Structural and superconducting properties of Y1-2xPrxCaxBa2Cu3O7-δ: high-Tc superconductors

Y1-2xPrxCaxBa2Cu3O7-δ (YPrCaBCO) high-Tc superconductors were prepared and characterized. Tc was found to decrease linearly with respect to x. The X-ray diffraction pattern indicates that all specimens contain a small amount of impurity phase BaCuO2, from which Cu2+ gives rise to an X-band electron spin resonant (ESR) absorption peak at ∝310 mT (g∝2.05) in the undoped (x=0) YPrCaBCO. The ESR peak shifts towards low fields as the temperature is lowered, which is due to the change in crystal field experienced by Cu2+(3d9) ions. The copper ions in the undoped YPrCaBCO itself are ESR silent due to a very short relaxation time. At x=0.10 and 0.20 dopings, a new six-peak hyperfine ESR signal arising from 141Pr4+(4f1, nuclear spin I=5/2) appears at ∝330 mT (g∝2.20) while the Cu2+ signal disappears. This signal might arise from some Pr ions entering the Y site with a valence of four, thus lending support to the hole-filling and pair-breaking models. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)