Novel Photocaloric Effects in Archetypal Ferroelectrics for Solid-State Cooling Applications

Solid-state cooling represents an energy efficient and ecologically friendly solution to the environmental problems posed by conventional refrigeration technologies based on compression cycles of greenhouse gases [1-3]. Upon small and moderate magnetic, electric and/or mechanical field shifts, promising caloric materials experience large adiabatic temperature variations (|ΔT|~1-10 K) as a result of phase transformations entailing large isothermal entropy changes (|ΔS|~10-100 J K⁻¹kg⁻¹). Solid-state cooling relies on such caloric effects to engineer multi-step refrigeration cycles. Nevertheless, conventional magneto-, electro- and mechano-caloric effects present a series of critical drawbacks that keep hindering their practical implementation in commercial refrigeration devices. For example, operation temperature conditions should be close to zero-bias transition points, since otherwise the required driving fields grow unfeasibly too large, but these only serendipitously occur at ambient conditions. Here, we will show, based on advanced first-principles simulation methods, that macroscopic light-driven phase transitions in ferroelectrics have the potential to overcome such a materials selection limitation. In particular, we demonstrate for the archetypal ferroelectric KNbO₃ the existence of giant photocaloric effects (i.e., |ΔT|~10 K and |ΔS|~100 J K⁻¹kg⁻¹), that is, induced by light absorption, over a vast temperature span of several hundreds of Kelvin containing room temperature. Our results can be qualitatively generalized to other ferroelectrics displaying similar types of ferroelectric to paraelectric phase transitions [4].<br/><br/><br/>[1] I. Takeuchi and K. Sandeman, Phys. Today 68, 48 (2015)<br/>[2] C. Cazorla, Appl. Phys. Rev. 6, 041316 (2019)<br/>[3] C. Menéndez-Muñiz, R. Rurali and C. Cazorla, Phys. Chem. Chem. Phys. 25, 17450 (2023)<br/>[4] C. Paillard, et al., Phys. Rev. Lett. 123, 087601 (2019)