Structural investigation of Pb-y(Zr0.57Ti0.43)(2-y)O-3 films deposited on Pt(001)/MgO(001) substrates by rf sputtering

We performed structural studies on PZT thin films, Pb y (Zr 0 . 5 7 Ti 0 . 4 3 ) 2 - y O 3 ; y=0.97, 1.07, 1.15. The thin films were deposited on Pt (001)/MgO (001) substrates by rf-magnetron sputtering. Every film grew epitaxially in a tetragonal phase with the "cube on cube" relationship to the substrate, and contained no other crystalline phases, such as PbO or pyrochlore. It is known that PZT bulk ceramic with Zr/Ti of about 57/43, the composition of which is on the Zr-rich side of the morphotropic phase boundary (MPB), has a rhombohedral structure at room temperature. These PZT films, however, had tetragonal perovskite structures (space group: P4mm). The Pb atoms mainly occupy the A (1a) site, and the Zr and Ti atoms occupy the B ( 1b) site at random. When y is less than unity in Pb y (Zr 0 . 5 7 Ti 0 . 4 3 ) 2 - y O 3 , the excess Zr/Ti tends to enter the Pb (A) sites and randomly occupy the sites together with Pb; and when y is more than unity, the excess Pb tends to mix with the Zr and Ti at Zr/Ti (B) sites. In all these films, the atomic positions of Zr/Ti, O(1), and O(2) shift mutually along the c axis in the tetragonal structure. With increasing y, cla approaches unity and the crystal structure shifts toward the rhombohedral phase, especially in the O(2) atomic position, where a large shift was observed. The PZT thin films were grown under the restraint of a Pt (001) square lattice, and under isotropic compressive plane stress. These are the major reasons that the film crystallizes into tetragonal perovskite and polarizes spontaneously in the c-axis direction perpendicular to the substrate surface.