Determination of ferroelectric contributions to electromechanical response by frequency dependent piezoresponse force microscopy

Abstract

Hysteresis loop analysis via piezoresponse force microscopy (PFM) is typically performed to probe the existence of ferroelectricity at the nanoscale. However, such an approach is rather complex in accurately determining the pure contribution of ferroelectricity to the PFM. Here, we suggest a facile method to discriminate the ferroelectric effect from the electromechanical (EM) response through the use of frequency dependent ac amplitude sweep with combination of hysteresis loops in PFM. Our combined study through experimental and theoretical approaches verifies that this method can be used as a new tool to differentiate the ferroelectric effect from the other factors that contribute to the EM response.

Ferroelectric or non-ferroelectric: Why so many materials exhibit “ferroelectricity” on the nanoscale

“…Reprinted from Strelcov et al 334 with the permission of AIP Publishing. Another method to determine whether a material is piezoelectric is to determine the frequency dispersion, as shown by Seol et al 336 Reproduced from Seol et al 336 . A similar example is indicated by Chen et al 118 (e-h) Comparison of soda-lime glass (e,f) and PZT sample (g,h) hysteresis loops as a function of voltage window and frequency of the applied DC switching waveform.…”

“…This technique is shown in Figure 10 (a,b). 335 Alternatively, one can also explore the frequency dependence of the signal, a technique explored recently by Kim et al 336 Here, the authors exploit the fact that across a frequency range of a few hundred kHz, the (intrinsic) piezoelectric properties of ferroelectrics are not heavily dependent on the probing frequency, whereas they are likely heavily frequency dependent for ionic redistribution. The surface displacement induced by ionic motion can be modeled as process is contributing to the observed electromechanical response.…”

Non-piezoelectric effects in piezoresponse force microscopy

“…For instance, Seol et al reported that it is two orders of magnitudes smaller than the electrochemical strain. [112] However, flexoelectricity is still poorly understood and, furthermore, its contribution cannot be clearly discriminated from the ionically induced chemical effect, e.g., the electrochemical strain. [114] Further investigation will be necessary to clarify the contribution of the flexoelectricity to the observed PFM response explicitly.…”

“…In order to differentiate a ferroelectric contribution from the EM response, several approaches have been suggested, based on observed variations in the EM response due to experimental conditions. [96,97,112] We here introduce several approaches that can be readily implemented using PFM. frequency-dependent amplitude sweep was employed, as schematically depicted in Fig.…”

“…Nonetheless, it is generally expected that electrostriction may be small compared to the piezoresponse and electrochemical strain. [112] Flexoelectricity is an interaction between the electrical polarization and the mechanical strain gradient, as described in Figs. 10(b) and (c).…”