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Chemistry of materials 28(9), 2941 - 2948(2016). doi:10.1021/acs.chemmater.5b04719, Significant developments of Li-ion batteries will be necessary to cope with the growing demands in electromobility or home storage of (sustainable) electrical energy. A detailed knowledge on the microscopic processes during battery cycling will be increasingly crucial for improvements. Involved phase changes at ambient temperature often involve metastable intermediate states, making both experimental observation and theoretical prediction of process pathways difficult. Here we describe an in situ high energy X-ray diffraction study following the initial alloying and dealloying of Li with an Au thin-film model anode using ionic liquid electrolyte. Six different crystalline alloy phases were observed to be involved in the cyclic phase transitions. Apart from the highest lithiated phase determined in this study, Li3Au, none of the observed phases could be related to known, thermodynamically stable Li–Au phases. Structural search calculations following the minima hopping method (MHM) allowed the assignment of these phases to distinct metastable Au–Li alloy unit cells., Published by American Chemical Society, Washington, DC

We report a new multiferroic family of $(R,\mathrm{Y}){\mathrm{CrO}}_{4}(R=\mathrm{Sm},\mathrm{Gd},\text{and} \mathrm{Ho})$. The ferroelectric ordering temperatures are observed at much higher temperatures than their corresponding magnetic ordering temperatures for all the members. The values of electric polarization ($P$) are significantly high, which vary from $\ensuremath{\sim}217$ to $\ensuremath{\sim}640\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}{\mathrm{C}/\mathrm{m}}^{2}$ for a 4 kV/cm poling field. The large value of $P\phantom{\rule{0.16em}{0ex}}(\ensuremath{\sim}590\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}{\mathrm{C}/\mathrm{m}}^{2})$ for ${\mathrm{YCrO}}_{4}$ compared to the smallest $P$ value in the series for ${\mathrm{GdCrO}}_{4}$ signifies that the magnetic rare-earth element does not directly influence the $P$ value. Our careful analysis of the low-temperature synchrotron diffraction studies confirms that the distortion of ${\mathrm{CrO}}_{4}$ tetrahedra directs the $P$ value. The structural transformation from the centrosymmetric $I{4}_{1}/amd$ structure to a noncentrosymmetric $I\overline{4}2d$ space group at the onset of polar order is found to be correlated with the appearance of spontaneous electric polarization.

Physical review / B 96(19), 195433 (2017). doi:10.1103/PhysRevB.96.195433, High-energy surface-sensitive x-ray diffraction (HESXRD) is a powerful high-energy photon technique (E>70 keV) that has in recent years proven to allow a fast data acquisition for the 3D structure determination of surfaces and nanoparticles under in situ and operando conditions. The use of a large-area detector facilitates thedirect collection of nearly distortion-free diffraction patterns over a wide q range, including crystal truncation rods perpendicular to the surface and large-area reciprocal space maps from epitaxial nanoparticles, which is not possible in the conventional low-photon energy approach (E=10−20 keV). Here, we present a comprehensivemathematical approach, explaining the working principle of HESXRD for both single-crystal surfaces and epitaxial nanostructures on single-crystal supports. The angular calculations used in conventional crystal truncation rod measurements at low-photon energies are adopted for the high-photon-energy regime, illustratingwhy and to which extent large reciprocal-space areas can be probed in stationary geometry with fixed sample rotation. We discuss how imperfections such as mosaicity and finite domain size aid in sampling a substantial part of reciprocal space without the need of rotating the sample. An exact account is given of the area probed inreciprocal space using such a stationary mode, which is essential for in situ or operando time-resolved experiments on surfaces and nanostructures., Published by Inst., Woodbury, NY

We report significant correlation of the multiferroic order and ferroelectric polarization to the orthorhombic structural distortion for ${\mathrm{Ca}}_{1\ensuremath{-}x}{\mathrm{La}}_{x}{\mathrm{BaCo}}_{4}{\mathrm{O}}_{7}$ ($x\ensuremath{\le}$ 0.05). Analysis of the synchrotron diffraction studies reveal that La doping increases considerable structural distortion, which is associated with the increase of multiferroic ordering temperature and electric polarization. Intriguingly, the value of polarization increases remarkably to $\ensuremath{\approx}385\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{C}/{\mathrm{m}}^{2}$ ($x=0.05$) from $\ensuremath{\approx}150\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{C}/{\mathrm{m}}^{2}$ ($x=0$) for a 3 kV/cm poling field. Synchrotron diffraction studies in magnetic field provides an important clue, where structural distortion provides more impact on the polarization value than the contribution from the change in unit cell volume. Geometric magnetic frustration holds the key for the occurrence of the structural distortions, around which multiferroic ordering takes place for ${\mathrm{CaBaCo}}_{4}{\mathrm{O}}_{7}$. Our work thus highlights crystal structural distortion as a rich playground for tuning multiferroic order as well as polarization value.

Review of scientific instruments 88(10), 104102 (2017). doi:10.1063/1.4999688, A new versatile and easy-to-use remote-controlled reactor setup aimed at the analysis of chemical reactions under solvothermal conditions has been constructed. The reactor includes a heating system that can precisely control the temperature inside the reaction vessels in a range between ambient temperature and 180 °C. As reaction vessels, two sizes of commercially available borosilicate vessels (V$_{max}$ = 5 and 11 ml) can be used. The setup furthermore includes the option of stirring and injecting of up to two liquid additives or one solid during the reaction to initiate very fast reactions, quench reactions, or alter chemical parameters. In addition to a detailed description of the general setup and its functionality, three examples of studies conducted using this setup are presented., Published by American Institute of Physics, [S.l.]

Physical chemistry, chemical physics 19(39), 26651 - 26661 (2017). doi:10.1039/C7CP04852A, Surface induced smectic order was found for the ionic liquid 1-methyl-3-docosylimidazolium bis(trifluoromethlysulfonyl)imide by X-ray reflectivity and grazing incidence scattering experiments. Near the free liquid surface, an ordered structure of alternating layers composed of polar and non-polar moieties is observed. This leads to an oscillatory interfacial profile perpendicular to the liquid surface with a periodicity of 3.7 nm. Small angle X-ray scattering and polarized light microscopy measurements suggest that the observed surface structure is related to fluctuations into a metastable liquid crystalline SmA2 phase that was found by supercooling the bulk liquid. The observed surface ordering persists up to 157 °C, i.e. more than 88 K above the bulk melting temperature of 68.1 °C. Close to the bulk melting point, we find a thickness of the ordered layer of L = 30 nm. The dependency of L(τ) = Λ ln(τ/τ1) vs. reduced temperature τ follows a logarithmic growth law. In agreement with theory, the pre-factor Λ is governed by the correlation length of the isotropic bulk phase., Published by RSC Publ., Cambridge

We report ferroelectricity around ∼88 K that appears well below T N (∼25 K), unlike other members of RCrO3 series. A synchrotron diffraction study suggests that the occurrence of ferroelectricity in NdCrO3 is coupled to the structural transformation from centrosymmetric Pnma to a non-centrosymmetric Pna21 space group. A strong magnetoelectric coupling is observed in the electric polarization [P(T)]. This coupling is significantly influenced by the magnetic field cooling effect, suggesting an exchange bias effect in P(T). This exchange bias effect is also revealed by the systematic shift of the magnetic hysteresis loops below T(N). The rare occurrence of an exchange bias effect in both the magnetic and electric polarizations associated with a strong magnetoelectric coupling is of fundamental interest, as well as being attractive for technological applications close to liquid nitrogen temperature.

Physical chemistry, chemical physics 20(37), 24494 - 24495 (2018). doi:10.1039/C8CP91851A, Surface induced smectic order was found for the ionic liquid 1-methyl-3-docosylimidazolium bis(trifluoromethlysulfonyl)imide by X-ray reflectivity and grazing incidence scattering experiments. Near the free liquid surface, an ordered structure of alternating layers composed of polar and non-polar moieties is observed. This leads to an oscillatory interfacial profile perpendicular to the liquid surface with a periodicity of 3.7 nm. Small angle X-ray scattering and polarized light microscopy measurements suggest that the observed surface structure is related to fluctuations into a metastable liquid crystalline SmA2 phase that was found by supercooling the bulk liquid. The observed surface ordering persists up to 157 °C, i.e. more than 88 K above the bulk melting temperature of 68.1 °C. Close to the bulk melting point, we find a thickness of the ordered layer of L = 30 nm. The dependency of L(τ) = Λ ln(τ/τ1) vs. reduced temperature τ follows a logarithmic growth law. In agreement with theory, the pre-factor Λ is governed by the correlation length of the isotropic bulk phase., Published by RSC Publ., Cambridge

We report appearance of polar order with a ordering temperature $({T}_{C})$ at 28 K, which is well below the ferrimagnetic order at 225 K $({T}_{N})$ for ${\mathrm{CoCr}}_{2}{\mathrm{S}}_{4}$. Intriguingly, the value of spontaneous electric polarization $(P)$ is $\ensuremath{\sim}122 \ensuremath{\mu}\mathrm{C}/{\mathrm{m}}^{2}$ at 15 K, which is the second largest value in Cr octahedra-based spinels after ${\mathrm{CdCr}}_{2}{\mathrm{S}}_{4}$. Incidentally, the $P$ value is $\ensuremath{\sim}60$ times larger than the value of $P$ for the oxide counterpart ${\mathrm{CoCr}}_{2}{\mathrm{O}}_{4}$. The significant magnetoelectric coupling is verified from the magnetodielectric response and magnetic field dependent enhancement of $P$. We note that the field-dependent dielectric permittivity scales linearly to the squared magnetization in the low field regime below $\ensuremath{\sim}10$ kOe as described by the Ginzburg-Landau theory. Synchrotron diffraction studies over a wide temperature range, $15\text{--}300$ K, illustrate strong magnetoelastic coupling at ${T}_{N}$ and isostructural distortion at ${T}_{C}$. Analyses of the diffraction patterns reveal that the occurrence of polar order involves expansion of Co tetrahedra and contraction of Cr octahedra of the spinel structure and these distortions are further enhanced driven by the magnetic field. The delicate interplay between magnetoelastic, magnetoelectric, and electroelastic couplings in ${\mathrm{CoCr}}_{2}{\mathrm{S}}_{4}$ proposes the system as a potential candidate in multiferroics.