Chemistry and Electrocrystallization of Organic Metals and Superconductors

Abstract

Considerable variation in the conditions of electrochemical crystal growth of TMTSF₂X (i.e., constant current versus constant potential, ambient versus inert atmosphere, etc.) and in the purity of the constituents (donor, electrolyte, solvent) does not significantly affect the unusual low-temperature properties of this class of materials. Our results suggest that the electrocrystallization procedure may be self-purifying by selecting for conducting crystal phases with constituents having specific oxidation potentials and solubility properties. However, doping solutions with structurally and chemically similar constituents (i.e., TMTTF, and IO^? ₄ in CIO^? ₄) leads to their incorporation in the crystal structure where they have a profound effect. Several mole percent of these dopants suppress superconductivity in the PF^? ₆ and CIO^? ₄ salts, and increase and broaden the metal-insulator phase transition.     

Transport Properties of (NH4)2 CuCl4.2H2O Low Dimensional Single Crystals

The X‐ray diffraction and Infrared (IR) spectral studies of (NH₄)₂ CuCl₄.2H₂O single crystals reveals that these crystals contains tetragonal crystal structure with the unit cell dimensions of a = 7.58Å, c = 7.95Å, z= 2, β =90° and two water molecules in the unit cell. The temperature dependence of thermally stimulated depolarization current (TSDC) and dc electrical conductivity (σ) studies of this two‐dimensional (NH₄)₂ CuCl₄.2H₂O single crystal have been carried out in 77K–300K temperature region. The TSDC thermograph shows only one sharp peak at 248K with a peak current of 130nA, which is attributed to the Maxwell‐Wagner peak. The activation energy (U), relaxation time (τ) are calculated as 0.78eV and 3.44×10^‐15 s respectively. Dc electrical conductivity studies of these crystals show a first order phase transition at about 248K.     

Some Properties of the (TMTSF)2X Superconductors

Measurements of the anisotropy of the critical field in (TMTSF)₂X superconductors are presented. The results show that the a axis H_c2 is Pauli limited based on a T_c near 1K. The large energy gap obtained from tunneling data is therefore thermodynamically untenable in terms of the present critical field studies and the superconductivity is singlet rather than triplet. Moreover, we find that low levels of irradiation induced defects eliminate the superconductivity in the ClO₄ and PF₆ salts and leave the thermopower of the ClO₄ salt below 100K unchanged. These results are incompatible with the proposal for 1D superconducting fluctuations below 40K. A discussion of the arguments for and against the occurance of superconducting fluctuations in the (TMTSF)₂X salts is given with emphasis on the role of interchain interactions and other possible interpretations of the tunneling data.     

Electrosynthesis and properties of poly(3-methylthiophene-pyrrole) composites

Poly(3-methylthiophene/overoxidized pyrrole) (PMT/OPPy) composites were electrochemically prepared by simultaneous polymerization of 3-methylthiophene and pyrrole, which were added together at a 10:1 concentration ratio into a non-aqueous medium (acetonitrile). The films were characterized by cyclic voltammetry, spectroscopic (FTIR, UV-VIS, and photocurrent) and current-voltage measurements, and with atomic force microscopy (AFM). The PMT/OPPy films exhibited intermediate characteristics than those seen for the homopolymers, OPPy and PMT, but with PMT as the predominant element of the PMT/OPPy composition. Optical, morphological, and electrical properties of the OPPy, PMT, and PMT/OPPy films were compared aiming toward application in optoelectronic devices and sensors.     

Microstructural and optoelectrical properties of transparent conducting ZnO:Al thin films for organic solar cells

The Al‐doped zinc oxide (ZnO:Al) thin films were grown on glass substrates by the magnetron sputtering technique. The films were characterized with X‐ray diffractometer, four‐point probe and optical transmission spectroscopy, respectively. The dependence of microstructural, electrical and optical properties on deposition temperature was investigated. The results show that all the films have hexagonal wurtzite structure with highly c‐axis orientation. And the microstrural and optoelectrical properties of the films are observed to be subjected to the deposition temperature. The ZnO:Al film prepared at the deposition temperature of 650 K possesses the best optoelectrical properties, with the lowest electrical resistivity (6.1×10⁻⁴ Ω·cm), the highest average visible transmittance (85.3%) and the maximum figure of merit (0.41 Ω⁻¹). The optical energy gap of the films was estimated from Tauc's law and observed to be an increasing tendency with the increment of the deposition temperature. Furthermore, the refractive index of the films was determined by the optical characterization methods and the dispersion behavior was studied by the single electronic oscillator model.     

Low Dimensional Triangular Magnetic Systems in Transition Metal Intercalates of Misfit Layer Compounds

Abstract

Low dimensional triangle magnetism was studied for transition metal intercalates of incommensurate misfit layer compounds (RS)^x[M^0.33(NbS²)²] (R = La, Ce, M = Fe, Mn). Magnetization measurements for the single crystals of the Fe intercalated compounds (RS)^x[Fe^0.33(NbS²)²] show the successive magnetic transition at 14 K and 22 K. The strong frustration appears between two transition temperatures as quasi two-dimensional antiferro-magnetic triangular Ising spin system. In contrast, the Mn compounds (RS)^x[Mn^0.33(NbS²)²] has very low transition temperature of 3.0 K due to the nature of quasi two-dimensional Heisenberg spin system.     

Electrical Properties of CuIn3Se5 Bulk Crystal at Low Temperature

CuIn₃Se₅ crystals were grown from the melt containing stoichiometric quantities of the elements of at least 5 N purity. The structure was analyzed by X‐ray powder diffraction, and shows mainly a tetragonal single phase. The chemical composition was determined by EDAX and Total X‐Ray Fluorescence (TXRF). The conductivity and the Hall effect have been measured in the temperature range from 10 to 300 K. The polar optical scattering was found to dominate at low temperatures, while in the high temperature region ionized impurity scattering mechanism was observed.     

Molecular Structure and Dynamics in Organic Solids: High Resolution Low Temperature 13 C NMR Studies

The development of cross polarization-magic angle spinning (CPMAS) has resulted in the achievement of near-liquid resolution in solid state ¹³ C NMR spectra. Therefore, the structure and dynamics of organic solids can now be studied on a carbon-by-carbon basis. Low temperature CPMAS capability permits the investigation of molecular dynamics in solids, and in particular in a temperature range heretofore inaccessible to high resolution NMR (15-200 K). We have developed and used low temperature CPMAS to study solid state effects on chemical exchange processes in organic and organometallic compounds and in carbonium ions. We have also developed a technique for measuring carbon-carbon bond lengths in amorphous solids using NMR. The geometry of cis-and trans-polyacetylene has been determined using this method.     

On the Spatio‐Temporal Flow Phenomena in Low Prandtl Number Melts Part 1: The Case of Stationary Vertical Molten Zones

Thermal buoyancy driven flow in semiconductor melts contained in closed silica glass ampoules was studied experimentally in dependence on the height of the molten zone. The onset of temperature oscillations in the melt and further transitions of the temporal convective behaviour were detected by in‐situ temperature measurements. It was shown for low Prandtl number melts that the flow in stationary vertical molten zones strongly tends to become unsteady. For the periodic unsteady flow regime two fundamentally different periodic oscillation modes were revealed. Transitions to chaos are announced in nearly all cases by period doubling events. First return maps of selected typical time series are used to characterize the temporal dynamics of the non‐linear dynamic system. Based on the phase relations and amplitudes of the signals measured simultaneously in axial and azimuthal direction spatio‐temporal oscillating flow structures can be carefully interpreted. “Mode switching” and the rotation of a vortex configuration are assumed to be the preferred oscillation mechanisms.     

A New Organic Solid State Reaction: Hydrogenation of Phenols

During the past fifteen years there has been a number of detailed studies devoted to the chemistry of organic molecular solids and made by a number of groups involving chemists and crystallographers. These workers were interested in the reactions of the organic solids subjected either to a physical agent like light or heat or to a chemical one which can be a solid, a liquid or a gas.¹     

Synthesis,Structure and Electrical Conductivity of (BEDT-TTF)X(BrO4)Y Organic Metals

The electrochemical oxidation of BEDT-TTF (bis(ethylenedithio)-tetrathiafulvalene) in 1,1,2-trichloroethane solution in the presence of (n-Bu4N)Br04 as supporting electrolyte produces three distinct morphologies: needles, thick plates, and thin plates. These crystal habits have been identified with different crystallographic phases: needles as (BEDT-TTF) ₂Br04, thick plates as (BEDT-TTF)₂(Br0₄)(TCE)_0.5, and thin plates as (BEDT-TTF)₃(Br04)₂. The structural characterization and conductivity for these materials is presented.     

Solution-Processable Low Voltage Organic Transistors of Thieno[3,2-b]thiophene-Based Conducting Polymer

A low-operating voltage and high performance polymeric field effect transistors using octadecylphosphonic acid-treated high-k AlOx and HfO₂ hybrid dielectrics were demonstrated. High-k metal oxide hybrid dielectrics were prepared by oxygen plasma treatment of deposited Al film for AlOx and by spin coating of solution-processable HfO₂ sol-gel solution for HfO₂ in combination with phosphoric acid-based self-assembled monolayer (SAM), resulting in high capacitance (10 nF/cm² for SiO₂, 600 nF/cm² for AlOx and 580 nF/cm² for HfO₂). With phosphoric acid-based SAM on high-k metal oxide and thermal annealing of thieno[3,2-b]thiophene-based conducting polymer, the device performance was significantly enhanced. The highest mobility of the transistors using ODPA-treated AlOx as a gate dielectric is 2.3 × 10^?2 cm² V^?1 s^?1 in the saturation region with the source-drain of ?2 V. In ODPA-treated HfO₂ hybrid dielectric, the saturated mobility is 1.1 × 10^?2 cm² V^?1 s^?1 and the threshold voltage was measured to be ?0.31 V, which is at least one order lower than SiO₂ hybrid dielectric (?3 V).     

利用直流磁控溅射法在柔性衬底上制备ZnO: Zr新型透明导电薄膜

室温下利用直流磁控溅射法在有ZnO缓冲层的柔性衬底 PET上制备出了可见光透过率高、电阻率低的掺锆氧化锌(ZnO: Zr)透明导电薄膜,研究了厚度对ZnO: Zr薄膜结构及光电性能的影响.结果表明,ZnO: Zr薄膜为六方纤锌矿结构的多晶薄膜.实验获得ZnO: Zr薄膜的最小电阻率为2.4×10-3 Ω·cm,其霍尔迁移率为18.9 cm2·V-1·s-1 ,载流子浓度为2.3×1020 cm-3.实验制备的ZnO: Zr薄膜具有良好的附着性能,其可见光平均透过率超过92;.     

Chemical synthesis, characterization and transport properties of copolymer: Poly(aniline-co-m-methylaniline)

Poly(aniline-co-m-methylaniline) were copolymerized by chemical peroxidation of aniline and m-methylaniline in aqueous acidic medium under nitrogen atmosphere at 0–4oC. The molar feed ratio of the monomers were varied to prepare copolymers of different composition. The copolymers product were characterized by solubility, spectroscopic methods, elemental analysis and electrical conductivity measurements. The solubility and spectroscopic analysis suggested that the product is a copolymer of aniline and m-methylaniline. The optical spectra of the copolymer shows hypsochromic shift with the increase in dielectric constant of the solvent and with increasing the content of m-methylaniline in the copolymer chain. The electrical conductivity of copolymer salts were measured as a function of temperature. The conductivity of copolymer decreases with increasing the content of m-methylaniline in the copolymer chain, due to change in coplanarity of polymer and reduction of mobility of charge carrier along the main chain. The conduction mechanism of copolymer is polaron hopping conduction as similar to the case of polyaniline. The coherence, most probable hopping distance, hopping energy and localization length of copolymers have been compared to those of homopolymers.     

Principal Electrical Conductivities in the Organic Conductors TEA.(TCNQ)2 and TTF.TCNQ: The Microwave Approach

Abstract

We describe a microwave technique to measure the directions and magnitude of the principal electrical conductivities and permittivities of organic conductors. The method is applied to single crystals of triethylammonium-bis 7,7,8,8-tetracyano-p-quinodimethane (TEA.(TCNQ)₂) and of tetrathiafulvalenium-7,7,8,8-tetracyano-p-quinodimethane (TTF.TCNQ). For the former, the apriori set of principal axes (a*, (a*∧c), c) is confirmed with principal conductivities of 430, 5.3 and 0.41–0.77 Ω^?1m^?1 respectively. The room temperature permittivities have been measured for the first time (ε*_α ～ 5.4–5.5, ε*_α∧c ～ 7.5). For the latter it is clearly shown that the principal electrical axes are (a, b, c*) and, in contrary to earlier d.c data, we observe σ_c· < σ<a which is more consistent with the anisotropy of interchain interactions in this compound. The observed transverse and longitudinal anisotropies (～3.3 10² and 2.8 10⁴ respectively) are larger than believed up to now.     

有机非线性光学晶体一水甲酸锂的研究综述

甲酸盐晶体是一族引人瞩目的非线性光学材料,一水甲酸锂(LFM)是甲酸盐系列中综合性能优良的晶体之一.本文较全面地介绍了一水甲酸锂晶体的发展、生长技术、生长机理及其非线性光学性能.指出一水甲酸锂是很有发展潜力的紫外非线性光学有机晶体,并提出了进一步开发其应用需要解决的问题.     

Benzo-1,3,2-Dithiazol-2-YL and its Derivatives: A New Class of Donor Molecules for Highly Conducting Charge Transfer Complexes

Abstract

Benzo-1,3,2-dithiazol-2-yl and its derivatives form charge transfer complexes with tetracyanoquinodimethane; their powder conductivities are as high as 3 Ω^?1 cm^?1.     

Scaled Particle Theory of a System of Spherocylinders: Extension of Calculations to High Pressures

The viscosity coefficients of nematic substances for corresponding orientation geometry introduced and measured for PAA and PAP by the author in the thirties are discussed from the actual point of view.

The great universality of these coefficients of viscosity and their utility for describing several dynamical phenomena has been shown. There is a quantitative agreement between the experimental data of those investigations and continuum hydrodynamical theory of nematics with the numerical values of viscosities measured by the author.

As a new field of application of flow in definite orientation geometry, the properties of smectics and closely connected problems of phase transitions, pretransition effects and reentrant phase has been discussed.     

A Low Temperature Structure of Nonane-1,9-Diaminium Chloride Chloroacetate: Hydroxyacetic Acid (1:1)

Abstract  

The crystal structure of nonane-1,9-diaminium chloride chloroacetate–hydroxyacetic acid (1:1) was determined by X-ray diffraction at 100(1)K. The asymmetric unit is composed of diaminium dication, chloroacetate and chloride anions, and neutral hydroxyacetic acid molecule. The aliphatic chain of 1,9-diamine is fully extended and it deviates only slightly from the perfect all-trans conformation. The two acidic residues are also nearly planar. The layer structure is obtained as a consequence of hydrogen bond interactions of a different lengths, with N–H and O–H groups playing the role of donors and oxygen atoms and chloride cations as acceptors. The pattern of H bonding is investigated by graph-set analysis. Crystal data: crystal system: monoclinic, a = 4.6418 (2) ?, b = 25.5128 (11) ?, c = 15.9943 (9) ?, β = 99.784 (5)°, Z = 4, space group: P21/c, V = 1866.6(1) ?³.