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 several 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 D-E hysteresis loops under cyclic electric field loading, no matter what the inherent physical mechanism is. To verify our viewpoint, both the macroscopic D-E and microscopic SS-PFM testing are conducted on a soda-lime glass and a non-ferroelectric dielectric material Ba0.4Sr0.6TiO3. Results show that both materials can exhibit D-E hysteresis loops and SS-PFM phase hysteresis loops, which can well support our viewpoint.