TWO TYPES OF DEFECTS INVOLVED IN THE TRANSPORTATION OF HELIUM ATOMS IN THE DISORDERED STRUCTURE OF QUARTZ

Abstract

The motion of the helium atom through a disordered quartz structure, described by the local chain approximation, is investigated. The number of local chains is equal to the number of nearest neighbours surrounding the He atom. Each local chain includes the He atom. Upon a transition of the He atom from one to another nearest location, two different situations are considered: (i) short order is conserved, and (ii) short order is changed. Distortion of short order leads to the appearance of a defect (excess or deficit of O atoms of SiO4 tetrahedrons) around the He atom. Increasing the number of defects creates voids with a surface area proportional to the square of the number of defects. In this case, two types of defects arise, more precisely voids, which involve and push out the helium atom. A conclusion is drawn that the approximation of local chains shows that the helium atom moves through a disordered quartz structure as a Frenkel-Kontorova soliton with rest (activation) energy, depending on the number of defects as well as the area and the shape of the emerging voids around the helium atom.