Superconducting Properties of (Bi,Pb)-Sr-Ca-Cu-O Ceramics

Transcription

1 Kasetsart J. (Nat. Sci.) 34 : (2000) Superconducting Properties of (Bi,Pb)-Sr-Ca-Cu-O Ceramics Supreya Trivijitkasem and Wunchai Sratongluan ABSTRACT Sixteen specimens of four initial nominal composition ceramics were synthesized by solid state reaction for a given initial cation ratio (Bi:Pb)/Sr = (1.5:0.5)/2.0, and the varied cation ratio Ca/Cu = 2.5/ 4.0, 2.5/4.5, 3.0/4.0 and 3.5/4.5. SEM images of each specimen showed different grain sizes with porous structure. The grain size increased with sintering time. The specimen synthesized by reground-repressed process and sintered for 50 h, possessed smallest grain size. Three different grain structures were observed. The platelike dark gray grain, flake-pellet bright grain and sphere-like bright grain corresponded to high T C phase, low T C phase and Ca 2 PbO 4, respectively. The platelike grain changed to granular after the second grinding. XRD spectra showed high T C phase coexisting with low T C phase and Ca 2 PbO 4 in each specimen. The ratio of lattice parameter of high T C and low T C phases, c/a, were and , respectively. Magnetic-susceptibility measurement showed that T C was significantly affected by the composition changed. Each specimen revealed nearly the same onset critical temperature, T C onset, at K. T C and H C2 increased when the sintering time was extended from 50 h to 100 h. An intermediate ground-pressed process enhanced T C but depressed H C2 at 90 K. The optimum atomic ratio leading to the formation of the Bi-2223 phase was Ca/Cu = The highest T C =106.0 K belonged to the specimen which was sintered for 100 h by an intermediate ground-pressed process, the critical field at 90 K was 427 A/m. The highest H C2 = 539 A/m at 90 K belonged to the specimen which was sintered for 100 h by reground-repressed process,and T C =105.2 K. Key words : fixed (Bi:Pb)/Sr, varied Ca/Cu, superconductivity INTRODUCTION High critical temperature,t C, copper oxide superconductors are based on perovskite-like structure. The Bi-based superconducting oxide is well known to have mixed structure of Bi-2212 low T C and Bi-2223 high T C phases, which involves several layers that insulate the CuO 2 layer, the main superconducting zone. It was found that substituting lead for part of bismuth increased easily volume fraction of high- T C phase, and a number of mechanisms were proposed to explain the reaction route in forming this phase. Yet, the formation mechanisms have not been well understood. Rhee et al. (1989) studied the effects of Pb on the formation of the high T C phase with various Bi/Pb ratios and found that substitution of 30% Pb for Bi was the most preferable for forming high T C phase. Partial substitution of bismuth by lead in Bi system shows three types of superconducting compounds : (Bi,Pb) 2 Sr 2 CuO x semiconducting Department of Physics, Faculty of Science, Kasetsart University, Bangkok,10900,Thailand.

2 160 Kasetsart J. (Nat. Sci.) 34 (1) phase,(bi,pb) 2 Sr 2 CaCu 2 O y low T C phase and (Bi,Pb) 2 Sr 2 Ca 2 Cu 3 O z high T C phase with superconducting transition temperatures of ~7 K, ~ 80 K and ~110 K, respectively. It is obvious that the 110 K superconducting phase is likely the most interesting one for practical applications; and the most efficient way to synthesize this phase is to start with initial composition close to the nominal composition (Bi,Pb) 2 Sr 2 Ca 2 Cu 3 O z. Kikuchi et al. (1989) reported characteristics of Bi-Pb-Sr-Ca-Cu oxide superconductor closely related to the preparatory conditions such as the sintering temperature and cooling rate. Xu et al. (1990) studied the superconductivity and microstructure of Bi 1.92 Pb 0.48 Sb 0.1 Sr 2 Ca 2 Cu 3.2 O x and Bi 1.8 Pb 0.3 Sb 0.1 Sr 2 Ca 2 Cu 3 O y samples, they found that different superconducting behavior due to different sintering conditions and were controlled by powder grain size and chemical activity. Kusano et al. (1994) annealed the Pbsubstituted Bi ceramics at 500 C to 850 C and subsequently reheating at 850 C, they reported that the composition of high T C phase changed while the superconducting properties remained unaffected. Toledano et al. (1995) examined the effect of varying the ratio (Bi:Pb)/Cu as well as the ratio Sr/Ca, and found that the kinetics of forming high T C phase greatly enhanced by an excess of calcium, while an excess of strontium prevented its formation. Sung and Hellstrom (1995) found that Ca 2 PbO 4 had both positive and negative roles in forming (Bi,Pb) The positive role was Ca and Pb which released from Ca 2 PbO 4 reacted with (Bi,Pb)-2212 and CuO to form (Bi,Pb) The negative role was Ca which could also react with CuO to form (Sr,Ca) 2 CuO 3, since forming (Sr,Ca) 2 CuO 3 added an extra reaction path to form (Bi,Pb) The extensive studies for the equilibrium of the lead-substitute system as a function of composition and temperature has been performed by us recently. The phase equilibrium of Bi 1.5 Pb 0.5 Sr 2.0 Ca 2.0 Cu 3.5 O s and Bi 1.5 Pb 0.5 Sr 2.0 Ca 2.5 Cu 3.5 O β were determined (1999), the second composition with atomic ratio Ca/Cu = 0.71 formed more high T C phase. Prunglag et al. (1997) determined the phase equilibrium of (Bi 0.85 Pb 0.15 ) 2.0 Sr 2.0 Ca x Cu y O α, 2.0 x 3.5 and 3.0 y 4.5, and found that high T C phase increased when the atomic ratio of Ca to Cu was In order to complete the knowledge of the range of the 2223 phase, this study was extended to nominal compositions of (Bi : Pb): Sr : Ca : Cu =(1.5 : 0.5) : 2.0 : x : y, here x=2.5,2.5,3.0,3.5 and y= 4.0,4.5,4.0,4.5, respectively. The procedure of determination of the phase equilibrium was described in another paper (1999). In the present work the influence of calcium and copper contents for the formation of the 2223 phase with various sintering conditions are reported. The results of x- ray diffraction (XRD) spectra and scanning electron microscope (SEM) observations are specified. Superconductivity determined from AC susceptibility as a function of temperature are discussed. The high critical field will be characterized in a separate study. MATERIALS AND METHODS The starting materials were Bi 2 O 3 (99.5%, purity), PbO (99.0%), SrCO 3 (98.0%), CaCO 3 (99.0%) and CuO (99.0%), powders were weighed in the cation ratio of (Bi:Pb):Sr:Ca:Cu = (1.5:0.5): 2.0:2.5:4.0, (1.5:0.5):2.0: 2.5:4.5, (1.5: 0.5): 2.0: 3.0:4.0 and (1.5:0.5):2.0:3.5:4.5. The powders were mixed and ground in a mortar and pestle for 1 h, put the mixed powders in an alumina crucible and calcined in air at 800 C for 12 h at a heating rate of 10 C/min, then ground and cold pressed at 107 MPa into pellet with dimension of 13.1 mm diameter and ~4.7 mm thickness, sintered (first time) in air

3 Kasetsart J. (Nat. Sci.) 34 (1) 161 at 840 C for 20 h, the heating rate from C was 5 C/min. The specimen was cooled down in the furnace until 300 C and quenched in air. Then the process was repeated by not reground-repressed (process I) or reground-repressed (process II), and sintered (second time) the specimen at 845 C in air for 50 h or 100 h. Weight and diameter of specimens were measured before and after sintering process. Mass density of the bulk specimens were determined by density determination (Sartorius). The identification of the superconducting phases was deduced from x-ray powder diffraction spectra at room temperature with Ni-filtered Cuk α radiation at 30 kv and 25 ma, on a Philips model PW 3710 wide angle goniometer. Microstructure was taken by SEM, JEOL, model JSM-220A. AC susceptibility measurement was performed by means of an AC susceptometer, Lake Shore model The pellet specimen was cut in a rectangular shape of dimensions ~1.5x1.6x9.1 mm 3 and mass ~0.1 g, cooled the specimen down to K in the AC susceptometer by zero field cooling (ZFC), then applied AC magnetic field H ac (t)=h sin ωt at the fundamental frequency f= 125 Hz and various field amplitude H. The specimen was heated at a rate of 0.86 C/min and fundamental susceptibility χ was recorded as a function of increasing temperature. RESULTS AND DISCUSSION Four initial nominal compositions, Bi 1.5 Pb 0.5 Sr 2.0 Ca 2.5 Cu 4.0 O a (A), Bi 1.5 Pb 0.5 Sr 2.0 Ca 2.5 Cu 4.5 O b (B), Bi 1.5 Pb 0.5 Sr 2.0 Ca 3.0 Cu 4.0 O c (C) and Bi 1.5 Pb 0.5 Sr 2.0 Ca 3.5 Cu 4.5 O d (D), were prepared by the conventional solid state reaction. Initial atomic ratio, mass density and mass change, m/m 0, of the specimens are shown in Table 1; here m= m 0 -m, m 0 was mass of pellet specimen before the first sintering in process I or before the second sintering in process II, and m was mass of Table 1 Initial atomic ratio, mass change m/m 0 and mass density ρ of specimens, here I, II denotes number of pressing and 50, 100 denotes 50, 100 h in sintering. Specimen (Bi:Pb):Sr:Ca:Cu m/m o ρ (%) (g/cm 3 ) IA50 (1.5:0.5):2.0:2.5: IA IIA IIA IB50 (1.5:0.5):2.0:2.5: IB IIB IIB IC50 (1.5:0.5):2.0:3.0: IC IIC IIC ID50 (1.5:0.5):2.0:3.5: ID IID IID pellet specimen after the second sintering. Mass change of the specimen is shown in Figure 1 (a). Here m 0 of process I and process II were not at the same condition. It was found that the mass of specimens decreased significantly when sintering time t s increased ; the mass lost was due to evaporation of specific chemical substance, such as PbO, of specimen. Mass density of the specimen depended on the process of synthesis as shown in Figure1(b). The specimen sintered for 50 h by intermediate reground-repressed process, revealed highest mass density and least mass lost. Specimen IA100 and IC100 exhibited lowest mass density ρ=3.0 g/cm 3, while the mass density of specimen IIA50 increased significantly as shown in Figure 1 (b). The powder XRD patterns of 16 pellet

4 162 Kasetsart J. (Nat. Sci.) 34 (1) Figure 1 (a) Mass change and (b) mass density vs. atomic ratio Ca/Cu of specimens. specimens were recorded from 2θ = 3-70 as shown in Figure 2. The 2θ ranging from was a specifically region for pointing out of the main superconducting phases of (Bi,Pb)-2212 and (Bi,Pb) Peaks corresponding to different phases were marked by various patterns for clarity. XRD pattern showed peaks belonging to the high T C (Bi,Pb)-2223 phase (H) as a major component together with peaks due to the low T C (Bi,Pb)-2212 phase (L). The high T C phase was labeled in the form of (00P) and (11Q); here P and Q were even and odd number, respectively. There was no peak of semiconducting phase (Bi,Pb) at 2θ =21.9. Each specimen showed a peak at 2θ =17.8 which belonged to Ca 2 PbO 4. The present of Ca 2 PbO 4 was known to result in a liquid phase which accelerated the anisotropic growth of (Bi,Pb)-2223 phase. The diffraction peaks of (002)H, (002)L, (115)L and (0012)H appeared at 2θ=4.7,4.8, 27.7 and 28.8, respectively. It could be seen from Figure 2 that more high T C phase appeared in specimen C and D than specimen A and B. Only strong diffraction peaks of (002)H appeared in specimen A, B and D, while specimen C exhibited both diffraction peaks of (002)H and (002)L. The peak intensity of (002)H of specimen IC100 was stronger than specimen IC50, partly due to more Ca 2 PbO 4 occurred in specimen IC50. The peak intensity of (0012)H and (119)H of specimen C became stronger, while (115)L became weaker with increasing sintering time t s. More high T C phase was formed in specimen C than the others and the formation of the high T C phase in each specimen enhanced when the sintering time increased. Lattice parameter, a,b,c,c/a; and cell volume v of low and high T C phases are shown in Table 2. The crystal structure of low T C phase was tetragonal; the ratio of c/a was between and cell volume v was between (A ) 3. The crystal structure of high T C phase was orthorhombic; the ratio of c/a was between , and cell volume v was (A ) 3. Since the Bi(Pb)-Sr-Ca-Cu-O ceramics contains five cations, the phase relations for forming 2223 phase are more complicated. In order to characterized the formation of phase in the specimen, microstructure of all specimens were carried out by SEM. Figure 3 showed grain orientation of specimens. Each specimen was polycrystal and the grains were anisotropic. Three different grain structures were observed; the platelike dark gray grain, flake-pellet bright grain and sphere-like bright grain corresponded to high T C phase, low T C phase

5 Kasetsart J. (Nat. Sci.) 34 (1) 163 Figure 2 Powder x-ray diffraction patterns of specimen (a) A, (b) B, (c) C and (d) D ; denotes peak due to Ca 2 PbO 4, denotes low T C (Bi,Pb)-2212 phase and denotes high T C (Bi,Pb)-2223 phase.

6 164 Kasetsart J. (Nat. Sci.) 34 (1) Table 2 Lattice parameter (a,b,c,c/a) and cell volume (v) of low T C and high T C phases. Specimen Tetragonal Orthorhombic a(a ) c(a ) c/a v(a ) 3 a(a ) b(a ) c(a ) c/a v(a ) 3 IA IA IIA IIA IB IB IIB IIB IC IC IIC IIC ID ID IID IID and Ca 2 PbO 4, respectively. The areas with black contrast corresponded to pores. The grain size increased with sintering time. The platelike grain changed to granular after second grinding. The broad face of grain corresponded to the ab plane. The specimen sintered for 50 h by regroundrepressed process, exhibited the smallest grain size and relatively dense, while the intermediate groundpressed specimen showed more porous structure. The grain size of specimen IIC100 was smaller and more ordering than specimen IC100. The SEM micrograph of specimen IIC100 showed that the grains were oriented more dense than specimen IC100,which was agree well with the mass density of the specimen. Zero-field-cooled measurement of the superconducting transition was determined from heating curve of fundamental susceptibility χ=χ / - iχ //. The applied field amplitude for each running were H=0.1,1,10,50,100,200,300,400 and 500 A/ m. Figure 4 shows temperature dependence of external susceptibility at field amplitude H=0.1 A/ m of specimen A and B. Figure 5 shows χ(t) of specimen C and D at various fields. AC susceptibility was separated into 2 components : real part or dispersive component χ / and imaginary part or dissipative component χ //. χ / and χ // showed two steps of superconducting transition. According to Mazaki et al. (1988), the upper component of heating curve of χ / corresponded to high T C phase, which was regarded as the superconductivity of the grain or the bulk phase; and the lower component of χ / corresponded to low T C phase, which was regarded as the diamagnetism due to the Josephson-like coupling or the coupling phase. Two maxima of χ // corresponded to intrinsic and coupling losses, respectively. It was obvious from Figure 5 that χ / of low T C phase had stronger amplitude dependence than χ / of high T C phase. The second maximum of heating curve χ // (T) in process II of all specimens

7 Kasetsart J. (Nat. Sci.) 34 (1) 165 IA50 IA100 IIA50 IIA100 IB50 IB100 IIB50 IIB100 IC50 IC100 IIC50 IIC100 ID50 ID100 IID50 IID100 Figure 3 SEM micrographs of powder specimen showing microstructural characteristics. was smaller than that in process I, i.e., there was only small intrinsic loss in reground repressed process. According to Sumiyama et al.(1989), the diamagnetism attributed to the Josephson-like weak coupling was sensitive to the synthetic conditions and grain contact-structure. When the applied field H was lower than low critical field H C1, χ / would show perfect diamagnetism, i.e., χ / = 1, exactly in SI unit; and χ // =0, since the magnetization was linear reversible and lossless. When H>H C1, χ / increased from -1 and χ // 0. But the data in Figure 4 and Figure 5 were not corrected for demagnetization factor, hence χ / deviated from 1. Critical temperature was determined from χ / at applied external field amplitude H=0.1 A/m and f = 125 Hz. The onset of the coupling between grains in χ / (T) was defined as critical temperature T C of the specimen, and T c onset was defined as the temperature at which χ / and χ // separated into 2 parts. Table 3 shows atomic ratio of Ca/Cu, critical temperature and onset of critical temperature of specimens. Each specimen revealed T C onset at K. Figure 6(a) shows critical temperature T C as a function of atomic ratio Ca/Cu, which increases with increasing sintering time; reground-repressed

8 166 Kasetsart J. (Nat. Sci.) 34 (1) Table 3 Atomic ratio, critical temperature T C,onset of critical temperature T C onset and high critical field H c2 at 90 K of specimens. Specimen Ca/Cu T c (K) T c onset (K) H c2 (A/m) IA50 2.5/4.0= IA IIA IIA IB50 2.5/4.5= IB IIB IIB IC50 3.0/4.0= IC IIC IIC ID50 3.5/4.5= ID IID IID process depresses slightly the critical temperature. The synthetic process that provided higher critical temperature was to sinter specimen at 845 C for 100 h by an intermediate ground-pressed process. T C of all specimens were significantly affected by the composition changed. The highest critical temperature was K which belonged to specimen IC100, atomic ratio of Ca/Cu=0.75. The next higher T C =105.7 K belonged to specimen ID100. The other 2 compositions, IA100 and IB100 revealed much lower critical temperature, T C =102.8K and 96.8 K, respectively. It could be seen from Figure 1(b) and Figure 6(a) that lower mass density pellet specimen revealed higher T C. Low and high critical field of the specimen could be determined from the AC χ measurement at various magnetic field. The onset of the first maximum of χ // 0 from heating curve was defined as low critical field H C1 (T), and the onset of the coupling between grain in χ / (T) at various field was defined as high critical field H C2 (T) of the specimen (Dodrill and Krause. 1996). The temperature dependence of H C2 at 90 K are shown in Table 3 and Figure 6(b). H C2 at 90 K of process II was higher than that of process I, and H C2 increased with sintering time. It was obvious from Figure 6(b) that H C2 of specimen C was slightly higher than specimen D. The highest H C2 =539 A/m at 90 K belonged to specimen IIC100, while specimen IID100 showed H C2 = 527 A/m at 90 K. The high critical field of the other 2 compositions, IIA100 and IIB100 were much lower. H C2 at 90 K of specimen II-50 was lower than that of specimen I-100. Specimen IC100 which exhibited highest T C revealed rather low H C2 = 427 A/m at 90 K. Hence the optimum atomic ratio that formed more volume fraction of Bi-2223 phase was Ca/Cu = The best synthetic condition that

9 Kasetsart J. (Nat. Sci.) 34 (1) 167 Figure 4 Volume susceptibility of specimen A and B as a function of increasing temperature T, at H=0.1A/m and f=125 Hz.

10 168 Kasetsart J. (Nat. Sci.) 34 (1) Figure 5 Volume susceptibility of specimen C and D as a function of increasing temperature T, at f=125 Hz and various field amplitude H, here a,b,c,d,e,f,g,h and i denotes H=0.1,1,10, 50,100,200,300,400 and 500 A/m, respectively.

11 Kasetsart J. (Nat. Sci.) 34 (1) 169 Figure 6 (a) Critical temperature and (b) high critical field at 90 K vs. atomic ratio Ca/Cu of specimens. lead to higher T C and highest H C2 at 90 K was to sinter the specimen at 845 C for 100 h by regroundrepressed process. CONCLUSION Sixteen specimens of four initial nominal composition ceramics were synthesized by solid state reaction. The fixed initial cation ratio was (Bi:Pb)/Sr = (1.5:0.5)/2.0 and the varied ratios were Ca/Cu = 2.5/4.0, 2.5/4.5, 3.0/4.0 and 3.5/4.5. Mass density, critical temperature and high critical field of the specimen depended on the process of synthesis. More mass loss was found when the sintering time was prolonged. The mass lost, m/ m 0, of the specimens was %. Mass density decreased with increasing sintering time. Specimen sintered for 50 h by intermediate reground-repressed process revealed the highest mass density and least mass lost. Powder XRD pattern taken from the pellet specimen showed that each specimen contained Bi-2223, Bi-2212 and Ca 2 PbO 4 phases. More high T C phase was formed in the specimen than low T C phase, when the duration of the sintering was prolonged. The ratio of lattice parameter of high T C and low T C phases were c/a= ,and , respectively. SEM micrograph revealed different grain sizes in each specimen. Three different grain structures were found; platelike dark gray grain, flake-pellet bright grain and sphere-like bright grain corresponded to high T C phase, low T C phase and Ca 2 PbO 4, respectively. The areas with black contrast corresponded to pores. The grain size of specimen I-100 was larger than that of specimen II- 100, which was sintered by reground-repressed process; that is the platelike grain changed to granular after the second grinding. The AC susceptibility χ =χ / -iχ // depended on temperature T, and was separated into 2 parts : real susceptibility χ / and imaginary susceptibility χ // at T<T C onset. Magnetic-susceptibility measurements showed that T C was significantly affected by the composition changed, and T C increased while mass density decreased with increasing sintering time. Each specimen revealed nearly the same onset critical temperature, T C onset = K. Critical temperature T C and high critical field H C2 were determined from χ /. Each specimen showed increasing T C and H C2 at 90 K when the sintering time was extended from 50 h to 100 h. Reground-repressed process depressed T C but enhanced H C2 at 90 K. The highest T C and H C2 belonged to the

12 170 Kasetsart J. (Nat. Sci.) 34 (1) initial composition Bi 1.5 Pb 0.5 Sr 2.0 Ca 3.0 Cu 4.0 O C whose initial atomic ratio of Ca/Cu was The specimen IIC100, which was sintered for 100 h by reground-repressed process, exhibited a superconducting transition at K and highest critical field H C2 =539 A/m at 90 K, while the specimen IC100 exhibited the highest T C =106.0 K and much lower critical field, H C2 = 427 A/m at 90 K. Critical temperature and H C2 at 90 K of specimen IID100 were slightly lower than that of specimen IIC100. ACKNOWLEDGEMENT The authors are grateful to the Kasetsart University Research and Development Institute for the grant support of this paper under project No LITERATURE CITED Dodrill, B. C. and J. K. Krause AC magnetic susceptibility measurements of organic superconducting materials. Mol. Cryst. Liq. Cryst. 284 p. Kikuchi, A., M. Matsuda, M. Takata, M. Tshii, T. Yamashita, and H. Koinuma Influence of cooling rate on superconducting characteristics of Bi-Pb-Sr-Ca-Cu-O ceramics. Jpn. J. Appl. Phys. 28 (3) : L371-L372. Kusano, Y., T. Nanba, J. Takada, T. Egi, Y. Ikeda, and M. Takano Segregation and dissolution reactions of the 2223 phase in the Bi,Pb-Sr-Ca-Cu-O system on annealing in air. Phys. C. 219 : Mazaki, H., T. Ishida, and T. Sakuma Twostep superconducting transition of a Bi-Sr-Ca- Cu-O system. Jpn. J. Appl. Phys. 27 (5) : L811-L813. Prunglag, N., S. Trivijitkasem, and K. Treechairusmee Study of superconductor in (Bi 0.85 Pb 0.15 ) 2.0 Sr 2.0 Ca x Cu y O 10-s when 2.0 x 3.5 and 3.0 y 4.5, pp In The 35th Kasetsart University Annual Conference, Science section. Bangkok. Rhee, C. K., C. J. Kim, H. G. Lee, I. H. Kuk, J. M. Lee, I. S. Chang, C. S. Rim, P. S. Han, S. I. Pyun, and D. Y. Won Effects of Pb content on the formation of the high-t C phase in the (Bi,Pb)-Sr-Ca-Cu-O system. Jpn. J. Appl. Phys. 28 (7) : L1137-L1139. Sumiyama, A., H. Endo, J. Tsuchiya, N. Kijima, M. Mizuno, and Y. Oguri A.C. susceptibility of superconducting Bi- (Pb)-Sr- Ca-Cu-O system. Jpn. J. Appl. Phys. 28 (3) : L373-L376. Sung, Y. S. and E. E. Hellstrom A study of reactions amongst (Bi,Pb)Sr 2 Ca 2 Cu 3 O x and phases on the line between CaO and CuO to form (Bi,Pb) 2 Sr 2 Ca 2 Cu 3 O x. Phys. C. 252 : Toledano, J. C., D. Morin, J. Schneck, H. Fagir, O. Monnereau, G. Vacquier, P. Strobel, and V. Barnole Stability of the 2223 phase in the lead-substituted bismuth cuprates. Phys. C. 253 : Trivijitkasem, S. and W. Sratongluan Microstructural evolution in forming Bi 2223 superconductor from Bi-Pb-Sr-Ca-Cu-O system. The Kasetsart J. (Nat. Science) 33 (4) : Trivijitkasem, S. and W. Sratongluan Grain orientation and growth of high T C Bi(Pb)-Sr- Ca-Cu-O superconductor, pp In The 37th Kasetsart University Annual Conference, Science section. Bangkok. Xu, Q., Z. Chen, G. Meng, and D. Peng Microstructure and superconductivity in Bi- Sr-Ca-Cu-O system doped with Pb and Sb. Jpn. J. Appl. Phys. 29 (10) : L1918-L1923. Received date : 17/08/99 Accepted date : 27/12/99