Phase transition of $(Pb_{1-x}Ba_x)(Zr_{0.4}Ti_{0.6})O_3$ solid solutions which are in the highly disordered state has been investigated.
X-ray diffraction patterns of sintered compacts show that tetragonality(c/a) decreases with increasing Ba content. As Ba content increases, phase transition appears more diffuse.
Decreasing tetragonality means that oxygen octahedra in the perovskite structure changes from distorted to undistorted shape.
As tetragonality decreases, near the transition temperature potential energy curve takes different shape, that is, the potential well depth becomes shallow and the probability that fluctuation of the order parameter occurs becomes larger. The easily excitable fluctuation leads to the local disorder and further causes the local disorder mode to couple the polar lattice mode. As the disregistry of lattice parameter δ(=c/a-1) decreases, phase transition takes more diffuse characteristics.
The solid solutions undergoing DPT tend to show large relaxation time whereas those of sharp transition tend to show small relaxation time. From this fact, an attempt was made to explain the dielectric maximum temperature(Tm) shift to high temperature with increasing external frequencies.
Hysteresis loop and T.M.A. experiments show that very diffuse transition (x=0.4) appears to be field-induced transition.
