Observation of spontaneous polarization of tourmaline

Abstract

Since Tetsujiro Kubo indirectly found the spontaneous polarization of tourmaline through absorbing copper ions in copper sulfate aqueous solutions in 1980s, there is no other evidence to demonstrate the existence of the spontaneous polarization in tourmaline. It was found that after a tourmaline particle was bombarded by electron beams, a spot appeared on the surface of the sample and that one half of the spot was brighter than the other half under scanning electron microscope. After tourmaline was treated for 2 h at 1223K and then bombarded by electron beams, the bombardment spot did not appear because the crystal structure of tourmaline is destroyed. The existence of the bombardment spot accounts for the spontaneous polarization. The shape and brightness of the bombardment spot not only shows the existence of a surface electric field induced by spontaneous polarization, but also the relation with the direction of the crystal plane of tourmaline.