Paul G. Nixon

Specific heat and critical fields of the organic superconductor β″–(BEDT-TTF)2SF5CH2CF2SO3

We report on specific-heat, magnetization, and ac-susceptibility measurements of {beta}{sup {double_prime}}-(BEDT-TTF){sub 2}SF{sub 5}CH{sub 2}CF{sub 2}SO{sub 3}, an organic superconductor with T{sub c}=4.5 K, where BEDT-TTF stands for bis(ethylenedithio)-tetrathiafulvalene. The jump of the specific heat C at T{sub c} and the exact form of the specific-heat difference between C in the superconducting (B=0 T) and in the normal (B=3.5 T) state can be well described by BCS theory with strong coupling. We estimate an electron-phonon coupling parameter {lambda}{approx}1.1. From measurements of C in magnetic fields we extract the upper critical field B{sub c2}(T). Low-field dc-magnetization measurements were used to determine the temperature dependence of the lower critical field B{sub c1}. From T{sub c} down to {approximately}3 K the characteristic suppression of B{sub c1}{sup {perpendicular}}(T) below the sensitivity limit is observed. {copyright} {ital 1998} {ital The American Physical Society}

Fermiology of the organic superconductor β″-(ET)2SF5CH2CF2SO3

We present a detailed Fermi-surface (FS) investigation of the quasi two-dimensional (2D) organic superconductor (T c = 4.5 K) β-(ET) 2 SF 5 CH 2 CF 2 SO 3 . In line with previous investigations, de Haas-van Alphen measurements in pulsed fields up to 60 T show a single oscillation frequency, F 0 = 200 T, which corresponds to a FS size of about 5% of the first Brillouin zone. Angular dependent magnetoresistance oscillations (AMROs) are utilized for the exact determination of the in-plane FS, which is found to be a strongly elongated ellipsoid with an axes ratio of about 1:9. Transport measurements in static fields up to 33 T show an unusual temperature dependence of the Shubnikov-de Haas (SdH) signal, i.e., a decrease of the SdH amplitude with decreasing temperature.

New fluoroalkenes and alcohol with pentafluoro-λ6-sulfanyl (SF5) terminal groupings

Abstract The synthesis of new compounds that contain both a terminal pentafluoro-λ 6 -sulfanyl (SF 5 ) group and an alkene or alcohol functional group is reported. Five new SF 5 containing alkenes and one new SF 5 containing alcohol were prepared: SF 5 CH 2 CHBrCH 2 CF CF 5 ( 1 ), SF 5 CF 2 CF 2 CH 2 CHICH 2 CF CF 2 ( 2 ), SF 5 CF 2 CF 2 CH 2 CH 2 CH 2 CF CF 2 ( 3 ), SF 5 CF 2 CF 2 CH CH 2 ( 4 ), SF 5 (CF 2 CF 2 ) 2 CH CH 2 ( 5 ) and SF 5 CF 2 CF 2 CH 2 CH 2 OH ( 6 ). These compounds are useful as monomers or as intermediates in the preparation of polymers, polymer surface coatings, and surfactants.

A new preparation of disulfur decafluoride

Abstract A facile and high yield preparation of disulfur decafluoride (S 2 F 10 ) by the photochemical reaction of pentafluorosulfur bromide (SF 5 Br) is described.

New SF5-long chain carbon systems

Abstract A new SF 5 -terminated perfluoroalkyl thiol — SF 5 (CF 2 ) 6 CH 2 CH 2 SH — and a symmetric SF 5 -terminated dialkyl disulfide — [SF 5 CH–CH(CH 2 ) 8 S] 2 — were synthesized from the corresponding SF 5 -terminated precursors. The chemistry employed in the preparation of the disulfide encompasses high yield pathways for the preparation of new SF 5 -long chain derivatives.

Dependence of Tc on hydrostatic pressure in β″-(ET)2SF5CH2CF2SO3 and κ-(ET)2Cu(NCS)2

Abstract The dependence of Tc on hydrostatic (He-gas) pressure is determined for the recently discovered organic superconductor β″-(ET)2SF5CH2CF2SO3 [ET = bis(ethylenedithio)-tetrathiafulvalene] with T c (0) ⋍ 5 K , yielding the pressure derivative d T c d P ⋍ −1.34 K kbar −1 . The present experiments also included κ-(ET)2Cu(NCS)2 where we find the extremely large value d T c d P ⋍ −3.84 K kbar −1 , in agreement with earlier studies. For both samples the pressure dependence Tc(P) does not depend on the temperature at which the pressure is changed.

Esr studies of two new organic superconductors: β″-(BEDT-TTF)2SF5CH2CF2SO3 and κL′-(BEDT-TTF)2Cu(CF3)4(DBCE)

Abstract The normal-state ESR properties of two new organic superconductors, β″-(BEDT-TTF) 2 SF 5 CH 2 CF 2 SO 3 and κ L ′-(BEDTTTF) 2 Cu(CF 3 ) 4 (DBCE) are reported. Both compounds showed metallic properties below 140 K. The former gave ESR line widths and g -values of 23 to 34 G and 2.004 to 2.012, respectively. The latter gave line widths and g -values of 45 to 58 G and 2.006 to 2.012, respectively. The orientation-dependent line widths and g -values of the κ L ′-phase were found to be similar to that of the κ-(ET) 4 Hg 3 Br 8 but not to the κ L -phases in general.

Rational design of organic superconductors through the use of the large, discrete molecular anions M(CF3)4-(M = Cu, Ag, Au) and SO3CF2CH2SF5-

A new approach to the synthesis of organic superconductors has recently been pioneered which involves the use of large, discrete, molecular anions as the charge-compensating entities in these charge transfer salts. The organic electron-donor molecule bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF or ET) has been electrocrystallized with the novel organometallic M(CF3)4 (M = Cu, Ag, and Au) anions in a variety of 1,1,2-trihaloethane solvents. Over twenty organic superconductors have been synthesized which can be described by the general formula (ET) 2 M(CF 3 ) 4 (1,1,2-trihaloethane). These solvated salts are shown to have highly anisotropic physical properties which can be tuned via modifications of each of their three molecular components: ET electron donor molecule, M(CF3)4 anion, and neutral 1,1,2-trihaloethane solvent molecule. Superconductivity has also been observed in an ET salt containing the discrete SF 5 CH 2 CF 2 SO 3 - anion with an onset temperature near 5.2 K.

Synthesis of LiCH(SO{sub 2}CF{sub 3}){sub 2} and ionic conductivity of polyether-salt complexes

LiCH(SO{sub 2}CF{sub 3}){sub 2} is prepared by reaction of CH{sub 2}(CF{sub 3}SO{sub 2}){sub 2} with Li{sub 2}CO{sub 3} and the product identity confirmed by nuclear magnetic resonance, infrared, and elemental analysis. Differential scanning calorimetry/thermogravometric analysis data indicate a decomposition temperature near 280 C under N{sub 2}. PEO{sub x}LiCH(SO{sub 2}CF{sub 3}){sub 2} complexes show ionic conductivities as high, or higher than, those derived from other plasticizing salts, with {sigma} near 10{sup {minus}4} ({Omega} cm){sup {minus}1} at 30 C and 10{sup {minus}3} ({Omega} cm){sup {minus}1} at 80 C for the x = 16 complex. Differential scanning calorimetry data indicate that the polymer-salt complexes exhibit reduced crystallinity at ambient temperature and show minor crystalline phases at higher salt concentrations. Glass transition temperatures increase with salt content for the complexes. Cyclic voltammetry shows an electrolyte stability window of approximately 4.5 V.

Lithium salts of SF5 alkylsulfonic acids: synthesis, characterization and conductivity

Abstract The lithium sulfonates, SF 5 CFHSO 3 Li ( 1 ) and SF 5 CF 2 SO 3 Li ( 2 ), were prepared by reaction of the corresponding sulfonyl fluorides SF 5 CFXSO 2 F (X = H or F) with lithium hydroxide. The product identities were confirmed by IR and NMR spectroscopies, MS and elemental analysis, and the thermal stabilities were determined via DSC and TGA. The poly (ethylene oxide) (PEO)-salt complexes, PEO x LiSO 3 CFHSF 5 ( 3 ), were prepared for x = 2 to 16 (where x = O/Li mole ratio) and the bulk conductivities measured between 40 °C and 120 °C. Unlike the PEO x LiSO 3 CF 2 SF 5 ( 4 ) complexes, thermal and conductivity measurements do not indicate a plasticizing effect for these complexes; these observations are discussed in terms of hydrogen bonding between SF 5 CFHSO 3 poststaggred− anions.