Microstructural studies of polytype formation in oxygen-containing aluminium nitride

Oxygen-doped AlN polycrystals were investigated by transmission electron microscope, and different stages of multilayered polytype formation during pressureless sintering were fixed. The decomposition of polytypes was found to take place during quasihydrostatic compression of samples at high temperatures. A model of multilayered polytypes appearing is proposed. The process of polytype formation is represented as isostructural delamination of the AlN-O solid solution at the expense of oxygen extraction on stacking faults, causing the oxygen-rich interlayer formation.