Abstract A simple Born model has been seen to explain reasonably well the optical and neutron data available for the Nd 1.85 Ce 0.15 CuO 4 high — T c oxide superconductor. The high frequency phonon bands reveal highly two-dimensional behaviour. Planar dispersions are significant for the different layers. The lattice specific heat in the low temperature region shows a non-Debye behaviour i.e., a variation different from a T 3 — one.