Fluorination of (Tl0.5, Pb0.5)Sr1.6Ba0.4Ca2Cu3Oy high-temperature superconductors has been performed through partial replacement of CuO by CuF2 in the starting materials. Seven samples with nominal fluorine content x atom per formula unit (0≤x≤3.6) were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), resistivity and magnetization M(H) measurements. Fluorine addition has raised the onset transition temperature to 128 K, and increased the critical current density to 300%, the value of the fluorine free sample. XRD, SEM and energy dispersive X-ray (EDX) results showed that the formation of the Tl-1223 phase was enhanced as fluorine was introduced, and the formation of large grains was observed. EDX spot analysis revealed the presence of fluorine as a species of the structure of the Tl-1223 grains. The c-axis of Tl-1223 decreased with increasing x, indicating that fluorine had replaced oxygen in the structure. The behavior of the normal state resistivity with temperature indicated that fluorine addition changed this material from overdoped to optimally doped, and upon further fluorine addition, changes it to slightly underdoped state. That provided an additional evidence that fluorine addition changes the density of charge carrier concentration in the Cu-O planes and improves the superconducting properties of this material.
Bibliographical noteFunding Information:
The authors would like to acknowledge the support of King Fahd University of Petroleum and Minerals. This project was supported in part by SABIC under grant number PH/SABIC 96-2. We are also thankful to Dr. M. Faiz and Dr. J. Shirokoff for useful discussions.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Energy Engineering and Power Technology
- Electrical and Electronic Engineering