Investigations of substitution of Bi and Tl for rare earth elements in superconducting RBa2Cu3Oy

Author

Jian Tang, New Jersey Institute of Technology

Document Type

Thesis

Date of Award

1-31-1991

Degree Name

Master of Science in Applied Chemistry - (M.S.)

Department

Chemical Engineering, Chemistry and Environmental Science

First Advisor

Lawrence Suchow

Second Advisor

R. P. T. Tomkins

Third Advisor

Barbara B. Kebbekus

Abstract

Substitution of some other elements for rare earth or yttrium in high-T_c superconducting RBa₂Cu₃O_y compounds (R = Y, Nd, etc.) may improve chemical and physical properties of the materials, shed light on the superconducting mechanism of the new materials, and help to find new superconducting materials with even higher transition temperatures.

Bi³⁺ and Tl³⁺ have been reported earlier to result in higher T_c's in the related layer-structure compounds. The effect of electronegativity on superconductivity could be studied if substitution of Bi or Tl for Y or other rare earth elements in RBa₂Cu₃O_y could be realized.

Earlier researchers have indicated that, under oxidizing conditions at the reaction temperature (about 900°C), Bi³⁺ does not enter YBa₂Cu₃O_y but that a non-superconducting perovskite phase Ba₂BiYO₆ (with Bi⁵⁺) is formed instead. In the present work, attempts have been made to prepare superconducting (R,Bi)Ba₂Cu₃O_y by first forming the non-superconducting, oxygen-deficient, tetragonal form in an inert atmosphere and then introducing additional oxygen and converting to the orthorhombic form by reheating in air or oxygen at lower temperature (about 250 - 500°C). x-ray diffraction, optical microscopy, thermogravimetric analysis, and electrical measurements were used to study the reaction products.

It was found that, in an inert atmosphere, YBa₂Cu₃O_y is very difficult to form while Ba₂BiYO₆, a non-superconducting phase, still forms as it does under oxidizing conditions, with oxidation of Bi³⁺ to Bi⁵⁺ probably due to reduction of Cu²⁺ to Cu⁺; (Y,Bi)Ba₂Cu₃O_y is not formed.

In an oxidizing atmosphere, both NdBa₂Cu₃O_y and Ba₂BiNdO₆ with a structure similar to that of Ba₂BiYO₆ result; there is no evidence for the formation of (Nd,Bi)Ba₂Cu₃O_y to any significant degree. The presence of Ba₂BiNdO₆, a minority and insulating phase, along with NdBa₂Cu₃O_y results in a broader transition temperature and an increase in normal state resistivity.

In an inert atmosphere, the formation of both NdBa₂Cu₃O_y and Ba₂BiNdO₆ is hindered and a tetragonal NdBa₂Cu₃O_y and poorly crystallized and probably oxygen-deficient Ba₂BiNdO_x result. Superconductivity of the samples with Bi addition is severely deteriorated since the tetragonal NdBa₂Cu₃O_y is not easily converted to an optimum orthorhombic structure while the insulating Ba₂BiNdO₆ appears in the samples during the after-annealing.

Tl was found not to enter the Y sites of YBa₂Cu₃O_y under oxidizing conditions.

Recommended Citation

Tang, Jian, "Investigations of substitution of Bi and Tl for rare earth elements in superconducting RBa2Cu3Oy" (1991). Theses. 1881.
https://digitalcommons.njit.edu/theses/1881