Stoichiometry and Tc of Bi-2201 doped with La, Pr, Nd and Pb

✍ Scribed by P.V.P.S.S. Sastry; A.R. West

• Publisher: Elsevier Science
• Year: 1994
• Tongue: English
• Weight: 501 KB
• Volume: 225
• Category: Article
• ISSN: 0921-4534
• DOI: 10.1016/0921-4534(94)90342-5

✦ Synopsis

The Tc of rare-earth doped Bi-2201 depends on the post-sintering treatment, with a change of behaviour occuring around x=0.40 in the formula Bil.asSr2.os_xRxCuOq, R=La, Pr and Nd. For x_<0.4, samples prepared in air are overdoped and T¢ is increased by annealing in argon. For a given x, Tc is independent of the magnetic moment and size of the rare-earth ion. Tc increases with x and passes through a maximum of 36 K at x=0.40. For x> 0.4, samples prepared in air are underdoped and T¢ can be increased by annealing in oxygen; superconductivity is found for x_<0.80 but so far has not been attained at higher x. Solubility limits are x= 1.30 (La), 0.80 (Pr) and 0.60 (Nd). The effect of Sr deficiency, starting from the composition x=0.40, is to decrease T¢; the decrease is greater after 02 annealing treatment, indicating that Sr deficient samples are overdoped. Substitution of Pb for Bi in the composition x = 0.40 does not affect T¢ but does lead to an increase in sample crystallinity, as shown by the sharpness of X-ray powder diffraction peaks and to an increase in the superconducting volume fraction, as shown by an increase in the diamagnetic signal at T< T~.