Piezoelectric Ceramic

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Piezoelectric ceramic but also piezo ceramic

Physical principles

Piezoelectric ceramics are functional ceramic materials that are capable of converting mechanical energy into electrical energy and vice versa.

The physical phenomenon in polar and insulating crystals, whereby mechanical deformation (pressure) causes proportional electrical charges on the crystal surface, is referred to as the direct piezoelectric effect, and the associated property is called piezoelectricity.

The basic piezoelectric behaviour of ceramic materials was discovered in 1880 by the brothers Jaques and Pierre Curie in tourmaline and signet salt crystals and later in quartz and topaz. In 1881, Gabriel Lippmann postulated the reverse piezoelectric effect, which states that a voltage applied to a crystal causes deformation of the crystal lattice (Fig. 1). This effect was also experimentally proven by Jaques and Pierre Curie [1, 2].

Fig. 1:

Polar, insulating crystal lattice (a) in an undeformed state and (b) in a deformed state due to a compressive force

In principle, a distinction is made between the direct and inverse piezoelectric effects. In the direct piezoelectric effect, the mechanical deformation of a piezoelectric material (crystal) causes a shift in the electrical polarisation at the surface (surface tension or charges), which can be technically utilised, e.g. as measurable electrical signals using charge amplifiers for sensors. In the inverse piezoelectric effect, an electric field is applied, e.g. via capacitor plates, which leads to deformation inside the material and can be used technically for switching operations in actuators [3].

The piezoelectric effect

Technical piezo-ceramics or crystals such as quartz (SiO₂) can be cut in different spatial directions, resulting in different piezoelectric effects and sensor sensitivities depending on the geometric dimensions and the type of load. These are the piezoelectric longitudinal, transverse and shear effects, which cause different charges but also different types of technical applications (Fig. 2) [4].

Fig. 2a:

Principle of the longitudinal piezoelectric effect on polar, insulating crystal lattices (a) in the undeformed and (b) deformed state [4]

Fig. 2b:

Principle of the transverse piezoelectric effect at the polar, insulating crystal lattice (a) in the undeformed and (b) deformed state [4]

Fig. 2c:

Principle of the piezoelectric shear effect on the polar, insulating crystal lattice (a) in the undeformed and (b) deformed state [4]

In the longitudinal effect, the tappable charges arise on the load contact surfaces, whereby the charge does not depend on the geometry, but only on the absolute amount of force (Fig. 2a). By connecting such elements in series, the charge amount and thus the voltage can be increased. In the case of the piezoelectric transverse effect, the geometry of the piezo element has a significant influence on the charge yield (Fig. 2b). In the case of the shear effect, the conditions are similar to those of the longitudinal effect, i.e. the magnitude of the charge is independent of the geometric dimensions (Fig. 2c) [4].

Technical Applications

The sensor and actuator behaviour of piezoelectric materials enables a wide range of technically demanding applications in complex assemblies and systems in many areas of electrical engineering, mechanical engineering, acoustics, automation technology, communications engineering, information technology and automotive engineering, as such sensors can be used uniaxially or multiaxially.

Examples of this are [5]:

• Quartz crystals as timers in quartz watches
• Piezo igniters in firelighters
• Piezo actuators for fuel injection systems in direct injection diesel engines
• Oscillators for generating ultrasound, e.g. in ultrasonic cleaning devices
• Pickup systems for stringed instruments
• Charge amplifiers
• Piezoelectric ceramic transducer in ultrasonic and acceleration test sensors
• Force, strain and torque sensors

Today's technical solutions have been made possible by the development of highly efficient, cost-effective piezoelectric ceramic materials and components optimised for technical applications, such as lead zirconate titanate (PZT) ceramics.

Such PZT ceramics have a transition temperature with regard to the crystal lattice, which is referred to as the Curie temperature T_c or Curie point, at which an energy-induced shift of individual ions in the crystal lattice occurs. Above the Curie point, no piezoelectric effect occurs. Below the Curie point, the positive and negative charge centres within the crystal lattice no longer coincide, spontaneous polarisation occurs and electric dipoles form. Below the Curie point (T < T_c), lead zirconate titanate has a tetragonal or rhombohedral lattice, while for T > T_c it has a cubic crystal lattice.

To produce PZT ceramics, the piezoelectric material is further processed in polycrystalline form. The two most common manufacturing processes for piezoceramics are the pressing process and the film casting process. In the pressing technique, a block of piezo material is pressed into a mould and then fired and further processed. In the film casting technique, the piezo material is cast onto a film, punched and then fired.

See also

• Piezoelectric force transducer
• Piezoelectric ceramic transducer
• Ultrasonic composite sensors
• Ultrasonic immersion bath sensors
• Servo-hydraulic testing machine

References

[1]	Wagner, J., Burgemeister, J.: Piezoelektrische Beschleunigungsaufnehmer. In: Weber, M. (Ed.): Piezoelektrische Beschleunigungsaufnehmer. Theorie und Anwendung. Metra Mess- und Frequenztechnik e. K., Radebeul, 7th Edition (2021)
[2]	Schmidt, G.: Kompendium der Physik. Gustav Fischer Verlag Jena, Gebundene Ausgabe (1971) (see AMK-Library under I 27)
[3]	Hering, E., Modler, K.-H. (Hrsg.): Grundwissen des Ingenieurs. Fachbuchverlag Leipzig. 13th Edition (2002), Carl Hanser, Munich Vienna (ISBN 3-446-21443-7, see AMK-Library under L 37)
[4]	Laible, M., Müller, R. K., Bill, B., Gehrke, K.: Mechanische Größen, elektrisch messen – Grundlagen und Beispiele zur technischen Ausführung. Expert-Verlag, Renningen, 7th Edition (2009) (ISBN 978-3-8169-2892-8)
[5]	Schmid, A. J.: Piezokeramik-Funktion, Bauarten und Anwendungen. Argillon GmbH Piezoproducts Rewitz a. d. Rodach, www.keramverband.de/keramik/pdf/05/sem05_04.pdf (last access on January 21, 2026)