“…The ¹ onset varied slightly with Pb content as 87, 85, 83, and 85 K for x"0, 0.4, 0.6, and 0.7, respectively. It was reported in a previous study on polycrystalline samples annealed at 750°C in nitrogen flow that ¹ was raised above 90 K by the Pb substitution (10). The observed decrease in ¹ for the present crystals prepared in air must be due to the overdoping effect resulting from higher oxygen content.…”