Thiacalix[4]monocrowns substituted by sulfur-containing anchoring groups: New ligands for gold surface modification

Crown containing calix[4]arenes 2a-f with thioacetate-functionalized carbon chains on lower rim in 1,3-alternate conformation were synthesized starting from corresponding bromo-derivatives. The use of thiacalixcrowns monolayer films improves adhesion between gold and biomolecules (cytochrome c and catalase). The structures of these monolayers were analyzed using contact angle measurements and AFM visualization by discontinuous contact mode. © ISUCT Publishing

Progress on lead-free metal halide perovskites for photovoltaic applications: a review

ABSTRACT: Metal halide perovskites have revolutionized the field of solution-processable photovoltaics. Within just a few years, the power conversion efficiencies of perovskite-based solar cells have been improved significantly to over 20%, which makes them now already comparably efficient to silicon-based photovoltaics. This breakthrough in solution-based photovoltaics, however, has the drawback that these high efficiencies can only be obtained with lead-based perovskites and this will arguably be a substantial hurdle for various applications of perovskite-based photovoltaics and their acceptance in society, even though the amounts of lead in the solar cells are low. This fact opened up a new research field on lead-free metal halide perovskites, which is currently remarkably vivid. We took this as incentive to review this emerging research field and discuss possible alternative elements to replace lead in metal halide perovskites and the properties of the corresponding perovskite materials based on recent theoretical and experimental studies. Up to now, tin-based perovskites turned out to be most promising in terms of power conversion efficiency; however, also the toxicity of these tin-based perovskites is argued. In the focus of the research community are other elements as well including germanium, copper, antimony, or bismuth, and the corresponding perovskite compounds are already showing promising properties. GRAPHICAL ABSTRACT: [Image: see text

Static and Dynamic Charge Inhomogeneity and Crystal-field Fluctuations for 4f Ions in High-Jc Cuprates

The main mechanism in homogeneous broadening and relaxation of crystal-field excitations for R-ions in cuprates is believed to be provided by the fluctuations of crystalline electric field induced by a static and dynamic charge inhomogeneity generic to doped cuprates. Such an inhomogeneity is assumed to be the result of topological phase separation. We address the generalized granular model as one of the model scenarios for describing the static and dynamic charge inhomogeneity in cuprates. The charge subsystem is believed to be similar to that of a Wigner crystal with melting transition and phononlike positional excitation modes. We consider a simple model of charge inhomogeneity that allows us to elucidate the main universal features of the density of CF states and the respective inhomogeneous broadening. The formal description of R-ion relaxation mainly coincides with that of the recently suggested magnetoelastic mechanism by Lovesey and Staub. © 2004 MAIK "Nauka/Interperiodica".ACKNOWLEDGMENTS This paper was supported in part by INTAS (grant no. 01-0654), the CRDF (grant no. REC-005), RME (grant nos. 02.-3.4-392 and UR.01.01.062), and the Russian Foundation for Basic Research (project no. 04-02-96077). A. S. M. has benefited from stimulating discussions with A. T. Boothroyd, A. Mirmel-stein, and J. Mesot

Mixed-valence hydrated iron fluoridotitanate: Synthesis, optics and calorimetry

Текст статьи не публикуется в открытом доступе в соответствии с политикой журнала.Mixed-valence hydrated fluoridotitanate with idealized formula FeTiF6·6H2O is the main product of fluoride processing of natural mineral ilmenite with hydrofluoric acid. Its single crystals were grown and optical and calorimetric experiments were carried out in the temperature range 200–350 K. Charge re-distribution, Fe2+Ti4+ to Fe3+Ti3+, in the compound studied was evident in XPS spectra. A first order ferroelastic phase transition occurs at temperatures T0↓ = 271.5 K, T0↑ = 274 ÷ 275.5 K with the symmetry change P3‾↔ P1‾. The structural transformation is accompanied by the appearance of a very weak optical anisotropy in the slice (001), a small anomaly of the heat capacity (ΔS = 1.5 J/mol K = 0.2R), and positive baric coefficients dT0/dp ≈ 30 ± 10 K/GPa. © 2020 Elsevier Lt

Sequence of phase transitions in (NH4)3SiF7

Текст статьи не публикуется в открытом доступе в соответствии с политикой журнала.Single crystals of silicon double salt (NH4)(3)SiF7 = (NH4)(2)SiF6 center dot NH4F = (NH4)(3)[SiF6]F were grown and studied by the methods of polarization optics, X-ray diffraction and calorimetry. A sequence of symmetry transformations with the temperature change was established: P4/mbm (Z = 2) (G(1)) Pbam (Z = 4) (G(2)) P2(1)/c (Z = 4) (G(3)) P (1) over bar (Z = 4) (G(4)) P2(1)/c (Z = 8) (G(5)). Crystal structures of different phases were determined. The experimental data were also interpreted by a group-theoretical analysis of the complete condensate of order parameters taking into account critical and noncritical atomic displacements. Strengthening of the N-H center dot center dot center dot F hydrogen bonds can be a driving force of the observed phase transitions

Sequence of phase transitions in (NH4)3SiF7

Текст статьи не публикуется в открытом доступе в соответствии с политикой журнала.Single crystals of silicon double salt (NH4)(3)SiF7 = (NH4)(2)SiF6 center dot NH4F = (NH4)(3)[SiF6]F were grown and studied by the methods of polarization optics, X-ray diffraction and calorimetry. A sequence of symmetry transformations with the temperature change was established: P4/mbm (Z = 2) (G(1)) Pbam (Z = 4) (G(2)) P2(1)/c (Z = 4) (G(3)) P (1) over bar (Z = 4) (G(4)) P2(1)/c (Z = 8) (G(5)). Crystal structures of different phases were determined. The experimental data were also interpreted by a group-theoretical analysis of the complete condensate of order parameters taking into account critical and noncritical atomic displacements. Strengthening of the N-H center dot center dot center dot F hydrogen bonds can be a driving force of the observed phase transitions