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Abstract: The longitudinal acoustic (LA) mode of Pb[(Zn1/3Nb2/3)0.93Ti0.07]O3 (PZN-0.07PT) single crystals grown by Bridgman method was investigated over a wide temperature range by using a micro-Brillouin scattering technique. The ferroelectric phase transition of PZN-0.07PT at ∼166 °C was accompanied by a minimum of the Brillouin frequency shift and a sharp maximum of hypersonic damping. These acoustic properties exhibited a thermal hysteresis between cooling and heating processes indicating the first-order nature of the phase transition. The substantial softening of the frequency shift and the increasing damping are typical in ferroelectric relaxors where nano-sized polar clusters appear in the paraelectric phase and interact with acoustic waves via electrostrictive coupling. However, in the present case, acoustic damping consists of a small, sharp peak at the transition temperature (T c) superposed on the broad increasing damping. The broad damping, which becomes substantially large already in the prototype cubic phase, is due to the fluctuation interactions, while the additional sudden peak at T c may be attributed to the growth and merging of polar nanoregions approaching percolation limit that drives the system into a long-range ferroelectric phase at T c. [Copyright &y& Elsevier]