability and high ionicconductivity. In this work, we present the discovery of a novel lithium aluminumsulfide-chloride phase. The structure is strongly affected by the presence ofchloride anions on the sulfur site, as this stabilizes a higher symmetry phasepresenting a large degree of cationic site disorder, as well as disorderedoctahedral lithium vacancies, in comparison with Li-Al-S ternaries. The effectof disorder on the lithium conductivity properties was assessed by a combinedexperimental-theoretical approach. In particular, the conductivity is increasedby a factor 103 compared to the pure sulfide phases. Although itremains moderate (10−6 S·cm-1),Ab Initio Molecular Dynamics and Maximum Entropy (applied to neutrondiffraction data) methods show that disorder leads to a 3D diffusion pathway,where Li atoms move thanks to a concerted mechanism. An understanding of thestructure-property relationships is developed to determine the limiting factorgoverning lithium ion conductivity. This analysis, added to the strong stepforward obtained in the determination of the dimensionality of diffusion pavesthe way for accessing even higher conductivity in materials comprising an hcp anion arrangement.

A hexagonal analogue, Li6SiO4Cl2, of the cubic lithium argyrodite family of solid electrolytes is isolated by a computation–experiment approach. We show that the argyrodite structure is equivalent to the cubic antiperovskite solid electrolyte structure through anion site and vacancy ordering within a cubic stacking of two close-packed layers. Construction of models that assemble these layers with the combination of hexagonal and cubic stacking motifs, both well known in the large family of perovskite structural variants, followed by energy minimization identifies Li6SiO4Cl2 as a stable candidate composition. Synthesis and structure determination demonstrate that the material adopts the predicted lithium site-ordered structure with a low lithium conductivity of ∼10–10 S cm–1 at room temperature and the predicted hexagonal argyrodite structure above an order–disorder transition at 469.3(1) K. This transition establishes dynamic Li site disorder analogous to that of cubic argyrodite solid electrolytes in hexagonal argyrodite Li6SiO4Cl2 and increases Li-ion mobility observed via NMR and AC impedance spectroscopy. The compositional flexibility of both argyrodite and perovskite alongside this newly established structural connection, which enables the use of hexagonal and cubic stacking motifs, identifies a wealth of unexplored chemistry significant to the field of solid electrolytes.

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 Li 3.3 SnS 3.3 Cl 0.7. The interstitial site occupancy combination in this defect stuffed wurtzite enables a low-barrier ion transport pathway in hexagonal close-packing.

We synthesized a new layered Na2Fe2OS2 phase, our study paves the way to further design of oxysulfides as cathode materials.

BiCuOS is a nontoxic p-type semiconductor that is a promising candidate for photoelectric applications. The formation of thin films with a good electronic transport at the grain boundaries, while avoiding thermal treatment detrimental to its chemical stability is a challenge. We have developed a chemical method for the direct synthesis of stable colloidal suspensions of BiCuOS nanoparticles from soluble precursors. These colloidal solutions were stabilized with a catechol functionalized poly-3-hexylthiophene that allows easy spin-coating deposition and favors electronic transport along the grain boundaries. Stacking of ZnO-BiCuOS layers were achieved, allowing preparation of n-p junctions. These act as rectifying diodes and are strongly photosensitive, with Iph /Idark =85 corresponding to an enhancement of the photocurrent of more than two orders of magnitude compared to that of BiCuOS alone. This energy-efficient and low-cost method is a further step in the development of new sulfide semiconductor devices.

We report here the synthesis and grafting of easily accessible catechol-terminated poly(3-hexylthiophenes) onto Al-doped ZnO particles (ZnO:Al) to obtain a performance-improved polycrystalline assembly. These macromolecular binding species favor electronic conduction from one grain to another. Resistivity measurements of the grafted ZnO:Al powders performed under compression show an increased conductivity as compared to the pure ZnO:Al powders. The catechol function terminating the polymer appears to play an important role on its effect by forming a strong covalent bond with the surface of the zinc oxide. In particular, the conductivity obtained under characteristic pressures of lamination processes gives 1-10 Omega cm, evidencing the great potential of such an approach for preparation of flexible or thermoreactive films.