Dielectric, anelastic, and ${}^{139}\mathrm{La}$ NMR relaxation measurements have been made on the relaxor ferroelectric ${\mathrm{Pb}}_{1-3x∕2}{\mathrm{La}}_x{\mathrm{Zr}}_{0.2}{\mathrm{Ti}}_{0.8}{\mathrm{O}}_3$ (PLZT) with $x=0.22$. The dielectric susceptibility exhibits the frequency dispersive maximum due to the freezing of the polar degrees of freedom around $T\simeq 250\mathrm{K}$. 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.

• Received 4 November 2004

DOI:https://doi.org/10.1103/PhysRevB.71.094112