  Just like the artefact found in ferroelectric hysteresis loops, the nearly
identical NDR effect shown in Sr3Co2Fe24O41, TiO2, Al2O3, glass and even banana
skins is confirmed to be a kind of water behavior. The combination of water
induced tunneling effect, water decomposition and absorption plays a crucial
role in the NDR effect. The results and mechanism demonstrated here illustrate
that much attention should be paid to the chemical environment when studying
electrical properties of materials / devices.
