Physical, electrical, transport and magnetic properties of Nd(Ba,Nd)_(2.1)Cu_3O_(7-δ) system

摘要

In this study, the superconducting Nd(Ba,Nd)_(2.1)Cu_3O_(7-δ) system has been prepared using conventional solid-state reaction technique. Transport properties including structural/microstructural evolution, electrical, magnetic and critical current density properties were investigated. After high temperature heat treatments at over 1,000 ℃, large and strongly connected grains were obtained but weakly connected and small in size granular formation were obtained for the low temperature heat treated samples at around 900 ℃. The best T_c. and T_o values were obtained as 93 and 89 K respectively for the sample prepared at 1,020 ℃ for 24 h, which is very close to peritectic temperature of YBCO material. Magnetization of the sample heat treated at 1,020 ℃ was investigated in detail. The magnetization hysteresis loops are expounded to be the product of Nd-123 grains and unscreened Nd~(3+) ions within intergranular boundaries and vortex cores. The peak effect on the magnetization curves was described by the extended critical state model. Temperature dependencies of the irreversibility field, the peak field and the full penetration field correlate and there is scaling behavior of the pinning force as well. Thermoelectric power data was analyzed by "Modified two band model with linear T-term for superconductors". Temperature dependence of thermal conductivity of the samples showed small peak with broad maximum just below the T_c value. Thermal conductivity of samples prepared was calculated by using "The Modified Callaway Model and Wiedermann-Franz law" and results obtained discussed.