Figure 1.

Working mechanisms of FEMs interacting with physical stimuli. Diagrams illustrating the corresponding mechanisms in a unit cell: a) spontaneous polarization (P _s) with induced polar charged surfaces; b) ferroelectricity, inversion of polarization by applied electric field; c) pyroelectricity, generation of electric signal upon temperature change; d) piezoelectricity, generation of electric signal by applied force; e) inverse‐ piezoelectricity, generation of mechanical strain/vibrations by applied electric signal. f) The relationship between piezoelectricity, pyroelectricity, and ferroelectricity. g) Nonlinear optics, generation of harmonic photon when excited by a pulsed laser; h) Photovoltaic effect, generation of photovoltage when excited by illumination with photon energy (hν) higher than the band gap (E _g).