The delafossite compounds PdCoO2 and PtCoO2 show extremely high electrical conductivity at low temperatures. In this system Pt,Pd layers with triangular arrangement are separated by edge-sharing CoO6 octahedra. Raman and infrared spectroscopy revealed high-energy optical phonons well beyond 100 meV and were attributed to oxygen vibrations. It is suspected that these high-frequency phonons are involved in the high conductivity seen at low temperature. So far, no detailed measurements of the phonons have been performed. The present proposal aims at studying the phonon density of states in PdCoO2 to shed light on the unusual low temperature properties. Therefore we ask for 4 days of beamtime on MARI. Theoretical calculations are currently in progress to complement the proposed experiment.