Disorder and relaxation mode in the lattice dynamics of PbMg${}_{1/3}$Nb${}_{2/3}$O${}_3$ relaxor ferroelectric

Abstract

The low-energy part of vibration spectrum in PbMg${}_{1/3}$Nb${}_{2/3}$O${}_3$ relaxor ferroelectric was studied by inelastic neutron scattering. We observed the coexistence of a resolution-limited central peak with strong quasielastic scattering. The line-width of the quasielastic component follows a ${\Gamma }_0+D{q}^2$ dependence. We find that ${\Gamma }_0$ is temperature-dependent. The relaxation time follows the Arrhenius law well. The presence of a relaxation mode associated with quasi-elastic scattering in PMN indicates that order-disorder behaviour plays an important rôle in the dynamics of diffuse phase transitions.

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