Spontaneous Trasition between Relaxor and Ferroelectric States in Lanthanum-Modified Lead Zirconate Titanate (6–7)/65/35

Abstract

Dielectric and light scattering measurements are performed in lanthanum modified lead zirconate titanate (PLZT) (6–8)/65/35 hot-pressed ceramics in order to refine the phase diagram. A relaxor-ferroelectric phase transition takes place in PLZT (6–7)/65/35 at temperature lower than the temperature of the dispersive dielectric constant maximum. At this temperature the size of polar regions “a” essentially increases up to a>λ (=0.63 µ m). The appearence of ferroelectric long-range order in PLZT with decreased concentration of La ions is explained by larger coupling between ferroelectrically active BO₆ octahedrons due to the smaller concentration of defects and higher dielectric constant.