Low field electrocaloric effect at isotropic–ferroelectric nematic phase transition†

Electrocaloric effects (ECE) in solid state materials, such as ferroelectric ceramics and ferroelectric polymers, have a great impact in developing cooling systems. Herein, we describe the ECE of a newly synthesized ferroelectric nematic liquid crystal compound at the isotropic–ferroelectric nematic (I–N_F) phase transition. While the Joule heat completely suppressed the ECE in a DC field, in an AC field with E < 1.2 V μm⁻¹ and f ≥ 40 Hz, an increase in optical transmittance was observed, which in comparison with a zero-field transmittance versus temperature plot indicated a shift in the transition temperature. These findings implied that one can induce the desired phase transition using an electric field via ECE with an EC responsivity of ∼1.7 × 10⁻⁶ km V⁻¹. Notably, the required electric field was two orders of magnitude smaller than the typical fields for other EC materials. EC effects observed under such low fields is a unique property of ferroelectric nematic liquid crystals. Furthermore, the specific EC energy could be increased considerably by reducing the ionic content, thus suppressing the Joule heat.