A straightforward method using the sign of the piezoelectric coefficient to identify the ferroelectric switching mechanism

Some organic ferroelectrics have two possible switching modes: molecular reorientation and proton transfer. Typical examples include 2,5-dihydroxybenzoic acid (DHBA) and Hdabco-ReO _4 (dabco = diazabicyclo[2.2.2]octane). The direction and amplitude of the expected polarization depends on the switching mode. Herein a straightforward method to identify the ferroelectric switching mechanism is demonstrated. First, the relationship between the polarization vectors corresponding to the two modes is illustrated using the Berry phase. Second, the theoretical background for the sign of the piezoelectric coefficient is used to decide which mode occurs. Finally, comparing the theoretically calculated piezoelectric coefficients to the experimental results confirms the switching mode of each compound.