1.5 Constant temp.:920℃ (c) 0.5 c 0 -0.5 02004006008001000 2004006008001000 Temperature(℃) In 0.16 10008006004002000 Temperature(℃) ig. 1 The in-situ HT P-T curves of SG-YBCO sample sintered in the first cycle: (a) heating, (b) onstant temperature at 920C, and(c)cooling in the furnace Figures 1(a),(b), and(c)show the heating, keeping constant temperature at 920C and cooling processes respectively of the ht p-t curves of the SG-YBCO sample sintered in the first cycle. From Fig. 1(a)it can be seen that the SG-YBCO sample is initially an insulator at room temperature. Its resistivity is about 2X 10.cm with some jitter observed till the temperature reaches 110C during the heating process. The resistivity of the SG- YBCO sample is decreased gradually with increasing temperature, but it reduces rapidly at temperatures higher than 200C This may be caused by some kind of chemical reaction occurring in the heating process. For example, some residual nitrate and citrate decompose, and send off some kinds of gases, such as NO, CO2, and NH, to produce BaCO3, Y203, CuO, and CuO2 etc. 8) The thermogravity curve also shows that the SG-YBCO sample has a high weight loss at temperatures of 200--300'C. IS There are two special temperature points Ty and Tp, where the yBCO sample changes its conductivity for every HT p-T curve in the heating process: at T the YBCO sample changes from semiconducting to conducting and presents a minimum resistivity value p v, while at Tp the YBCO sample changes from conducting to semiconducting again, and presents a maximum resistivity value pp. In different sintering processes, the temperatures Ty and Tp are different. In order to compare the sintering processes between the SG-YBCO samples and the YBCO samples sintered in ambient air(hereafter refer to as A-YBCO sample), we must compare their HT p-T curves in each sintering process The curve shape in Fig. I(a) is similar to that obtained from the second cycle to sixth cycle of the A- YBCO samples in the heating process We believe that the SG-YBCO samples produced using sol gel method have already undergone an active chemical reaction during the preparation, which corresponds to the first3 (a) (b) (c) Fig. 1 The in-situ HT ρ-T curves of SG-YBCO sample sintered in the first cycle： (a) heating, (b) constant temperature at 920℃, and (c) cooling in the furnace. Figures 1(a), (b), and (c) show the heating , keeping constant temperature at 920℃ and cooling processes respectively of the HT ρ–T curves of the SG-YBCO sample sintered in the first cycle. From Fig. 1(a) it can be seen that the SG-YBCO sample is initially an insulator at room temperature. Its resistivity is about 2×107 Ω·cm with some jitter observed till the temperature reaches 110℃ during the heating process. The resistivity of the SG-YBCO sample is decreased gradually with increasing temperature, but it reduces rapidly at temperatures higher than 200℃. This may be caused by some kind of chemical reaction occurring in the heating process. For example, some residual nitrate and citrate decompose, and send off some kinds of gases, such as NOx, CO2, and NH3 to produce BaCO3, Y2O3, CuO, and CuO2 etc．[18] The thermogravity curve also shows that the SG-YBCO sample has a high weight loss at temperatures of 200～300℃．[18] There are two special temperature points Tv and Tp, where the YBCO sample changes its conductivity for every HT ρ-T curve in the heating process: at Tv the YBCO sample changes from semiconducting to conducting and presents a minimum resistivity valueρv; while at Tp the YBCO sample changes from conducting to semiconducting again, and presents a maximum resistivity valueρp. In different sintering processes, the temperatures Tv and Tp are different. In order to compare the sintering processes between the SG-YBCO samples and the YBCO samples sintered in ambient air (hereafter refer to as A-YBCO sample), we must compare their HT ρ-T curves in each sintering process. The curve shape in Fig.1(a) is similar to that obtained from the second cycle to sixth cycle of the A-YBCO samples in the heating process．[11] We believe that the SG-YBCO samples produced using sol gel method have already undergone an active chemical reaction during the preparation, which corresponds to the first 0 5 10 15 20 0 200 400 600 800 1000 ln ρ ρ ( Ω·cm) Temperature ( ) ℃ 14 15 16 17 40 80 120 160 lnρ ρ (Ω·cm) Temperature ( ) ℃ -0.5 0 0.5 1 1.5 2 200 400 600 800 1000 ln ρ ρ ( Ω·cm) Time (min.) Constant temp. : 920℃ 0.08 0.16 0.24 0.32 1000 800 600 400 200 0 ρ ( Ω·cm) Temperature ( ) ℃