Piezoelectric compound performs under pressure

Piezoelectric materials could soon be made far more simply, according to researchers in the US. When squeezed, even gently, these materials respond by generating electricity - an unusual property that has made them invaluable in applications from ultra-sensitive balances to scanning probe microscopes.

But while some naturally occurring crystals such as quartz produce small currents when they’re squeezed, materials with stronger piezoelectric properties are currently made from complex metal alloys in specially-designed crystal structures - a costly process that has prevented them from finding an even broader range of applications.

The piezoelectric properties of these man-made crystals arises because their structure changes abruptly when light pressure is applied to them. This causes the arrangement of ions to shift and the resulting charge difference generates a voltage. 

Now, a team at Carnegie Institution in Washington DC have shown that with much higher pressures, simple crystals of lead titanate (PbTiO₃) can undergo the piezoelectric transitions observed in these more expensive materials. PbTiO₃ is known to have weak piezoelectric properties at ambient pressure and has been extensively studied over the years, so the researchers were surprised by the findings. 

The team used a diamond anvil cell to generate very high pressures and observed the structure of PbTiO₃ with high-energy x-ray beams.

’At a critical degree of compression, the piezoelectric properties are dramatically enhanced,’ explained Russell Hemley, who led the research with Ronald Cohen.’This suggests that a specific range of inter-atomic distances are crucial for introducing these properties.’

In future, Hemley added, ’The aim would be to make a material with these same inter-atomic distances at ambient pressure - it would already be optimised.’

Zuo-Guang Ye, an expert in piezoelectric materials at Simon Fraser University, Canada, is more cautious about the prospect of the discovery leading to new piezoelectric materials very soon. But, he told Chemistry World, ’This is interesting work that may improve our understanding of phase transition mechanisms.’

Lewis Brindley