This multilayer film constricts under an electric field

Researchers have discovered a new way to engineer thin films that change volume under an electric field. Their technique could help scientists create small, energy-efficient biomedical devices (Nature 2022, DOI: 10.1038/s41586-022-05073-6).

Electrostrictive materials generate strain in response to an electric field. Researchers are interested in harnessing this property, measured by a material’s electrostriction coefficient, to build low-power biomedical devices such as microsensors. But many of the highest-performing electrostrictors contain lead, which can be toxic. Recently, scientists discovered electrostriction properties in gadolinium-​doped cerium oxide (CGO), which is used in solid oxide fuel cells. Materials scientists Haiwu Zhang, Nini Pryds, and Vincenzo Esposito of the Technical University of Denmark wanted to know if they could improve its performance.

They started by depositing alternating layers of CGO and erbium-stabilized bismuth oxide onto a neodymium gallate substrate, making multilayer films about 17 nm thick. Chemical defects in the oxide layers create local lattice distortions in the form of dipole moments that exert strain when oriented to an electric current. At each interface, stress generated from the lattice mismatch between oxides shifts the dipoles into partial alignment. The researchers then apply voltage to elongate the film by fully aligning the dipoles (shown).

Increasing the number of interfaces allowed the team to make films with electrostriction coefficients 1,000 times as high as commercial lead-based electrostrictors, they say.

“The effect of the interface on electrostriction is surprisingly large,” says Shujun Zhang, a materials scientist at the University of Wollongong who was not involved in the study. It’s a discovery that could benefit the design of future electrostrictors, he says.