Planar defects in metastably retained hexagonal BaTiO₃ ceramics: α-type extended stacking faults

Planar faults are analysed in hexagonal barium titanate (h-BaTiO ₃) (polytype 6H). This present paper is restricted to widely extended faults. Nanosize (approximately 120 nm) stoichiometric tetragonal BaTiO ₃ powder hot pressed at 1300°C for 2 h under a pressure of about 25.8 MPa contains the h-BaTiO₃ phase that is metastably retained at room temperature. Planar defects have_been characterized by transmission electron microscopy. The fault vectors R_FA =1/6[4̄223], R _FB=1/3[011̄2], 1/3[1̄012] and 1/3[11̄02], R _FC =1/6[022̄1], 1/6[2̄021] and 1/6[22̄01] and R _FD =1/6[022̄5], 1/6[2̄025], and 1/6[22̄05] have been determined by application of the invisibility criterion, and the shear component along the prismatic directions has been confirmed by high-resolution imaging. It is suggested that oxygen vacancies generated during hot pressing in the reducing atmosphere of the graphite-die assembly facilitate the metastable retention of the h-BaTiO₃ phase. The stacking faults in the hexagonal matrix are identified as (pseudo)cubic lamellae intergrown with h-BaTiO ₃.