National Physical Laboratory

Functional materials in harsh environments

Functional materials are widely used for sensing, actuation and energy storage and generation and electronic devices. The emergence of new materials and new applications is increasing the demands for performance and reliability. Materials need to operate reliably under highly stressed conditions and in a range of environments. A central theme of our functional materials research is investigations into the effects of environmental conditions, such as temperature and humidity, on materials' performance and relating these effects to the underlying materials physics and properties.

Microstructure damage caused by humidity induced breakdown
Microstructure damage caused by humidity induced breakdown


Piezoelectric materials are used as electro-mechanical transducers in a wide range of applications both as actuators and as sensors. Piezoelectric actuation is used in devices such as injector valves for diesel engines, ultralow power electronic locks and valves for industrial and domestic fluid controls. Piezoelectric actuators also underpin much of modern nanoscale science and technology through their ability to control movement with atomic scale resolution in scanning probe microscopy.

For d.c. or low frequency actuator applications, these materials provide low power consumption, making possible novel applications for remote or inaccessible locations, autonomous operation using energy harvesting, or long-lived miniaturised battery powered devices. As these materials become more widely used, the demands on their performance increase, particularly with regard to lifetime and reliability in humid environments and at high electric field across a wide temperature range.

Humidity in the environment can cause electrochemical reactions in the pores and grains of a piezoelectric material which can lead to increased power consumption and eventually failure through excessive leakage current. Research at NPL has shown how the microstructure of the piezoelectric material, the composition of the electrodes, processing methods and operational requirements can strongly affect reliability in humid conditions. Our measurements show how significant improvements to be achieved through selection of materials and design of barrier coatings.

Temperature dependent linearization of piezoelectric actuator strain
Temperature dependent linearization of piezoelectric actuator strain
Temperature dependent electrostriction in a piezoelectric ceramic
Temperature dependent electrostriction in a piezoelectric ceramic


In many actuator applications large electric fields are employed to maximise the energy density. In this high field regime nonlinearity and hysteresis dominate performance. These effects are highly temperature dependent and wide variations in performance with temperature are encountered. Because of the strong electromechanical coupling thermal expansion is strongly coupled to the electric field and polarisation. Our research has led to improved understanding of the physics of thermal coupling in ferroelectric and piezoelectric materials resulting significant improvements in temperature stability, substrate thermal matching, and control of non-linearities in electronic controls.

Our measurement facilities include multiplexed measurement of leakage current, piezoelectric and ferroelectric properties at high electric field in controlled temperature and humidity environments.

Publications

  • Electromechanical Coupling and Temperature Dependent Polarisation Reversal in Piezoelectric Ceramics
    P. M. Weaver, M. G. Cain, T. M. Correia, M. Stewart
    IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, 58, pages 1730-1736 (2011)
  • A Sensorless Drive System for Controlling Temperature Dependent Hysteresis in Piezoelectric Actuators
    P. M. Weaver
    Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, 58, pages 704-710 (2011)
  • Electrical conduction mechanisms in piezoelectric ceramics under harsh operating conditions
    D. Zheng, J. Swingler, P. M. Weaver
    Sensors and Actuators A: Physical, 167, pages 19-24 (2011)
  • Temperature dependence of strain--polarization coupling in ferroelectric ceramics
    P. M. Weaver, M. G. Cain, M. Stewart
    Applied Physics Letters, AIP, 96, 142905 (2010)
  • Temperature dependence of high field electromechanical coupling in ferroelectric ceramics
    P. M. Weaver, M. G. Cain, M. Stewart
    Journal of Physics D: Applied Physics, 43, 165404 (2010)
  • Current leakage and transients in ferroelectric ceramics under high humidity conditions
    D. Zheng, J. Swingler, P. M. Weaver
    Sensors and Actuators A: Physical, 158, pages 106-111 (2010)
  • The Effect of Relative Humidity, Temperature and Electrical Field on Leakage Currents in Piezo-ceramic Actuators under D.C. Bias
    I. P. Lipscomb, P. M. Weaver, J. Swingler, J. W. McBride
    Sensors and Actuators A: Physical, 151, pages 179-186 (2009)
Last Updated: 18 Sep 2017
Created: 12 Mar 2012

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