MICROSTRUCTURE OF PBTIO3 THIN-FILMS DEPOSITED ON (001)MGO BY MOCVD

PbTiO3 thin films deposited on (001)MgO by the MOCVD technique have been characterized by x-ray diffraction and transmission electron microscopy (TEM). The PbTiO3 films grown at temperatures below T(C) (approximately 500-degrees-C) are c-axis oriented polycrystals, while the PbTiO3 films growth ai temperatures above T(C) are single crystals with a bi-layer structure at room temperature. The top layers of the films near the free surface are c-axis oriented with the orientation relationship of (001)[100]PbTiO3//(001)[100]MgO. The bottom layers of the films near the substrate are a-axis oriented with the orientation relationship of (100)[001BAR]PbTiO3//(001BAR)[100]MgO. The formation of the bi-layer microstructure of the PbTiO3 films will be discussed in terms of the effect of the cooling rate and the substrate on the phase transition of PbTiO3 from the cubic to the tetragonal phase. When the PbTiO3 films were grown with a large excess of the Pb precursor vapor in the vapor mixture, PbO and PbTiO3 coexisted in the films. Both PbO and PbTiO3 were grown epitaxially on (001)MgO. The epitaxial orientation relationships were found to be (100) [001]PbO//(001)[100]MgO and (001) [100]PbTiO3//(001)[100]MgO. The 90-degrees domains were observed in the PbTiO3 films deposited at temperatures above T(C). The domain walls are the {101} and {011} twin boundaries, which were formed during the phase transition from the cubic to the tetragonal phase.