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 <i>E</i> < 1.2 V μm^-1 and <i>f</i> ≥ 40 Hz, an increase in optical transmittance was observed, which in comparison with a zero-field transmittance <i>versus</i> temperature plot indicated a shift in the transition temperature. These findings implied that one can induce the desired phase transition using an electric field <i>via</i> 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.