Abstract
The polarizable point-ion model has been applied to the electrostatics of the three ferroelectric phases of KNbO3. If we use the experimental spontaneous polarization for the tetragonal phase PS = 30 C/cm2 as fitting data, the PS values 35.8 and 39.0 C/cm2 for the orthorhombic and rhombohedral phases, respectively, are calculated. The effect of nonlinearity is considered.