Abstract
ABSTRACT The importance of the environment-friendly lead-free piezoelectric materials has attracted much attention. The (K0.5Na0.5)NbO3 (KNN) crystals with the perovskite structure undergo the cubic (C) to tetragonal (T) ferroelectric phase transition at T CT = 430 °C, and the tetragonal to monoclinic (M) structural phase transition at T TM = 190 °C. The elastic properties and relaxation process of these phase transitions of the KNN crystals have been studied by broadband Brillouin scattering. The softening of the LA and TA velocities was observed in the vicinity of T CT and T TM. The power law behavior of the velocity indicates three-dimensional fluctuations. The broadband central peak showed the critical slowing down in the vicinity of the T CT and T TM. The slowing down is attributed to the order-disorder nature of the off-center displacement of Nb in KNN.
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