Structural investigation ofPby(Zr0.57Ti0.43)2−yO3films deposited on Pt(001)/MgO(001) substrates by rf sputtering

Abstract

We performed structural studies on PZT thin films, ${\mathrm{Pb}}_{y}({\mathrm{Zr}}_{0.57}{\mathrm{Ti}}_{0.43}{)}_{2\ensuremath{-}y}{\mathrm{O}}_{3};$ $y=0.97,$ 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 ${\mathrm{Pb}}_{y}({\mathrm{Zr}}_{0.57}{\mathrm{Ti}}_{0.43}{)}_{2\ensuremath{-}y}{\mathrm{O}}_{3},$ 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, $c/a$ 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.