**Acknowledgement**

58 Superconductors – Materials, Properties and Applications


measured in the K0.05MoO2-δ sample.

**2. Conclusions** 

**Author details** 

*Departments of Physics and Astronomy, University of California at Irvine, Irvine, USA* 

Z. Fisk




0

2

4

6

0 50 100 150 200 250 300

<sup>4</sup> TC = 4 K


properties for the MeB2 and AxMoO2-δ compounds have been reported.

A.J.S. Machado, S.T. Renosto, C.A.M. dos Santos and L.M.S. Alves *Escola de Engenharia de Lorena, Universidade de São Paulo, Lorena, SP, Brazil* 

**Figure 13.** Magnetization as a function of temperature measured in the ZFC and FC procedures

This chapter reported the influence of the defects in the crystalline structure on the superconducting properties of intermetallic and low-dimensional compounds. The superconducting critical temperature of the materials can be associated with the electronic properties of the normal state. CDW, SDW, anisotropic behavior, structural phase transition, and doping content play important role on the superconducting properties of the compounds. Results about the influence of the crystalline structure on the superconducting

0 20 40 60 -8

K0.05MoO2-<sup>δ</sup>

The authors are grateful by financial support through of the following grants (CNPq Brazilian Agency grant no 303813/2008-3, 490182/2009-7 and 309084/2010-5) (Fapesp Brazilian Agency grant no 2011/05961-3, 2009/54001-2, 2009/14524-6, 2010/06637-2 and 2010/11770-3) and AFOSR MURI.

### **3. References**

	- [24] M. A. Tanatar, N. Ni, C. Martin, R. T. Gordon, H. Kim, V. G. Kogan, G. D. Samolyuk, S. L. Bud'ko, P. C. Canfield, and R. Prozorov, Phys. Rev. B 79, 094507 (2009).

**Chapter 4** 

© 2012 Izumi and Noudem, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2012 Izumi and Noudem, licensee InTech. This is a paper distributed under the terms of the Creative Commons

**Improvement of Critical Current Density and** 

Mitsuru Izumi and Jacques Noudem

http://dx.doi.org/10.5772/46197

**1. Introduction** 

flux pinning properties.

Additional information is available at the end of the chapter

Cu-O grain is expressed in a simple model, such as:

**Flux Trapping in Bulk High-Tc Superconductors** 

The present chapter describes an overview of flux trapping with enhancement of the critical current density (*Jc*) of a melt-growth large domain (RE)Ba2Cu3O7-d, where RE is a light rare earth ions such as Y, Gd or Sm. These high-Tc superconductor bulks have attracted much interest for a variety of magnet applications, since high density and large volume materials potentially provide an intensified magnetic flux trapping, thanks to the optimized distribution of pinning centres. The melt growth process and material processing to introduce well-defined flux pinning properties are overviewed. As a first step, we summarize an effort to achieve a growth of homogeneous large grains with the second phase RE211 in the RE123/Ag matrix. RE-Ba-Cu-O material has a short coherence length and a large anisotropy, and thus any high-angle grain boundary acts as a weak link and seriously reduces the critical current density [1, 2]. In engineering applications, high texture and *c*-axis-orientated single grains/domains are required. Large-sized, high-performance RE-Ba-Cu-O single grains are now commercially available. The trapped flux density (*B*trap) due to flux pinning or associated superconducting currents flowing persistently in a RE-Ba-

*B*trap = *Aµ*0*J*c*r*, where *A* is a geometrical constant, *µ*0 is the permeability of the vacuum and *r* is the radius of the grain [1]. There are two approaches to enhancing the trapped flux of the grain. One is to enhance the critical current density and the other is to increase the radial dimension of the crystals. Increasing the dimension requires the formation of homogeneous grain growth, and the enhancement of the critical current density is encouraged with the improvement of

The top-seeded melt-growth (TSMG) method has been widely used to fabricate large, single-grain RE-Ba-Cu-O superconducting bulks that show a considerable ability in

