Improper ferroelectrics as high‐efficiency energy conversion materials (Phys. Status Solidi RRL 5/2017)

A pyroelectric material can produce electrical energy from a temporal variation of temperature that exists everywhere in our society. An excellent performance of pyroelectric energy conversion has been demonstrated in a stuffed aluminate zeolite (Ca 0.84 Sr 0.16 ) 8 [Al 12 O 24 ](MoO 4 ) 2 (CSAM‐16) in the study by Wakamatsu et al. (article no. 1700009 ). CSAM‐16 shows an improper ferroelectric phase transition at 440 K, giving rise to spontaneous polarization of 0.2 µC/cm 2 . Although a pyroelectric property of CSAM‐16 is not as large as conventional ferroelectrics, its small dielectric permittivity ( ε ' ∼ 10) even around the phase transition temperature, which is a unique feature of the improper ferroelectrics, boosts a figure‐of‐merit for the pyroelectric energy conversion to a value exceeding that for lead‐based ferroelectric ceramics such as PZT. The result of the present study provides a new route to designing efficient pyroelectric energy harvesters with improper ferroelectrics for a development of innovative stand‐alone micro‐energy harvesting devices.