The Y123, Y358 and Y257 bulk superconductors mixed with various ratio of non-superconducting Y211 (Y2BaCu05) were synthesized by solid state reaction. The physical properties of pellets were investigated by d.c. four-probes measurement. The crystal structure was determined using powder X-ray diffraction and the characteristic peaks were determined using the Rietveld full-profile analysis method. Results showed that the Tconset and Tcoffset decreased with the increasing of Y211 doping. The samples consist of both superconducting phase and the non-superconducting phase. The lattice parameter of Y211 doped samples showed lower c direction than pure samples. The superconducting phase decreased with increasing Y211 content. The non-superconducting phases consists of Pccm (Ba2Cu306) and เทา-3m (BaCu02) respectively. According to the percentage of superconducting phase, the anisotropy increased with Y211 contents.
Since YBa2Cu307(Y123) superconductor which has highest critical temperature at 93K was found in 1987 (พน et al., 1987), many researchers have performed vigorously to improve its superconducting properties and the results have been applied to the fabrication of various film or bulk type superconductors. เท 2009, the Y3Ba5Cu8Oi8(Y358) was found (Alibadi et al., 2009). This is the highest critical temperature of Y-based superconductor that has highest critical temperature at 102K. เท 2013, Kruaehong (2013) could synthesize the new superconductors, Y2Ba5Cu7015(Y257) by solid state reaction. This superconductor has highest critical temperature about 94K. Because superconducting
properties of the Y123, Y358, and Y257 can be performed in liquid nitrogen, this cheap cryogenic medium makes the materials promising in many fields such as superconducting magnetic bearings (Jiqiang et al., 2012), superconducting electric motors (Hiroyuki and Yuichi, 2001), magnetic separation devices (Oka et al., 2013), non-contact transport systems (Smith and Jr. Dolan, 2013), flywheel energy storage systems (Arai et al., 2013) and permanent magnets with high trapped field (มน et al., 2011) operating above 77K (Moon and Chang, 1990; Hull, 2001).
It is well known that Y211 (Sandiumeng et al., 1997) which is the second phase of the Y123, Y211 doping.