Improper Ferroelectricity in Stuffed Aluminate Sodalites for Pyroelectric Energy Harvesting

In the present study, we demonstrate ferroelectricity in stuffed aluminate sodalites (Ca1-xSrx)(8)[AlO2](12)WO4)(2) (x <= 0.2) (C(1-x)S(x)AW). Pyroelectric measurements clarify switchable spontaneous polarization in polycrystalline C(1-x)S(x)AW, whose polarization values are on the order of 10(-2) mu C/cm(2) at room temperature. A weak anomaly in the dielectric permittivity at temperatures near the ferroelectric transition temperature suggests improper ferroelectricity of C(1-x)S(x)AW for all investigated values of x. A comprehensive study involving synchrotron x-ray powder diffraction measurements, molecular dynamics simulations, and first-principles calculations clarifies that the ferroelectric phase transition of C(1-x)S(x)AW is driven by the freezing of the fluctuations of WO4 tetrahedra in the voids of an [AlO2](12)(12-) framework. The voltage response and electromechanical coupling factor of C(1-x)S(x)AW estimated from the present results indicate that this material exhibits excellent performance as a pyroelectric energy harvester, suggesting that aluminate sodalites exhibit great promise as a class of materials for highly efficient energy-harvesting devices.