Comment on ``Superconducting PrBa2Cu3Ox''
Abstract
Recently, Zou et al. (Phys. Rev. Lett. 80, 1074, 1998) reported the observation of bulk superconductivity (SC) for a PrBa2Cu3Ox (Pr123) single crystal grown by the traveling-solvent floating zone (TSFZ) method. The aim of this Comment is to show the inconsistency of the value of effective magnetic moment μeff reported by Zou et al. (2.92μB) with their magnetic susceptibility data. The estimation made directly from their data points gives a considerably smaller value of μeff=2.09μB. At the same time the values of mueff=2.9μB and 3.1μB were obtained for our Pr123 single crystals grown by flux method for H||ab-plane and H||c-axis, respectively. This suggests that Pr occupies only about a half of the RE sites in TSFZ crystal. The other half of the RE sites is occupied most probably by the nonmagnetic Ba. Noteworthy, SC with Tc=43 K was observed earlier for Pr0.5Ca0.5Ba2Cu3O7-y thin films. Ba2+ has a larger ionic radius than Pr3+ and so the substitution of Ba for Pr could give a natural explanation not only for the SC in TSFZ Pr123 but also for the elongation of the distance between the CuO2 planes observed by Zou et al.
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