PZT, or Lead Zirconium Titanate, Pb(ZrxTi1-x)O3, is the most widely used piezoelectric. It has the perovskite structure, with Zr and Ti ions randomly placed in the B sites in perovskite.
Its composition is varied by altering the value x. This greatly changes the properties, giving the phase diagram below.
If the PZT is used at 50% Mol PbTiO3, then it is near the rhombohedral/tetragonal phase boundary. This allows it to form many different polarisation states, in the <100> and <111> directions. There are many possible orientations for dipole moments to form, giving easy poling, and making it a useful piezoelectric.