Since the piezoelectric effect in natural single crystals is rather small, polycrystalline ceramic materials such as Lead Zirconate Titanate (PZT) have been developed with improved piezoelectric properties. An additional benefit of polycrystalline ceramics is the fact that during their preparation they can be molded into nearly any shape.
With respect to piezoelectricity and the inherent need for anisotropy, polycrystalline ceramics differ significantly from single crystals. Polycrystalline ceramics, on a macroscopic level, are in general isotropic, even in case the single crystals they consist of are non-centrosymmetric. As a consequence, a polycrystalline ceramic body in general does not exhibit piezoelectricity.
However, in case the crystals in a polycrystalline ceramic are of the ferroelectric type, then it can be given an artificial anisotropy, and thus piezoelectricity, on a macroscopic level. The anisotropy results from a treatment called poling, i.e., the application of a large electric field.