Highly exciting interferometry

Functional materials such as, e.g., piezoceramics, are used in numerous application fields, among other things in the automotive industry, in aeronautical engineering, in metrology, in energy production and in process monitoring. Use at high temperatures is increasingly aimed at. Developing such new materials, together with the corresponding metrological infrastructure, is the aim of the European cooperation project METCO. Concretely, the activities revolve around the ability to measure the coupling between mechanical, electrical and thermal properties in a wide temperature range. PTB's task hereby consists in measuring changes in length interferometrically, at high temperatures (currently up to 200 °C) and with an electric field applied (from -2 kV/mm to +2 kV/mm). To this end, a special sample environment was developed at PTB and tested with a commercially available lead zirconate titanate (PZT) ceramic at various temperatures.

From the measured piezoelectrically induced length change, the piezoelectric coefficient was determined at 20 °C as well as at 100 °C. The results are in agreement with measurements which were carried out by partners with commercially available measuring systems; they could also be reproduced on other samples under investigation. The advantage of PTB's interferometer resides in the fact that it is an imaging system, so that not only point-by-point length measurements, but also spatially resolved length variations (length topography) of the entire surface of the sample are possi-ble. This provides additional information, e.g., on inhomogeneities or edge effects.

After initial tests have been successfully completed, the next step will consist of investigating high-temperature piezo-materials which have been newly developed by our project partner, the University of Leeds (UK).