Fig. 3.

Ferroelectric response measurement. (A) Dielectric response at 204 K of a MAPbI₃ crystal along its <001> direction, measured at 2,222 Hz and V_AC = 0.1 V, as a function of applied bias, E_DC (x axis), showing that the imaginary (dissipative) part dominates the dielectric response. (B) P–E hysteresis loop obtained from integration of ε_im over E_DC (Eq. 1). The hysteresis loop is convoluted from a lossy bulk (i.e., resistor) response and ferroelectric polarization response, as illustrated in SI Appendix, Fig. S7A.