Growth Speed and Substitution Effects on Alignment and Thermal Transport

Abstract

Fe-substituted superconducting thin BiSrCaCuO rods with nominal compositions of Bi2Sr2Ca1Cu2-x Fe (x) O8+delta (x = 0, 0.01, 0.03, 0.05, and 0.1) were fabricated using the laser floating zone technique at two different growth speeds, 15 mm h(-1) and 30 mm h(-1). The influences of growth speed and Fe substitution on the grain alignment in the rods were evaluated by means of x-ray pole figure studies. The obtained results showed that both applied growth speed and Fe substitution play a crucial role on grain alignment, which is strongly connected with the current-carrying capacity of the rods. It was found that the rods grown at 15 mm h(-1) (G15) have stronger orientation than the rods grown at 30 mm h(-1) (G30). However, in contrast to the G15 rods, an increased substitution rate improved the orientation of the G30 rods. Another important observation is that the increase on the substitution caused a decrease on the grain size of all the rods. The decrease of critical temperature values of the rods upon substitution was ascribed to both grain size effect and formation of a nonsuperconducting Fe-rich phase detected in scanning electron microscope/energy-dispersive x-ray analyses. The thermal conductivity values of the G15 and G30 rods were found to be in the range of 0.9-1.9 and 1.1-1.18 W m(-1) K-1 at 150 K, respectively. The higher values of figure of merit (ZT), at all temperature ranges, were obtained from the highest substituted rods (x = 0.1) for both of the applied growth speeds. In addition, it was observed that the ZT of G30 rods are up to three times higher than that of G15 ones.

C1 [Ozabaci, M.] Inonu Univ, Sci & Technol Res Ctr, TR-44280 Malatya, Turkey.

[Rasekh, Sh.; Madre, M. A.; Sotelo, A.] Univ Zaragoza, CSIC, ICMA, Zaragoza 50018, Spain.

[Kizilaslan, O.] Inonu Univ, Fac Arts & Sci, Dept Phys, TR-44280 Malatya, Turkey.

[Yakinci, M. E.] Inonu Univ, Dept Biomed Engn, Fac Engn, TR-44280 Malatya, Turkey.