A non-classical electromechanical effect in highly defective bulk cerium oxides

Abstract

In recent times, a new class of environmentally friendly electromechanically active materials, "non-classical ionic electrostrictors (iES)" based on highly defective cerium and bismuth oxides are discovered. These materials demonstrate an anomalously large and uncapped electromechanical behavior that are even superior to state-of-the-art lead-based electrostrictors used in industry. The governing electromechanical mechanism is attributed to be the lability of electrodynamic ionic defects. i.e., highly polarizable elastic dipole: cation-oxygen vacancy active pair in the crystal lattice. In this collaborative research, we investigate the role of different dopants on the electro-chemo-mechanical properties of bulk ceria ceramics. Nanoscale ceria powders were uniaxially cold pressed at 200 Mpa for 30s, followed by sintering at 1450 ◦C in air for 10 hours to produce polycrystalline samples with equivalent oxygen vacancy concentration. The electromechanical strain was estimated at room temperature with a proximity sensor of the capacitive type in lock-in detection. We find two distinct electromechanical behaviors, predominated by electrostatic-elastic interaction in the crystal lattice. When the dopant-defect interaction is weak, electrostriction displays a high coefficient (M33), up to 5·10˗17 m2/V2, with a strong frequency-dependent relaxation effect. On the other hand, relatively lower but a steady M33 is observed for the compounds having a strong dopant-defect interaction i.e. formation of 'immobile' oxygen vacancy clusters. These findings highlights the designing of ionic defects configuration in tuning electrostrictive properties, specially at the high-frequency ranges up to ultrasound (few kHz-MHz).