Synthesis of Tl2CanBa2Cun+1O6+2n (n=1, 2) from stoichiometric reactant mixtures
Journal
Physica C: Superconductivity and its applications
Journal Volume
161
Journal Issue
3
Pages
302-312
Date Issued
1989
Author(s)
Abstract
New powder synthesis methods have been developed for the preparation of single-phase Tl2CaBa2Cu2O8 (the 2122 compound) and Tl2Ca2Ba2Cu3O10 (the 2223 compound) powders from stoichiometric reactant mixtures. The 2122 compound was prepared from a stoichiometric mixture of Tl2O3, CuO and CaBa2CuO4, while the 2223 compound was prepared from the same mixture but with additional CaO and CuO to match the correct (Tl:Ca:Ba:Cu=2:2:2:3) stoichiometry. For the 2122 compound, XRD single-phase samples with zero-resistivity temperatures (Tc, zero) above 100 K were obtained by using a one-step calcination at 830° C for a period between 6 and 23 h. A maximum of Tc, zero of 116 K was obtained for 14 h of calcination. For the 2223 compound, XRD single-phase samples with Tc, zero between 110 and 118 K were obtained by employing a two-step calcination procedure consisting of a first calcination at 830° C for 5 h and a second calcination at 870° C for a period between 2 and 6 h. Both the 2122 and 2223 samples thus prepared exhibit sharp superconducting transitions and typically have a saturation Meissner effect of about 20% of (-1/4π) under a field of 20 G. Powder melting is completely eliminated during the preparation of the 2122 compound and much reduced, by employing the pre-calcination step, during the preparation of the 2223 compound. Compared with the conventional method, the new methods require less stringent calcination conditions, and hence allow for a better process control of the synthesis of Tl2CanBa2Cun+1O6+n superconducting powders. © 1989.
Type
journal article