Size effects of electrocaloric cooling in ferroelectric nanowires

Abstract

Considering finite size effect, ferroelectric nanowires may show novel phenomena compared to ferroelectric thin film and bulk. Here we investigated the effect of width and surface compressive stress on electrocaloric cooling in ferroelectric nanowire by using thermodynamic calculations and phase-field simulations. It was found that the isothermal entropy change and adiabatic temperature change in nanowire are 50% larger than that in thin film due to different mechanical boundary conditions of nanowire and thin film. The largest electrocaloric temperature changes were shown to increase significantly either with the decrease in nanowire width or the increase with the surface compressive stress. It was also revealed that the largest intrinsic entropy changes are almost the same for different nanowires with different widths and various stresses. The present study therefore contributes to the understanding of size effects of electrocaloric cooling and provides guidance for experiments to design high-efficiency cooling devices using ferroelectric nanosystems. K E Y W O R D S electrocaloric effect, ferroelectric nanowire, nanosize effects, phase-field simulation, thermodynamic calculation

Simultaneously achieving giant piezoelectricity and record coercive field enhancement in relaxor-based ferroelectric crystals

“…In the phase-field simulations, the polarization P i ( r,t )( x,y,z ) denotes the order parameter, which describes the ferroelectric polarization evolution. The temporal evolution of the polarization can be described by the time-dependent Ginzburg–Landau equation: where t is the simulation time, L is the kinetic coefficient, r is the spatial position, and F P is the total free energy of the system that is denoted as follows 46 : where f bulk , f elas , f elec and f grad represent the Landau bulk, elastic, electrostatic, and gradient energy densities, respectively. A stress-free boundary condition is adopted.…”

Understanding electrocaloric cooling of ferroelectrics guided by phase‐field modeling

“…(A–C) The domain structures of PbZr (1– x ) Ti x O 3 (PZT) thin films with different compositions 34 . (D–F) The domain structures of ferroelectric Ba 0.67 Sr 0.33 TiO 3 (BST) with different shapes and sizes 35 . (G–I) The domain structures of PbZr 0.2 Ti 0.8 O 3 thin films under different strains 34 …”

“…34 (D-F) The domain structures of ferroelectric Ba 0.67 Sr 0.33 TiO 3 (BST) with different shapes and sizes. 35 (G-I) The domain structures of PbZr 0.2 Ti 0.8 O 3 thin films under different strains 34 The electrostatic energy density is expressed by using…”

“…However, it is not feasible to enhance the ECE by continuously reducing the size of the NWs, because NWs with smaller diameters (such as 150 nm) cannot stand vertically, and the array becomes more susceptible to dielectric breakdown. Afterward, Huang et al 35 further simulated the nanosize effect of ECE and domain structure change in ferroelectric Ba 0.67 Sr 0.33 TiO 3 nanosystem in detail, and the results indicated that the ΔS and ΔT of the NWs were 50% larger than the TFs. The proportion of c-domains in NW is larger, so the polarization component P 3 in the direction of the electric field of it is also larger than that of the TF, which results in large entropy and temperature changes in the NW.…”

Wide Electrocaloric Temperature Range Induced by Ferroelectric to Antiferroelectric Phase Transition

“…According the results reported earlier, doping can vary the temperature range of different materials. Additionally, it has been demonstrated that the compressive or tensile strain induced by external stimuli (electric field, stress, pressure) can also remarkably change the spontaneous polarization of ferroelectrics, which influences the transition temperature range of the EC effect further [20][21][22][23].…”