Organic superconductors method

The electrocrystallization technique has provided the most general method for the synthesis of high-quality organic molecular conductors and has given rise to the majority of organic superconductors. In an electrocrystallization experiment, a donor or an acceptor is oxidized or reduced electrochemically to form radical cations or radical anions. Crystal formation takes place at the working electrode when the radical cations/anions combine with suitable counterions that are furnished by the supporting electrolyte. 

Although in principle every experimental setup that measures the field dependence of the magnetization or a derivative of M could be used to observe the dHvA effect, usually an apparatus with a very high sensitivity has to be designed to resolve the oscillations. An overview of the different experimental techniques is given in Ref. [249], Two main realizations used to detect dHvA oscillations in organic superconductors are the torque and the modulation-field method. 

The radical cation salts (BEDT-TTF)2l3 have drawn much attention, since one of them was found to be an organic superconductor. This series of salts can appear in many modifications, known as the a-, p-, 0-, K-phases. Under ambient pressure, the a-(BEDT-TTF)2l3 phase undergoes a metal-insulator phase transition at 135 K [1], while the p-, 0-, and K- (BEDT-TTF)2l3 become superconductors below -- 1.3 K, 3.6 K and 3.6 K, respectively [2-5]. After some particular pressure and temperature processing, the P-phase shows superconductivity at ambient pressure, up to a temperature as high as 8.1 K [6]. Unlike these phases, which are usually synthesized by an electrochemical method, two new phases, called p j - and -(BEDT-TTF)2l3, were synthesized recently by D. Zhu and co-workers by a diffusion method [7,8]. 

The 1-2-3 ceramic superconductor YBa2Cu307 has been synthesized by the sol-gel method from a stoichiometric mixture of yttrium ethoxide, barium ethoxide, and cop-per(II) ethoxide in an appropriate organic solvent. The oxide product, before being heated in oxygen, has the formula YBa2Cu3065. Write a balanced equation for the hydrolysis of the stoichiometric mixture of metal ethoxides. 

This chapter first gives background on compounds that can be qualified as benchmarks in the field of molecular organic and inorganic conductors and superconductors. Focus is then further given to systems based on metal bis-dithiolene complexes. The last section considers the processing methods that can be applied to grow films of molecular conductors and superconductors. 

An alternative method for introducing localized magnetic moments into the Cu oxide superconductors is similar to the method used in the organics, though,in this case,by substituting the cations rather than anions. Thus,in category B, all Ln + except Pr and Ce,yield superconductors,but the Ln moments do not order until far below T. . Then they order antiferro-... 

Many works have been devoted to the deposition of droplets in liquid phase and subsequent solvent evaporation (process A), or to the direct precipitation of precursor compounds in solid phase onto the substrate surface (process B) (see a review in ref. Gurav, 1993). This method generally involves the use of organic or mineral acidic salt precursors, which are deposited on substrates heated at 200-500°C. This is an easy method, which allowed the deposition of a wide variety of multi-component materials in the form of thick films (typically 10-20 jum thickness). For instance, it was proposed for low cost processes able to produce high Tc superconductor coatings for power applications (Jergel, 1996). Primary drawbacks include porous and rough powder-like films of rather poor optical and mechanical quality, as well as low purity of the as-deposited conpounds. Such drawbacks necessitate... 

This chapter is divided into a number of sections that describe important details related to the conductive polymer/superconductor structures. First, information is provided concerning the preparation and characterization of various polymer/superconductor structures. Chemical and electrochemical deposition methods for localizing the polymers onto a number of cuprate phases are discussed. Section III is devoted to relevant background information related to the induction of superconductivity into metals and semiconductor systems via the proximity effect. More specifically, the four basic methods that have been used to study the occurrence of proximity effects in classical solid-state conductors are described (i.e., contact resistance, modulation of superconductivity in normal/superconductor bilayer structures, passage of supercurrent through superconductor/ normal/superconductor systems, and theoretical analyses). Sections IV and V are devoted to experimental studies of conductive polymer/superconductor interface resistances and modulation of superconductivity in the hybrid systems. Finally, there is a discussion of the initial experimental results that explores the possible induction of superconductivity into organic materials. 

Although there are now a large number of conductors and superconductors based on BEDT-TTF salts, the majority of these materials have been prepared only as single crystals via electrochemical methods [54J. To make functional systems that can be interfaced readily with high-Tc structures, it is necessary to prepare thin films of these organic conductors. Recently, methods have been developed for the deposition of thin films of (BEDT-TTF)2l3 via vapor processing steps [55-57J. 

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