Conventional PZT piezoceramics – used in everything from spark generators and parking sensors to medical ultrasonics – can’t function at high temperatures, limiting their industrial applications. They’re also lead-based materials, which face legal restrictions due to their toxicity to people and the environment. In light of these issues, there is considerable interest in developing lead-free, high temperature piezoelectric materials. BiFeO3-BaTiO3 (BF-BT) ceramics are promising candidates, and researchers at the University of Manchester have been seeking to understand the mechanisms of how we can process and modify the composition of these materials to improve their properties. In work recently published in the Journal of Materiomics, they investigated the unusual technique of adding strontium as an acceptor dopant. Although the strontium disrupted the microstructure – as expected – the team found that, in small amounts, it still improved the ferroelectric and piezoelectric properties. This work demonstrates that acceptor dopants can be used to tune piezoelectric properties, and that strontium-doped BF-BT ceramics are potential candidates for high temperature lead-free piezoelectric materials.
Developing Lead-Free Piezoceramics for Extreme Condition
Increasing demand for applications in piezoelectric sensors, accelerometers and transducers has created considerable interest in high temperature piezoceramics. Conventional lead-based ceramics have two important limitations. Firstly, their low Curie temperature (TC) means they can only be used at temperatures below 200°C. Secondly, they have strong toxic effects on the environment and human health, and their use is increasingly restricted.
Materials based on bismuth ferrite (BF) combine strong ferro/antiferromagnetism and high spontaneous polarization (>100 mC/cm2) with a high ferroelectric Curie temperature of around 825 °C.
Senior author Dr David Hall, from the University of Manchester, said:
For many years now, we’ve been working with Ionix Advanced Technologies, a spin-out company from the University of Leeds. Ionix uses piezoelectric compositions to generate ultrasound for high temperature applications. It’s very similar to the way ultrasound is used for medical imaging, but in this case, it’s used for inspecting structural components like cooling systems that can operate up to nearly 400 °C. There are similar applications in high temperature processing systems operating at around 580 °C. At the moment, there isn’t a lead-free material that can match that performance.
We’ve been working on a lead-free BiFeO3–BaTiO3 (BF-BT) solid solution. In principle, if you make a piezoelectric device from this compound it would operate up to very high temperatures, and then it could have applications in the real world as a piezoelectric electromechanical transducer material.
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