ELSEVIER Physica C 256 Q996) 358-364 PHYSICA g Characterization of superconducting (T1,Bi)Sr2CaCu2Oy P.G. Wahlbeck *, D.E. Peterson, J.O. Willis, E.J. Peterson, J.Y. Coulter, D.S. Phillips, K.V. Salazar Superconductivity Technology Center, MS-K763 Los Alamos National Laboratory, Los Alamos, NM 87545, USA Received 15 June 1995; revised manuscript received 27 July 1995 Abstract The superconducting phase with mixed TI and Bi, namely (Tlo.55Bio.45)Sr2CaCu20y, was synthesized and characterized. Synthesis conditions were studied, and this phase, (TI,Bi)-1212, was found to form preferentially to (TI,Bi)-1223 when Sr was present with no Ba present. X-ray powder diffraction with Rietveld refinement provided structural data. The phase is tetragonal with a = 3.7988(4) A and c = 12.076(1) A, with space group symmetry P4/mmm, and with a platelet crystal morphology. Magnetic-susceptibility data gave an onset of superconductivity T c at 94.9 + 1.3 K with a T c mid of 86.0 + 1.1 K. Magnetic-hysteresis measurements showed that substantial flux pinning occurs in this phase at high temperatures. I. Introduction The superconducting phase of particular interest in this paper is (T10.55Bio.45)Sr2CaCu2Oy, abbrevi- ated as (T1,Bi)-1212. From the chemical composi- tion, this phase contains a single (TI,Bi)-O layer and two Cu-O superconducting layers. This paper will examine the properties of this compound. The phase (T1,Bi)-1212 had been prepared previously by Haldar et al. [1], and by Li and Greenblatt [2]. Haldar et al. [3] initially prepared the (T1,Bi)-1201 phase. In a second paper, Haldar et al. [1] prepared (T1,Bi)-1212 giving the composition as (T11 xBix)l.33Srl.33Cal.33 - Cu206.67+6. Li and Greenblatt [2] gave a careful analysis of several of the superconducting properties of the (T1,Bi)-1212 phase. Subramanian et al. [4], Inoue et al. [5], and Huang et al. [6] have published * Corresponding author. Permanent address: Department of Chemistry, Wichita State University, Wichita, KS 67260-0051. results for the synthesis of (TI,Bi)-1223, a related superconducting phase. Doi et al. [7] synthesized T1Sr2CaCu2Oy containing no Bi, and it was not superconducting above 4.2 K. However, Martin et al. [8] reported superconductivity with a T c of 20 K for T1Sr2CaCueOy. In addition, Martin et al. [8] studied Tl0.sPbo.sSr2CaCu20 7. Kuroda and Yokogawa [9] studied composition variables for the T1-Bi-Pb sys- tem for producing superconducting compounds. The authors of the above investigations have found the crystal structure for (TI,Bi)-1201, (T1,Bi)-1212, (TI,Pb)-1212, and T1-1212 to be tetragonal with space group symmetry P4/mmm. Li et al. [2] also did band calculations which indicated that the (T1,Bi) layer contributed holes to the Cu-O superconducting planes. Presland et al. [11] prepared T1Sr2CaCu20 7 and (TI,Pb)-1212, and they found with Sr instead of Ba in the samples that T c was not dependent on the pressure of 0 2 during heat treatments. They also studied the effect of the amount of Pb and of doping with Y. 0921-4534/96/$15.00 © 1996 Elsevier Science B.V. All rights reserved SSDI 0921-4534(95)00490-4