Computational insights into the electronic structure of TCNDQ and TCNP: the effect of Si substitution

Structural Chemistry - Tetracyanodiphenoquinodimethane (TCNDQ) and tetracyanopyrenoquinodimethane (TCNP) are larger cyanocarbons related to tetracyanoethylene (TCNE) and tetracyanoquinodimethane...     

Spectroscopic understanding of ultra-high rate performance for LiMn(0.75)Fe(0.25)PO4 nanorods-graphene hybrid in lithium ion battery

Comprehensive X-ray absorption near-edge structure spectroscopy at the C, O and Li K-edges and the Mn, Fe, and P L-edges of LiMn(0.75)Fe(0.25)PO(4) nanorods-graphene has been reported in great detail. Compared to that of free standing graphene and LiMn(0.75)Fe(0.25)PO(4), the intimate interaction between the nanorods and graphene via charge redistribution has been unambiguously confirmed. This interaction not only anchors the nanorods onto the graphene but also modifies its surface chemistry, both of which afford the nanorods-graphene hybrid an ultra-high rate performance in lithium ion batteries. Such knowledge is important for the understanding of hybrid nanomaterials for lithium ion batteries and allows rational design for further improvements in performance.     

On the areas of cyclic and semicyclic polygons

We investigate the “generalized Heron polynomial” that relates the squared area of an n-gon inscribed in a circle to the squares of its side lengths. For a (2m+1)-gon or (2m+2)-gon, we express it as the defining polynomial of a certain variety derived from the variety of binary (2m−1)-forms having m−1 double roots. Thus we obtain explicit formulas for the areas of cyclic heptagons and octagons, and illuminate some mysterious features of Robbins' formulas for the areas of cyclic pentagons and hexagons. We also introduce a companion family of polynomials that relate the squared area of an n-gon inscribed in a circle, one of whose sides is a diameter, to the squared lengths of the other sides. By similar algebraic techniques we obtain explicit formulas for these polynomials for all n7.     

The electron affinities of TCNE and TCNQ: the effect of silicon substitution

The cyanocarbons tetracyanoethylene (TCNE) and tetracyanoquinodimethane (TCNQ) are important electron acceptors used in organic electronic applications. A common approach to enhancing their performance is by structural modification with previous studies focusing on substituting the cyano ligands or annular moiety. In this work, we assess the effect of hypovalent substitution, swapping carbon for silicon, on the potential energy surfaces and adiabatic electron affinities (AEAs). Si-substitution generally enhances AEA, and in the case of TCNQ stabilizes an open-shell singlet diradical state. Such findings may find value in the design of new materials based on the cyanocarbon platform.

     

High-field quasiparticle tunneling in Bi2Sr2CaCu2O(8+delta): negative magnetoresistance in the superconducting state

We report on the c-axis resistivity rho(c)(H) in Bi(2)Sr(2)CaCu(2)O(8+delta) that peaks in quasistatic magnetic fields up to 60 T. By suppressing the Josephson part of the two-channel (Cooper pair/quasiparticle) conductivity sigma(c)(H), we find that the negative slope of rho(c)(H) above the peak is due to quasiparticle tunneling conductivity sigma(q)(H) across the CuO2 layers below H(c2). At high fields (a) sigma(q)(H) grows linearly with H, and (b) rho(c)(T) tends to saturate ( sigma(c) not equal0) as T-->0, consistent with the scattering at the nodes of the d-wave gap. A superlinear sigma(q)(H) marks the normal state above T(c).     

Bi-axial texture in Ca0.1Y0.9Ba2Cu4O8 composite wires made by metallic precursors

High filament count, silver-sheathed composite wires of Ca_0.1Y_0.9Ba₂Cu₄O₈ (Y–124) were prepared by a metallic precursor route. The ductility of the metallic precursor enabled one to manufacture tapes containing up to 962 407 filaments, with filament dimensions as fine as 0.25 μm thick and 1 μm wide. By using a thermal-mechanical treatment to texture the Y–124 grains, transport critical current densities in the oxide filaments of 69 500 A/cm² at 4.2 K in self-field were obtained. Moreover, in an applied field of 0.1 T, the samples retained 39% of their self-field critical current density. A TEM investigation revealed significant bi-axial crystallographic texture: in areas viewed, c-axis alignment of adjacent grains was within 10° and oriented perpendicular to the tape face; a-axis alignment of adjacent grains was within 15° and oriented parallel to the longitudinal direction of the filaments. Furthermore, c-axis texture alone did not adequately predict the performance of these Y−124 composite conductors. Instead, performance scaled with the degree of bi-axial texture. These wires exhibited among the best reported J_c for a polycrystalline, sintered wire of YBCO in an applied magnetic field.     

Syntheses and structures of N-phenylmaleimidetriazoles and by-products

The syntheses, properties, and structures of N-phenylmaleimidetriazole derivatives are described. Intermediates and by-products are also discussed. 1b. a = 43.997(7) Å, 5.7610(9) Å, 8.245(1) Å, = 99.339(4), C₂/c; 2a. a = 13.646(4) Å, b = 7.744(2) Å, c = 10.612(3) Å, = 91.979(6), P2₁/c. 3a. a = 22.245(1) Å, b = 22.245(1) Å, 10.010(1) Å, P42/n. 3a. a = 11.727(2) Å, b = 14.075(3) Å, c = 16.080(3) Å, = 105.859(3), = 105.331(3), = 98.187(3), P-1. 3b. a = 8.561(3) Å, b = 14.755(5) Å, c = 22.771(7) Å, = 97.006(5), P2₁/c. 3c. a = 10.500(2) Å, b = 12.189(2) Å, c = 13.040(2) Å, = 109.091(3), = 106.089(3), = 101.022(3), P-1. 8a. a = 16.389(8) Å, b = 5.749(3) Å, c = 19.316(3) Å, = 97.467(9), P2₁/n. 8b. a = 5.822(2) Å, b = 10.114(3) Å, c = 16.705(4) Å, = 84.681(5), = 82.840(5), = 75.769(4), P-1. 9b. a = 11.251(1) Å, 13.335(3) Å, 13.376(3) Å, = 102.456(4), P2₁/n. 9c. a = 15.836(3) Å, b = 8.236(2) Å, c = 5.447(3) Å, = 92.551(3), P2₁/c. 10a. a = 13.177(2) Å, b = 14.597(2) Å, c = 5.5505(8) Å, = 110.979(2), Cc. 11a. a = 14.720(2) Å, b = 13.995(2) Å, c = 38.245(6) Å, = 94.430(3), P2₁/n. 12b. a = 15.067(5) Å, b = 20.378(6) Å, c = 8.669(5) Å, = 99.16(4), = 99.32(3), = 105.23(3), P-1. 13b. a = 8.2824(6) Å, b = 10.5245(7) Å, c = 15.518(1) Å, = 92.305(1), = 100.473(1), = 100.124(1), P-1. 15a. a = 15.357(3) Å, b = 7.778(2) Å, c = 22.957(2) Å, Pbca. 16b. a = 18.0384(4) Å, b = 12.474(3) Å, c = 20.078(5) Å, Pbca.