Improper ferroelectrics as high‐efficiency energy conversion materials

Abstract

An improper ferroelectric is a certain type of ferroelectrics whose primary order parameter is not polarization but another physical quantity such as magnetization. In contrast to a conventional proper ferroelectrics as represented by Pb(Zr,Ti)O3 and BaTiO3, the improper ferroelectrics has been inconceivable for practical applications thus far. Herein, we illustrate the great potential of improper ferroelectrics for efficient conversion of temperature fluctuation to electric energy, as demonstrated with (Ca0.84Sr0.16)8[AlO2]12(MoO4)2 (CSAM‐16). The present study has experimentally proven that CSAM‐16 achieves an excellent electrothermal coupling factor and high electric field sensitivity for pyroelectric energy conversion that approach a practical level for application to self‐powered autonomous electronic devices for rapidly spreading wireless sensor networks. The present results provide a novel approach to developing innovative pyroelectric energy harvesting devices using improper ferroelectrics.

Hybrid Improper Ferroelectricity in (Sr,Ca)3Sn2O7 and Beyond: Universal Relationship between Ferroelectric Transition Temperature and Tolerance Factor in n = 2 Ruddlesden–Popper Phases

“…This relationship provides a predictive guideline for estimating T C of a given material, which would complement the design approach based on group theory and first principles. Further, the findings open routes to the possible use of hybrid improper ferroelectrics in technological applications: for example, pyroelectric energy harvesting [83][84][85] , where the tunability of T C is advantageous for achieving a large electrothermal coupling factor.…”

Improper molecular ferroelectrics with simultaneous ultrahigh pyroelectricity and figures of merit

“…Contrary to proper ferroelectric whose primary order parameter is polarization, the polarization of improper ferroelectric is a secondary order parameter that develops following the primary order parameter (12)(13)(14). In improper ferroelectrics, the dielectric constant remains low even close to the phase transition temperature, which is usually more than one to two orders of magnitude lower than those of proper ones (4,9,15 (7,17). Nevertheless, the pyroelectric coefficients of DLP and TMO, for example, are ~60 and ~ 80 C m −2 K −1 , respectively, which are vastly inferior to those of PMN-PT (3000 to 5000 C m −2 K −1 ) and PZT (210 C m −2 K −1 ) (4,18).…”

“…F V denotes the maximum pyroelectric voltage for a given energy input, while F D characterizes the ability of detectors to sense weak signals that compete with noises. For pyroelectric energy harvesting, the FOMs are F E = p 2 /( 0  r ) and F EN = p 2 T h /( 0  r c V ) (also termed as the electrothermal coupling factor k 2 , where T h is the maximum temperature in the thermal cycle), which represent the amount and efficiency of electric power converted from a given thermal energy input, respectively (1,(6)(7)(8). Therefore, to achieve high pyroelectric FOMs and factors, it necessitates that pyroelectric materials have simultaneously a high pyroelectric coefficient and a low dielectric constant.…”

“…Relatively high pyroelectric FOMs have been demonstrated in improper ferroelectric dicalcium-lead-propionate [Ca 2 Pb(CH 3 CH 2 COO) 6 (DLP)] and iron-iodine-boracite [FeB 7 O 13 I (TMO)] stemming from their relatively low dielectric constant of 4 to 13 (16). A favorable electrothermal coupling factor has been revealed in stuffed aluminate sodalite [(Ca 0.84 Sr 0.16 ) 8 [AlO 2 ] 12 (MoO 4 ) 2 , CSAM-16] for thermal energy harvesting (7,17). Nevertheless, the pyroelectric coefficients of DLP and TMO, for example, are ~60 and ~ 80 C m −2 K −1 , respectively, which are vastly inferior to those of PMN-PT (3000 to 5000 C m −2 K −1 ) and PZT (210 C m −2 K −1 ) (4,18).…”

Size effect of the guest cation on the AlO4framework in aluminate sodalite-type oxidesM8[Al12O24](SO4)2(M = Sr2+and Ca2+) in theI43mphase

“…Quartz (SiO 2 ) was originally used as a piezoelectric material with high stability. Ferroelectricity in Bi 2 SiO 5 (Taniguchi et al, 2013;Kim et al, 2014;Park et al, 2016) and BaAl 2 O 4 (Huang et al, 1994;Stokes et al, 2002;Ishii et al, 2016) [Al 12 O 24 ](MoO 4 ) 2 , with a small spontaneous polarization of 10 À2 -10 0 mC cm À2 (Setter et al, 1984;Maeda et al, 2017;Wakamatsu et al, 2017). The geometry of the cornershared TO 4 tetrahedral framework in aluminate sodalite-type oxides has been discussed systematically by Depmeier et al (Depmeier, 1988(Depmeier, , 1992(Depmeier, , 2005Depmeier et al, 1993).…”