# Ultra-fast electric field control of giant electrocaloric effect in ferroelectrics

## TL;DR

This paper demonstrates that ultrafast electric field pulses can induce a giant negative electrocaloric effect in ferroelectrics like PbTiO3, enabling rapid, efficient solid-state cooling through internal energy redistribution.

## Contribution

It introduces a new understanding of electrocaloric effect via internal energy redistribution and proposes electric field engineering to achieve fast, large, and negative ECE in ferroelectrics.

## Key findings

- Negative ECE up to 35 K in PbTiO3 with picosecond electric pulses
- Mechanism explained through internal energy redistribution during adiabatic processes
- Simulations confirm the feasibility of ultrafast, giant electrocaloric effects

## Abstract

There is a surge of interest in developing environmentally friendly cooling technology based on the solid--state electrocaloric effect (ECE). Here, we point out that negative ECE with a fast cooling rate ($\approx$10$^{11}$ K/s) can be achieved by driving solid crystals to a high--temperature phase with a properly designed electric field pulse. Specifically, we predict that an ultrafast electric field pulse can cause a negative ECE up to 35 K in PbTiO$_3$ occurring on few picosecond time scales. We acquire and analyze these results by clarifying the mechanism of ECE during an adiabatic irreversible process; In addition to the conventional explanation of the ECE with entropy reallocation, we simply portray the ECE with the concept of internal energy redistribution. Electric field does work on a ferroelectric crystal and redistributes its internal energy. How the kinetic energy is redistributed determines the temperature change and strongly depends on the electric field temporal profile. This concept is supported by our all--atom molecular dynamics simulations of PbTiO$_3$ and BaTiO$_3$. Based on this improved understanding of ECE, we propose strategies for inducing both giant and negative ECE. This work offers a more general framework to understand the ECE and highlights the opportunities of electric--field engineering for controlled design of fast and efficient cooling technology.