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Elpasolite- and cryolite-type oxyfluorides can be regarded as superstructures of perovskite and exhibit structural diversity. While maintaining a similar structural topology with the prototype structures, changes in the size, electronegativity, and charge of cation and/or anion inevitably lead to structural evolution. Therefore, the nominal one-to-one relation suggested by a doubled formula of perovskite does not guarantee a simple 2-fold superstructure for many cases. Herein, the commensurately modulated perovskite-like K3TiOF5 was refined at 100 K from single-crystal X-ray diffraction data by using a pseudotetragonal subcell with lattice parameters of a = b = 6.066(2) A and c = 8.628(2) A. The length of the modulation vector was refined to 0.3a* + 0.1b* + 0.25c*. In the commensurate supercell of K3TiOF5, the B-site Ti4+ and K+ cations in [TiOF5]3- and [KOF5]6- octahedral units were found to be significantly displaced from the average atomic positions refined in the subcell. The displacements of the K+ cations are ±0.76 A, and those for the Ti4+ cations are approximately ±0.13 A. One- and two-dimensional solid-state 19F NMR measurements revealed two tightly clustered groups of resonances in a ratio of ca. 4:1, assigned to equatorial and axial fluorine, respectively, consistent with local [TiOF5]3- units. S/TEM results confirmed the average structure. Electronic structure calculations of the idealized I4mm subcell indicate the instability to a modulated structure arises from soft optical modes that is controlled by the octahedrally coordinated B-site potassium ions in the cryolite-type structure.

Metal heteroanionic compounds such as oxynitrides, oxysulfides, and oxyhalides have emerged as promising photocatalysts for water splitting, owing to their reduced band gaps compared to conventiona...

The centrosymmetric polymorph of KNaNbOF5 undergoes a reconstructive transition from a rare A-site vacancy ordered perovskite to a unique nonperovskite high-temperature phase. Previously, the high ...

A new ferroelectric perovskite oxynitride is proposed and demonstrated for photocatalytic applications using a systematic first-principles study. Ruddlesden–Popper (RP) Ca3Nb2N2O5, a layered struct...

Elpasolite- and cryolite-type oxyfluorides can be regarded as superstructures of perovskite and exhibit structural diversity. While maintaining a similar structural topology with the prototype structures, changes in the size, electronegativity, and charge of cation and/or anion inevitably lead to structural evolution. Therefore, the nominal one-to-one relation suggested by a doubled formula of perovskite does not guarantee a simple 2-fold superstructure for many cases. Herein, the commensurately modulated perovskite-like K

We describe a strategy to design ferroelectric heteroanionic materials based on the coupling of anion order and octahedral tilts in $n=1$ Ruddlesden-Popper structures, which allows noncentrosymmetric and polar compounds to arise from centrosymmetric anion-ordered structures. We investigate the relative phase stabilities of the polymorphs of ${\mathrm{Sr}}_{2}{\mathrm{ScO}}_{3}\mathrm{F}$ and ${\mathrm{Ca}}_{2}{\mathrm{ScO}}_{3}\mathrm{F}$ derived from this coupling using electronic structure calculations. We find that large degrees of octahedral tilting can stabilize different anion orders derived from assembly of $[{\mathrm{ScO}}_{5}{\mathrm{F}]}^{8\ensuremath{-}}$ octahedra. To further understand the link between octahedral tilting and anion order, we quantitatively separate the contributions of electrostatics and covalent interactions to the stability of tilts. We find that the tilts are driven primarily by covalent interactions and that local out-of-plane polar displacements, induced from the anion order, further stabilize the octahedral tilts through the pseudo-Jahn-Teller effect.

We report a workflow for heteroanionic materials discovery using Pauling's second rule to filter for and predict new candidate materials for synthesis with reduced computational overhead. Using oxyfluoride and oxynitride n = 1 Ruddlesden-Popper compounds as a use-case, we show that a minimization scheme based on the global instability index (GII) efficiently filters up to 50% of highly unstable candidate compositions based on crystal-chemistry grounds. We then validate the minimization scheme using density functional theory (DFT) calculations and find that unexpectedly the GII of stable heteroanionic materials is higher than that of homoanionic oxides owing to significant charge redistribution in compounds containing more than one anionic species. Using this workflow, we predict Sr2AlO3F to be stable and describe our attempts to synthesize a phase-pure material.

The burgeoning field of anion engineering in oxide-based compounds aims to tune physical properties by incorporating additional anions of different size, electronegativity, and charge. For example, oxychalcogenides, oxynitrides, oxypnictides, and oxyhalides may display new or enhanced responses not readily predicted from or even absent in the simpler homoanionic (oxide) compounds because of their proximity to the ionocovalent-bonding boundary provided by contrasting polarizabilities of the anions. In addition, multiple anions allow heteroanionic materials to span a more complex atomic structure design palette and interaction space than the homoanionic oxide-only analogs. Here, established atomic and electronic principles for the rational design of properties in heteroanionic materials are contextualized. Also described are synergistic quantum mechanical methods and laboratory experiments guided by these principles to achieve superior properties. Lastly, open challenges in both the synthesis and the understanding and prediction of the electronic, optical, and magnetic properties afforded by anion-engineering principles in heteroanionic materials are reviewed.

In this work we present a data-driven approach to the rational design of battery materials based on both resource and performance considerations. A large database of Li-ion battery material has been created by abstracting information from over 200 publications. The database consists of over 16 000 data points from various classes of materials. In addition to reference information, key parameters and variables determining the performance of batteries were collected. This work also includes resource considerations such as crustal abundance and the Herfindahl–Hirschman index, a commonly used measure of market concentration. The data is organized into a free web-based resource where battery researchers can employ a unique visualization method to plot database parameters against one another. This contribution is concerned with cathode and anode electrode materials. Cathode materials are mostly based on an intercalation mechanism, while anode materials are primarily based on conversion and alloying. Results indicate that cathode materials follow a common trend consistent with their crystal structure. On the other hand anode materials display similar behavior, based on elemental composition. Of particular interest is that high energy cathodes are scarcer than high power materials and high performance anode materials are less available. More sustainable materials for both electrodes based on alternative compositions are identified.

We report magnetodielectric coupling in rhombohedral ilmenites ${\mathrm{CoTiO}}_{3}$ and ${\mathrm{NiTiO}}_{3}$ along with heat capacity and magnetic measurements. ${\mathrm{CoTiO}}_{3}$ and ${\mathrm{NiTiO}}_{3}$ undergo antiferromagnetic ordering at $\ensuremath{\approx}$ 38 and $\ensuremath{\approx}$ 22 K, respectively. The dielectric permittivity of ${\mathrm{CoTiO}}_{3}$ decreases below its magnetic ordering temperature while the dielectric permittivity of ${\mathrm{NiTiO}}_{3}$ increases below the N\'eel temperature. The dielectric permittivity of ${\mathrm{CoTiO}}_{3}$ and ${\mathrm{NiTiO}}_{3}$ are dependent on the applied magnetic field and temperature with the strongest dependence observed close to the magnetic-ordering temperature. We analyze magnetodielectric coupling in ${\mathrm{CoTiO}}_{3}$ and ${\mathrm{NiTiO}}_{3}$ on the basis of spin-phonon coupling and suggest other possible mechanisms such as exchange coupling and magnetostrictive effects.

In this work we present a data-driven approach to the rational design of battery materials based on both resource and performance considerations. This work builds upon previous efforts by Gaultois and coworkers to use data mining to explore battery materials. A large database of Li-ion battery material has been created by abstracting information from over 200 publications. The database consists of over 16,000 data points from various classes of materials. In addition to reference information regarding author, publication, synthesis and material composition, key parameters and variables determining the performance of batteries were collected including energy density, power density, discharge capacity, lithiation potential, capacity retention upon cycling and many others. In addition to performance considerations, this work also includes resource considerations such as crustal abundance and the Herfindahl-Hirschman index, a commonly accepted measure of market concentration, calculated from geological data (known elemental reserves) and geopolitical data (elemental production). The data is organized into a free web-based resource where battery researchers can employ a unique visualization method to plot database parameters against one another. The resulting high-information density plots are well suited to explore correlation, comparison and analysis of both performance and resource considerations in battery materials simultaneously. This contribution is concerned with cathode and anode electrode materials. Cathode materials are mostly based on the intercalation mechanism while anode materials are primarily based on conversion and alloying. Also Na and Li resources are compared to determine viability of one battery type that can supply worldwide energy by renewable resources. Results indicate that cathode materials follow a common trend consistent with their crystal structure. On the other hand anode materials display behavior based on elemental composition. Of particular interest is that cobaltate electrodes may not be justifiable in terms of performance and resource consideration in cathodes and those silicate materials may be a good candidate for next generation anode electrodes. Resource consideration of Li-ion batteries showed that, there is an exhaustible supply that necessitates production of other type of batteries such as Na-ion batteries.

Cooperative Jahn-Teller ordering is well-known to drive the cubic $Fd\overline{3}m$ to tetragonal $I$4$_1$/$amd$ structural distortion in Mn$_3$O$_4$ at 1170 $^{\circ}$C. Further structural distortion occurs in Mn$_3$O$_4$ upon magnetic ordering at 42 K. Employing high-resolution variable-temperature synchrotron x-ray diffraction we show that tetragonal $I$4$_1$/$amd$ and orthorhombic $Fddd$ phases coexist, with nearly equal fractions, below the Neel temperature of Mn$_3$O$_4$. Significant variation of the orthorhombic $a$ and $b$ lattice constants from the tetragonal $a$ lattice constant is observed. Structural phase coexistence in Mn$_3$O$_4$ is attributed to large strains due to the lattice mismatch between the tetragonal $I$4$_1$/$amd$ and the orthorhombic $Fddd$ phases. Strain tensors determined from Rietveld refinement show a highly strained matrix of the $I4_1/amd$ phase that accommodates the nucleated orthorhombic $Fddd$ phase in the phase coexistence regime. A comparison of the deformation observed in Mn$_3$O$_4$ to structural deformations of other magnetic spinels shows that phase coexistence may be a common theme when structural distortions occur below 50 K.

© 2014 American Chemical Society. Strong and particularly long ranged (>100 nm) interaction forces between apposing hydrophobic lipid monolayers are now well understood in terms of a partial turnover of mobile lipid patches, giving rise to a correlated long-range electrostatic attraction. Here we describe similarly strong long-ranged attractive forces between self-assembled monolayers of carboranethiols, with dipole moments aligned either parallel or perpendicular to the surface, and hydrophobic lipid monolayers deposited on mica. We compare the interaction forces measured at very different length scales using atomic force microscope and surface forces apparatus measurements. Both systems gave a long-ranged exponential attraction with a decay length of 2.0 ± 0.2 nm for dipole alignments perpendicular to the surface. The effect of dipole alignment parallel to the surface is larger than for perpendicular dipoles, likely due to greater lateral correlation of in-plane surface dipoles. The magnitudes and range of the measured interaction forces also depend on the surface area of the probe used: At extended surfaces, dipole alignment parallel to the surface leads to a stronger attraction due to electrostatic correlations of freely rotating surface dipoles and charge patches on the apposing surfaces. In contrast, perpendicular dipoles at extended surfaces, where molecular rotation cannot lead to large dipole correlations, do not depend on the scale of the probe used. Our results may be important to a range of scale-dependent interaction phenomena related to solvent/water structuring on dipolar and hydrophobic surfaces at interfaces.

Dense pellets of > 99% purity trirutile Cr2WO6 were prepared in one step from starting oxides using spark plasma sintering, leading to simultaneous reaction and consolidation in 3 min at 1473 K. The reducing environment during processing may be partly responsible for the rapid reaction time in these oxides, with partial reduction of Cr3+ and the associated oxygen vacancies allowing rapid diffusion of cations. The low-temperature physical properties of Cr2WO6 were examined, and a new transition at T = 5.9 K was observed as an anomaly in the temperature-dependent dielectric permittivity and a corresponding anomaly in the specific heat. A strong enhancement of the magnetocapacitance is observed below this transition temperature at T = 5.9 K and may be associated with a change from collinear spin order to more complex spin order.

Non-specific physical and specific chemical interactions of cells, bacteria, and biomembranes with non-biological target surfaces (e.g., metallic and metal oxides) are crucial in determining the interfacial behavior (interaction forces, adhesion, local deformations and structuring) of many bio- and nano-inspired materials. Knowledge of the governing interactions provides physicochemical understanding of biological systems, and enables engineering of new nano-systems for biomaterials or biomedical benefit. We have directly measured and visualized membrane adhesion and detachment at nanoscopic and extended rough gold electrode surfaces through a multi-scale approach: interactions and contact mechanics measured by surface forces apparatus (SFA) are in quantitative agreement with atomic force microscopy (AFM) measurements, both of which show that membranes can strongly adhere to rough gold surfaces and asperities via specific amine–gold binding and non-specific hydrophobic interactions. The results give insights into membrane interactions at smooth and rough metallic surfaces, and provide a basis for improved design of nanoparticle and extended surface biomaterials.