The electrocaloric effect in ferroics is considered a powerful solid-state cooling technology. Its potential is enhanced by correlation to the inverse electrocaloric effect and leads into mechanisms of decreasing or increasing dipolar entropy under applied electric field. Nevertheless, the mechanism underlying the increase of the dipolar entropy with applied electric field remains unclear and controversial. This study investigates the electrocaloric response of the antiferroelectric $\mathrm{P}{\mathrm{b}}_{0.99}\mathrm{N}{\mathrm{b}}_{0.02}{\left[{\left(\mathrm{Z}{\mathrm{r}}_{0.58}\mathrm{S}{\mathrm{n}}_{0.43}\right)}_{0.92}\mathrm{T}{\mathrm{i}}_{0.08}\right]}_{0.98}{\mathrm{O}}_3$ in which the critical electric field is low enough to induce the ferroelectric phase over a broad temperature range. Utilizing temperature- and electric-field-dependent dielectric measurements, direct electrocaloric measurements, and in situ transmission electron microscopy, a crossover from conventional to inverse electrocaloric response is demonstrated. The origin of the inverse electrocaloric effect is rationalized by investigating the field-induced phase transition between antiferroelectric and ferroelectric phases. The disappearance of the latent heat at field-induced transition coincides with the crossover of the electrocaloric effect and demonstrates that the overall electrocaloric response is an interplay of different entropy contributions. This opens new opportunities for highly efficient, environmentally friendly cooling devices based on ferroic materials.

This work simultaneously achieved a large temperature change (ΔT, ∼0.70 K) at room temperature and ultra-stable ΔT(±1.4% variation between 300 K with 380 K) in 0.78NaNbO₃–0.22BaTiO₃bulk ceramic.

The formation of polar nanoregions through solid-solution additions is known to enhance significantly the functional properties of ferroelectric materials. Despite considerable progress in characterizing the microscopic behavior of polar nanoregions (PNR), understanding their real-space atomic structure and dynamics of their formation remains a considerable challenge. Here, using the method of dynamic pair distribution function, we provide direct insights into the role of solid-solution additions towards the stabilization of polar nanoregions in the Pb-free ferroelectric of $\mathrm{Ba}(\mathrm{Zr},\mathrm{Ti}){\mathrm{O}}_3$. It is shown that for an optimum level of substitution of Ti by larger Zr ions, the dynamics of atomic displacements for ferroelectric polarization are slowed sufficiently below THz frequencies, which leads to increased local correlation among dipoles within PNRs. The dynamic pair distribution function technique demonstrates a unique capability to obtain insights into locally correlated atomic dynamics in disordered materials, including new Pb-free ferroelectrics, which is necessary to understand and control their functional properties.