1/8 Doping Anomalies and Oxygen Vacancies in Underdoped Superconducting Cuprates

Measurements of thermal conductivity ($\kappa$) versus temperature and doping for several cuprate superconductors are discussed. Suppressed values of the normal-state $\kappa$ and the slope change in $\kappa$ at $T_c$, observed near 1/8 doping in both YBa$_2$Cu$_3$O$_{6+x}$ and Hg cuprates, are attributed to local lattice distortions and the suppression of the superconducting condensate, respectively. Both phenomena are proposed to arise from small domains of localized planar holes, presumably a manifestation of phase separation. It is suggested that the phase behavior of $\kappa$ reflects stripe dynamics and the 1/8 doping anomalies stripe pinning by oxygen-vacancy clusters.