X-ray diffraction and infrared investigation of RBa 2Cu 3O 7 and R 0.5Pr 0.5Ba 2Cu 3O 7 compounds (RY and lanthanides)

Abstract

RBa 2Cu 3O 7 and [R 0.5Pr 0.5]Ba 2Cu 3O 7 compounds with RY and lanthanides have been prepared and studied at ambient temperature by means of XRD and infrared-reflectance spectroscopy. In Pr free compounds, increasing the Shannon radius of R, r R, leaves the puckering of the Cu(2)−O(2, 3) sheet unaffected. In the Pr containing compounds, the PrO coordination polyhedron is typical of R +3 ions in eight-fold coordination and argues against differentiating Pr in terms of valence or hybridization. Instead, a repositioning of Ba within the cuprate block is observed, leading to the flattening of the sheet and the anomalously high frequency of the Ba and Cu(2)−O(2, 3) B 1u modes. In RPr compounds the c-axis and the interplanar distances related to the position of Ba and O(2, 3) are found to exhibit a sigmoidal dependence on r R. It is argued that this sigmoidal dependence is related to the two-mode behavior exhibited by several phonon modes of these compounds.