Polar and nonpolar atomic motions in the relaxor ferroelectric Pb1−3x/2LaxZr0.2Ti0.8O3 from dielectric, anelastic, and NMR relaxation

Dielectric, anelastic, and 139La NMR relaxation measurements have been made on the relaxor ferroelectric Pb1−3x/2LaxZr0.2Ti0.8O3 (PLZT) with x=0.22. The dielectric susceptibility exhibits the frequency dispersive maximum due to the freezing of the polar degrees of freedom around T=250 K. The anelastic and especially NMR relaxation, besides this maximum, indicate an intense and broad component at lower temperatures, attributed to rotational modes of the O octahedra, weakly coupled to the polar modes. It is discussed why such short range rotational instabilities, known to occur in the Zr-rich rhombohedral region of the PLZT phase diagram, might appear also in the Ti-rich region.