  Piezoresponse force microscopy (PFM) has been used extensively for exploring
nanoscale ferro/piezoelectric phenomena over the past two decades. The imaging
mechanism of PFM is based on the detection of the electromechanical (EM)
response induced by the inverse piezoelectric effect through the cantilever
dynamics of an atomic force microscopy. However, several non-piezoelectric
effects can induce additional contributions to the EM response, which often
lead to a misinterpretation of the measured PFM response. This review aims to
summarize the non-piezoelectric origins of the EM response that impair the
interpretation of PFM measurements. We primarily discuss two major
non-piezoelectric origins, namely, the electrostatic effect and electrochemical
strain. Several approaches for differentiating the ferroelectric contribution
from the EM response are also discussed. The review suggests a undamental
guideline for the proper utilization of the PFM technique, as well as for
achieving a reasonable interpretation of observed PFM responses.
