Investigating Curie point transformations in thin film piezoelectric using a HFS91-PB4 stage

The piezoelectric charge is the charge which accumulates in certain solid materials such as crystals, ceramics and biological materials and is where an applied pressure generates an electrical charge. This characteristic of materials is useful for the production and detection of sound, generation of high voltages, generation of electron frequencies, and ultrafine focusing of optical assemblies. This affect also forms the basis of scanning probe microscopy techniques.

At the RMIT University in Melbourne, Australia, Dr. Sharath Sriram and his colleagues have been investigating reversal and pinning of Curie point transformation in thin film piezoelectrics.  

HFS91-PB4 Linkam stage is used to heat and cool PSZT thin films Using an HFS91-PB4 (HFS600) Linkam stage PSZT thin films were heated to 350°C and cooled at 10°C/min in situ with real-time collection of Raman spectra. This enabled the researchers to determine two main Raman peaks for the film at room temperature, ~575 and ~ 744cm¯¹ ( at which point the film had a rhombohedral structure). Controlled heating and cooling of the thin film causes peaks and intensity changes at the Curie point. This is indicative of a phase change occurring at the Curie point, where the film changes from a rhombohedral arrangement to a symmetrical cubic arrangement. This phase change coincides with loss of piezoelectric charge and piezoelectrical structure. With controlled cooling the cubic phase reverses back to the rhombohedral phase with minimum hysteresis, and piezoelectrical potential. 

The HFS91-PB4 stage in the RMIT Laboratory

This Curie point transformation from cubic to rhombohedral can be disrupted by uncontrolled cooling, which results in locking in place the peak positions and intensities indicating a permanent phase change and the material remaining “locked” in the cubic phase. This shows fast cooling permanently removes the piezoelectric charge within a material.

 

Posted by Caroline Feltham