Tunable oxygen vacancy diffusion and electronic conduction through strain engineering in PZT films

This study elucidates the roles of strain gradients in enhancing both electronic and ionic conductivity of Nb doped lead zirconate titanate (PNZT) films. Increasing the applied strain in bent PNZT films from 0 to 0.5% reduced the energy barrier for vacancy diffusion from 0.75 ± 0.1 to 0.5 ± 0.1 eV, resulting in an increase in mobile [Formula: see text] from 2.1 ± 0.2 × 10¹⁸/cm³ to 1.6 ± 0.4 × 10¹⁹/cm³. Notably, [Formula: see text] migration was detected even in bent samples not subjected to prior electrical degradation. The enhancement of migration is attributed to the electric field induced by coupled flexoelectric and piezoelectric effects. The increasing population of mobile [Formula: see text] due to bending strain enhances electron trapping by Ti⁴⁺ ions, raising the electronic conductivity. Concurrently, hole hopping between Pb²⁺ and Pb³⁺ decreases with increasing bending strain, indicating a decline in hole concentration and a shift in the n-p transition to higher [Formula: see text] and temperature ranges. In pristine films on Ni metal foils, increasing the bending strain from 0 to 0.5% increased the volume fraction of a-domains from 15 to 64% due to ferroelastic domain reorientation. Consequently, the reversible Rayleigh coefficient [Formula: see text] rose from 540 ± 6 to 790 ± 8, as the permittivity of a-domains is higher than that of c-domains. Furthermore, ferroelastic domain reorientation increased the concentration of non-180° domain walls, amplifying the irreversible Rayleigh parameter, α from 28 ± 4 to 47 ± 5 cm/kV. In the electrically degraded state, both [Formula: see text]and α decreased, due to (1) loss of switchable units from localized dielectric breakdowns, (2) changes in domain configurations, and (3) the internal bias field. These results will influence the vast majority of piezoelectric microelectromechanical systems which utilize bending to enhance displacements.