Structural and magnetic properties of the (Bi2-xPrx)Ru2O7 pyrochlore solid solution (0 <= x <= 2)

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We report a detailed study of structural and magnetic properties of the pyrochlore-type (Bi2-xPrx)Ru2O7 series. Eleven compositions with 0 <= x <= 2 were prepared by solid state reaction at 1050 degrees C and found to form a solid solution in the whole range of compositions. Structural refinements from X-ray powder diffraction data by the Rietveld method show that the main variation concerns the ruthenium site. Ru-O distances increase and the Ru-O-Ru angle (bridging corner-sharing Ru-O octahedra) decreases with increasing praseodymium content, in agreement with the metal-semiconductor transition observed previously in this system. Magnetic measurements show that the metallic Pauli paramagnetism of Ru in Bi2Ru2O7 evolves to a magnetism of localized low spin moments coexisting with the magnetism of Pr3+ cations moments. Strong magnetic correlations are present at high Pr content, as illustrated by a Néel temperature of -224 K for Pr2Ru2O7. However no evidence of a magnetic ordering was found, suggesting that the end compound Pr2Ru2O7 of the series might stabilize a spin liquid phase.