A peak in loss angle accompanied by a fall in permittivity is a common dielectric behaviour but the Maxwell–Wagner model [118], which is used to explain the dielectric behaviour of inhomogeneous solids and polycrystalline semiconductors, fails to account for the decreasing parallel resistivity with increasing frequency. The highly disordered intergranular layer and the existence of interface states and electron traps are thought to be the cause of the model failure. The loss angle peak can be interpreted as being caused by electron trapping [119].