September 1999 Ž . Materials Letters 40 1999 222–227 www.elsevier.comrlocatermatlet Preparation condition, structure and superconductivity of ž / LaBaMCu O M s Ba, Sr, Ca 3 y F. Tao a,b, ) , C.G. Che a , X.J. Zhou c , Z. Zhao a , S.F. Zhu b , C. Dong a , S.L. Jia a , H. Chen a a Chinese Academy of Sciences, Beijing, 100080, China b Department of Materials Sciences, Sichuan UniÕersity, Chengdu, 610064, China c Yuzhou UniÕersity, Chongqing, 400000, China Received 28 January 1999; accepted 8 March 1999 Abstract The effects of preparation conditions on the phase formation, structure and superconductivity for LaBaMCu O system 3 y have been investigated systematically for obtaining and understanding the optimum preparation condition of La123 type superconductors. It is found that in LaBa Cu O , La can substitute for Ba, but Ba cannot be substituted for La. The 2 3 y atmosphere of O or air is favorable for the substitution of La for Ba. The sintering and cooling atmospheres of N can 2 2 suppress the substitution of La for Ba, which is one key procedure to obtain high quality single phase La123 superconduc- Ž. Ž . tors. The single phase LaBa Cu O superconductor with the highest T 0 of 97 K and T onset of 101 K which is the best 2 3 y c c result in La Ba Cu O system at present, has been obtained when the sample was prepared by A–B2–C3–D–E. With 1qz 2yz 3 y Ž. the same condition, LaBaSrCu O and LaBaCaCu O superconductors with T 0 of 85.5 K and 80 K were prepared, 3 y 3 y c respectively. q 1999 Elsevier Science B.V. All rights reserved. Keywords: LaBaMCu O ; Preparation condition; Structure; Superconductivity 3 y 1. Introduction Tallon and Flower predicted that a superconduct- ing transition temperature, T of about 100 K, should c be achievable for the z s 0 composition of w x La Ba Cu O superconductors 1–3 . Yossefor 1qz 2yz 3 y Ž. et al. reported that the highest T 0 of 98.7 K for c Nd Ba Cu O superconductors with x s 0 had 1qx 2yx 3 y wx been achieved 4 . During the past 10 years of high-T c cuprate superconductors, a large number of investi- gators made considerable progress in preparing high- ) Corresponding author. T La123 superconductors. They obtained the maxi- c Ž . mum T onset at z s 0, several degrees below 100 c w x K, and zero resistance at 80–93 K 5–23 . In this work, the effect of preparation condition on the phase formation, structure and superconduc- tivity was investigated in detail. The optimum prepa- ration condition was obtained. With the condition, high-quality single phase LaBaMCu O supercon- 3 y ductors were prepared. 2. Experimental Samples were prepared by using the starting ma- terials La O , BaCO , SrCO , CaCO and CuO with 2 3 3 3 3 00167-577Xr99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. Ž . PII: S0167-577X 99 00079-8