Leigh C. Porter

(MDT-TTF)2 AuI2: An ambient pressure organic superconductor (Tc = 4.5 K) based on an unsymmetrical electron donor

Abstract R f penetration depth measurements show (MDT-TTF) 2 AuI 2 to be an ambient pressure superconductor with a T c ∼4.5 K. The effectof hydrostatic pressure on T c was found to be −0.92 K/kbar, which suggests that anions longer than AuI 2 - may puff up the lattice and may yield cation-radical salts of MDT-TTF with even higher superconducting transition temperatures. (MDT-TTF) 2 AuI 2 has a room temperature ESR linewidth of ∼ 100 G, which gradually increases as the temperature is lowered. The structure and properties of (MDT-TTF) 2 AuI 2 bear a close resemblance to those of the 10 K organic superconductor κ-(BEDT-TTF) 2 Cu(NCS) 2 . The band electronic structure of (MDT-TTF) 2 AuI 2 is two-dimensional, with a closed Fermi surface. The MDT-TTF donor molecule prossesses only four CH bonds to form short contacts with anions, as compared to eight for BEDT-TTF. Thus, the translational and/or librational modes of vibration are expected to be substantially different in (MDT-TTF) 2 AuI 2 and κ-(BEDT-TTF) 2 Cu(NCS) 2 .

Ba3A2PtCu2O10 (A = Y or Ho): The crystal structure of a reaction by-product of high transition temperature superconductors with platinum metal

Mixtures of CuO, BaCO/sub 3/, and A/sub 2/O/sub 3/ (A = Y, rare earth) react at temperatures between 600 and 1000/sup 0/C with platinum containers to produce crystals of composition Ba/sub 3/A/sub 2/PtCu/sub 2/O/sub 10/. The crystal structures of the compounds with A = Y or Ho were determined from single-crystal X-ray diffraction data. They are isostructural, monoclinic, space group C2/m, with Z = 2. Lattice parameters for Ba/sub 3/Y/sub 2/PtCu/sub 2/O/sub 10/ are a = 12.520(3) A, b = 5.817(1) A, c = 7.357(1) A, ..beta.. = 105.53(2)/sup 0/, V = 516.2(2) A/sup 3/. Lattice parameters for Ba/sub 3/Ho/sub 2/PtCu/sub 2/O/sub 10/ are a = 12.516(3) A, b = 5.813(1) A, c = 7.350(3) A, ..beta.. = 105.54(2)/sup 0/, V = 512.2(3) A/sup 3/. The structure of these complex oxides has the four metal ions in five distinct coordination environments; two barium sites with coordination number (CN) 8 and 11, yttrium or holmium with CN 7, platinum(IV) with CN 6, and copper with CN 5.

Temperature dependence of conductivity of κ(BEDTTTF)2Cu(SCN)2; Resolution into two components; Small polaron

Abstract The variation of resistance with temperature of κ(BEDTTTF)2Cu(NCS)2 displays a maximum or a suppressed maximum near 90 K. These unusual variations can be interpreted in terms of a model which resolves the variation into metal-like and thermally activated components. The resolution suggests the applicability of the small polaron model of Bottger and Bryksin with tunneling and hopping conductivities (Hopping Conduction in Solids, VCH Verlagsgesellchaft, 1985).

The X-ray crystal structure and physical properties of (BEDT-TTF) AuBr2Cl2

Abstract The X-ray crystal structure and electrical conductivity properties of a 1:1 BEDT-TTF salt containing (AuBr2Cl2)- are reported. The unit cell consists of square-planar gold (III) anions segregated by stacks of BEDT-TTF+ cations with a repeat pattern of 4.467(2) A along the crystallographic a axis. Four-probe variable-temperature conductivity measurements indicate that this material is a semiconductor with an activation energy of 0.13 eV. ESR measurements carried out on an oriented single-crystal specimen show a monotonic decrease in linewidth from 19 to 2.1 G over the temperature range 300-100 K.

Crystal structure and electrical conductivity of (TTF)5Hg6(SCN)16

Abstract The crystal structure and electrical properties of (TTF)5Hg6(SCN)16 have been determined. The crystals are monoclinic, space group P21/a, with unit cell dimensions a = 15.032(3) , b = 16.846(5) , c = 17.364(3) A and β = 108.92(1)°. The TTF units are stacked along the c axis. Within the stacks, dimers and trimers alternate. The complex anion contains bridging as well as non-bridging SCN− ligands. The crystals exhibit semiconducting behavior with a room temperature conductivity of 8.7 × 10−4 S·cm−1.

Synthesis, conductivity, and X-ray photoelectron spectrum of Bi2Sr2CuO7+X. A new ternary bismuth-oxide system exhibiting metallic conductivity

Abstract The preparation and some of the properties relating to the superconductive state of the newly discovered ternary bismuth oxide, Bi2Sr2Cu2O7+x, are described. Conductivity behavior ranging from semiconductive to metallic is observed when four-probe AC resistivity measurements are carried out on pressed pellet specimens that have been annealed under different conditions. From a determination of the total oxygen present by an iodometric titration, it was found that metallic conductivity was associated with a higher oxygen content. An X-ray photoelectron experiment was carried out in order to determine whether bismuth or copper was present as the mixed-valent species. The XPS spectrum of the Bi 4f orbital electrons in the oxide was nearly identical to that observed in Bi2O3, with no evidence of any Bi5+.

Electrical conductivity, crystal structure, and variable temperature ESR investigation of (BEDSe-TTF)2IBr2

Abstract The electrocrystallization of 3,4;3′,4′-bis(ethylenediseleno)-2,2′,5,5′-tetrathiafulvalene in the presence of [NBu 4 ] [IBr 2 ] in THF yields a 2:1 charge transfer complex that crystallizes with space group PĪ and lattice parameters a = 6.863(2) A , b = 10.065(3) A , c = 13.0183 (3) A , α = 87.94(2)°, β = 100.49(2)°, γ = 98.84(2)°, Z = 1, V = 884.8(4) A 3 . This product is semiconducting with a room temperature resistivity of 285 Ωcm and is isostructural with the 2:1 s-phase BEDT-TTF salts containing the ICI 2 − and BrICI − anions. ESR data obtained over the temperature interval 10–300 K show a monotonic decrease in peak-to-peak linewidth and the spin susceptibility data show that a sharp decrease in the sample magnetic susceptibility occurs with an onset temperature of approximately 12 K.