New alternative to pollutive ferroelectric material used in sensors

Researchers in Japan have used an ultra-fast technique to explore the fine structure of a potential alternative to lead titanate, a ferroelectric material widely used for sensors in many devices.

As published in Acta Materialia, ferroelectric materials are used in a wide range of practical applications, from capacitors to memory cells, medical ultrasound to data storage and displays. These materials have a spontaneous polarisation of their electrons that can be switched back and forth via the application of an electric field, called ferroelectricity.

Lead titanate is a common ferroelectric material that is often used in sensors that measure pressure, acceleration, temperature, strain, or force in a raft of common devices. Lead pollution has long since been shown to be tremendously damaging to the human brain, and while most jurisdictions have outlawed lead in paint and gasoline, the quest to develop alternative materials for such devices remains yet to be completed.

Some research has been performed on perovskite titanates, a family of ferroelectric materials that combine titanium oxide (TiO) with either lead, barium, strontium, or calcium. This research had identified a clear link between the hybridisation of electron orbitals of perovskite titanate’s different constituent atoms and its ferroelectric properties.

Nobuo Nakajima of the Graduate School of Advanced Science and Engineering at Hiroshima University, a co-author of this new study, said: “The next step therefore was to somehow achieve direct observation of the state of these electrons as the electric field was being applied. This required ultra-fast observations.”

Developing an alternative to lead titanate

The team at Hiroshima University combined x-ray absorption spectroscopy (XAS) with a time-resolved approach. XAS involves the interaction of an x-ray with the deep-core electrons of an atom rather than its outer (or valence) electrons. Measurement of this interaction permits description of the fine structure of the material. A time-resolved approach involves use of this technique to study the dynamic changes in the material on the sort of extremely short time scales in which phenomena such as ferroelectric polarisation reversal occur. It allows the researchers to detect the smallest of changes in spectra and electronic states under electric fields. The combination of the two techniques was performed for the first time, on barium titanate.

The researchers found that in addition to the orbital hybridisation between titanium and oxygen that had already been identified, a similar effect was spotted between the barium and the state of titanium electrons. This also contributed to the polarisation reversal in barium titanate.

The team hopes that their novel technique applied to a parallel perovskite titanate could provide clues to what they describe as the nature of lead titanate and take the world a step closer to elimination of lead pollution.

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