@article{oai:nagoya.repo.nii.ac.jp:02001409,
 author = {Nakanishi, Toru and Miyajima, Takeshi and Chokawa, Kenta and Araidai, Masaaki and Toshiyoshi, Hiroshi and Sugiyama, Tatsuhiko and Hashiguchi, Gen and Shiraishi, Kenji},
 issue = {19},
 journal = {Applied Physics Letters},
 month = {Nov},
 note = {A potassium-ion electret, which is a key element of vibration-powered microelectromechanical generators, can store negative charge almost permanently. However, the mechanism by which this negative charge is stored is still unclear. We theoretically study the atomic and electronic structures of amorphous silica (a-SiO2) with and without potassium atoms using first-principles molecular-dynamics calculations. Our calculations show that a fivefold-coordinated Si atom with five Si–O bonds (an SiO5 structure) is the characteristic local structure of a-SiO2 with potassium atoms, which becomes negatively charged and remains so even after removal of the potassium atoms. These results indicate that this SiO5 structure is the physical origin of the robust negative charge observed in potassium-ion electrets. We also find that the SiO5 structure has a Raman peak at 1000 cm^−1.},
 title = {Negative-charge-storing mechanism of potassium-ion SiO2-based electrets for vibration-powered generators},
 volume = {117},
 year = {2020}
}