Intergrain ordering processes of YBa2Cu4O8 and related complex ceramic systems

Intergrain ordering phenomena of frustrated ceramic YBa2Cu4O8 (Y124) and dual phase mixed ceramic containing CuO are studied by both magnetic and resistivity observations. Magnetically estimated intergrain ordering temperature Tc2 and zero-resistivity attainment temperature Tz are both decreased with CuO content. However, it is also revealed that mutual location of Tc2 and Tz is changed. For the mixed ceramic with torn intergrain network structure, Tz stays above Tc2, indicating local dissolution of frustration by cluster structure. On the other side, remaining resistivity tails blow Tc2, indicating intrinsic fluctuation effect on the resistivity caused by frustration in the ordered state. It is known then that, superconductive ceramic samples which is free from structural phase inhomogeneity is essential in order to clarify the frustration effect.