Basics of materials
 

Piezoelectricity is the property of nearly all materials that have a non-centrosymetric crystal structure.

 

Some naturally occurring crystalline materials possessing these properties are quartz and tourmaline. Some artificially produced piezoelectric crystals are Rochelle salt, ammonium dihydrogen phosphate and lithium sulphate. Another class of materials possessing these properties is polarized piezoelectric ceramic. In contrast to the naturally occurring piezoelectric crystals, piezoelectric ceramics are of a “polycrystalline” structure.

 

The most commonly produced piezoelectric ceramics are lead zirconate titanate (PZT), barium titanate and lead titanate. Ceramic materials have several advantages over single crystal, especially the ease of fabrication into a variety of shapes and sizes. In contrast, single crystals must be cut along certain crystallographic directions, limiting the possible geometric shapes.
 
PZT (and many other piezoelectric materials) have crystal structures belonging to the perovskite family with the general formula AB03. In the following figure the ideal, cubic perovskite structure is shown. PZT crystallites are centro-symmetric cubic (isotropic) before poling and after poling exhibit tetragonal symmetry (anisotropic structure) below the Curie temperature.

 

Before poling, a piezoelectric ceramic material consists of small grains (crystallites), each containing domains in which the polar direction of the unit cells are aligned. These grains and domains are randomly oriented; hence the net polarization of the material is zero, i.e. the ceramic does not exhibit piezoelectric properties. The application of a sufficiently high DC field (called poling process) will orient the domains in the field direction and lead to a remanent polarization of the material.
 

The perovskite structure is very tolerant to element substitution (doping) by formation of solid solutions. The possibilities of doping in these materials lead to an unlimited number of possible perovskite-type oxides. Even small amounts of a dopant may cause huge changes in the properties of a material.
 
The coupling of electrical and mechanical energy makes piezoelectric materials useful in a wide range of applications.
 

Multilayer and bulk components are manufactured in different grades of piezoelectric (e.g. PZT) or electrostrictive (e.g. PMN) materials, each material having optimised properties for the broad range of applications of actuators, generators, transformers, etc.

For multilayer components various materials for internal as well as external electrodes are available. 

Noliac standard materials