Fabrication of YBa2Cu3Ox in a radio-frequency heating furnace

We fabricated high-Tc superconducting YBCO polycrystals in a radio-frequency (rf) wave heating furnace. The sintering temperatures 600 ∼ 900 .deg. C and the sintering times 0.5, 1, and 2 hours were tried for fabricating the polycrystals, and the polycrystal sintered at 900 .deg. C for 0.5 hour (sample R) showed the best intergranular connectivity and the zero resistivity at 90 K in the resistivity-temperature measurement. Longer sintering-times instead led to degraded intergranular connectivity, showing the zero resistivity at 65 K for 1 hour and at 77 K for 2 hours, respectively. Sample R was compared with the sample (sample E) sintered at 900 .deg. C for 0.5 hour in a conventional electrical-resistance (ER) furnace through the magnetic hysteresis loop measured at 77 K. The intergranular critical current densities calculated from the critical state model analysis were 28.9 A/cm2 for sample R and 9.6 A/cm2 for sample E at 77 K. This is due to self-heating of the polycrystal by resonances absorption of the rf wave and shows that rf heating can be more efficient in fabrications of high-Tc superconductors than ER heating, provided that the sintering-time is controlled properly.