1,2-Dithiolene complexes of transition metals-structural systematics and physical properties

The crystal structure analyses along with other physical measurements of 1,2-dithiolene complexes have made it possible to derive many interesting properties of these complexes. This review focuses attention mainly on the structural aspects and physical properties of 1,2-dithiolene complexes of transition metals. Brief mention of the structural aspects of complexes such as 1,2-dithiooxalate complexes and dithiosquarate complexes is included. In addition, structural aspects of a few available non-transition metal complexes are briefly discussed. The idea that bulky counterions lead to nonplanar structures has been disproved by the nonplanarity observed in the anion of [(CH₃)₄N]₂[Cu(S₂C₂(CN)₂)₂]. The analysis of the significance of overall charge shows that the ionic effect is prevalent in [M(dithiolene)₂] ^n– systems. Crystal structure analyses of some bis(dithiolene) complexes of transition metals along with conductivity measurements have shown that it is possible to correlate the electrical behavior to the crystal structure, provided the sample crystals are good. The two-dimensional network structure of the mixed valence compound, [(n-C₄H₉)₄N]_0.29 [Ni(S₂C₂S₂CS)₂], proposes the possibility of reaching the ultimate goal (superconductivity) with this type of compounds.     

AC impedance analysis of CsNO3:Al2O3 composite solid electrolyte systems

Complex impedance spectroscopic studies were carried out on CsNO₃ and CsNO₃-Al₂O₃ dispersed solid electrolyte systems (DSES) in the temperature range of 100-350 °C and the frequency 50 kHz-1 MHz. Dielectric constant, loss tangent, ac conductivity and dc ionic conductivity (obtained from CIS) in these systems are presented. DC ionic conductivity is noticed to increase with temperature in the extrinsic region in pure and dispersed systems. The enhancement of conductivity in DSES was observed to be about two orders of magnitude over its pure form in the extrinsic region. This enhancement of conductivity was attributed to the formation of space charge layer between the host material and the dispersoid. Enhancement in conductivity is found to increase with m/o up to 40 m/o where as it decreased for 80 m/o. Dielectric constant, dielectric loss and ac conductivity are also found to increase with temperature, and with mole percent it maintained the similar behavior as that of dc conductivity. These dielectric properties are interpreted in terms of space charge polarization and increased concentration of defects in the interfacial layer formed between the host and the dispersoid.     

Relationship Between Structure and Properties for Donor-Doped and for Acceptor-Doped Polyacetylene

Two basic structural types are experimentally derived for polyacetylene complexes: channel structures (Na, K, Rb, and Cs) and layered structures (iodine and a variety of other acceptors). Observed variants for the layered structures include first-stage and higher-stage complexes, with either complete or fractional occupation of dopant on the dopant-containing planes. A third structural type, in which dopant is statistically distributed, is predicted up to high dopant levels for lithium dopant. These structural results are used to explain observed properties and to predict properties obtainable for nearly defect-free single crystals. Discussions will include the structural origin of electrochemical discharge curves, major increases in conductivity on annealing K-doped and Rb-doped polyacetylene, the extremely high thermal stability of alkali metal channel complexes, and predicted mechanicals and transport properties for single-crystal complexes.     

Ionic Conductivity Studies in Yttrium-doped KCl Crystals

Ionic conductivity measurements have been made on Potassium Chloride crystals doped with different concentrations of Yttrium, in the temperature range 200 °C to 600 °C, to understand the nature of impurity vacancy (I–V) complexes, various types of their formation and to understand how these I–V complexes affect the conduction process. The conductivity-temperature plots of KCl: Y showed three distinct regions. These regions are explained on the basis of Dryfus and Nowick notation, formation and dissociation of yttrium impurity precipitates.     

Thin-film aerogel thermal conductivity measurements via 3ω

The limiting constraint in a growing number of nano systems is the inability to thermally tune devices. Silica aerogel is widely accepted as the best solid thermal insulator in existence and offers a promising solution for microelectronic systems needing superior thermal isolation. In this study, thin-film silica aerogel films varying in thickness from 250 to 1280 nm were deposited on SiO2 substrates under a variety of deposition conditions. These samples were then thermally characterized using the 3ω technique. Deposition processes for depositing the 3ω testing mask to the sample were optimized and it was demonstrated that thin-film aerogel can maintain its structure in common fabrication processes for microelectromechanical systems. Results indicate that thin-film silica aerogel can maintain the unique, ultra-low thermal conductivity commonly observed in bulk aerogel, with a directly measured thermal conductivity as low as 0.024 W/m-K at temperature of 295 K and pressure between 0.1 and 1 Pa.     

Spectroscopic properties of Zn‐naphtholimines‐TCNQ charge transfer complexes with variable ligand radicals

Over the last decades, many different types of charge transfer complexes have been discussed as organic metals. The design and synthesis of the required efficient p‐electron donors constitutes an active area of modern materials chemistry. An important family with these properties is based on naphtholimines, which are known to form electrically conductive salts with a variety of organic acceptor molecules such as tetracyano‐pquinodimethane (TCNQ). Since the reduction potential of transition metal complexes can be readily modified by the selection of proper ligands and ligand substitution, such complexes are favored candidates for designed syntheses. The present work is aimed toward the study of Zn‐Naphtholimines‐TCNQ charge transfer complexes with fractional electron transfer per formula unit. The electron transfer is an essential factor in the control of electrical conductivity. Of particular interest was the effect of ligand volume variations on the degree of charge transfer. Both IR‐ spectroscopy and electron paramagnetic resonance (EPR) spectroscopy were used as analytic tools. We found, that Zn[RNAFIN]₂‐2TCNQ molecules are partially ionized, and that the electron delocalization is strongly affected by the chosen ligand volume.     

C和F掺杂p型ZnO的第一性原理研究

采用基于密度泛函理论的第一性原理计算方法对C/F单掺杂ZnO和C-F共掺杂ZnO的O位体系进行了研究,讨论了掺杂体系的稳定性、电子结构和电学性质、光学性质.研究结果表明C和F共掺的形成能比C单掺的形成能小很多,即C和F共掺增加了体系的稳定性;计算获得的电导率之比分别为σC-ZnO/σZnO=9.45,σF-ZnO/σZnO=6.78,σC-F-ZnO/σZnO=19.62,显然,C和F共掺杂对ZnO体系的电导率增强效果最明显;载流子迁移率之比μC-ZnO/μZnO=1.67,μF-ZnO/μZnO =2.31,μC-F-ZnO/μZnO=2.50,说明C和F共掺增加了载流子迁移率.综合电导率和载流子迁移率二者结果,可认为C和F共掺极大地提高了ZnO的导电性.ZnO掺杂体系在可见光波长范围内透射率大于95;,具有良好的透光性.计算结果为实验上制备p型透明导电ZnO材料提供了理论指导.     

Some new electrically conducting complexes of nickel chelates

Some new complexes of organo-metallic nickel chelates with organic donors and acceptors and with halogens are found to have electrical resistivities lying in the semiconducting range. The results are discussed here briefly in terms of intermolecular interactions and molecular packing in the solid state. Ni₃O₂(OH)₄ — a mixed valence nickel compound was found to have metallic conductivity in the form of single crystals.     

Numerical modeling of thermally-stimulated currents for the density-of-states determination in thin-film semiconductors

The paper reports on thermally stimulated conductivity studies used for characterization of the density of states profile in thin film semiconductors, by numerically solving the non-linear time-dependent rate equations for free and trapped charge. We explore the derivation of energy and density scales from temperature and conductivity data. We examine the distinction between ‘strong’ and ‘weak’ re-trapping and the use of low ‘effective’ values of attempt-to-escape frequencies in establishing an energy scale, and the ad hoc inclusion of a temperature-dependent lifetime. It is confirmed for several illustrative model systems that the technique can afford surprisingly good fidelity in recovery of the density of states under a range of conditions.     

Effects of pressure on the electrical conductivity of chalcogenide glasses

The effects of hydrostatic pressure (to ～2.4 GPa) on the electrical conductivity of AsTe, AsTeI and AsTeGe bulk semiconducting glasses have been determined. The electrical conductivity σ increases nearly exponentially with increasing pressure P. The Δ 1n σ/ΔP values are dependent upon composition and pressure, and vary from about 2 to 6 GPa^?1. This is a narrow range of values considering that the initial conductivies vary over five orders of magnitude for the compositions studied. Many of the glasses exhibited time-dependent conductivity changes both at high pressure and after cycling to high pressure. At high pressure the conductivity drifted to higher values over a period of several hours, initially following a logarithmic time dependence. Generally, the drifts were observed for P ? 0.8 GPa and for $\text{σ ? 10}{}^{\mathrm{t-1}}\text{(Ω-}\text{m}\text{)}{}^{\mathrm{?1}}$. Following the high-pressure experiment, the conductivity (and also the density) of some glasses were above that for the as-prepared material. These same samples had a slightly different conductivity temperature dependence. The conductivity slowly relaxed (over many months) toward the original conductivity state, again initially following a logarithmic time dependence. Much of our data can be interpreted consistently if we assumed that the conductivity changes depend primarily on “expected” volume changes. The kinds of behavior reported here are similar to those observed for a wide variety of glass systems. Any models developed for describing electrical transport under pressure must account for time-dependent as well as pressure-dependent effects.     

Effect of LiCF3SO3 on L-Chitosan/PMMA Blend Polymer Electrolytes

This paper focuses on the effect of lithium triflate (LiCF₃SO₃) on the structural and conduction properties of lauroyl (L)-chitosan/poly(metylmethacryalate) (PMMA)-based polymer electrolytes. Films of L-chitosan/PMMA blends and its complexes were prepared using a solution-casting technique. The ionic conductivity of the system was measured over a wide range of frequency between 50 Hz-1 MHz. Impedance plot for the samples demonstrates two well-defined regions. The disappearance of the high frequency semicircular region led to a conclusion that the current carriers are ions. Sample with 30 wt% of LiCF₃SO₃ showed the highest conductivity of 7.59 ± 3.64 × 10^?4 Scm^?1 at room temperature. This is consistent with the results obtained from infrared spectroscopy.     

Synthesis and Characterisation of Scandium (III)-, Yttrium (III)-, and Lanthanum (III) Violurate Complexes

Sc³⁺-, Y³⁺ -and La³⁺ violurate complexes were prepared. The isolated complexes are freely soluble in water, dilute mineral acids, MeOH, Me₂CO, DMF, DMS, partially soluble in AcOH and insoluble in EtOH, CHCl₃ and CCl₄. Molecular compositions of the complexes were formulated on the basis of elemental analysis, molar conductivity and infrared spectra. The IR spectra of violuric acid and its metal complexes reveal that bonding takes place through coordination bond between the central metal ion and the oxygen atom of the oxygen atom of the oximino (C N = O) group and convalenet bond between the central metal ion and oxygen atom of the phenolic (ketonic, C O H) group in the case of 1:2 and 1:3 complexes, and through coordination bond between the central metal ion and C O H and N H groups in the case of 2:3 complexes. All the isomorphous complexes detected by the X-ray powder patterns [the (2:3) Sc³⁺-VA and (2:3) Y³⁺-VA complexes, (1:2) Sc³⁺-VA, (1:2) Y³⁺-VA and (1:2) La³⁺-VA complexes, and the (1:3) Y³⁺-VA and (1:3) La³⁺-VA complexes] have similar X-ray, eletronic and IR spetrograms and chemical formulae. The electronic spectra in DMF and in nujol mulls characterise the octahedral stereochemistry for the investigated complexes.     

Toward the rational design of materials

The emphasis of computational chemistry has traditionally been slanted toward the study of isolated organic systems, and in particular toward methods of drug design. The requirements for the study of materials are different, we are often concerned with metal containing species and properties that arise from interactions between unit molecules in the solid state. We have developedcrystal, a molecular modeling environment that provides both the capability to perform calculations on metal complexes, and an array of visualization tools to aid in the design of solid-state systems.     

Low-energy excitations in polyvinyl chloride: Raman scattering and thermal properties

The low-energy excitations of a very fragile glass-former (in the sense of Angell), poly(vinyl chloride), have been studied by low-frequency Raman scattering and by measurements of the low-temperature heat capacity and thermal conductivity. Two different samples were investigated : one with a crystallinity of about 15%, the other quenched and amorphous, as measured by small-angle neutron scattering. The boson peak in Raman scattering was observed in both samples even at room temperature. A clear correspondance between the Raman boson peak, the excess of heat capacity and the plateau of thermal conductivity was shown. It is confirmed that the boson peak or the heat capacity excess are relatively small in this very fragile glass-former. However it is deduced that the high concentration of tunnelling systems in the amorphous sample is the result of a rapid quenching rather than an intrinsic property of fragile glass-formers.     

Current-controlled growth,segregation and amphoteric behavior of Si IN GaAs from Si-doped solutions

An unusual behavior of the growth kinetics and the segregation of Si during current-controlled LPE of GaAs is reported. The growth velocity (for a fiven current density) decreased by about two orders of magnitude from a value higher to a value smaller than that found in undoped solutions as the growth temperature decreased from 975 to 850°C; at 825°C dissolution of the substrate took place and a reversed current polarity was required for growth. At the same temperature range the growth velocity from undoped solutions decreased by a factor of only 3. Similarly, a two orders of magnitude decrease of the silicon segregation coefficient was observed for the same temperature change compared to changes by a factor or two in the thermally grown layers. For a given growth temperature (900°C) a change in conductivity from p- to n-type took place in the grown layers as the current density was increased. These findings were accounted for with a qualitative model based on the presence in the solution of different charged complexes containing silicon with different electromigrating characteristics. According to this model, the behavior of Si as p- and as n-type dopant (amphoteric dopant) in GaAs is related to the existence in the solution of the different charged complexes containing silicon.     

Electrochemical characterizations and the effect of glycerol in biopolymer electrolytes based on methylcellulose-potato starch blend

ABSTRACT

Polymer electrolytes have been prepared by blending methylcellulose (MC)-potato starch, doped with lithium perchlorate (LiClO₄) and plasticized with glycerol. The blend of 60 wt% MC-40 wt% starch was found to be the most suitable ratio to serve as polymer host. Fourier transform infrared (FTIR) spectroscopy analysis proved the interaction among the components. X-ray diffraction (XRD) analysis indicated that the conductivity enhancement is due to the increase in amorphous content. The highest ionic conductivity obtained at room temperature was (4.25 ± 0.82) × 10^?4 S cm^?1 for MC-starch-LiClO₄-20 wt% glycerol. The highest conducting samples in both systems were found to obey Arrhenius rule. Dielectric study further strengthens the conductivity result.     

Highly Conductive TCNQ Salts of Cu Chelates

Abstract

Cu(II) chelates with ethylenediamine, 2,2′-bipyridine, 1,10-phenanthroline and their analogues form highly conductive TCNQ salts CuL_n(TCNQ)₂. The powder conductivity at room temperature amounts to 7 × 10^?4-1.9 Ω_?1cm^?1, depending on the coordinating ligands. The ESR and magnetic susceptibility studies indicate that the Cu atoms of the complexes have incomplete oxidation states.     

Crystallization kinetics of 1Na2O · 2CaO · 3SiO2 · glass monitored by electrical conductivity measurements

We investigated the kinetics of crystal nucleation, growth, and overall crystallization of a glass with composition close to the stoichiometric 1Na₂O · 2CaO · 3SiO₂. The nucleation and subsequent growth of sodium-rich crystals in this glass decreases the sodium content in the glassy matrix, drastically hindering further nucleation and growth. Compositional changes of the crystals and glassy matrix at different stages of the crystallization process were determined by EDS. These compositional variations were also monitored by electrical conductivity measurements, carried out by impedance spectroscopy, in glassy, partially, and fully crystallized samples. The electrical conductivity of both crystalline and glassy phases decreases with the increase of the crystallized volume fraction. Starting at a crystallized volume fraction of about 0.5, the crystalline phase dominates the electrical conductivity of the sample. This behavior was corroborated by an analysis of the activation energy for conduction. We show that electrical conductivity is highly sensitive and can indicate compositional shifts, changes in the spatial distribution of mobile ions in the glassy matrix. Conductivity measurements are thus a powerful tool for the investigation of complex heterogeneous systems, such as partially crystallized glasses and glass-ceramics.     

Induced SA phases in binary systems with EDA complexing

The phase diagrams of 13 binary systems are presented in which electron donor-acceptor (EDA) complexing is clearly detectable. In all binary systems studied the same electron donor compound was used whereas the electron acceptor compounds were members of two homologous series. It was found that the induction of smectic A phases increases with increasing length of the alkyl chain of the acceptor compound and with increasing stability of the complexes.     

Role of concentration fluctuations in metallic glass formation

The glass forming composition range in several binary metallic systems is correlated with the composition dependence of S_cc(0), the concentration-concentration fluctuation structure factor at its long wavelength limit. The magnitude of S_cc(0) has been evaluated for the liquid phase from available thermodynamic data. It has been observed that S_cc(0) exhibits a maximum and tends to the ideal value in the glass forming composition range. Significant and systematic negative deviations from ideal values or the tending to zero of S_cc(0) are observed at the stoichiometry corresponding to complexes in the liquid state in the case of compound forming or associated systems. These observations are discussed in terms of the chemical short-range order in the liquid state. It is concluded that while a reasonable degree of order may exist for the compound forming compositions, in the glass forming region itself the liquids are nearly random mixtures of complexes and unassociated component atoms.