Study on Structural Anomalies of Mullite Crystals Using Computer Chemistry

Abstract

Mullite has a complicated crystal structure in which double occupancy of metal atoms and oxygen vacancies take a random arrangement．Various attempts have been made to describe its structure，but it has not yet been fully described．The purpose of this study is to clarify that the random arrangement has regularity. Excluding arbitrariness，the arrangement of metal atoms and oxygen vacancies of mullite crystals of three compositions (1.58Al₂O₃，1.75Al₂O₃，1.95Al₂O₃ for 1SiO₂) was randomly generated．Structural relaxation calculations of these models were performed，and their stability was examined．The wide distribution of the heat of formation obtained by the structural relaxation calculation was consistent with the composition．