Spontaneous trasition between relaxor and ferroelectric states in lanthanum-modified lead zirconate titanate (6-7)/65/35

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 BO 6 octahedrons due to the smaller concentration of defects and higher dielectric constant.