Thermal conductivity of R2CuO4, with R = La, Pr and Gd

We present measurements of the in-plane kappa_ab and out-of-plane kappa_c thermal conductivity of Pr2CuO4 and Gd2CuO4 single crystals. The anisotropy gives strong evidence for a large contribution of magnetic excitations to kappa_ab i.e. for a heat current within the CuO2 planes. However, the absolute values of kappa_mag are lower than previous results on La2CuO4. These differences probably arise from deviations from the nominal oxygen stoichiometry. This has a drastic influence on kappa_mag, which is shown by an investigation of a La2CuO4+delta polycrystal.