More ferroelectrics discovered by switching spectroscopy piezoresponse force microscopy?

The local hysteresis loop obtained by switching spectroscopy piezoresponse force microscopy (SS-PFM) is usually regarded as a typical signature of ferroelectric switching. However, such hysteresis loops were also observed in a broad variety of non-ferroelectric materials in the past few years, which casts doubts on the viewpoint that the local hysteresis loops in SS-PFM originate from ferroelectricity. Therefore, it is crucial to explore the mechanism of local hysteresis loops obtained in SS-PFM testing. Here we proposed that non-ferroelectric materials can also exhibit amplitude butterfly loops and phase hysteresis loops in SS-PFM testing, due to the Maxwell force as long as the material can show macroscopic hysteresis loops under cyclic electric field loading, no matter what the inherent physical mechanism is. To verify our viewpoint, both the macroscopic and microscopic SS-PFM testing are conducted on a soda-lime glass and a non-ferroelectric dielectric material . Results show that both materials can exhibit hysteresis loops and SS-PFM phase hysteresis loops, which can well support our viewpoint.