High superconductor

Plenary 5. Manuel Cardona, e-mail address cardona .cardix.mpi-stuttgart.de (RS). Studies of high superconductors. These offer all possible Raman transitions—phonons, magnons, free carrier excitations, pair... 

Phinyocheep, P. Tang, 1. M. Determination of the Hole Concentration (Copper Valency) in the High Superconductors, /. Chem. Educ. 1994, 71, A115-A118. 

Gross Levi, B. Learning about high superconductors from their imperfections, Phys. Today (March 2000), 17-8. 

The central problem in organic solid-state photochemistry is the preorganization of molecules satisfying the topochemical postulates. Schmidt coined the term crystal engineering for this problem of supramolecular assembly. Indeed, the importance of crystal engineering is fundamental to areas as diverse as nonlinear optics, high- /) superconductors, and the generation of polymorph forms in pharmaceuticals. 

J. C. Phdlips, Physics of High Superconductors , Academic Press, Boston, MA, 1989. 

First electrochemical studies on structuring and modification of different high superconductor surfaces have recently been started [6.190]. One of the main problems is the instability of oxide ceramic material in neutral and acidic aqueous electrolyte solutions at room temperature [6.196-6.198]. HTSC surfaces corrode, and superconductivity was found to decrease within the topmost layers of IfTSC samples after water contact. This aging effect decreases in alkaline media [6.197]. However, sufficient long term stability of HTSC samples was only found in aprotic solvents such as acetonitrile. Therefore, experiments were carried out in acetonitrile-containing... 

Crucibles of titanium nitride and zirconium nitride are utilized for the melting of lanthanum alloys. ZrN, HfN and TaN are also used as electrodes in electronic valves. Niobium and zirconium nitrides could be used as superconductors due to their relatively high superconductor transition temperatures of 16.8 and 10 K respectively. 

Niobium and zirconium nitrides have relatively high superconductor transition temperatures... 

Metal oxides such as high % superconductors (HTS) and the high dielectric perov-skites have come to the forefront of electronics research over the last few years. The... 

Figure 2. The Meissner effect, or the levitation of a strong magnet by the internal diamagnetic field of a high superconductor.

Since all the current high superconductors are oxides, low oxides are important. NbO was first found to be superconducting in 1933. Since then much effort has been devoted to investigating superconductivity in oxides, but not many oxides display this property. Table 1 presents a chronological listing of the different oxide superconductors reported prior to 1975. Of particular interest is the compound Ba(Pbi cBiJ03 with T, of 13 K and Bao.6Ko.4Bi03- , with a T, of 28 K. ... 

Since the first observation of high superconductivity at 110 K (onset) in (Sri cCaJi, Cu02 which was first synthesized by Siegrist et al.. The synthesis and superconductivity of this compound have been widely studied because the cuprate represents the core part, known as the infinite layer , of cuprate high superconductors. The preparation of infinite layers in a single phase is difficult at ambient pressure and must be carried under high pressure up to 6 GPa. 

There are now quite a sizeable number of high superconductors, and in the plot [33] shown in Fig. 15 it is apparent that the Cu-O distance is a useful parameter to describe their superconducting properties. A connection can be made between these Cu-O distances and the number of holes in the CuOj layer by consideration of the bond valence sum, v, at the copper atoms. This concept dates from Pauling s idea of the electrostatic bond sum rule and has been refined in the intervening period [34]. Modern usage defines it as the sum of the bond strengths over all bonds coordinated to copper in the following way. The bond valence sum, u = E, exp(r, - r(,)/0.37, where the parameter depends on the... 

Phase distributions in electron beams can be measured to within 2n /100, which has opened the way to measuring microscopic objects and fields with ultra-high precision. These developments allow the direct observation of individual vortices in a superconductor. Electron phase microscopy can be used to clarify the fundamental and practical applications of superconductivity, especially in the field of high superconductors. 

Some of the low loss EELS work on high superconductors using a dedicated EELS spectrometer has been reported earlier by several groups [8.6,... 

These bicrystals are the substrates that have been typically used for the preparation of individual grain boundaries in YBCO thin films [11.1-11.3]. The reason that SrTiOs is chosen as the substrate for YBCO is primarily due to the closeness of the lattice parameters (3.905 A for SrTiOs compared with a = 3.81 A and b = 3.88 A in YBCO). In view of the fact that YBCO, and for that matter all of the high superconductors, have structures that are essentially perovskite, it is reasonable to assume that the structure of the YBCO grain boundary would follow that of the SrTiOs bicrystal. Indeed, in terms of the dislocation core models, the only difference between SrTiOs and YBCO are that the Sr columns are replaced by Y/Ba columns and the Ti—O columns are replaced by Cu—O columns. The structure in the [001] projection is the... 

This is is a clear and up-to-date account of the application of electron-based microscopies to the study of high superconductors. 

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