Anion Sublattice Research Articles

Stability of inorganic ionic structures: the uniformity approach.

The crystal structure uniformity is numerically estimated as the standard deviation of the crystal space quantizer 〈G3〉. This criterion has been applied to explore the uniformity of ionic sublattices in 21465 crystal structures of inorganic ionic compounds. In most cases, at least one kind of sublattice (whole ionic lattice, cationic or anionic sublattice) was found to be highly uniform with a small 〈G3〉 value. Non-uniform structures appeared to be either erroneous or essentially non-ionic. As a result, a set of uniformity criteria is proposed for the estimation of the stability of ionic crystal structures.

Phonon spectroscopy and features of low-temperature heat capacity of solid solutions of electrolytes

The kinetic characteristics of thermal frequency phonons in the region of helium temperatures in ceramic samples of the Ce1–xGdxO2–y electrolyte solid solution have been studied. To explain the temperature dependence of the phonon mean free path, we used the previously performed calculations of the energy of vacancy formation in the anion sublattice of a solid solution of zirconium dioxide stabilized by yttrium ZrO2:Y2O3 (YSZ) with a similar crystal structure. It is shown that in the Ce1–xGdxO2–y system under study, the formation of structural defects associated with the presence of vacancies in the anion sublattice with energy Δ = 8.53 K is possible. It has been established that analysis of the temperature dependences of the YSZ heat capacity allows one to trace the degree of disorder (amorphization) of the solid solution depending on its level of stabilization.

Site Disorder Drives Cyanide Dynamics and Fast Ion Transport in Li6PS5CN.

Halide argyrodite solid-state electrolytes of the general formula Li6PS5 X exhibit complex static and dynamic disorder that plays a crucial role in ion transport processes. Here, we unravel the rich interplay between site disorder and dynamics in the plastic crystal argyrodite Li6PS5CN and the impact on ion diffusion processes through a suite of experimental and computational methodologies, including temperature-dependent synchrotron powder X-ray diffraction, AC electrochemical impedance spectroscopy, 7Li solid-state NMR, and machine learning-assisted molecular dynamics simulations. Sulfide and (pseudo)halide site disorder between the two anion sublattices unilaterally improves long-range lithium diffusion irrespective of the (pseudo)halide identity, which demonstrates the importance of site disorder in dictating bulk ionic conductivity in the argyrodite family. Furthermore, we find that anion site disorder modulates the presence and time scales of cyanide rotational dynamics. Ordered configurations of anions enable fast, quasi-free rotations of cyanides that occur on time scales of 1011 Hz at T = 300 K. In contrast, we find that cyanide dynamics are slow or frozen in Li6PS5CN when site disorder between the cyanide and sulfide sublattices is present at T = 300 K. We rationalize the observed differences in cyanide dynamics in the context of elastic dipole interactions between neighboring cyanide anions and local strain induced by the configurations of site disorder that may impact the energetic landscape for cyanide rotational dynamics. Through this study, we find that anion disorder plays a decisive role in dictating the extent and time scales of both lithium ion and cyanide dynamics in Li6PS5CN.

Dual Polyanion Mechanism for Superionic Transport in BH4‐Based Argyrodites

AbstractPolyanion rotations are often linked to cation diffusion, but the study of multiple polyanion systems is scarce due to the complexities in experimentally determining their dynamic interactions. This work focuses on BH4‐based argyrodites, synthesized to achieve a high conductivity of 11 mS cm−1. Advanced tools, including high‐resolution X‐ray diffraction, neutron pair distribution function analysis, and mutinuclear magic‐angle‐spinning nuclear magnetic resonance (NMR) spectroscopy and relaxometry, along with theoretical calculations, are employed to unravel the dynamic intricacies among the dual polyanion lattice and active charge carriers. The findings reveal that the anion sublattice of Li5.07PS4.07(BH4)1.93 affords an even temporal distribution of Li among PS43− and BH4−, suggesting minimal trapping of the charge carriers. Moreover, the NMR relaxometry unveils rapid BH4− rotation on the order of ∼GHz, affecting the slower rotation of neighboring PS43− at ∼100 MHz. The PS43− rotation synchronizes with Li+ motion and drives superionic transport. Thus, the PS43− and BH4− polyanions act as two‐staged dual motors, facilitating rapid Li+ diffusion.

Raman spectroscopy study of disorder in cation sublattice of nonstoichiometric and annealed ZnSnN2

This study examines the specific characteristics of Raman scattering observed in ZnSnN2 samples produced via magnetron co-sputtering. The spectra demonstrate a high degree of similarity to the phonon density of states. This phenomenon is caused by the presence of SnZn substitutional defects, which disrupt the ideal crystal structure and generate so-called defect-induced Raman modes across the entire first Brillouin zone. An increase in the elemental content of Sn leads to a decrease in the intensity of the 230 cm⁻1 and 660 cm⁻1 peaks and to their broadening. This suggests an intensification of the disorder within the cation sublattice. Following annealing at 450 °C in a vacuum, an increase in the intensity of the peaks at 450 cm⁻1 and 560 cm⁻1, as well as the Boson peak, was observed. We attribute these changes to the increased formation of Zn–N–Sn bonds within the film structure due to the ordering of the anion (nitrogen) sublattice. However, zinc and tin atoms still occupy random positions in their sublattices, contributing to the overall increase in structural disorder.

Superionic Conduction in K3SbS4 Enabled by Cl‐Modified Anion Lattice

AbstractAll‐solid‐state potassium batteries emerge as promising alternatives to lithium batteries, leveraging their high natural abundance and cost‐effectiveness. Developing potassium solid electrolytes (SEs) with high room‐temperature ionic conductivity is critical for realizing efficient potassium batteries. In this study, we present the synthesis of K2.98Sb0.91S3.53Cl0.47, showcasing a room‐temperature ionic conductivity of 0.32 mS/cm and a low activation energy of 0.26 eV. This represents an increase of over two orders of magnitude compared to the parent compound K3SbS4, marking the highest reported ionic conductivity for non‐oxide potassium SEs. Solid‐state 39K magic‐angle‐spinning nuclear magnetic resonance on K2.98Sb0.91S3.53Cl0.47 reveals an increased population of mobile K+ ions with fast dynamics. Ab initio molecular dynamics (AIMD) simulations further confirm a delocalized K+ density and significantly enhanced K+ diffusion. This work demonstrates diversification of the anion sublattice as an effective approach to enhance ion transport and highlights K2.98Sb0.91S3.53Cl0.47 as a promising SE for all‐solid‐state potassium batteries.

Superionic Conduction in K3SbS4 Enabled by Cl-Modified Anion Lattice.

All-solid-state potassium batteries emerge as promising alternatives to lithium batteries, leveraging their high natural abundance and cost-effectiveness. Developing potassium solid electrolytes (SEs) with high room-temperature ionic conductivity is critical for realizing efficient potassium batteries. In this study, we present the synthesis of K2.98Sb0.91S3.53Cl0.47, showcasing a room-temperature ionic conductivity of 0.32 mS/cm and a low activation energy of 0.26 eV. This represents an increase of over two orders of magnitude compared to the parent compound K3SbS4, marking the highest reported ionic conductivity for non-oxide potassium SEs. Solid-state 39K magic-angle-spinning nuclear magnetic resonance on K2.98Sb0.91S3.53Cl0.47 reveals an increased population of mobile K+ ions with fast dynamics. Ab initio molecular dynamics (AIMD) simulations further confirm a delocalized K+ density and significantly enhanced K+ diffusion. This work demonstrates diversification of the anion sublattice as an effective approach to enhance ion transport and highlights K2.98Sb0.91S3.53Cl0.47 as a promising SE for all-solid-state potassium batteries.

Insights into a Defective Potassium Sulfido Cobaltate: Giant Magnetic Exchange Bias, Ionic Conductivity, and Electrical Permittivity

AbstractThe novel potassium sulfido cobaltate, K2[Co3S4] is introduced, with 25% vacancies of the cobalt positions within a layered anionic sublattice. The impedance and dielectric investigations indicate a remarkable ionic conductivity of 21.4 mS cm−1 at room temperature, which is in the range of highest ever reported values for potassium‐ions, as well as a high electrical permittivity of 2650 at 1 kHz, respectively. Magnetometry results indicate an antiferromagnetic structure with giant intrinsic exchange bias fields of 0.432 and 0.161 T at 3 and 20 K respectively, potentially induced by a combination of the interfacial effect of combined magnetic anionic and nonmagnetic cationic sublattices, as well as partial spin canting. The stability of the exchange bias behavior is confirmed by a training effect of less than 18% upon 10 hysteresis cycles. The semiconductivity of the material is determined, both experimentally and theoretically, with a bandgap energy of 1.68 eV. The findings render this material as a promising candidate for both, active electrode material in potassium‐ion batteries, and for spintronic applications.

Remnant Copper Cation-Assisted Atom Mixing in Multicomponent Nanoparticles.

Nanostructured high-/medium-entropy compounds have emerged as important catalytic materials for energy conversion technologies, but complex thermodynamic relationships involved with the element mixing enthalpy have been a considerable roadblock to the formation of stable single-phase structures. Cation exchange reactions (CERs), in particular with copper sulfide templates, have been extensively investigated for the synthesis of multicomponent heteronanoparticles with unconventional structural features. Because copper cations within the host copper sulfide templates are stoichiometrically released with incoming foreign cations in CERs to maintain the overall charge balance, the complete absence of Cu cations in the nanocrystals after initial CERs would mean that further compositional variation would not be possible by subsequent CERs. Herin, we successfully retained a portion of Cu cations within the silver sulfide (Ag2S) and gold sulfide (Au2S) phases of Janus Cu2-xS-M2S (M = Ag, Au) nanocrystals after the CERs, by partially suppressing the transformation of the anion sublattice that inevitably occurs during the introduction of external cations. Interestingly, the subsequent CERs on Janus Cu1.81S-M2S (M = Ag, Au), by utilizing the remnant Cu cations, allowed the construction of Janus Cu1.81S-AgxAuyS, which preserved the initial heterointerface. The synthetic strategy described in this work to suppress the complete removal of the Cu cation from the template could fabricate the CER-driven heterostructures with greatly diversified compositions, which exhibit unusual optical and catalytic properties.

Reducing Voltage Hysteresis in Li-Rich Sulfide Cathodes by Incorporation of Mn.

Conventional intercalation-based cathode materials in Li-ion batteries are based on charge compensation of the redox-active cation and can only intercalate one mole of electron per formula unit. Anion redox, which employs the anion sublattice to compensate charge, is a promising way to achieve multielectron cathode materials. Most anion redox materials still face the problems of slow kinetics and large voltage hysteresis. One potential solution to reduce voltage hysteresis is to increase the covalency of the metal-ligand bonds. By substituting Mn into the electrochemically inert Li1.33Ti0.67S2 (Li2TiS3), anion redox can be activated in the Li1.33-2y/3Ti0.67-y/3Mn y S2 (y = 0-0.5) series. Not only do we observe substantial anion redox, but the voltage hysteresis is significantly reduced, and the rate capability is dramatically enhanced. The y = 0.3 phase exhibits excellent rate and cycling performance, maintaining 90% of the C/10 capacity at 1C, which indicates fast kinetics for anion redox. X-ray absorption spectroscopy (XAS) shows that both the cation and anion redox processes contribute to the charge compensation. We attribute the drop in hysteresis and increase in rate performance to the increased covalency between the metal and the anion. Electrochemical signatures suggest the anion redox mechanism resembles holes on the anion, but the S K-edge XAS data confirm persulfide formation. The mechanism of anion redox shows that forming persulfides can be a low hysteresis, high rate capability mechanism enabled by the appropriate metal-ligand covalency. This work provides insights into how to design cathode materials with anion redox to achieve fast kinetics and low voltage hysteresis.

Investigation of structural, thermo–electrical, and morphological features of the (Bi2O3)1–x–y (Tm2O3)x (Yb2O3)y ternary systems for intermediate temperatures

In this paper, the (Bi2O3)1–x–y (Tm2O3)x (Yb2O3)y ternary systems were successfully synthesized by the solid–state reaction method under air conditions. All powder compositions were then heat treated for 100 h at 750 °C to allow for partial substitution of dopant cations, Tm3+ and Yb3+, between host Bi3+ cations. Characterizations of fabricated compositions were carried out by XRD, TG and DTA, FPPT, and FE–SEM techniques. Stacked XRD patterns verified that all compositions included solely single–phase peaks, with the exception of Bi0.92Tm0.04Yb0.04O1.5–δ and Bi0.88Tm0.04Yb0.08O1.5–δ, whose patterns suggested mixed phases. The DTA curves, depending on temperature, detected the endothermic peaks at around 600 °C, implying that an order–disorder transition occurs in the anion sublattice of the doped crystal. At 700 °C, the conductivity of the Bi0.88Tm0.08Yb0.04O1.5–δ system was found to be 0.432 S/cm, surpassing the conductivity of a single–doped (Bi2O3)0.80 (Er2O3)0.20 system, which had a value of 0.37 S/cm at the same temperature.

Exploring Reversible Redox Behavior in the 6H-BaFeO3-δ (0 < δ < 0.4) System: Impact of Fe3+/Fe4+ Ratio on CO Oxidation.

This work is devoted to evaluating the relationship between the oxygen content and catalytic activity in the CO oxidation process of the 6H-type BaFeO3-δ system. Strong evidence is provided about the improvement of catalytic performance with increasing Fe average oxidation state, thus suggesting the involvement of lattice oxygen in the catalytic process. The compositional and structural changes taking place in both the anionic and cationic sublattices of the catalysts during redox cycles have been determined by temperature-resolved neutron diffraction. The obtained results evidence a structural transition from hexagonal (P63/mmc) to orthorhombic (Cmcm) symmetry. This transition is linked to octahedra distortion when the Fe3+ concentration exceeds 40% (δ values higher than 0.2). The topotactical character of the redox process is maintained in the δ range 0 < δ < 0.4. This suggests that the cationic framework is only subjected to slight structural modifications during the oxygen exchange process occurring during the catalytic cycle.

High entropy pyrochlore (La0.3Gd0.3Ca0.4)2(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)2O7 ceramic with amorphous-like thermal conductivity for environmental/thermal barrier coating applications

Low thermal conductivity and excellent mechanical strength are essential to pyrochlore A2B2O7 ceramic for environmental/thermal barrier coating applications. To collaboratively tailor the mechanical and thermal properties of A2B2O7 ceramic, a novel high entropy pyrochlore ceramic (La0.3Gd0.3Ca0.4)2(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)2O7 with significant atomic radius and mass fluctuation is proposed by simultaneously introducing various elements with different valence states at A and B cation sites. The as-synthesized (La0.3Gd0.3Ca0.4)2(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)2O7 exhibits enhanced fracture toughness (1.68 MPa m1/2), amorphous-like low thermal conductivity (1.45 W m–1 K–1 at 900 °C) and matched thermal expansion coefficient (9.0 × 10–6 K–1 at 1200 °C) with Al2O3/Al2O3 CMCs. The extensive misfits in atomic weight, ionic radius among the substitutional cations in combination with the intrinsic oxygen vacancies in the anion sublattice play significant roles in the thermal conductivity reduction of (La0.3Gd0.3Ca0.4)2(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)2O7 ceramic. The combination of outstanding mechanical and thermal properties indicates that this type of material has a good application prospect for environmental/thermal barrier coatings.

The effect of nitrogen on the isothermal oxidation of substoichiometric zirconium carbide: Microstructural and spectroscopic investigations

The oxidation behavior of hot-pressed sub-stoichiometric zirconium carbide was investigated through isothermal flow-tube furnace experiments at temperatures ranging from 1000 to 1600 °C. Auxiliary gas composition influence on the oxidation of ZrC0.63 was studied by introducing oxygen to substrates held under either pure argon or nitrogen environments. During furnace ramp-up, prior to isothermal oxygen exposure, nitrogen flow was found to infiltrate the substrate resulting in ZrCxNy formation which provided superior oxidation resistance to the as-received ZrC0.63. Ex situ investigation of ceramic-oxide interfacial regions revealed the presence of carbon precipitate in both material sets at treatment temperatures of up to 1400 °C, along with the presence of the ZrCxOy system. At sufficiently high test temperatures, resulting scale formations for the N2/O2 systems were found to be less porous than the Ar/O2 counterparts, with a higher degree of c-/t-ZrO2 crystallites present at room temperature attributed to nitrogen incorporation into the anion sublattice of ZrO2.

Efficient single-step mechanosynthesis route of nanostructured Hf0.2Nb0.2Ta0.2V0.2Zr0.2C0.5N0.5 High Entropy Carbonitride Powder

Nowadays high entropy carbides (HECs) are an important group of advanced ceramics. They are composed by at least by five transition metals (TMs) in nearly equiatomic proportion and disordered distributed in the cationic sublattice of face centered cubic structures, with carbon atoms in the octahedral interstitial voids, with general formula (TM1,TM2,TM3,TM4,TM5)C. These HECs belong to the recent novel group of ultra-high temperature ceramics (UHTCs), with superior properties in comparison with the constituent binary carbides. However, the synthesis of those HECs can be modified to develop high entropy carbonitrides, HECNs, where the C are partially substituted by N, to form a solid solution in the anionic sublattice, with expected improved properties as UHTCs, but they are in an incipient state of development. Here, we report the synthesis and deep characterization of a non-previously obtained Hf0.2Nb0.2Ta0.2V0.2Zr0.2C0.5N0.5 HECN, via a facile, single step and reproducible solid-gas reaction mechanosynthesis route. The synthesis was successfully completed in a planetary ball mill device, after 2h of milling time, at 400 rpm and using a ball-to- powder ratio of 60:1 in a pure N2 atmosphere at room temperature. The as-synthesized HECNs powdered showed nanostructured morphology and outstanding high-temperature oxidation resistance up to 1500 °C.

Can large lattice volume always facilitate ion diffusion in solids?

Large lattice volume is usually expected to expand the bottleneck size and enlarge free volume for fast Li ion transport in solids. But the universality of lattice expansion decreasing activation energy barrier for Li ion migration is still debatable. Herein, our molecular dynamics simulations and density functional theory calculations detect the unconventional phenomenon of lattice expansion increasing activation energy barrier for Li ion migration in β-Li3PS4, Li4SnS4 and Li4GeS4 sulfides with the hcp-type anion sublattice, and discover the underlying mechanism. On one hand, lattice expansion enlarges the relative energies between the octahedral and tetrahedral Li sites, and correspondingly increase activation energy barrier for tetrahedral Li ions migration along the Tet-Oct-Tet migration paths in β-Li3PS4, Li4SnS4 and Li4GeS4. On the other hand, the lattice dynamics calculations show Li energy landscapes of β-Li3PS4, Li4SnS4 and Li4GeS4 are anharmonic and enlarging lattice volume make the local minimum of Li potential energy surface flatter, simultaneously reduce the relative energy of Li occupation site, eventually resulting in the higher activation energy barrier for Li ion migration. Thus, understanding the effect of lattice volume on ion migration in solids should not only consider the factor of bottleneck size and free volume, but also combine the aspects of Li ion occupation type, Li ion migration path and anion sublattice type. These new understandings of the lattice expansion increasing activation energy barrier for ion migration would further promote the further optimization and rational design of superionic conductors by element doping or strain engineering.

Resistive Switching Mechanism in Ferroelectric Memristors with Thin Polycrystalline Barium Titanate Film

In a ferroelectric memristor, the manifestation of resistive effects is most often associated with the influence of polarization and dynamics of the domain structure on the charge transport. The role of point defects is either not taken into account or is reduced to the modulation of potential barriers at the interfaces with electrodes. However, the similarity of charge transport mechanisms in memristors based on thin ferroelectric and metal-oxide films suggests that the contribution of point defects in the anionic sublattice, namely, oxygen vacancies, to the resistive switching in ferroelectric memristors may be dominant. In order to identify the key factors responsible for resistive tuning in a ferroelectric memristor, a combined experimental and theoretical study of resistive switching effects in 10-nm polycrystalline barium titanate films was performed. X-ray photoelectron spectroscopy, piezoresponse force microscopy and scanning tunneling microscopy were employed to investigate the local resistive and ferroelectric properties and to estimate the stoichiometry of the films. A drift-diffusion numerical model of non-stationary processes in thin ferroelectric films was developed, including the Poisson equation and the continuity equation for each component of mobile charge carriers. Using the developed model as well as experimental I—V characteristics taken with scanning tunneling spectroscopy, the contribution of various mechanisms to the resistive switching in ferroelectric memristors with polycrystalline barium titanate has been studied. Non-stationary processes involving oxygen vacancies were found to govern the resistive switching.

Fluorite-structured high-entropy oxide sputtered thin films from bixbyite target

The prototype high-entropy oxide (HEO) Y0.2La0.2Ce0.2Pr0.2Sm0.2O2−δ represents a particularly complex class of HEOs with significant anion sublattice entropy. The system takes either a fluorite or bixbyite-type crystal structure, depending on synthesis kinetics and thermal history. Here, we synthesize bulk ceramics and epitaxial thin films of Y0.2La0.2Ce0.2Pr0.2Sm0.2O2−δ and use diffraction to explore crystal symmetry and phase. Thin films exhibit the high symmetry fluorite phase, while bulk ceramics adopt the lower symmetry bixbyite phase. The difference in chemical ordering and observed symmetry between vapor-deposited and reactively sintered specimens suggests that synthesis kinetics can influence accessible local atomic configurations, i.e., the high kinetic energy adatoms quench in a higher-effective temperature, and thus higher symmetry structure with more configurational entropy. More generally, this demonstration shows that recovered HEO specimens can exhibit appreciably different local configurations depending on synthesis kinetics, with potential ramifications on macroscopic physical properties.

Localisation of vibrational modes in high-entropy oxides

The recently-discovered high-entropy oxides (HEO’s) offer a paradoxical combination of crystalline arrangement and high disorder. They differ qualitatively from established paradigms for disordered solids such as glasses and alloys. In these latter systems, it is well known that disorder induces localised vibrational excitations. In this article, we explore the possibility of disorder-induced localisation in Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O, the prototypical HEO with rock-salt structure. To describe phononic excitations, we model the interatomic potentials for the cation–oxygen interactions by fitting to the physical properties of the parent binary oxides. We validate our model against the experimentally determined crystal structure and optical conductivity. The resulting phonon spectrum shows wave-like propagating modes at low energies and localised modes at high energies. Localisation is reflected in signatures such as participation ratio and correlation amplitude. Finally, we argue that mass disorder can be increased to enhance localisation. We consider a hypothetical material, high-entropy telluride-oxide, where tellurium atoms are admixed into the anion sublattice. This shows a larger localised fraction, with additional localised modes appearing in the middle of the spectrum. Our results demonstrate that HEO’s are a promising platform to study Anderson localisation of phonons.

Structural Characterization of La0.6Sr0.4CoO3-δ Thin Films Grown on (100)-, (110)-, and (111)-Oriented La0.95Sr0.05Ga0.95Mg0.05O3-δ.

In this study, a detailed structural characterization of epitaxial La0.6Sr0.4CoO3-δ (LSC) films grown in (100), (110), and (111) orientations was conducted. LSC is a model air electrode material in solid oxide fuel and electrolysis cells and understanding the correlation of bulk structure and catalytic activity is essential for the design of future electrode materials. Thin films were grown on single crystals of the perovskite material La0.95Sr0.05Ga0.95Mg0.05O3-δ cut in three different directions. This enabled an examination of structural details at the atomic scale for a realistic material combination in solid oxide cells. The investigation involved the application of atomic force microscopy, X-ray diffraction, and high-resolution transmission electron microscopy to explore the distinct properties of these thin films. Interestingly, ordering phenomena in both cationic as well as anionic sublattices were found, despite the fact that the thin films were never at higher temperatures than 600 °C. Cationic ordering was found in spherical precipitates, whereas the ordering of oxygen vacancies led to the partial transition to brownmillerite in all three orientations. Our results indicate a very high oxygen vacancy concentration in all three thin films. Lattice strains in-plane and out-of-plane was measured, and its implications for the structural modifications are discussed.