Strain-Engineered Ferroelastic Structures in PbTiO₃ Films and Their Control by Electric Fields

Abstract

We study the interplay between epitaxial strain, film thickness, and electric field in the creation, modification, and design of distinct ferroelastic structures in PbTiO3 thin films. Strain and thickness greatly affect the structures formed, providing a two-variable parameterization of the resulting self assembly. Under applied electric fields these strain-engineered ferroelastic structures are highly malleable, especially when a/c and a1/a2 superdomains coexist. To reconfigure the ferroelastic structures and achieve self-assembled nanoscale-ordered morphologies, pure ferroelectric switching of individual c-domains within the a/c superdomains is essential. The stability, however, of the electrically written ferroelastic structures is in most cases ephemeral; the speed of the relaxation process depends sensitively on strain and thickness. Only under low tensile strain-as is the case for PbTiO3 on GdScO3-and below a critical thickness do the electrically created a/c superdomain structures become stable for days or longer, making them relevant for reconfigurable nanoscale electronics or non-volatile electromechanical applications.

Relaxation Mechanisms and Strain-Controlled Oxygen Vacancies in Epitaxial SrMnO3 Films

“…There is wide evidence that Matthews–Blakeslee’s model underestimates the critical thickness in many materials as a consequence of a number of simplifications used in its derivation, mainly the neglect of kinetic barriers for the nucleation and propagation of dislocations. , Furthermore, the versatile structure of ABO 3 perovskite oxides allows a rich variety of additional mechanisms for the relaxation of epitaxial strain, such as twinning, lack of stoichiometry, or rotations of the BO 6 octahedra, , occasionally with complex interactions between them . In the case of ferroelectrics, another possible way to release the stress is by forming different ferroelectric–ferroelastic domain patterns, whose configuration arises from the epitaxial strain and film thickness. − In particular, polar epitaxially strained SMO films on LSAT show both a lateral inhomogeneity in the distribution of oxygen vacancies (which accumulate in the walls separating polar domains) and concentration gradients along the out-of-plane direction . This complex scenario makes the application of Matthews–Blakeslee and similar models too simplistic and explains the large discrepancy between the calculated and observed values of t c in our films.…”

Mechanical reading of ferroelectric polarization

“…The growth conditions and the structural characterization can be found elsewhere. 18,19 BiFeO 3 (111) films were epitaxially grown by pulsed layer deposition on the LaSrMnO 3 bottom electrode.…”

Deconvolution of Phonon Scattering by Ferroelectric Domain Walls and Point Defects in a PbTiO3 Thin Film Deposited in a Composition-Spread Geometry

“…The possibility of dynamically controlling the thermal conductivity in solid-state devices using ferroelectric materials − is an exciting emerging research direction. , At the heart of this process is the nature of the ferroelectric domain walls (DWs): they may be very efficient phonon-scattering centers, − ,,− and at the same time, they can be moved, created, and erased with an electric field, − providing a unique opportunity to electrically modulate phonon transport. This would enable the development of thermal transistors and thermal switches, key elements of effective thermal circuitry, basic phononic logic operations, and novel devices in thermal energy management and harvesting.…”

“…Thus, the electric-field control of the phonon transport in ferroelectric materials might arise from the ferroelectric switching, from mobile point defects, or, more likely, from a combination of both. Yet, while the electrical modification of the domain wall patterns can be stable, enabling stable “phononic” states, the fact that the ion vacancies gradually diffuse back to the original configuration once the electric field is removed would create transitory “phononic” states. It is thus very important to disentangle both contributions to the phonon scattering and thermal conductivity in ferroelectric materials.…”