The CaO-CuO-TlO sub(1.5) system and its key role in the formation of the Tl-based superconductors

• Published in: Physica. C, Superconductivity Vol. 372-376; pp. 1191 - 1194
• Main Authors: Jondo, T K, Jorda, J L, Galez, Ph, Phok, Sovannary
• Format: Journal Article
• Language: English
• Published: 01.08.2002
• ISSN: 0921-4534

It has been shown recently that the formation of Tl sub(2)Ba sub(2)Ca sub(2)Cu sub(3 )O sub(z) is conditioned by an equilibrium plane with the Tl-rich limit of the (Ca,Tl) sub(1-x)CuO sub(2) solid solution as one of the apices. The parent phase for the latter solid solution is the binary compound Ca sub(0.80)CuO sub(1.93). We report here on the phase relations in the CaO-CuO and the CaO-CuO-TlO sub(1.5 ) systems. The emphasis is also put on the thermodynamic stability and the crystallographic properties of Ca sub(0.80)CuO sub(1.93) (space group P2/c, a = 10.9456(4) A, b = 6.3192(2) A, c = 16.8408 A and beta = 104.952(2) degree ). The kinetics for phase formation and decomposition have been studied. In particular, we show that the decomposition reaction into Ca sub(2)CuO sub(3) and CuO which occurs at 870 degree C in p(O sub(2)) = 1 bar and at 720 degree C in vacuum, is rate limited by a two-dimensional process consistent with structural considerations and has an activation energy of 656 kJ/mol. copyright 2002 Elsevier Science B.V. All rights reserved.