The coexistence of unstable, metastable, and separated Frenkel pair defects in solids. III. Theory of the non‐impact mechanisms for defect formation in non‐metals

Abstract

AbstractA general theory is developed of non‐impact mechanisms of the unstable (U), metastable (M), and separated (S) Frenkel pair defect creation in non‐metals that is realized at the decay of excitons, electron‐hole (e‐h) pairs, and holes. A two stage self‐trapping model of excitons (holes) is proposed. The initial stage of self‐trapping is considered in the framework of a simple continuum model and its final stage in the framework of a quasi‐molecular model. The formation of a quasimolecular type self‐trapped exciton (STE) is followed by its spontaneous transition or by the transition with overcoming the potential barrier from centrosymmetric (CS) to different off‐centrosymmetric (OCS) positions. In this configuration the dynamic displacement and dissociative decay of an STE molecular ion with the creation of Frenkel pairs become possible. The direct displacement possibility of an STE molecular ion from the CS to an interstitial position is also analysed. The reasons of the low efficiency of Frenkel pair creation in alkali halides at the decay of e‐h pairs and holes is clarified. The possibility is shown of STE decay into the neutral U, M, and S anion Frenkel pairs as well as into the charged U and M cation Frenkel pairs. The theory proposed explains satisfactorily all the experimental data available.