TRANSMISSION ELECTRON-MICROSCOPY STUDY OF HIGH-ZR-CONTENT LEAD-ZIRCONATE-TITANATE

Transmission electron microscopy studies have been performed on a seri es of Pb(Zr1-xTix)O-3 compositions for 0 less than or equal to x less than or equal to 0.2. These studies revealed several important feature s of the phase transformational sequence. Locally ordered R-type and M -type oxygen octahedral rotations were found in the paraelectric state . Near the Curie temperature, a longer-range ordering of oxygen octahe dral rotations was observed to develop. For x less than or equal to 0. 05, bright-field imaging and convergent beam electron-diffraction patt erns revealed an intermediate ferroelectric phase with rhombohedral sy mmetry between low-temperature antiferroelectric orthorhombic and high -temperature paraelectric cubic states. This intermediate ferroelectri c state was characterized by the presence of 1/2 [110] superlattice re flections, associated with ordered M-type oxygen octahedral rotations. Lattice imaging revealed nanosized domains which contained [110] stru ctural modulations. With increasing Ti content, the intensity of the 1 /2 [110] reflections was found to decrease. For 0.10<x less than or eq ual to 0.20, only weak diffuse 1/2 [110] reflections were observed; ho wever on cooling strong 1/2 [111] reflections were found to develop. I t is believed that a hierarchy of symmetries exists over a wide region of the rhombohedral ferroelectric phase field. A modification of the high-Zr-content end of the Pb(Zr1-xTix)O-3 phase diagram is then propo sed to acount for this hierarchy.