Control of successive phase transition in YBCO superconductive ceramics

• Published in: Journal of magnetism and magnetic materials Vol. 310; no. 2; pp. e113 - e115
• Main Authors: Koyama, K., Houda, H., Amano, H., Saito, T., Sugawara, H., Magishi, K., Deguchi, H.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-03-2007
• Subjects: Chiral glass; Grain boundaries; Josephson network; Nonlinear conductivity; YBCO ceramics; YBCO ceramics; Grain boundaries; 61.72.M; 74.72.B; 64.70.P; Nonlinear conductivity; Josephson network; 81.05.J,M; 74.25F; Chiral glass
• ISSN: 0304-8853
• DOI: 10.1016/j.jmmm.2006.10.091

The ceramic YBa
2Cu
3O
7–
δ
samples composed of sub-micron size grains are considered as random Josephson-coupled networks of 0 and
π junctions and show successive phase transition. With decreasing temperature, a transition occurs at first inside each grain at
T
c1 (just the same with the bulk superconducting transition temperature
T
c) and successively another transition occurs among the grains at
T
c2 (<
T
c1). The various ceramic samples were prepared with not only changing the calcination and the sintering temperature but also changing the pressure in pelleterizing process between calcination and sintering, using sub-micron size powder prepared by the coprecipitation method. With increasing sintering temperature (equal to calcination temperature),
T
c2 increases and both the absolute values of linear resistivity and the divergence of nonlinear resistivity (just above
T
c2) decrease. With increasing the density of sample by increasing the pressure in the pelleterizing process, the
T
c2 and the absolute value of conductivity increase monotonously. These effects may be considered as the changes in Josephson-couple strength between superconducting grains in the ceramic specimens.