The study of inter-plane coupling in Cu 0.5Tl 0.5Ba 2Ca 2Cu 3O 10− δ superconductor by Mg and Pr substitution at Ca site

Abstract

The effects of inter-plane coupling on the superconducting properties of Cu 0.5Tl 0.5Ba 2Ca 2− y M y Cu 3O 10− δ (M = Mg, Pr) superconductor (atmospheric pressure synthesized) have been studied by the substitution of Mg and Pr at the Ca site. Magnesium is found to improve the inter-plane coupling of CuO 2 planes. Improved inter-plane coupling is evidenced in the form of decreased c-axis length and softening of apical oxygen mode when Mg concentration is increased in the material. The zero resistivity critical temperature systematically increases with the increase of Mg concentration in the unit cell. The critical current density in the samples with y = 1.5 has increased by two orders of magnitude compared to the values observed in samples with y = 0. The effects of decreased inter-plane coupling on the superconducting properties of Cu 0.5Tl 0.5Ba 2Ca 2Cu 3O 10− δ (Cu 0.5Tl 0.5-1223) was studied by substituting Pr at the Ca site. The Pr substitution at the Ca site enhances the de-coupling of CuO 2 planes; the c-axis length is increased with the substitution of Pr. With the increased Pr concentration in the material semiconductivity of the samples is also increased and zero resistivity critical temperature is decreased. The effects of improved inter-plane coupling/de-coupling on the phonon modes have been studied by FTIR absorption measurements. The phonon modes of apical oxygen of types Cu(1)–O A–Cu(2) and Tl–O A–Cu(2) have been observed at 534 cm −1 and 485 cm −1 in the sample with y = 0; the relative intensity of former mode is smaller than the latter mode. With the increased Pr concentration in the material, the 534 cm −1 mode is hardened to 564 cm −1 while the 485 cm −1 mode is softened to 436 cm −1. The relative intensity of the former mode is substantially enhanced while the intensity of latter mode is substantially reduced. These observations provide an evidence of CuO 2 planes de-couplings induced by Pr substitution.