  Analytical results obtained within Landau-Ginzburg-Devonshire approach and
effective media models, predict that the synergy of size effects and Vegard
stresses can significantly enhance the electrocaloric cooling (up to 7 times)
of the BaTiO3 nanoparticles in comparison with a bulk BaTiO3. To compare with
the considered effective media models, we measured the capacitance-voltage and
current-voltage characteristics of the dense nanocomposites consisting of
(28-35) vol.% BaTiO3 nanoparticles incorporated in organic polymers and
determined experimentally the effective dielectric permittivity and losses of
the composites. Generalizing obtained analytical results, various ferroelectric
nanoparticles spontaneously stressed by elastic defects, such as oxygen
vacancies or any other elastic dipoles, which create a strong chemical
pressure, can cause the giant electrocaloric response of dense ferroelectric
nanocomposites. We have shown that the advantages of the studied lead-free
dense nanocomposites are the good tunability of electrocaloric cooling
temperature due to the size effects in ferroelectric nanoparticles and the easy
control of the high electrocaloric cooling by electric fields. This makes the
dense ferroelectric nanocomposites promising for cooling of conventional and
innovative electronic elements, such as FETs with high-temperature
superconductor channels.

Applied Physics;Mesoscale and Nanoscale Physics