High Tc

Some of the above discussed precursor phenomena are also observed prior to diffusion driven phase transformations. A typical example are the conventional EM tweed images obtained in the tetragonal parent phase in high Tc superconductors and other ceramics. In a recent survey by Putnis St e of such observations it was concluded that in these cases the tweed contrast resulted from underlying microstructures fomied by symmetry changes driven by cation ordering. These symmetry changes yield a fine patchwork of twin related domains which coarsen when the transfomiation proceeds. However, in view of the diffusion driven character of the latter examples, these cases should be clearly separated from those in the field of the martensites. 

Barron, A. R., Group Ila Metal Organics as MOCVD-Precursors for High Tc Superconductors, The Strem Chemiker, XIII-1, Strem Chemicals, Newburyport, MA 01950 (1990)... 

Egami T (2005) Electron-Phonon Coupling in High-Tc Superconductors 114 267-286 Egami T (2007) Local Structure and Dynamics of Ferroelectric Solids. 124 69-88 Eisenstein O, see Clot E (2004) 113 1-36... 

Kittilstved KR, Gamelin DR (2005) Activation of high-Tc ferromagnetism in Mn+2-doped ZnO using amines. J Am Chem Soc 127(15) 5292-5293... 

This review will include both types of studies, but will not discuss in any detail optically pumped NMR of semiconductors, which has been well-reviewed [5, 11, 12,14], or other unconventional techniques for detection of NMR signals. Physics-related NMR studies of more complicated semiconductor behavior such as Kondo insulators or semiconductors and other unusual semiconducting phases, and semiconducting phases of high-Tc superconductors, while very important in physics, will be neglected here. I have deemed it of some value to provide rather extensive citation of the older as well as of the more recent literature, since many of the key concepts and approaches relevant to current studies (e.g., of nanoparticle semiconductors) can be found in the older, often lesser-known, literature. My overall aim is to provide a necessarily individual perspective on experimental and theoretical approaches to the study of semiconductors by NMR techniques that will prove useful to chemists and other scientists. 

Odier, P. Supardi, Z. De-Barros, D. Vergnieres, L. Ramirez-Castellanos, J. Gonzales-Calbet, J. M. Vallet-Regi, M. Villard, C. Peroz, Ch. Weiss, F. 2004. Spray pyrolysis for high Tc superconductor films. Supercond. Sci. Technol. 17 1303-1310. 

In refs (Kim,2004 Kim, 2005) we take one step further estimating corrections to the Gaussian effective potential for the U(l) scalar electrodynamics where it represents the standard static GL effective model of superconductivity. Although it was found that, in the covariant pure (f)4 theory in 3 + 1 dimensions,corrections to the GEP are not large (Stancu,1990), we do not expect them to be negligible in three dimensions for high Tc superconductivity, where the system is strongly correlated. 

The paper is organized as follows in Section II the GL action is introduced and the post Gaussian approximation is applied in Section III we discuss the input parameters of the model in Section IV the theoretical results for D = 3 and D = 2+2e will be compared to existing high Tc experimental data in Section V we bring a brief summary. 

All the above numerical calculations were made in D=3 dimension. On the other hand it is widely known that, most of high Tc cuprates have layered structures with 2D CuO2 planes which play an essential role in the high Tc superconductivity.Therefore, it is nessesary to consider the dimensional contribution in the calculation.For this purpose,we consider the case of D = 2 + 2e (e / 0) in the post Gaussian approximation.In this case the optimal values of m and A also depend on e. Using Eq.(25) and the procedure outlined above one finds the e dependence of m2 presented in Fig.3 (solid line). 

For e > 0.1,there is a possibility to adjust e to the recent experimental data on k(T) (Brandstatter,1994) for high — Tc cuprate superconductor TI2CC12(7 — 2223). Our calculations show that,the best choice of e is found to be e = 0.21.The appropriate k(t) is presented in Fig.4 (solid line). The dashed line in this figure shows k(t) for D = 3. This fitting process allows us to get an estimation on the effective dimensionality of the high — Tc superconducting materials. 

For importance sampling in the lattice simulation, one can use the leading part of the determinant, [real, positive]. This proposal provides a nontrivial check on analytic results at asymptotic density and can be used to extrapolate to intermediate density. Furthermore, it can be applied to condensed matter systems like High-Tc superconductors, which in general suffers from a sign problem. 

We will demonstrate below that the Ginzburg number Gi = AT/Tc), which determines the broadness of the energy region near the critical temperature, where fluctuations essentially contribute, is Gi A(Tc/iiq)4 with A 500 in our case. To compare, for clean metals A 100, p,q — fi,., the latter is the electron chemical potential. Thus Gi 1, if Tc is rather high, Tc (f -t- )p,q, and we expect a broad region of temperatures, where fluctuation effects might be important. 

The recent discovery of high Tc superconductors means that applications of electrochemistry in this field are still in the initial phases... 

For other examples involving materials see, for example, the determination of the crystal structure of the high Tc superconductor YBa2Cus07by Huang et al. [26], and K20.Nb205 [27]. 

After more than ten years of extensive experimental and theoretical studies of the phenomenon of the high Tc superconductivity (HTSC) [1], we still do not know a microscopic mechanism responsible for this phenomenon. Numerous theories of pairing, which lead to high Tc values, are based on models [2-9] and cannot connect a specific chemical composition of HTSC ceramics with the value of the transition temperature Tc. For creating a quantitative theory of the HTSC phenomenon further comparative studies of the electronic structure and their relative properties of SC and non-SC ceramics are needed. In this paper, we confine ourselves to calculations of the electronic structure of the SC yttrium ceramics. 

E. Kaldis et al. (eds) High - Tc superconductivity 1996 Ten Years after the Discovery, Klumer Acad. Publ., the Netherlands, (1997)... 

A.S. Alexandrov and N.F. Mott High Tc Superconductivity and Other Superfluids, Taylor, London 1994 Polarons andBipolarons, World Scientific, Singapore, (1995)... 

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