sintering in the solid reaction process of the A-YBCO sample. This is why the first sintering cycle of the SG-YBCO samples is equivalent to the second sintering cycle of the A-YBCO samples; the second sintering cycle of the SG-Y BCO samples is corresponding to the sixth sintering cycle of A-YBCO samples The points Tv and Tp for p v and p p appear at 534 and 871C respectively for the A-YBCO samples in the second cycle. However, the T and Tp for the SG-YBCO samples appear at 609 and 785C in the first sintering cycle. The T and Tp for the A-Y BCO samples appear at 487 and 871C respectively in the sixth cycle, but the Ty and Tp for the SG-YBCO samples appear at 597 and 721C in the second sintering cycle. The comparison of these characters between the SG-YBCO and the A- YBCO samples are listed in Table 1 Table 1. The comparison between the resistivities of SG-YBCO and A-YBCO samples Process st round of SG-YBCO and 2nd round of 2 d round of SG-YBCO and 6th round of End testing A-YBC A-YBCO measuring Parameters Tp (℃)(g·cm)(℃)(g·cm)(℃)(9·cm) SG-YBCO 6096779 388.8 5972.59 2.772 0.0098 A-YBCO 5340.1425 871 0.554 4870.1124871 0.341 0.0047 The SG-YBCO and the A- YBCO samples have the same variation trend in resistivity. But the difference of Tp and Tv is different. In the second cycle of the A-YBCO samples, the temperature difference is AT =337C, but in the 1 cycle of the SG-YBCO samples, the temperature difference is△T=176℃. In the sixth cycle of the A-ybCO,△T=384℃, but in the second cycle of the SG- YBCO sample,△T=124℃ The above results reveal that it is easier for the SG-YBCO samples to finish the transition from semiconducting to conductiving at T and then from conducting to semiconducting at Tp than for the A-YBCO samples. The reasons for this are: 1. the SG-YBCO samples are sintered in a flowing oxygen atmosphere, but the A-YBCO samples are in ambient air; 2. the raw materials of the SG-YBCO samples of nanometer powders are easier to get into solid reaction than those of the A-YBCO samples of micrometer powders. This also can be confirmed from the sintering process of MgB2 samples by using nanometer magnesium powders as the raw material. 4 While keeping the SG-YBCO sample at 920C for about 11 he first cycle, the resistivity decreased continuously. This is similar to the behaviour of the A- YBCO samples kept at constant temperature in the second sintering process In the cooling process of the SG-YBCO samples, the resistivity continuously decrease from 920 to 505C, then suddenly turns to increase from 505C down to room temperature. The A-YBCO samples in the cooling process from the first cycle to the fifth cycle show the same variation trend. This indicates that oxygen content is still not enough to keep the YBCO samples in the conducting state in higher temperature. Obviously, such a kind of YBCO sample is certainly not in the superconducting state at low temperatures Figure 2 shows the in-situ HT p-T curves of the SG- YBCO sample which underwent the first cycle of sintering process, and then pulverized, reground, and the gold wires re-pressed into4 sintering in the solid reaction process of the A-YBCO sample. This is why the first sintering cycle of the SG-YBCO samples is equivalent to the second sintering cycle of the A-YBCO samples; the second sintering cycle of the SG-YBCO samples is corresponding to the sixth sintering cycle of A-YBCO samples. The points Tv and Tp forρv andρp appear at 534 and 871℃ respectively for the A-YBCO samples in the second cycle. However, the Tv and Tp for the SG-YBCO samples appear at 609 and 785℃ in the first sintering cycle. The Tv and Tp for the A-YBCO samples appear at 487 and 871℃ respectively in the sixth cycle, but the Tv and Tp for the SG-YBCO samples appear at 597 and 721℃ in the second sintering cycle. The comparison of these characters between the SG-YBCO and the A-YBCO samples are listed in Table 1. Table 1. The comparison between the resistivities of SG-YBCO and A-YBCO samples Process 1st round of SG-YBCO and 2nd round of A-YBCO 2nd round of SG-YBCO and 6th round of A-YBCO End testing measuring Parameters Tv ρv Tp ρp (℃) (Ω•cm) (℃) (Ω•cm) Tv ρv Tp ρp (℃) (Ω•cm) (℃) (Ω•cm) ρend (Ω•cm) SG-YBCO 609 67.79 785 388.8 0.0098 A-YBCO 534 0.1425 871 0.554 597 2.59 721 2.772 487 0.1124 871 0.341 0.0047 The SG-YBCO and the A-YBCO samples have the same variation trend in resistivity. But the difference of Tp and Tv is different. In the second cycle of the A-YBCO samples, the temperature difference is ΔT =337℃, but in the 1st cycle of the SG-YBCO samples, the temperature difference is ΔT =176℃. In the sixth cycle of the A-YBCO, ΔT =384℃, but in the second cycle of the SG-YBCO sample, ΔT =124℃. The above results reveal that it is easier for the SG-YBCO samples to finish the transition from semiconducting to conductiving at Tv and then from conducting to semiconducting at Tp than for the A-YBCO samples. The reasons for this are: 1. the SG-YBCO samples are sintered in a flowing oxygen atmosphere, but the A-YBCO samples are in ambient air; 2. the raw materials of the SG-YBCO samples of nanometer powders are easier to get into solid reaction than those of the A-YBCO samples of micrometer powders. This also can be confirmed from the sintering process of MgB2 samples by using nanometer magnesium powders as the raw material．[14] While keeping the SG-YBCO sample at 920℃ for about 11.5 h in the first cycle, the resistivity decreased continuously. This is similar to the behaviour of the A-YBCO samples kept at constant temperature in the second sintering process. In the cooling process of the SG-YBCO samples, the resistivity continuously decreases from 920 to 505℃, then suddenly turns to increase from 505℃ down to room temperature. The A-YBCO samples in the cooling process from the first cycle to the fifth cycle show the same variation trend. This indicates that oxygen content is still not enough to keep the YBCO samples in the conducting state in higher temperature. Obviously, such a kind of YBCO sample is certainly not in the superconducting state at low temperatures. Figure 2 shows the in-situ HT ρ–T curves of the SG-YBCO sample which underwent the first cycle of sintering process, and then pulverized, reground, and the gold wires re-pressed into