Prospects to attain room temperature superconductivity

With a generic model for the electron-phonon spectral density, two simple expressions are derived to estimate the transition temperature and gap-to-temperature ratio in conventional superconductors. They entail that on average the numerical value of the phonon exchange factor, $\lambda$, is limited to 2.67, so that room temperature superconductivity may be attained only with a Debye temperature of about 1800 K or higher, in materials that may or may not involve hydrogen. They also show that a Be-Pb alloy may become a superconductor at $\sim$44 K.
Comment: An application of the model to alloys is added to the manuscript, previously accepted into Solid State Communications on 03/05/19