We have used powder neutron diffraction to study the magnetic ordering and the crystallographic structure of the orthorhombically distorted perovskite BaPr03. Reitveld refinement of high-resolution neutron-powder-diffraction patterns showed that BaPr03 belongs to space group Pbnm, with a =6. 2137(3) A, b =6.1787(3) A, and c =8.7261{4)A at room temperature. Our structural determination, confirmed by high-resolution x-ray powder diffraction, corrects the erroneous reversal of the a and b lattice parameters previously reported in the literature. The Pr moment is observed to order continuously and reversibly below Tn= 11.7(2) K. The Pr spins are staggered along the c axis and the [110] direction with a low-temperature thermally averaged moment of ()M, ) =0. 35 (5)pe.

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The temperature dependences of the electrical resistivity, magnetic susceptibility, and specific heat have been measured in Bi~Sr2Ca& M Cu208, where M= Y, Gd, and Pr, for concentrations 0 x~1.0 and temperatures 1.6 K T 300 K. All three dopants substitute a trivalent ion for divalent Ca and cause a depression of T, observable in the resistivity and susceptibility. Both Pr and Gd retain their free-ion magnetic moment and appear to cause little, if any, magnetic pair breaking. Instead, the dominant suppression mechanism in all three cases is driven by the filling of the Cu 3d hole by the extra electron and the breaking of the Cu 3d -02p hybridization. Consequent localization of Cu 3d holes causes an observable antiferromagnetic ordering of Cu ions within the planes in the case of Y. The evidence for Cu ordering for Gd and Pr is obscured by the large Curie contribution to the magnetic susceptibility due to the rare-earth ions.

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