Download files
Abstract
The mechanical properties of BiFeO3 (BFO) thin films grown on SrTiO3 (001) substrates that are manually bent are studied using a specially designed uniaxial bending stage. X-ray measurements under variable uniaxial strain show that excessive strains up to ̴ 2% could be applied along the [100] direction with little cross talk between [100] and [010] directions. X-ray reciprocal space maps are acquired to investigate the evolution of -a and c-axis lattice constants under variable strain and Poisson’s ratio of BFO thin films vzx is determined to be 0.30 ± 0.01.
The effect of variable uniaxial tensile strain on the evolution of 71° ferroelastic domains in (001)-oriented epitaxial BiFeO3 (BFO) thin films using piezoresponse force microscopy (PFM) are investigated. For this purpose, a newly designed bending stage has been employed which allows for tensile bending as wells as in-situ PFM characterization. In-situ PFM imaging reveals polarization-strain correlations at the nanoscale. Specifically, ferroelastic domains with in-plane polarization along the direction of applied tensile strain expand, while the adjoining domains with orthogonal in-plane polarization contract. The switching is mediated by significant domain wall roughening and opposite displacement of the successive walls. Further, the domains with long-range order are more susceptible to an applied external mechanical stimulus compared to the domains, which exhibits short-range periodicity. In addition, the imprint state of film reverses direction under applied tensile strain. Finally, the strain-induced changes in the domain structure and wall motion are fully reversible and revert to their as-grown state upon release of the applied stress. The strain-induced non-180° polarization rotation constitutes a route to control connected functionalities such as magnetism via coupled in-plane rotation of the magnetic plane in multiferroic BFO thin films.
Ferroelectric domain structure and piezoelectric response under variable mechanical compressive stress in Pb(Zr0.2TiO0.8)O3 (PZT) thin films using high-resolution piezoresponse force microscopy (PFM) and an in-situ sample bending stage are studied. Measurements reveal a drastic change in the ferroelectric domain structure which is presented along with details of the mediating switching process involving domain wall motion, nucleation, and domain wall roughening under an applied external mechanical stimulus. Furthermore, local PFM hysteresis loops reveal significant changes in the observed coercive biases under applied stress. The PFM hysteresis loops become strongly imprinted under increasing applied compressive stress.