  For most metals, increasing temperature (T) or disorder will quicken electron
scattering. This hypothesis informs the Drude model of electronic conductivity.
However, for so-called bad metals this predicts scattering times so short as to
conflict with Heisenberg's uncertainty principle. Here we introduce the
rare-earth nickelates (RNiO_3, R = rare earth) as a class of bad metals. We
study SmNiO_3 thin films using infrared spectroscopy while varying T and
disorder. We show that the interaction between lattice distortions and Ni-O
bond covalence explains both the bad metal conduction and the insulator-metal
transition in the nickelates by shifting spectral weight over the large energy
scale established by the Ni-O orbital interaction, thus enabling very low
\sigma while preserving the Drude model and without violating the uncertainty
principle.
