X-ray diffraction and infrared investigation of RBa2Cu3O7 and R0.5Pr0.5Ba2Cu3O7 compounds (RY and lanthanides)

Abstract RBa 2 Cu 3 O 7 and [R 0.5 Pr 0.5 ]Ba 2 Cu 3 O 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.