Electrostrictive Materials - Relaxor Ferroelectrics

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About Ecertec

Ecertec leads the way with electrostrictive materials research, development and supply.

Ecertec has a 15 year history in the development of electrostrictive materials and devices - many of which are now found in commercial devices.

Ecertec PMN is more dense and mechanically stronger than other PMN ceramics and it is absolutely single phase perovskite (no pyrochlore).

Lead Magnesium Niobate ( PMN ) and it's doped derivatives are the classical electrostrictive materials. These materials known as relaxor ferroelectrics possess high relative permittivities ( 20,000 - 35,000 ) and extrodinarily high electrostrictive coefficients.

Often, very difficult and expensive to synthesize in single phase ceramic form - PMN has often been passed over by system designers and actuator users due to high cost and poor mechanical properties.

Ecertec electrostrictive materials overcome these limitations and provide unparalleled performance in high frequency and low power application areas.

Electrostrictive materials are not piezoelectric and possess no spontaneous polarisation. When correctly used they can be virtually loss free up to hundereds of kilo hertz.

The electrostrictive effect (dimensional change under the influence of applied field) is found in all materials although it is usually too small (approx 10E-5 to10E-7 strain%) to utilise practically. Electrostrictive ceramics, based on a class of materials known as relaxor ferroelectrics, however show strains comparable to piezoelectrics (10E-1strain%) and have already found application in many commercial systems.

The lack of a spontaneous polarisation means that electrostrictors display little or no hysteretic loss even at very high frequencies of operation. The advantages are however gained at the expense of temperature stability. Relaxors operate best in situations where the temperature can be stabilised to within approximately 10 °C. This may seem extremely limiting at first glance, but given that electrostrictors excel at high frequencies and very low driving fields, then the applications tend to be in specialised micro actuators. Temperature stabilisation of such small devices is relatively simple and often presents only a minor problem in the overall design and development process.

Most commercial electrostrictive ceramics are based upon the classical relaxor ferroelectric PMN (lead magnesium niobate) and its doped derivatives. The most useful family of actuator materials are solid solutions of PMN and lead titanate (PT). PMN-PT materials are available from virtually all piezoelectric suppliers although they remain a minority low volume product in most cases.

Ecertec PMN-PT (PMNT) technologies (powders, processes and ceramics) solve many of the problems associated with the production and use of electrtostrictives; namely contol of both chemical/phase composition and microstructure. The resultant materials are superior both mechanically and electrically - all without the need for exotic and expensive hot pressing techniques.

Phase Change Actuators....

Ultra high strains may be realised by electrically driving certain materials through a structural phase transition. These phase change materials are relatively new and are attracting considerable interest from many application sectors. Unfortunately the severity of the induced strain means that single crystals are required in order that the material doesn't literally pull itself apart.

Phase change materials and single crystals are currently under investigation for various applications including adaptive aerodynamics. Ecertec Ultra-Active Powders have been used by many groups as a starting material for single crystal growth due to their excellent chemical purity and homogeneity.