Aaron N. Bloch

Semi-metallic behaviour of HMTSF-TCNQ at low temperatures under pressure☆

Abstract Some results of electrical resistivity (ϱ) and transverse magnetoresistance measurements on single crystals of the charge transfer compound HMTSF-TCNQ under pressure are reported. There is evidence that dϱ/d T remains positive over the whole temperature range under pressure, and that a T 2 law is obeyed from 0.19 to 2 K at 14 kbar. Together with a relatively large magnetoresistance this is an indication of semi-metallic behaviour.

A current-controlled electrically switched memory state in silver and copper-TCNQF4 radical-ion salts

Abstract An electric field is found to induce current-controlled memory switching in polycrystalline films of copper and silver complexed to the organic electron acceptor 2,3,5,6,-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (TCNQF 4 ). The effect occurs in a two-terminal lamellar structure with the organic semi-conductor between two metal electrodes. Switching is reproducible and insensitive to moisture, light, and temperature. A memory state is created in these materials when an external field surpasses a threshold value. At this critical field the impedance of the material drops by more than four orders of magnitude. Typical impedance values in a 1.87-μm thick Cu-TCNQF 4 film for the high and low states are 1.6 × 10 6 and 60 ohms, respectively. Fast-pulse measurements made on these materials show the switching from the low to the high conductivity state occurs with a combined delay and switching time of less than 4 ns. The memory cannot be “erased” by subsequent voltage pulses, yet the memory is not permanent; its duration is controlled by sample thickness and the amount of energy used to invoke the state. General properties of metal-TCNQF 4 films are compared with the corresponding TCNQ salts.

Crystal Coulomb energies. VII. The electrostatic binding energy defect in Tetrathiofulvalinium 7,7,8,8,‐tetracyanoquinodimethanide

The Madelung energy EC of TTF TCNQ was computed by Ewald’s method using the 300 and 100 °K crystal structures and several charge models based on CNDO/2, PPP, and INDO atom charge densities, and as a function of charge transfer. In all cases EC compares unfavorably, by several electron volts, with the cost of ionizing the lattice. This had been noted previously for NMP TCNQ. This binding energy defect is too large to be explained by metallic binding or exchange forces, or by electron correlation, even in the Wigner crystal limit. We speculate that polarization forces, or covalent effects may play a large role in stabilizing the lattice. The Madelung site potentials in the TTF+1TCNQ−1 lattice are sufficient to explain the observed core level splittings in the photoelectron spectrum.

Microwave conductivities of the organic conductors TTF-TCNQ and ATTF-TCNQ

Abstract The complex microwave conductivities of the organic salts TTF-TCNQ and ATTF-TCNQ show a metal-to-insulator transition near 60 K and distinguish these materials from the class of disordered one-dimensional conductors. The data show no evidence for the high-temperature superconducting fluctuations recently proposed by Heeger and co-workers.

Synthesis of the organic conductor tetramethyltetraselenofulvalenium 7,7,8,8-tetracyano-p-quinodimethanide (TMTSF–TCNQ)[4,4′,5,5′-tetramethyl-Δ2,2′-bis-1,3-diselenolium 3,6-bis-(dicyanomethylene)cyclohexadienide]

Tetramethyltetraselenofulvalene reacts with tetracyanoquinodimethane to form a highly conducting organic solid.

Electron transfer in TTF–TCNQ and related compounds

Abstract The S(2p) binding energies have been measured at room temperature in TTF–TCNQ and related compounds. The results indicate an electron transfer of 1.0 ± 0.5 electrons/molecule for TTF–TCNQ.

X-Ray crystal structure of the organic conductor from 2,2′-bi-(2,4-diselenabicyclo[3.3.0]octylidene) and 7,7,8,8-tetracyano-p-quinodimethane (HMTSF–TCNQ)

The X-ray crystal structure of the organic conductor HMTSF–TCNQ consists of separate stacks of radical cations and radical anions coupled so as to make this the most two-dimensional member of the TTF–TCNQ family of organic metals.

Synthesis of Δ2,2′-bithieno[3,4-d]-1,3-dithiole (DTTTF) and some of its charge-transfer salts

The title compound (DTTTF) was prepared by the coupling of the corresponding thieno-1,3-dithiolium salt, obtained from thieno-1, 3-dithiolane-2-thione synthesized from 3,4-dibromothiophen.

The Organic Metallic State: Some Physical Aspects and Chemical Trends

To a degree unmatched among other intrinsic conductors, the electronic properties of organic charge-transfer salts1 are subject to chemical control. Among the derivatives and analogs of TTF-TCNQ,2-7 for example, even minor differences in molecular structure often manifest thanselves as sharp contrasts in electrical behavior. Indeed, despite their general chemical and crystallographic similarities, such compounds span the full range from insulators to the best organic conductors known.

Stabilization of the Organic Metallic State: The Properties of Two Substituted Tetraselenafulvalenes and Their TCNQ Salts

Abstract Results are described for two new one-dimensional organic conducting solids. 2,3,6,7-Tetramethyl-tetraselenafulvalene-TCNQ (1 : 1) crystallizes in a triclinic structure and undergoes a metal-to-insulator transition at low temperature. Introduction of a new substituent pattern leaves the electronic properties of the donor unchanged, but 2,3;6,7-bis-(trimethylene)-tetraselenafulvalene crystallizes in a nearly orthorhombic structure and retains metallic properties to 0.07 K.