Thermal Conductivity of YBa$_2$Cu$_3$O$_7$

It is widely, but incorrectly, believed that the thermal conductivity of YBa$_2$Cu$_3$O$_7$ can only be explained in terms of a d-wave model. We show that an s-wave model of hole- pairing, combined with muon spectra that are observed to be s- wave, specific heat data with an observed zero-field linear-T term, superconductivity determined to be in the BaO layers, and non-superconducting CuO$_2$-plane bands describe the YBa$_2 $Cu$_3$O$_7$ data better than any d-wave model. Unlike any d- wave model, the s-wave explanation is also consistent with the superconductivity of Cu-doped Sr$_2$YRuO$_6$ and Ba$_2$YRuO$_6$, at $\approx$49~K and $\approx$83~K, despite these compounds having no cuprate-planes, and the superconductivity of GdSr$_2 $Cu$_2$RuO$_8$ and Gd$_{2-z}$Ce$_z$Sr$_2$Cu$_2$RuO$_{10}$ occurring at $\approx$40~K, despite the fact that their cuprate- planes are either antiferromagnetic or weakly ferromagnetic. In all of these compounds, the superconducting layer is the SrO or BaO layer. The errors which led to the widely believed erroneous concept of cuprate-plane superconductivity are discussed.