Cation antiphase boundaries in ionic crystals based on anion close packing

Abstract

Characteristic planar lattice defects have been observed in ionic crystals based on a close packed anion' structure. They are characterized as antiphase boundaries with regard to cation arrangement in the approximately perfect anion lattice, and are referred to as “Cation Antiphase Boundaries” (CAB). Cation antiphase boundaries are classified into two types depending on the symmetry operation involved. The CAB which is formed by translating a part of a crystal by the shortest anion-anion vector is called as CAB of the first sort, and that with a symmetry operation other than translation is called a CAB of the second sort. The latter causes twinning of the crystal owing to its symmetry operation. Among the principal crystal structures based on the close packing of anions, spinel, corundum, ilmenite and olivine type structures are expected to show CAB of the first sort. CAB of the second sort are expected to appear in zinc blende, wurtzite, corundum, ilmenite and olivine type structures. The occurence of CAB is attributed to the formation of the crystal nucleus which contains incoherent cation arrangement in the close-packed anion array.