Energy Landscape Calculations Research Articles

Screening of FDA-approved Drugs against Protein Thymidine Kinase 2 Using Machine Learning Method Validated Applying Molecular Dynamics and Free Energy Landscape Calculation

Background: Thymidine kinase 2 (TK2) is a crucial enzyme in the mitochondrial pyrimidine salvage pathway, strongly associated with several mitochondrial diseases. Current treatments frequently damage mitochondria, leading to a decrease in cellular energy output. Objective: This study aimed to use computational approaches to identify inhibitors of TK2 that could prevent these harmful consequences. Method: The initial screening process entailed the application of machine learning algorithms, more particularly a Random Forest model, which was trained on 189 FDA-approved drugs and decoy datasets obtained from the DUD-E database. Its purpose was to identify potential inhibitors. The molecular docking technique was employed to evaluate the affinity of the chosen medicines towards TK2. Molecular dynamics (MD) simulations lasting 100 nanoseconds were employed to conduct additional validation by examining the dynamic interactions between the top-found compounds and TK2. Results: Three hit compounds (3168, 5209502, and 135402009) were identified through the screening process for their high affinity for TK2. Compound 5209502 had the most stable interaction with the lowest root-mean-square deviation (RMSD) in the molecular dynamics (MD) simulations and maintained 12 hydrogen bonds consistently. MM/GBSA computations verified that 5209502 exhibited the strongest binding affinity with a binding free energy of -62.14 kcal/mol, which was notably lower than that of the control ligand. Conclusion: Compound 5209502 is a promising candidate for additional experimental evaluation because of its notable stability and great affinity for TK2. This chemical may provide a focused and less harmful treatment for mitochondrial illnesses linked to TK2 malfunction.

Identification of Peregrin inhibitors-modulators by harnessing the computational prowess of molecular simulation and machine learning algorithms

Peregrin is marked as a potential drug target due to its pivotal role in the epigenetic maintenance of cellular metabolism. It is counted among those of the bromodomain-containing protein family. The protein binds to the acetylated lysine of N-terminus histone proteins of the nucleosomes. This bound form neutralizes the otherwise positively charged histone and, thus, crucially impacts the DNA replication mechanism. In several diseases like cancer, bone loss, and leukemia, this peregrin binding impacts the genes’ overexpression. Hence, the present study, computational screening of the bromodomain-specific inhibitors from a library of 5430 compounds retrieved from the ChemDiv database. Two different scoring functions based molecular docking studies have been employed for molecular interaction analysis. Followed by an artificial intelligence-based absolute binding affinity prediction has been confirmed through KDeep, which follows a machine learning step to obtain a precise binding energy score for the set of best compounds in the screening process. The resultant compounds were then screened for pharmacokinetics and drug-likeliness properties. Using molecular dynamics (MD) simulation analysis, the dynamic behavior of the four suggested compounds and Peregrin has been investigated for a 100 ns period. Identified compounds are found to be sufficiently effective in holding their strong interaction affinity toward Peregrin for an adequate time span, and structural integrity is also found to be comparable with the standard compound considered in the study. Mostly, all four potent compounds (K788-9421, S357-0084, S357-0893, S357-0915) are hydrophobic and evaluated for thermodynamics property analysis using MM-GBSA and free energy landscape (FEL) calculations. However, among all, K788-9421 shows comparatively better and energetically most favorable interactions with peregrin. Overall, study findings can lead to further research in developing next-generation broad-spectrum Peregrin inhibitors-modulators; they need extensive experimental validation for considering the compounds for clinical-trial application for being an excellent drug-candidate entity against Peregrin protein.

KTaCl6: High-voltage stable potassium-ion conducting chloride solid electrolyte

The exceptional electrochemical oxidative stabilities of halide solid electrolytes (SEs) have led to extensive research on Li and Na all-solid-state batteries. In this study, we report a new K+ SE, cubic KTaCl6, with a remarkable K+ conductivity of 1.0 × 10−5 S cm−1, synthesized via a mechanochemical method. This value represents a 1000-fold enhancement over that of samples prepared through heat treatment, which is remarkable among halide K+ SEs reported to date. Through structural characterization via X-ray diffraction, Rietveld analysis, and bond valence energy landscape calculations, we reveal three-dimensional K+ migration pathways facilitated by face-sharing KCl1211− cuboctahedra. This configuration is in contrast to that of the monoclinic KTaCl6 produced through annealing, which features discontinuous K+ migration pathways. These pathways are formed by the edge- or corner-sharing of KCl1211− anti-cuboctahedra, resulting in a significantly reduced K+ conductivity. Cyclic voltammetry measurements employing three-electrode cells indicate high electrochemical stability up to ≈3.7 V (vs. K/K+).

Design and evaluation of piperidine carboxamide derivatives as potent ALK inhibitors through 3D-QSAR modeling, artificial neural network and computational analysis

Tumor stands as one of the principal contributors to global mortality. As research into tumor treatments advances, tumor inhibitors emerge as pivotal milestones in tumor therapy. Among these inhibitors, Anaplastic Lymphoma Kinase (ALK), a receptor tyrosine kinase, is critical owing to its close association with tumor cell proliferation and growth, which renders it a critical therapeutic target. This work systematically explores the relationship between the chemical structures of 36 piperidine carboxamide derivatives and their efficacy in inhibiting Karpas-299 tumor cell activity by employing a rigorous 3D-QSAR modeling approach. A robust Topomer CoMFA model was generated and was meticulously validated through ANN neural network analysis (q2 = 0.597, r2 = 0.939, F = 84.401, N = 4, SEE = 0.268). Based on the model, 60 new compounds with desirable inhibitory activities were successfully designed. Combined with Lipinski’s rule and ADMET criteria alongside molecular docking and dynamics simulations, a lead compound with high inhibitory activity and good drug-likeness was selected. Further computational analyses, encompassing free energy landscape and binding free energy calculations, provided compelling evidence of the stable binding conformation of the lead compound and the superior affinity with the target protein at the active site, underscoring its potential therapeutic utility. In summary, this investigation offers valuable insights and methodological guidance for advancing tumor therapy and underscores the promise of piperidine carboxamide derivatives as prospective ALK inhibitors.

Antiviral actions of natural compounds against dengue virus RNA dependent RNA polymerase: insights from molecular dynamics and Gibbs free energy landscape

Dengue fever, a major global health challenge, affects nearly half the world’s population and lacks effective treatments or vaccines. Addressing this, our study focused on natural compounds that potentially inhibit the dengue virus’s RNA-dependent RNA polymerase (RdRp), a crucial target in the viral replication cycle. Utilizing the MTiOpenScreen webserver, we screened 1226 natural compounds from the NP-lib database. This screening identified four promising compounds ZINC000059779788, ZINC0000044404209, ZINC0000253504517 and ZINC0000253499146), each demonstrating high negative binding energies between −10.4 and −9.9 kcal/mol, indicative of strong potential as RdRp inhibitors. These compounds underwent rigorous validation through re-docking and a detailed 100 ns molecular dynamics (MD) simulation. This analysis affirmed the dynamic stability of the protein-ligand complexes, a critical factor in the effectiveness of potential drug candidates. Additionally, we conducted essential dynamics and free energy landscape calculations to understand the structural transitions in the RdRp protein upon ligand binding, providing valuable insights into the mechanism of inhibition. Our findings present these natural molecules as promising therapeutic agents against the dengue virus. By targeting the allosteric site of RdRp, these compounds offer a novel approach to hinder the viral replication process. This research significantly contributes to the search for effective anti-dengue treatments, positioning natural compounds as potential key players in dengue virus control strategies. Communicated by Ramaswamy H. Sarma

Na2.5Cr0.5Zr0.5Cl6: A New Halide-Based Fast Sodium-Ion Conductor.

All-solid-state batteries employing solid electrolytes (SEs) have received widespread attention due to their high safety. Recently, lithium halides are intensively investigated as promising SEs while their sodium counterparts are less studied. Herein, a new sodium-ion conductor with a chemical formula of Na2.5Cr0.5Zr0.5Cl6 is reported, which exhibits high room temperature ionic conductivity of 0.1 mScm-1 with low migration energy barrier of ≈0.41eV. Na2.5Cr0.5Zr0.5Cl6 has a Fm-3m structure with 41.67mol.% of cationic vacancies owing to the occupation of Cr (8.33mol.%) and Zr (8.33mol.%) ions at Na sites. Supercell calculations show that the lowest columbic energy configuration has Cr/Zr/V (where V is the vacancy) clusters in the structure. Nonetheless, the clusters have mixed effects on the sodium ion conduction pathway, based on the Bond Valence Energy Landscape calculation. A global 3D Na-ion transport percolation network can be revealed in the lowest energy supercell. Effective pathways are connected through the NaCl6 and VCl6 nodes. Besides, Raman spectroscopy and 23Na solid-state nuclear magnetic resonance spectroscopy further prove the tunable structure of the SEs with different Cr to Zr ratios. The optimization between the concentration of Na+ and vacancies is crucial to create an improved network of Na+ diffusion channels.

Li2GeS3: New Structural Type of Lithium Solid Electrolyte for All-Solid-State Batteries

Sulfide inorganic materials exhibit favorable qualities such as high ionic conductivity and mechanical softness, making them promising candidates for solid electrolytes in Li-ion all-solid-state batteries. Sulfide solid electrolytes exist in various structural types, including β-Li3PS4, Li10GeP2S12, argyrodite, Li4PS4I, Li7P3S11, and Li1.82SiP0.036S3. While these materials exhibit high ionic conductivities of up to ~10− 2 S cm− 1 at room temperature and possess mechanical softness, they also have limitations, such as a narrow electrochemical stability window and air instability, which can hinder their scalability. The electrochemical and air stabilities of a solid electrolyte (Li–M–S, where M = non-Li metal ions) are largely governed by its stability of crystal structure consisting of MSn polyhedra and Li ions. A material with a different crystal structure would show its distinct properties. However, despite extensive research, no single structure known to date has proven superior in all aspects of performance. Given the importance of crystal structure in developing high-performance solid electrolytes, exploring and identifying novel ion-conducting materials with unique crystal structures is imperative. Additionally, once a new structural type of material is discovered, its performance can be adjusted, enhanced, or optimized through various techniques, such as chemical substitution, morphology and particle size control, and surface coating. In this work, we discovered a new crystal structural type of Li-ion conductor Li2GeS3. It was first known in 2000 by Kanno et al., with only orthorhombic unit cell dimension reported. However, our study using ab initio structure determination techniques from powder X-ray diffraction data, similar to our previous works, unveiled its structure possessing a hexagonal P61 symmetry with lattice parameters of a = 6.80098(4) Å and c = 17.92827(11) Å, revealing a new type of crystal structure. Its structure is comprised of a distorted hexagonal close-packed arrangement of sulfur anions with three asymmetric metal atoms: Ge and Li2 are in tetrahedral cavities surrounded by sulfur atoms; Li1 is in the trigonal bipyramidal cavity. The material displayed an ionic conductivity of 1.63 × 10− 8 S cm− 1 at 303 K and 2.45 × 10− 7 S cm− 1 at 383 K. Bond valence energy landscape calculations revealed three-dimensional lithium diffusion pathways within the structure. These results suggest that Li2GeS3 is expected to be a host structure from which improved ionic conductors can be derived through appropriate chemical substitution.

Li2GeS3: Lithium Ionic Conductor with an Unprecedented Structural Type.

Lithium-ion batteries (LIBs) are widely used in electric vehicles, mobile electronic devices, and large-scale stationary energy storage systems. However, their liquid electrolytes present significant safety concerns due to their inherent flammability. To address this, the focus has shifted toward all-solid-state batteries (ASSBs) utilizing inorganic solid electrolytes that promise enhanced safety. In this work, we report the discovery of a new crystal structural type of Li-ion conductor, Li2GeS3, with a unique structure, synthesized by a solid-state reaction from Li2S and GeS2. It was first reported in 2000 with an orthorhombic unit cell, but its detailed crystal structure remains veiled. We have unveiled its structure for the first time, employing an ab initio structure determination technique from powder X-ray and time-of-flight neutron diffraction data. The compound has an unprecedented crystal structural type with a hexagonal P61 symmetry and a unit cell of a = 6.79364(4) Å and c = 17.90724(14) Å. Its structure is comprised of a distorted hexagonal close-packed arrangement of sulfur anions with three asymmetric metal atoms: Li1, Li2, and Ge are in tetrahedral cavities surrounded by sulfur atoms. The ionic conductivity of Li2GeS3 was measured to be 1.63 × 10-8 S cm-1 at 303 K and 2.45 × 10-7 S cm-1 at 383 K. Bond valence energy landscape calculations revealed three-dimensional lithium diffusion pathways within the structure. This novel crystal structure in Li2GeS3 holds the potential for developing high-performance ionic conductors through suitable chemical substitution and offers valuable insights into designing new ionic conductors for ASSBs.

Assembling Biocompatible Polymers on Gold Nanoparticles: Toward a Rational Design of Particle Shape by Molecular Dynamics.

Gold nanoparticles (AuNPs) have received great attention in a number of fields ranging from the energy sector to biomedical applications. As far as the latter is concerned, due to rapid renal clearance and a short lifetime in blood, AuNPs are often encapsulated in a poly(lactic-co-glycolic acid) (PLGA) matrix owing to its biocompatibility and biodegradability. A better understanding of the PLGA polymers on the AuNP surface is crucial to improve and optimize the above encapsulation process. In this study, we combine a number of computational approaches to explore the adsorption mechanisms of PLGA oligomers on a Au crystalline NP and to rationalize the PLGA coating process toward a more efficient design of the NP shape. Atomistic simulations supported by a recently developed unsupervised machine learning scheme show the temporal evolution and behavior of PLGA clusterization by tuning the oligomer concentration in aqueous solutions. Then, a detailed surface coverage analysis coupled with free energy landscape calculations sheds light on the anisotropic nature of PLGA adsorption onto the AuNP. Our results prove that the NP shape and topology may address and privilege specific sites of adsorption, such as the Au {1 1 1} crystal planes in selected NP samples. The modeling-based investigation suggested in this article offers a solid platform to guide the design of coated NPs.

The investigation of highly stable low strain orthorhombic Na2TiSiO5 as anode material for lithium ion batteries and the migration behavior of Na-Li ions

As a member of silicate anode materials, orthorhombic Na2TiSiO5, synthesized by solid state method, has excellent electrochemical properties and is a promising Lithium-ion battery anode material with long cycle stability and low strain. At a current density of 100 mA g−1, Na2TiSiO5 has a reversible capacity of 395.2 mA h g−1 after 200 cycles with Coulombic efficiencies more than 97%. A reversible capacity of 251.3 mA h g−1 after 1000 cycles is retained with Coulombic efficiencies more than 98%. ex-situ experiments show the high structural stability and a less than 0.67% change of unit cell parameters in the charge/discharge process. The bond valence energy landscape (BVEL) calculation reveals 12 voids, namely, 4c-1, 4c-2, 2b and 2a, in a unit cell. That corresponds to a nominal composition Na2Li(4c-1)Li(4c-2)Li0.5(2b)Li0.5(2a)TiSiO5 and a theoretical capacity of 398.1 mAh g−1. The ab initio molecular dynamics (AIMD) simulations and density functional theory (DFT) calculations show that for both primitive orthorhombic Na2TiSiO5 and Li+ inserted Na2TiSiO5, Na+/Li+ are not active. However, with the insertion of 4C Li+, the occurrence of the synergic diffusion of Na+ and Ti4+ (4c Na+ -> 4c Ti4+ and 4c Ti4+ -> 2b vacancy) reliefs the extra strain, improves the structural stability during charge/discharge. The formation energy convex hull reveals 3 intermediate phases, that is Na2LiTiSiO5, Na2Li2TiSiO5 and Na2Li2.75TiSiO5, in the charge/discharge process.

NaAlCl4: New Halide Solid Electrolyte for 3 V Stable Cost-Effective All-Solid-State Na-Ion Batteries

Although high-voltage-stable halide solid electrolytes (SEs) have emerged, only a few Na+ halide SEs have been developed thus far. Moreover, the use of expensive elements reduces the suitability of all-solid-state Na-ion batteries (ASNBs). Herein, the new mechanochemically prepared orthorhombic NaAlCl4 is demonstrated to exhibit a 10-fold enhancement in Na+ conductivity (3.9 × 10–6 S cm–1 at 30 °C) compared to annealed samples. The feasibility of NaAlCl4 for ASNBs is also validated for the first time. X-ray Rietveld refinement with bond valence energy landscape calculations reveals 1D-preferable 2D Na+ conduction pathways. High-voltage stability up to ∼4.0 V (vs Na/Na+) is confirmed by electrochemical measurements and theoretical calculations. Furthermore, the outstanding electrochemical performance of NaCrO2/Na3Sn ASNBs at 30 and 60 °C is demonstrated (e.g., 82.9% capacity retention at the 500th cycle at 60 °C and 1C), shedding light on the potential of the cost-effective and safe energy storage systems.

Formation of phosphorus monoxide through the [Formula: see text] reaction.

Phosphorus is a key and vital element for a diverse set of important biological molecules, being indispensable for life as we know. A deeper comprehension of its role in astrochemistry and atmospheric chemistry may aid in finding answers to how this element became available on Earth. The PO molecule is one of the main reservoirs of phosphorus in the interstellar medium (ISM), and a better understanding of the mechanisms and rate coefficients for its formation in the ISM is important for modelling its abundances. In this work, we perform multireference configuration interaction calculations on the formation of PO via the [Formula: see text] reaction, analyzing its potential energy surface and rate coefficients for the global reaction on both doublet and quartet states. We also perform DFT (M06-2X) and CCSD(T) calculations, in order to compare the results. We found that the OPO system possesses a high multiconfigurational character, making DFT and CCSD methodologies not suitable for its potential energy landscape calculation. The rate coefficients have been calculated using the master equation system solver (MESS) package, and the results compared to recent experimental data. It is shown that the quartet state contributes for temperatures higher than 700K. The computed rate coefficient can be described by a modified Arrhenius equation [[Formula: see text]] with [Formula: see text], [Formula: see text] and [Formula: see text] K.

Polymorphism and sodium-ion conductivity of NaTa2PO8 synthesized via the Li+/Na+ ion-exchange reaction of LiTa2PO8

Ion exchange reaction is a promising method to explore metastable compounds that could not be synthesized by conventional high-temperature solid-phase reactions. Herein, a new sodium tantalum phosphate, NaTa2PO8 was synthesized via the Li+/Na+ ion-exchange reaction of the parent compound, LiTa2PO8 in molten NaNO3 medium. NaTa2PO8 underwent an irreversible phase transition from the low- (LT-NaTa2PO8) to the high-temperature polymorph (HT-NaTa2PO8) at approximately 1000 °C. The crystal structures were solved using an ab initio structural determination method based on synchrotron X-ray powder diffraction data. The LT-NaTa2PO8 presented an orthorhombic structure, closely related to that of the parent LiTa2PO8 structure. In contrast, the HT-NaTa2PO8 was found to adopt a monoclinic structure, belonging to a family of monophosphate tungsten bronzes with pentagonal tunnels. The ionic conductivities of LT-NaTa2PO8 (σ = 5 × 10−5 S/cm at 309 °C) and HT-NaTa2PO8 (σ = 2 × 10−7 S/cm at 300 °C) exhibited Arrhenius behavior with activation energies of 0.49 and 0.79 eV, respectively. Bond valence energy landscape (BVEL) calculations indicated that a three-dimensional (3D) conduction pathway is formed in LT-NaTa2PO8 structure, while the conduction pathway in HT-NaTa2PO8 shows a two-dimensional (2D) character.

Reconstructions of the As-Terminated GaAs(001) Surface Exposed to Atomic Hydrogen.

We explore the atomic structures and electronic properties of the As-terminated GaAs(001) surface in the presence of hydrogen based on ab initio density functional theory. We calculate a phase diagram dependent on the chemical potentials of As and H, showing which surface reconstruction is the most stable for a given set of chemical potentials. The findings are supported by the calculation of energy landscapes of the surfaces, which indicate possible H bonding sites as well as the density of states, which show the effect of hydrogen adsorption on the states near the fundamental band gap.

Sliding energy landscape governs interfacial failure of nanotube-reinforced ceramic nanocomposites

We report the sliding adhesion of hexagonal boron nitride (hBN) and graphene on silica using single nanotube pullout force measurements and potential energy landscape calculations by density functional theory (DFT). In contrast to isotropic sliding of graphene on silica, the sliding of hBN on silica exhibits strong directional dependence with unusually high energy barriers formed by stacking of unterminated Si or O atoms on N atoms. Stronger interfacial adhesion energy and shear strength across possible termination structures of silica with hBN versus graphene cumulate in the measured interfacial shear strength of ∼34.7 MPa versus ∼19.2 MPa for the respective nanotube-reinforced composites

Computational study of non-conductive selectivity filter conformations and C-type inactivation in a voltage-dependent potassium channel.

C-type inactivation is a time-dependent process of great physiological significance that is observed in a large class of K+ channels. Experimental and computational studies of the pH-activated KcsA channel show that the functional C-type inactivated state, for this channel, is associated with a structural constriction of the selectivity filter at the level of the central glycine residue in the signature sequence, TTV(G)YGD. The structural constriction is allosterically promoted by the wide opening of the intracellular activation gate. However, whether this is a universal mechanism for C-type inactivation has not been established with certainty because similar constricted structures have not been observed for other K+ channels. Seeking to ascertain the general plausibility of the constricted filter conformation, molecular dynamics simulations of a homology model of the pore domain of the voltage-gated potassium channel Shaker were performed. Simulations performed with an open intracellular gate spontaneously resulted in a stable constricted-like filter conformation, providing a plausible nonconductive state responsible for C-type inactivation in the Shaker channel. While there are broad similarities with the constricted structure of KcsA, the hypothetical constricted-like conformation of Shaker also displays some subtle differences. Interestingly, those are recapitulated by the Shaker-like E71V KcsA mutant, suggesting that the residue at this position along the pore helix plays a pivotal role in determining the C-type inactivation behavior. Free energy landscape calculations show that the conductive-to-constricted transition in Shaker is allosterically controlled by the degree of opening of the intracellular activation gate, as observed with the KcsA channel. The behavior of the classic inactivating W434F Shaker mutant is also characterized from a 10-μs MD simulation, revealing that the selectivity filter spontaneously adopts a nonconductive conformation that is constricted at the level of the second glycine in the signature sequence, TTVGY(G)D.

Phase transformation and ionic conductivity mechanism of a low-temperature sintering semiconductor Na2CaV4O12

Alkaline earth metal vanadates have drawn attention because of their potential applications in electrochemical devices. Here, Na2CaV4O12 was prepared at extremely low temperatures (350–550 °C) and showed a semiconductor behavior with a bandgap of 2.92 eV. A phase transition from P4/nbm to P4̅b2 occurred at 510 °C was identified by an in-situ XRD upon heating, where the 16 n site for oxygen atoms in the P4/nbm phase evolves into two distinguishable 8i sites in the P4̅b2 phase. Ionic conduction in Na2CaV4O12 at elevated temperatures was reported for the first time in the present work. A strong correlation between ionic conductivity and phase structure of Na2CaV4O12 is observed. The charged carriers are mainly sodium ions for the low-temperature P4/nbm phase, while mixed conduction contributed by sodium ions and oxide ions happened in the transformed phase. Bond valence-based energy landscape calculations disclosed a two-dimensional interstitial diffusion mechanism for Na+ ions in the Na2Ca-layers, as well as a two-dimensional diffusion mechanism for oxide ions in the V4O12-layers. The novel semiconductor ceramic would have potential applications in all-solid sodium ions batteries or solid oxide fuel cells as electrolytes.

Electrical Properties, Defect Structures, and Ionic Conducting Mechanisms in Alkali Tungstate Li2W2O7.

Discovery of new high-conductivity solid-state ionic conductors has been a long-lasting interest in the field of solid-state ionics for their important applications in solid-state electrochemical devices. Here, we report the mixed oxide-ion and Li-ion conductions, together with their conducting mechanisms in the Li2W2O7 material with triclinic symmetry. The process for the ionic identity is supported by several electrochemical measurements including electrochemical impedance spectroscopy, DC polarization, oxygen concentration cell, and theoretical analysis of neutron diffraction data and bond-valence-based energy landscape calculations. We show from electrochemical measurements strong evidences of the predominating oxide-ion conducting and minor Li-ion chemistry in Li2W2O7 at high temperatures, while the bond-valence-based energy landscape analysis reveals possible multidimensional ionic migration pathways for both oxide-ions and Li-ions. Thus, the presented results provide fundamental insights into new mixed ionic conduction mechanisms in low-symmetry materials and have implications for discoveries of new ionic conductors in years to come.

Benefit of high-pressure structure on sodium transport properties: Example with NaFeF3 post-perovskite

In the search of promising Na-ion cathode materials, high-pressure synthesis method was applied to obtain sodium iron fluoride NaFeF3 with the post-perovskite lamellar structure. A two-step synthesis was performed: first, the Pnma orthorhombic perovskite structure NaFeF3 form (or Pv-NaFeF3, GdFeO3 type) was synthesized at 1270 ​K and 7.7 ​GPa, then the Cmcm orthorhombic post-perovskite structure (or pPv-NaFeF3, CaIrO3 type) was obtained using a second step at 700 ​K and 15 ​GPa. The post-perovskite form was stabilized under ambient conditions with a low amount of remaining perovskite phase (5 ​mol%). The Mössbauer analysis of pPv-NaFeF3 was firstly investigated with a paramagnetic structure obtained at 300 and 77 ​K, opposed to Pv-NaFeF3 magnetism reflecting the different [FeF6] polyhedra arrangements. Finally, the sodium migration within the framework of both structures was evaluated with the use of Bond Valence Energy Landscape (BVEL) calculations, resulting with an enhanced Na+ mobility within the pPv-NaFeF3 structure.

Coupling behavior between lattice dynamics and Li self-diffusion in layered α-LiAlO2 ceramic

In molten carbonate fuel cells (MCFC), α-LiAlO2 ceramic matrix, at higher temperature or H-rich atmosphere, undergoes an irreversible phase transition of α-LiAlO2 to γ-phase that causes a large volume change and greatly impacts the lifetime of the cells. In this manuscript, we unravel an unusual coupling property between the lattice dynamic and Li+ ions diffusion for the first time, near the common operating temperature of 923 K. A temperature-dependent lattice dynamics study on α-LiAlO2 was performed by probing the in-situ Raman spectroscopy. In addition, the phonon density of states was estimated theoretically through first-principles calculations. Notably, in-situ Raman spectroscopy combined with the calculated atom-projected phonons density of states (PDOS) and Bond Valence Energy Landscape (BVEL) calculations demonstrated that the phonon mode Eg dominated by oxygen atoms decays into three acoustical phonons that couple with the diffusion of mobile Li+ ions in ab-plane above 600 K. In MCFC environments, large amounts of Li+ ions or H+ ion in the electrolyte will diffuse into the lattice of α-LiAlO2. This would further enhance the coupling behavior between oxygen atoms and diffusion ion and finally results in the instability of lattice dynamics of oxygen atoms.