Effect of thallium concentration on Tl-2201 superconducting phase by flash sintering process

• Published in: Physica. C, Superconductivity Superconductivity, 1993-10, Vol.216 (1), p.59-65
• Main Authors: Saini, K.K., Sharma, C.P., Chanderkant, Suri, D.K., Ravat, K.B., Chandra, Subhas, Tewari, S.P.
• Format: Article
• Language: English
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Effects of material synthesis, crystal structure, and chemical composition; Exact sciences and technology; Inorganic compounds; Miscellaneous; Physics; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; Superconductivity; Transition temperature variations
• ISSN: 0921-4534; 1873-2143
• DOI: 10.1016/0921-4534(93)90633-2

Samples with nominal composition Tl x Ba 2Cu 2O 6 where x = 0.5, 1.0, 1.5, 1.75, 2.0, 2.5 and 3.0 were calcined at 890°C for 10 h and sintered at various temperatures for 3 1 2 min. X-ray powder diffraction patterns of all the samples show the characteristics of the 2201 phase which suggests the transformation of all the nominal compositions to 2201 phase. In some cases extra peaks due to BaCuO 2 and Tl 2O 3 are also present. The samples having Tl contents 1.5, 1.75 and 2.0 are monophase material with unit cell parameters a = 3.86 A ̊ , c = 23.20±0.02 A ̊ . The overall symmetry is tetragonal. All the lines are indexible on the I4/mmm space group. Samples with Tl content 1.5-2.0, sintered at 930–950°C, show the best superconducting properties. The highest T c is obtained in Tl 2.0 and the highest Meissner fraction in Tl 1.5. Chemical analysis indicates Tl deficiency in all the samples, which suggests substitution of Tl 3+ by Cu 1+ or Cu 2+ and oxidation of copper to Cu 3+, which increases monotonically with T c. Tl contents in optimum samples lie in the range 1.14-1.82 and oxygen content varies from 5.6-6.1