Strong Closed-Shell Interactions in Inorganic Chemistry.

Since the discovery of superconductivity above 30 K by Bednorz and M\"uller in the La copper oxide system, the critical temperature has been raised to 90 K in Y${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ and to 110 and 125 K in Bi-based and Tl-based copper oxides, respectively. In the two years since this Nobel-prize-winning discovery, a large number of electronic structure calculations have been carried out as a first step in understanding the electronic properties of these materials. In this paper these calculations (mostly of the density-functional type) are gathered and reviewed, and their results are compared with the relevant experimental data. The picture that emerges is one in which the important electronic states are dominated by the copper $d$ and oxygen $p$ orbitals, with strong hybridization between them. Photon, electron, and positron spectroscopies provide important information about the electronic states, and comparison with electronic structure calculations indicates that, while many features can be interpreted in terms of existing calculations, self-energy corrections ("correlations") are important for a more detailed understanding. The antiferromagnetism that occurs in some regions of the phase diagram poses a particularly challenging problem for any detailed theory. The study of structural stability, lattice dynamics, and electron-phonon coupling in the copper oxides is also discussed. Finally, a brief review is given of the attempts so far to identify interaction constants appropriate for a model Hamiltonian treatment of many-body interactions in these materials.

Electronic structure of the high-temperature oxide superconductors

Structure and magnetism of coordination polymers containing dicyanamide and tricyanomethanide

In the Editor's Choice [1] the development and demonstration of a highly efficient warm-white all-nitride phosphor-converted light emitting diode (pc-LED) is presented utilizing a GaN based quantum well blue LED and two novel nitrogen containing luminescent materials doped with Eu2+. These novel LEDs are superior to both incandescent and fluorescent lamps and may therefore become the next generation of general lighting sources.



The cover picture is an artist's view of the 2-pc-LED: On a copper slug and underneath a plastic lens a ‘flip-chip’ is soldered to metal contacts; ‘flip-chip’ meaning the substrate on which the stack of GaN and InGaN layers has been deposited is used as light exit, the (bottom) p-contacts being highly reflective. The color converting phosphors are placed on top of the chip, embedded in silicone. Primary blue as well as color-converted red and green photons are emitted.



The first author, Regina Mueller-Mach, manages the Charac-terization Laboratory at Lumileds which runs R&D work on phosphor converted LEDs in close cooperation with Philips Research Laboratories and the Department of Chemistry and Biochemistry of the University of Munich.

Highly efficient all‐nitride phosphor‐converted white light emitting diode

Nouveau Traité de Chimie Minérale.

The similarities and differences in the crystal and band electronic structures of four {kappa}-phase tetrathiafulvalene-based organic conducting salts {kappa}-(BEDT-TTF){sub 2}X (X{sup {minus}} = Cu(NCS){sub 2}{sup {minus}}, I{sub 3}{sup {minus}}), {kappa}-(MDT-TTF){sub 2}AuI{sub 2}, and {kappa}-(BMDT-TTF){sub 2}AU(CN){sub 2} have been examined. Donor dimers have a bond-over-ring arrangement in the superconducting salts {kappa}-(BEDT-TTF){sub 2}X (X{sup {minus}} = Cu(NCS){sub 2}{sup {minus}}, I{sub 3}{sup {minus}}) and {kappa}-(MDT-TTF){sub 2}AuI{sub 2} but a bond-over-bond arrangement in the nonsuperconducting salt {kappa}-(BEDT-TTF){sub 2}Au(CN){sub 2}, so that the intradimer spacing is considerably larger in the nonsuperconducting than in the superconducting {kappa}-phases. The terminal ethylene groups of BEDT-TTF have a staggered arrangement in the high-T{sub c} salts {kappa}-(BEDT-TTF){sub 2}Cu(NCS){sub 2} (T{sub c} = 10.4 K) and {beta}*-(BEDT-TTF){sub 2}I{sub 3} (T{sub c} = {approximately} 8 K) but are eclipsed in the low-T{sub c} salts {kappa}(BEDT-TTF){sub 2}I{sub 3} (T{sub c} = 3.6 K), {beta}-(BEDT-TTF){sub 2}AuI{sub 2} (T{sub c} = 5.0 K), and {beta}-(BEDT-TTF){sub 2}IBr{sub 2} (T{sub c} = 2.8 K). All the Fermi surfaces of the {kappa}-phase can be described in terms of overlapping distorted circles and hence are essentially two-dimensional in nature. However, the Fermi surface of the nonsuperconducting {kappa}-phase, {kappa}-(BMDT-TTF){sub 2}Au(CN){sub 2} exhibits a partial nesting in contrast to the casemore » of the superconducting {kappa}-phases, which is probably responsible for the metal-insulator transition at {approximately} 60 K. 26 refs., 8 figs., 2 tabs.« less

Similarities and differences in the structural and electronic properties of. kappa. -phase organic conducting and superconducting salts

[Bi6O4.5(OH)3.5]2(NO3)11: a new anhydrous bismuth basic nitrate. Synthesis and structure determination from twinned crystals

The nature of the 135 K metal-insulator (MI) transition in α-(BEDT-TTF)2l3, abbreviated α-(ET)2l3, was examined by determining the crystal structures above (298 K) and below (120 K) the phase transition and also by calculating the band electronic structures at both temperatures. This study demonstrates that both the crystal and band electronic structures of α-(ET)2l3 change only slightly upon passing through the MI transition. Within each sheetlike network of ET radical cations, the magnitudes of interactions between adjacent pairs of ET molecules (i-j) above and below the MI transition temperature (T MI) were evaluated by calculating their interaction energies, β ij = ⟨Ψ, H off|Ψ⟩, where Ψ1); and Ψ1 are the HOMO's of ET molecules i and j, respectively. The band electronic structures calculated by using single-zeta Slater type orbitals show that α-(ET)2l3 is a semiconductor with band gaps of 13 meV (298 K) and 35 meV (120 K). Thus, within the one-electron model, the apparently metallic properties...

Structural Characterization and Band Electronic Structure of α-(BEDT-TTF)2I3 below its 135 K Phase Transition

The Ce−S−Si system has been explored in search of new, yellow nontoxic pigments. We prepared a new Ce−S−Si phase (Ce6Si4S17), determined the crystal structures of Ce2SiS5, Ce4Si3S12, and Ce6Si4S17, and measured the chromatic properties of these Ce−S−Si phases. The differences in the yellow hue of these compounds were probed by analyzing their Ce3+ ion environments and calculating their electronic band structures. Ce6Si4S17 is distinguished from Ce2SiS5 and Ce4Si3S12 in terms of the Ce3+ structural environment and the Ce3+ 4f1→5d0 transition gap. This gap is wider for Ce6Si4S17 than for Ce2SiS5 and Ce4Si3S12 (i.e., 2.51 vs. ∼2.36 eV), and Ce6Si4S17 exhibits room-temperature luminescence whereas Ce2SiS5 and Ce4Si3S12 do not. Ce4Si3S12 and Ce6Si4S17 possess chromatic properties similar to those found for industrial pigments such as PbCrO4, BiVO4, and CdS, and show thermal and chemical stabilities.

Michel Evain

Papers

Similarities and differences in the structural and electronic properties of. kappa. -phase organic conducting and superconducting salts

[Bi6O4.5(OH)3.5]2(NO3)11: a new anhydrous bismuth basic nitrate. Synthesis and structure determination from twinned crystals

Structural Characterization and Band Electronic Structure of α-(BEDT-TTF)2I3 below its 135 K Phase Transition

Syntheses, Structures, and Optical Properties of Yellow Ce2SiS5, Ce6Si4S17, and Ce4Si3S12 Materials

Synthesis, characterization, and crystal structure of a new truly one-dimensional compound: PV2S10