L.J. Azevedo

Correlations of Anion Size and Symmetry with the Structure and Electronic Properties of β-(BEDTTTF)2X Conducting Salts with Trihalide Anions X = 13-, 12Br-, 1Br2-

Abstract In the isostructural series of β-(BEDT-TTF)2X organic metals, abbreviated β-(ET)2X, where X is a trihalide anion, I3-, I2Br- or IBr2-, and where ET is bis-(ethylenedithio) tetrathiafulvalene (C10S8H8), the salt containing the disordered asymmetric I2Br- anion has atypical structural and electronic properties compared to those containing the symmetrical and ordered I-3 and IBr2- anions.

Magnetic Order in Organic Superconductors

Abstract We have undertaken an electron spin resonance study at both low and high magnetic field on the superconducting phase of the ambient pressure superconductor (BEDT-TTF>2I3, (ET)2I3, over the temperature range 1-300 K and hydrostatic pressure range from 0 to 2 kbar. At ambient pressure the ESR results are consistent with the picture of (ET)2I3 as a metal. Superconductivity is observed at 1.6 K via low field ESR. Application of modest pressures strongly suppresses the superconducting transition temperature. At pressures above about 0.3 kbar the superconductivity is suppressed in favor of an as-yet-unidentified magnetic state whose onset is at 7K. Through an analysis of the microwave ESR lineshape we find that the microwave conductivity over the temperature range 5-50 K is in agreement with dc measurements.

Low temperature heat capacity and magnetic study of the Al80Mn20 icosahedral alloy

Abstract Low temperature heat capacity and magnetization measurements are reported for the Al 80 Mn 20 alloy in the quasicrystalline icosahedral phase. The heat capacity, which was measured for temperatures ranging from 0.5 to 5.0 K and magnetic fields up to 11.7 kOe, shows a broad magnetic contribution around 1.0 K. The linear electronic contribution does not indicate an anomalously high density-of-states at the Fermi energy as predicted theoretically for quasicrystalline systems. The d.c. magnetization, which was measured from 2.0 to 300 K and with magnetic fields up to 50 kOe, indicates an effective number of one 11 μ B localized magnetic moment for approximately every 100 Mn atoms. The low field susceptibility follows the Curie-Weiss law for temperatures ≧ 10 K, while a spin-glass-like ordering is observed at low temperatures.

SYNTHETIC METALS BASED ON BIS(ETHYLENEDITHIO)TETRATHIAFULVALENE (BEDT-TTF): SYNTHESIS, STRUCTURE (T = 298 AND 125 K) AND NMR OF (BEDT-TTF)2X, X = REO4- AND BRO4-

Die elektrochemische Oxidation von Bis-[ethylendithiol-tetrathiafulven in 1,1,2-Trichlorethan in Gegenwart von Bu4N[ReO4] oder Bu4N[BrO4] als unterstutzende Elektrolyte fuhrt zu den Radikalkation-Titelsalzen.

Low temperature heat capacity and magnetic study of the quasicrystalline decagonal Al7 8Mn2 2 alloy

Abstract Low temperature heat capacity and magnetization measurements are reported for the quasicrystalline decagonal (T-phase) alloy Al7 8Mn2 2. The heat capacity measurements were performed over the temperature range from 0.5 to 5.0 K and for applied magnetic fields of zero and 12.7 kOe. In this range, the heat capacity is characterized by a broad anomaly near 1 K and no field dependence. The dc magnetization, which was measured from 1.7 to 300 K and with magnetic fields up to 50 kOe, indicates an effective number of one 25.6 μB localized moment for approximately every 240 Mn atoms. The magnetic susceptibility follows the Curie-Weiss law for T ≧ 15 K, while a spin-glass-like ordering is observed at 7.8 K. Comparisons are made with similar measurements previously reported for the related quasicrystalline icosahedral (I-phase) Al8 0Mn2 0 alloy.

High field phase transition in (TMTSF)2PF6 under pressure

Abstract A high field phase transition in the metallic phase of the organic conductor (TMTSF) 2 PF 6 at low temperatures has been studied by measuring the spin lattice relaxation rate of the methyl group protons. The transition temperature increases with field, is highly pressure dependent and depends on the projection of the magnetic field along the crystalline c axis.

Small bipolaronic hopping in boron carbides

D.c. conductivity, Hall mobility and Seebeck coefficient measurements on boron carbides, B1−xCx (0.1 ⩽ x ⩽ 0.2), between 300 and 1200 K are interpreted in terms on the hopping of small bipolaronic holes between B11C icosahedra that are inequivalent in energy and electron-lattice coupling strength.

Phase Diagrams of Organic Superconductors

Abstract A contactless technique has been developed for tracking the metallic, spin density wave and superconducting ground states of organic superconductors as a function of pressure and temperature.

Simple recipe for formation or recovery at ambient pressure of the 8K superconducting state of β-(BEDT-TTF)2I3

Abstract A simple recipe for the formation and recovery at ambient pressure of the 8K superconducting state of β-(BEDT-TTF) 2 I 3 is described. This technique will facilitate detailed studies of the 8K state.

Exotic organic superconductors based on BEDT-TTF and the prospects of raising Tc'S

Invited paper Ambient-pressure superconductivity has now been discovered in five systems based on BEDT-TTF:X, X - = polyatomic, monovalent anion. The highest T c reported is 5 K, in (BEDT-TTF) 2 AuI 2 , and it appears that much higher T c s are possible if disorder (molecular and anionic), and structural modulation, can be avoided in new derivatives containing monovalent triatomic anions. A modulated structure has been observed in (BEDT-TTF) 2 1, using neutron and X-ray scattering, but does not appear to form in (BEDT-TFF) 2 X, X = I 2 Br - , AuI - 2 and IBr2 down to T = 10-20 K.