The temperature-dependent electrical properties of CaCuP were also investigated using Boltzmann transport theory (AMSET package) and are summarised in Figure . Unless otherwise specified, the hole concentration is fixed at n h = 1 × 10 20 cm -3 for comparison with experiment. First we consider limits to the hole mo-bility by the following competing scattering mechanisms: acoustic deformation potentials (ADP), ionised impurities (IMP), grain boundaries (GBS) and polar optical phonons (POP), in Figure . Note that the grain boundary scattering rate in AMSET is simply set to v g /L, where v g is the group velocity and L is the grain diameter. In case other hole-scattering extended defects exist within grains, L then represents their average distance. Potential barriers at grain boundaries are ignored, but this may be a reasonable approximation in a material with a high hole concentration.