Defect chemistry of lone-pair semiconductors

Abstract

A chemical-bond approach reveals the possibility of several unusual bonding configurations that have relatively low energy in materials with lone-pair valence electrons. Valence-alternation pairs (V.A.P.) are the lowest energy charged defects. The interconversion between positive and negative centres is described in detail. The nature of V.A.P.s in pnictides (group V elements) is discussed. The possibility that valence-alternation centres can form intimate or bound pairs is explored. It is pointed out that certain unusual bonding configurations (configuration distortions) arise even in an ideal lone-pair material. It is stressed that the unusual bonding configurations discussed are a result of the special bonding in lone-pair materials and are, therefore, expected to arise in crystals as well as amorphous materials.