FIG. 7 is a diagram illustrating a typical firing profile of the first embodiment. A mixed gas is dried up to tb1 at 100° C., but humidification is performed. A humidification start temperature may be 100° C. or higher and 400° C. or lower. It seems that the formation of the quasi-liquid layer starts from around 550° C., and the humidification is performed at a temperature lower than that so that the humidifying gas spreads inside the film and the quasi-liquid layer is uniformly formed.
FIG. 7 illustrates a typical temperature profile of firing at 800° C., but the temperature rise profile is gentle at 775° C. or higher and 800° C. or lower so that there is no temperature overshoot at tb3. However, an overshoot at 800° C. can remain at 2 to 3° C., which is not particularly a problem. An oxygen partial pressure at the highest temperature depends on the matrix phase. In the case of YBCO superconductor firing, the partial pressure is 1000 ppm at 800° C., and the optimum oxygen partial pressure is halved every time the temperature drops by 25° C. That is, the partial pressure is 500 ppm at 775° C. and 250 ppm at 750° C. In the case of the YBCO system, YBa2Cu3O6 is formed in this firing. At this point, no superconductor exists.
For example, the highest temperature of firing may be 750° C. In this case, for example, the same temperature rise rate as in FIG. 7 is performed to a temperature 25° C. lower than the highest temperature, and the temperature rise rate is reduced to raise the temperature to the highest temperature.
