Voltage Controlled Bistable Thermal Conductivity in Suspended Ferroelectric Thin Film Membranes.

Ferroelastic domain walls in ferroelectric materials possess two properties known to affect phonon transport: a change in crystallographic orientation and a lattice strain. Changing populations and spacing of nanoscale-spaced ferroelastic domain walls leads to manipulation of phonon scattering rates enabling control of thermal conduction at ambient temperatures. In the present work, lead zirconate titanate (PZT) thin film membrane structures were fabricated to reduce mechanical clamping to the substrate and enable a subsequent increase in ferroelastic domain wall mobility. Under application of an electric field, the thermal conductivity of the PZT increases abruptly at ~100 kV/cm by ~13% owing to a reduction in the number of phonon scattering domain walls in the thermal conduction path. The thermal conductivity modulation is rapid, repeatable, and discrete, resulting in a bistable-state, or "digital" modulation scheme. The modulation of thermal conductivity due to changes in domain wall configuration is supported by polarization-field, mechanical stiffness, and in situ microdiffraction experiments. This work opens a path toward a new means to control phonons and phonon-mediated energy in a digital manner at room temperature using only an electric field.