4.8.1 Piezoelectric effect We use polarization intensity vector to express the piezoelectric effect of a material P=P+p+p (4.78) Where x, y and z form a coordinate system relating to crystal axes Fig. 4.55 Axis numbering system for piezoelectric constantsWe use polarization intensity vector to express the piezoelectric effect of a material: P = Pxx + Pyy + Pz z (4.78) Where x , y and z form a coordinate system relating to crystal axes 4.8.1 Piezoelectric effect Fig. 4.55 Axis numbering system for piezoelectric constants