Porous materials find widespread application in storage, separation, and catalytic technologies. We report a crystalline porous solid with adaptable porosity, in which a simple dipeptide linker is arranged in a regular array by coordination to metal centers. Experiments reinforced by molecular dynamics simulations showed that low-energy torsions and displacements of the peptides enabled the available pore volume to evolve smoothly from zero as the guest loading increased. The observed cooperative feedback in sorption isotherms resembled the response of proteins undergoing conformational selection, suggesting an energy landscape similar to that required for protein folding. The flexible peptide linker was shown to play the pivotal role in changing the pore conformation
We investigate the normal state of the ''11'' iron-based superconductor FeSe 0:42 Te 0:58 by angle-resolved photoemission. Our data reveal a highly renormalized quasiparticle dispersion characteristic of a strongly correlated metal. We find sheet dependent effective carrier masses between %3 and 16m e corresponding to a mass enhancement over band structure values of m à =m band % 6-20. This is nearly an order of magnitude higher than the renormalization reported previously for iron-arsenide superconductors of the ''1111'' and ''122'' families but fully consistent with the bulk specific heat.
The ceramic Ba8ZnTa6O24 has been synthesized in isolation and its dielectric and crystallographic properties characterized. The material affords excellent dielectric properties, with a high unloaded quality factor Qu=20 800 at 3.28 GHz, high relative permittivity εr=29 and a temperature coefficient of resonant frequency τf=29.4 ppm/°C. The crystal structure adopted is complex, comprising mixed cubic and hexagonal perovskite subunits, and contains cation vacancies on the octahedral sites. A second phase with a closely related structure is identified, demonstrating the existence of a family of materials. This structural complexity offers diverse opportunities for substitutions calculated to enhance the figures of merit reported.
In situ methods are ideally suited for the study of the development of property-critical structural features during materials processing. As an example of their potential in the area of complex oxide electroceramics, here, we apply in situ synchrotron powder diffraction to investigate the ordering processes responsible for optimizing the microwave dielectric properties of the commercial electroceramic barium zinc tantalate. The collection of synchrotron diffraction data with high resolution and high intensity during processing has allowed the growth of cation site order within a domain and the size of the ordered domains to be separated during the multistage thermal treatment processing used by industry. Domain growth does not commence until the extent of order within a domain is maximized. Analysis of the superstructure intensities with the Avrami equation shows that nucleation is not important in this process. Domain growth then occurs by the curvature-driven Allen-Cahn mechanism. The complex nature of the ordering is confirmed by the coexistence of two phases whose temporal evolution divides into two stages according to the two stages of ordering and domain growth mentioned above. The implications of these observations for industrial processing procedures aimed at reducing the processing time are discussed.
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