G. Sekretarczyk

ESR Study of (TMTTF)2BF4 and TTF-TCNQ under Hydrostatic Pressure

Abstract We have measured the susceptibility, g-factor and linewidth of (TMTTF)2BF4, and TTF-TCNQ single crystals in the 80-300K temperature range up to 5 kbars of hydrostatic pressure in X-band. The decrease of the susceptibility and the increase in the 1inewidth on pressure is less expressed in (TMTTF)2 BF4, than In TTF-TCNQ. The g-factor does not depend on pressure in both cases.

A new highly conducting TCNQ salt. II: Spectroscopic properties of MPht (TCNQ)2

Abstract The highly conducting MPht(TCNQ) 2 salt has been studied by infrared and electron spin resonance spectroscopies. The absorption IR spectrum is characteristic for highly-conducting salts; the oscillation bands, situated in the wing of the CT band, are very broad, pointing to strong electron-phonon coupling in the salt. The paramagnetic susceptibility is temperature dependent in the metal-like region also. The susceptibility of the material is described in terms of a singlet-triplet antiferromagnetic chain with a spin activation energy almost the same as has previously been used to describe the conductivity in terms of a metal-like semiconductor.

The ESR study of organic metals series ET8[Hg4X12(C6H5Y)2]; X, Y = Cl, Br

Abstract A new type of organic metals based on bis(ethylenedithio)-tetrathiafulvalene (ET) has been investigated by ESR method. These salts have the following formula ET 8 [Hg 4 X 12 (C 6 H 5 Y) 2 ], where X, Y = Cl, Br. They are isostructural, two solvent molecules are contained in the composition of the anion. Characteristic feature of these crystals is the absence of the overlapping of the cation-radicals between the molecular planes. They are connected only by side by side type interactions of sulphur atoms. Angular and temperature dependence of the g-factor and the linewidth of ESR line of single crystals has been investigated. There is a slight influence of the salt composition on ESR parameters. Temperature dependence of the linewidth is typical of organic metals and can be understood in the frame of the Elliott mechanism.

Influence of electron irradiation on the phase transition of the organic semiconductor MTPP(TCNQ)2

Abstract An ESR study of the phase transition of electron-irradiated single crystals of MTPP(TCNQ) 2 was performed. It was found that the phase transition is suppressed for doses above 16 mC/cm 2 , the transition temperature is reduced linearly with d T /d D ≈ 4 K cm 2 /mC. This shows that the structural phase transition in the organic semiconductor MTPP(TCNQ) 2 is less open to influence of the electron radiation then the Peierls or superconducting phase transitions in organic conductors.

E.S.R. and electrical properties of the organic metal (BEDT-TTF)4Hg3Cl8

Abstract (BEDT-TTF) 4 Hg 3 Cl 8 is a new ion-radical salt in which superconductivity has been observed at 1.8 K under pressure of 12 kbar. The angular dependences of the g factor and the linewidth, ΔH , at room temperature, for three perpendicular crystal orientations have been studied. The angular study of g and ΔH indicated strong two dimensionality of the spin ordering of the crystals. The temperature dependences of the spin susceptibility χ of monocrystals of (BEDT-TTF) 4 Hg 3 Cl 8 were analysed. Above 220 K, a temperature-independent spin susceptibility seems to characterize the Pauli spin susceptibility; χ of (BEDT-TTF) 4 Hg 3 Cl 8 was about 2.1 × 10 −4 emu/mole. The e.s.r. study has been complemented by thermopower, S , measurements along the a and b axes. On the basis of an analysis of the anisotropic thermopower, we attributed the isotropic part of S to a term depending on the band contribution and the anisotropic part of S to the scattering mechanism.

Changes of crystal structure and electrical properties of organic metal (ET)2Br·C2H4(OH)2 in the process of crystal storage

Abstract Monocrystals of (ET) 2 Br·C 2 H 4 (OH) 2 have been found to display four-fold line broadening in ESR-spectrum, σ 293K increase and decrease of T max of conductivity from ∼195 K to ∼160 K after a year storage. X-ray reinvestigation of these crystals showed shortening of S…S side-by-side distances by 0.03–0.05 A, while the crystal structure of cation layer was preserved. In the anion layer change of ethylene glycol conformers relation from 1:1 to 1:2 has been found to occur.

Influence of the radiation induced disorder on physical properties of the MTPP(TCNQ)2 salt

Abstract Extensive studies of the physical properties of electron irradiated single crystals of the anion radical salt of methyltriphenylphosphonium with tetracyanoquinodimethane (MTPP (TCNQ) 2 ) were performed. It was found that the irradiation of the salt leads to considerable changes in spectral (IR, NIR, VIS, UV), radiospectroscopic (ESR) and electrical properties of the MTPP(TCNQ) 2 . The structural phase transition of the salt is suppressed for electron radiation doses above 16 mC/cm 2 . The changes in the electronic and spectral properties were discussed; especially the origin of distinct doublets of activated a g vibrational modes was commented.

Pressure Dependence of Triplet Excitons In (NPQn).5 (NBQn).5 (TCNQ)2

Abstract N-Propyl-Qn (TCNQ)2, alloyed with N-Butyl-Qn (TCNQ)2 shows the characteristic two Tine ESR spectra due to thermally excited triplet excitones. We have performed the pressure dependence (up to 5 kbars) of zero-field splitting parameters, singlet-triplet activation energy and exchange parameters. The drastic decrease of the susceptibility and linewidth has been attributed to the increased singlet-triplet activation energy 80K/kbars. The activation energy for the exciton propagation decreases on pressure with the rate of 36 K/kbars.

Spectroscopic and Electrical Investigations of MeDABCO/TCNQ/2 Salt

Abstract Spectral studies of MeDABCO/TCNQ/2 salt were performed in the IR and visible regions respectively on KBr compactions at 85K–293K and in acetonitrile solutions. Electric conductivity was measured vs. temperature for polycrystalline MeDABCO/TCNQ/2, permitting the calculation of the activation energy. Measurements of the thermoelectric force yielded the Seebeck coefficient.