Improper molecular ferroelectrics with simultaneous ultrahigh pyroelectricity and figures of merit

Although ferroelectric materials exhibit large pyroelectric coefficients, their pyroelectric figures of merit (FOMs) are severely limited by their high dielectric constants because of the inverse relationship between FOMs and dielectric constant. Here, we report the molecular ferroelectric [Hdabco]CIO4 and [Hdabco]BF4 (dabco = diazabicyclo[2.2.2]octane) exhibiting improper ferroelectric behavior and pyroelectric FOMs outperforming the current ferroelectrics. Concurrently, the improper molecular ferroelectrics have pyroelectric coefficients that are more than one order of magnitude greater than the state-of-the-art pyroelectric Pb(Mg1/3Nb2/3)O-3-PbTiO3. Our first-principles and thermodynamic calculations show that the strong coupling between the order parameters, i.e., the rotation angle of anions and polarization, is responsible for the colossal pyroelectric coefficient of the molecular ferroelectrics. Along with the facile preparation and self-poling features, the improper molecular ferroelectrics hold great promise for high-performance pyroelectric devices.

Automated summary

Improper molecular ferroelectric materials [Hdabco]CIO4 and [Hdabco]BF4 show superior pyroelectric performance compared to current ferroelectrics, with pyroelectric coefficients exceeding that of Pb(Mg1/3Nb2/3)O-3-PbTiO3. First-principles and thermodynamic calculations reveal that the strong coupling between anion rotation angle and polarization is responsible for the colossal pyroelectric coefficient of these materials, offering great promise for high-performance pyroelectric devices.