Two different types of hysteresis are considered for loss mechanism of piezoelectric materials: one addressing the energy required to align the dipole orientation with the direction of electric field through 180° and 90° domain switching, and the other addressing the energy required to overcome the cracks in piezoelectric materials. By modeling piezoelectric materials as tetragonal crystallites with dipole moments, evolution of polarization due to applied electric filed is derived. Furthermore, dielectric, mechanical, and electromechanical losses due to the inclusions of cracks in piezoelectric solids are investigated. The influence of the existence of a crack is described through the characterization of the perturbation to stress and strain distribution. The strain energy release rates are used to determine the energy dissipation due to the crack. Correspondence principle is then applied to determine loss factors such that the constitutive laws governing the energy loss in dielectric, mechanical, and piezoelectric domains can be quantified. Therefore, the complex electromechanical coupling relations can be expressed by using a phase lag, which indicates the property degradation of piezoelectric materials.