Enhancement of electrocaloric effect in compositionally graded ferroelectric nanowires

We report on numerical investigation of the electrocaloric effect, an important physical phenomenon in compositionally graded ferroelectric (CGFE) nanowires made of $Pb(1−x)SrxTiO3$ whose material compositions spatially vary along the longitudinal direction of nanowires. In this study, all numerical evidences are demonstrated through the phase field model based on the Ginzburg–Landau theory. Here, the change of polarization with temperature can be tailored by controlling the gradient of material compositions in CGFE nanowires. The isothermal entropy and adiabatic temperature changes are enhanced with an increasing compositional gradient in CGFE nanowires. The electrocaloric effect is found to have high magnitude near room temperature in CGFE nanowires of $PbTiO3$ (top surface)/$SrTiO3$ (bottom surface), which is much larger than that in homogeneous ferroelectric nanowire with the same average material composition. In addition, the high electrocaloric effect in CGFE nanowires of $PbTiO3/SrTiO3$ is achieved in a wide range near room temperature. We also discuss the potential of CGFE nanowires for electrocaloric cooling applications, and more importantly, this work, in essence, opens a new route to enhance the electrocaloric properties of ferroelectric nanowires near room temperature by controlling the gradient of material compositions.