pattern of sol-gel powders. After the SG-YBCO sample finished the first sintering cycle, the main diffraction peaks of the Y Ba2 Cu3 Oy appeared as shows in the x-ray pattern index of the first sintering. After the second cycle sintering, not only the intensity of those main diffraction peaks enhanced, but also the (0, 0, 2)peak appeared. This indicates that the SG-YBCO sample has changed into real Y Ba2 Cu3O sample although there are still some impurity peaks 4. Conclusion We have measured the in-situ HT p-T curves of the sol-gel Y Bay CuyOy samples sintered in various temperature range. The resulting curves are shown in figures 1, 2, and 3 for the 3 consecutive runs of the sintering cycles. The resistivities of SG-YBa2 Cu3 Ov 300=9.8X10Q2 .cm in the room temperature and p1223=6.68X 10-Qcm at 950C can be seen from these figures According to these results, the o-t phase transformation process can also be studied. The transformation temperature of the SG-YBCO sample is lower than that of the A-Y BCO sample which has not been reported previously to our knowledge. This could be due to the fine particles of the SG-YBCO chemically active, leading to an easier solid reaction sintering process. The present work suggests that the technology of the in-situ HT p-T measurement is an effective probe in the superconducting research. By this method, the O-T phase transition temperature has been shown to be lower for the SG-YBCO than the A-YBCO samples References [1] Ginsberg D M 1989 Physical Properties of High Temperature Superconductors(World Scientific Press, Singapore)I(pp39-70), I(pp121-198) Ill(pp285-362), and IV(1-6) 2] Charles P. Poole, Jr, Timir Datta, Horacio A Farach, 1988 Copper Oxide Superconductors, Wiley-Interscience Publication, John Wiley Sons Inc(United States of America)59-170 3] Liu L H, Dong C, Deng D M, Chen Z P, and Zhang J C, 2001 Acta Phys. Sin. 50 769(in 4]Oguchi T, 1987Jpn.J Appl. Phys. 26. 417 5]Beech F, Miraglia S, Santoro A, and Roth R S, 1987 Phys. Rev. B 35, 8778 [6] Hagen M, Jing T W,. Wang Z Z, Horvath J, and Ong N. P, 1988 Phys. Rev. B 37, 7928 [7 Dinger TR, Worthington TK, Gallagher WJ,et al, 1987 Phys. Rev. Lett. 58, 2687 [8]Salamon M B, Shi J, Overend N, et al, 1993 Phys. Rev. B47, 5520 19] Freitas P P, and Plaskett TS,1987 Phys. Rev. B 36, 5723 [10] Cooke S, Allison J and Woods R C, 1999 Solid State Communications 112 229 [11] Feng QR, Wang X J, and Cao K, 2003 Physica C 390, 151 [12] Feng Q R, Chen X, Wang Y H, et al, 2003 Physica C 386 653 [13] Feng QR, Wang X, Xu J, et al, 2002 Solid State Communication, 122 455 [14] Chen C, Zhou Z J, Li G, et al, 2004 Solid State Communication, 131 275 [15] Feng R, Chen C P, Xu J, et al. 2004 Journal of Low Temperature Physics, 26, No. 1 18.(in7 pattern of sol-gel powders. After the SG-YBCO sample finished the first sintering cycle, the main diffraction peaks of the YBa2Cu3Oy appeared as shows in the x-ray pattern index of the first sintering. After the second cycle sintering, not only the intensity of those main diffraction peaks enhanced, but also the (0, 0, 2) peak appeared. This indicates that the SG-YBCO sample has changed into real YBa2Cu3Oy sample although there are still some impurity peaks. 4. Conclusion We have measured the in-situ HTρ–T curves of the sol-gel YBa2Cu3Oy samples sintered in various temperature range. The resulting curves are shown in figures 1, 2, and 3 for the 3 consecutive runs of the sintering cycles. The resistivities of SG-YBa2Cu3Oy ρ300 = 9.8×10-3Ω •cm in the room temperature and ρ1223 =6.68×10-2Ω•cm at 950℃ can be seen from these figures. According to these results, the O-T phase transformation process can also be studied. The transformation temperature of the SG-YBCO sample is lower than that of the A-YBCO sample which has not been reported previously to our knowledge. This could be due to the fine particles of the SG-YBCO chemically active, leading to an easier solid reaction sintering process. The present work suggests that the technology of the in-situ HTρ–T measurement is an effective probe in the superconducting research. By this method, the O-T phase transition temperature has been shown to be lower for the SG-YBCO than the A-YBCO samples. References [1] Ginsberg D M 1989 Physical Properties of High Temperature Superconductors (World Scientific Press, Singapore)Ⅰ(pp39-70), Ⅱ(pp121-198), Ⅲ(pp285-362), and Ⅳ(1-6). [2] Charles P. Poole, Jr., Timir Datta, Horacio A.Farach, 1988 Copper Oxide Superconductors, A Wiley-Interscience Publication, John Wiley & Sons Inc(United States of America) 59-170 [3] Liu L H, Dong C, Deng D M, Chen Z P, and Zhang J C, 2001 Acta Phys. Sin. 50 769 (in Chinese) [4] Oguchi T, 1987 Jpn. J. Appl. Phys.26. 417 [5] Beech F, Miraglia S, Santoro A, and Roth R.S, 1987 Phys. Rev. B 35, 8778 [6] Hagen M, Jing T W,. Wang Z Z, Horvath J, and Ong N. P, 1988 Phys. Rev. B 37, 7928 [7] Dinger T R, Worthington T K, Gallagher W J,et al, 1987 Phys. Rev. Lett. 58, 2687 [8] Salamon M B, Shi J, Overend N, et al, 1993 Phys. Rev. B 47, 5520 [9] Freitas P P , and Plaskett T S, 1987 Phys. Rev. B 36, 5723 [10] Cooke S G, Allison J. and Woods R C, 1999 Solid State Communications 112 229 [11] Feng Q R, Wang X J, and Cao K, 2003 Physica C 390, 151 [12] Feng Q R, Chen X, Wang Y H, et al, 2003 Physica C 386 653. [13] Feng Q R, Wang X, Xu J, et al, 2002 Solid State Communication, 122 455. [14] Chen C , Zhou Z J, Li X G, et al, 2004 Solid State Communication ,131 275. [15] Feng Q R, Chen C P, Xu J, et al. 2004 Journal of Low Temperature Physics, 26, No.1 18. ( in