Far-infrared c-axis conductivity of flux-grown   Y$_{1-x}$Pr$_{x}$Ba$_{2}$Cu$_{3}$O$_{7}$ single crystals studied by spectral   ellipsometry
  The far-infrared c-axis conductivity of flux-grown Y$_{1-x}$Pr$_{x}$Ba$_{2}$Cu$_{3}$O$_{7}$ single crystals with 0.2$\leq $x$\leq $0.5 has been studied by sepectral ellipsometry. We find that the c-axis response exhibits spectral features similar to deoxygenated underdoped YBa$_{2}$Cu$_{3}$O$_{7-\delta}$, i.e., a pseudogap develops in the normal state, the phonon mode at 320 cm$^{-1}$ exhibits an anomalous T-dependence and an additional absorption peak forms at T. This suggests that the T$_{c}$ suppression in flux grown Pr-substituted crystals is caused by a decrease of the hole content and/or by carrier localization rather than by pair breaking. 
C. Bernhard, T. Holden, A. Golnik, C.T. Lin, and M. Cardona   (Max-Planck-Institut f\"ur Festk\"orperforschung)